Science.gov

Sample records for premixed combustion progress

  1. Studies in premixed combustion

    SciTech Connect

    Sivashinsky, G.I.

    1992-01-01

    This report discusses the following topics on premixed combustion: theory of turbulent flame propagation; pattern formation in premixed flames and related problems; and pattern formation in extended systems. (LSP)

  2. Studies in premixed combustion. Progress report, November 1, 1990--October 31, 1992

    SciTech Connect

    Sivashinsky, G.I.

    1992-08-01

    This report discusses the following topics on premixed combustion: theory of turbulent flame propagation; pattern formation in premixed flames and related problems; and pattern formation in extended systems. (LSP)

  3. Studies in premixed combustion. Annual progress report, November 1, 1992--October 31, 1993

    SciTech Connect

    Sivashinsky, G.I.

    1993-03-01

    During the period under review, significant progress was been made in studying the intrinsic dynamics of premixed flames and the problems of flame-flow interaction. (1) A weakly nonlinear model for Bunsen burner stabilized flames was proposed and employed for the simulation of three-dimensional polyhedral flames -- one of the most graphic manifestations of thermal-diffusive instability in premixed combustion. (2) A high-precision large-scale numerical simulation of Bunsen burner tip structure was conducted. The results obtained supported the earlier conjecture that the tip opening observed in low Lewis number systems is a purely optical effect not involving either flame extinction or leakage of unburned fuel. (3) A one-dimensional model describing a reaction wave moving through a unidirectional periodic flow field is proposed and studied numerically. For long-wavelength fields the system exhibits a peculiar non-uniqueness of possible propagation regimes. The transition from one regime to another occurs in a manner of hysteresis.

  4. Lean premixed/prevaporized combustion

    NASA Technical Reports Server (NTRS)

    Lefebvre, A. H. (Editor)

    1977-01-01

    Recommendations were formulated on the status and application of lean premixed/prevaporized combustion to the aircraft gas turbine for the reduction of pollutant emissions. The approach taken by the NASA Stratospheric Cruise Emission Reduction Program (SCERP) in pursuing the lean premixed/prevaporized combustion technique was also discussed. The proceedings contains an overview of the SCERP program, the discussions and recommendations of the participants, and an overall summary.

  5. A general flamelet transformation useful for distinguishing between premixed and non-premixed modes of combustion

    SciTech Connect

    Knudsen, E.; Pitsch, H.

    2009-03-15

    The flame index was originally proposed by Yamashita et al. as a method of locally distinguishing between premixed and non-premixed combustion. Although this index has been applied both passively in the analysis of direct numerical simulation data, and actively using single step combustion models, certain limitations restrict its use in more detailed combustion models. In this work a general flamelet transformation that holds in the limits of both premixed and non-premixed combustion is developed. This transformation makes use of two statistically independent variables: a mixture fraction and a reaction progress parameter. The transformation is used to produce a model for distinguishing between premixed and non-premixed combustion regimes. The new model locally examines the term budget of the general flamelet transformation. The magnitudes of each of the terms in the budget are calculated and compared to the chemical source term. Determining whether a flame burns in a premixed or a non-premixed regime then amounts to determining which sets of these terms most significantly contribute to balancing the source term. The model is tested in a numerical simulation of a laminar triple flame, and is compared to a recent manifestation of the flame index approach. Additionally, the model is applied in a presumed probability density function (PDF) large eddy simulation (LES) of a lean premixed swirl burner. The model is used to locally select whether tabulated premixed or tabulated non-premixed chemistry should be referenced in the LES. Results from the LES are compared to experiments. (author)

  6. Mechanisms of combustion limits in premixed gas flames at microgravity

    NASA Technical Reports Server (NTRS)

    Ronney, Paul D.

    1991-01-01

    A three-year experimental and theoretical research program on the mechanisms of combustion limits of premixed gasflames at microgravity was conducted. Progress during this program is identified and avenues for future studies are discussed.

  7. Oscillating combustion from a premix fuel nozzle

    SciTech Connect

    Richards, G.A.; Yip, M.J.

    1995-08-01

    Stringent emissions requirements for stationary gas turbines have produced new challenges in combustor design. In the past, very low NOx pollutant emissions have been achieved through various combustion modifications, such as steam or water injection, or post-combustion cleanup methods such as selective catalytic reduction (SCR). An emerging approach to NOx abatement is lean premix combustion. Lean premix combustion avoids the cost and operational problems associated with other NOx control methods. By premixing fuel and air at very low equivalence ratios, the high temperatures which produce NOx are avoided. The challenges of premix combustion include avoiding flashback, and ensuring adequate fuel/air premixing. In addition, the combustion must be stable. The combustor should not operate so close to extinction that a momentary upset will extinguish the flame (static stability), and the flame should not oscillate (dynamic stability). Oscillations are undesirable because the associated pressure fluctuations can shorten component lifetime. Unfortunately, experience has shown that premix fuel nozzles burning natural gas are susceptible to oscillations. Eliminating these oscillations can be a costly and time consuming part of new engine development. As part of the U.S. Department of Energy`s Advanced Turbine Systems Program, the Morgantown Energy Technology Center (METC) is investigating the issue of combustion oscillations produced by lean premix fuel nozzles. METC is evaluating various techniques to stabilize oscillating combustion in gas turbines. Tests results from a premix fuel nozzle using swirl stabilization and a pilot flame are reported here.

  8. Lagrangian formulation of turbulent premixed combustion.

    PubMed

    Pagnini, Gianni; Bonomi, Ernesto

    2011-07-22

    The lagrangian point of view is adopted to study turbulent premixed combustion. The evolution of the volume fraction of combustion products is established by the Reynolds transport theorem. It emerges that the burned-mass fraction is led by the turbulent particle motion, by the flame front velocity, and by the mean curvature of the flame front. A physical requirement connecting particle turbulent dispersion and flame front velocity is obtained from equating the expansion rates of the flame front progression and of the unburned particles spread. The resulting description compares favorably with experimental data. In the case of a zero-curvature flame, with a non-markovian parabolic model for turbulent dispersion, the formulation yields the Zimont equation extended to all elapsed times and fully determined by turbulence characteristics. The exact solution of the extended Zimont equation is calculated and analyzed to bring out different regimes.

  9. Design factors for stable lean premix combustion

    SciTech Connect

    Richards, G.A.; Yip, M.J.; Gemmen, R.S.

    1995-10-01

    The Advanced Turbine Systems (ATS) program includes the development of low-emission combustors. Low emissions have already been achieved by premixing fuel and air to avoid the hot gas pockets produced by nozzles without premixing. While the advantages of premixed combustion have been widely recognized, turbine developers using premixed nozzles have experienced repeated problems with combustion oscillations. Left uncontrolled, these oscillations can lead to pressure fluctuations capable of damaging engine hardware. Elimination of such oscillations is often difficult and time consuming - particularly when oscillations are discovered in the last stages of engine development. To address this issue, METC is studying oscillating combustion from lean premixing fuel nozzles. These tests are providing generic information on the mechanisms that contribute to oscillating behavior in gas turbines. METC is also investigating the use of so-called {open_quotes}active{close_quotes} control of combustion oscillations. This technique periodically injects fuel pulses into the combustor to disrupt the oscillating behavior. Recent results on active combustion control are presented in Gemmen et al. (1995) and Richards et al. (1995). This paper describes the status of METC efforts to avoid oscillations through simple design changes.

  10. A filtered tabulated chemistry model for LES of premixed combustion

    SciTech Connect

    Fiorina, B.; Auzillon, P.; Darabiha, N.; Gicquel, O.; Veynante, D.; Vicquelin, R.

    2010-03-15

    A new modeling strategy called F-TACLES (Filtered Tabulated Chemistry for Large Eddy Simulation) is developed to introduce tabulated chemistry methods in Large Eddy Simulation (LES) of turbulent premixed combustion. The objective is to recover the correct laminar flame propagation speed of the filtered flame front when subgrid scale turbulence vanishes as LES should tend toward Direct Numerical Simulation (DNS). The filtered flame structure is mapped using 1-D filtered laminar premixed flames. Closure of the filtered progress variable and the energy balance equations are carefully addressed in a fully compressible formulation. The methodology is first applied to 1-D filtered laminar flames, showing the ability of the model to recover the laminar flame speed and the correct chemical structure when the flame wrinkling is completely resolved. The model is then extended to turbulent combustion regimes by including subgrid scale wrinkling effects in the flame front propagation. Finally, preliminary tests of LES in a 3-D turbulent premixed flame are performed. (author)

  11. Computations of turbulent lean premixed combustion using conditional moment closure

    NASA Astrophysics Data System (ADS)

    Amzin, Shokri; Swaminathan, Nedunchezhian

    2013-12-01

    Conditional Moment Closure (CMC) is a suitable method for predicting scalars such as carbon monoxide with slow chemical time scales in turbulent combustion. Although this method has been successfully applied to non-premixed combustion, its application to lean premixed combustion is rare. In this study the CMC method is used to compute piloted lean premixed combustion in a distributed combustion regime. The conditional scalar dissipation rate of the conditioning scalar, the progress variable, is closed using an algebraic model and turbulence is modelled using the standard k-ɛ model. The conditional mean reaction rate is closed using a first order CMC closure with the GRI-3.0 chemical mechanism to represent the chemical kinetics of methane oxidation. The PDF of the progress variable is obtained using a presumed shape with the Beta function. The computed results are compared with the experimental measurements and earlier computations using the transported PDF approach. The results show reasonable agreement with the experimental measurements and are consistent with the transported PDF computations. When the compounded effects of shear-turbulence and flame are strong, second order closures may be required for the CMC.

  12. Simulation of lean premixed turbulent combustion

    SciTech Connect

    Bell, John B.; Day, Marcus S.; Almgren, Ann S.; Lijewski, MichaelJ.; Rendleman, Charles A.; Cheng, Robert K.; Shepherd, Ian G.

    2006-06-25

    There is considerable technological interest in developingnew fuel-flexible combustion systems that can burn fuels such ashydrogenor syngas. Lean premixed systems have the potential to burn thesetypes of fuels with high efficiency and low NOx emissions due to reducedburnt gas temperatures. Although traditional scientific approaches basedon theory and laboratory experiment have played essential roles indeveloping our current understanding of premixed combustion, they areunable to meet the challenges of designing fuel-flexible lean premixedcombustion devices. Computation, with itsability to deal with complexityand its unlimited access to data, hasthe potential for addressing thesechallenges. Realizing this potential requires the ability to perform highfidelity simulations of turbulent lean premixed flames under realisticconditions. In this paper, we examine the specialized mathematicalstructure of these combustion problems and discuss simulation approachesthat exploit this structure. Using these ideas we can dramatically reducecomputational cost, making it possible to perform high-fidelitysimulations of realistic flames. We illustrate this methodology byconsidering ultra-lean hydrogen flames and discuss how this type ofsimulation is changing the way researchers study combustion.

  13. Premixed Combustion Model for Boron Clouds

    NASA Astrophysics Data System (ADS)

    Wang, Mengze; Han, Wang; Chen, Zheng

    2015-11-01

    Boron particle is an ideal additive in solid propellants and fuels due to its very high volumetric heat release. In this study, a premixed combustion model for boron clouds is developed based on a previous combustion model for single boron particle. The flame structure is assumed to be composed of three zones: the preheat zone, the ignition zone, and the reaction zone, and analytical solutions are derived from the governing equations. Consequently the influence of the boron clouds' physical properties on the flame propagation process is investigated.

  14. A model for premixed combustion oscillations

    SciTech Connect

    Janus, M.C.; Richards, G.A.

    1996-03-01

    Combustion oscillations are receiving renewed research interest due to increasing application of lean premix (LPM) combustion to gas turbines. A simple, nonlinear model for premixed combustion is described; it was developed to explain experimental results and to provide guidance for developing active control schemes based on nonlinear concepts. The model can be used to quickly examine instability trends associated with changes in equivalence ratio, mass flow rate, geometry, ambient conditions, etc. The model represents the relevant processes occurring in a fuel nozzle and combustor analogous to current LPM turbine combustors. Conservation equations for the nozzle and combustor are developed from simple control volume analysis, providing ordinary differential equations that can be solved on a PC. Combustion is modeled as a stirred reactor, with bimolecular reaction between fuel and air. Although focus is on the model, it and experimental results are compared to understand effects of inlet air temperature and open loop control schemes. The model shows that both are related to changes in transport time.

  15. Internal combustion engine using premixed combustion of stratified charges

    DOEpatents

    Marriott, Craig D.; Reitz, Rolf D. (Madison, WI

    2003-12-30

    During a combustion cycle, a first stoichiometrically lean fuel charge is injected well prior to top dead center, preferably during the intake stroke. This first fuel charge is substantially mixed with the combustion chamber air during subsequent motion of the piston towards top dead center. A subsequent fuel charge is then injected prior to top dead center to create a stratified, locally richer mixture (but still leaner than stoichiometric) within the combustion chamber. The locally rich region within the combustion chamber has sufficient fuel density to autoignite, and its self-ignition serves to activate ignition for the lean mixture existing within the remainder of the combustion chamber. Because the mixture within the combustion chamber is overall premixed and relatively lean, NO.sub.x and soot production are significantly diminished.

  16. Analysis of flame surface density measurements in turbulent premixed combustion

    SciTech Connect

    Halter, Fabien; Chauveau, Christian; Goekalp, Iskender; Veynante, Denis

    2009-03-15

    In premixed turbulent combustion, reaction rates can be estimated from the flame surface density. This parameter, which measures the mean flame surface area available per unit volume, may be obtained from algebraic expressions or by solving a transport equation. In this study, detailed measurements were performed on a Bunsen-type burner fed with methane/air mixtures in order to determine the local flame surface density experimentally. This burner, located in a high-pressure combustion chamber, allows investigation of turbulent premixed flames under various flow, mixture, and pressure conditions. In the present work, equivalence ratio was varied from 0.6 to 0.8 and pressure from 0.1 to 0.9 MPa. Flame front visualizations by Mie scattering laser tomography are used to obtain experimental data on the instantaneous flame front dynamics. The exact equation given by Pope is used to obtain flame surface density maps for different flame conditions. Some assumptions are made in order to access three-dimensional information from our two-dimensional experiments. Two different methodologies are proposed and tested in term of global mass balance (what enters compared to what is burned). The detailed experimental flame surface data provided for the first time in this work should progressively allow improvement of turbulent premixed flame modeling approaches. (author)

  17. Premixed turbulent combustion to opposed streams

    SciTech Connect

    Kostiuk, L.W.; Cheng, R.K.

    1992-03-01

    Premixed turbulent combustion in opposed streams has been studied experimentally by the use of two component laser doppler aneomometry. This flow geometry is part of a class of stagnating flows used to study turbulent combustion in recent years. It does not involve any surface near the flames because of the flow symmetry thus circumventing many of the effects of flame surface interaction. The mean non-reacting flow is found to be self-similar for all the conditions studied in this and the stagnation plate configuration. A homogeneous region of plane straining is produced in the vicinity of the stagnation and there is a strong interaction between the turbulence in the flow and the mean straining which can increase the rms velocity as the flow stagnates. The reacting flow fields are found to be symmetric about the free stagnation point. The traverses of mean axial velocity in the stagnation streamlines for reaction flows are not dramatically different from the non-reaction flows. These results differ from turbulent combustion experiments where the flow is stagnated by a flat plate. The extinction limits was studied for propane:air mixtures. 11 refs.

  18. Dry low NOx combustion system with pre-mixed direct-injection secondary fuel nozzle

    DOEpatents

    Zuo, Baifang; Johnson, Thomas; Ziminsky, Willy; Khan, Abdul

    2013-12-17

    A combustion system includes a first combustion chamber and a second combustion chamber. The second combustion chamber is positioned downstream of the first combustion chamber. The combustion system also includes a pre-mixed, direct-injection secondary fuel nozzle. The pre-mixed, direct-injection secondary fuel nozzle extends through the first combustion chamber into the second combustion chamber.

  19. Numerical simulation of premixed turbulent methane combustion

    SciTech Connect

    Bell, John B.; Day, Marcus S.; Grcar, Joseph F.

    2001-12-14

    In this paper we study the behavior of a premixed turbulent methane flame in three dimensions using numerical simulation. The simulations are performed using an adaptive time-dependent low Mach number combustion algorithm based on a second-order projection formulation that conserves both species mass and total enthalpy. The species and enthalpy equations are treated using an operator-split approach that incorporates stiff integration techniques for modeling detailed chemical kinetics. The methodology also incorporates a mixture model for differential diffusion. For the simulations presented here, methane chemistry and transport are modeled using the DRM-19 (19-species, 84-reaction) mechanism derived from the GRIMech-1.2 mechanism along with its associated thermodynamics and transport databases. We consider a lean flame with equivalence ratio 0.8 for two different levels of turbulent intensity. For each case we examine the basic structure of the flame including turbulent flame speed and flame surface area. The results indicate that flame wrinkling is the dominant factor leading to the increased turbulent flame speed. Joint probability distributions are computed to establish a correlation between heat release and curvature. We also investigate the effect of turbulent flame interaction on the flame chemistry. We identify specific flame intermediates that are sensitive to turbulence and explore various correlations between these species and local flame curvature. We identify different mechanisms by which turbulence modulates the chemistry of the flame.

  20. Combustion-acoustic stability analysis for premixed gas turbine combustors

    NASA Technical Reports Server (NTRS)

    Darling, Douglas; Radhakrishnan, Krishnan; Oyediran, Ayo; Cowan, Lizabeth

    1995-01-01

    Lean, prevaporized, premixed combustors are susceptible to combustion-acoustic instabilities. A model was developed to predict eigenvalues of axial modes for combustion-acoustic interactions in a premixed combustor. This work extends previous work by including variable area and detailed chemical kinetics mechanisms, using the code LSENS. Thus the acoustic equations could be integrated through the flame zone. Linear perturbations were made of the continuity, momentum, energy, chemical species, and state equations. The qualitative accuracy of our approach was checked by examining its predictions for various unsteady heat release rate models. Perturbations in fuel flow rate are currently being added to the model.

  1. Large-Eddy Simulation of Premixed and Partially Premixed Turbulent Combustion Using a Level Set Method

    NASA Astrophysics Data System (ADS)

    Duchamp de Lageneste, Laurent; Pitsch, Heinz

    2001-11-01

    Level-set methods (G-equation) have been recently used in the context of RANS to model turbulent premixed (Hermann 2000) or partially premixed (Chen 1999) combustion. By directly taking into account unsteady effects, LES can be expected to improve predictions over RANS. Since the reaction zone thickness of premixed flames in technical devices is usually much smaller than the LES grid spacing, chemical reactions completely occur on the sub-grid scales and hence have to be modeled entirely. In the level-set methodology, the flame front is represented by an arbitrary iso-surface G0 of a scalar field G whose evolution is described by the so-called G-equation. This equation is only valid at G=G_0, and hence decoupled from other G levels. Heat release is then modeled using a flamelet approach in which temperature is determined as a function of G and the mixture-fraction Z. In the present study, the proposed approach has been formulated for LES and validated using data from a turbulent Bunsen burner experiment (Chen, Peters 1996). Simulation of an experimental Lean Premixed Prevapourised (LPP) dump combustor (Besson, Bruel 1999, 2000) under different premixed or partially premixed conditions will also be presented.

  2. Partially premixed prevalorized kerosene spray combustion in turbulent flow

    SciTech Connect

    Chrigui, M.; Ahmadi, W.; Sadiki, A.; Janicka, J.; Moesl, K.

    2010-04-15

    A detailed numerical simulation of kerosene spray combustion was carried out on a partially premixed, prevaporized, three-dimensional configuration. The focus was on the flame temperature profile dependency on the length of the pre-vaporization zone. The results were analyzed and compared to experimental data. A fundamental study was performed to observe the temperature variation and flame flashback. Changes were made to the droplet diameter, kerosene flammability limits, a combustion model parameter and the location of the combustion initialization. Investigations were performed for atmospheric pressure, inlet air temperature of 90 C and a global equivalence ratio of 0.7. The simulations were carried out using the Eulerian Lagrangian procedure under a fully two-way coupling. The Bray-Moss-Libby model was adjusted to account for the partially premixed combustion. (author)

  3. Characterization of oscillations during premix gas turbine combustion

    SciTech Connect

    Richards, G.A.; Janus, M.C.

    1998-04-01

    The use of premix combustion in stationary gas turbines can produce very low levels of NO{sub x} emissions. This benefit is widely recognized, but turbine developers routinely encounter problems with combustion oscillations during the testing of new premix combustors. Because of the associated pressure fluctuations, combustion oscillations must be eliminated in a final combustor design. Eliminating these oscillations is often time-consuming and costly because there is no single approach to solve an oscillation problem. Previous investigations of combustion stability have focused on rocket applications, industrial furnaces, and some aeroengine gas turbines. Comparatively little published data is available for premixed combustion at conditions typical of an industrial gas turbine. In this paper, the authors report experimental observations of oscillations produced by a fuel nozzle typical of industrial gas turbines. Tests are conducted in a specially designed combustor capable of providing the acoustic feedback needed to study oscillations. Tests results are presented for pressures up to 10 atmospheres, theoretical considerations, it is expected that oscillations can be characterized by a nozzle reference velocity, with operating pressure playing a smaller role. This expectation is compared to observed data that shows both the benefits and limitations of characterizing the combustor oscillating behavior in terms of a reference velocity rather than other engine operating parameters. This approach to characterizing oscillations is then used to evaluate how geometric changes to the fuel nozzle will affect the boundary between stable and oscillating combustion.

  4. Tabulated Combustion Model Development For Non-Premixed Flames

    NASA Astrophysics Data System (ADS)

    Kundu, Prithwish

    D diffusion flame solver. The proposed model did not use progress variables like the traditional chemistry tabulation methods. The resulting model demonstrated an order of magnitude computational speed up over the RIF model. The results were validated across a wide range of operating conditions for diesel injections and the results were in close agreement to those of the experimental data. History of scalar dissipation rates plays a very important role in non premixed flames. However, tabulated methods have not been able to incorporate this physics in their models. A comparative approach is developed that can quantify these effects and find correlations with flow variables. A new model is proposed to include these effects in tabulated combustion models. The model is initially validated for 1D counterflow diffusion flame problems at engine conditions. The model is further implemented and validated in a 3D RANS code across a range of operating conditions for spray flames.

  5. A model for premixed combustion oscillations

    SciTech Connect

    Janus, M.C.; Richards, G.A.

    1996-09-01

    This paper describes a simulation based on a time dependent, nonlinear control volume analysis. The combustion is modeled as a well-stirred reactor having finite kinetics. Flow properties and species in the nozzle, combustion, and tailpipe regions are determined using a control volume formulation of the conservation equation.

  6. Pulsed jet combustion generator for non-premixed charge engines

    DOEpatents

    Oppenheim, A. K.; Stewart, H. E.

    1990-01-01

    A device for introducing fuel into the head space of cylinder of non-premixed charge (diesel) engines is disclosed, which distributes fuel in atomized form in a plume, whose fluid dynamic properties are such that the compression heated air in the cylinder head space is entrained into the interior of the plume where it is mixed with and ignites the fuel in the plume interior, to thereby control combustion, particularly by use of a multiplicity of individually controllable devices per cylinder.

  7. Analysis of Lean Premixed/Prevaporized Combustion with KIVA-2

    NASA Technical Reports Server (NTRS)

    Deur, J. M.; Kundu, K. P.; Darling, D. D.; Cline, M. C.; Micklow, G. J.; Harper, M. R.; Simons, T. A.

    1994-01-01

    Requirements to reduce the emissions of pollutants from gas turbines used in aircraft propulsion and ground based power generation have led to consideration of lean premixed/prevaporized (LPP) combustion concept. This paper describes some of the LPP flame tube analyses performed at the NASA Research Center with KIVA-2, a well-known multi-dimensional CFD code for problems including sprays, turbulence, and combustion. Modifications to KIVA-2's boundary condition and chemistry treatments have been made to meet the needs of the present study. The study itself focuses on two key aspects of the LPP concept, low emissions and flame stability (including flashback and lean blowoff.

  8. Results of a model for premixed combustion oscillations

    SciTech Connect

    Janus, M.C.; Richards, G.A.

    1996-09-01

    Combustion oscillations are receiving renewed research interest due to increasing use of lean premix (LPM) combustion to gas turbines. A simple, nonlinear model for premixed combustion is described in this paper. The model was developed to help explain specific experimental observations and to provide guidance for development of active control schemes based on nonlinear concepts. The model can be used to quickly examine instability trends associated with changes in equivalence ratio, mass flow rate, geometry, ambient conditions, etc. The model represents the relevant processes occurring in a fuel nozzle and combustor which are analogous to current LPM turbine combustors. Conservation equations for the fuel nozzle and combustor are developed from simple control volume analysis, providing a set of ordinary differential equations that can be solved on a personal computer. Combustion is modeled as a stirred reactor, with a bimolecular reaction rate between fuel and air. A variety of numerical results and comparisons to experimental data are presented to demonstrate the utility of the model. Model results are used to understand the fundamental mechanisms which drive combustion oscillations, effects of inlet air temperature and nozzle geometry on instability, and effectiveness of open loop control schemes.

  9. Premixed Gas Combustion: An Excitable System

    NASA Technical Reports Server (NTRS)

    Pearlman, Howard

    1997-01-01

    Rotating spiral and target patterns have been observed experimentally on freely-propagating premixed gas flames in large diameter tubes at normal gravity (1-g). These modes of propagation occur in near-limit mixtures which have a Lewis number (Le, defined as the ratio of the thermal diffusivity of the cold mixture to the mass diffusivity of the scarce component into the mixture) sufficiently greater than one. However, at 1-g, buoyant flows strongly distort the flame curvature, hydrodynamics (thus stretch) and convective transport of species and heat. In turn, these alter the critical Le required for onset of instability. To isolate and better understand the mechanisms which drive the observed patterns and their dynamics, 1-g and microgravity (micro-g) experiments are being conducted to determine: (1) the structure and dynamics of the patterns, (2) a map of the critical Le and heat loss for their occurrence, (3) the relative significance of the chemical kinetics, and (4) the effect of curvature (local wave and global flame front) on wave propagation. With this in hand, we will be better prepared to discuss an additional mode, a state of 'chemical turbulence,' which seems to be the ultimate fate of many of these near-limit flames prior to extinction.

  10. Combustion Oscillation Analysis of Premixed Flames at Elevated Pressures

    NASA Astrophysics Data System (ADS)

    Ohtsuka, Masaya; Yoshida, Shohei; Inage, Shin'Ichi; Kobayashi, Nariyoshi

    A new analytical time lag flame model based on Bloxidge’s flame model was introduced, which calculates the combustion oscillation of premixed flame to take into account the distribution of heat release rate and flame speed that was calculated by analytical formulas dependent on pressure, temperature, fuel-to-air ratio and velocity. The transfer matrix technique using the new flame model was applied to the calculation of acoustic resonance characteristics. To verify the model, combustion oscillation experiments were performed for methane-air premixed flames stabilized by a swirl burner at elevated pressures in a range of 0.6-0.9MPa. The fluctuating pressure had a maximum peak at a specific value of fτf, where f is the resonance frequency and τf is the passing time of premixed gas through the flame zone. The analytical model could simulate the dependency of the fluctuating pressure local peak on the fuel-to-air ratio and the static pressure.

  11. Subfilter scale combustion modelling for large eddy simulation of turbulent premixed flames

    NASA Astrophysics Data System (ADS)

    Shahbazian, Nasim

    Large eddy simulation (LES) is a powerful computational tool for modelling turbulent combustion processes. However, for reactive flows, LES is still under significant development. In particular, for turbulent premixed flames, a considerable complication of LES is that the flame thickness is generally much smaller than the LES filter width such that the flame front and chemical reactions cannot be resolved on the grid. Accurate and robust subfilter-scale (SFS) models of the unresolved turbulence-chemistry interactions are therefore required and studies are needed to evaluate and improve them. In this thesis, a detailed comparison and evaluation of five different SFS models for turbulence-chemistry interactions in LES of premixed flames is presented. These approaches include both flamelet- and non-flamelet-based models, coupled with simple or tabulated chemistry. The modelling approaches considered herein are: algebraic- and transport-equation variants of the flame surface density (FSD) model, the presumed conditional moment (PCM) with flame prolongation of intrinsic low-dimensional manifold (FPI) tabulated chemistry, or PCM-FPI approach, evaluated with two different presumed probability density function (PDF) models; and conditional source-term estimation (CSE) approach. The predicted LES solutions are compared to the existing laboratory-scale experimental observation of Bunsen-type turbulent premixed methane-air flames, corresponding to lean and stoichiometric conditions lying from the upper limit of the flamelet regime to well within the thin reaction zones regime of the standard regimes diagram. Direct comparison of different SFS approaches allows investigation of stability and performance of the models, while the weaknesses and strengths of each approach are identified. Evaluation of algebraic and transported FSD models highlights the importance of non-equilibrium transport in turbulent premixed flames. The effect of the PDF type for the reaction progress

  12. Subfilter Scale Combustion Modelling for Large Eddy Simulation of Turbulent Premixed Flames

    NASA Astrophysics Data System (ADS)

    Shahbazian, Nasim

    Large eddy simulation (LES) is a powerful computational tool for modelling turbulent combustion processes. However, for reactive flows, LES is still under significant development. In particular, for turbulent premixed flames, a considerable complication of LES is that the flame thickness is generally much smaller than the LES filter width such that the flame front and chemical reactions cannot be resolved on the grid. Accurate and robust subfilter-scale (SFS) models of the unresolved turbulence-chemistry interactions are therefore required and studies are needed to evaluate and improve them. In this thesis, a detailed comparison and evaluation of five different SFS models for turbulence- chemistry interactions in LES of premixed flames is presented. These approaches include both flamelet- and non-flamelet-based models, coupled with simple or tabulated chemistry. The mod- elling approaches considered herein are: algebraic- and transport-equation variants of the flame surface density (FSD) model, the presumed conditional moment (PCM) with flame prolongation of intrinsic low-dimensional manifold (FPI) tabulated chemistry, or PCM-FPI approach, evaluated with two different presumed probability density function (PDF) models; and conditional source-term estimation (CSE) approach. The predicted LES solutions are compared to the existing laboratory-scale experimental observation of Bunsen-type turbulent premixed methane-air flames, corresponding to lean and stoichiometric conditions lying from the upper limit of the flamelet regime to well within the thin reaction zones regime of the standard regimes diagram. Direct comparison of different SFS approaches allows investigation of stability and performance of the models, while the weaknesses and strengths of each approach are identified. Evaluation of algebraic and transported FSD models highlights the importance of non-equilibrium transport in turbulent premixed flames. The effect of the PDF type for the reaction progress

  13. Lean Premixed Combustion/Active Control

    SciTech Connect

    D. J. Seery

    2000-02-01

    An experimental comparison between two contrasting fuel-air swirlers for industrial gas turbine applications was undertaken at the United Technologies Research Center. The first, termed an Aerodynamic nozzle, relied on the prevailing aerodynamic forces to stabilize the downstream combustion zone. The second configuration relied on a conventional bluff plate for combustion stability and was hence named a Bluff-Body nozzle. Performance mapping over the power curve revealed the acoustic superiority of the Bluff-Body nozzle. Two dimensional Rayleigh indices calculated from CCD images identified larger acoustic driving zones associated with the Aerodynamic nozzle relative to its bluff counterpart. The Bluff-Body's success is due to increased flame stabilization (superior anchoring ability) which reduced flame motion and thermal/acoustic coupling.

  14. FUEL INTERCHANGEABILITY FOR LEAN PREMIXED COMBUSTION IN GAS TURBINE ENGINES

    SciTech Connect

    Don Ferguson; Geo. A. Richard; Doug Straub

    2008-06-13

    In response to environmental concerns of NOx emissions, gas turbine manufacturers have developed engines that operate under lean, pre-mixed fuel and air conditions. While this has proven to reduce NOx emissions by lowering peak flame temperatures, it is not without its limitations as engines utilizing this technology are more susceptible to combustion dynamics. Although dependent on a number of mechanisms, changes in fuel composition can alter the dynamic response of a given combustion system. This is of particular interest as increases in demand of domestic natural gas have fueled efforts to utilize alternatives such as coal derived syngas, imported liquefied natural gas and hydrogen or hydrogen augmented fuels. However, prior to changing the fuel supply end-users need to understand how their system will respond. A variety of historical parameters have been utilized to determine fuel interchangeability such as Wobbe and Weaver Indices, however these parameters were never optimized for today’s engines operating under lean pre-mixed combustion. This paper provides a discussion of currently available parameters to describe fuel interchangeability. Through the analysis of the dynamic response of a lab-scale Rijke tube combustor operating on various fuel blends, it is shown that commonly used indices are inadequate for describing combustion specific phenomena.

  15. A numerical investigation of premixed combustion in wave rotors

    NASA Technical Reports Server (NTRS)

    Nalim, M. Razi; Paxson, Daniel E.

    1996-01-01

    Wave rotor cycles which utilize premixed combustion processes within the passages are examined numerically using a one-dimensional CFD-based simulation. Internal-combustion wave rotors are envisioned for use as pressure-gain combustors in gas turbine engines. The simulation methodology is described, including a presentation of the assumed governing equations for the flow and reaction in the channels, the numerical integration method used, and the modeling of external components such as recirculation ducts. A number of cycle simulations are then presented which illustrate both turbulent-deflagration and detonation modes of combustion. Estimates of performance and rotor wall temperatures for the various cycles are made, and the advantages and disadvantages of each are discussed.

  16. Stretching and quenching of flamelets in premixed turbulent combustion

    SciTech Connect

    Meneveau, C. ); Poinsot, T. )

    1991-09-01

    This paper reports on the stretch rate of flamelets in premixed turbulent combustion which is computed using detailed numerical simulations of vortex-flame interactions and a model for intermittent turbulence taking into account all possible turbulence scales acting on the flame front. Simulations of interactions between isolated vortices and a laminar flame front are used to obtain a relation between the characteristics of a given vortex and the actual flame stretch generated by this structure. Quenching conditions and quenching times are also given by these simulations. A net rate of stretch is then defined in the case of a complete turbulent flow field as the difference between the total rate of flame stretch and the quenching rate due to scales that have a high enough energy and a long enough lifetime to quench locally the flame front. The net rate of stretch is computed for a variety of parameters of interest in practical applications. It is a function of the large-scale turbulence parameters and the laminar flame speed and flame thickness and may be used as an input in most flamelet models for premixed turbulent combustion.

  17. Development of a Premixed Combustion Capability for Scramjet Combustion Experiments

    NASA Technical Reports Server (NTRS)

    Rockwell, Robert D.; Goyne, Christopher P.; Rice, Brian E.; Chelliah, Harsha; McDaniel, James C.; Edwards, Jack R.; Cantu, Luca M. L.; Gallo, Emanuela C. A.; Cutler, Andrew D.; Danehy, Paul M.

    2015-01-01

    Hypersonic air-breathing engines rely on scramjet combustion processes, which involve high speed, compressible, and highly turbulent flows. The combustion environment and the turbulent flames at the heart of these engines are difficult to simulate and study in the laboratory under well controlled conditions. Typically, wind-tunnel testing is performed that more closely approximates engine testing rather than a careful investigation of the underlying physics that drives the combustion process. The experiments described in this paper, along with companion data sets being developed separately, aim to isolate the chemical kinetic effects from the fuel-air mixing process in a dual-mode scramjet combustion environment. A unique fuel injection approach is taken that produces a nearly uniform fuel-air mixture at the entrance to the combustor. This approach relies on the precombustion shock train upstream of the dual-mode scramjet combustor. A stable ethylene flame anchored on a cavity flameholder with a uniformly mixed combustor inflow has been achieved in these experiments allowing numerous companion studies involving coherent anti-Stokes Raman scattering (CARS), particle image velocimetry (PIV), and planar laser induced fluorescence (PLIF) to be performed.

  18. The conditional moment closure method for modeling lean premixed turbulent combustion

    NASA Astrophysics Data System (ADS)

    Martin, Scott Montgomery

    Natural gas fired lean premixed gas turbines have become the method of choice for new power generation systems due to their high efficiency and low pollutant emissions. As emission regulations for these combustion systems become more stringent, the use of numerical modeling has become an important a priori tool in designing clean and efficient combustors. Here a new turbulent combustion model is developed in an attempt to improve the state of the art. The Conditional Moment Closure (CMC) method is a new theory that has been applied to non-premixed combustion with good success. The application of the CMC method to premixed systems has been proposed, but has not yet been done. The premixed CMC method replaces the species mass fractions as independent variables with the species mass fractions that are conditioned on a reaction progress variable (RPV). Conservation equations for these new variables are then derived and solved. The general idea behind the CMC method is that the behavior of the chemical species is closely coupled to the reaction progress variable. Thus, species conservation equations that are conditioned on the RPV will have terms involving the fluctuating quantities that are much more likely to be negligible. The CMC method accounts for the interaction between scalar dissipation (micromixing) and chemistry, while de-coupling the kinetics from the bulk flow (macromixing). Here the CMC method is combined with a commercial computational fluid dynamics program, which calculates the large-scale fluid motions. The CMC model is validated by comparison to 2-D reacting backward facing step data. Predicted species, temperature and velocity fields are compared to experimental data with good success. The CMC model is also validated against the University of Washington's 3-D jet stirred reactor (JSR) data, which is an idealized lean premixed combustor. The JSR results are encouraging, but not as good as the backward facing step. The largest source of error is from

  19. Partially-Premixed Flames in Internal Combustion Engines

    SciTech Connect

    Robert W. Pitz; Michael C. Drake; Todd D. Fansler; Volker Sick

    2003-11-05

    This was a joint university-industry research program funded by the Partnerships for the Academic-Industrial Research Program (PAIR). The research examined partially premixed flames in laboratory and internal combustion engine environments at Vanderbilt University, University of Michigan, and General Motors Research and Development. At Vanderbilt University, stretched and curved ''tubular'' premixed flames were measured in a unique optically accessible burner with laser-induced spontaneous Raman scattering. Comparisons of optically measured temperature and species concentration profiles to detailed transport, complex chemistry simulations showed good correspondence at low-stretch conditions in the tubular flame. However, there were significant discrepancies at high-stretch conditions near flame extinction. The tubular flame predictions were found to be very sensitive to the specific hydrogen-air chemical kinetic mechanism and four different mechanisms were compared. In addition, the thermo-diffusive properties of the deficient reactant, H2, strongly affected the tubular flame structure. The poor prediction near extinction is most likely due to deficiencies in the chemical kinetic mechanisms near extinction. At the University of Michigan, an optical direct-injected engine was built up for laser-induced fluorescence imaging experiments on mixing and combustion under stratified charge combustion conditions with the assistance of General Motors. Laser attenuation effects were characterized both experimentally and numerically to improve laser imaging during the initial phase of the gasoline-air mixture development. Toluene was added to the isooctane fuel to image the fuel-air equivalence ratio in an optically accessible direct-injected gasoline engine. Temperature effects on the toluene imaging of fuel-air equivalence ratio were characterized. For the first time, oxygen imaging was accomplished in an internal combustion engine by combination of two fluorescence trackers

  20. Subfilter Scale Modelling for Large Eddy Simulation of Lean Hydrogen-Enriched Turbulent Premixed Combustion

    NASA Astrophysics Data System (ADS)

    Hernandez Perez, Francisco Emanuel

    Hydrogen (H2) enrichment of hydrocarbon fuels in lean premixed systems is desirable since it can lead to a progressive reduction in greenhouse-gas emissions, while paving the way towards pure hydrogen combustion. In recent decades, large-eddy simulation (LES) has emerged as a promising tool to computationally describe and represent turbulent combustion processes. However, a considerable complication of LES for turbulent premixed combustion is that chemical reactions occur in a thin reacting layer at small scales which cannot be entirely resolved on computational grids and need to be modelled. In this thesis, subfilter-scale (SFS) modelling for LES of lean H 2-enriched methane-air turbulent premixed combustion was investigated. Two- and three-dimensional fully-compressible LES solvers for a thermally perfect reactive mixture of gases were developed and systematically validated. Two modelling strategies for the chemistry-turbulence interaction were pursued: the artificially thickened flame model with a power-law SFS wrinkling approach and the presumed conditional moment (PCM) coupled with the flame prolongation of intrinsic low-dimensional manifold (FPI) chemistry tabulation technique. Freely propagating and Bunsen-type flames corresponding to stoichiometric and lean premixed mixtures were considered. Validation of the LES solvers was carried out by comparing predicted solutions with experimental data and other published numerical results. Head-to-head comparisons of different SFS approaches, including a transported flame surface density (FSD) model, allowed to identify weaknesses and strengths of the various models. Based on the predictive capabilities of the models examined, the PCM-FPI model was selected for the study of hydrogen-enrichment of methane. A new progress of reaction variable was proposed to account for NO. The importance of transporting species with different diffusion coefficients was demonstrated, in particular for H2. The proposed approach was

  1. Dynamic properties of combustion instability in a lean premixed gas-turbine combustor.

    PubMed

    Gotoda, Hiroshi; Nikimoto, Hiroyuki; Miyano, Takaya; Tachibana, Shigeru

    2011-03-01

    We experimentally investigate the dynamic behavior of the combustion instability in a lean premixed gas-turbine combustor from the viewpoint of nonlinear dynamics. A nonlinear time series analysis in combination with a surrogate data method clearly reveals that as the equivalence ratio increases, the dynamic behavior of the combustion instability undergoes a significant transition from stochastic fluctuation to periodic oscillation through low-dimensional chaotic oscillation. We also show that a nonlinear forecasting method is useful for predicting the short-term dynamic behavior of the combustion instability in a lean premixed gas-turbine combustor, which has not been addressed in the fields of combustion science and physics.

  2. Large eddy simulation of premixed and non-premixed combustion in a Stagnation Point Reverse Flow combustor

    NASA Astrophysics Data System (ADS)

    Undapalli, Satish

    A new combustor referred to as Stagnation Point Reverse Flow (SPRF) combustor has been developed at Georgia Tech to meet the increasingly stringent emission regulations. The combustor incorporates a novel design to meet the conflicting requirements of low pollution and high stability in both premixed and non-premixed modes. The objective of this thesis work is to perform Large Eddy Simulations (LES) on this lab-scale combustor and elucidate the underlying physics that has resulted in its excellent performance. To achieve this, numerical simulations have been performed in both the premixed and non-premixed combustion modes, and velocity field, species field, entrainment characteristics, flame structure, emissions, and mixing characteristics have been analyzed. Simulations have been carried out first for a non-reactive case to resolve relevant fluid mechanics without heat release by the computational grid. The computed mean and RMS quantities in the non-reacting case compared well with the experimental data. Next, the simulations were extended for the premixed reactive case by employing different sub-grid scale combustion chemistry closures: Eddy Break Up (EBU), Artificially Thickened Flame (TF) and Linear Eddy Mixing (LEM) models. Results from the EBU and TF models exhibit reasonable agreement with the experimental velocity field. However, the computed thermal and species fields have noticeable discrepancies. Only LEM with LES (LEMLES), which is an advanced scalar approach, has been able to accurately predict both the velocity and species fields. Scalar mixing plays an important role in combustion, and this is solved directly at the sub-grid scales in LEM. As a result, LEM accurately predicts the scalar fields. Due to the two way coupling between the super-grid and sub-grid quantities, the velocity predictions also compare very well with the experiments. In other approaches, the sub-grid effects have been either modeled using conventional approaches (EBU) or need

  3. Influence of drop size distribution and fuel vapor fraction on premixed spray combustion

    NASA Astrophysics Data System (ADS)

    Machiroutu, Sridhar Venkatabojji

    Premixed spray combustion is affected by fuel and oxidizer properties, mixture equivalence ratio and spray quality. The spray quality is characterized by a mean droplet diameter (SMD) and a droplet size distribution (DSD). Prior experimental studies have considered only the influence of SMD, in part due to the difficulty in controlling the DSD independently. The present work provides experimental evidence demonstrating the effect of the fuel droplet size distribution and fuel vapor fraction on premixed spray combustion. Combustion experiments were performed in a pilot-ignited, continuous flow, tubular, vertical test rig wherein fuel sprays were injected into an air stream. A novel twin-atomizer technique that allowed control over overall equivalence ratio, SMD, DSD, and fuel vapor fraction of the premixed spray was used to generate test sprays. A line-of-sight, infrared (IR) extinction technique was developed to quantify the fuel vapor fraction in premixed sprays. Radial distributions of fuel vapor were evaluated using an 'onion peeling' deconvolution technique. Combustion of test sprays indicated flame propagation among regions of high fuel vapor fraction to generate a high rate of combustion. In lean premixed sprays, the presence of a low fuel vapor concentration does not impact the combustion process. Experimental evidence demonstrating the enhancement of flame propagation velocity for optimal SMDs of ethanol sprays has been found. It was observed that test sprays with narrower DSDs have faster burning rates and more complete combustion. The DSD of the sprays were characterized with a droplet surface-area-based standard deviation of the DSD.

  4. A test device for premixed gas turbine combustion oscillations

    SciTech Connect

    Richards, G.A.; Gemmen, R.S.; Yip, M.J.

    1996-03-01

    This report discusses design and operation of a single-nozzle test combustor for studying lean, premixed combustion oscillations from gas turbine fuel nozzles. It was used to study oscillations from a prototype fuel nozzle that produced oscillations during testing in a commercial engine. Similar, but not identical, oscillations were recorded in the test device. Basic requirements of the device design were that the flame geometry be maintained and acoustic losses be minimized; this was achieved by using a Helmholtz resonator as the combustor geometry. Surprisingly, the combustor oscillated strongly at several frequencies, without modification of the resonator. Brief survey of operating conditions suggests that it may be helpful to characterize oscillating behavior in terms of reference velocity and inlet air temperature with the rig backpressure playing a smaller role. The preliminary results do not guarantee that the single-nozzle test device will reproduce arbitrary oscillations that occur on a complete engine test. Nozzle/nozzle interactions may complicate the response, and oscillations controlled by acoustic velocities transverse to the nozzle axis may not be reproduced in a test device that relies on a bulk Helmholtz mode. Nevertheless, some oscillations can be reproduced, and the single-nozzle test device allows both active and passive control strategies to be tested relatively inexpensively.

  5. Study on the potential of BML-approach and G-equation concept-based models for predicting swirling partially premixed combustion systems: URANS computations

    SciTech Connect

    Schneider, E.; Maltsev, A.; Sadiki, A.; Janicka, J.

    2008-03-15

    In this work the potential of two combustion modeling approaches (BML and G-equation based models) for partially premixed flames in combustion systems of various complexities is investigated using URANS computations. The first configuration consists of a nonconfined swirled premixed methane/air flame (swirl number 0.75) exhibiting partially premixed effects due to coflowing. The system is studied either in the isothermal case or in the reacting mode and for different thermal powers. The second configuration represents a model GT combustion chamber and features the main properties of real GT combustors: a confined swirled flow with multiple recirculation zones and reattachment points, resulting in a partially premixed methane/air aerodynamically stabilized flame and an additional diffusion flame formed by the fuel and oxidizer not consumed in the premixed flame. This makes it possible to subject the modeling to variation of different parameters, such as confinement, Re-number or flame power, or adiabatic or nonadiabatic conditions. For this purpose an extended Bray-Moss-Libby model and a G-equation-based approach, both coupled to the mixture fraction transport equation to account for partially premixed effects, are used following the so-called conditional progress variable approach (CPVA). The radiation effects are also taken into account. To account for the turbulence-chemistry interaction, a (multivariate) presumed PDF approach is applied. The results are compared with LDV, Raman, and PLIF measurements. Beyond a pure validation, the URANS is used to capture the presence of the precessing vortex core and to analyze the performance of different modeling strategies of partially premixed combustion in capturing the expansion ratio, species formation conditioned on the flame front, and flame front stabilization. It appears that the combustion models used are able to achieve plausible results in the complex combustion systems under study, while the BML-based model

  6. Experimental investigation on plasma-assisted combustion characteristics of premixed propane/air mixture

    NASA Astrophysics Data System (ADS)

    Liu, Xingjian; He, Liming; Yu, Jinlu; Zeng, Hao; Jin, Tao

    2015-06-01

    A detailed study on the plasma-assisted combustion (PAC) characteristics of premixed propane/air mixture is presented. The PAC is measured electrically, as well as optically with a multichannel spectrometer. The characteristics are demonstrated by stable combustion temperature and combustion stability limits, and the results are compared with conventional combustion (CC). Stable combustion temperature measurements show that the introduction of PAC into combustion system can increase the stable combustion temperature, and the increment is more notable with an increase of discharge voltage. Besides, the rich and weak limits of combustion stability are both enlarged when plasma is applied into the combustion process and the increase of discharge voltage results in the expansion of combustion stability limits as well. The measurements of temperature head and emission spectrum illustrate that the kinetic enhancement caused by reactive species in plasma is the main enhancement pathway for current combustion system.

  7. Unstrained and strained flamelets for LES of premixed combustion

    NASA Astrophysics Data System (ADS)

    Langella, Ivan; Swaminathan, Nedunchezhian

    2016-05-01

    The unstrained and strained flamelet closures for filtered reaction rate in large eddy simulation (LES) of premixed flames are studied. The required sub-grid scale (SGS) PDF in these closures is presumed using the Beta function. The relative performances of these closures are assessed by comparing numerical results from large eddy simulations of piloted Bunsen flames of stoichiometric methane-air mixture with experimental measurements. The strained flamelets closure is observed to underestimate the burn rate and thus the reactive scalars mass fractions are under-predicted with an over-prediction of fuel mass fraction compared with the unstrained flamelet closure. The physical reasons for this relative behaviour are discussed. The results of unstrained flamelet closure compare well with experimental data. The SGS variance of the progress variable required for the presumed PDF is obtained by solving its transport equation. An order of magnitude analysis of this equation suggests that the commonly used algebraic model obtained by balancing source and sink in this transport equation does not hold. This algebraic model is shown to underestimate the SGS variance substantially and the implications of this variance model for the filtered reaction rate closures are highlighted.

  8. The hybrid RANS/LES of partially premixed supersonic combustion using G/Z flamelet model

    NASA Astrophysics Data System (ADS)

    Wu, Jinshui; Wang, Zhenguo; Bai, Xuesong; Sun, Mingbo; Wang, Hongbo

    2016-10-01

    In order to describe partially premixed supersonic combustion numerically, G/Z flamelet model is developed and compared with finite rate model in hybrid RANS/LES simulation to study the strut-injection supersonic combustion flow field designed by the German Aerospace Center. A new temperature calculation method based on time-splitting method of total energy is introduced in G/Z flamelet model. Simulation results show that temperature predictions in partially premixed zone by G/Z flamelet model are more consistent with experiment than finite rate model. It is worth mentioning that low temperature reaction zone behind the strut is well reproduced. Other quantities such as average velocity and average velocity fluctuation obtained by developed G/Z flamelet model are also in good agreement with experiment. Besides, simulation results by G/Z flamelet also reveal the mechanism of partially premixed supersonic combustion by the analyses of the interaction between turbulent burning velocity and flow field.

  9. DNS assessment of relation between mean reaction and scalar dissipation rates in the flamelet regime of premixed turbulent combustion

    NASA Astrophysics Data System (ADS)

    Nikolaevich Lipatnikov, Andrei; Nishiki, Shinnosuke; Hasegawa, Tatsuya

    2015-05-01

    The linear relation between the mean rate of product creation and the mean scalar dissipation rate, derived in the seminal paper by K.N.C. Bray ['The interaction between turbulence and combustion', Proceedings of the Combustion Institute, Vol. 17 (1979), pp. 223-233], is the cornerstone for models of premixed turbulent combustion that deal with the dissipation rate in order to close the reaction rate. In the present work, this linear relation is straightforwardly validated by analysing data computed earlier in the 3D Direct Numerical Simulation (DNS) of three statistically stationary, 1D, planar turbulent flames associated with the flamelet regime of premixed combustion. Although the linear relation does not hold at the leading and trailing edges of the mean flame brush, such a result is expected within the framework of Bray's theory. However, the present DNS yields substantially larger (smaller) values of an input parameter cm (or K2 = 1/(2cm - 1)), involved by the studied linear relation, when compared to the commonly used value of cm = 0.7 (or K2 = 2.5). To gain further insight into the issue and into the eventual dependence of cm on mixture composition, the DNS data are combined with the results of numerical simulations of stationary, 1D, planar laminar methane-air flames with complex chemistry, with the results being reported in terms of differently defined combustion progress variables c, i.e. the normalised temperature, density, or mole fraction of CH4, O2, CO2 or H2O. Such a study indicates the dependence of cm both on the definition of c and on the equivalence ratio. Nevertheless, K2 and cm can be estimated by processing the results of simulations of counterpart laminar premixed flames. Similar conclusions were also drawn by skipping the DNS data, but invoking a presumed beta probability density function in order to evaluate cm for the differently defined c's and various equivalence ratios.

  10. Relationships for maximum flame surface density and brush thickness through conditional analysis in turbulent premixed combustion

    NASA Astrophysics Data System (ADS)

    Huh, Kang Y.; Kwon, Jaesung; Lee, Dongkyu

    2013-07-01

    A new conditional averaging method is introduced in terms of the reaction progress variable, c, and its derivatives of successively higher orders, Σ _f^' (or -∂c/∂n) and ∂2c/∂n2, in high Damköhler number (Da) turbulent premixed combustion. c is continuous and differentiable in space so that conditional averages may be defined for flamelets of finite thicknesses as well as for infinitesimally thin flamelets. A coupled set of transport equations are derived with corresponding conditional coefficient terms for mean reaction progress variable, bar c, and flame surface density (FSD), Σf. Statistics for all component terms are consistent with previous results and show the same qualitative trends irrespective of compressibility by the new averaging practice. It is shown that the maximum FSD, Σmax, occurs at the location where the relationship, nabla ^2 bar c + < {nabla \\cdot {n}} rangle _f Σ _f = 0, holds in a flame brush. An analytical expression is derived for Σmax under the assumption of constant tangential strain rate and linear variation of mean curvature and mean displacement speed, ⟨Sd⟩f, in the bar c space. Σmax becomes equal to one fourth ⟨|∇.n|⟩f or half the mean absolute curvature for fully turbulent flames with the magnitude of ⟨n⟩f close to zero. Once the turbulent burning velocity, ST, is determined by asymptotic behavior at the leading edge, the brush thickness, ℓF, may be obtained from local and integral relationships for the product, ℓFΣmax, in a steadily propagating one-dimensional flame. The newly proposed relationships reproduce proper trends of variation for ST, Σmax, and ℓF against measurement data in literature. They are validated to show good agreement with direct numerical simulation (DNS) results of the Lewis number equal to unity for freely propagating incompressible and stagnating compressible turbulent premixed flames.

  11. Characterization of complexities in combustion instability in a lean premixed gas-turbine model combustor.

    PubMed

    Gotoda, Hiroshi; Amano, Masahito; Miyano, Takaya; Ikawa, Takuya; Maki, Koshiro; Tachibana, Shigeru

    2012-12-01

    We characterize complexities in combustion instability in a lean premixed gas-turbine model combustor by nonlinear time series analysis to evaluate permutation entropy, fractal dimensions, and short-term predictability. The dynamic behavior in combustion instability near lean blowout exhibits a self-affine structure and is ascribed to fractional Brownian motion. It undergoes chaos by the onset of combustion oscillations with slow amplitude modulation. Our results indicate that nonlinear time series analysis is capable of characterizing complexities in combustion instability close to lean blowout.

  12. Characterization of complexities in combustion instability in a lean premixed gas-turbine model combustor.

    PubMed

    Gotoda, Hiroshi; Amano, Masahito; Miyano, Takaya; Ikawa, Takuya; Maki, Koshiro; Tachibana, Shigeru

    2012-12-01

    We characterize complexities in combustion instability in a lean premixed gas-turbine model combustor by nonlinear time series analysis to evaluate permutation entropy, fractal dimensions, and short-term predictability. The dynamic behavior in combustion instability near lean blowout exhibits a self-affine structure and is ascribed to fractional Brownian motion. It undergoes chaos by the onset of combustion oscillations with slow amplitude modulation. Our results indicate that nonlinear time series analysis is capable of characterizing complexities in combustion instability close to lean blowout. PMID:23278063

  13. Swozzle based burner tube premixer including inlet air conditioner for low emissions combustion

    DOEpatents

    Tuthill, Richard Sterling; Bechtel, II, William Theodore; Benoit, Jeffrey Arthur; Black, Stephen Hugh; Bland, Robert James; DeLeonardo, Guy Wayne; Meyer, Stefan Martin; Taura, Joseph Charles; Battaglioli, John Luigi

    2002-01-01

    A burner for use in a combustion system of a heavy-duty industrial gas turbine includes a fuel/air premixer having an air inlet, a fuel inlet, and an annular mixing passage. The fuel/air premixer mixes fuel and air into a uniform mixture for injection into a combustor reaction zone. The burner also includes an inlet flow conditioner disposed at the air inlet of the fuel/air premixer for controlling a radial and circumferential distribution of incoming air. The pattern of perforations in the inlet flow conditioner is designed such that a uniform air flow distribution is produced at the swirler inlet annulus in both the radial and circumference directions. The premixer includes a swozzle assembly having a series of preferably air foil shaped turning vanes that impart swirl to the airflow entering via the inlet flow conditioner. Each air foil contains internal fuel flow passages that introduce natural gas fuel into the air stream via fuel metering holes that pass through the walls of the air foil shaped turning vanes. By injecting fuel in this manner, an aerodynamically clean flow field is maintained throughout the premixer. By injecting fuel via two separate passages, the fuel/air mixture strength distribution can be controlled in the radial direction to obtain optimum radial concentration profiles for control of emissions, lean blow outs, and combustion driven dynamic pressure activity as machine and combustor load are varied.

  14. Numerical analysis of reaction-diffusion effects on species mixing rates in turbulent premixed methane-air combustion

    SciTech Connect

    Richardson, E.S.; Grout, R.W.; Chen, J.H.; Sankaran, R.

    2010-03-15

    The scalar mixing time scale, a key quantity in many turbulent combustion models, is investigated for reactive scalars in premixed combustion. Direct numerical simulations (DNS) of three-dimensional, turbulent Bunsen flames with reduced methane-air chemistry have been analyzed in the thin reaction zones regime. Previous conclusions from single step chemistry DNS studies are confirmed regarding the role of dilatation and turbulence-chemistry interactions on the progress variable dissipation rate. Compared to the progress variable, the mixing rates of intermediate species is found to be several times greater. The variation of species mixing rates are explained with reference to the structure of one-dimensional premixed laminar flames. According to this analysis, mixing rates are governed by the strong gradients which are imposed by flamelet structures at high Damkoehler numbers. This suggests a modeling approach to estimate the mixing rate of individual species which can be applied, for example, in transported probability density function simulations. Flame-turbulence interactions which modify the flamelet based representation are analyzed. (author)

  15. Large-Eddy Simulation of Premixed Turbulent Combustion Using the G-Equation

    NASA Astrophysics Data System (ADS)

    Duchamp de Lageneste, Laurent; Pitsch, Heinz

    2000-11-01

    Large eddy simulation (LES) of premixed turbulent combustion is now considered to be a promising field. It has the potential to improve predictions of reacting flows over classical Reynolds-averaged Navier-Stokes (RANS) approaches which lack precision. The difficulties associated with large eddy simulations of such flows are related to the fact that the reaction zone is usually much smaller than the LES grid. In the present study, a level-set approach is used to describe turbulent flame propagation. In this method, the flame is represented by an iso-surface of a scalar field described by the G-equation. The main problem in this method is to specify the turbulent burning velocity which replaces the chemical source term appearing in progress variable approaches. An expression for this quantity, valid in both the corrugated flamelet and thin reaction zone regime has recently been proposed in the context of RANS by Peters (Journal of Fluid Mechanics 1999). In the present work a formulation of the G-equation and the subgrid part of the turbulent burning velocity will be given. In particular, the G-field is treated as a distance function in order to be able to define quantities as strain or curvature. Periodic reinitializations are performed to maintain this structure and avoid the use of an artificial diffusion term. To validate the model, computational results from the large eddy simulation of a bunsen-burner flame is compared with experimental data.

  16. Hydrodynamic instability and shear layer effects in turbulent premixed combustion

    NASA Astrophysics Data System (ADS)

    Schlimpert, S.; Feldhusen, A.; Grimmen, J. H.; Roidl, B.; Meinke, M.; Schröder, W.

    2016-01-01

    A turbulent premixed plane jet flame is analyzed by large-eddy simulations. The analysis shows that the flame front wrinkling is strongly influenced by the shear layer effect when the gas expansion effects are small leading to larger flame front amplitudes at the flame base than at high gas expansion ratios. However, the hydrodynamic instability effect induces a continuously increasing flame front amplitude which yields an enhanced flame pocket generation at the flame tip. Both phenomena influence the magnitude of the turbulent burning area and burning area rate response through the flame front deflections which are determined by the contribution coefficient. This coefficient represents the mutual interaction between the flame and the flow. At low gas expansion ratios, the total heat release rate spectra of the turbulent flame are wider in terms of dominant modes at Strouhal numbers which are linked to the mean flame height oscillations. Thus, at low gas expansion ratios, the vortex-flame interaction is less damped by the flame in the sense that vortices can perturb the flame front stronger. The total heat release rate trend of St-2.2 previously found for a round jet flame is also determined for the current slot jet at realistic gas expansion ratios indicating a general tendency to transfer energy from large to small flame structures. At high gas expansion ratios, an increasing Markstein length leads to an energy transfer between neighboring dominant modes in the low frequency range 1 < St < 10 and the burning area rate response becomes more important for the total heat release rate spectra of the turbulent slot flames which agrees with recent findings for a laminar premixed plane flame.

  17. Cyclic Combustion Variations in Dual Fuel Partially Premixed Pilot-Ignited Natural Gas Engines

    SciTech Connect

    Srinivasan, K. K.; Krishnan, S. R.; Qi, Y.

    2012-05-09

    Dual fuel pilot ignited natural gas engines are identified as an efficient and viable alternative to conventional diesel engines. This paper examines cyclic combustion fluctuations in conventional dual fuel and in dual fuel partially premixed low temperature combustion (LTC). Conventional dual fueling with 95% (energy basis) natural gas (NG) substitution reduces NOx emissions by almost 90%t relative to straight diesel operation; however, this is accompanied by 98% increase in HC emissions, 10 percentage points reduction in fuel conversion efficiency (FCE) and 12 percentage points increase in COVimep. Dual fuel LTC is achieved by injection of a small amount of diesel fuel (2-3 percent on an energy basis) to ignite a premixed natural gas₋air mixture to attain very low NOx emissions (less than 0.2 g/kWh). Cyclic variations in both combustion modes were analyzed by observing the cyclic fluctuations in start of combustion (SOC), peak cylinder pressures (Pmax), combustion phasing (Ca50), and the separation between the diesel injection event and Ca50 (termed "relative combustion phasing" ). For conventional dual fueling, as % NG increases, Pmax decreases, SOC and Ca50 are delayed, and cyclic variations increase. For dual fuel LTC, as diesel injection timing is advanced from 20° to 60° BTDC, the relative combustion phasing is identified as an important combustion parameter along with SoC, Pmax, and CaPmax. For both combustion modes, cyclic variations were characterized by alternating slow and fast burn cycles, especially at high %NG and advanced injection timings. Finally, heat release return maps were analyzed to demonstrate thermal management strategies as an effective tool to mitigate cyclic combustion variations, especially in dual fuel LTC.

  18. Bluff-body stabilized flame dynamics of lean premixed syngas combustion

    NASA Astrophysics Data System (ADS)

    Im, Hong G.; Kim, Yu Jeong; Lee, Bok Jik; Kaust Team

    2015-11-01

    Recently, syngas combustion has been actively investigated for the potential application to integrated gasification combined cycle (IGCC) systems. While lean premixed combustion is attractive for both reduced emission and enhanced efficiency, flame instability becomes often an issue. Bluff-bodies have been adopted as effective flame holders for practical application of premixed flames. In the present study, high-fidelity direct numerical simulations are conducted to investigate the dynamics of lean premixed syngas flames stabilized on a bluff-body, in particular at the near blow-off regime of the flame. A two-dimensional domain of 4 mm height and 20 mm length with a flame holder of a 1 mm-by-1 mm square geometry is used. For a syngas mixture with the equivalence ratio of 0.5 and the CO:H2 ratio of 1, several distinct flame modes are identified as the inflow velocity approaches to the blowoff limit. The sequences of extinction pathway and combustion characteristics are discussed.

  19. Pulsed jet combustion generator for premixed charge engines

    DOEpatents

    Oppenheim, A. K.; Stewart, H. E.; Hom, K.

    1990-01-01

    A method and device for generating pulsed jets which will form plumes comprising eddie structures, which will entrain a fuel/air mixture from the head space of an internal combustion engine, and mixing this fuel/air mixture with a pre-ignited fuel/air mixture of the plumes thereby causing combustion of the reactants to occur within the interior of the eddie structures.

  20. Hybrid lean premixing catalytic combustion system for gas turbines

    DOEpatents

    Critchley, Ian L.

    2003-12-09

    A system and method of combusting a hydrocarbon fuel is disclosed. The system combines the accuracy and controllability of an air staging system with the ultra-low emissions achieved by catalytic combustion systems without the need for a pre-heater. The result is a system and method that is mechanically simple and offers ultra-low emissions over a wide range of power levels, fuel properties and ambient operating conditions.

  1. Pdf modeling for premixed turbulent combustion based on the properties of iso-concentration surfaces

    NASA Technical Reports Server (NTRS)

    Vervisch, L.; Kollmann, W.; Bray, K. N. C.; Mantel, T.

    1994-01-01

    In premixed turbulent flames the presence of intense mixing zones located in front of and behind the flame surface leads to a requirement to study the behavior of iso-concentration surfaces defined for all values of the progress variable (equal to unity in burnt gases and to zero in fresh mixtures). To support this study, some theoretical and mathematical tools devoted to level surfaces are first developed. Then a database of direct numerical simulations of turbulent premixed flames is generated and used to investigate the internal structure of the flame brush, and a new pdf model based on the properties of iso-surfaces is proposed.

  2. Effect of degree of fuel vaporization upon emissions for a premixed prevaporized combustion system

    NASA Technical Reports Server (NTRS)

    Cooper, L. P.

    1979-01-01

    An experimental and analytical study of the combustion of partially vaporized fuel/air mixtures was performed to assess the impact of the degree of fuel vaporization upon emissions for a premixing-prevaporizing flametube combustor. Data collected showed near-linear increases in NOx emmissions with decreasing vaporization at equivalence ratios of 0.6. For equivalence ratios of 0.72, the degree of vaporization had very little impact on NOx emissions. A simple mechanism which accounts for the combustion of liquid droplets in partially vaporized mixtures was found to agree with the measured results with fair accuracy with respect to both trends and magnitudes.

  3. Premixed CH4/O2-enriched air combustion: Identification of thermal, chemical and aerodynamic effects

    NASA Astrophysics Data System (ADS)

    Most, J.-M.; Dahikar, S.; Pal, S.; Claverie, A.; Denis, D.; Pillier, L.; de Persis, S.

    2012-11-01

    This work contributes to the evaluation of a new innovative process focused on the reduction of the cost of a post-combustion capture of CO2 in a Carbon Capture and Storage system (CCS). The process based on the separation of dried fumes composed mainly by CO2 and N2 by using membranes, which should lead to a lower energetic separation cost than amines. But the membranes become efficient if the upstream CO2 concentration is higher than 30% at their entrance that requires enriching the oxidizer flow by O2. To maintain the exhaust temperature compatible with materials thermal resistance, the reactants are diluted by a recirculation of a part of the flue gases (like N2/O2/CO2). But, the chemical kinetic, the energetic efficiencies, the radiation transfer, the transport and thermal properties of the flow can be affected by CO2. The objective of this work will be to identify the behaviour of the combustion of premixed CH4/O2-enriched air, both diluted in N2 and CO2 and to determine the combustion parameters. This allows to recover the CH4/air conditions in terms of CO2 concentration in reactants, O2 excess, dilution rate, temperature of the reactants, etc. Experiments are performed on the laminar premixed flame using counterflow burner. To characterize the combustion behaviour, the flammability limits are determined and flame thickness and position are measured from PLIF-OH diagnostic. Further, CHEMKIN simulations are performed to check the validity of the GRI3.0 chemical kinetic mechanism for premixed CH4/air synthetic combustion and identify the leading phenomena.

  4. Lean Premixed Combustion Stabilized by Low Swirl a Promising Concept for Practical Applications

    NASA Technical Reports Server (NTRS)

    Cheng, R. K.

    1999-01-01

    Since its inception, the low-swirl burner (LSB) has shown to be a useful laboratory apparatus for fundamental studies of premixed turbulent flames. The LSB operates under wide ranges of equivalence ratios, flow rates, and turbulence intensities. Its flame is lifted and detached from the burner and allows easy access for laser diagnostics. The flame brush is axisymmetric and propagates normal to the incident reactants. Therefore, the LSB is well suited for investigating detailed flame structures and empirical coefficients such as flame speed, turbulence transport, and flame generated turbulence. Due to its capability to stabilize ultra-lean premixed turbulent flames (phi approx. = 0.55), the LSB has generated interest from the gas appliance industry for use as an economical low-NO(x) burner. Lean premixed combustion emits low levels of NO(x), due primarily to the low flame temperature. Therefore, it is a very effective NO(x) prevention method without involving selective catalytic reduction (SCR), fuel-air staging, or flue gas recirculation (FGR). En the gas turbine industry, substantial research efforts have already been undertaken and engines with lean premixed combustors are already in use. For commercial and residential applications, premixed pulsed combustors and premixed ceramic matrix burners are commercially available. These lean premixed combustion technologies, however, tend to be elaborate but have relatively limited operational flexibility, and higher capital, operating and maintenance costs. Consequently, these industries are continuing the development of lean premixed combustion technologies as well as exploring new concepts. This paper summarizes the research effects we have undertaken in the past few years to demonstrate the feasibility of applying the low-swirl flame stabilization method for a wide range of heating and power generation systems. The principle of flame stabilization by low-swirl is counter to the conventional high-swirl methods that

  5. Lean premixed combustion stabilized by radiation feedback and heterogeneous catalysis

    SciTech Connect

    Dibble, R.W.; Jyh-Yuan Chen; Sawyer, R.F.

    1995-10-01

    Gas-turbine based systems are becoming the preferred approach to electric power generation from gaseous and liquid fossil-fuels and from biomass. As coal gasification becomes, gas turbines will also become important in the generation of electricity from coal. In smaller, distributed installations, gas turbines will also become important in the generation of electricity from coal. In smaller, distributed installations, gas turbines offer the prospect of cogeneration of electricity and heat, with increased efficiency and reduced pollutant emissions. One of the most important problems facing combustion-based power generation is the control of air pollutants, primarily nitrogen oxides (NO{sub x}, consisting of NO and NO{sub 2}) and carbon monoxide (CO). Nitric oxide (NO) is formed during gas-phase combustion and is the precursor of nitrogen dioxide (NO{sub 2}), the principal component of photochemical smog. Recent research into the mechanisms and control of NO{sub x} formation has been spurred by increasingly stringent emission standards. The principal objective of this research project is the development of effective models for the simulation of catalytic combustion applications.

  6. PREMIXED FLAME PROPAGATION AND MORPHOLOGY IN A CONSTANT VOLUME COMBUSTION CHAMBER

    SciTech Connect

    Hariharan, A; Wichman, IS

    2014-06-04

    This work presents an experimental and numerical investigation of premixed flame propagation in a constant volume rectangular channel with an aspect ratio of six (6) that serves as a combustion chamber. Ignition is followed by an accelerating cusped finger-shaped flame-front. A deceleration of the flame is followed by the formation of a "tulip"-shaped flame-front. Eventually, the flame is extinguished when it collides with the cold wall on the opposite channel end. Numerical computations are performed to understand the influence of pressure waves, instabilities, and flow field effects causing changes to the flame structure and morphology. The transient 2D numerical simulation results are compared with transient 3D experimental results. Issues discussed are the appearance of oscillatory motions along the flame front and the influences of gravity on flame structure. An explanation is provided for the formation of the "tulip" shape of the premixed flame front.

  7. Low and High Temperature Combustion Chemistry of Butanol Isomers in Premixed Flames and Autoignition Systems

    SciTech Connect

    Sarathy, S M; Pitz, W J; Westbrook, C K; Mehl, M; Yasunaga, K; Curran, H J; Tsujimura, T; Osswald, P; Kohse-Hoinghaus, K

    2010-12-12

    Butanol is a fuel that has been proposed as a bio-derived alternative to conventional petroleum derived fuels. The structural isomer in traditional 'bio-butanol' fuel is n-butanol, but newer conversion technologies produce iso-butanol as a fuel. In order to better understand the combustion chemistry of bio-butanol, this study presents a comprehensive chemical kinetic model for all the four isomers of butanol (e.g., 1-, 2-, iso- and tert-butanol). The proposed model includes detailed high temperature and low temperature reaction pathways. In this study, the primary experimental validation target for the model is premixed flat low-pressure flame species profiles obtained using molecular beam mass spectrometry (MBMS). The model is also validated against previously published data for premixed flame velocity and n-butanol rapid compression machine and shock tube ignition delay. The agreement with these data sets is reasonably good. The dominant reaction pathways at the various pressures and temperatures studied are elucidated. At low temperature conditions, we found that the reaction of alphahydroxybutyl with O{sub 2} was important in controlling the reactivity of the system, and for correctly predicting C{sub 4} aldehyde profiles in low pressure premixed flames. Enol-keto isomerization reactions assisted by HO{sub 2} were also found to be important in converting enols to aldehydes and ketones in the low pressure premixed flames. In the paper, we describe how the structural features of the four different butanol isomers lead to differences in the combustion properties of each isomer.

  8. A test device for premixed gas turbine combustion oscillations

    SciTech Connect

    Richards, G.A.; Gemmen, R.S.; Yip, M.J.

    1996-09-01

    This paper discusses the design and operation of a test combustor suitable for studying combustion oscillations caused by a commercial-scale gas turbine fuel nozzle. Aside from the need to be conducted at elevated pressures and temperatures, it is desirable for the experimental device to be flexible in its geometry so as to provide an acoustic environment representative of the commercial device. The combustor design, capabilities, and relevant instrumentation for such a device are presented, along with initial operating experience and preliminary data that suggests the importance of nozzle reference velocity and air temperature.

  9. Lean premixed combustion stabilized by radiation feedback and heterogeneous catalysis

    SciTech Connect

    Dibble, R.W.; Chen, J.Y.; Sawyer, R.F.

    1995-12-31

    Gas-turbine based systems are becoming the preferred approach to electric power generation from gaseous and liquid fossil-fuels and from biomass. As coal gasification becomes more prevalent, gas turbines will also become important in the generation of electricity from coal. In smaller, distributed installations, gas turbines offer the prospect of cogeneration of electricity and heat, with increased efficiency and reduced pollutant emissions. One of the most important problems facing combustion-based power generation is the control of air pollutants, primarily nitrogen oxides and carbon monoxide. Catalytic combustion over noble-metal catalysts offers a method for controlling NO{sub x} emissions. This report describes tests on a gas-fired catalytic combustor and the development of a mathematical model to describe the process. The authors anticipate that the models they develop under this research program will be useful by industry and researchers alike in the design of both experiments and practical gas turbine catalytic combustors. The model--which includes transport codes, mechanisms, and postprocessing routines--is portable and can be run on UNIX workstations. Intelligent design of experiments, guided by this model, can reduce unnecessary expenditures of time and money spent in the laboratory. Likewise, the development of low-NO{sub x} gas turbine systems can be accelerated by using these models to test the effectiveness of combustor designs prior to engaging in time-consuming prototyping.

  10. The coupling between flame surface dynamics and species mass conservation in premixed turbulent combustion

    NASA Technical Reports Server (NTRS)

    Trouve, A.; Veynante, D.; Bray, K. N. C.; Mantel, T.

    1994-01-01

    Current flamelot models based on a description of the flame surface dynamics require the closure of two inter-related equations: a transport equation for the mean reaction progress variable, (tilde)c, and a transport equation for the flame surface density, Sigma. The coupling between these two equations is investigated using direct numerical simulations (DNS) with emphasis on the correlation between the turbulent fluxes of (tilde)c, bar(pu''c''), and Sigma, (u'')(sub S)Sigma. Two different DNS databases are used in the present work: a database developed at CTR by A. Trouve and a database developed by C. J. Rutland using a different code. Both databases correspond to statistically one-dimensional premixed flames in isotropic turbulent flow. The run parameters, however, are significantly different, and the two databases correspond to different combustion regimes. It is found that in all simulated flames, the correlation between bar(pu''c'') and (u'')(sub S)Sigma is always strong. The sign, however, of the turbulent flux of (tilde)c or Sigma with respect to the mean gradients, delta(tilde)c/delta(x) or delta(Sigma)/delta(x), is case-dependent. The CTR database is found to exhibit gradient turbulent transport of (tilde)c and Sigma, whereas the Rutland DNS features counter-gradient diffusion. The two databases are analyzed and compared using various tools (a local analysis of the flow field near the flame, a classical analysis of the conservation equation for (tilde)(u''c''), and a thin flame theoretical analysis). A mechanism is then proposed to explain the discrepancies between the two databases and a preliminary simple criterion is derived to predict the occurrence of gradient/counter-gradient turbulent diffusion.

  11. Sensitivity of Combustion-Acoustic Instabilities to Boundary Conditions for Premixed Gas Turbine Combustors

    NASA Technical Reports Server (NTRS)

    Darling, Douglas; Radhakrishnan, Krishnan; Oyediran, Ayo

    1995-01-01

    Premixed combustors, which are being considered for low NOx engines, are susceptible to instabilities due to feedback between pressure perturbations and combustion. This feedback can cause damaging mechanical vibrations of the system as well as degrade the emissions characteristics and combustion efficiency. In a lean combustor instabilities can also lead to blowout. A model was developed to perform linear combustion-acoustic stability analysis using detailed chemical kinetic mechanisms. The Lewis Kinetics and Sensitivity Analysis Code, LSENS, was used to calculate the sensitivities of the heat release rate to perturbations in density and temperature. In the present work, an assumption was made that the mean flow velocity was small relative to the speed of sound. Results of this model showed the regions of growth of perturbations to be most sensitive to the reflectivity of the boundary when reflectivities were close to unity.

  12. Control of the low-load region in partially premixed combustion

    NASA Astrophysics Data System (ADS)

    Ingesson, Gabriel; Yin, Lianhao; Johansson, Rolf; Tunestal, Per

    2016-09-01

    Partially premixed combustion (PPC) is a low temperature, direct-injection combustion concept that has shown to give promising emission levels and efficiencies over a wide operating range. In this concept, high EGR ratios, high octane-number fuels and early injection timings are used to slow down the auto-ignition reactions and to enhance the fuel and are mixing before the start of combustion. A drawback with this concept is the combustion stability in the low-load region where a high octane-number fuel might cause misfire and low combustion efficiency. This paper investigates the problem of low-load PPC controller design for increased engine efficiency. First, low-load PPC data, obtained from a multi-cylinder heavy- duty engine is presented. The data shows that combustion efficiency could be increased by using a pilot injection and that there is a non-linearity in the relation between injection and combustion timing. Furthermore, intake conditions should be set in order to avoid operating points with unfavourable global equivalence ratio and in-cylinder temperature combinations. Model predictive control simulations were used together with a calibrated engine model to find a gas-system controller that fulfilled this task. The findings are then summarized in a suggested engine controller design. Finally, an experimental performance evaluation of the suggested controller is presented.

  13. Studies in premixed combustion. [Benjamin Levich Inst. for Physico-Chemical Hydrodynamics, City College of CUNY, New York, New York

    SciTech Connect

    Sivashinsky, G.I.

    1993-01-01

    During the period under review, significant progress was been made in studying the intrinsic dynamics of premixed flames and the problems of flame-flow interaction. (1) A weakly nonlinear model for Bunsen burner stabilized flames was proposed and employed for the simulation of three-dimensional polyhedral flames -- one of the most graphic manifestations of thermal-diffusive instability in premixed combustion. (2) A high-precision large-scale numerical simulation of Bunsen burner tip structure was conducted. The results obtained supported the earlier conjecture that the tip opening observed in low Lewis number systems is a purely optical effect not involving either flame extinction or leakage of unburned fuel. (3) A one-dimensional model describing a reaction wave moving through a unidirectional periodic flow field is proposed and studied numerically. For long-wavelength fields the system exhibits a peculiar non-uniqueness of possible propagation regimes. The transition from one regime to another occurs in a manner of hysteresis.

  14. Model-based control of thermoacoustic instabilities in partially premixed lean combustion - a design case study

    NASA Astrophysics Data System (ADS)

    Yuan, Xiao-Chuan; Glover, Keith

    2013-11-01

    Self-excited oscillation is becoming a major issue in low-emission, lean partially premixed combustion systems, and active control has been shown to be a feasible method to suppress such instabilities. A number of robust control methods are employed to obtain a feedback controller and it is observed that the robustness to system uncertainty is significantly better for a low complexity controller in spite of the norms being similar. Moreover, we demonstrate that closed-loop stability for such a complex system can be proved via use of the integral quadratic constraint method. Open- and closed-loop nonlinear simulations are provided.

  15. Route to chaos for combustion instability in ducted laminar premixed flames

    NASA Astrophysics Data System (ADS)

    Kabiraj, Lipika; Saurabh, Aditya; Wahi, Pankaj; Sujith, R. I.

    2012-06-01

    Complex thermoacoustic oscillations are observed experimentally in a simple laboratory combustor that burns lean premixed fuel-air mixture, as a result of nonlinear interaction between the acoustic field and the combustion processes. The application of nonlinear time series analysis, particularly techniques based on phase space reconstruction from acquired pressure data, reveals rich dynamical behavior and the existence of several complex states. A route to chaos for thermoacoustic instability is established experimentally for the first time. We show that, as the location of the heat source is gradually varied, self-excited periodic thermoacoustic oscillations undergo transition to chaos via the Ruelle-Takens scenario.

  16. Stochastic modeling of unsteady extinction in turbulent non-premixed combustion

    DOE PAGES

    Lackmann, T.; Hewson, J. C.; Knaus, R. C.; Kerstein, A. R.; Oevermann, M.

    2016-07-19

    Turbulent fluctuations of the scalar dissipation rate have a major impact on extinction in non-premixed combustion. Recently, an unsteady extinction criterion has been developed (Hewson, 2013) that predicts extinction dependent on the duration and the magnitude of dissipation rate fluctuations exceeding a critical quenching value; this quantity is referred to as the dissipation impulse. Furthermore, the magnitude of the dissipation impulse corresponding to unsteady extinction is related to the difficulty with which a flamelet is exintguished, based on the steady-state S-curve.

  17. A dynamic model for the turbulent burning velocity for large eddy simulation of premixed combustion

    SciTech Connect

    Knudsen, E.; Pitsch, H.

    2008-09-15

    Turbulent premixed combustion is particularly difficult to describe using large eddy simulation (LES). In LES, premixed flame structures typically exist on subfilter length scales. Consequently, premixed LES models must be capable of describing how completely unresolved flame structures propagate under the influence of completely unresolved eddies. This description is usually accomplished through the implementation of a model for the turbulent burning velocity. Here, a dynamic model for describing the turbulent burning velocity in the context of LES is presented. This model uses a new surface filtering procedure that is consistent with standard LES filtering. Additionally, it only uses information that comes directly from the flame front. This latter attribute is important for two reasons. First, it guarantees that the model can be consistently applied when level set methods, where arbitrary constraints can be imposed on field variables away from fronts, are used to track the flame. Second, it forces the model to recognize that the physics governing flame front propagation are only valid locally at the front. Results showing model validation in the context of direct numerical simulation (DNS), and model application in the context of LES, are presented. (author)

  18. Evaluation of a hybrid kinetics/mixing-controlled combustion model for turbulent premixed and diffusion combustion using KIVA-2

    NASA Technical Reports Server (NTRS)

    Nguyen, H. Lee; Wey, Ming-Jyh

    1990-01-01

    Two dimensional calculations were made of spark ignited premixed-charge combustion and direct injection stratified-charge combustion in gasoline fueled piston engines. Results are obtained using kinetic-controlled combustion submodel governed by a four-step global chemical reaction or a hybrid laminar kinetics/mixing-controlled combustion submodel that accounts for laminar kinetics and turbulent mixing effects. The numerical solutions are obtained by using KIVA-2 computer code which uses a kinetic-controlled combustion submodel governed by a four-step global chemical reaction (i.e., it assumes that the mixing time is smaller than the chemistry). A hybrid laminar/mixing-controlled combustion submodel was implemented into KIVA-2. In this model, chemical species approach their thermodynamics equilibrium with a rate that is a combination of the turbulent-mixing time and the chemical-kinetics time. The combination is formed in such a way that the longer of the two times has more influence on the conversion rate and the energy release. An additional element of the model is that the laminar-flame kinetics strongly influence the early flame development following ignition.

  19. Evaluation of a hybrid kinetics/mixing-controlled combustion model for turbulent premixed and diffusion combustion using KIVA-II

    NASA Technical Reports Server (NTRS)

    Nguyen, H. Lee; Wey, Ming-Jyh

    1990-01-01

    Two-dimensional calculations were made of spark ignited premixed-charge combustion and direct injection stratified-charge combustion in gasoline fueled piston engines. Results are obtained using kinetic-controlled combustion submodel governed by a four-step global chemical reaction or a hybrid laminar kinetics/mixing-controlled combustion submodel that accounts for laminar kinetics and turbulent mixing effects. The numerical solutions are obtained by using KIVA-2 computer code which uses a kinetic-controlled combustion submodel governed by a four-step global chemical reaction (i.e., it assumes that the mixing time is smaller than the chemistry). A hybrid laminar/mixing-controlled combustion submodel was implemented into KIVA-2. In this model, chemical species approach their thermodynamics equilibrium with a rate that is a combination of the turbulent-mixing time and the chemical-kinetics time. The combination is formed in such a way that the longer of the two times has more influence on the conversion rate and the energy release. An additional element of the model is that the laminar-flame kinetics strongly influence the early flame development following ignition.

  20. Numerical simulation of premixed combustion using an enriched finite element method

    NASA Astrophysics Data System (ADS)

    van der Bos, Fedderik; Gravemeier, Volker

    2009-06-01

    In this paper we present a novel discretization technique for the simulation of premixed combustion based on a locally enriched finite element method (FEM). Use is made of the G-function approach to premixed combustion in which the domain is divided into two parts, one part containing the burned and another containing the unburned gases. A level-set or G-function is used to define the flame interface separating burned from unburned gases. The eXtended finite element method (X-FEM) is employed, which allows for velocity and pressure fields that are discontinuous across the flame interface. Lagrange multipliers are used to enforce the correct essential interface conditions in the form of jump conditions across the embedded flame interface. A persisting problem with the use of Lagrange multipliers in X-FEM has been the discretization of the Lagrange multipliers. In this paper the distributed Lagrange multiplier technique is adopted. We will provide results from a spatial convergence analysis showing good convergence. However, a small modification of the interface is required to ensure a unique solution. Finally, results are presented from the application of the method to the problems of moving flame fronts, the Darrieus-Landau instability and a piloted Bunsen burner flame.

  1. A simple one-step chemistry model for partially premixed hydrocarbon combustion

    SciTech Connect

    Fernandez-Tarrazo, Eduardo; Sanchez, Antonio L.; Linan, Amable; Williams, Forman A.

    2006-10-15

    This work explores the applicability of one-step irreversible Arrhenius kinetics with unity reaction order to the numerical description of partially premixed hydrocarbon combustion. Computations of planar premixed flames are used in the selection of the three model parameters: the heat of reaction q, the activation temperature T{sub a}, and the preexponential factor B. It is seen that changes in q with equivalence ratio f need to be introduced in fuel-rich combustion to describe the effect of partial fuel oxidation on the amount of heat released, leading to a universal linear variation q(f) for f>1 for all hydrocarbons. The model also employs a variable activation temperature T{sub a}(f) to mimic changes in the underlying chemistry in rich and very lean flames. The resulting chemistry description is able to reproduce propagation velocities of diluted and undiluted flames accurately over the whole flammability limit. Furthermore, computations of methane-air counterflow diffusion flames are used to test the proposed chemistry under nonpremixed conditions. The model not only predicts the critical strain rate at extinction accurately but also gives near-extinction flames with oxygen leakage, thereby overcoming known predictive limitations of one-step Arrhenius kinetics. (author)

  2. Assessment of dynamic closure for premixed combustion large eddy simulation

    NASA Astrophysics Data System (ADS)

    Langella, Ivan; Swaminathan, Nedunchezhian; Gao, Yuan; Chakraborty, Nilanjan

    2015-09-01

    Turbulent piloted Bunsen flames of stoichiometric methane-air mixtures are computed using the large eddy simulation (LES) paradigm involving an algebraic closure for the filtered reaction rate. This closure involves the filtered scalar dissipation rate of a reaction progress variable. The model for this dissipation rate involves a parameter βc representing the flame front curvature effects induced by turbulence, chemical reactions, molecular dissipation, and their interactions at the sub-grid level, suggesting that this parameter may vary with filter width or be a scale-dependent. Thus, it would be ideal to evaluate this parameter dynamically by LES. A procedure for this evaluation is discussed and assessed using direct numerical simulation (DNS) data and LES calculations. The probability density functions of βc obtained from the DNS and LES calculations are very similar when the turbulent Reynolds number is sufficiently large and when the filter width normalised by the laminar flame thermal thickness is larger than unity. Results obtained using a constant (static) value for this parameter are also used for comparative evaluation. Detailed discussion presented in this paper suggests that the dynamic procedure works well and physical insights and reasonings are provided to explain the observed behaviour.

  3. Numerical study of premixed HCCI engine combustion and its sensitivity to computational mesh and model uncertainties

    NASA Astrophysics Data System (ADS)

    Kong, Song-Charng; Reitz, Rolf D.

    2003-06-01

    This study used a numerical model to investigate the combustion process in a premixed iso-octane homogeneous charge compression ignition (HCCI) engine. The engine was a supercharged Cummins C engine operated under HCCI conditions. The CHEMKIN code was implemented into an updated KIVA-3V code so that the combustion could be modelled using detailed chemistry in the context of engine CFD simulations. The model was able to accurately simulate the ignition timing and combustion phasing for various engine conditions. The unburned hydrocarbon emissions were also well predicted while the carbon monoxide emissions were under predicted. Model results showed that the majority of unburned hydrocarbon is located in the piston-ring crevice region and the carbon monoxide resides in the vicinity of the cylinder walls. A sensitivity study of the computational grid resolution indicated that the combustion predictions were relatively insensitive to the grid density. However, the piston-ring crevice region needed to be simulated with high resolution to obtain accurate emissions predictions. The model results also indicated that HCCI combustion and emissions are very sensitive to the initial mixture temperature. The computations also show that the carbon monoxide emissions prediction can be significantly improved by modifying a key oxidation reaction rate constant.

  4. The effect of nitrogen on biogas flame propagation characteristic in premix combustion

    NASA Astrophysics Data System (ADS)

    Anggono, Willyanto; Suprianto, Fandi D.; Hartanto, Tan Ivan; Purnomo, Kenny; Wijaya, Tubagus P.

    2016-03-01

    Biogas is one of alternative energy and categorized as renewable energy. The main sources of biogas come from animal waste, garbage, and household waste that are organic waste. Primarily, over 50% of this energy contains methane (CH4). The other substances or inhibitors are nitrogen and carbon dioxide. Previously, carbon dioxide effect on biogas combustion is already experimented. The result shows that carbon dioxide reduces the flame propagation speed of biogas combustion. Then, nitrogen as an inhibitor obviously also brings some effects to the biogas combustion, flame propagation speed, and flame characteristics. Spark ignited cylinder is used for the premixed biogas combustion research. An acrylic glass is used as the material of this transparent cylinder chamber. The cylinder is filled with methane (CH4), oxygen (O2), and nitrogen (N2) with particular percentage. In this experiment, the nitrogen composition are set to 0%, 5%, 10%, 20%, 30%, 40%, and 50%. The result shows that the flame propagation speed is reduced in regard to the increased level of nitrogen. It can also be implied that nitrogen can decrease the biogas combustion rate.

  5. Combustion oscillation monitoring using flame ionization in a turbulent premixed combustor

    SciTech Connect

    Chorpening, B.T.; Thornton, J.D.; Huckaby, E.D.; Benson, K.J.

    2007-04-01

    To achieve very low NOx emission levels, lean-premixed gas turbine combustors have been commercially implemented that operate near the fuel-lean flame extinction limit. Near the lean limit, however, flashback, lean blow off, and combustion dynamics have appeared as problems during operation. To help address these operational problems, a combustion control and diagnostics sensor (CCADS) for gas turbine combustors is being developed. CCADS uses the electrical properties of the flame to detect key events and monitor critical operating parameters within the combustor. Previous development efforts have shown the capability of CCADS to monitor flashback and equivalence ratio. Recent work has focused on detecting and measuring combustion instabilities. A highly instrumented atmospheric combustor has been used to measure the pressure oscillations in the combustor, the OH emission, and the flame ion field at the premix injector outlet and along the walls of the combustor. This instrumentation allows examination of the downstream extent of the combustion field using both the OH emission and the corresponding electron and ion distribution near the walls of the combustor. In most cases, the strongest pressure oscillation dominates the frequency behavior of the OH emission and the flame ion signals. Using this highly instrumented combustor, tests were run over a matrix of equivalence ratios from 0.6 to 0.8, with an inlet reference velocity of 25 m/s 82 ft/ s . The acoustics of the fuel system for the combustor were tuned using an active-passive technique with an adjustable quarter-wave resonator. Although several statistics were investigated for correlation with the dynamic pressure in the combustor, the best correlation was found with the standard deviation of the guard current. The data show a monotonic relationship between the standard deviation of the guard current (the current through the flame at the premix injector outlet) and the standard deviation of the chamber

  6. Large eddy simulation of a lean premixed swirl flame in complex geometry - comparison of two turbulent combustion models

    NASA Astrophysics Data System (ADS)

    Wang, P.; Fröhlich, J.; Maas, U.

    Lean premixed combustion is employed to reduce emission, but can exhibit undesired effects such as lean blow-off and thermo-acoustic resonance. To cope with these, burners with strong swirl are utilized for flame stabilization. In the resulting complex flow system, flow instabilities are observed in both experiments and simulations. To date, large eddy simulation (LES) is becoming a widely used approach for understanding the properties of turbulent flow phenomena. However, LES of lean premixed combustion still constitutes an open challenge. Many turbulent combustion modeling methods have been developed for LES of such flows [1, 2]. Two types of them are the thickened flame (TF) model [3] and the flame surface density (FSD) model [4]. However, none of these models is ideal and suitable for all kinds of flame configurations. A detailed comparison was made between the TF and FSD by Lin et al. [5] for freely propagating premixed flames in homogeneous isotropic decaying turbulent fields, and qualitative agreement between them was found. In the present work, the performances of the two cited turbulent combustion models, TF and FSD, in simulating the lean premixed swirl flames in an industrial gas trubine model combustor is compared against the well-documented experiment data obtained by Meier et al. [6].

  7. Combustion dynamics linked to flame behaviour in a partially premixed swirled industrial burner

    SciTech Connect

    Biagioli, Fernando; Guethe, Felix; Schuermans, Bruno

    2008-07-15

    Previous work [Biagioli, F., Stabilization mechanism of turbulent premixed flames in strongly swirled flows, Combustion, Theory and Modelling 10 (3) (2006) 389-412; Guethe, F., Lachner, R., Schuermans, B., Biagioli, F., Geng, W., Inauen, A., Schenker, S., Bombach, R., Hubschmid, W., Flame imaging on the ALSTOM EV-burner: thermo acoustic pulsations and CFD-validation, in: AIAA Paper 2006-437 presented at the 44th AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada, January 9-12, 2006] has shown that turbulent dry low NO{sub x} (partially premixed) flames in high swirl conical burners may be subject to a large change of their anchoring location at the symmetry axis when a critical value of the bulk equivalence ratio is reached, i.e. they are bi-stable. This flame behavior is linked here to combustion pressure dynamics measured in an atmospheric test rig for a prototype version of the Alstom EnVironmental (EV) conical burner. The link is made via the solution of the problem of the 'travelling flameholder', which shows that the unsteady displacement of the flame anchoring location implies an unsteady variation of the flame surface area and therefore unsteady heat release. The relevance of this source of unsteady heat release - which is different from more usual ones due to variations in turbulent burning rate and in the sensible enthalpy jump across the flame - to the generation of combustion dynamics in strongly swirled flows is confirmed here by the strong positive correlation between the tendency of the flame to be displaced and the measured amplitude of pressure pulsations. (author)

  8. The evolution equation for the flame surface density in turbulent premixed combustion

    NASA Technical Reports Server (NTRS)

    Trouve, Arnaud

    1993-01-01

    The mean reaction rate in flamelet models for turbulent premixed combustion depends on two basic quantities: a mean chemical rate, called the flamelet speed, and the flame surface density. Our previous work had been primarily focused on the problem of the structure and topology of turbulent premixed flames, and it was then determined that the flamelet speed, when space-averaged, is only weakly sensitive to the turbulent flow field. Consequently, the flame surface density is the key quantity that conveys most of the effects of the turbulence on the rate of energy release. In flamelet models, this quantity is obtained via a modeled transport equation called the Sigma-equation. Past theoretical work has produced a rigorous approach that leads to an exact but unclosed formulation for the turbulent Sigma-equation. In the exact Sigma-equation, it appears that the dynamical properties of the flame surface density are determined by a single parameter, namely the turbulent flame stretch. Unfortunately, the turbulent flame stretch as well as the flame surface density is not available from experiments, and, in the absence of experimental data, little is known on the validity of the closure assumptions used in current flamelet models. Direct Numerical Simulation (DNS) is the alternative approach to get basic information on these fundamental quantities. In the present work, three-dimensional DNS of premixed flames in isotropic turbulent flow is used to estimate the different terms appearing in the Sigma-equation. A new methodology is proposed to provide the source and sink terms for the flame surface density, resolved both temporally and spatially throughout the turbulent flame brush. Using this methodology, our objective is to extract the turbulent flame stretch from the DNS data base and then perform extensive comparisons with flamelet models. Thanks to the detailed information produced by the DNS-based analysis, it is expected that this type of comparison will not only

  9. Modelling of the subgrid scale wrinkling factor for large eddy simulation of turbulent premixed combustion

    NASA Astrophysics Data System (ADS)

    Thiesset, Fabien; Maurice, Guillaume; Halter, Fabien; Mazellier, Nicolas; Chauveau, Christian; Gökalp, Iskender

    2016-05-01

    We propose a model for assessing the unresolved wrinkling factor in the large eddy simulation of turbulent premixed combustion. It relies essentially on a power-law dependence of the wrinkling factor on the filter size and an original expression for the 'active' corrugating strain rate. The latter is written as the turbulent strain multiplied by an efficiency function that accounts for viscous effects and the kinematic constraint of Peters. This yields functional expressions for the fractal dimension and the inner cut-off length scale, the latter being (i) filter-size independent and (ii) consistent with the Damköhler asymptotic behaviours at both large and small Karlovitz numbers. A new expression for the wrinkling factor that incorporates finite Reynolds number effects is further proposed. Finally, the model is successfully assessed on an experimental filtered database.

  10. Nanosecond repetitively pulsed discharge control of premixed lean methane-air combustion

    NASA Astrophysics Data System (ADS)

    Bak, Moon Soo; Cappelli, Mark A.

    2012-10-01

    Two-dimensional kinetic simulations are carried out to investigate the effects of the discharge repetition rate and pulse width of nanosecond repetitively pulsed discharges on stabilizing premixed lean methane-air combustion. The repetition rate and pulse widths are varied from 10 kHz to 50 kHz and from 9 ns to 2 ns respectively, while the total power is held constant. The lower repetition rates, because of their higher pulse energies, produce a larger fraction of radicals such as O, H, and OH. Surprisingly, however, the effect on flame stabilization is found to be essentially the same for all of the tested repetition rates. The shorter pulse width is found to favor the production of species in higher electronic states, but the varying effects on stabilization is also found to be small. Our results indicate that the total deposited power is the critical element that determines the extent of stabilization over this range of discharge properties studied.

  11. Combustion characteristics of pulverized coal and air/gas premixed flame in a double swirl combustor

    SciTech Connect

    Kamal, M.M.

    2009-07-01

    An experimental work was performed to investigate the co-firing of pulverized coal and premixed gas/air streams in a double swirl combustor. The results showed that the NOx emissions are affected by the relative rates of thermal NOx formation and destruction via the pyrolysis of the fuel-N species in high temperature fuel-rich zones. Various burner designs were tested in order to vary the temperature history and the residence time across both coal and gas flames inside the furnace. It was found that by injecting the coal with a gas/air mixture as a combined central jet surrounded by a swirled air stream, a double flame envelope develops with high temperature fuel-rich conditions in between the two reaction zones such that the pyrolysis reactions to N{sub 2} are accelerated. A further reduction in the minimum NOx emissions, as well as in the minimum CO concentrations, was reported for the case where the coal particles are fed with the gas/air mixture in the region between the two swirled air streams. On the other hand, allocating the gas/air mixture around the swirled air-coal combustion zone provides an earlier contact with air and retards the NOx reduction mechanism in such a way that the elevated temperatures around the coal particles allow higher overall NOx emissions. The downstream impingement of opposing air jets was found more efficient than the impinging of particle non-laden premixed flames for effective NOx reduction. In both cases, there is an upstream flow from the stagnation region to the coal primary combustion region, but with the case of air impingement, the hot fuel-rich zone develops earlier. The optimum configuration was found by impinging all jets of air and coal-gas/air mixtures that pronounced minimum NOx and CO concentrations of 310 and 480ppm, respectively.

  12. Emissions from premixed charge compression ignition (PCCI) combustion and affect on emission control devices

    SciTech Connect

    Parks, II, James E; Kass, Michael D; Huff, Shean P; Barone, Teresa L; Lewis Sr, Samuel Arthur; Prikhodko, Vitaly Y; Storey, John Morse

    2010-01-01

    A light-duty diesel engine has been operated in advanced combustion modes known generally as premixed charge compression ignition (PCCI). The emissions have been characterized for several load and speed combinations. Fewer NO{sub x} and particulate matter (PM) emissions are produced by PCCI, but higher CO and hydrocarbon (HC) emissions result. In addition, the nature of the PM differs from conventional combustion; the PM is smaller and has a much higher soluble organic fraction (SOF) content (68% vs. 30% for conventional combustion). Three catalyst technologies were studied to determine the affects of HECC on catalyst performance; the technologies were a lean NO{sub x} trap (LNT), diesel oxidation catalyst (DOC), and diesel particulate filter (DPF). The LNT benefited greatly from the reduced NO{sub x} emissions associated with PCCI. NO{sub x} capacity requirements are reduced as well as overall tailpipe NO{sub x} levels particularly at low load and temperature conditions where regeneration of the LNT is difficult. The DOC performance requirements for PCCI are more stringent due to the higher CO and HC emissions; however, the DOC was effective at controlling the higher CO and HC emissions at conditions above the light-off temperature. Below light-off, CO and HC emissions are problematic. The study of DPF technology focused on the fuel penalties associated with DPF regeneration or 'desoot' due to the different PM loading rates from PCCI vs. conventional combustion. Less frequent desoot events were required from the lower PM from PCCI and, when used in conjunction with an LNT, the lower PM from less frequent LNT regeneration. The lower desoot frequency leads a {approx}3% fuel penalty for a mixture of PCCI and conventional loads vs. {approx}4% for conventional only combustion.

  13. Turbulence, combustion, pollutant, and stability characterization of a premixed, step combustor

    NASA Technical Reports Server (NTRS)

    Ganji, A. T.; Sawyer, R. F.

    1980-01-01

    A two dimensional combustion tunnel was constructed to study a lean premixed turbulent propane/air flame stablized behind a rearward facing step. Studied were: (1) the existence and importance of large coherent structures in turbulent reacting and nonreacting free shear layers behind the steps; (2) the effect of inlet temperature and reference velocity on combustion efficiency; (3) CO, NO2 and NO sub x production in the flame; and (4) the blowout and upstream propagation of the flame. In the ranges studied, the large coherent structures dominated both the reacting and the nonreacting free shear layers behind the step. The growth of the vortices and the propagation of the flamer were intimately linked. Vortex pairing was observed to be one of the mechanisms for introduction of fresh reactants into the shear layer and growth of the shear layer. Probe composition measurements of the flame showed that, in the recirculation zone, the reaction was above 99 percent complete, CO and unburnt hydrocarbons were above the equilibrium level NO sub x concentration was far below the equilibrium level and NO2 comprised a negligible fraction of NO sub x.

  14. Lagrangian Model of Bluffbody-Stabilized Premixed Combustion for Flow Control

    NASA Astrophysics Data System (ADS)

    Soteriou, Marios; Prashant, Mehta

    2002-11-01

    Thermoacoustic instabilities develop in various power generation devices such as gas turbines and rockets when acoustic modes couple with unsteady heat release in a positive feedback loop. Active control of these instabilities requires an in depth understanding of the reacting flow physics. Moreover, proposed control algorithms need to be tested in a dynamic and realistic modeling environment prior to implementation in an engineering device. These issues necessitate the development of physics-based models that inexpensively capture the flow dynamics. In this work, we present such a model for the case of flameholder stabilized premixed combustion. Computational savings are achieved by restricting the model to two spatial dimensions and by seeking solutions of the governing equations in the Lagrangian frame of reference. Specifically, a compressible form of the Vortex Element Method is coupled to a G-equation based flame-sheet representation of the reacting field. Model results are compared to experimental evidence. It is shown that the model reproduces the shift from asymmetric to symmetric vortex shedding witnessed when combustion exothermicity is present. Mean velocity profiles and shedding frequency spectra provide further evidence of the ability of the model to capture the physics of the flameholder wake.

  15. Stretch-rate relationships for turbulent premixed combustion LES subgrid models measured using temporally resolved diagnostics

    SciTech Connect

    Steinberg, Adam M.; Driscoll, James F.

    2010-07-15

    implemented in numerical simulations of turbulent premixed combustion. (author)

  16. The evolution equation for the flame surface density in turbulent premixed combustion

    NASA Technical Reports Server (NTRS)

    Trouve, A.; Poinsot, T.

    1992-01-01

    One central ingredient in flamelet models for turbulent premixed combustion is the flame surface density. This quantity conveys most of the effects of the turbulence on the rate of energy release and is obtained via a modeled transport equation, called the Sigma-equation. Past theoretical work has produced a rigorous approach that leads to an exact, but unclosed, formulation for the turbulent Sigma-equation. In this exact Sigma-equation, it appears that the dynamical properties of the flame surface density are determined by a single parameter, namely the turbulent flame stretch. Unfortunately, the flame surface density and the turbulent flame stretch are not available from experiments and, in the absence of experimental data, little is known on the validity of the closure assumptions used in current flamelet models. Direct Numerical Simulation (DNS) is the obvious, complementary approach to get basic information on these fundamental quantities. Three-dimensional DNS of premixed flames in isotropic turbulent flow is used to estimate the different terms appearing in the Sigma-equation. A new methodology is proposed to provide the source and sink terms for the flame surface density, resolved both temporally and spatially throughout the turbulent flame brush. Using this methodology, the effects of the Lewis number on the rate of production of flame surface area are described in great detail and meaningful comparisons with flamelet models can be performed. The analysis reveals in particular the tendency of the models to overpredict flame surface dissipation as well as their inability to reproduce variations due to thermo-diffusive phenomena. Thanks to the detailed information produced by a DNS-based analysis, this type of comparison not only underscores the shortcomings of current models but also suggests ways to improve them.

  17. Effect of Premixed Fuel Preparation for Partially Premixed Combustion with a Low Octane Gasoline on a Light-Duty Multi-Cylinder Compression Ignition Engine

    SciTech Connect

    Dempsey, Adam B.; Curran, Scott; Wagner, Robert M.; Cannella, William C.

    2015-05-12

    Gasoline compression ignition concepts with the majority of the fuel being introduced early in the cycle are known as partially premixed combustion (PPC). Previous research on single- and multi-cylinder engines has shown that PPC has the potential for high thermal efficiency with low NOx and soot emissions. A variety of fuel injection strategies has been proposed in the literature. These injection strategies aim to create a partially stratified charge to simultaneously reduce NOx and soot emissions while maintaining some level of control over the combustion process through the fuel delivery system. The impact of the direct injection strategy to create a premixed charge of fuel and air has not previously been explored, and its impact on engine efficiency and emissions is not well understood. This paper explores the effect of sweeping the direct injected pilot timing from -91° to -324° ATDC, which is just after the exhaust valve closes for the engine used in this study. During the sweep, the pilot injection consistently contained 65% of the total fuel (based on command duration ratio), and the main injection timing was adjusted slightly to maintain combustion phasing near top dead center. A modern four cylinder, 1.9 L diesel engine with a variable geometry turbocharger, high pressure common rail injection system, wide included angle injectors, and variable swirl actuation was used in this study. The pistons were modified to an open bowl configuration suitable for highly premixed combustion modes. The stock diesel injection system was unmodified, and the gasoline fuel was doped with a lubricity additive to protect the high pressure fuel pump and the injectors. The study was conducted at a fixed speed/load condition of 2000 rpm and 4.0 bar brake mean effective pressure (BMEP). The pilot injection timing sweep was conducted at different intake manifold pressures, swirl levels, and fuel injection GTP-15-1067, Dempsey 2 pressures. The gasoline used in this study has

  18. Effect of Premixed Fuel Preparation for Partially Premixed Combustion with a Low Octane Gasoline on a Light-Duty Multi-Cylinder Compression Ignition Engine

    DOE PAGES

    Dempsey, Adam B.; Curran, Scott; Wagner, Robert M.; Cannella, William C.

    2015-05-12

    Gasoline compression ignition concepts with the majority of the fuel being introduced early in the cycle are known as partially premixed combustion (PPC). Previous research on single- and multi-cylinder engines has shown that PPC has the potential for high thermal efficiency with low NOx and soot emissions. A variety of fuel injection strategies has been proposed in the literature. These injection strategies aim to create a partially stratified charge to simultaneously reduce NOx and soot emissions while maintaining some level of control over the combustion process through the fuel delivery system. The impact of the direct injection strategy to createmore » a premixed charge of fuel and air has not previously been explored, and its impact on engine efficiency and emissions is not well understood. This paper explores the effect of sweeping the direct injected pilot timing from -91° to -324° ATDC, which is just after the exhaust valve closes for the engine used in this study. During the sweep, the pilot injection consistently contained 65% of the total fuel (based on command duration ratio), and the main injection timing was adjusted slightly to maintain combustion phasing near top dead center. A modern four cylinder, 1.9 L diesel engine with a variable geometry turbocharger, high pressure common rail injection system, wide included angle injectors, and variable swirl actuation was used in this study. The pistons were modified to an open bowl configuration suitable for highly premixed combustion modes. The stock diesel injection system was unmodified, and the gasoline fuel was doped with a lubricity additive to protect the high pressure fuel pump and the injectors. The study was conducted at a fixed speed/load condition of 2000 rpm and 4.0 bar brake mean effective pressure (BMEP). The pilot injection timing sweep was conducted at different intake manifold pressures, swirl levels, and fuel injection GTP-15-1067, Dempsey 2 pressures. The gasoline used in this study

  19. Laminar lean premixed methane/air combustion near the lean flammability limit using nanosecond repetitive pulsed discharge plasmas

    NASA Astrophysics Data System (ADS)

    Bak, Moon Soo; Do, Hyungrok; Mungal, Mark G.; Cappelli, Mark A.

    2011-10-01

    Gas chromatographic and temperature measurements have been carried out to investigate the extent of premixed methane/air combustion with the application of nanosecond repetitive pulsed discharges around the lean flammability limit for laminar flows. The results show that the discharges lead to the complete combustion when the equivalence ratio is above 0.54, but when the ratio is below the limit, the combustion is quenched at the downstream flow. To investigate the kinetics in detail, 2-D simulations of plasma-induced combustion have been conducted for methane/air mixtures at below and above the lean flammability limit. The simulations reveal that methane is mostly combusted in the discharge region since the discharge repetition timescale is much shorter than the species diffusion and advection timescales, and so the discharge serves more as a heat and radical source rather than a small combustor, to flame hold near the lean flammability limit.

  20. Modeling and simulation of combustion dynamics in lean-premixed swirl-stabilized gas-turbine engines

    NASA Astrophysics Data System (ADS)

    Huang, Ying

    This research focuses on the modeling and simulation of combustion dynamics in lean-premixed gas-turbines engines. The primary objectives are: (1) to establish an efficient and accurate numerical framework for the treatment of unsteady flame dynamics; and (2) to investigate the parameters and mechanisms responsible for driving flow oscillations in a lean-premixed gas-turbine combustor. The energy transfer mechanisms among mean flow motions, periodic motions and background turbulent motions in turbulent reacting flow are first explored using a triple decomposition technique. Then a comprehensive numerical study of the combustion dynamics in a lean-premixed swirl-stabilized combustor is performed. The analysis treats the conservation equations in three dimensions and takes into account finite-rate chemical reactions and variable thermophysical properties. Turbulence closure is achieved using a large-eddy-simulation (LES) technique. The compressible-flow version of the Smagorinsky model is employed to describe subgrid-scale turbulent motions and their effect on large-scale structures. A level-set flamelet library approach is used to simulate premixed turbulent combustion. In this approach, the mean flame location is modeled using a level-set G-equation, where G is defined as a distance function. Thermophysical properties are obtained using a presumed probability density function (PDF) along with a laminar flamelet library. The governing equations and the associated boundary conditions are solved by means of a four-step Runge-Kutta scheme along with the implementation of the message passing interface (MPI) parallel computing architecture. The analysis allows for a detailed investigation into the interaction between turbulent flow motions and oscillatory combustion of a swirl-stabilized injector. Results show good agreement with an analytical solution and experimental data in terms of acoustic properties and flame evolution. A study of flame bifurcation from a stable

  1. Micro-Mixing Lean-Premix System for Ultra-Low Emission Hydrogen/Syngas Combustion

    SciTech Connect

    Erlendur Steinthorsson; Brian Hollon; Adel Mansour

    2010-06-30

    The focus of this project was to develop the next generation of fuel injection technologies for environmentally friendly, hydrogen syngas combustion in gas turbine engines that satisfy DOE's objectives of reducing NOx emissions to 3 ppm. Building on Parker Hannifin's proven Macrolamination technology for liquid fuels, Parker developed a scalable high-performing multi-point injector that utilizes multiple, small mixing cups in place of a single conventional large-scale premixer. Due to the small size, fuel and air mix rapidly within the cups, providing a well-premixed fuel-air mixture at the cup exit in a short time. Detailed studies and experimentation with single-cup micro-mixing injectors were conducted to elucidate the effects of various injector design attributes and operating conditions on combustion efficiency, lean stability and emissions and strategies were developed to mitigate the impact of flashback. In the final phase of the program, a full-scale 1.3-MWth multi-cup injector was built and tested at pressures from 6.9bar (100psi) to 12.4bar (180psi) and flame temperatures up to 2000K (3150 F) using mixtures of hydrogen and natural gas as fuel with nitrogen and carbon dioxide as diluents. The injector operated without flash back on fuel mixtures ranging from 100% natural gas to 100% hydrogen and emissions were shown to be insensitive to combustor pressure. NOx emissions of 3-ppm were achieved at a flame temperature of 1750K (2690 F) when operating on a fuel mixture containing 50% hydrogen and 50% natural gas by volume with 40% nitrogen dilution and 1.5-ppm NOx was achieved at a flame temperature of 1680K (2564 F) using only 10% nitrogen dilution. NOx emissions of 3.5-ppm were demonstrated at a flame temperature of 1730K (2650 F) with only 10% carbon dioxide dilution. Finally, 3.6-ppm NOx emissions were demonstrated at a flame temperature over 1600K (2420 F) when operating on 100% hydrogen fuel with 30% carbon dioxide dilution. Superior operability was

  2. Effect of degree of fuel vaporization upon emissions for a premixed prevaporized combustion system. [for gas turbine engines

    NASA Technical Reports Server (NTRS)

    Cooper, L. P.

    1979-01-01

    An experimental and analytical study of the combustion of partially vaporized fuelair mixtures was performed to assess the impact of the degree of fuel vaporization upon emissions for a premixing-prevaporizing flametube combustor. Data collected show near linear increases in nitrogen oxide emissions with decreasing vaporization at equivalence ratios of 0.6. For equivalence ratio of 0.72, the degree of vaporization had very little impact on nitrogen oxide emissions. A simple mechanism which accounts for the combustion of liquid droplets in partially vaporized mixtures was found to agree with the measured results with fair accuracy with respect to both trends and magnitudes.

  3. Effect of degree of fuel vaporization upon emissions for a premixed partially vaporized combustion system. [for gas turbine engines

    NASA Technical Reports Server (NTRS)

    Cooper, L. P.

    1980-01-01

    An experimental and analytical study of the combustion of partially vaporized fuel-air mixtures was performed to assess the impact of the degree of fuel vaporization upon emissions for a premixing-prevaporizing flametube combustor. Data collected in this study showed near linear increases in nitric oxide emissions with decreasing vaporization at equivalence ratios of 0.6. For equivalence ratios of 0.72, the degree of vaporization had very little impact on nitric oxide emissions. A simple mechanism which accounts for the combustion of liquid droplets in partially vaporized mixtures was found to agree with the measured results with fair accuracy with respect to both trends and magnitudes.

  4. Experimental and kinetic modeling study of combustion of JP-8, its surrogates and components in laminar premixed flows

    NASA Astrophysics Data System (ADS)

    Seshadri, Kalyanasundaram; Frassoldati, Alessio; Cuoci, Alberto; Faravelli, Tiziano; Niemann, Ulrich; Weydert, Patrick; Ranzi, Eliseo

    2011-08-01

    Experimental and kinetic modeling studies are carried out to characterize premixed combustion of jet fuels, their surrogates, and reference components in laminar nonuniform flows. In previous studies, it was established that the Aachen surrogate made up of 80 % n-decane and 20 % trimethylbenzene by weight, and surrogate C made up of 57 % n-dodecane, 21 % methylcyclohexane and 22 % o-xylene by weight, reproduce key aspects of combustion of jet fuels in laminar nonpremixed flows. Here, these surrogates and a jet fuel are tested in premixed, nonuniform flows. The counterflow configuration is employed, and critical conditions of extinction are measured. In addition, the reference components tested are n-heptane, n-decane, n-dodecane, methylcyclohexane, trimethylbenzene, and o-xylene. Measured critical conditions of extinction of the Aachen surrogate and surrogate C are compared with those for the jet fuel. In general the alkanes n-heptane, n-decane, and n-dodecane, and methylcyclohexane are found to be more reactive than the aromatics o-xylene and trimethylbenzene. Flame structure and critical conditions of extinction are predicted for the reference components and the surrogates using a semi-detailed kinetic model. The predicted values are compared with experimental data. Sensitivity analysis shows that the lower reactivity of the aromatic species arises from the formation of resonantly stabilized radicals. These radicals are found to have a scavenging effect. The present study on premixed flows together with previous studies on nonpremixed flows show that the Aachen surrogate and surrogate C reproduce many aspects of premixed and nonpremixed combustion of jet fuels.

  5. Two-Dimensional Failure Waves and Ignition Fronts in Premixed Combustion

    NASA Technical Reports Server (NTRS)

    Vedarajan, T. G.; Buckmaster J.; Ronney, P.

    1998-01-01

    This paper is a continuation of our work on edge-flames in premixed combustion. An edge-flame is a two-dimensional structure constructed from a one-dimensional configuration that has two stable solutions (bistable equilibrium). Edge-flames can display wavelike behavior, advancing as ignition fronts or retreating as failure waves. Here we consider two one-dimensional configurations: twin deflagrations in a straining flow generated by the counterflow of fresh streams of mixture: and a single deflagration subject to radiation losses. The edge-flames constructed from the first configuration have positive or negative speeds, according to the value of the strain rate. But our numerical solutions strongly suggest that only positive speeds (corresponding to ignition fronts) can exist for the second configuration. We show that this phenomenon can also occur in diffusion flames when the Lewis numbers are small. And we discuss the asymptotics of the one-dimensional twin deflagration configuration. an overlooked problem from the 70s.

  6. Experimental and numerical study of premixed hydrogen/air flame propagating in a combustion chamber.

    PubMed

    Xiao, Huahua; Sun, Jinhua; Chen, Peng

    2014-03-15

    An experimental and numerical study of dynamics of premixed hydrogen/air flame in a closed explosion vessel is described. High-speed shlieren cinematography and pressure recording are used to elucidate the dynamics of the combustion process in the experiment. A dynamically thickened flame model associated with a detailed reaction mechanism is employed in the numerical simulation to examine the flame-flow interaction and effect of wall friction on the flame dynamics. The shlieren photographs show that the flame develops into a distorted tulip shape after a well-pronounced classical tulip front has been formed. The experimental results reveal that the distorted tulip flame disappears with the primary tulip cusp and the distortions merging into each other, and then a classical tulip is repeated. The combustion dynamics is reasonably reproduced in the numerical simulations, including the variations in flame shape and position, pressure build-up and periodically oscillating behavior. It is found that both the tulip and distorted tulip flames can be created in the simulation with free-slip boundary condition at the walls of the vessel and behave in a manner quite close to that in the experiments. This means that the wall friction could be unimportant for the tulip and distorted tulip formation although the boundary layer formed along the sidewalls has an influence to a certain extent on the flame behavior near the sidewalls. The distorted tulip flame is also observed to be produced in the absence of vortex flow in the numerical simulations. The TF model with a detailed chemical scheme is reliable for investigating the dynamics of distorted tulip flame propagation and its underlying mechanism. PMID:24486615

  7. Multi-zone modelling of partially premixed low-temperature combustion in pilot-ignited natural-gas engines

    SciTech Connect

    Krishnan, S. R.; inivasan, K. K.

    2010-09-14

    Detailed results from a multi-zone phenomenological simulation of partially premixed advanced-injection low-pilot-ignited natural-gas low-temperature combustion are presented with a focus on early injection timings (the beginning of (pilot) injection (BOI)) and very small diesel quantities (2-3 per cent of total fuel energy). Combining several aspects of diesel and spark ignition engine combustion models, the closed-cycle simulation accounted for diesel autoignition, diesel spray combustion, and natural-gas combustion by premixed turbulent flame propagation. The cylinder contents were divided into an unburned zone, several pilot fuel zones (or 'packets') that modelled diesel evaporation and ignition, a flame zone for natural-gas combustion, and a burned zone. The simulation predicted the onset of ignition, cylinder pressures, and heat release rate profiles satisfactorily over a wide range of BOIs (20-60° before top dead centre (before TDC)) but especially well at early BOIs. Strong coupling was observed between pilot spray combustion in the packets and premixed turbulent combustion in the flame zone and, therefore, the number of ignition centres (packets) profoundly affected flame combustion. The highest local peak temperatures (greater than 2000 K) were observed in the packets, while the flame zone was much cooler (about 1650 K), indicating that pilot diesel spray combustion is probably the dominant source of engine-out emissions of nitrogen oxide (NOx). Further, the 60° before TDC BOI yielded the lowest average peak packet temperatures (about 1720 K) compared with the 20° before TDC BOI (about 2480 K) and 40° before TDC BOI (about 2700 K). These trends support experimental NOx trends, which showed the lowest NOx emissions for the 60°, 20°, and 40° before TDC BOIs in that order. Parametric studies showed that increasing the intake charge temperature, pilot quantity, and natural-gas equivalence ratio all led to higher peak

  8. Gas turbine premixing systems

    DOEpatents

    Kraemer, Gilbert Otto; Varatharajan, Balachandar; Evulet, Andrei Tristan; Yilmaz, Ertan; Lacy, Benjamin Paul

    2013-12-31

    Methods and systems are provided for premixing combustion fuel and air within gas turbines. In one embodiment, a combustor includes an upstream mixing panel configured to direct compressed air and combustion fuel through premixing zone to form a fuel-air mixture. The combustor includes a downstream mixing panel configured to mix additional combustion fuel with the fule-air mixture to form a combustion mixture.

  9. Combustion characteristics in a pre-vaporizing pre-mixing lean combustor for an automotive ceramic gas turbine

    SciTech Connect

    Yoshida, Yusaku; Oguchi, Makoto

    1999-07-01

    A pre-vaporizing pre-mixing lean combustor (PPL) was developed for an automotive ceramic gas turbine which had high thermal efficiency and clean exhaust emissions. This study has been performed to obtain design data by investigating the basic characteristics of this combustor. Experiments were conducted under a high combustor inlet air temperature of 973K since the combustor inlet air was heated by regenerators to achieve high thermal efficiency. At first, the following measurements were conducted to survey the phenomena in the PPL combustion system; the required distance of vaporizing tube for complete evaporation and uniform mixture formation, and the flow pattern and velocity distribution and flame behaviors in the combustion chamber. Then it has clarified how the emission characteristics were influenced by non-uniformity of the mixture that flew into the combustion chamber. And also the possibility of reducing NOx emission by introducing dilution air into the post flame region has been shown.

  10. Microwave plasma jet assisted combustion of premixed methane-air: Roles of OH(A) and OH(X) radicals

    NASA Astrophysics Data System (ADS)

    Wang, Chuji; Wu, Wei

    2013-09-01

    Plasma assisted combustion (PAC) technology can enhance combustion performance by pre-heating combustion fuels, shortening ignition delay time, enhancing flame holding, or increasing flame volume and flame speed. PAC can also increase fuel efficiency by extending fuel lean flammability limit (LFL) and help reduce combustion pollutant emissions. Experiment results have shown that microwave plasma could modify flame structure, increase flame volume, flame speed, flame temperature, and flame stability, and could also extend the fuel lean flammability limit. We report on a novel microwave PAC system that allows us to study PAC using complicated yet well-controlled combinations of operating parameters, such as fuel equivalence ratio (φ) , fuel mixture flow rate, plasma gas flow rate, plasma gases, plasma jet configurations, symmetric or asymmetric fuel-oxidant injection patterns, etc. We have investigated the roles of the stated-resolved OH(A, X) radicals in plasma assisted ignition and combustion of premixed methane-air fuel mixtures. Results suggest that that both the electronically excited state OH(A) and the electronic ground state OH(X) enhance the methane-air ignition process, i.e. extending the fuel LFL, but the flame stabilization and flame holding is primarily determined by the electronic ground state OH(X) as compared to the role of the OH(A). E-mail: cw175@msstate.edu. Supported by National Science Foundation through the grant of ``A quantitative survey of combustion intermediates toward understanding of plasma-assisted combustion mechanism'' (CBET-1066486).

  11. Effects of gasoline reactivity and ethanol content on boosted premixed and partially stratified low-temperature gasoline combustion (LTGC)

    DOE PAGES

    Dec, John E.; Yang, Yi; Ji, Chunsheng; Dernotte, Jeremie

    2015-04-14

    Low-temperature gasoline combustion (LTGC), based on the compression ignition of a premixed or partially premixed dilute charge, can provide thermal efficiencies (TE) and maximum loads comparable to those of turbo-charged diesel engines, and ultra-low NOx and particulate emissions. Intake boosting is key to achieving high loads with dilute combustion, and it also enhances the fuel's autoignition reactivity, reducing the required intake heating or hot residuals. These effects have the advantages of increasing TE and charge density, allowing greater timing retard with good stability, and making the fuel Φ- sensitive so that partial fuel stratification (PFS) can be applied for highermore » loads and further TE improvements. However, at high boost the autoignition reactivity enhancement can become excessive, and substantial amounts of EGR are required to prevent overly advanced combustion. Accordingly, an experimental investigation has been conducted to determine how the tradeoff between the effects of intake boost varies with fuel-type and its impact on load range and TE. Five fuels are investigated: a conventional AKI=87 petroleum-based gasoline (E0), and blends of 10 and 20% ethanol with this gasoline to reduce its reactivity enhancement with boost (E10 and E20). Furthermore, a second zero-ethanol gasoline with AKI=93 (matching that of E20) was also investigated (CF-E0), and some neat ethanol data are also reported.« less

  12. Effects of gasoline reactivity and ethanol content on boosted premixed and partially stratified low-temperature gasoline combustion (LTGC)

    SciTech Connect

    Dec, John E.; Yang, Yi; Ji, Chunsheng; Dernotte, Jeremie

    2015-04-14

    Low-temperature gasoline combustion (LTGC), based on the compression ignition of a premixed or partially premixed dilute charge, can provide thermal efficiencies (TE) and maximum loads comparable to those of turbo-charged diesel engines, and ultra-low NOx and particulate emissions. Intake boosting is key to achieving high loads with dilute combustion, and it also enhances the fuel's autoignition reactivity, reducing the required intake heating or hot residuals. These effects have the advantages of increasing TE and charge density, allowing greater timing retard with good stability, and making the fuel Φ- sensitive so that partial fuel stratification (PFS) can be applied for higher loads and further TE improvements. However, at high boost the autoignition reactivity enhancement can become excessive, and substantial amounts of EGR are required to prevent overly advanced combustion. Accordingly, an experimental investigation has been conducted to determine how the tradeoff between the effects of intake boost varies with fuel-type and its impact on load range and TE. Five fuels are investigated: a conventional AKI=87 petroleum-based gasoline (E0), and blends of 10 and 20% ethanol with this gasoline to reduce its reactivity enhancement with boost (E10 and E20). Furthermore, a second zero-ethanol gasoline with AKI=93 (matching that of E20) was also investigated (CF-E0), and some neat ethanol data are also reported.

  13. Biogas Laminar Burning Velocity and Flammability Characteristics in Spark Ignited Premix Combustion

    NASA Astrophysics Data System (ADS)

    Anggono, Willyanto; Wardana, I. N. G.; Lawes, M.; Hughes, K. J.; Wahyudi, Slamet; Hamidi, Nurkholis; Hayakawa, Akihiro

    2013-04-01

    Spherically expanding flames propagating at constant pressure were employed to determine the laminar burning velocity and flammability characteristics of biogas-air mixtures in premixed combustion to uncover the fundamental flame propagation characteristics of a new alternative and renewable fuel. The results are compared with those from a methane-air flame. Biogas is a sustainable and renewable fuel that is produced in digestion facilities. The composition of biogas discussed in this paper consists of 66.4% methane, 30.6% carbon dioxide and 3% nitrogen. Burning velocity was measured at various equivalence ratios (phi) using a photographic technique in a high pressure fan-stirred bomb, the initial condition being at room temperature and atmospheric pressure. The flame for methane-air mixtures propagates from phi=0.6 till phi=1.3. The flame at phi >= 1.4 does not propagate because the combustion reaction is quenched by the larger mass of fuel. At phi<=0.5, it does not propagate as well since the heat of reaction is insufficient to burn the mixtures. The flame for biogas-air mixtures propagates in a narrower range, that is from phi=0.6 to phi=1.2. Different from the methane flame, the biogas flame does not propagate at phi>=1.3 because the heat absorbed by inhibitors strengthens the quenching effect by the larger mass of fuel. As in the methane flame, the biogas flame at phi<=0.5 does not propagate. This shows that the effect of inhibitors in extremely lean mixtures is small. Compared to a methane-air mixture, the flammability characteristic (flammable region) of biogas becomes narrower in the presence of inhibitors (carbon dioxide and nitrogen) and the presence of inhibitors causes a reduction in the laminar burning velocity. The inhibitor gases work more effectively at rich mixtures because the rich biogas-air mixtures have a higher fraction of carbon dioxide and nitrogen components compared to the lean biogas-air mixtures.

  14. An Improved Flamelet-Based Model for Non-Premixed Supersonic Combustion

    NASA Astrophysics Data System (ADS)

    Lou, Zhipeng; Ladeinde, Foluso; Li, Wenhai

    2015-11-01

    The flamelet approach to turbulent reacting flows, though originally developed for essentially incompressible flows, has been used by many authors to simulate supersonic combustion, often without much justification other than that pressure scales in certain ways. In a compressible flow, pressure and temperature vary strongly, meaning that the use of a fixed value of pressure for generating flamelet libraries may be prone to errors in the flamelet modeling of supersonic combustion. We study the influence of static pressure on the flamelet solutions intended for use in modeling supersonic combustion. With various values of static pressure, we found significant differences in the values of the quenching stoichiometric scalar dissipation rate, reaction rate of species and progress variable, heat release rate and the temperature profile. As a result, at high static pressures, the flame is less likely to extinguish and the S-curve shows a steeper angle. We have experimented with the addition of pressure as an independent variable in the flamelet table, toward modeling pressure-sensitive properties and the variable quenching conditions. The effects of this kind of scheme on supersonic combustion will be discussed.

  15. A New Type of Steady and Stable, Laminar, Premixed Flame in Ultra-Lean, Hydrogen-Air Combustion

    SciTech Connect

    Grcar, Joseph F; Grcar, Joseph F

    2008-06-30

    Ultra-lean, hydrogen-air mixtures are found to support another kind of laminar flame that is steady and stable beside flat flames and flame balls. Direct numerical simulations are performed of flames that develop into steadily and stably propagating cells. These cells were the original meaning of the word"flamelet'' when they were observed in lean flammability studies conducted early in the development of combustion science. Several aspects of these two-dimensional flame cells are identified and are contrasted with the properties of one-dimensional flame balls and flat flames. Although lean hydrogen-air flames are subject to thermo-diffusive effects, in this case the result is to stabilize the flame rather than to render it unstable. The flame cells may be useful as basic components of engineering models for premixed combustion when the other types of idealized flames are inapplicable.

  16. Premixed turbulent flame propagation in microgravity

    NASA Technical Reports Server (NTRS)

    Menon, S.; Jagoda, J.; Sujith, R.

    1995-01-01

    To reduce pollutant formation there is, at present, an increased interest in employing premixed fuel/air mixture in combustion devices. It is well known that greater control over local temperature can be achieved with premixed flames and with lean premixed mixtures, significant reduction of pollutants such as NO(x) can be achieved. However, an issue that is still unresolved is the predictability of the flame propagation speed in turbulent premixed mixtures, especially in lean mixtures. Although substantial progress has been made in recent years, there is still no direct verification that flame speeds in turbulent premixed flows are highly predictable in complex flow fields found in realistic combustors. One of the problems associated with experimental verification is the difficulty in obtaining access to all scales of motion in typical high Reynolds number flows, since, such flows contain scales of motion that range from the size of the device to the smallest Kolmogorov scale. The overall objective of this study is to characterize the behavior of turbulent premixed flames at reasonable high Reynolds number, Re(sub L). Of particular interest here is the thin flame limit where the laminar flame thickness is much smaller than the Kolmogorov scale. Thin flames occur in many practical combustion devices and will be numerically studied using a recently developed new formulation that is briefly described.

  17. Effects of percentage of blockage and flameholder downstream counterbores on lean combustion limits of premixed, prevaporized propane-air mixture

    NASA Technical Reports Server (NTRS)

    Fernandez, M. A. B.

    1983-01-01

    Lean combustion limits were determined for a premixed prevaporized propane air mixture with flat plate flame stabilizers. Experiments were conducted in a constant area flame tube combustor utilizing flameholders of varying percentages of blockage and downstream counterbores. Combustor inlet air velocity at ambient conditions was varied from 4 to 9 meters per second. Flameholders with a center hole and four half holes surrounding it were tested with 63, 73, and 85 percent blockage and counterbore diameters of 112 and 125 percent of the thru hole diameter, in addition to the no counterbore configuration. Improved stability was obtained by using counterbore flameholders and higher percentages of blockage. Increases in mixture velocity caused the equivalence ratio at blowout to increase in all cases.

  18. Two-time correlation of heat release rate and spectrum of combustion noise from turbulent premixed flames

    NASA Astrophysics Data System (ADS)

    Liu, Yu

    2015-09-01

    The spectral characteristics of combustion noise are dictated by the temporal correlation of the overall change of heat release rate fluctuations which has not received sufficient attention in prior studies. In this work, the two-time correlation of the volumetric heat release rate fluctuations within the flame brush and its role in modeling combustion noise spectrum are investigated by analyzing direct numerical simulation (DNS) data of turbulent premixed V-flames. This two-time correlation can be well represented by Gaussian-type functions and it captures the slow global variation of the fluctuating heat release rate and hence the low-frequency noise sources of unsteady combustion. The resulting correlation model is applied to predict the far-field noise spectrum from test open flames, and different reference time scales are used to scale this correlation from the DNS data to the test flames. The comparison between predictions and measurements indicates that the correlation models of all reference time scales are capable of reproducing the essential spectral shape including the low- and high-frequency dependencies. Reasonable agreement in the peak frequency, peak sound pressure level, and the Strouhal number scaling of peak frequency is also achieved for two turbulent time scales. A promising convective time scale shows great potential for characterizing the spectral features, yet its predictive capabilities are to be further verified through a longer DNS signal of a bounded flame configuration.

  19. High-bandwidth Modulation of H2/Syngas Fuel to Control Combustion Dynamics in Micro-Mixing Lean Premix Systems

    SciTech Connect

    Jeff Melzak; Tim Lieuwen; Adel Mansour

    2012-01-31

    The goal of this program was to develop and demonstrate fuel injection technologies that will facilitate the development of cost-effective turbine engines for Integrated Gasification Combined Cycle (IGCC) power plants, while improving efficiency and reducing emissions. The program involved developing a next-generation multi-point injector with enhanced stability performance for lean premix turbine systems that burn hydrogen (H2) or synthesis gas (syngas) fuels. A previously developed injector that demonstrated superior emissions performance was improved to enhance static flame stability through zone staging and pilot sheltering. In addition, piezo valve technology was implemented to investigate the potential for enhanced dynamic stability through high-bandwidth modulation of the fuel supply. Prototype injector and valve hardware were tested in an atmospheric combustion facility. The program was successful in meeting its objectives. Specifically, the following was accomplished: Demonstrated improvement of lean operability of the Parker multi-point injector through staging of fuel flow and primary zone sheltering; Developed a piezo valve capable of proportional and high-bandwidth modulation of gaseous fuel flow at frequencies as high as 500 Hz; The valve was shown to be capable of effecting changes to flame dynamics, heat release, and acoustic signature of an atmospheric combustor. The latter achievement indicates the viability of the Parker piezo valve technology for use in future adaptively controlled systems for the mitigation of combustion instabilities, particularly for attenuating combustion dynamics under ultra-lean conditions.

  20. Computational study of inlet injection for a Pre-Mixed, Shock-Induced Combustion (PM/SIC) engine

    NASA Technical Reports Server (NTRS)

    Gonzalez, D. E.

    1995-01-01

    A computational simulation of reacting 2-D and 3-D flowfields in a model inlet section of a Pre-Mixed, Shock-Induced Combustion (PM/SIC) engine concept was performed. LARCK, a multi-dimensional Navier-Stokes code with finite-rate kinetics chemistry developed at NASA LaRC by J.A. White, was adapted for this simulation. The flow conditions in the simulation match those envisioned for the PM/SIC engine experiments currently planned at LaRC. The reacting flowfields were Mach 6.3 freestream air and Mach 2 hydrogen at various pressure and temperature conditions injected through a slot injector at the base of the inlet section. In the PM/SIC engine, fuel is injected at the inlet section upstream of the combustor, and reaction is initiated by the shock wave at the inlet which increases the gas temperature and pressure beyond the kinetic limits for reaction. Many challenges exist prior to establishing shock-controlled combustion as a practical engine concept. These challenges include fuel injection schemes that can provide proper fuel-air mixing without creating large losses in the inlet section, and control of the combustion process so that early ignition or combustion propagation through the inlet boundary layer does not occur. For this project, a parametrics study was carried out to model the fuel injection of hydrogen at different flow conditions. It was found that, as the fuel temperature and pressure were increased, the potential for pre-ignition was high at a short distance downstream of the slot injector. The next stage of this work will investigate injection techniques for enhancing mixing of fuel and air in a manner that prevents or reduces the potential for premature ignition observed numerically.

  1. Direct simulation and modeling of flame-wall interaction for premixed turbulent combustion

    SciTech Connect

    Poinsot, T.J.; Haworth, D.C.; Bruneaux, G. . Inst. de Mecanique des Fluides de Toulouse General Motors Research, Warren, MI Inst. Francais du Petrole, Rueil Malmaison )

    1993-10-01

    The interaction between turbulent premixed flames and walls is studied using a two-dimensional full Navier-Stokes solver with simple chemistry. The effects of wall distance on the local and global flame structure are investigated. Quenching distances and maximum wall heat fluxes during quenching are computed in laminar cases and are found to be comparable to experimental and analytical results. For turbulent cases, it is shown that quenching distances and maximum heat fluxes remain of the same order as for laminar flames. Based on simulation results, a law-of-the-wall'' model is derived to describe the interaction between a turbulent premixed flame and a wall. This model is constructed to provide reasonable behavior of flame surface density near a wall under the assumption that flame -- wall interaction takes place at scales smaller than the computational mesh. It can be implemented in conjunction with any of several recent flamelet models based on a modeled surface density equation, with no additional constraints on mesh size or time step. Preliminary tests of this model are presented for the case of a spark-ignited piston engine.

  2. Finite rate chemistry and presumed PDF models for premixed turbulent combustion

    SciTech Connect

    Bray, K.N.C.; Swaminathan, N.; Champion, M.; Libby, P.A.

    2006-09-15

    The sensitivity of the prediction of mean reaction rates in turbulent premixed flames to presumed PDF shape is studied. Three different presumed PDF shapes are considered: (i) a beta function PDF, (ii) a twin delta function PDF, and (iii) a PDF based on unstrained laminar flame properties. The unstrained laminar flame has the same thermochemistry as the turbulent flame. Emphasis is placed on capturing the finite rate chemistry effects and obtaining a simple expression for the mean reaction rate. It is shown that, as the PDFs approach their bimodal limit, the mean reaction rate expressions obtained using the above three PDFs reduce to a common form. These expressions differ only in the numerical value of a multiplying factor. Predictions are compared with DNS data. Under the conditions of this comparison, the beta function and twin delta function PDFs lead to significant errors, while the PDF based on properties of an unstrained laminar flame gives good agreement with the DNS. (author)

  3. Systematically reduced rate mechanisms and presumed PDF models for premixed turbulent combustion

    SciTech Connect

    Bray, Ken; Champion, Michel; Libby, Paul A.

    2010-03-15

    The use of reduced kinetic mechanisms in models for turbulent premixed flames, at large but finite Damkoehler numbers, is described. Taking as examples the two cases of hydrogen-air and methane-air systems for which there exist reduced kinetic schemes characterized by two independent scalar variables only, it is shown that the mean chemical production rate can be in a general way expressed as the product of a mixing factor, depending on the segregation of species due to turbulence, with a reaction rate factor. In this latter factor the probability density function (PDF) of the two scalars appears only as a constant integral quantity. The extension of this analysis to systems involving more than two independent scalars is envisaged. The general result is applied to the two specific cases of interior PDF's modelled by (i) a single Dirac delta function and (ii) a laminar flamelet. (author)

  4. Combustion Characteristics in a Non-Premixed Cool-Flame Regime of n-Heptane in Microgravity

    NASA Technical Reports Server (NTRS)

    Takahashi, Fumiaki; Katta, Viswanath R.; Hicks, Michael C.

    2015-01-01

    A series of distinct phenomena have recently been observed in single-fuel-droplet combustion tests performed on the International Space Station (ISS). This study attempts to simulate the observed flame behavior numerically using a gaseous n-heptane fuel source in zero gravity and a time-dependent axisymmetric (2D) code, which includes a detailed reaction mechanism (127 species and 1130 reactions), diffusive transport, and a radiation model (for CH4, CO, CO2, H2O, and soot). The calculated combustion characteristics depend strongly on the air velocity around the fuel source. In a near-quiescent air environment (< or = 2 mm/s), with a sufficiently large fuel injection velocity (1 cm/s), a growing spherical diffusion flame extinguishes at ˜1200 K due to radiative heat losses. This is typically followed by a transition to the low-temperature (cool-flame) regime with a reaction zone (at ˜700 K) in close proximity to the fuel source. The 'cool flame' regime is formed due to the negative temperature coefficient in the low-temperature chemistry. After a relatively long period (˜18 s) of the cool flame regime, a flash re-ignition occurs, associated with flame-edge propagation and subsequent extinction of the re-ignited flame. In a low-speed (˜3 mm/s) airstream (which simulates the slight droplet movement), the diffusion flame is enhanced upstream and experiences a local extinction downstream at ˜1200 K, followed by steady flame pulsations (˜0.4 Hz). At higher air velocities (4-10 mm/s), the locally extinguished flame becomes steady state. The present axisymmetric computational approach helps in revealing the non-premixed 'cool flame' structure and 2D flame-flow interactions observed in recent microgravity droplet combustion experiments.

  5. Excitable dynamics in high-Lewis number premixed gas combustion at normal and microgravity

    NASA Technical Reports Server (NTRS)

    Pearlman, Howard

    1995-01-01

    Freely-propagating, premixed gas flames in high-Lewis (Le) number, quiescent mixtures are studied experimentally in tubes of various diameter at normal (lg) and microgravity (mu g). A premixture of lean butane and oxygen diluted with helium, argon, neon, nitrogen or a mixture of multiple diluents is examined such that the thermal diffusivity of the mixture (and to a lesser extent, the mass diffusivity of the rate-limiting component) is systematically varied. In effect, different diluents allow variation of the Le without changing the chemistry. The flames are recorded with high speed cinematography and their stability is visually assessed. Different modes of propagation were observed depending on the diameter of the tubes (different conductive heat loss), the composition of the mixture and the g-level. At 1g, four modes of propagation were observed in small and intermediate diameter tubes (large conductive heat loss): (1) steadily propagating flames, (2) radial and longitudinal pulsating flames, (3) 'wavering' flames, and (4) rotating spiral flames. As the diameter of the tube increases, the radial modes become more pronounced while the longitudinal modes systematically disappear. Also, multiple, simultaneous, spatially-separated 'pacemaker' sites are observed in intermediate and large diameter tubes. Each site starts as a small region of high luminosity and develops into a flamelet which assumes the form of one of the fore mentioned modes. These flamelets eventually interact, annihilate each other in their regions of intersection and merge at their newly created free-ends. For very large tubes, radially-propagating wave-trains (believed to be 'trigger waves') are observed. These are analogous to the radial pulsations observed in the smaller diameter tubes. At mu g, three modes of propagation have been observed: (1) steadily propagating flames, (2) radial and longitudinal pulsating flames, and (3) multi-armed, rotating flames. Since the pulsating mode exists at mu

  6. A Study of Premixed, Shock-Induced Combustion With Application to Hypervelocity Flight

    NASA Technical Reports Server (NTRS)

    Axdahl, Erik L.

    2013-01-01

    One of the current goals of research in hypersonic, airbreathing propulsion is access to higher Mach numbers. A strong driver of this goal is the desire to integrate a scramjet engine into a transatmospheric vehicle airframe in order to improve performance to low Earth orbit (LEO) or the performance of a semiglobal transport. An engine concept designed to access hypervelocity speeds in excess of Mach 10 is the shock-induced combustion ramjet (i.e. shcramjet). This dissertation presents numerical studies simulating the physics of a shcramjet vehicle traveling at hypervelocity speeds with the goal of understanding the physics of fuel injection, wall autoignition mitigation, and combustion instability in this flow regime.

  7. Lean premixed recirculating flow combustion for control of oxides of nitrogen

    NASA Technical Reports Server (NTRS)

    Schefer, R. W.; Sawyer, R. F.

    1977-01-01

    The objectives of the reported investigation included the demonstration of a system in which combustion can be maintained under very lean conditions. Aspects of pollutant formation and the stability characteristics of the system were studied. An opposed reacting jet model laboratory combustor was employed in the experiments. Results obtained with the aid of an analytical modeling technique based on the computational scheme reported by Gosman et al. (1969) are also presented. The investigation indicates that fuel lean combustion might provide an effective means of achieving low pollutant emission levels.

  8. Effects of Turbulence on the Combustion Properties of Partially Premixed Flames of Canola Methyl Ester and Diesel Blends

    DOE PAGES

    Dhamale, N.; Parthasarathy, R. N.; Gollahalli, S. R.

    2011-01-01

    Canola methyl ester (CME) is a biofuel that is a renewable alternative energy resource and is produced by the transesterification of canola oil. The objective of this study was to document the effects of turbulence on the combustion characteristics of blends of CME and No 2 diesel fuel in a partially-premixed flame environment. The experiments were conducted with mixtures of pre-vaporized fuel and air at an initial equivalence ratio of 7 and three burner exit Reynolds numbers, 2700, 3600, and 4500. Three blends with 25, 50, and 75% volume concentration of CME were studied. The soot volume fraction was highestmore » for the pure diesel flames and did not change significantly with Reynolds number due to the mutually compensating effects of increased carbon input rate and increased air entrainment as the Reynolds number was increased. The global NOx emission index was highest and the CO emission index was the lowest for the pure CME flame, and varied non-monotonically with biofuel content in the blend The mean temperature and the NOx concentration at three-quarter flame height were generally correlated, indicating that the thermal mechanism of NOx formation was dominant in the turbulent biofuel flames also.« less

  9. Spatially distributed flame transfer functions for predicting combustion dynamics in lean premixed gas turbine combustors

    SciTech Connect

    Kim, K.T.; Lee, J.G.; Quay, B.D.; Santavicca, D.A.

    2010-09-15

    The present paper describes a methodology to improve the accuracy of prediction of the eigenfrequencies and growth rates of self-induced instabilities and demonstrates its application to a laboratory-scale, swirl-stabilized, lean-premixed, gas turbine combustor. The influence of the spatial heat release distribution is accounted for using local flame transfer function (FTF) measurements. The two-microphone technique and CH{sup *} chemiluminescence intensity measurements are used to determine the input (inlet velocity perturbation) and the output functions (heat release oscillation), respectively, for the local flame transfer functions. The experimentally determined local flame transfer functions are superposed using the flame transfer function superposition principle, and the result is incorporated into an analytic thermoacoustic model, in order to predict the linear stability characteristics of a given system. Results show that when the flame length is not acoustically compact the model prediction calculated using the local flame transfer functions is better than the prediction made using the global flame transfer function. In the case of a flame in the compact flame regime, accurate predictions of eigenfrequencies and growth rates can be obtained using the global flame transfer function. It was also found that the general response characteristics of the local FTF (gain and phase) are qualitatively the same as those of the global FTF. (author)

  10. Fuel-Air Mixing Effect on Nox Emissions for a Lean Premixed-Prevaporized Combustion System

    NASA Technical Reports Server (NTRS)

    Lee, Chi-Ming; Chun, Kue S.; Locke, Randy J.

    1995-01-01

    The lean premixed-prevaporized (LPP) concept effectively meets low nitrogen oxides (NOx) emission requirements for combustors with the high inlet temperature and pressure typical of the High-Speed Civil Transport (HSCT). For the LPP system fuel-air mixture uniformity is probably the most important factor for low NOx emissions. Previous studies have suggested that the fuel-air mixture uniformity can be severely affected by changing the number and configuration of fuel injection points. Therefore, an experimental study was performed to determine how the number of fuel injection points and their arrangement affect NOx emissions from an LPP system. The NOx emissions were measured by a gas-sampling probe in a flame-tube rig at the following conditions: inlet temperature of 810 K (1000 F), rig pressure of 10 atm, reference velocity of 150 ft/s, and residence time near 0.005 s. Additionally, a focused Schlieren diagnostic technique coupled with a high speed camera was used to provide a qualitative description of the spatial flow field.

  11. A Sectored-One-Dimensional Model for Simulating Combustion Instabilities in Premix Combustors

    NASA Technical Reports Server (NTRS)

    Paxson, Daniel E.

    1999-01-01

    A one-dimensional, CFD based combustor simulation has been developed that exhibits self-excited, thermoacoustic oscillations in premixed combustor geometries that typically have large, abrupt changes in cross sectional area. The combustor geometry is approximated by dividing it into a finite number of one-dimensional sectors. Within each sector, the equations of motion are integrated numerically, along with a species transport and a reaction equation. Across the sectors, mass and energy are conserved, and momentum loss is prescribed using appropriately compatible boundary conditions that account for the area change. The resulting simulation and associated boundary conditions essentially represent a one-dimensional, multi-block technique. Details of the simulation code are presented herein. Results are then shown comparing experimentally observed and simulated operation of a particular combustor rig that exhibited different instabilities at different operating points. It will be shown that the simulation closely matched the rig data in oscillation amplitudes, frequencies, and operating points at which the instabilities occurred. Finally, advantages and limitations of the simulation technique are discussed.

  12. Flame front surface characteristics in turbulent premixed propane/air combustion

    SciTech Connect

    Guelder, O.L.; Smallwood, G.J.; Wong, R.; Snelling, D.R.; Smith, R.; Deschamps, B.M.; Sautet, J.C.

    2000-03-01

    The characteristics of the flame front surfaces in turbulent premixed propane/air flames were investigated. Flame front images were obtained using laser-induced fluorescence (LIF) of OH and Mie scattering on two Bunsen-type burners of 11.2-mm and 22.4-mm diameters. Nondimensional turbulence intensity, u{prime}/S{sub L}, was varied from 0.9 to 15, and the Reynolds number, based on the integral length scale, varied from 40 to 467. Approximately 100 images were recorded for each experimental condition. Fractal parameters (fractal dimension, inner and outer cutoffs) and corresponding standard deviations were determined by analysis of the flame front images using the caliper technique. The fractal dimensions derived from OH and Mie scattering images are almost identical. However, inner and outer cutoffs from OH images are consistently higher than those obtained from Mie scattering. The self-similar region of the flame front wrinkling is about a decade for all flames studied. In the nondimensional turbulence intensity range from 1 to 15, it was found that the mean fractal dimension is about 2.2 and it does not show any dependence on turbulence intensity. This contradicts the findings of the previous studies that showed that the fractal dimension asymptotically reaches to 2.35--2.37 when the nondimensional turbulence intensity u{prime}/S{sub L} exceeds 3. It is shown that the reason for this discrepancy is the image analysis method used in the previous studies. Examples are given to show the inadequacy of the circle method used in previous studies for extraction of fractal parameters from flame front images. The fractal parameters obtained so far, in this and previous studies, are not capable of correctly predicting the turbulent burning velocity using the available fractal area closure model.

  13. Computational modeling of thermodynamic irreversibilities in turbulent non-premixed combustion

    NASA Astrophysics Data System (ADS)

    Bouras, Fethi; Khaldi, Fouad

    2016-04-01

    This work is focused on the analysis of various computed terms of entropy generation rate in the gaseous combustion processes at different inlet temperatures of air and CH4. Therefore, the expression of the entropy generation rate includes the effect of the viscosity friction, the thermal diffusion, the species diffusion and the chemical reaction. The expressions have been used for each term of entropy generation in order to examine the influence of each one in the overall system.

  14. The influence of CO2 in biogas flammability limit and laminar burning velocity in spark ignited premix combustion at various pressures

    NASA Astrophysics Data System (ADS)

    Anggono, W.; Wardana, I. N. G.; Lawes, M.; Hughes, K. J.; Wahyudi, S.; Hamidi, N.; Hayakawa, A.

    2016-03-01

    Biogas is an alternative energy source that is sustainable and renewable containing more than 50% CH4 and its biggest impurity or inhibitor is CO2. Demands for replacing fossil fuels require an improved fundamental understanding of its combustion processes. Flammability limits and laminar burning velocities are important characteristics in these processes. Thus, this research focused on the effects of CO2 on biogas flammability limits and laminar burning velocities in spark ignited premixed combustion. Biogas was burned in a spark ignited spherical combustion bomb. Spherically expanding laminar premixed flames, freely propagating from spark ignition in initial, were continuously recorded by a high-speed digital camera. The combustion bomb was filled with biogas-air mixtures at various pressures, CO2 levels and equivalence ratios (ϕ) at ambient temperature. The results were also compared to those of the previous study into inhibitorless biogas (methane) at various pressures and equivalence ratios (ϕ). Either the flammable areas become narrower with increased percentages of carbon dioxide or the pressure become lower. In biogas with 50% CO2 content, there was no biogas flame propagation for any equivalence ratio at reduced pressure (0.5 atm). The results show that the laminar burning velocity at the same equivalence ratio declined in respect with the increased level of CO2. The laminar burning velocities were higher at the same equivalence ratio by reducing the initial pressure.

  15. An experimental study of the effect of a pilot flame on technically pre-mixed, self-excited combustion instabilities

    NASA Astrophysics Data System (ADS)

    O'Meara, Bridget C.

    Combustion instabilities are a problem facing the gas turbine industry in the operation of lean, pre-mixed combustors. Secondary flames known as "pilot flames" are a common passive control strategy for eliminating combustion instabilities in industrial gas turbines, but the underlying mechanisms responsible for the pilot flame's stabilizing effect are not well understood. This dissertation presents an experimental study of a pilot flame in a single-nozzle, swirl-stabilized, variable length atmospheric combustion test facility and the effect of the pilot on combustion instabilities. A variable length combustor tuned the acoustics of the system to excite instabilities over a range of operating conditions without a pilot flame. The inlet velocity was varied from 25 -- 50 m/s and the equivalence ratio was varied from 0.525 -- 0.65. This range of operating conditions was determined by the operating range of the combustion test facility. Stability at each operating condition and combustor length was characterized by measurements of pressure oscillations in the combustor. The effect of the pilot flame on the magnitude and frequency of combustor stability was then investigated. The mechanisms responsible for the pilot flame effect were studied using chemiluminescence flame images of both stable and unstable flames. Stable flame structure was investigated using stable flame images of CH* chemiluminescence emission. The effect of the pilot on stable flame metrics such as flame length, flame angle, and flame width was investigated. In addition, a new flame metric, flame base distance, was defined to characterize the effect of the pilot flame on stable flame anchoring of the flame base to the centerbody. The effect of the pilot flame on flame base anchoring was investigated because the improved stability with a pilot flame is usually attributed to improved flame anchoring through the recirculation of hot products from the pilot to the main flame base. Chemiluminescence images

  16. Turbulent premixed combustion in V-shaped flames: Characteristics of flame front

    NASA Astrophysics Data System (ADS)

    Kheirkhah, S.; Gülder, Ö. L.

    2013-05-01

    Flame front characteristics of turbulent premixed V-shaped flames were investigated experimentally using the Mie scattering and the particle image velocimetry techniques. The experiments were performed at mean streamwise exit velocities of 4.0, 6.2, and 8.6 m/s, along with fuel-air equivalence ratios of 0.7, 0.8, and 0.9. Effects of vertical distance from the flame-holder, mean streamwise exit velocity, and fuel-air equivalence ratio on statistics of the distance between the flame front and the vertical axis, flame brush thickness, flame front curvature, and angle between tangent to the flame front and the horizontal axis were studied. The results show that increasing the vertical distance from the flame-holder and the fuel-air equivalence ratio increase the mean and root-mean-square (RMS) of the distance between the flame front and the vertical axis; however, increasing the mean streamwise exit velocity decreases these statistics. Spectral analysis of the fluctuations of the flame front position depicts that the normalized and averaged power-spectrum-densities collapse and show a power-law relation with the normalized wave number. The flame brush thickness is linearly correlated with RMS of the distance between the flame front and the vertical axis. Analysis of the curvature of the flame front data shows that the mean curvature is independent of the experimental conditions tested and equals to zero. Values of the inverse of the RMS of flame front curvature are similar to those of the integral length scale, suggesting that the large eddies in the flow make a significant contribution in wrinkling of the flame front. Spectral analyses of the flame front curvature as well as the angle between tangent to the flame front and the horizontal axis show that the power-spectrum-densities feature a peak. Value of the inverse of the wave number pertaining to the peak is larger than that of the integral length scale.

  17. Experimental investigation of the dynamics and structure of lean-premixed turbulent combustion

    NASA Astrophysics Data System (ADS)

    Yuen, Frank Tat Cheong

    2009-12-01

    Turbulent premixed propane/air and methane/air flames were studied using planar Rayleigh scattering and particle image velocimetry on a stabilized Bunsen type burner. The fuel-air equivalence ratio was varied from φ = 0:7 to 1.0 for propane flames, and from φ = 0:6 to 1.0 for methane flames. The non-dimensional turbulence intensity, u'/ SL (ratio of fluctuation velocity to laminar burning velocity), covered the range from 3 to 24, equivalent to conditions of corrugated flamelets and thin reaction zones regimes. Temperature gradients decreased with the increasing u'/SL and levelled off beyond u'/SL > 10 for both propane and methane flames. Flame front thickness increased slightly as u'/SL increased for both mixtures, although the thickness increase was more noticeable for propane flames, which meant the thermal flame front structure was being thickened. A zone of higher temperature was observed on the average temperature profile in the preheat zone of the flame front as well as some instantaneous temperature profiles at the highest u'/SL. Curvature probability density functions were similar to the Gaussian distribution at all u'/ SL for both mixtures and for all the flame sections. The mean curvature values decreased as a function of u'/ SL and approached zero. Flame front thickness was smaller when evaluated at flame front locations with zero curvature than that with curvature. Temperature gradients and FSD were larger when the flame curvature was zero. The combined thickness and FSD data suggest that the curvature effect is more dominant than that of the stretch by turbulent eddies during flame propagation. Integrated flame surface density for both propane and methane flames exhibited no dependance on u'/S L regardless of the FSD method used for evaluation. This observation implies that flame surface area may not be the dominant factor in increasing the turbulent burning velocity and the flamelet assumption may not be valid under the conditions studied. Dkappa

  18. Modelling of Landau-Darrieus and thermo-diffusive instability effects for CFD simulations of laminar and turbulent premixed combustion

    NASA Astrophysics Data System (ADS)

    Keppeler, Roman; Pfitzner, Michael

    2015-01-01

    An algebraic model is derived that accounts for the effects of non-resolved Landau-Darrieus and thermo-diffusive instabilities on the propagation speed of fully premixed laminar and turbulent flame fronts in the Large Eddy Simulation (LES) context provided that the laminar flame speed appears as a model parameter in the LES combustion model. The model is derived assuming fractal characteristics of flames which exhibit cellular structures due to instabilities. The smallest and largest unstable wavelengths are computed employing a dispersion relation for nominally planar flames. Values for the fractal dimension characterising the flame structures are taken from the literature. A phenomenological model accounts for the stabilising effect of strain. Based on experimental data, a correlation for a critical strain rate, which indicates the onset of instabilities, is formulated. To validate the new model which accounts for instabilities on the effective speed of laminar flame propagation, laminar expanding spherical methane-air flames at p = 5 bar and p = 10 bar are simulated in the LES context. Values for the fractal dimension, as proposed in the literature, are varied. The predicted flame propagation speed is in very good agreement with experimental data when applying a fractal dimension of about D = 2.06. The critical strain turns out to be a suitable parameter to indicate the onset of instabilities and to quantify the influence of instabilities. Simulations applying a second model proposed by Bradley and valid for spherically expanding flames show similar results. LES of turbulent Bunsen flames at 1, 5 and 10 bar, which are characterised by u‧/s0L < 1, are performed to evaluate the derived instability model for turbulent flames. The simulated flames (from the Kobayashi database) have already been experimentally investigated in the context of Landau-Darrieus and thermo-diffusive instabilities. In agreement with conclusions from these investigations, for the

  19. Chemical structures of low-pressure premixed methylcyclohexane flames as benchmarks for the development of a predictive combustion chemistry model

    SciTech Connect

    Skeen, Scott A.; Yang, Bin; Jasper, Ahren W.; Pitz, William J.; Hansen, Nils

    2011-11-14

    The chemical compositions of three low-pressure premixed flames of methylcyclohexane (MCH) are investigated with the emphasis on the chemistry of MCH decomposition and the formation of aromatic species, including benzene and toluene. The flames are stabilized on a flat-flame (McKenna type) burner at equivalence ratios of φ = 1.0, 1.75, and 1.9 and at low pressures between 15 Torr (= 20 mbar) and 30 Torr (= 40 mbar). The complex chemistry of MCH consumption is illustrated in the experimental identification of several C7H12, C7H10, C6H12, and C6H10 isomers sampled from the flames as a function of distance from the burner. Three initiation steps for MCH consumption are discussed: ring-opening to heptenes and methyl-hexenes (isomerization), methyl radical loss yielding the cyclohexyl radical (dissociation), and H abstraction from MCH. Mole fraction profiles as a function of distance from the burner for the C7 species supplemented by theoretical calculations are presented, indicating that flame structures resulting in steeper temperature gradients and/or greater peak temperatures can lead to a relative increase in MCH consumption through the dissociation and isomerization channels. Trends observed among the stable C6 species as well as 1,3-pentadiene and isoprene also support this conclusion. Relatively large amounts of toluene and benzene are observed in the experiments, illustrating the importance of sequential H-abstraction steps from MCH to toluene and from cyclohexyl to benzene. Furthermore, modeled results using the detailed chemical model of Pitz et al. (Proc. Combust. Inst.2007, 31, 267–275) are also provided to illustrate the use of these data as a benchmark for the improvement or future development of a MCH mechanism.

  20. Chemical structures of low-pressure premixed methylcyclohexane flames as benchmarks for the development of a predictive combustion chemistry model

    DOE PAGES

    Skeen, Scott A.; Yang, Bin; Jasper, Ahren W.; Pitz, William J.; Hansen, Nils

    2011-11-14

    The chemical compositions of three low-pressure premixed flames of methylcyclohexane (MCH) are investigated with the emphasis on the chemistry of MCH decomposition and the formation of aromatic species, including benzene and toluene. The flames are stabilized on a flat-flame (McKenna type) burner at equivalence ratios of φ = 1.0, 1.75, and 1.9 and at low pressures between 15 Torr (= 20 mbar) and 30 Torr (= 40 mbar). The complex chemistry of MCH consumption is illustrated in the experimental identification of several C7H12, C7H10, C6H12, and C6H10 isomers sampled from the flames as a function of distance from the burner.more » Three initiation steps for MCH consumption are discussed: ring-opening to heptenes and methyl-hexenes (isomerization), methyl radical loss yielding the cyclohexyl radical (dissociation), and H abstraction from MCH. Mole fraction profiles as a function of distance from the burner for the C7 species supplemented by theoretical calculations are presented, indicating that flame structures resulting in steeper temperature gradients and/or greater peak temperatures can lead to a relative increase in MCH consumption through the dissociation and isomerization channels. Trends observed among the stable C6 species as well as 1,3-pentadiene and isoprene also support this conclusion. Relatively large amounts of toluene and benzene are observed in the experiments, illustrating the importance of sequential H-abstraction steps from MCH to toluene and from cyclohexyl to benzene. Furthermore, modeled results using the detailed chemical model of Pitz et al. (Proc. Combust. Inst.2007, 31, 267–275) are also provided to illustrate the use of these data as a benchmark for the improvement or future development of a MCH mechanism.« less

  1. Progress in Advanced Spray Combustion Code Integration

    NASA Technical Reports Server (NTRS)

    Liang, Pak-Yan

    1993-01-01

    A multiyear project to assemble a robust, muitiphase spray combustion code is now underway and gradually building up to full speed. The overall effort involves several university and government research teams as well as Rocketdyne. The first part of this paper will give an overview of the respective roles of the different participants involved, the master strategy, the evolutionary milestones, and an assessment of the state-of-the-art of various key components. The second half of this paper will highlight the progress made to date in extending the baseline Navier-Stokes solver to handle multiphase, multispecies, chemically reactive sub- to supersonic flows. The major hurdles to overcome in order to achieve significant speed ups are delineated and the approaches to overcoming them will be discussed.

  2. Experimental Characterization of Combustion Instabilities and Flow-Flame Dynamics in a Partially-Premixed Gas Turbine Model Combustor

    NASA Astrophysics Data System (ADS)

    Allison, Patton Manuel

    Partially-premixed, swirl combustion is applied in gas turbine combustors to achieve flame stabilization and reduced emission production. However, this method is also inherently sensitive to combustion instabilities which can cause large pressure, velocity, and heat release fluctuations. This thesis investigates thermoacoustic coupling created by flow-flame dynamics in a gas turbine model combustor (GTMC) for a variety of fuels and operating flow rates. Several naturally occurring instability modes were identified to control the acoustic response of the system, including Helmholtz resonances from the plenum and convective-acoustic effects which cause equivalence ratio oscillations. Laser Doppler velocimetry was used to measure radial flow in the GTMC, which can set up flow-fields which create loudly resonating flat-shaped flames, in comparison to quiet V-shaped flames. Flame location and shape altered convective time delays which determine the relative phases of pressure and heat release oscillations. Simultaneous pressure and chemiluminescence imaging showed that the heat release, pressure fluctuations, and flame motion are all coupled at the same instability frequency. Videos of the flame motion also revealed that the precessing vortex core (PVC), created by the swirling flow, influences the rocking behavior of the flame. Acetone was added to the fuel to act as a tracer in fluorescence measurements which indicated the localization of unburned fuel. It was discovered that fuel was distributed in lobes which corresponded to locations surrounding the shear layer outside of the central recirculation zone, and that the relative distribution of the lobes adjusted to forcing by the flow. Finally, high-speed formaldehyde planar laser-induced fluorescence was applied to study the motion of preheat zone surfaces in response to the oscillations of the instability. The flame surface density and wrinkling fluctuated at the acoustic frequency and displayed dampened motions

  3. Combustion Noise at Elevated Pressures in a Liquid-Fueled Premixed Combustor

    NASA Technical Reports Server (NTRS)

    Darling, Douglas; Radhakrishnan, Krishnan; Oyediran, Ayo

    1997-01-01

    Noise generated in gas turbine combustors can exist in several forms-broadband noise, sharp resonant peaks, and regular or intermittent nonlinear pulsing. In the present study, dynamic pressure measurements were made in several JP-5-fueled combustor configurations, at various mean pressures and temperatures. The fluctuating pressure was measured at mean pressures from 6 to 14 atm and inlet temperatures from 550 K to 850 K. The goal of the present work was to study the effect of changes in mean flow conditions on combustor noise: both broadband noise and sharp tones were considered. In general, the shape of the broadband noise spectrum was consistent from one configuration to another. The shape of the spectrum was influenced by the acoustic filtering of the combustion zone. This filtering ensured the basic consistency of the spectra. In general, the trends in broadband noise observed at low mean pressures were also seen at high mean pressures; that is, the total sound level decreased with both increasing equivalence ratio and increasing inlet temperature. The combustor configurations without a central pilot experienced higher broadband noise levels and were more susceptible to narrow peak resonances than configurations with a central pilot. The sharp peaks were more sensitive to the mean flow than was the broadband noise, and the effects were not always the same. In some situations, increasing the equivalence ratio made the sharp peaks grow, while at other conditions, increasing the equivalence ratio made the sharp peaks shrink. Thus, it was difficult to predict when resonances would occur; however, they were reproducible. Acoustic coupling between the upstream and downstream regions of the combustor may play a role in the sharp-peaked oscillations. Noise was also observed near lean blow out. As with other types of noise, lean blow out noise was affected by the combustion chamber acoustics, which apparently maintains the fluctuations at a uniform frequency. However

  4. Numerical simulation of the interaction between a flowfield and chemical reaction on premixed pulsed jet combustion

    NASA Astrophysics Data System (ADS)

    Hishida, Manabu; Hayashi, A. Koichi

    1992-12-01

    Pulsed Jet Combustion (PJC) is numerically simulated using time-dependent, axisymmetric, full Navier-Stokes equations with the mass, momentum, energy, and species conservation equations for a hydrogen-air mixture. A hydrogen-air reaction mechanism is modeled by nine species and nineteen elementary forward and backward reactions to evaluate the effect of the chemical reactions accurately. A point implicit method with the Harten and Yee's non-MUSCL (Monotone Upstream-centerd Schemes for Conservation Laws) modified-flux type TVD (Total Variation Diminishing) scheme is applied to deal with the stiff partial differential equations. Furthermore, a zonal method making use of the Fortified Solution Algorithm (FSA) is applied to simulate the phenomena in the complicated shape of the sub-chamber. The numerical result shows that flames propagating in the sub-chamber interact with pressure waves and are deformed to be wrinkled like a 'tulip' flame and a jet passed through the orifice changes its mass flux quasi-periodically.

  5. A Study of Pollutant Formation from the Lean Premixed Combustion of Gaseous Fuel Alternatives to Natural Gas

    NASA Astrophysics Data System (ADS)

    Fackler, Keith Boyd, Jr.

    The goal of this research is to identify how nitrogen oxide (NO x) emissions and flame stability (blowout) are impacted by the use of fuels that are alternatives to typical pipeline natural gas. The research focuses on lean, premixed combustors that are typically used in state-of-the-art natural gas fueled systems. An idealized laboratory lean premixed combustor, specifically the jet-stirred reactor, is used for experimental data. A series of models, including those featuring detailed fluid dynamics and those focusing on detailed chemistry, are used to interpret the data and understand the underlying chemical kinetic reasons for differences in emissions between the various fuel blends. An ultimate goal is to use these data and interpretive tools to develop a way to predict the emission and stability impacts of changing fuels within practical combustors. All experimental results are obtained from a high intensity, single-jet stirred reactor (JSR). Five fuel categories are studied: (1) pure H 2, (2) process and refinery gas, including combinations of H2, CH4, C2H6, and C3H8, (3) oxygen blown gasified coal/petcoke composed of H2, CO, and CO2, (4) landfill and digester gas composed of CH4, CO2, and N2, and (5) liquified natural gas (LNG)/shale/associated gases composed of CH4, C2H6, and C3 H8. NOx measurements are taken at a nominal combustion temperature of 1800 K, atmospheric pressure, and a reactor residence time of 3 ms. This is done to focus the results on differences caused by fuel chemistry by comparing all fuels at a common temperature, pressure, and residence time. This is one of the few studies in the literature that attempts to remove these effects when studying fuels varying in composition. Additionally, the effects of changing temperature and residence time are investigated for selected fuels. At the nominal temperature and residence time, the experimental and modeling results show the following trends for NOx emissions as a function of fuel type: 1.) NOx

  6. Investigation of non-premixed flame combustion characters in GO2/GH2 shear coaxial injectors using non-intrusive optical diagnostics

    NASA Astrophysics Data System (ADS)

    Dai, Jian; Yu, NanJia; Cai, GuoBiao

    2015-12-01

    Single-element combustor experiments are conducted for three shear coaxial geometry configuration injectors by using gaseous oxygen and gaseous hydrogen (GO2/GH2) as propellants. During the combustion process, several spatially and timeresolved non-intrusive optical techniques, such as OH planar laser induced fluorescence (PLIF), high speed imaging, and infrared imaging, are simultaneously employed to observe the OH radical concentration distribution, flame fluctuations, and temperature fields. The results demonstrate that the turbulent flow phenomenon of non-premixed flame exhibits a remarkable periodicity, and the mixing ratio becomes a crucial factor to influence the combustion flame length. The high speed and infrared images have a consistent temperature field trend. As for the OH-PLIF images, an intuitionistic local flame structure is revealed by single-shot instantaneous images. Furthermore, the means and standard deviations of OH radical intensity are acquired to provide statistical information regarding the flame, which may be helpful for validation of numerical simulations in future. Parameters of structure configurations, such as impinging angle and oxygen post thickness, play an important role in the reaction zone distribution. Based on a successful flame contour extraction method assembled with non-linear anisotropic diffusive filtering and variational level-set, it is possible to implement a fractal analysis to describe the fractal characteristics of the non-premixed flame contour. As a result, the flame front cannot be regarded as a fractal object. However, this turbulent process presents a self-similarity characteristic.

  7. A Study of Pollutant Formation from the Lean Premixed Combustion of Gaseous Fuel Alternatives to Natural Gas

    NASA Astrophysics Data System (ADS)

    Fackler, Keith Boyd, Jr.

    The goal of this research is to identify how nitrogen oxide (NO x) emissions and flame stability (blowout) are impacted by the use of fuels that are alternatives to typical pipeline natural gas. The research focuses on lean, premixed combustors that are typically used in state-of-the-art natural gas fueled systems. An idealized laboratory lean premixed combustor, specifically the jet-stirred reactor, is used for experimental data. A series of models, including those featuring detailed fluid dynamics and those focusing on detailed chemistry, are used to interpret the data and understand the underlying chemical kinetic reasons for differences in emissions between the various fuel blends. An ultimate goal is to use these data and interpretive tools to develop a way to predict the emission and stability impacts of changing fuels within practical combustors. All experimental results are obtained from a high intensity, single-jet stirred reactor (JSR). Five fuel categories are studied: (1) pure H 2, (2) process and refinery gas, including combinations of H2, CH4, C2H6, and C3H8, (3) oxygen blown gasified coal/petcoke composed of H2, CO, and CO2, (4) landfill and digester gas composed of CH4, CO2, and N2, and (5) liquified natural gas (LNG)/shale/associated gases composed of CH4, C2H6, and C3 H8. NOx measurements are taken at a nominal combustion temperature of 1800 K, atmospheric pressure, and a reactor residence time of 3 ms. This is done to focus the results on differences caused by fuel chemistry by comparing all fuels at a common temperature, pressure, and residence time. This is one of the few studies in the literature that attempts to remove these effects when studying fuels varying in composition. Additionally, the effects of changing temperature and residence time are investigated for selected fuels. At the nominal temperature and residence time, the experimental and modeling results show the following trends for NOx emissions as a function of fuel type: 1.) NOx

  8. Experimental and numerical comparison of extractive and in situ laser measurements of non-equilibrium carbon monoxide in lean-premixed natural gas combustion

    SciTech Connect

    Nguyen, Q.V.; Edgar, B.L.; Dibble, R.W.; Gulati, A.

    1995-02-01

    Measurements of carbon monoxide (CO) in the high-temperature combustion product stream of an atmospheric pressure, lean-premixed combustion, natural gas reactor were obtained using line-of-sight tunable diode laser absorption and extractive probe sampling in conjunction with nondispersive infrared analyzers over various equivalence ratios and flow residence times. The measurements are compared with (1) a numerical model using comprehensive chemical kinetics for methane combustion in conjunction with perfectly stirred reactor (PSR) and plug-flow reactor (PFR) modeling approaches, and (2) chemical equilibrium at the measured temperatures. Temperatures ranging from 1,500 to 2,000 K were measured using a radiation corrected thermocouple and also by a diode laser thermometry technique. The laser based in situ measurements of CO concentration ranged from 50 to 5,000 ppm depending on the equivalence ratio and flow residence time. Results of the numerical model were consistent with the laser-based measurements. The extractive probe measurements were found to be as much as 10 times less than the laser-based measurements. However, laser and probe measurements for fuel-rich equivalence ratios agreed. In an effort to improve the performance of extractive sampling probes, the authors tested several aerodynamic quench probe designs. They were unable to achieve an aerodynamic quench of the CO in a high-temperature combustion product stream. A model of the sampling probe as a PFR indicates that extractive sampling of [CO] is increasingly inaccurate at gas temperatures above 1,000 K.

  9. A Simulation of the Effects of Varying Repetition Rate and Pulse Width of Nanosecond Discharges on Premixed Lean Methane-Air Combustion

    DOE PAGES

    Bak, Moon Soo; Cappelli, Mark A.

    2012-01-01

    Two-dimensional kinetic simulation has been carried out to investigate the effects of repetition rate and pulse width of nanosecond repetitively pulsed discharges on stabilizing premixed lean methane-air combustion. The repetition rate and pulse width are varied from 10 kHz to 50 kHz and from 9 ns to 2 ns while the total power is kept constant. The lower repetition rates provide larger amounts of radicals such as O, H, and OH. However, the effect on stabilization is found to be the same for all of the tested repetition rates. The shorter pulse width is found to favor the production of species in higher electronicmore » states, but the varying effects on stabilization are also found to be small. Our results indicate that the total deposited power is the critical element that determines the extent of stabilization over this range of discharge properties studied.« less

  10. Fundamental characterization of alternate fuel effects in continuous combustion systems. Summary technical progress report, August 15, 1978-January 31, 1980

    SciTech Connect

    Blazowski, W.S.; Edelman, R.B.; Wong, E.

    1980-02-27

    The overall objective of this contract is to assist in the development of fuel-flexible combustion systems for gas turbines as well as Rankine and Stirling cycle engines. The primary emphasis of the program is on liquid hydrocarbons produced from non-petroleum resources. Fuel-flexible combustion systems will provide for more rapid transition of these alternative fuels into important future energy utilization centers (especially utility power generation with the combined cycle gas turbine). The specific technical objectives of the program are: (a) develop an improved understanding of relationships between alternative fuel properties and continuous combustion system effects, and (b) provide analytical modeling/correlation capabilities to be used as design aids for development of fuel-tolerant combustion systems. This is the second major report of the program. Key experimental findings during this reporting period concern stirred combustor soot production during operation at controlled temperature conditions, soot production as a function of combustor residence time, an improved measurement technique for total hydrocarbons and initial stirred combustor results of fuel nitrogen conversion. While the results to be presented concern a stirred combustor which utilizes premixed fuel vapor/oxidant mixtures, a new combustor which combusts liquid fuel injected into the reactor as a spray has been developed and will be described. Analytical program progress includes the development of new quasiglobal models of soot formation and assessment of needs for other submodel development.

  11. Microgravity combustion science: Progress, plans, and opportunities

    NASA Technical Reports Server (NTRS)

    1992-01-01

    An earlier overview is updated which introduced the promise of microgravity combustion research and provided a brief survey of results and then current research participants, the available set of reduced gravity facilities, and plans for experimental capabilities in the space station era. Since that time, several research studies have been completed in drop towers and aircraft, and the first space based combustion experiments since Skylab have been conducted on the Shuttle. The microgravity environment enables a new range of experiments to be performed since buoyancy induced flows are nearly eliminated, normally obscured forces and flows may be isolated, gravitational settling or sedimentation is nearly eliminated, and larger time or length scales in experiments are feasible. In addition to new examinations of classical problems, (e.g., droplet burning), current areas of interest include soot formation and weak turbulence, as influenced by gravity.

  12. Studies of Premixed Laminar and Turbulent Flames at Microgravity

    NASA Technical Reports Server (NTRS)

    Abid, M.; Aung, K.; Ronney, P. D.; Sharif, J. A.; Wu, M.-S.

    1999-01-01

    Several topics relating to combustion limits in premixed flames at reduced gravity have been studied. These topics include: (1) flame balls; (2) numerical simulation of flame ball and planar flame structure and stability; (3) experimental simulation of buoyancy effects in premixed flames using aqueous autocatalytic reactions; and (4) premixed flame propagation in Hele-Shaw cells.

  13. Dry low combustion system with means for eliminating combustion noise

    DOEpatents

    Verdouw, Albert J.; Smith, Duane; McCormick, Keith; Razdan, Mohan K.

    2004-02-17

    A combustion system including a plurality of axially staged tubular premixers to control emissions and minimize combustion noise. The combustion system includes a radial inflow premixer that delivers the combustion mixture across a contoured dome into the combustion chamber. The axially staged premixers having a twist mixing apparatus to rotate the fluid flow and cause improved mixing without causing flow recirculation that could lead to pre-ignition or flashback.

  14. Premixed Prevaporized Combustor Technology Forum

    NASA Technical Reports Server (NTRS)

    1979-01-01

    The Forum was held to present the results of recent and current work intended to provide basic information required for demonstration of lean, premixed prevaporized combustors for aircraft gas turbine engine application. Papers are presented which deal with the following major topics: (1) engine interfaces; (2) fuel-air preparation; (3) autoignition; (4) lean combustion; and (5) concept design studies.

  15. The mechanism of two-dimensional pocket formation in lean premixed methane-air flames with implications to turbulent combustion

    SciTech Connect

    Chen, J.H.; Echekki, T.; Kollmann, W.

    1999-01-01

    The mechanism of unburnt pocket formation in an unsteady two-dimensional premixed lean methane-air flame is investigated using direct numerical simulations. Theoretical results for nonlinear diffusion equations combined with analytical examples are used to interpret some of the results. Flame structure and propagation show three distinct stages of pocket formation: (1) flame channel closing involving head-on quenching of flames, (2) cusp recovery, and (3) pocket burnout. The flame channel closing and subsequent pocket burnout are mutual annihilation events that feature curvature, diffusion normal to the flame front, unsteady strain rate effects, and singularities in flame propagation and stretch rate. The results show that during channel closing and pocket burnout thermo-diffusive and chemical interactions result in the acceleration of the flames prior to annihilation; the time scales associated with the final stage of mutual annihilation and the initial stage of cusp recovery are significantly smaller than diffusive and convective time scales. Peak radical concentrations resulting from flame channel closing and pocket burnout exceed peak laminar values by as much as 25%. After the merging of the fuel consumption layers, radical production and flame structure shifts more towards an H{sub 2}/CO/O{sub 2} system at the expense of hydrocarbon reactions. Species thermodiffusive interaction times are shorter than the unstrained one-dimensional counterpart due to unsteady strain and convection. Curvature effects on the flame propagation are prominent during pocket burnout and cusp recovery. The recovery stage shows strong dependence on diffusion of radicals left from the channel closing stage. This diffusion is amplified by the strong curvature of the flame cusp.

  16. Experimental study on premixed CH{sub 4}/air mixture combustion in micro Swiss-roll combustors

    SciTech Connect

    Zhong, Bei-Jing; Wang, Jian-Hua

    2010-12-15

    Excess enthalpy combustion is a promising approach to stabilize flame in micro-combustors. Using a Swiss-roll combustor configuration, excess enthalpy combustion can be conveniently achieved. In this work, three types of Swiss-roll combustors with double spiral-shaped channels were designed and fabricated. The combustors were tested using methane/air mixtures of various equivalence ratios. Both temperature distributions and extinction limits were determined for each combustor configuration at different methane mass flow rates. Results indicate that the Swiss-roll combustors developed in the current study greatly enhance combustion stability in center regions of the combustors. At the same time, excess enthalpy combustors of the Swiss-roll configuration significantly extend the extinction limits of methane/air mixtures. In addition, the effects of combustor configurations and thermal insulation arrangements on temperature distributions and extinction limits were evaluated. With heat losses to the environment being significant, the use of thermal insulations further enhances the flame stability in center regions of the Swiss-roll combustors and extends flammable ranges. (author)

  17. Reaction and diffusion in turbulent combustion. Progress report

    SciTech Connect

    Pope, S.B.

    1992-10-02

    Progress was made on the following: Development of two-variable ({xi} - y) thermochemistry suitable for DNS (direct numerical simulation) studies; determination of laminar flame properties based on this thermochemistry; determination of the parameter range that can be accessed by DNS with good resolution; implementation of the thermochemistry in the DNS code; performance of exploratory simulations, and the development of techniques of relating Eulerian DNS data to turbulent combustion theories; implementation of the DNS code on parallel and distributed computers, and the study of relative molecular motion in turbulence.

  18. Flashback resistant pre-mixer assembly

    DOEpatents

    Laster, Walter R.; Gambacorta, Domenico

    2012-02-14

    A pre-mixer assembly associated with a fuel supply system for mixing of air and fuel upstream from a main combustion zone in a gas turbine engine. The pre-mixer assembly includes a swirler assembly disposed about a fuel injector of the fuel supply system and a pre-mixer transition member. The swirler assembly includes a forward end defining an air inlet and an opposed aft end. The pre-mixer transition member has a forward end affixed to the aft end of the swirler assembly and an opposed aft end defining an outlet of the pre-mixer assembly. The aft end of the pre-mixer transition member is spaced from a base plate such that a gap is formed between the aft end of the pre-mixer transition member and the base plate for permitting a flow of purge air therethrough to increase a velocity of the air/fuel mixture exiting the pre-mixer assembly.

  19. Effects of Lewis number on conditional fluid velocity statistics in low Damköhler number turbulent premixed combustion: A direct numerical simulation analysis

    NASA Astrophysics Data System (ADS)

    Chakraborty, Nilanjan; Lipatnikov, Andrei N.

    2013-04-01

    The effects of global Lewis number Le on the statistics of fluid velocity components conditional in unburned reactants and fully burned products in the context of Reynolds Averaged Navier Stokes simulations have been analysed using a Direct Numerical Simulations (DNS) database of statistically planar turbulent premixed flames with a low Damköhler number and Lewis number ranging from 0.34 to 1.2. The conditional velocity statistics extracted from DNS data have been analysed with respect to the well-known Bray-Moss-Libby (BML) expressions which were derived based on bi-modal probability density function of reaction progress variable for high Damköhler number flames. It has been shown that the Lewis number substantially affects the mean velocity and the velocity fluctuation correlation conditional in products, with the effect being particularly pronounced for low Le. As far as the mean velocity and the velocity fluctuation correlation conditional in reactants are concerned, the BML expressions agree reasonably well with the DNS data reported in the present work. Based on a priori analysis of present and previously reported DNS data, the BML expressions have been empirically modified here in order to account for Lewis number effects, and the non-bimodal distribution of reaction progress variable. Moreover, it has been demonstrated for the first time that surface averaged velocity components and Reynolds stresses conditional in unburned reactants can be modelled without invoking expressions involving the Lewis number, as these surface averaged conditional quantities remain approximately equal to their conditionally averaged counterparts in the unburned mixture.

  20. FY2013 Progress Report for Advanced Combustion Engine Research and Development

    SciTech Connect

    none,

    2013-12-01

    Annual progress report on the work of the the Advanced Combustion Engine Program. The Advanced Combustion Engine Program supports the Vehicle Technologies Office mission by addressing critical technical barriers to commercializing higher efficiency, very low emissions, advanced combustion engines for passenger and commercial vehicles that meet future federal emissions regulations.

  1. Coal Combustion Science quarterly progress report, April--June 1990

    SciTech Connect

    Hardesty, D.R.; Baxter, L.L.; Fletcher, T.H.; Mitchell, R.E.

    1990-11-01

    This document provides a quarterly status report of the Coal Combustion Science Program that is being conducted at the Combustion, Research Facility, Sandia National Laboratories, Livermore, California. Coal devolatilization, coal char combustion, and fate of mineral matter during coal combustion. 56 refs., 25 figs., 13 tabs.

  2. Premixed direct injection disk

    SciTech Connect

    York, William David; Ziminsky, Willy Steve; Johnson, Thomas Edward; Lacy, Benjamin; Zuo, Baifang; Uhm, Jong Ho

    2013-04-23

    A fuel/air mixing disk for use in a fuel/air mixing combustor assembly is provided. The disk includes a first face, a second face, and at least one fuel plenum disposed therebetween. A plurality of fuel/air mixing tubes extend through the pre-mixing disk, each mixing tube including an outer tube wall extending axially along a tube axis and in fluid communication with the at least one fuel plenum. At least a portion of the plurality of fuel/air mixing tubes further includes at least one fuel injection hole have a fuel injection hole diameter extending through said outer tube wall, the fuel injection hole having an injection angle relative to the tube axis. The invention provides good fuel air mixing with low combustion generated NOx and low flow pressure loss translating to a high gas turbine efficiency, that is durable, and resistant to flame holding and flash back.

  3. Studies of Premixed Laminar and Turbulent Flames at Microgravity

    NASA Technical Reports Server (NTRS)

    Ronney, Paul D.

    1993-01-01

    The work of the Principal Investigator (PI) has encompassed four topics related to the experimental and theoretical study of combustion limits in premixed flames at microgravity, as discussed in the following sections. These topics include: (1) radiation effects on premixed gas flames; (2) flame structure and stability at low Lewis number; (3) flame propagation and extinction is cylindrical tubes; and (4) experimental simulation of combustion processes using autocatalytic chemical reactions.

  4. Multiple tube premixing device

    DOEpatents

    Uhm, Jong Ho; Naidu, Balachandar; Ziminksy, Willy Steve; Kraemer, Gilbert Otto; Yilmaz, Ertan; Lacy, Benjamin; Stevenson, Christian; Felling, David

    2013-08-13

    The present application provides a premixer for a combustor. The premixer may include a fuel plenum with a number of fuel tubes and a burner tube with a number of air tubes. The fuel tubes extend about the air tubes.

  5. Multiple tube premixing device

    DOEpatents

    Uhm, Jong Ho; Varatharajan, Balachandar; Ziminsky, Willy Steve; Kraemer, Gilbert Otto; Yilmaz, Ertan; Lacy, Benjamin; Stevenson, Christian; Felling, David

    2012-12-11

    The present application provides a premixer for a combustor. The premixer may include a fuel plenum with a number of fuel tubes and a burner tube with a number of air tubes. The fuel tubes extend about the air tubes.

  6. Coal combustion science. Quarterly progress report, July--September 1994

    SciTech Connect

    Hardesty, D.R.; Baxter, L.L.; Davis, K.A.; Hurt, R.H.; Yang, N.Y.C.

    1995-09-01

    This document is a quarterly status report of the Coal Combustion Science Project that is being conducted at the Combustion Research Facility, Sandia National Laboratories, Livermore, California. The information reported is for the period July-September 1994. The objective of this work is to support the Office of Fossil Energy in executing research on coal combustion science. This project consists of basic research on coal combustion that supports both the Pittsburgh Energy Technology Center (PETC) Direct Utilization Advanced Research and Technology Development Program, and the International Energy Agency (IEA) Coal Combustion Science Project.

  7. Gravitational Influences on Flame Propagation through Non-Uniform, Premixed Gas Systems

    NASA Technical Reports Server (NTRS)

    Miller, Fletcher J.; Easton, John; Ross, Howard D.; Marchese, Anthony; Perry, David; Kulis, Michael

    2001-01-01

    Flame propagation through non-uniformly premixed (or layered) gases has importance both in useful combustion systems and in unintentional fires. As summarized previously, non-uniform premixed gas combustion receives scant attention compared to the more usual limiting cases of diffusion or uniformly premixed flames, especially regarding the role gravity plays. This paper summarizes our progress on furthering the knowledge of layered combustion, in which a fuel concentration gradient exists normal to the direction of flame spread. We present experimental and numerical results for flame spread through propanol-air layers formed near the flash point temperature (25 C) or near the stoichiometric temperature (33 C). Both the model and experimental results show that the removal of gravity results in a faster spreading flame, by as much as 80% depending on conditions. This is exactly the opposite effect as that predicted by an earlier model reported. We also found that having a gallery lid results in faster flame spread, an effect more pronounced at normal gravity, demonstrating the importance of enclosure geometry. Also reported here is the beginning of our spectroscopic measurements of fuel vapor.

  8. Coal combustion science. Quarterly progress report, April 1993--June 1993

    SciTech Connect

    Hardesty, D.R.

    1994-05-01

    This document is a quarterly status report of the Coal Combustion Science Project that is being conducted at the Combustion Research Facility, Sandia National Laboratories. The information reported is for Apr-Jun 1993. The objective of this work is to support the Office of Fossil Energy in executing research on coal combustion science. This project consists of basic research on coal combustion that supports both the PETC Direct Utilization Advanced Research and Technology Development Program, and the International Energy Agency Coal Combustion Science Project. The objective of the kinetics and mechanisms of pulverized coal char combustion task is to characterize the combustion behavior of selected US coals under conditions relevant to industrial pulverized coal-fired furnaces. Work is being done in four areas: kinetics of heterogeneous fuel particle populations; char combustion kinetics at high carbon conversion; the role of particle structure and the char formation process in combustion and; unification of the Sandia char combustion data base. This data base on the high temperature reactivities of chars from strategic US coals will permit identification of important fuel-specific trends and development of predictive capabilities for advanced coal combustion systems. The objective of the fate of inorganic material during coal combustion task is the establish a quantitative understanding of the mechanisms and rates of transformation, fragmentation, and deposition of inorganic material during coal combustion as a function of coal type, particle size and temperature, the initial forms and distribution of inorganic species in the unreacted coal, and the local gas temperature and composition. In addition, optical diagnostic capabilities are being developed for in situ, real-time detection of inorganic vapor species and surface species during ash deposition. Selected papers have been indexed separately for inclusion in the Energy Science and Technology Database.

  9. Coal Combustion Science. Quarterly progress report, October--December 1994

    SciTech Connect

    Hardesty, D.R.; Baxter, L.L.; Davis, K.A.; Hurt, R.H.; Yang, N.Y.C.

    1996-02-01

    The objective of this work is to support the Office of Fossil Energy in executing research on coal combustion science. This project consists of basic research on coal combustion that supports both the Pittsburgh Energy Technology Center (PETC) Direct Utilization Advanced Research and Technology Development Program, and the International Energy Agency (IEA) Coal Combustion Science Project. Specific tasks include: Task 1--Kinetics and mechanisms of pulverized coal char combustion; and Task 2--deposit growth and property development in coal-fired furnaces. The objective of task 1 is to characterize the combustion behavior of selected US coals under conditions relevant to industrial pulverized coal-fired furnaces. Work is being done in four areas: (a) kinetics of heterogeneous fuel particle populations; (b) char combustion kinetics at high carbon conversion; (c) the role of particle structure and the char formation process in combustion and; (d) unification of the Sandia char combustion data base. The objectives of Task 2 are to provide a self-consistent database of simultaneously measured, time-resolved, ash deposit properties in well-controlled and well-defined environments and to provide analytical expressions that relate deposit composition and structure to deposit properties of immediate relevance to PETC`s Combustion 2000 program. The task include the development and use of diagnostics to monitor, in situ and in real time, deposit properties, including information on both the structure and composition of the deposits.

  10. FY2011 Annual Progress Report for Advanced Combustion Engine Research and Development

    SciTech Connect

    none,

    2011-12-01

    Annual Progress Report for the Advanced Combustion Engine Research and Development (R&D) subprogram supporting the mission of the Vehicle Technologies Program by removing the critical technical barriers to commercialization of advanced internal combustion engines (ICEs) for passenger and commercial vehicles that meet future federal emissions regulations.

  11. FY2014 Advanced Combustion Engine Annual Progress Report

    SciTech Connect

    2015-03-01

    The Advanced Combustion Engine research and development (R&D) subprogram within the DOE Vehicle Technologies Office (VTO) provides support and guidance for many cutting-edge automotive technologies under development. Research focuses on addressing critical barriers to commercializing higher efficiency, very low emissions advanced internal combustion engines for passenger and commercial vehicles.

  12. Progress on the Combustion Integrated Rack Component of the Fluids and Combustion Facility

    NASA Technical Reports Server (NTRS)

    Weiland, Karen J.; Urban, Dave (Technical Monitor)

    1999-01-01

    The Fluids and Combustion Facility (FCF) is a facility-class payload planned for the International Space Station. It is designed to accommodate a wide variety of investigations encompassing most of the range of microgravity fluid physics and combustion science. The Combustion Integrated Rack component of the FCF is currently scheduled to be launched in 2003 and will operate independently until additional racks of the FCF are launched. The FCF is intended to complete between five and fifteen combustion experiments per year over its planned ten-year lifetime. Combustion arm that may be studied include laminar flames, reaction kinetics, droplet and spray combustion, flame spread, fire and fire suppressants, condensed phase organic fuel combustion, turbulent combustion, soot and polycyclic aromatic hydrocarbons, and flame-synthesized materials. Three different chamber inserts, one each for investigations of droplet, solid fuel, and gaseous fuel combustion, that can accommodate multiple experiments will be used initially so as to maximize the reuse of hardware. The current flight and flight-definition investigations are briefly described.

  13. Lean, Premixed-Prevaporized (LPP) combustor conceptual design study

    NASA Technical Reports Server (NTRS)

    Dickman, R. A.; Dodds, W. J.; Ekstedt, E. E.

    1979-01-01

    Four combustion systems were designed and sized for the energy efficient engine. A fifth combustor was designed for the cycle and envelope of the twin-spool, high bypass ratio, high pressure ratio turbofan engine. Emission levels, combustion performance, life, and reliability assessments were made for these five combustion systems. Results of these design studies indicate that cruise NOx emission can be reduced by the use of lean, premixed-prevaporaized combustion and airflow modulation.

  14. Soot Formation in Laminar Premixed Flames

    NASA Technical Reports Server (NTRS)

    Xu, F.; Krishnan, S. S.; Faeth, G. M.

    1999-01-01

    Soot processes within hydrocarbon-fueled flames affect emissions of pollutant soot, thermal loads on combustors, hazards of unwanted fires and capabilities for computational combustion. In view of these observations, the present study is considering processes of soot formation in both burner-stabilized and freely-propagating laminar premixed flames. These flames are being studied in order to simplify the interpretation of measurements and to enhance computational tractability compared to the diffusion flame environments of greatest interest for soot processes. In addition, earlier studies of soot formation in laminar premixed flames used approximations of soot optical and structure properties that have not been effective during recent evaluations, as well as questionable estimates of flow residence times). The objective of present work was to exploit methods of avoiding these difficulties developed for laminar diffusion flames to study soot growth in laminar premixed flames. The following description of these studies is brief.

  15. FY 2007 Progress Report for Advanced Combustion Engine Technologies

    SciTech Connect

    None, None

    2007-12-01

    Advanced combustion engines have great potential for achieving dramatic energy efficiency improvements in light-duty vehicle applications, where it is suited to both conventional and hybrid- electric powertrain configurations. Light-duty vehicles with advanced combustion engines can compete directly with gasoline engine hybrid vehicles in terms of fuel economy and consumer-friendly driving characteristics; also, they are projected to have energy efficiencies that are competitive with hydrogen fuel cell vehicles when used in hybrid applications.Advanced engine technologies being researched and developed by the Advanced Combustion Engine R&D Sub-Program will also allow the use of hydrogen as a fuel in ICEs and will provide an energy-efficient interim hydrogen-based powertrain technology during the transition to hydrogen/fuelcell-powered transportation vehicles.

  16. Counter-gradient transport in the combustion of a premixed CH{sub 4}/air annular jet by combined PIV/OH-LIF

    SciTech Connect

    Troiani, G.; Marrocco, M.; Giammartini, S.; Casciola, C.M.

    2009-03-15

    A combination of PIV/OH laser induced fluorescence technique is used to measure the conditional - burned and unburned - gas velocity in a turbulent premixed CH{sub 4}/air annular bluff-body stabilized burner. By changing the equivalence ratio from lean to almost stoichiometric, the energy budget of the recirculating region anchoring the flame is altered in such a way to increasingly lift the flame away from the jet exit. The overall turbulence intensity interacting with each flame is thus systematically varied in a significant range, allowing for a parametric study of its effect on turbulent scalar transport under well controlled conditions, always well within the flamelet regime. The component of the flux normal to the average front is found to reverse its direction, confirming the Bray number as a good indicator of gradient/counter-gradient behavior, once the actual incoming turbulence level felt locally by the flame is assumed as the proper control parameter. (author)

  17. Combustion diagnostic for active engine feedback control

    DOEpatents

    Green, Jr., Johney Boyd; Daw, Charles Stuart; Wagner, Robert Milton

    2007-10-02

    This invention detects the crank angle location where combustion switches from premixed to diffusion, referred to as the transition index, and uses that location to define integration limits that measure the portions of heat released during the combustion process that occur during the premixed and diffusion phases. Those integrated premixed and diffusion values are used to develop a metric referred to as the combustion index. The combustion index is defined as the integrated diffusion contribution divided by the integrated premixed contribution. As the EGR rate is increased enough to enter the low temperature combustion regime, PM emissions decrease because more of the combustion process is occurring over the premixed portion of the heat release rate profile and the diffusion portion has been significantly reduced. This information is used to detect when the engine is or is not operating in a low temperature combustion mode and provides that feedback to an engine control algorithm.

  18. Theoretical studies of hydrocarbon combustion chemistry. Annual progress report

    SciTech Connect

    Schaefer, H.F. III

    1994-08-01

    The author reports here the results of DZP CISD calculations for methylcarbene. Geometry, symmetry, and vibrational modes for the radical are reported for both the singlet and the triplet state. Future work will focus on the ethyl radical-oxygen interaction relevant to hydrocarbon combustion.

  19. FY2009 Annual Progress Report for Advanced Combustion Engine Research and Development

    SciTech Connect

    none,

    2009-12-01

    Fiscal Year 2009 Annual Progress Report for the Advanced Combustion Engine Research and Development (R&D) subprogram. The Advanced Combustion Engine R&D subprogram supports the mission of the VTP program by removing the critical technical barriers to commercialization of advanced internal combustion engines (ICEs) for passenger and commercial vehicles that meet future Federal emissions regulations. Dramatically improving the efficiency of ICEs and enabling their introduction in conventional as well as hybrid electric vehicles is the most promising and cost-effective approach to increasing vehicle fuel economy over the next 30 years.

  20. Progress in Fabrication of Rocket Combustion Chambers by VPS

    NASA Technical Reports Server (NTRS)

    Holmes, Richard R.; McKechnie, Timothy N.

    2004-01-01

    Several documents in a collection describe aspects of the development of advanced materials and fabrication processes intended to enable the manufacture of advanced rocket combustion chambers and nozzles at relatively low cost. One concept discussed in most of the documents is the fabrication of combustion-chamber liners by vacuum plasma spraying (VPS) of an alloy of 88Cu/8Cr/4Nb (numbers indicate atomic percentages) -- a concept that was reported in "Improved Alloy for Fabrication of Combustion Chambers by VPS" (MFS-26546). Another concept is the deposition of graded-composition wall and liner structures by VPS in order to make liners integral parts of wall structures and to make oxidation- and thermal-protection layers integral parts of liners: The VPS process is started at 100 percent of a first alloy, then the proportion of a second alloy is increased gradually from zero as deposition continues, ending at 100 percent of the second alloy. Yet another concept discussed in one of the documents is the VPS of oxidation-protection coats in the forms of nickel-and-chromium-containing refractory alloys on VPS-deposited 88Cu/8Cr/4Nb liners.

  1. Progress in the development of PDF turbulence models for combustion

    NASA Technical Reports Server (NTRS)

    Hsu, Andrew T.

    1991-01-01

    A combined Monte Carlo-computational fluid dynamic (CFD) algorithm was developed recently at Lewis Research Center (LeRC) for turbulent reacting flows. In this algorithm, conventional CFD schemes are employed to obtain the velocity field and other velocity related turbulent quantities, and a Monte Carlo scheme is used to solve the evolution equation for the probability density function (pdf) of species mass fraction and temperature. In combustion computations, the predictions of chemical reaction rates (the source terms in the species conservation equation) are poor if conventional turbulence modles are used. The main difficulty lies in the fact that the reaction rate is highly nonlinear, and the use of averaged temperature produces excessively large errors. Moment closure models for the source terms have attained only limited success. The probability density function (pdf) method seems to be the only alternative at the present time that uses local instantaneous values of the temperature, density, etc., in predicting chemical reaction rates, and thus may be the only viable approach for more accurate turbulent combustion calculations. Assumed pdf's are useful in simple problems; however, for more general combustion problems, the solution of an evolution equation for the pdf is necessary.

  2. Premixed flame propagation in vertical tubes

    NASA Astrophysics Data System (ADS)

    Kazakov, Kirill A.

    2016-04-01

    Analytical treatment of the premixed flame propagation in vertical tubes with smooth walls is given. Using the on-shell flame description, equations for a quasi-steady flame with a small but finite front thickness are obtained and solved numerically. It is found that near the limits of inflammability, solutions describing upward flame propagation come in pairs having close propagation speeds and that the effect of gravity is to reverse the burnt gas velocity profile generated by the flame. On the basis of these results, a theory of partial flame propagation driven by a strong gravitational field is developed. A complete explanation is given of the intricate observed behavior of limit flames, including dependence of the inflammability range on the size of the combustion domain, the large distances of partial flame propagation, and the progression of flame extinction. The role of the finite front-thickness effects is discussed in detail. Also, various mechanisms governing flame acceleration in smooth tubes are identified. Acceleration of methane-air flames in open tubes is shown to be a combined effect of the hydrostatic pressure difference produced by the ambient cold air and the difference of dynamic gas pressure at the tube ends. On the other hand, a strong spontaneous acceleration of the fast methane-oxygen flames at the initial stage of their evolution in open-closed tubes is conditioned by metastability of the quasi-steady propagation regimes. An extensive comparison of the obtained results with the experimental data is made.

  3. Progress in hypersonic combustion technology with computation and experiment

    NASA Technical Reports Server (NTRS)

    Anderson, Griffin Y.; Kumar, Ajay; Erdos, John I.

    1990-01-01

    Design of successful airbreathing engines for operation at near-orbital speeds presents significant challenges in all the disciplines involved, including propulsion. This paper presents a discussion of the important physics of hypersonic combustion and an assessment of the state of the art of ground simulations with pulse facilities and with computational techniques. Recent examples of experimental and computational simulations are presented and discussed. The need for continued application of these tools to establish the credibility and fidelity of engineering design methods for practical hypersonic combustors is emphasized along with the critical need for improved diagnostic methods for hypervelocity reacting flows.

  4. RANS/PDF and LES/FDF for prediction of turbulent premixed flames

    NASA Astrophysics Data System (ADS)

    Yilmaz, Server Levent

    Probability density function (PDF) and filtered density function (FDF) methodologies are developed and implemented, respectively, for Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) of turbulent premixed flames. RANS predictions are made of a lean premixed bluff-body flame via the joint velocity-scalar-frequency PDF model. LES of a premixed Bunsen-burner flame is conducted via the scalar FDF methodology. Both simulations employ finite rate kinetics via a reduced methane chemistry mechanism to account for combustion. Prediction results are compared with experimental data, and are shown to capture some of the intricate physics of turbulent premixed combustion. Keywords. large eddy simulation, filtered density function, Reynolds-averaged Navier-Stokes, probability density function, turbulent reacting flows, lean premixed combustion.

  5. Studies of premixed laminar and turbulent flames at microgravity

    NASA Technical Reports Server (NTRS)

    Ronney, Paul D.

    1993-01-01

    A two and one-half year experimental and theoretical research program on the properties of laminar and turbulent premixed gas flames at microgravity was conducted. Progress during this program is identified and avenues for future studies are discussed.

  6. Fully Premixed Low Emission, High Pressure Multi-Fuel Burner

    NASA Technical Reports Server (NTRS)

    Nguyen, Quang-Viet (Inventor)

    2012-01-01

    A low-emissions high-pressure multi-fuel burner includes a fuel inlet, for receiving a fuel, an oxidizer inlet, for receiving an oxidizer gas, an injector plate, having a plurality of nozzles that are aligned with premix face of the injector plate, the plurality of nozzles in communication with the fuel and oxidizer inlets and each nozzle providing flow for one of the fuel and the oxidizer gas and an impingement-cooled face, parallel to the premix face of the injector plate and forming a micro-premix chamber between the impingement-cooled face and the in injector face. The fuel and the oxidizer gas are mixed in the micro-premix chamber through impingement-enhanced mixing of flows of the fuel and the oxidizer gas. The burner can be used for low-emissions fuel-lean fully-premixed, or fuel-rich fully-premixed hydrogen-air combustion, or for combustion with other gases such as methane or other hydrocarbons, or even liquid fuels.

  7. Gravity Effects Observed In Partially Premixed Flames

    NASA Technical Reports Server (NTRS)

    Puri, Ishwar K.; Aggarwal, Suresh K.; Lock, Andrew J.; Gauguly, Ranjan; Hegde, Uday

    2003-01-01

    Partially premixed flames (PPFs) contain a rich premixed fuel air mixture in a pocket or stream, and, for complete combustion to occur, they require the transport of oxidizer from an appropriately oxidizer-rich (or fuel-lean) mixture that is present in another pocket or stream. Partial oxidation reactions occur in fuel-rich portions of the mixture and any remaining unburned fuel and/or intermediate species are consumed in the oxidizer-rich portions. Partial premixing, therefore, represents that condition when the equivalence ratio (phi) in one portion of the flowfield is greater than unity, and in another section its value is less than unity. In general, for combustion to occur efficiently, the global equivalence ratio is in the range fuel-lean to stoichiometric. These flames can be established by design by placing a fuel-rich mixture in contact with a fuel-lean mixture, but they also occur otherwise in many practical systems, which include nonpremixed lifted flames, turbulent nonpremixed combustion, spray flames, and unwanted fires. Other practical applications of PPFs are reported elsewhere. Although extensive experimental studies have been conducted on premixed and nonpremixed flames under microgravity, there is a absence of previous experimental work on burner stabilized PPFs in this regard. Previous numerical studies by our group employing a detailed numerical model showed gravity effects to be significant on the PPF structure. We report on the results of microgravity experiments conducted on two-dimensional (established on a Wolfhard-Parker slot burner) and axisymmetric flames (on a coannular burner) that were investigated in a self-contained multipurpose rig. Thermocouple and radiometer data were also used to characterize the thermal transport in the flame.

  8. Numerical study of transient evolution of lifted jet flames: partially premixed flame propagation and influence of physical dimensions

    NASA Astrophysics Data System (ADS)

    Chen, Zhi; Ruan, Shaohong; Swaminathan, Nedunchezhian

    2016-07-01

    Three-dimensional (3D) unsteady Reynolds-averaged Navier-Stokes simulations of a spark-ignited turbulent methane/air jet flame evolving from ignition to stabilisation are conducted for different jet velocities. A partially premixed combustion model is used involving a correlated joint probability density function and both premixed and non-premixed combustion mode contributions. The 3D simulation results for the temporal evolution of the flame's leading edge are compared with previous two-dimensional (2D) results and experimental data. The comparison shows that the final stabilised flame lift-off height is well predicted by both 2D and 3D computations. However, the transient evolution of the flame's leading edge computed from 3D simulation agrees reasonably well with experiment, whereas evident discrepancies were found in the previous 2D study. This difference suggests that the third physical dimension plays an important role during the flame transient evolution process. The flame brush's leading edge displacement speed resulting from reaction, normal and tangential diffusion processes are studied at different typical stages after ignition in order to understand the effect of the third physical dimension further. Substantial differences are found for the reaction and normal diffusion components between 2D and 3D simulations especially in the initial propagation stage. The evolution of reaction progress variable scalar gradients and its interaction with the flow and mixing field in the 3D physical space have an important effect on the flame's leading edge propagation.

  9. Soot Formation in Freely-Propagating Laminar Premixed Flames

    NASA Technical Reports Server (NTRS)

    Lin, K.-C.; Hassan, M. I.; Faeth, G. M.

    1997-01-01

    Soot formation within hydrocarbon-fueled flames is an important unresolved problem of combustion science. Thus, the present study is considering soot formation in freely-propagating laminar premixed flames, exploiting the microgravity environment to simplify measurements at the high-pressure conditions of interest for many practical applications. The findings of the investigation are relevant to reducing emissions of soot and continuum radiation from combustion processes, to improving terrestrial and spacecraft fire safety, and to developing methods of computational combustion, among others. Laminar premixed flames are attractive for studying soot formation because they are simple one-dimensional flows that are computationally tractable for detailed numerical simulations. Nevertheless, studying soot-containing burner-stabilized laminar premixed flames is problematical: spatial resolution and residence times are limited at the pressures of interest for practical applications, flame structure is sensitive to minor burner construction details so that experimental reproducibility is not very good, consistent burner behavior over the lengthy test programs needed to measure soot formation properties is hard to achieve, and burners have poor durability. Fortunately, many of these problems are mitigated for soot-containing, freely-propagating laminar premixed flames. The present investigation seeks to extend work in this laboratory for various soot processes in flames by observing soot formation in freely-propagating laminar premixed flames. Measurements are being made at both Normal Gravity (NG) and MicroGravity (MG), using a short-drop free-fall facility to provide MG conditions.

  10. Flame-acoustic coupling of combustion instability in a non-premixed backward-facing step combustor: the role of acoustic-Reynolds stress

    NASA Astrophysics Data System (ADS)

    Kannan, Ashwin; Chellappan, Balaji; Chakravarthy, Satyanarayanan

    2016-07-01

    Combustion instability in a laboratory scale backward-facing step combustor is numerically investigated by carrying out an acoustically coupled incompressible large eddy simulation of turbulent reacting flow for various Reynolds numbers with fuel injection at the step. The problem is mathematically formulated as a decomposition of the full compressible Navier-Stokes equations using multi-scale analysis by recognising the small length scale and large time scale of the flow field relative to a longitudinal mode acoustic field for low mean Mach numbers. The equations are decomposed into those for an incompressible flow with temperature-dependent density to zeroth order and linearised Euler equations for acoustics as a first order compressibility correction. Explicit coupling terms between the two equation sets are identified to be the flow dilatation as a source of acoustic energy and the acoustic Reynolds stress (ARS) as a source of flow momentum. The numerical simulations are able to capture the experimentally observed flow-acoustic lock-on that signifies the onset of combustion instability, marked by a shift in the dominant frequency from an acoustic to a hydrodynamic mode and accompanied by a nonlinear variation of pressure amplitude. Attention is devoted to flow conditions at two Reynolds numbers before and after lock-on to show that, after lock-on, the ARS causes large-scale vortical rollup resulting in the evolution of a compact flame. As compared to acoustically uncoupled simulations at these Reynolds numbers that show an elongated flame with no significant roll up and disturbance in the upstream flow field, the ARS is seen to alter the shear layer dynamics by affecting the flow field upstream of the step as well, when acoustically coupled.

  11. Turbulent Methane-Air Combustion

    NASA Technical Reports Server (NTRS)

    Yaboah, Yaw D.; Njokwe, Anny; James, LaShanda

    1996-01-01

    This study is aimed at enhancing the understanding of turbulent premixed methane-air combustion. Such understanding is essential since: (1) many industries are now pursuing lighter hydrocarbon alternative fuels and the use of premixed flames to reduce pollutant emissions, and (2) the characteristic dimensions and flow rates of most industrial combustors are often large for flows to be turbulent. The specific objectives of the study are: (1) to establish the effects of process variables (e.g., flow rate, fuel/air ratio, chlorinated hydro-carbons, and pressure) on the emissions and flow structure (velocity distribution, streamlines, vorticity and flame shape), and (2) to develop a mechanistic model to explain the observed trends. This includes the acquisition of Dantec FlowMap Particle Image Velocimeter. The design and fabrication of the premixed burner has also been completed. The study is now at the stage of testing of equipment and analytical instruments. The presentation will give details on the tasks completed and on the current and future plans. The project is progressing well and all activities are on schedule. The outlook for the success of the project is bright.

  12. Combustor nozzle for a fuel-flexible combustion system

    DOEpatents

    Haynes, Joel Meier; Mosbacher, David Matthew; Janssen, Jonathan Sebastian; Iyer, Venkatraman Ananthakrishnan

    2011-03-22

    A combustor nozzle is provided. The combustor nozzle includes a first fuel system configured to introduce a syngas fuel into a combustion chamber to enable lean premixed combustion within the combustion chamber and a second fuel system configured to introduce the syngas fuel, or a hydrocarbon fuel, or diluents, or combinations thereof into the combustion chamber to enable diffusion combustion within the combustion chamber.

  13. A Method to Measure Flame Index in Turbulent Partially-Premixed Flames

    NASA Astrophysics Data System (ADS)

    Rosenberg, David Ari

    This dissertation describes the development of a diagnostic technique and data processing routine to measure the flame index in partially-premixed flames, called the Flame Index Measurement Method. Many modern combustion applications involve conditions in which the fuel and oxidizer are only partially mixed prior to entering the flame. These partially-premixed flames contain some regions of premixed and some regions of non-premixed flamelets. New computational approaches use the flame index concept: premixed regions are identified and a premixed model is applied; non-premixed regions are also identified and a non-premixed model is applied. The flame index is defined as the normalized dot product of the gradients of the fuel and oxidizer mass fractions; it is +1 in premixed flamelets and is -1 in non-premixed flamelets. Previously there had been no experimentally measured values of flame index available to assess the modeling approaches. A new method has been developed to measure the flame index using planar laser-induced fluorescence tracers to indicate the sign and direction of the fuel and oxygen gradients. Through the modeling of premixed and non-premixed flamelets, acetone was selected as a fuel tracer and nitrogen dioxide was selected as an oxygen tracer. The fluorescence properties of both acetone and nitrogen dioxide were studied. With acetone seeded into the fuel, and nitrogen dioxide seeded into the air, the Flame Index Measurement Method was evaluated in laminar premixed and non-premixed methane/acetone/air flames, as well as in a well-defined turbulent partially-premixed burner, the Gas Turbine Model Combustor (GTMC). The flame index was measured in the GTMC with methane, propane, and syngas flames. Statistics (mean, variance, and probability mass functions) of the flame index are reported for the highly-turbulent partially-premixed GTMC flames. Two new statistical quantities were developed that describe the probability for the occurrence of premixed

  14. Characteristics of non-premixed oxygen-enhanced combustion: II. Flame structure effects on soot precursor kinetics resulting in soot-free flames

    SciTech Connect

    Skeen, S.A.; Axelbaum, R.L.; Yablonsky, G.

    2010-09-15

    A detailed computational study was performed to understand the effects of the flame structure on the formation and destruction of soot precursors during ethylene combustion. Using the USC Mech Version II mechanism the contributions of different pathways to the formation of benzene and phenyl were determined in a wide domain of Z{sub st} values via a reverse-pathway analysis. It was shown that for conventional ethylene-air flames two sequential reversible reactions play primary roles in the propargyl (C{sub 3}H{sub 3}) chemistry, namely (1) C{sub 2}H{sub 2}+CH{sub 3}= pC{sub 3} H{sub 4}+H, (2) pC{sub 3} H{sub 4}= C{sub 3} H{sub 3}+ H with the corresponding overall endothermic reaction of propargyl formation (3) C{sub 2} H{sub 2}+CH{sub 3}= C{sub 3} H{sub 3}+2H. The contributions of these reactions to propyne (pC{sub 3}H{sub 4}) and propargyl formation and propargyl self-combination leading to benzene and phenyl were studied as a function of physical position, temperature, Z{sub st}, and H concentration. In particular, the role of H radicals on soot precursor destruction was studied in detail. At low Z{sub st}, Reactions 1 and 2 contribute significantly to propyne and propargyl formation on the fuel side of the radical pool at temperatures greater than approx. 1600 K. At higher local temperatures near the radical pool where the concentration of H is significant, the reverse reactions begin to dominate resulting in soot precursor destruction. As Z{sub st} is increased, these regions merge and only net propargyl consumption is observed. Based on the equilibrium constant of Reaction 3, a Z{sub st} value was estimated above which the rate of propargyl formation as a soot precursor is greatly reduced (Z{sub st} = 0.3). This condition compares well with the experimental results for permanently blue counterflow flames in the literature. (author)

  15. Premixed turbulent flame calculation

    NASA Technical Reports Server (NTRS)

    El-Tahry, S.; Rutland, C. J.; Ferziger, J. H.; Rogers, M. M.

    1987-01-01

    The importance of turbulent premixed flames in a variety of applications has led to a substantial amount of effort towards improving the understanding of these flames. Although these efforts have increased the understanding, many questions still remain. The use of direct numerical simulation (DNS) in solving these questions is examined.

  16. Combustion

    NASA Technical Reports Server (NTRS)

    Bulzan, Dan

    2007-01-01

    An overview of the emissions related research being conducted as part of the Fundamental Aeronautics Subsonics Fixed Wing Project is presented. The overview includes project metrics, milestones, and descriptions of major research areas. The overview also includes information on some of the emissions research being conducted under NASA Research Announcements. Objective: Development of comprehensive detailed and reduced kinetic mechanisms of jet fuels for chemically-reacting flow modeling. Scientific Challenges: 1) Developing experimental facilities capable of handling higher hydrocarbons and providing benchmark combustion data. 2) Determining and understanding ignition and combustion characteristics, such as laminar flame speeds, extinction stretch rates, and autoignition delays, of jet fuels and hydrocarbons relevant to jet surrogates. 3) Developing comprehensive kinetic models for jet fuels.

  17. Field Effects of Buoyancy on Lean Premixed Turbulent Flames

    NASA Technical Reports Server (NTRS)

    Cheng, R. K.; Johnson, M. R.; Greenberg, P. S.; Wernet, M. P.

    2003-01-01

    The study of field effects of buoyancy on premixed turbulent flames is directed towards the advancement of turbulent combustion theory and the development of cleaner combustion technologies. Turbulent combustion is considered the most important unsolved problem in combustion science and laboratory studies of turbulence flame processes are vital to theoretical development. Although buoyancy is dominant in laboratory flames, most combustion models are not yet capable to consider buoyancy effects. This inconsistency has impeded the validation of theories and numerical simulations with experiments. Conversely, the understanding of buoyancy effects is far too limited to help develop buoyant flame models. Our research is also relevant to combustion technology because lean premixed combustion is a proven method to reduce the formation of oxides of nitrogen (NOx). In industrial lean premixed combustion systems, their operating conditions make them susceptible to buoyancy thus affecting heat distribution, emissions, stability, flashback and blowoff. But little knowledge is available to guide combustion engineers as to how to avoid or overcome these problems. Our hypothesis is that through its influence on the mean pressure field, buoyancy has direct and indirect effects on local flame/turbulence interactions. Although buoyancy acts on the hot products in the farfield the effect is also felt in the nearfield region upstream of the flame. These changes also influence the generation and dissipation of turbulent kinetic energy inside the flame brush and throughout the flowfield. Moreover, the plume of an open flame is unstable and the periodic fluctuations make additional contributions to flame front dynamics in the farfield. Therefore, processes such as flame wrinkling, flow acceleration due to heat release and flame- generated vorticity are all affected. Other global flame properties (e.g. flame stabilization limits and flame speed) may all be coupled to buoyancy. This

  18. Preliminary assessment of combustion modes for internal combustion wave rotors

    NASA Technical Reports Server (NTRS)

    Nalim, M. Razi

    1995-01-01

    Combustion within the channels of a wave rotor is examined as a means of obtaining pressure gain during heat addition in a gas turbine engine. Several modes of combustion are considered and the factors that determine the applicability of three modes are evaluated in detail; premixed autoignition/detonation, premixed deflagration, and non-premixed compression ignition. The last two will require strong turbulence for completion of combustion in a reasonable time in the wave rotor. The compression/autoignition modes will require inlet temperatures in excess of 1500 R for reliable ignition with most hydrocarbon fuels; otherwise, a supplementary ignition method must be provided. Examples of combustion mode selection are presented for two core engine applications that had been previously designed with equivalent 4-port wave rotor topping cycles using external combustion.

  19. Topics in physico-chemical hydrodynamics. Progress report No. 2, November 1, 1989--October 31, 1990

    SciTech Connect

    Sivashinsky, G.

    1990-12-31

    This report discusses: Theory of turbulent flame speed; flame extinction by periodic flow field; influence of swirl on the structure and extinction of premixed flames; propagation and extinction of nonsteady spherical flame fronts; geometrically invariant formulation of the intrinsic dynamics of premixed flames; nonlinear dynamics of oscillatory regime of premixed combustion; and pattern formation in premixed flames. (LSP)

  20. Premixed direct injection nozzle

    DOEpatents

    Zuo, Baifang; Johnson, Thomas Edward; Lacy, Benjamin Paul; Ziminsky, Willy Steve

    2011-02-15

    An injection nozzle having a main body portion with an outer peripheral wall is disclosed. The nozzle includes a plurality of fuel/air mixing tubes disposed within the main body portion and a fuel flow passage fluidly connected to the plurality of fuel/air mixing tubes. Fuel and air are partially premixed inside the plurality of the tubes. A second body portion, having an outer peripheral wall extending between a first end and an opposite second end, is connected to the main body portion. The partially premixed fuel and air mixture from the first body portion gets further mixed inside the second body portion. The second body portion converges from the first end toward said second end. The second body portion also includes cooling passages that extend along all the walls around the second body to provide thermal damage resistance for occasional flame flash back into the second body.

  1. Dynamics and structure of turbulent premixed flames

    NASA Technical Reports Server (NTRS)

    Bilger, R. W.; Swaminathan, N.; Ruetsch, G. R.; Smith, N. S. A.

    1995-01-01

    In earlier work (Mantel & Bilger, 1994) the structure of the turbulent premixed flame was investigated using statistics based on conditional averaging with the reaction progress variable as the conditioning variable. The DNS data base of Trouve and Poinsot (1994) was used in this investigation. Attention was focused on the conditional dissipation and conditional axial velocity in the flame with a view to modeling these quantities for use in the conditional moment closure (CMC) approach to analysis of kinetics in premixed flames (Bilger, 1993). Two remarkable findings were made: there was almost no acceleration of the axial velocity in the flame front itself; and the conditional scalar dissipation remained as high, or higher, than that found in laminar premixed flames. The first finding was surprising since in laminar flames all the fluid acceleration occurs through the flame front, and this could be expected also for turbulent premixed flames at the flamelet limit. The finding gave hope of inventing a new approach to the dynamics of turbulent premixed flames through use of rapid distortion theory or an unsteady Bernoulli equation. This could lead to a new second order closure for turbulent premixed flames. The second finding was contrary to our measurements with laser diagnostics in lean hydrocarbon flames where it is found that conditional scalar dissipation drops dramatically below that for laminar flamelets when the turbulence intensity becomes high. Such behavior was not explainable with a one-step kinetic model, even at non-unity Lewis number. It could be due to depletion of H2 from the reaction zone by preferential diffusion. The capacity of the flame to generate radicals is critically dependent on the levels of H2 present (Bilger, et al., 1991). It seemed that a DNS computation with a multistep reduced mechanism would be worthwhile if a way could be found to make this feasible. Truly innovative approaches to complex problems often come only when there is the

  2. Vortex combustor for low NOX emissions when burning lean premixed high hydrogen content fuel

    DOEpatents

    Steele, Robert C; Edmonds, Ryan G; Williams, Joseph T; Baldwin, Stephen P

    2012-11-20

    A trapped vortex combustor. The trapped vortex combustor is configured for receiving a lean premixed gaseous fuel and oxidant stream, where the fuel includes hydrogen gas. The trapped vortex combustor is configured to receive the lean premixed fuel and oxidant stream at a velocity which significantly exceeds combustion flame speed in a selected lean premixed fuel and oxidant mixture. The combustor is configured to operate at relatively high bulk fluid velocities while maintaining stable combustion, and low NOx emissions. The combustor is useful in gas turbines in a process of burning synfuels, as it offers the opportunity to avoid use of diluent gas to reduce combustion temperatures. The combustor also offers the possibility of avoiding the use of selected catalytic reaction units for removal of oxides of nitrogen from combustion gases exiting a gas turbine.

  3. Vortex combustor for low NOx emissions when burning lean premixed high hydrogen content fuel

    DOEpatents

    Steele, Robert C.; Edmonds, Ryan G.; Williams, Joseph T.; Baldwin, Stephen P.

    2009-10-20

    A trapped vortex combustor. The trapped vortex combustor is configured for receiving a lean premixed gaseous fuel and oxidant stream, where the fuel includes hydrogen gas. The trapped vortex combustor is configured to receive the lean premixed fuel and oxidant stream at a velocity which significantly exceeds combustion flame speed in a selected lean premixed fuel and oxidant mixture. The combustor is configured to operate at relatively high bulk fluid velocities while maintaining stable combustion, and low NOx emissions. The combustor is useful in gas turbines in a process of burning synfuels, as it offers the opportunity to avoid use of diluent gas to reduce combustion temperatures. The combustor also offers the possibility of avoiding the use of selected catalytic reaction units for removal of oxides of nitrogen from combustion gases exiting a gas turbine.

  4. Incomplete combustion in nonadiabatic premixed gas flames

    NASA Astrophysics Data System (ADS)

    Kagan, L.; Sivashinsky, G.

    1996-06-01

    The inward propagating spherical flame and burner stabilized Bunsen-type flame of low-Lewis-number premixtures are studied numerically. It is shown that reduction of the reaction rate induced by the flame stretch makes the flame vulnerable to the radiative heat losses which may well result in a partial or complete extinction of the flame.

  5. Fundamental combustion and diagnostics research at Sandia. Progress report, April-June 1980

    SciTech Connect

    Gusinow, M.A.

    1980-09-01

    The combustion research emphasizes basic research into fundamental problems associated with combustion. The overall program addresses detailed chemistry of combustion, fundamental processes associated with laminar and turbulent flames, development of research techniques specifically applicable to combustion environments, and operation of the user-oriented Combustion Research Facility. The first section of this report contains activities in Combustion Research, the second section contains activities in Molecular Physics and Spectroscopy, and the third section contains activities in Diagnostics Research.

  6. Coal combustion science: Task 1, Coal char combustion: Task 2, Fate of mineral matter. Quarterly progress report, July--September 1993

    SciTech Connect

    Hardesty, D.R.; Hurt, R.H.; Davis, K.A.; Baxter, L.L.

    1994-07-01

    Progress reports are presented for the following tasks: (1) kinetics and mechanisms of pulverized coal char combustion and (2) fate of inorganic material during coal combustion. The objective of Task 1 is to characterize the combustion behavior of selected US coals under conditions relevant to industrial pulverized coal-fired furnaces. In Sandia`s Coal Combustion Laboratory (CCL), optical techniques are used to obtain high-resolution images of individual burning coal char particles and to measure, in situ, their temperatures, sizes, and velocities. Detailed models of combustion transport processes are then used to determine kinetic parameters describing the combustion behavior as a function of coal type and combustion environment. Partially reacted char particles are also sampled and characterized with advanced materials diagnostics to understand the critical physical and chemical transformations that influence reaction rates and burnout times. The ultimate goal of the task is the establishment of a data base of the high temperature reactivities of chars from strategic US coals, from which important trends may be identified and predictive capabilities developed. The overall objectives for task 2 are: (1) to complete experimental and theoretical investigation of ash release mechanisms; (2) to complete experimental work on char fragmentation; (3) to establish the extent of coal (as opposed to char) fragmentation as a function of coal type and particle size; (4) to develop diagnostic capabilities for in situ, real-time, qualitative indications of surface species composition during ash deposition, with work continuing into FY94; (5) to develop diagnostic capabilities for in situ, real-time qualitative detection of inorganic vapor concentrations; and (6) to conduct a literature survey on the current state of understanding of ash deposition, with work continuing into FY94.

  7. Effects of operating pressure on flame oscillation and emission characteristics in a partially premixed swirl combustor

    SciTech Connect

    Kim, Jong-Ryul; Choi, Gyung-Min; Kim, Duck-Jool

    2011-01-15

    The influence of varying combustor pressure on flame oscillation and emission characteristics in the partially premixed turbulent flame were investigated. In order to investigate combustion characteristics in the partially premixed turbulent flame, the combustor pressure was controlled in the range of -30 to 30 kPa for each equivalence ratio ({phi} = 0.8-1.2). The r.m.s. of the pressure fluctuations increased with decreasing combustor pressure for the lean condition. The combustor pressure had a sizeable influence on combustion oscillation, whose dominant frequency varied with the combustor pressure. Combustion instabilities could be controlled by increasing the turbulent intensity of the unburned mixture under the lean condition. An unstable flame was caused by incomplete combustion; hence, EICO greatly increased. Furthermore, EINO{sub x} simply reduced with decreasing combustor pressure at a rate of 0.035 g/10 kPa. The possibility of combustion control on the combusting mode and exhaust gas emission was demonstrated. (author)

  8. Methods and systems for combustion dynamics reduction

    DOEpatents

    Kraemer, Gilbert Otto; Varatharajan, Balachandar; Srinivasan, Shiva; Lynch, John Joseph; Yilmaz, Ertan; Kim, Kwanwoo; Lacy, Benjamin; Crothers, Sarah; Singh, Kapil Kumar

    2009-08-25

    Methods and systems for combustion dynamics reduction are provided. A combustion chamber may include a first premixer and a second premixer. Each premixer may include at least one fuel injector, at least one air inlet duct, and at least one vane pack for at least partially mixing the air from the air inlet duct or ducts and fuel from the fuel injector or injectors. Each vane pack may include a plurality of fuel orifices through which at least a portion of the fuel and at least a portion of the air may pass. The vane pack or packs of the first premixer may be positioned at a first axial position and the vane pack or packs of the second premixer may be positioned at a second axial position axially staggered with respect to the first axial position.

  9. Flashback detection sensor for lean premix fuel nozzles

    DOEpatents

    Thornton, Jimmy Dean; Richards, George Alan; Straub, Douglas L.; Liese, Eric Arnold; Trader, Jr., John Lee; Fasching, George Edward

    2002-08-06

    A sensor for detecting the flame occurring during a flashback condition in the fuel nozzle of a lean premix combustion system is presented. The sensor comprises an electrically isolated flashback detection electrode and a guard electrode, both of which generate electrical fields extending to the walls of the combustion chamber and to the walls of the fuel nozzle. The sensor is positioned on the fuel nozzle center body at a location proximate the entrance to the combustion chamber of the gas turbine combustion system. The sensor provides 360.degree. detection of a flashback inside the fuel nozzle, by detecting the current conducted by the flame within a time frame that will prevent damage to the gas turbine combustion system caused by the flashback condition.

  10. Can we characterize turbulence in premixed flames?

    SciTech Connect

    Lipatnikov, A.N.

    2009-06-15

    Modeling of premixed turbulent combustion involves averaging reaction rates in turbulent flows. The focus of most approaches to resolving this problem has been placed on determining the dependence of the mean rate w of product creation on the laminar flame speed S{sub L}, the rms turbulence velocity u', etc. The goal of the present work is to draw attention to another issue: May the input quantity u{sup '} for a model of w= w(u'/S{sub L},..) be considered to be known? The point is that heat release substantially affects turbulence and, hence, turbulence characteristics in premixed flames should be modeled. However, standard moment methods for numerically simulating turbulent flows do not allow us to evaluate the true turbulence characteristics in a flame. For instance, the Reynolds stresses in premixed flames are affected not only by turbulence itself, but also by velocity jump across flamelets. A common way to resolving this problem consists of considering the Reynolds stresses conditioned on unburned (or burned) mixture to be the true turbulence characteristics. In the present paper, this widely accepted but never proved hypothesis is put into question, first, by considering simple model constant-density problems (flame motion in an oscillating one-dimensional laminar flow; flame stabilized in a periodic shear, one-dimensional, laminar flow; turbulent mixing). In all the cases, the magnitude of velocity fluctuations, calculated using the conditioned Reynolds stresses, is affected by the intermittency of reactants and products and, hence, is not the true rms velocity. Second, the above claim is further supported by comparing balance equations for the mean and conditioned Reynolds stresses. The conditioned Reynolds stresses do not characterize the true turbulence in flames, because conditional averaging cuts off flow regions characterized by either high or low velocities. (author)

  11. Effect of the composition of the hot product stream in the quasi-steady extinction of strained premixed flames

    SciTech Connect

    Coriton, Bruno; Smooke, Mitchell D.; Gomez, Alessandro

    2010-11-15

    The extinction of premixed CH{sub 4}/O{sub 2}/N{sub 2} flames counterflowing against a jet of combustion products in chemical equilibrium was investigated numerically using detailed chemistry and transport mechanisms. Such a problem is of relevance to combustion systems with non-homogeneous air/fuel mixtures or recirculation of the burnt gases. Contrary to similar studies that were focused on heat loss/gain, depending on the degree of non-adiabaticity of the system, the emphasis here was on the yet unexplored role of the composition of counterflowing burnt gases in the extinction of lean-to-stoichiometric premixed flames. For a given temperature of the counterflowing products of combustion, it was found that the decrease of heat release with increase in strain rate could be either monotonic or non-monotonic, depending on the equivalence ratio {phi}{sub b} of the flame feeding the hot combustion product stream. Two distinct extinction modes were observed: an abrupt one, when the hot counterflowing stream consists of either inert gas or equilibrium products of a stoichiometric premixed flame, and a smooth extinction, when there is an excess of oxidizing species in the combustion product stream. In the latter case four burning regimes can be distinguished as the strain rate is progressively increased while the heat release decreases smoothly: an adiabatic propagating flame regime, a non-adiabatic propagating flame regime, the so-called partially-extinguished flame regime, in which the location of the peak of heat release crosses the stagnation plane, and a frozen flow regime. The flame structure was analyzed in detail in the different burning regimes. Abrupt extinction was attributed to the quenching of the oxidation layer with the entire H-OH-O radical pool being comparably reduced. Under conditions of smooth extinction, the behavior is different and the concentration of the H radical decreases the most with increasing strain rate, whereas OH and O remain

  12. Progress in analytical methods to predict and control azimuthal combustion instability modes in annular chambers

    NASA Astrophysics Data System (ADS)

    Bauerheim, M.; Nicoud, F.; Poinsot, T.

    2016-02-01

    Longitudinal low-frequency thermoacoustic unstable modes in combustion chambers have been intensively studied experimentally, numerically, and theoretically, leading to significant progress in both understanding and controlling these acoustic modes. However, modern annular gas turbines may also exhibit azimuthal modes, which are much less studied and feature specific mode structures and dynamic behaviors, leading to more complex situations. Moreover, dealing with 10-20 burners mounted in the same chamber limits the use of high fidelity simulations or annular experiments to investigate these modes because of their complexity and costs. Consequently, for such circumferential acoustic modes, theoretical tools have been developed to uncover underlying phenomena controlling their stability, nature, and dynamics. This review presents recent progress in this field. First, Galerkin and network models are described with their pros and cons in both the temporal and frequency framework. Then, key features of such acoustic modes are unveiled, focusing on their specificities such as symmetry breaking, non-linear modal coupling, forcing by turbulence. Finally, recent works on uncertainty quantifications, guided by theoretical studies and applied to annular combustors, are presented. The objective is to provide a global view of theoretical research on azimuthal modes to highlight their complexities and potential.

  13. The Behavior of Methane-Air Partially Premixed Flames Under Normal- and Zero-G Conditions

    NASA Technical Reports Server (NTRS)

    Puri, Ishwar K.; Aggarwal, Suresh K.; Choi, Chun Wai; Hegde, Uday

    2001-01-01

    Partially premixed flames (PPFs) represent a class of hybrid flames containing multiple reaction zones. These flames are established when less than stoichiometric quantity of oxidizer is molecularly mixed with the fuel stream before entering the reaction zone where additional oxidizer is available for complete combustion. This mode of combustion can be used to exploit the advantages of both nonpremixed and premixed flames regarding operational safety, lower pollutant emissions and flame stabilization. A double flame containing a fuel-rich premixed reaction zone, which is anchored by a nonpremixed reaction zone, is one example of a partially premixed flame. A triple flame is also a PPF that contains three reaction zones, namely, a fuel-rich premixed zone, a fuel-lean premixed zone, and a nonpremixed reaction zone. Herein we focus on two aspects of our investigation, one involving the development of optical diagnostics that can be used on a microgravity rig, which has been recently fabricated, and the other on the numerically predicted differences between normal- and zero-gravity PPFs. Both the measurements and simulations examine the detailed structure of methane-air PPFs stabilized on a Wolfhard-Parker slot burner.

  14. FY2012 Annual Progress Report for Advanced Combustion Engine Research and Development

    SciTech Connect

    none,

    2013-02-01

    Annual report on the work of the the Advanced Combustion Engine R&D subprogram. The Advanced Combustion Engine R&D subprogram supports the Vehicle Technologies Office mission by removing the critical technical barriers to commercialization of advanced internal combustion engines (ICEs) for passenger and commercial vehicles that meet future federal emissions regulations.

  15. NOx Formation in a Premixed Syngas Flame

    SciTech Connect

    Yilmaz, S.L.; Givi, P.; Strakey, P.; Casleton, K.

    2006-11-01

    Reduction of NOx is a subject of significant current interest in stationary gas turbines. The objective of this study is to examine the effects of turbulence on non-thermal NOx formation in a syngas flame. This is archived by a detailed parametric study via PDF simulations of a partially stirred reactor and a dumped axisymmetric premixed flame. Several different detailed and reduced kinetics schemes are considered. The simulated results demonstrate the strong dependence of combustion process on turbulence. It is shown that the amount of NOx formation is significantly influenced by the inlet conditions. That is, the turbulence intensity can be tweaked to attain optimal ultra-low NOx emissions at a given temperature.

  16. Premixed burner experiments: Geometry, mixing, and flame structure issues

    SciTech Connect

    Gupta, A.K.; Lewis, M.J.; Gupta, M.

    1995-10-01

    This research program is exploring techniques for improved fuel-air mixing, with the aim of achieving combustor operations up to stoichiometric conditions with minimal NO x and maximum efficiency. The experimental studies involve the use of a double-concentric natural gas burner that is operable in either premixed or non-premixed modes, and the system allows systematic variation of equivalence ratio, swirl strength shear length region and flow momentum in each annulus. Flame structures formed with various combinations of swirl strengths, flow throughput and equivalence ratios in premixed mode show the significant impact of swirl flow distribution on flame structure emanating from the mixedness. This impact on flame structure is expected to have a pronounced effect on the heat release rate and the emission of NO{sub x}. Thus, swirler design and configuration remains a key factor in the quest for completely optimized combustion. Parallel numerical studies of the flow and combustion phenomena were carried out, using the RSM and thek-{epsilon} turbulence models. These results have not only indicated the strengths and limitations of CFD in performance and pollutants emission predictions, but have provided guidelines on the size and strength of the recirculation produced and the spatio-temporal structure of the combustion flowfield. The first stage of parametric studies on geometry and operational parameters at Morgan State University have culminated in the completion of a one-dimensional flow code that is integrated with a solid, virtual model of the existing premixed burner. This coupling will provide the unique opportunity to study the impact of geometry on the flowfield and vice-versa, with particular emphasis on concurrent design optimization.

  17. LES and acoustic analysis of thermo-acoustic instabilities in a partially premixed model combustor

    NASA Astrophysics Data System (ADS)

    Hernández, Ignacio; Staffelbach, Gabriel; Poinsot, Thierry; Román Casado, Juan C.; Kok, Jim B. W.

    2013-01-01

    Numerical simulations were performed using Large Eddy Simulation (LES) and acoustic analysis tools to study thermo-acoustic instabilities in a methane/air academic burner installed at the University of Twente (The Netherlands). It operates under fuel-lean partially premixed conditions at atmospheric pressure, and was built to study thermo-acoustic instabilities in conditions representative of gas turbine Lean Premixed systems: gaseous fuel is injected upstream of the combustor and has a limited time to mix with air. Even though the objective is to burn in a premixed mode, the actual regime corresponds to a partially premixed flame where strong equivalence ratio variations are created especially during combustion instabilities. Capturing these modes with LES is a challenge: here, simulations for both stable and unstable regimes are performed. In the unstable case, the limit cycle oscillations (LCO) are characterized and compared to experimental results. Reasonable agreement is found between simulations and experiments.

  18. Premixer Design for High Hydrogen Fuels

    SciTech Connect

    Benjamin P. Lacy; Keith R. McManus; Balachandar Varatharajan; Biswadip Shome

    2005-12-16

    This 21-month project translated DLN technology to the unique properties of high hydrogen content IGCC fuels, and yielded designs in preparation for a future testing and validation phase. Fundamental flame characterization, mixing, and flame property measurement experiments were conducted to tailor computational design tools and criteria to create a framework for predicting nozzle operability (e.g., flame stabilization, emissions, resistance to flashback/flame-holding and auto-ignition). This framework was then used to establish, rank, and evaluate potential solutions to the operability challenges of IGCC combustion. The leading contenders were studied and developed with the most promising concepts evaluated via computational fluid dynamics (CFD) modeling and using the design rules generated by the fundamental experiments, as well as using GE's combustion design tools and practices. Finally, the project scoped the necessary steps required to carry the design through mechanical and durability review, testing, and validation, towards full demonstration of this revolutionary technology. This project was carried out in three linked tasks with the following results. (1) Develop conceptual designs of premixer and down-select the promising options. This task defined the ''gap'' between existing design capabilities and the targeted range of IGCC fuel compositions and evaluated the current capability of DLN pre-mixer designs when operated at similar conditions. Two concepts (1) swirl based and (2) multiple point lean direct injection based premixers were selected via a QFD from 13 potential design concepts. (2) Carry out CFD on chosen options (1 or 2) to evaluate operability risks. This task developed the leading options down-selected in Task 1. Both a GE15 swozzle based premixer and a lean direct injection concept were examined by performing a detailed CFD study wherein the aerodynamics of the design, together with the chemical kinetics of the combustion process, were

  19. Gas turbine combustion instability

    SciTech Connect

    Richards, G.A.; Lee, G.T.

    1996-09-01

    Combustion oscillations are a common problem in development of LPM (lean premix) combustors. Unlike earlier, diffusion style combustors, LPM combustors are especially susceptible to oscillations because acoustic losses are smaller and operation near lean blowoff produces a greater combustion response to disturbances in reactant supply, mixing, etc. In ongoing tests at METC, five instability mechanisms have been identified in subscale and commercial scale nozzle tests. Changes to fuel nozzle geometry showed that it is possible to stabilize combustion by altering the timing of the feedback between acoustic waves and the variation in heat release.

  20. Investigation of mineral transformations and ash deposition during staged combustion. Quarterly technical progress report, July 1, 1995-- September 30, 1995

    SciTech Connect

    Harb, J.N.

    1995-12-31

    Progress during the eighth quarter of a three-year study was made in three task areas: (1) analysis of coals; (3) parametric testing of the target coals, and (4) analysis of samples from the combustion tests. Routines for automated analysis of coal and mineral associations were completed and are now functional on our new ISIS system. Work on data processing which led to the development of a new means of interpreting composition information from the SEM was also completed during the quarter. This work is expected to yield substantial benefits in understanding the ash transformations during combustion. Several additional ash and deposit samples were collected this quarter. Deposition results have been explained qualitatively and samples has been mounted for quantitative analysis. A detailed characterization of mixing and coalescence was performed during the quarter. Results indicate that combustion under stage conditions does not change the chemistry of the final ash produced. Specifically, both iron and potassium distributions in long residence time ashes did not change as a function of combustion conditions. Some differences were observed in the potassium distribution at shorter residence times. There was also a difference in the size distribution of particles formed during staged combustion. The nature and significance of these differences are still under investigation.

  1. The role of reactant unmixedness, strain rate, and length scale on premixed combustor performance

    SciTech Connect

    Samuelsen, S.; LaRue, J.; Vilayanur, S.

    1995-10-01

    Lean premixed combustion provides a means to reduce pollutant formation and increase combustion efficiency. However, fuel-air mixing is rarely uniform in space and time. This nonuniformity in concentration will lead to relative increases in pollutant formation and decreases in combustion efficiency. The nonuniformity of the concentration at the exit of the premixer has been defined by Lyons (1981) as the {open_quotes}unmixedness.{close_quotes} Although turbulence properties such as length scales and strain rate are known to effect unmixedness, the exact relationship is unknown. Evaluating this relationship and the effect of unmixedness in premixed combustion on pollutant formation and combustion efficiency are an important part of the overall goal of US Department of Energy`s Advanced Turbine Systems (ATS) program and are among the goals of the program described herein. The information obtained from ATS is intended to help to develop and commercialize gas turbines which have (1) a wide range of operation/stability, (2) a minimal amount of pollutant formation, and (3) high combustion efficiency. Specifically, with regard to pollutants, the goals are to reduce the NO{sub x} emissions by at least 10%, obtain less than 20 PPM of both CO and UHC, and increase the combustion efficiency by 5%.

  2. The role of reactant unmixedness, strain rate, and length scale on premixed combustor performance

    SciTech Connect

    Samuelsen, S.; LaRue, J.; Vilayanur, S.; Guillaume, D.

    1995-12-31

    Lean premixed combustion provides a means to reduce pollutant formation and increase combustion efficiency. However, fuel-air mixing is rarely uniform in space and time. This nonuniformity in concentration will lead to relative increases in pollutant formation and decreases in combustion efficiency. The nonuniformity of the concentration at the exit of the premixer has been defined by Lyons (1981) as the ``unmixedness.`` Although turbulence properties such as length scales and strain rate are known to effect unmixedness, the exact relationship is unknown. Evaluating this relationship and the effect of unmixedness in premixed combustion on pollutant formation and combustion efficiency are an important part of the overall goal of US Department of Energy`s Advanced Turbine System (ATS) program and are among the goals of the program described herein. The information obtained from ATS is intended to help to develop and commercialize gas turbines. The contributions to the program which the University of California (Irvine) Combustion Lab (UCICL) will provide are: (1) establish the relationship of inlet unmixedness, length scales, and mean strain rate to performance, (2) determine the optimal levels of inlet unmixedness, length scales, and mean strain rates to maximize combustor performance, and (3) identify efficient premixing methods for achieving the necessary inlet conditions. The program during this reporting period is focused on developing a means to measure and qualify different degrees of temporal and spatial unmixedness. Laser diagnostic methods for planer unmixedness measurements are being developed and preliminary results are presented herein. These results will be used to (1), aid in the design of experimental premixers, and (2), determine the unmixedness which will be correlated with the emissions of the combustor. This measure of unmixedness coupled with length scale, strain rate and intensity information is required to attain the UCI goals.

  3. Fluorosis caused by indoor coal combustion in China: discovery and progress.

    PubMed

    Zheng, Baoshan; Wu, Daishe; Wang, Binbin; Liu, Xiaojing; Wang, Mingshi; Wang, Aimin; Xiao, Guisen; Liu, Pugao; Finkelman, Robert B

    2007-04-01

    In this study, investigations into endemic fluorosis were conducted and fluorine concentration in environmental samples determined. In an indoor coal-combustion-type fluorosis area, local clay was used to mix with coal for indoor combustion. There are two key steps in the procedure of the indoor transition of fluorine: indoor wet corns and vegetables strongly absorbed fluorine from indoor air; and fluorine strongly accumulated in clay, which was mixed with coal for combustion. Therefore, with the increasing of the percentage of clay in the clay-mixed coal as well as corn in foodstuff, the ratio of fluorosis will be increased.

  4. Chemical Kinetic Study of Toluene Oxidation Under Premixed and Nonpremixed Conditions

    SciTech Connect

    Costa, I D; Bozzelli, J W; Seiser, R; Pitz, W J; Westbrook, C K; Chen, C -; Fournet, R; Seshadri, K; Battin-Leclerc, F; Billaud, F

    2003-12-10

    A study was performed to elucidate the chemical-kinetic mechanism of combustion of toluene. A detailed chemical-kinetic mechanism for toluene was improved by adding a more accurate description of the phenyl + O{sub 2} reaction channels, toluene decomposition reactions and the benzyl + O reaction. Results of the chemical kinetic mechanism are compared with experimental data obtained from premixed and non-premixed systems. Under premixed conditions, predicted ignition delay times are compared with new experimental data obtained in shock tube. Also, calculated species concentration histories are compared to experimental flow reactor data from the literature. Under non-premixed conditions, critical conditions of extinction and autoignition were measured in strained laminar flows in the counterflow configuration. Numerical calculations are performed using the chemical-kinetic mechanism at conditions corresponding to those in the experiments. Critical conditions of extinction and autoignition are predicted and compared with the experimental data. Comparisons between the model predictions and experimental results of ignition delay times in shock tube, and extinction and autoignition in non-premixed systems show that the chemical-kinetic mechanism predicts that toluene/air is overall less reactive than observed in the experiments. For both premixed and non-premixed systems, sensitivity analysis was used to identify the reaction rate constants that control the overall rate of oxidation in each of the systems considered. Under shock tube conditions, the reactions that influence ignition delay time are H + O{sub 2} chain branching, the toluene decomposition reaction to give an H atom, and the toluene + H abstraction reaction. The reactions that influence autoignition in non-premixed systems involve the benzyl + HO{sub 2} reaction and the phenyl + O{sub 2} reaction.

  5. Statistics of premixed flame cells

    NASA Technical Reports Server (NTRS)

    Noever, David A.

    1991-01-01

    The statistics of random cellular patterns in premixed flames are analyzed. Agreement is found with a variety of topological relations previously found for other networks, namely, Lewis's law and Aboav's law. Despite the diverse underlying physics, flame cells are shown to share a broad class of geometric properties with other random networks-metal grains, soap foams, bioconvection, and Langmuir monolayers.

  6. Statistics of premixed flame cells

    SciTech Connect

    Noever, D.A. )

    1991-07-15

    The statistics of random cellular patterns in premixed flames are analyzed. Agreement is found with a variety of topological relations previously found for other networks, namely, Lewis's law and Aboav's law. Despite the diverse underlying physics, flame cells are shown to share a broad class of geometric properties with other random networks---metal grains, soap foams, bioconvection, and Langmuir monolayers.

  7. FY2010 Annual Progress Report for Advanced Combustion Engine Research and Development

    SciTech Connect

    Singh, Gurpreet

    2010-12-01

    The Advanced Combustion Engine R&D subprogram supports the mission of the Vehicle Technologies Program by removing the critical technical barriers to commercialization of advanced internal combustion engines (ICEs) for passenger and commercial vehicles that meet future Federal emissions regulations. Dramatically improving the efficiency of ICEs and enabling their introduction in conventional as well as hybrid electric vehicles is the most promising and cost-effective approach to increasing vehicle fuel economy over the next 30 years.

  8. Modeling of microgravity combustion experiments

    NASA Technical Reports Server (NTRS)

    Buckmaster, John

    1995-01-01

    This program started in February 1991, and is designed to improve our understanding of basic combustion phenomena by the modeling of various configurations undergoing experimental study by others. Results through 1992 were reported in the second workshop. Work since that time has examined the following topics: Flame-balls; Intrinsic and acoustic instabilities in multiphase mixtures; Radiation effects in premixed combustion; Smouldering, both forward and reverse, as well as two dimensional smoulder.

  9. Spectral kinetic energy transfer in turbulent premixed reacting flows.

    PubMed

    Towery, C A Z; Poludnenko, A Y; Urzay, J; O'Brien, J; Ihme, M; Hamlington, P E

    2016-05-01

    Spectral kinetic energy transfer by advective processes in turbulent premixed reacting flows is examined using data from a direct numerical simulation of a statistically planar turbulent premixed flame. Two-dimensional turbulence kinetic-energy spectra conditioned on the planar-averaged reactant mass fraction are computed through the flame brush and variations in the spectra are connected to terms in the spectral kinetic energy transport equation. Conditional kinetic energy spectra show that turbulent small-scale motions are suppressed in the burnt combustion products, while the energy content of the mean flow increases. An analysis of spectral kinetic energy transfer further indicates that, contrary to the net down-scale transfer of energy found in the unburnt reactants, advective processes transfer energy from small to large scales in the flame brush close to the products. Triadic interactions calculated through the flame brush show that this net up-scale transfer of energy occurs primarily at spatial scales near the laminar flame thermal width. The present results thus indicate that advective processes in premixed reacting flows contribute to energy backscatter near the scale of the flame.

  10. Spectral kinetic energy transfer in turbulent premixed reacting flows

    NASA Astrophysics Data System (ADS)

    Towery, C. A. Z.; Poludnenko, A. Y.; Urzay, J.; O'Brien, J.; Ihme, M.; Hamlington, P. E.

    2016-05-01

    Spectral kinetic energy transfer by advective processes in turbulent premixed reacting flows is examined using data from a direct numerical simulation of a statistically planar turbulent premixed flame. Two-dimensional turbulence kinetic-energy spectra conditioned on the planar-averaged reactant mass fraction are computed through the flame brush and variations in the spectra are connected to terms in the spectral kinetic energy transport equation. Conditional kinetic energy spectra show that turbulent small-scale motions are suppressed in the burnt combustion products, while the energy content of the mean flow increases. An analysis of spectral kinetic energy transfer further indicates that, contrary to the net down-scale transfer of energy found in the unburnt reactants, advective processes transfer energy from small to large scales in the flame brush close to the products. Triadic interactions calculated through the flame brush show that this net up-scale transfer of energy occurs primarily at spatial scales near the laminar flame thermal width. The present results thus indicate that advective processes in premixed reacting flows contribute to energy backscatter near the scale of the flame.

  11. Direct numerical simulation of a turbulent premixed flame

    SciTech Connect

    Hasegawa, Tatsuya; Morifuji, Tetsuya; Borghi, R.

    1999-07-01

    Direct numerical simulation of a stationary turbulent premixed flame with a single-step irreversible Arrhenius-type reaction is performed in order to understand detail physics of turbulent premixed flames and to evaluate modeling of turbulent premixed flame. The 6th-order central finite difference method is used in the streamwise direction with non-periodic boundaries, giving enough grid points in the domain to assure reasonable accuracy. The pseudo spectral method is used for transversal directions with periodic boundaries. The results obtained by their preliminary simulation is presented here with the initial turbulent intensity of u{prime}{sub 0}/u{sub L} = 4.8, the initial integral scale of l{sub t0}/{delta} = 8, and the density ratio of {rho}{sub u}/{rho}{sub b} = 7.53. The obtained flame is a developing wrinkled flame. Mean temperature, mean mass fraction, mean reaction rate and mean velocity components in space show a thickened flame region where the reaction rate appears at all points. Turbulent kinetic energy decays along the stream, but it increases somewhat in the flame region due to the increase of streamwise component of velocity fluctuation. The energy spectra in front of the flame region and behind it show that small scale decays by combustion and that the microscale and the Kolmogorov scale increase several times behind the flame region. Local structure of the turbulent flame is then analyzed.

  12. Active Control for Statistically Stationary Turbulent PremixedFlame Simulations

    SciTech Connect

    Bell, J.B.; Day, M.S.; Grcar, J.F.; Lijewski, M.J.

    2005-08-30

    The speed of propagation of a premixed turbulent flame correlates with the intensity of the turbulence encountered by the flame. One consequence of this property is that premixed flames in both laboratory experiments and practical combustors require some type of stabilization mechanism to prevent blow-off and flashback. The stabilization devices often introduce a level of geometric complexity that is prohibitive for detailed computational studies of turbulent flame dynamics. Furthermore, the stabilization introduces additional fluid mechanical complexity into the overall combustion process that can complicate the analysis of fundamental flame properties. To circumvent these difficulties we introduce a feedback control algorithm that allows us to computationally stabilize a turbulent premixed flame in a simple geometric configuration. For the simulations, we specify turbulent inflow conditions and dynamically adjust the integrated fueling rate to control the mean location of the flame in the domain. We outline the numerical procedure, and illustrate the behavior of the control algorithm on methane flames at various equivalence ratios in two dimensions. The simulation data are used to study the local variation in the speed of propagation due to flame surface curvature.

  13. A flamelet-based approach for combustion systems with convective heat-losses

    NASA Astrophysics Data System (ADS)

    Shunn, Lee; Moin, Parviz

    2008-11-01

    A new flamelet method is proposed for modeling turbulence/chemistry interactions in large-eddy simulations (LES) of non-premixed combustion with convective heat-losses. The new method is based on the flamelet/progress-variable approach of Pierce & Moin (2004) and extends that work to include the effects of thermal-losses on the combustion chemistry. In the new model, chemistry databases are constructed by solving 1D diffusion/reaction equations which have been constrained by scaling the enthalpy of the system between the adiabatic state and a thermally-quenched reference state. The solutions are parameterized and tabulated as a function of the mapping variables: mixture fraction, progress-variable, and normalized enthalpy. The model is implemented in a LES solver which computes the filtered values of the mapping variables, and interpolates other pertinent quantities (such as density and reaction rates) from the chemistry database. The new model is applied to LES of non-premixed methane-air combustion in a coaxial-jet geometry with isothermal wall-conditions to describe heat transfer to the confinement. The resulting velocity, species concentration, and temperature fields are compared to the experiment of Spadaccini, et al. (1976) and numerical results from the adiabatic model.

  14. Emissions of oxides of nitrogen from an experimental premixed-hydrogen burner

    NASA Technical Reports Server (NTRS)

    Anderson, D. N.

    1976-01-01

    Flame-tube experiments using premixed hydrogen and air were conducted to determine the emissions of oxides of nitrogen (NOx) resulting from ultralean combustion. Measurements of NOx emissions and combustion efficiency were made for inlet mixture temperatures of 600 and 700 K, pressures of 3.8 x 10 to the 5th power and 5.2 x 10 to the 5th power N/m squared, reference velocities of 15 to 18 m/sec, and equivalence ratios of 0.2 to 0.4. At the 700 K inlet mixture temperature, NOx emissions were 0.06 ppmv, and combustion efficiency was 98 percent at an equivalence ratio of 0.24. The use of a high-blockage (92-percent blockage) flameholder made it possible to conduct tests without upstream burning in the premixing duct for mixtures with equivalence ratios less than 0.4. For richer mixtures upstream burning did occur and prevented further testing.

  15. Computational Combustion

    SciTech Connect

    Westbrook, C K; Mizobuchi, Y; Poinsot, T J; Smith, P J; Warnatz, J

    2004-08-26

    Progress in the field of computational combustion over the past 50 years is reviewed. Particular attention is given to those classes of models that are common to most system modeling efforts, including fluid dynamics, chemical kinetics, liquid sprays, and turbulent flame models. The developments in combustion modeling are placed into the time-dependent context of the accompanying exponential growth in computer capabilities and Moore's Law. Superimposed on this steady growth, the occasional sudden advances in modeling capabilities are identified and their impacts are discussed. Integration of submodels into system models for spark ignition, diesel and homogeneous charge, compression ignition engines, surface and catalytic combustion, pulse combustion, and detonations are described. Finally, the current state of combustion modeling is illustrated by descriptions of a very large jet lifted 3D turbulent hydrogen flame with direct numerical simulation and 3D large eddy simulations of practical gas burner combustion devices.

  16. Exhaust emissions from a premixing, prevaporizing flame tube using liquid jet A fuel

    NASA Technical Reports Server (NTRS)

    Marek, C. J.; Papathakos, L. C.

    1976-01-01

    Emissions of nitrogen oxides, carbon monoxide, and unburned hydrocarbons were measured in a burner where liquid Jet A fuel was sprayed into the heated air stream and vaporized upstream of a perforated plate flameholder. The burner was tested at inlet air temperatures at 640, 800, and 833 K, an inlet pressure of 5.6 X 100,000 N/m squared, a reference velocity of 25 m/sec, and equivalence ratios from lean blowout to 0.7. Nitrogen oxide levels of below 1.0 g NO2/kg fuel were obtained at combustion efficiencies greater than 99 percent. The measured emission levels for the liquid fuel agreed well with previously reported premixed gaseous propane data and agreed with well stirred reactor predictions. Autoignition of the premixed fuel air mixture was a problem at inlet temperatures above 650 K with 104 msec premixing time.

  17. Effect of premixing quality on oxides of nitrogen in gas turbine combustors foi HC

    NASA Technical Reports Server (NTRS)

    Roffe, G.; Ferri, A.

    1976-01-01

    Experiments were conducted to determine the effectiveness of several premixing prevaporizing gas turbine combustor designs in reducing formation of oxides of nitrogen at the supersonic cruise condition. An atomized spray from a single injector mounted on the axis of the mixer tube produced a high initial concentration of fuel near the axis and only moderate premixed conditions entering the combustor. A fuel spray produced by 12 flush-mounted normal injection orifices in the mixer tube wall produced a good initial despersion of fuel and resulted in nearly complete premixing. Oxides of nitrogen emission levels of the order of 0.2 g NO2/kg fuel were obtained at 99 percent combustion efficiency at an equivalence ratio of 0.4. Overall total pressure drop was less than 3 percent through the 1-meter combustor module.

  18. Turbulence and combustion interaction: High resolution local flame front structure visualization using simultaneous single-shot PLIF imaging of CH, OH, and CH{sub 2}O in a piloted premixed jet flame

    SciTech Connect

    Li, Z.S.; Li, B.; Sun, Z.W.; Alden, M.; Bai, X.S.

    2010-06-15

    High resolution planar laser-induced fluorescence (PLIF) was applied to investigate the local flame front structures of turbulent premixed methane/air jet flames in order to reveal details about turbulence and flame interaction. The targeted turbulent flames were generated on a specially designed coaxial jet burner, in which low speed stoichiometric gas mixture was fed through the outer large tube to provide a laminar pilot flame for stabilization of the high speed jet flame issued through the small inner tube. By varying the inner tube flow speed and keeping the mixture composition as that of the outer tube, different flames were obtained covering both the laminar and turbulent flame regimes with different turbulent intensities. Simultaneous CH/CH{sub 2}O, and also OH PLIF images were recorded to characterize the influence of turbulence eddies on the reaction zone structure, with a spatial resolution of about 40 {mu}m and temporal resolution of around 10 ns. Under all experimental conditions, the CH radicals were found to exist only in a thin layer; the CH{sub 2}O were found in the inner flame whereas the OH radicals were seen in the outer flame with the thin CH layer separating the OH and CH{sub 2}O layers. The outer OH layer is thick and it corresponds to the oxidation zone and post-flame zone; the CH{sub 2}O layer is thin in laminar flows; it becomes broad at high speed turbulent flow conditions. This phenomenon was analyzed using chemical kinetic calculations and eddy/flame interaction theory. It appears that under high turbulence intensity conditions, the small eddies in the preheat zone can transport species such as CH{sub 2}O from the reaction zones to the preheat zone. The CH{sub 2}O species are not consumed in the preheat zone due to the absence of H, O, and OH radicals by which CH{sub 2}O is to be oxidized. The CH radicals cannot exist in the preheat zone due to the rapid reactions of this species with O{sub 2} and CO{sub 2} in the inner-layer of the

  19. Progress towards an Optimization Methodology for Combustion-Driven Portable Thermoelectric Power Generation Systems

    SciTech Connect

    Krishnan, Shankar; Karri, Naveen K.; Gogna, Pawan K.; Chase, Jordan R.; Fleurial, Jean-Pierre; Hendricks, Terry J.

    2012-03-13

    Enormous military and commercial interests exist in developing quiet, lightweight, and compact thermoelectric (TE) power generation systems. This paper investigates design integration and analysis of an advanced TE power generation system implementing JP-8 fueled combustion and thermal recuperation. Design and development of a portable TE power system using a JP-8 combustor as a high temperature heat source and optimal process flows depend on efficient heat generation, transfer, and recovery within the system are explored. Design optimization of the system required considering the combustion system efficiency and TE conversion efficiency simultaneously. The combustor performance and TE sub-system performance were coupled directly through exhaust temperatures, fuel and air mass flow rates, heat exchanger performance, subsequent hot-side temperatures, and cold-side cooling techniques and temperatures. Systematic investigation of this system relied on accurate thermodynamic modeling of complex, high-temperature combustion processes concomitantly with detailed thermoelectric converter thermal/mechanical modeling. To this end, this work reports on design integration of systemlevel process flow simulations using commercial software CHEMCADTM with in-house thermoelectric converter and module optimization, and heat exchanger analyses using COMSOLTM software. High-performance, high-temperature TE materials and segmented TE element designs are incorporated in coupled design analyses to achieve predicted TE subsystem level conversion efficiencies exceeding 10%. These TE advances are integrated with a high performance microtechnology combustion reactor based on recent advances at the Pacific Northwest National Laboratory (PNNL). Predictions from this coupled simulation established a basis for optimal selection of fuel and air flow rates, thermoelectric module design and operating conditions, and microtechnology heat-exchanger design criteria. This paper will discuss this

  20. Combustion modeling for experimentation in a space environment

    NASA Technical Reports Server (NTRS)

    Berlad, A. L.

    1974-01-01

    The merits of combustion experimentation in a space environment are assessed, and the impact of such experimentation on current theoretical models is considered. It is noted that combustion theory and experimentation for less than normal gravitational conditions are incomplete, inadequate, or nonexistent. Extensive and systematic experimentation in a space environment is viewed as essential for more adequate and complete theoretical models of such processes as premixed flame propagation and extinction limits, premixed flame propagation in droplet and particle clouds, ignition and autoignition in premixed combustible media, and gas jet combustion of unpremixed reactants. Current theories and models in these areas are described, and some combustion studies that can be undertaken in the Space Shuttle Program are proposed, including crossed molecular beam, turbulence, and upper pressure limit (of gases) studies.

  1. Mechanisms of fouling, slagging and corrosion by pulverized coal combustion. Quarterly technical progress report No. 1, March 11-June 30, 1981

    SciTech Connect

    Gulden, M. E.; Hsu, L. L.; Stetson, A. R.

    1981-07-01

    Progress is reported on a program in which the objective is to conduct a detailed and comprehensive study of the mechanisms of fouling, slagging and corrosion in pulverized coal combustors by employing well controlled model systems which simulate the coal combustion environment. Emphasis during this period has been on design and construction of the combustion test rig. All design phases are complete. Construction of the diffuser and test sections is also complete.

  2. Pre-mixing apparatus for a turbine engine

    DOEpatents

    Lacy, Benjamin Paul; Varatharajan, Balachandar; Ziminsky, Willy Steve; Kraemer, Gilbert Otto; Yilmaz, Ertan; Melton, Patrick Benedict; Zuo, Baifang; Stevenson, Christian Xavier; Felling, David Kenton; Uhm, Jong Ho

    2012-04-03

    A pre-mixing apparatus for a turbine engine includes a main body having an inlet portion, an outlet portion and an exterior wall that collectively establish at least one fluid delivery plenum, and a plurality of fluid delivery tubes extending through at least a portion of the at least one fluid delivery plenum. Each of the plurality of fluid delivery tubes includes at least one fluid delivery opening fluidly connected to the at least one fluid delivery plenum. With this arrangement, a first fluid is selectively delivered to the at least one fluid delivery plenum, passed through the at least one fluid delivery opening and mixed with a second fluid flowing through the plurality of fluid delivery tubes prior to being combusted in a combustion chamber of a turbine engine.

  3. [Progress in biofixation of CO2 from combustion flue gas by microalgae].

    PubMed

    Zhang, Yixin; Zhao, Bingtao; Xiong, Kaibin; Zhang, Zhongxiao; Hao, Xiaohong; Liu, Tao

    2011-02-01

    Global warming caused by the increasing CO2 concentration in atmosphere is a serious problem in the international political, economic, scientific and environmental fields in recent years. Intensive carbon dioxide capture and storage (CCS) technologies have been developed for a feasible system to remove CO2 from industrial exhaust gases especially for combustion flue gas. In these technologies, the biofixation of CO2 by microalgae has the potential to diminish CO2 and produce the biomass. In this review, the current status focusing on biofixation of CO2 from combustion flue gases by microalgae including the selection of microalgal species and effect of flue gas conditions, the development of high efficient photobioreactor and the application of microalgae and its biomass product were reviewed and summarized. Finally, the perspectives of the technology were also discussed.

  4. Pulsed atmospheric fluidized bed combustion. Technical progress report, January 1992--March 1992

    SciTech Connect

    Not Available

    1992-05-01

    During this first quarter, a lab-scale water-cooled pulse combustor was designed, fabricated, and integrated with old pilot-scale PAFBC test systems. Characterization tests on this pulse combustor firing different kinds of fuel -- natural gas, pulverized coal and fine coal -- were conducted (without fluidized bed operation) for the purpose of finalizing PAFBC full-scale design. Steady-state tests were performed. Heat transfer performance and combustion efficiency of a coal-fired pulse combustor were evaluated.

  5. PROGRESS IN DETAILED KINETIC MODELING OF THE COMBUSTION OF OXYGENATED COMPONENTS OF BIOFUELS

    PubMed Central

    Sy Tran, Luc; Sirjean, Baptiste; Glaude, Pierre-Alexandre; Fournet, René; Battin-Leclerc, Frédérique

    2013-01-01

    Due to growing environmental concerns and diminishing petroleum reserves, a wide range of oxygenated species has been proposed as possible substitutes to fossil fuels: alcohols, methyl esters, acyclic and cyclic ethers. After a short review the major detailed kinetic models already proposed in the literature for the combustion of these molecules, the specific classes of reactions considered for modeling the oxidation of acyclic and cyclic oxygenated molecules respectively, are detailed. PMID:23700355

  6. Progress Towards an Optimization Methodology for Combustion-Driven Portable Thermoelectric Power Generation Systems

    NASA Astrophysics Data System (ADS)

    Krishnan, Shankar; Karri, Naveen K.; Gogna, Pawan K.; Chase, Jordan R.; Fleurial, Jean-Pierre; Hendricks, Terry J.

    2012-06-01

    There is enormous military and commercial interest in developing quiet, lightweight, and compact thermoelectric (TE) power generation systems. This paper investigates design integration and analysis of an advanced TE power generation system implementing JP-8 fueled combustion and thermal recuperation. In the design and development of this portable TE power system using a JP-8 combustor as a high-temperature heat source, optimal process flows depend on efficient heat generation, transfer, and recovery within the system. The combustor performance and TE subsystem performance were coupled directly through combustor exhaust temperatures, fuel and air mass flow rates, heat exchanger performance, subsequent hot-side temperatures, and cold-side cooling techniques and temperatures. Systematic investigation and design optimization of this TE power system relied on accurate thermodynamic modeling of complex, high-temperature combustion processes concomitantly with detailed TE converter thermal/mechanical modeling. To this end, this paper reports integration of system-level process flow simulations using CHEMCAD™ commercial software with in-house TE converter and module optimization, and heat exchanger analyses using COMSOL™ software. High-performance, high-temperature TE materials and segmented TE element designs are incorporated in coupled design analyses to achieve predicted TE subsystem-level conversion efficiencies exceeding 10%. These TE advances are integrated with a high-performance microtechnology combustion reactor based on recent advances at Pacific Northwest National Laboratory (PNNL). Predictions from this coupled simulation approach lead directly to system efficiency-power maps defining potentially available optimal system operating conditions and regimes. Further, it is shown that, for a given fuel flow rate, there exists a combination of recuperative effectiveness and hot-side heat exchanger effectiveness that provides a higher specific power output from

  7. Progress in Validation of Wind-US for Ramjet/Scramjet Combustion

    NASA Technical Reports Server (NTRS)

    Engblom, William A.; Frate, Franco C.; Nelson, Chris C.

    2005-01-01

    Validation of the Wind-US flow solver against two sets of experimental data involving high-speed combustion is attempted. First, the well-known Burrows- Kurkov supersonic hydrogen-air combustion test case is simulated, and the sensitively of ignition location and combustion performance to key parameters is explored. Second, a numerical model is developed for simulation of an X-43B candidate, full-scale, JP-7-fueled, internal flowpath operating in ramjet mode. Numerical results using an ethylene-air chemical kinetics model are directly compared against previously existing pressure-distribution data along the entire flowpath, obtained in direct-connect testing conducted at NASA Langley Research Center. Comparison to derived quantities such as burn efficiency and thermal throat location are also made. Reasonable to excellent agreement with experimental data is demonstrated for key parameters in both simulation efforts. Additional Wind-US feature needed to improve simulation efforts are described herein, including maintaining stagnation conditions at inflow boundaries for multi-species flow. An open issue regarding the sensitivity of isolator unstart to key model parameters is briefly discussed.

  8. Pulse combustion technology for heating applications. Quarterly progress report, April 1-June 30, 1980. [Pulse techniques

    SciTech Connect

    Blomquist, C.A.; Clinch, J.M.; Egbert, H.P.

    1980-08-01

    The primary purpose of this research program is to develop and expand the technology base for fossil-fuel-fired pulse combustion heating systems. A major goal is to develop design data and design procedures for pulse combustion burners. This design capability will contribute to the accelerated industrial development of cost-effective, high-efficiency systems for a variety of heating applications. Analytical and experimental studies will be carried out to establish a technology base and develop design procedures for gas-fired pulse combustion systems. A series of parametric experiments will be conducted with ANL's existing experimental pulse combustor. Basic performance characteristics including heat transfer rates, thermal efficiency, noise emissions, and exhaust gas composition will be obtained as a function of the primary combustor design parameters including combustor geometry, fuel/air ratio, valve geometry, and decoupling chamber size. Experimental data acquired under Section 1.1.1 above will be analyzed and correlated in a manner suitable for engineering design of gas-fired pulse combustors. Based on these data and correlations, a mathematical model of the combustor will be developed for use as an engineering design tool in establishing combustor geometry for specific applications and for defining trade-offs between system efficiency, noise emissions, and costs.

  9. Numerical simulation of pollutant emission and flame extinction in lean premixed systems

    NASA Astrophysics Data System (ADS)

    Eggenspieler, Gilles

    Premixed and partially-premixed combustion and pollutant emissions in full-scale gas turbines has been numerically investigated using a massively-parallel Large-Eddy Simulation Combustion Dynamics Model. Through the use of a flamelet library approach, it was observed that CO (Carbon Oxide) and NO (Nitric Oxide) emission can be predicted and match experimental results. The prediction of the CO emission trend is shown to be possible if the influence of the formation of UHC (Unburnt HydroCarbons) via flame extinction is taken into account. Simulations were repeated with two different combustion approach: the G-equation model and the Linear-Eddy Mixing (LEM) Model. Results are similar for these two set of numerical simulations. The LEM model was used to simulate flame extinction and flame lift-off in a dump combustion chamber. The LEM model is compared to the G-equation model and it was found that the LEM model is more versatile than the G-equation model with regard to accurate simulation of flame propagation in all turbulent premixed combustion regimes. With the addition of heat losses, flame extinction was observed for low equivalence ratio. Numerical simulation of flame propagation with transient inflow conditions were also carried out and demonstrated the ability of the LEM model to accurately simulate flame propagation in the case of a partially-premixed system. In all simulations where flame extinction and flame lift-off was simulated, release of unburnt fuel in the post-flame region through flame extinction was not observed.

  10. Plasma-Enhanced Combustion of Hydrocarbon Fuels and Fuel Blends Using Nanosecond Pulsed Discharges

    SciTech Connect

    Cappelli, Mark; Mungal, M Godfrey

    2014-10-28

    This project had as its goals the study of fundamental physical and chemical processes relevant to the sustained premixed and non-premixed jet ignition/combustion of low grade fuels or fuels under adverse flow conditions using non-equilibrium pulsed nanosecond discharges.

  11. Gas turbine premixer with internal cooling

    DOEpatents

    York, William David; Johnson, Thomas Edward; Lacy, Benjamin Paul; Stevenson, Christian Xavier

    2012-12-18

    A system that includes a turbine fuel nozzle comprising an air-fuel premixer. The air-fuel premixed includes a swirl vane configured to swirl fuel and air in a downstream direction, wherein the swirl vane comprises an internal coolant path from a downstream end portion in an upstream direction through a substantial length of the swirl vane.

  12. [Hot Gas Cleanup Test Facility for Gasification and Pressurized Combustion]. Quarterly technical progress report, October 1--December 31, 1993

    SciTech Connect

    Not Available

    1993-12-31

    This quarterly technical progress report summarizes work completed during the Second Quarter of the Second Budget Period, October 1 through December 31, 1993, under the Department of Energy (DOE) Cooperative Agreement No. DE-FC21-90MC25140 entitled ``Hot Gas Cleanup Test Facility for Gasification and Pressurized Combustion.`` The objective of this project is to evaluate hot gas particle control technologies using coal-derived gas streams. This will entail the design, construction, installation, and use of a flexible test facility which can operate under realistic gasification and combustion conditions. The major particulate control device issues to be addressed include the integration of the particulate control devices into coal utilization systems, on-line cleaning techniques, chemical and thermal degradation of components, fatigue or structural failures, blinding, collection efficiency as a function of particle size, and scaleup of particulate control systems to commercial size. The conceptual design of the facility was extended to include a within scope, phased expansion of the existing Hot Gas Cleanup Test Facility Cooperative Agreement to also address systems integration issues of hot particulate removal in advanced coal-based power generation systems. This expansion included the consideration of the following modules at the test facility in addition to the existing Transport Reactor gas source and Hot Gas Cleanup Units: (1) Carbonizer/pressurized circulating fluidized bed gas source; (2) hot gas cleanup units to mate to all gas streams; (3) combustion gas turbine; (4) fuel cell and associated gas treatment. This expansion to the Hot Gas Cleanup Test Facility is herein referred to as the Power Systems Development Facility (PSDF).

  13. Theoretical studies of combustion dynamics. Final progress report, August 1, 1986--July 31, 1997

    SciTech Connect

    Bowman, J.M.

    1998-03-01

    The authors completed a number of projects during this period of time. This resulted in fifty nine publications, which are listed below. The major thrusts of this research are the development and application of quantum methods to the study of fundamental chemical processes of importance in gas-phase combustion. Broadly speaking the work falls into two categories. One is the development and application of reduced dimensionality theories of chemical reactions, and the other into studies of radical-radical reactions that proceed mainly via complex formation. The various projects in these two areas and their intersection are reviewed.

  14. Response mechanisms of attached premixed flames subjected to harmonic forcing

    NASA Astrophysics Data System (ADS)

    Shreekrishna

    The persistent thrust for a cleaner, greener environment has prompted air pollution regulations to be enforced with increased stringency by environmental protection bodies all over the world. This has prompted gas turbine manufacturers to move from nonpremixed combustion to lean, premixed combustion. These lean premixed combustors operate quite fuel-lean compared to the stochiometric, in order to minimize CO and NOx productions, and are very susceptible to oscillations in any of the upstream flow variables. These oscillations cause the heat release rate of the flame to oscillate, which can engage one or more acoustic modes of the combustor or gas turbine components, and under certain conditions, lead to limit cycle oscillations. This phenomenon, called thermoacoustic instabilities, is characterized by very high pressure oscillations and increased heat fluxes at system walls, and can cause significant problems in the routine operability of these combustors, not to mention the occasional hardware damages that could occur, all of which cumulatively cost several millions of dollars. In a bid towards understanding this flow-flame interaction, this research works studies the heat release response of premixed flames to oscillations in reactant equivalence ratio, reactant velocity and pressure, under conditions where the flame preheat zone is convectively compact to these disturbances, using the G-equation. The heat release response is quantified by means of the flame transfer function and together with combustor acoustics, forms a critical component of the analytical models that can predict combustor dynamics. To this end, low excitation amplitude (linear) and high excitation amplitude (nonlinear) responses of the flame are studied in this work. The linear heat release response of lean, premixed flames are seen to be dominated by responses to velocity and equivalence ratio fluctuations at low frequencies, and to pressure fluctuations at high frequencies which are in the

  15. Hot gas cleanup test facility for gasification and pressurized combustion. Quarterly technical progress report, April 1--June 30, 1992

    SciTech Connect

    Not Available

    1992-12-01

    This quarterly technical progress report summarizes work completed during the Seventh Quarter of the First Budget Period, April 1 through June 30, 1992, under the Department of Energy (DOE) Cooperative Agreement No. DE-FC21-90MC25140 entitled ``Hot Gas Cleanup Test Facility for Gasification and Pressurized Combustion.`` The conceptual design of the facility was extended to include a within scope, phased expansion of the existing Hot Gas Cleanup Test Facility Cooperative Agreement to also address systems integration issues of hot particulate removal in advanced coal-based power generation systems. This expansion will include the consideration of the following modules at the test facility in addition to the existing Transport Reactor gas source and Hot Gas Cleanup Units: Carbonizer/Pressurized Circulating Fluidized Bed Gas Source; Hot Gas Cleanup Units to mate to all gas streams. Combustion Gas Turbine; Fuel Cell and associated gas treatment; and Externally Fired Gas Turbine/Water Augmented Gas Turbine. This expansion to the Hot Gas Cleanup Test Facility is herein referred to as the Power Systems Development Facility (PSDF).

  16. Analysis of effect of flameholder characteristics on lean, premixed, partially vaporized fuel-air mixtures quality and nitrogen oxides emissions

    NASA Technical Reports Server (NTRS)

    Cooper, L. P.

    1981-01-01

    An analysis was conducted of the effect of flameholding devices on the precombustion fuel-air characteristics and on oxides of nitrogen (NOx) emissions for combustion of premixed partially vaporized mixtures. The analysis includes the interrelationships of flameholder droplet collection efficiency, reatomization efficiency and blockage, and the initial droplet size distribution and accounts for the contribution of droplet combustion in partially vaporized mixtures to NOx emissions. Application of the analytical procedures is illustrated and parametric predictions of NOx emissions are presented.

  17. On the Interaction of a Premixed Flame with an Acoustic Disturbance

    NASA Technical Reports Server (NTRS)

    Hood, Caroline; Frendi, Abdelkader

    2005-01-01

    The main objective of this research is to analyze the effect of acoustic disturbances on a premixed flame and determine their role in the onset of combustion instabilities. Computations for the one-dimensional, unsteady combustion of a lean premixed methane-air mixture are performed. An acoustic excitation is introduced in the chamber and interacts with the flame front. Our results indicate that as the amplitude of the acoustic excitation is increased, the flame front position fluctuates rapidly. This phenomenon is even more intense when the frequency of the acoustic disturbance matches the fundamental frequency of the chamber. Our results suggest that the interactions between the flame and the acoustic excitation may result in flame extinguishment. In addition various passive control devices are tested and we found that the Helmholtz resonator with rounded inlet corners is the most efficient.

  18. Study of Turbulent Premixed Flame Propagation using a Laminar Flamelet Model

    NASA Technical Reports Server (NTRS)

    Im, H. G.

    1995-01-01

    The laminar flamelet concept in turbulent reacting flows is considered applicable to many practical combustion systems (Linan & Williams 1993). For turbulent premixed combustion, the laminar flamelet regime is valid when turbulent Karlovitz number is less than unity, which is equivalent to stating that the characteristic thickness of the flame is less than that of a Kolmogorov eddy; this is known as the Klimov-Williams criterion (Williams 1985). In such a case, the flame maintains its laminar structure, and the effect of turbulent flow is merely to wrinkle and strain the flame front. The propagating wrinkled premixed flame can then be described as an infinitesimally thin surface dividing the unburnt fresh mixture and the burnt product.

  19. Numerical simulation of thermoacoustic response of laboratory scale premixed multi-slit burner flames

    NASA Astrophysics Data System (ADS)

    O'Brien, Adam

    Thermoacoustic instabilities are an entirely unwanted, yet nearly inevitable phenomenon occurring in many practical premixed combustors. If not properly accounted and designed for, they can incur significant increases in the development combustion systems. The fact that such unexpected issues are encountered is indicative of a fundamental lack of understanding regarding the mechanisms that drive thermoacoustic phenomena. Numerical techniques are used to characterize the thermoacoustic response of premixed multi-slit bunsen burner flames. A symmetrical representation of the multi-slit burner is used, and the transfer function is computed at several different frequencies and at three different equivalence ratios. The numerical results are then compared against experimental results in order to determine the suitability of numerical techniques for studying thermoacoustics. A fully compressible Navier-Stokes combustion solver is used in conjunction with adaptive mesh refinement (AMR) for improved resolution at the flame interface.

  20. Fuel premixing module for gas turbine engine combustor

    NASA Technical Reports Server (NTRS)

    Chin, Jushan (Inventor); Rizk, Nader K. (Inventor); Razdan, Mohan K. (Inventor); Marshall, Andre W. (Inventor)

    2005-01-01

    A fuel-air premixing module is designed to reduce emissions from a gas turbine engine. In one form, the premixing module includes a central pilot premixer module with a main premixer module positioned thereround. Each of the portions of the fuel-air premixing module include an axial inflow swirler with a plurality of fixed swirler vanes. Fuel is injected into the main premixer module between the swirler vanes of the axial inflow swirler and at an acute angle relative to the centerline of the premixing module.

  1. Combustion synthesis of fullerenes

    SciTech Connect

    Mckinnon, J.T.; Bell, W.L. ); Barkley, R.M. )

    1992-01-01

    This paper reports the isolation of C{sub 60} and C{sub 70} from combustion soot that is produced in high-temperature, low-pressure premixed flat flames. A critical parameter for high fullerene yields in combustion appears to be a very high flame temperature. Equilibrium calculations indicate that low pressures are important, but the experimental evidence is not clear at this time. Combustion synthesis yields fullerenes with a C{sub 70}/C{sub 60} ratio of about 40%, as compared with the 12% reported for electric-arc-generated fullerenes. The overall yields from carbon are very low (ca. 0.03%) but the soot studied had been produced in flames that were in no way optimized for fullerene production.

  2. Effect of hydrogen injection stability and emissions of an experimental premixed prevaporized propane burner

    NASA Technical Reports Server (NTRS)

    Anderson, D. N.

    1975-01-01

    Hydrogen in quantities up to 5 percent by weight of the total fuel flow was injected into a premixed propane burner. The hydrogen was either premixed with the propane and air upstream of the burner or introduced as a torch at the flameholder. Emissions of total nitrogen oxides, carbon monoxide, and unburned hydrocarbon are reported as are combustion efficiencies and lean blowout limits. To maintain at least 99 percent combustion efficiency at a 700 K inlet mixture temperature with no hydrogen added, it was necessary to burn with a propane equivalence ratio of 0.525. When 4 percent hydrogen was premixed with the propane and air, a combustion efficiency greater than 99 percent was recorded at a propane equivalence ratio of 0.425. The total nitrogen oxides (NOx) emissions corresponding to these two conditions were 0.8 g NO2/kg equivalent propane and 0.44 g NO2/kg equivalent propane, respectively. The hydrogen torch did not reduce NOx emissions.

  3. Gravitational Influences on Flame Propagation Through Non-Uniform, Premixed Gas Systems

    NASA Technical Reports Server (NTRS)

    Miller, Fletcher J.; Easton, John; Marchese, Anthony; Hovermann, Fred

    2003-01-01

    Flame propagation through non-uniformly premixed (or layered) gases has importance both in useful combustion systems and in unintentional fires. As summarized recently and in previous Microgravity Workshop papers, non-uniform premixed gas combustion receives scant attention compared to the more usual limiting cases of diffusion or uniformly premixed flames, especially regarding the role gravity plays. This paper summarizes our recent findings on gravitational effects on layered combustion along a floor, in which the fuel concentration gradient exists normal to the direction of flame spread. In an effort to understand the mechanism by which the flames spread faster in microgravity (and much faster, in laboratory coordinates, than the laminar burning velocity for uniform mixtures), we have begun making pressure measurements across the spreading flame front that are described here. Earlier researchers, testing in 1g, claimed that hydrostatic pressure differences could account for the rapid spread rates. Additionally, we present the development of a new apparatus to study flame spread in free (i.e., far from walls), non-homogeneous fuel layers formed in a flow tunnel behind an airfoil that has been tested in normal gravity.

  4. A premixed hydrogen/oxygen catalytic igniter

    NASA Technical Reports Server (NTRS)

    Green, James M.

    1989-01-01

    The catalytic ignition of hydrogen and oxygen propellants was studied using a premixing hydrogen/oxygen injector. The premixed injector was designed to eliminate problems associated with catalytic ignition caused by poor propellant mixing in the catalyst bed. Mixture ratio, mass flow rate, and propellant inlet temperature were varied parametrically in testing, and a pulse mode life test of the igniter was conducted. The results of the tests showed that the premixed injector eliminated flame flashback in the reactor and increased the life of the igniter significantly. The results of the experimental program and a comparison with data collected in a previous program are given.

  5. A direct numerical simulation study of vorticity transformation in weakly turbulent premixed flames

    NASA Astrophysics Data System (ADS)

    Lipatnikov, A. N.; Nishiki, S.; Hasegawa, T.

    2014-10-01

    Database obtained earlier in 3D Direct Numerical Simulations (DNS) of statistically stationary, 1D, planar turbulent flames characterized by three different density ratios σ is processed in order to investigate vorticity transformation in premixed combustion under conditions of moderately weak turbulence (rms turbulent velocity and laminar flame speed are roughly equal to one another). In cases H and M characterized by σ = 7.53 and 5.0, respectively, anisotropic generation of vorticity within the flame brush is reported. In order to study physical mechanisms that control this phenomenon, various terms in vorticity and enstrophy balance equations are analyzed, with both mean terms and terms conditioned on a particular value c of the combustion progress variable being addressed. Results indicate an important role played by baroclinic torque and dilatation in transformation of average vorticity and enstrophy within both flamelets and flame brush. Besides these widely recognized physical mechanisms, two other effects are documented. First, viscous stresses redistribute enstrophy within flamelets, but play a minor role in the balance of the mean enstrophy overline{Ω } within turbulent flame brush. Second, negative correlation overline{mathbf {u}^' } \\cdot nabla Ω ^' }} between fluctuations in velocity u and enstrophy gradient contributes substantially to an increase in the mean overline{Ω } within turbulent flame brush. This negative correlation is mainly controlled by the positive correlation between fluctuations in the enstrophy and dilatation and, therefore, dilatation fluctuations substantially reduce the damping effect of the mean dilatation on the vorticity and enstrophy fields. In case L characterized by σ = 2.5, these effects are weakly pronounced and overline{Ω } is reduced mainly due to viscosity. Under conditions of the present DNS, vortex stretching plays a minor role in the balance of vorticity and enstrophy within turbulent flame brush in all three

  6. Some effects of heat release in premixed flames

    SciTech Connect

    Shepherd, I.G.

    1994-03-01

    Numerical and experimental results are presented to illustrate some hydrodynamic effects of heat release in premixed flames. The heat release is represented by a simple model which treats the flame front as a two dimensional line source of volume. The velocity and strain rate induced in the flow field are determined and the numerical solution for the case of a laminar double kernel ignition is obtained. Of primary interest is the strain induced in the reactants between the expanding flame kernels and, for heat release rates typical of hydrocarbon flames, the strain rate at the plane of symmetry midway between the kernels up to 150 s{sup {minus}1}. The effects of kernel size, density ratio across the flame front and laminar burning velocity are studied. For the case of turbulent combustion the velocity induced in the reactant stream is measured in a plane parallel to the flame holder of an open premixed turbulent V-shaped flame. A divergent flow field, with a strain rate of 50 s{sup {minus}1}, is induced by the heat release in the flame zone and the consequences of this for determining the turbulent burning velocity in this and similar systems is reviewed.

  7. Streamline segment statistics of premixed flames with nonunity Lewis numbers

    NASA Astrophysics Data System (ADS)

    Chakraborty, Nilanjan; Wang, Lipo; Klein, Markus

    2014-03-01

    The interaction of flame and surrounding fluid motion is of central importance in the fundamental understanding of turbulent combustion. It is demonstrated here that this interaction can be represented using streamline segment analysis, which was previously applied in nonreactive turbulence. The present work focuses on the effects of the global Lewis number (Le) on streamline segment statistics in premixed flames in the thin-reaction-zones regime. A direct numerical simulation database of freely propagating thin-reaction-zones regime flames with Le ranging from 0.34 to 1.2 is used to demonstrate that Le has significant influences on the characteristic features of the streamline segment, such as the curve length, the difference in the velocity magnitude at two extremal points, and their correlations with the local flame curvature. The strengthenings of the dilatation rate, flame normal acceleration, and flame-generated turbulence with decreasing Le are principally responsible for these observed effects. An expression for the probability density function (pdf) of the streamline segment length, originally developed for nonreacting turbulent flows, captures the qualitative behavior for turbulent premixed flames in the thin-reaction-zones regime for a wide range of Le values. The joint pdfs between the streamline length and the difference in the velocity magnitude at two extremal points for both unweighted and density-weighted velocity vectors are analyzed and compared. Detailed explanations are provided for the observed differences in the topological behaviors of the streamline segment in response to the global Le.

  8. Vorticity isotropy in high Karlovitz number premixed flames

    NASA Astrophysics Data System (ADS)

    Bobbitt, Brock; Blanquart, Guillaume

    2016-10-01

    The isotropy of the smallest turbulent scales is investigated in premixed turbulent combustion by analyzing the vorticity vector in a series of high Karlovitz number premixed flame direct numerical simulations. It is found that increasing the Karlovitz number and the ratio of the integral length scale to the flame thickness both reduce the level of anisotropy. By analyzing the vorticity transport equation, it is determined that the vortex stretching term is primarily responsible for the development of any anisotropy. The local dynamics of the vortex stretching term and vorticity resemble that of homogeneous isotropic turbulence to a greater extent at higher Karlovitz numbers. This results in small scale isotropy at sufficiently high Karlovitz numbers and supports a fundamental similarity of the behavior of the smallest turbulent scales throughout the flame and in homogeneous isotropic turbulence. At lower Karlovitz numbers, the vortex stretching term and the vorticity alignment in the strain-rate tensor eigenframe are altered by the flame. The integral length scale has minimal impact on these local dynamics but promotes the effects of the flame to be equal in all directions. The resulting isotropy in vorticity does not reflect a fundamental similarity between the smallest turbulent scales in the flame and in homogeneous isotropic turbulence.

  9. Bed material agglomeration during fluidized bed combustion. Technical progress report, April 1, 1995--June 30, 1995

    SciTech Connect

    Brown, R.C.; Dawson, M.R.; Smeenk, J.L.

    1995-07-01

    During this quarter, agglomeration tests were conducted in a laboratory-scale fluidized bed combustor using coal and {open_quotes}model{close_quotes} components which allowed controlled amounts of clays and pyrites to be added during the test. These tests permitted a more direct evaluation of the interaction between iron compounds and aluminosilicates. With additional clay and pyrite (under simulated local reducing conditions found at coal feed locations) large agglomerates formed. The agglomerates were many times larger than those formed with a standard coal feed. When only clay was added to the fuel (no additional pyrite), agglomerates formed but they were much smaller and very friable. These tests support the hypothesis that local reducing conditions promote the interaction of iron in a +2 state and aluminosilicate material in the coal which leads to agglomeration during fluidized bed combustion. Also during this quarter, a deposit which formed in a fluidized bed boiler of a Texas-New Mexico Power Company was analyzed to determine the chemical and mineralogic mechanisms responsible for deposit formation. Mineral phases were determined by x-ray diffraction (XRD). Bulk chemical composition was determined by x-ray fluorescence spectroscopy (XRF). Polished sections of the deposit were made for optical and scanning electron microscopy.

  10. LEM-CF Premixed Tool Kit

    SciTech Connect

    2015-01-19

    The purpose of LEM-CF Premixed Tool Kit is to process premixed flame simulation data from the LEM-CF solver (https://fileshare.craft-tech.com/clusters/view/lem-cf) into a large-eddy simulation (LES) subgrid model database. These databases may be used with a user-defined-function (UDF) that is included in the Tool Kit. The subgrid model UDF may be used with the ANSYS FLUENT flow solver or other commercial flow solvers.

  11. Application of the conditional source-term estimation model for turbulence-chemistry interactions in a premixed flame

    NASA Astrophysics Data System (ADS)

    Salehi, M. M.; Bushe, W. K.; Daun, K. J.

    2012-04-01

    Conditional Source-term Estimation (CSE) is a closure model for turbulence-chemistry interactions. This model uses the first-order CMC hypothesis to close the chemical reaction source terms. The conditional scalar field is estimated by solving an integral equation using inverse methods. It was originally developed and has been used extensively in non-premixed combustion. This work is the first application of this combustion model for a premixed flame. CSE is coupled with a Trajectory Generated Low-Dimensional Manifold (TGLDM) model for chemistry. The CSE-TGLDM combustion model is used in a RANS code to simulate a turbulent premixed Bunsen burner. Along with this combustion model, a similar model which relies on the flamelet assumption is also used for comparison. The results of these two approaches in the prediction of the velocity field, temperature and species mass fractions are compared together. Although the flamelet model is less computationally expensive, the CSE combustion model is more general and does not have the limiting assumption underlying the flamelet model.

  12. Cellular burning in lean premixed turbulent hydrogen-air flames: Coupling experimental and computational analysis at the laboratory scale

    NASA Astrophysics Data System (ADS)

    Day, M. S.; Bell, J. B.; Cheng, R. K.; Tachibana, S.; Beckner, V. E.; Lijewski, M. J.

    2009-07-01

    One strategy for reducing US dependence on petroleum is to develop new combustion technologies for burning the fuel-lean mixtures of hydrogen or hydrogen-rich syngas fuels obtained from the gasification of coal and biomass. Fuel-flexible combustion systems based on lean premixed combustion have the potential for dramatically reducing pollutant emissions in transportation systems, heat and stationary power generation. However, lean premixed flames are highly susceptible to fluid-dynamical combustion instabilities making robust and reliable systems difficult to design. Low swirl burners are emerging as an important technology for meeting design requirements in terms of both reliability and emissions for next generation combustion devices. In this paper, we present simulations of a lean, premixed hydrogen flame stabilized on a laboratory-scale low swirl burner. The simulations use detailed chemistry and transport without incorporating explicit models for turbulence or turbulence/chemistry interaction. Here we discuss the overall structure of the flame and compare with experimental data. We also use the simulation data to elucidate the characteristics of the turbulent flame interaction and how this impacts the analysis of experimental measurements.

  13. Progress in pressurized fluidized bed combustion (PFBC) filter cakes and filter cleaning

    SciTech Connect

    Smith, D.H.; Grimm, U.; Haddad, G.J.; VanOsdol, J.; Ferer, M.V.

    1996-12-31

    The Pressurized Fluidized Bed Combustion (PFBC) program of the US Department of Energy includes a Second Generation technology with a goal of 45% net efficiency and an Advanced Cycle technology with an efficiency greater than 50%. Both technologies require filtration, at temperatures in excess of 700 C, of fine particles of coal ash and spent and unreacted sorbent from the hot-gas stream. The authors have developed and tested physically realistic equations that allow real-time determination of filter-cake thicknesses from on-line measurements of tube-sheet pressure drops and gas and particle flow rates, and laboratory measurements of filter-cake porosities. The models also accommodate changes of cake-strengths and cleaning produced by changes in particle-size distributions before filtration (e.g., as produced by cyclone detuning). The degree of agglomeration in filter cakes strongly depends on chemical reactions, diffusion, and neck formation, which in turn depend on the operating temperature and frequency of filter-cleaning. When a dolomitic sorbent is used with a filter-vessel temperature of {approximately}700 C, capture of SO{sub 2} by sulfation of MgO (elutriated from the combustor) occurs in the filter cakes. Sulfation reactions produce bonding between particles and thus agglomeration. Agglomeration also can occur by sintering of MgSO{sub 4} or of CaSO{sub 4}; the latter compound also is elutriated from the combustor. However, the end-product produced by sulfation in the filter cakes of the Tidd PFBC demonstration plant was not MgSO{sub 4}, but Mg{sub 2}Ca(SO{sub 4}){sub 3}. The amounts of this compound and the rate at which it was produced also have been determined for the Tidd filter unit.

  14. Symposium /International/ on Combustion, 18th, University of Waterloo, Waterloo, Ontario, Canada, August 17-22, 1980, Proceedings

    NASA Technical Reports Server (NTRS)

    1981-01-01

    Problems related to combustion generated pollution are explored, taking into account the mechanism of NO formation from nitrogen compounds in hydrogen flames studied by laser fluorescence, the structure and similarity of nitric oxide production in turbulent diffusion flames, the effect of steam addition on NO formation, and the formation of NO2 by laminar flames. Other topics considered are concerned with propellant combustion, fluidized bed combustion, the combustion of droplets and sprays, premixed flame studies, fire studies, and flame stabilization. Attention is also given to coal flammability, chemical kinetics, turbulent combustion, soot, coal combustion, the modeling of combustion processes, combustion diagnostics, detonations and explosions, ignition, internal combustion engines, combustion studies, and furnaces.

  15. Emissions, combustion dynamics, and control of a multiple swirl combustor

    NASA Astrophysics Data System (ADS)

    Li, Guoqiang

    To achieve single digit NOx emission from gas turbine combustors and prevent the combustion dynamics encountered in Lean Premixed Combustion, it is essential to understand the correlations among emission characteristics, combustion dynamics, and dynamics and characteristics of swirling flow field. The focus of this dissertation is to investigate the emission characteristics and combustion dynamics of multiple swirl dump combustors either in premixing or non-premixed combustion (e.g. Lean Direct Injection), and correlate these combustion characteristics (emissions, combustion instability and lean flammability) to the fluids dynamics (flow structures and its evolution). This study covers measurement of velocity flow field, temperature field, and combustion under effects of various parameters, including inlet flow Reynolds number, inlet air temperature, swirl configurations, downstream exhaust nozzle contraction ratios, length of mixing tube. These parameters are tested in both liquid and gaseous fuel combustions. Knowledge obtained through this comprehensive study is applied to passive and active controls for improving gas turbine combustion performance in the aid of novel sensor and actuator technologies. Emissions and combustion characteristics are shown closely related to the shape and size of central recirculation zone (CRZ), the mean and turbulence velocity and strain rate, and dynamics of large vortical structures. The passive controls, mostly geometry factors, affect the combustion characteristics and emissions through their influences on flow fields, and consequently temperature and radical fields. Air assist, which is used to adjust the momentum of fuel spray, is effective in reducing NOx and depress combustion oscillation without hurting LBO. Fuel distribution/split is also one important factor for achieving low NOx emission and control of combustion dynamics. The dynamics of combustion, including flame oscillations close to LBO and acoustic combustion

  16. Study on the premixed laminar flames of iso-octane

    NASA Astrophysics Data System (ADS)

    Yang, Bo; Hong, Yan-ji; Xu, Qing-yao; Liu, Yi; Cheng, Qi-sheng; Ding, Xiao-yu

    2015-04-01

    Propagation characteristics of premixed laminar iso-octane flames at atmosphere and equivalence ratios from 0.8 to 1.4 are studied in a constant combustion bomb using a schlieren technique, the laminar burning velocity at different initial pressure, temperature, equivalence ratio are calculated through CHEMKIN program. The experimental and calculation results show that the laminar burning velocity of iso-octane rise with the decreasing of initial pressure and rise with the rising of initial temperature . Only changing the initial temperature or pressure ,the maximum laminar burning velocity of iso-octane were both obtained at equivalence ratio 1.1. Flame stability become weak ,when increased the equivalence ratio. The problem of the chemistry reaction mechanism to predict the laminar burning velocity were analysed.

  17. Dynamics of premixed hydrogen/air flames in mesoscale channels

    SciTech Connect

    Pizza, Gianmarco; Frouzakis, Christos E.; Boulouchos, Konstantinos; Mantzaras, John; Tomboulides, Ananias G.

    2008-10-15

    Direct numerical simulation with detailed chemistry and transport is used to study the stabilization and dynamics of lean ({phi}=0.5) premixed hydrogen/air atmospheric pressure flames in mesoscale planar channels. Channel heights of h=2, 4, and 7 mm, and inflow velocities in the range 0.3{<=}U{sub IN}{<=}1100cm/ s are investigated. Six different burning modes are identified: mild combustion, ignition/extinction, closed steady symmetric flames, open steady symmetric flames, oscillating and, finally, asymmetric flames. Chaotic behavior of cellular flame structures is observed for certain values of U{sub IN}. Stability maps delineating the regions of the different flame types are finally constructed. (author)

  18. Volatiles combustion in fluidized beds. Technical progress report, 4 March 1993--3 June 1993

    SciTech Connect

    Hesketh, R.P.

    1993-09-01

    The goal of this project is to investigate the conditions in which volatiles will burn within both the dense and freeboard regions of fluidized beds. Experiments using a fluidized bed operated at incipient fluidization will be performed to characterize the effect of particle surface area, initial fuel concentration, and particle type on the inhibition of volatiles within a fluidized bed. The work conducted during the period 4 March, 1993 through 3 June, 1993 is reported in this technical progress report. The work during this time period consists primarily of the startup and trouble shooting of the fluidized bed reactor and gas phase modeling of methane and propane.

  19. FY 2014 Annual Progress Report - Advanced Combustion Engine Research and Development (Book)

    SciTech Connect

    Not Available

    2014-11-01

    In the past year, the DOE Hydrogen Program (the Program) made substantial progress toward its goals and objectives. The Program has conducted comprehensive and focused efforts to enable the widespread commercialization of hydrogen and fuel cell technologies in diverse sectors of the economy. With emphasis on applications that will effectively strengthen our nation's energy security and improve our stewardship of the environment, the Program engages in research, development, and demonstration of critical improvements in the technologies. Highlights of the Program's accomplishments can be found in the sub-program chapters of this report.

  20. Symposium (International) on Combustion, 23rd, Universite d'Orleans, France, July 22-27, 1990, Proceedings

    NASA Technical Reports Server (NTRS)

    1991-01-01

    The present symposium on combustion discusses reaction kinetics, NO(x) kinetics, premixed, diffusion, and nonsteady flames, turbulent combustion, hazardous waste, fluidized bed combustion, coal boilers and furnaces, engines, heterogeneous kinetics, heterogeneous, droplet, and microgravity combustion, and high-temperature synthesis. Attention is given to reactions of biphenyl, methylnaphthalenes, and phenanthrene with atomic oxygen in the gas phase, the oxidation of ortho-xylene, the effects of water on combustion kinetics at high pressure, and the formation and measurement of N2O in combustion systems. Topics addressed include large ions in premixed benzene-oxygen flames, the structure and kinetics of CH4/N2O flames, the propagation of unsteady hydrogen premixed flames near flammability limits, and the basic structure of lean propane flames. Also considered are OH measurements of piloted diffusion flames of nitrogen-diluted methane near extinction, waste combustion, preferential oxidation of carbon surfaces, and reburning mechanisms in a pulverized coal combustor.

  1. Open-chamber combustion study

    NASA Astrophysics Data System (ADS)

    Meyers, D. P.; Meyer, R. C.

    1994-04-01

    The test program was undertaken to research trade-offs between engine design and operational parameters on open-chamber, premixed spark-ignited gas engines, with a primary focus on combustion effects. This included combustion chamber designs which are conceptually diametrically opposed -- a high squish design typical of diesel engines and a virtually quiescent design. The reader should note that these data are somewhat abstract compared to conventional engines, because the Labeco test engine has exceptionally high friction and the lean-burn data were run unboosted.

  2. Volatiles combustion in fluidized beds. [Quarterly] technical progress report, 4 March 1994--3 June 1994

    SciTech Connect

    Pendergrass, R.A. II; Hesketh, R.P.

    1994-08-01

    The goal of this project is to investigate the conditions in which volatiles will bum within both the dense and freeboard regions of fluidized beds. Experiments using a fluidized bed operated at incipient fluidization will be performed to characterize the effect of particle surface area, initial fuel concentration, and particle type on the, inhibition of volatiles within a fluidized bed. The work conducted during the period 4 March, 1994 through 3 June, 1994 is reported in this technical progress report. The experimental work during this time period consists primarily of data collection. Gas composition results using two sand particle diameters of 0.531 and 0.126 mm. Three graphs at equivalence ratios of 0.5, 1.0 and 2.0 for propane in air are reported for the 0.531 mm sand size. For the 0.126 nun sand size stoichiometric propane and air are results are reported.

  3. Combustion of dense streams of coal particles. Quarterly progress report No. 5, August 29, 1991--November 28, 1991

    SciTech Connect

    Annamalai, K.

    1991-12-31

    The main objective of our work is to obtain a specific velocity of the resulting flame and to maintain this flame consistent throughout the experiment. To optimize our work, theoretical study has been conducted relating the flow rate of the premixed gas (gas + air), stoichiometric coal mass flow rate, interparticle distance of the coal particles, number of particles and the max. coal mass flow rate needed to maintain a specific velocity. Runs were made for velocities of 1.5, 2.0, 2.5, and 3.0 m/s.

  4. Coal combustion science quarterly progress report, October--December 1992. Task 1, Coal char combustion [and] Task 2, Fate of mineral matter

    SciTech Connect

    Hardesty, D.R.; Hurt, R.H.; Baxter, L.L.

    1993-06-01

    In the Coal Combustion Laboratory (CCL) this quarter, controlled laboratory experiments were carried out to better understand the late stages of coal combustion and its relation to unburned carbon levels in fly ash. Optical in situ measurements were made during char combustion at high carbon conversions and the optical data were related to particle morphologies revealed by optical microscopy on samples extracted under the same conditions. Results of this work are reported in detail below. In the data presented below, we compare the fraction of alkali metal loss to that of the alkaline earth metals as a function of coal rank to draw conclusions about the mechanism of release for the latter. Figure 2.1 illustrates the fractional release of the major alkali and alkaline earth metals (Na, K, Ca, Mg) as a function of coal rank for a series of coals and for several coal blends. All data are derived from combustion experiments in Sandia`s Multifuel Combustor (MFC) and represent the average of three to eight experiments under conditions where the mass loss on a dry, ash-free (daf) basis exceeds 95 %. There are no missing data in the figure. The several coals with no indicated result exhibited no mass loss of the alkali or alkaline earth metals in our experiments. There is a clear rank dependence indicated by the data in Fig. 2.1, reflecting the mode of occurrence of the material in the coal.

  5. Investigation of mineral transformations and ash deposition during staged combustion. Quarterly technical progress report, October 1, 1995--December 31, 1995

    SciTech Connect

    Harb, J.N.

    1996-02-07

    Progress during the ninth quarter of a three-year study of ash formation and deposition was made in several areas. One of the key contributions this quarter was the development of an enhanced method for classification of CCSEM data. This classification algorithm permits grouping and comparison of particles previously labeled as ``unclassifiable.`` A second analytical advancement, also made this quarter, provides more detailed information on the distribution of minerals in the coal and the potential for coalescence. This new multiple analysis technique is also applicable to ash and will permit identification of heterogeneous ash particles. Additional analyses of ash samples were also performed and it was found that the firing of Pittsburgh {number_sign}8 under staged combustion conditions yields an ash with a significantly larger particle size distribution than that obtained under conventional firing conditions, but without a significant change in composition. the size difference was noted previously, but the new classification algorithm allowed a detailed comparison of all composition groups, including unclassifiable particles, in the ashes. A mechanistic explanation for this behavior has been developed and is provided in the report. Finally, a paper documenting the new classification algorithm has been prepared and is scheduled for presentation at the March ACS meeting in New Orleans.

  6. Investigation of heat transfer and combustion in the advanced Fluidized Bed Combustor (FBC). Technical progress report No. 13, October 1996--December 1996

    SciTech Connect

    Lee, Seong W.

    1997-01-01

    This technical report summarizes the research conducted and progress achieved during the period from October 1, 1996 to December 31, 1996. Numerical simulation was acquired from the particle trajectories by means of the Reynolds Stress Model (REM) with general algebraic expressions. The typical particle trajectories for bunch particle injection were predicted by the top view, the side view, and the isolated 3-dimensional view. The simulation of particle trajectories showed top view, side view, and isolated 3-dimensional view. Numerical simulation for the bunch particle injection will be continued to understand the particle characteristics in the combustion chamber. The system test was conducted on the exploratory hot model. Thermal performance and combustion products of the test results were analyzed and predicted. The effect of cooling water on the combustion chamber was studied using the natural gas as a one of firing fuel. Without a providing of cooling water, overall combustion temperatures are increased. A computer-assisted data acquisition system was employed to measure the flue gas compositions/stack temperature. The measurement of combustion products was conducted by the gas analyzer.

  7. Relevance of the Bray number in the small-scale modeling of turbulent premixed flames

    SciTech Connect

    Mura, Arnaud; Champion, Michel

    2009-03-15

    The present study is devoted to the analysis of the influence of expansion phenomena on turbulent small scales in premixed reactive flows. It is shown that, under certain conditions, the expansion that takes place across wrinkled laminar flamelet can be sufficient to control the fluctuating velocity gradients and associated dissipation rate functions. These conditions are fixed by the respective values of a set of nondimensional parameters, namely the turbulence Reynolds number Re{sub T}, the Bray number, and the ratio between integral length scale of turbulence and thermal flame front thickness. A new criterion is introduced that makes it possible to delineate the influence of expansion phenomena on small-scale turbulent premixed reactive flows. The relevance of this criterion is analyzed in the light of experimental results represented in the classical diagram of combustion regime. The present analysis confirms that special care is required to represent and include the influence of expansion phenomena when using either RANS or LES closures to model turbulent premixed combustion. (author)

  8. Tabulation of complex chemistry based on self-similar behavior of laminar premixed flames

    SciTech Connect

    Ribert, G.; Gicquel, O.; Darabiha, N.; Veynante, D.

    2006-09-15

    Detailed mechanisms describing complex phenomena of combustion chemistry, such as flame propagation or pollutant formation, involve hundreds of species and thousands of elementary reactions and cannot be handled in practical simulations of turbulent combustion. A widely used way to reduce chemistry is to build look-up tables where chemical parameters such as reaction rates and/or species mass fractions are determined from a reduced set of coordinates (ILDM, FPI, or FGM methods). Nevertheless, these tables may require large memory spaces and nonnegligible access times, especially when running on massively parallel computers. In this work, the self-similarity behavior of laminar premixed flames is first put into evidence and then theoretically sustained. This property provides a way to reduce the size of chemical databases, especially for computations on massively parallel machines, under the FPI (flame prolongation of ILDM) framework. The database is reduced to similarity profiles for the species reaction rates (or the species mass fractions), stored together with scaling rules. This new formulation is then implemented in the PREMIX code and numerical simulations of laminar premixed flames successfully compare with full chemistry computation, validating this promising approach. (author)

  9. Understanding Combustion Processes Through Microgravity Research

    NASA Technical Reports Server (NTRS)

    Ronney, Paul D.

    1998-01-01

    A review of research on the effects of gravity on combustion processes is presented, with an emphasis on a discussion of the ways in which reduced-gravity experiments and modeling has led to new understanding. Comparison of time scales shows that the removal of buoyancy-induced convection leads to manifestations of other transport mechanisms, notably radiative heat transfer and diffusional processes such as Lewis number effects. Examples from premixed-gas combustion, non-premixed gas-jet flames, droplet combustion, flame spread over solid and liquid fuels, and other fields are presented. Promising directions for new research are outlined, the most important of which is suggested to be radiative reabsorption effects in weakly burning flames.

  10. Turbulent Premixed Flames in Microgravity

    NASA Technical Reports Server (NTRS)

    Menon, Suresh

    1996-01-01

    The experimental cold-flow facility is now full operational and is currently being used to obtain baseline turbulence data in a Couette flow. The baseline turbulence data is necessary to confirm the capability of the chosen device to generate and maintain the required turbulence intensity. Subsequent reacting flow studies will assume that a similar turbulent flow field exists ahead of the premixed flame. Some modifications and refinements had to be made to enable accurate measurements. It consists of two rollers, one (driven by a motor) which drives a continuous belt and four smaller rollers used to set the belt spacing and tension to minimize belt flutter. The entire assemble is enclosed in a structure that has the dimensions to enable future drop tower experiments of the hot facility. All critical dimensions are the same as the original plans except for the pulley ratio which has been changed to enable a wider operating regime in terms of the Reynolds number. With the current setup, Reynolds numbers as low as 100 and as high as 14,000 can be achieved. This is because the in-between belt spacing can be varied from 1 cm to 7.6 cm, and the belt speed can be accurately varied from .15 m/sec to 3.1 m/sec.

  11. Computational/experimental studies of isolated, single component droplet combustion

    NASA Technical Reports Server (NTRS)

    Dryer, Frederick L.

    1993-01-01

    Isolated droplet combustion processes have been the subject of extensive experimental and theoretical investigations for nearly 40 years. The gross features of droplet burning are qualitatively embodied by simple theories and are relatively well understood. However, there remain significant aspects of droplet burning, particularly its dynamics, for which additional basic knowledge is needed for thorough interpretations and quantitative explanations of transient phenomena. Spherically-symmetric droplet combustion, which can only be approximated under conditions of both low Reynolds and Grashof numbers, represents the simplest geometrical configuration in which to study the coupled chemical/transport processes inherent within non-premixed flames. The research summarized here, concerns recent results on isolated, single component, droplet combustion under microgravity conditions, a program pursued jointly with F.A. Williams of the University of California, San Diego. The overall program involves developing and applying experimental methods to study the burning of isolated, single component droplets, in various atmospheres, primarily at atmospheric pressure and below, in both drop towers and aboard space-based platforms such as the Space Shuttle or Space Station. Both computational methods and asymptotic methods, the latter pursued mainly at UCSD, are used in developing the experimental test matrix, in analyzing results, and for extending theoretical understanding. Methanol, and the normal alkanes, n-heptane, and n-decane, have been selected as test fuels to study time-dependent droplet burning phenomena. The following sections summarizes the Princeton efforts on this program, describe work in progress, and briefly delineate future research directions.

  12. Flamelet Model Application for Non-Premixed Turbulent Combustion

    NASA Technical Reports Server (NTRS)

    Secundov, A.; Bezgin, L.; Buriko, Yu.; Guskov, O.; Kopchenov, V.; Laskin, I.; Lomkov, K.; Tshepin, S.; Volkov, D.; Zaitsev, S.

    1996-01-01

    The current Final Report contains results of the study which was performed in Scientific Research Center 'ECOLEN' (Moscow, Russia). The study concerns the development and verification of non-expensive approach for modeling of supersonic turbulent diffusion flames based on flamelet consideration of the chemistry/turbulence interaction (FL approach). Research work included: development of the approach and CFD tests of the flamelet model for supersonic jet flames; development of the simplified procedure for solution of the flamelet equations based on partial equilibrium chemistry assumption; study of the flame ignition/extinction predictions provided by flamelet model. The performed investigation demonstrated that FL approach allowed to describe satisfactory main features of supersonic H 2/air jet flames. Model demonstrated also high capabilities for reduction of the computational expenses in CFD modeling of the supersonic flames taking into account detailed oxidation chemistry. However, some disadvantages and restrictions of the existing version of approach were found in this study. They were: (1) inaccuracy in predictions of the passive scalar statistics by our turbulence model for one of the considered test cases; and (2) applicability of the available version of the flamelet model to flames without large ignition delay distance only. Based on the results of the performed investigation, we formulated and submitted to the National Aeronautics and Space Administration our Project Proposal for the next step research directed toward further improvement of the FL approach.

  13. Flamelet mathematical models for non-premixed laminar combustion

    SciTech Connect

    Carbonell, D.; Perez-Segarra, C.D.; Oliva, A.; Coelho, P.J.

    2009-02-15

    Detailed numerical calculations based on the solution of the full transport equations have been compared with flamelet calculations in order to analyse the flamelet concept for laminar diffusion flames. The goal of this work is to study the interactive (Lagrangian Flamelet Model and Interactive Steady Flamelet Model), and non-interactive (Steady Flamelet Model and Enthalpy Defect Flamelet Model) flamelet models considering both differential diffusion and non-differential diffusion situations, and adiabatic and non-adiabatic conditions. Moreover, a new procedure has been employed to obtain enthalpy defects in the flamelet library, the application of which has been found to be encouraging. The effect of using in-situ, local or stoichiometric scalar dissipation rate conditions, and also the effect of using local or stoichiometric conditions to evaluate the flamelet-like time has been analysed. To improve slow species predictions using the non-interactive models, their transport equations are solved with the reaction terms calculated from the flamelet library, also considering local or stoichiometric conditions in the so-called Extended Flamelet Models. (author)

  14. Degree of vaporization using an airblast type fuel injector for a premixed-prevaporized combustor

    NASA Technical Reports Server (NTRS)

    Tacina, R. R.

    1978-01-01

    Vaporization data are presented which could be useful in designing premixed-prevaporized fuel preparation systems for gas turbine combustors. Lean, premixed-prevaporized combustion systems are being developed because they operate with low flame temperatures and, therefore, produce low levels of nitrogen oxides. Parametric tests of the effect of inlet air temperature, length (residence time), reference velocity, pressure and fuel-air ratio on the degree of vaporization are reported. Jet A and Diesel no. 2 fuel were tested. A formula is provided which shows the effect of inlet air temperature, residence time, reference velocity, and pressure on the degree of vaporization for a constant fuel-air ratio of 0.020. The results of the effect of inlet air temperature on the degree of vaporization using Jet A and Diesel no. 2 are nearly identical.

  15. Consistent flamelet modeling of differential molecular diffusion for turbulent non-premixed flames

    NASA Astrophysics Data System (ADS)

    Wang, Haifeng

    2016-03-01

    Treating differential molecular diffusion correctly and accurately remains as a great challenge to the modeling of turbulent non-premixed combustion. The aim of this paper is to develop consistent modeling strategies for differential molecular diffusion in flamelet models. Two types of differential molecular diffusion models are introduced, linear differential diffusion models and nonlinear differential diffusion models. A multi-component turbulent mixing layer problem is analyzed in detail to gain insights into differential molecular diffusion and its characteristics, particularly the dependence of differential molecular diffusion on the Reynolds number and the Lewis number. These characteristics are then used to validate the differential molecular diffusion models. Finally, the new models are applied to the modeling of a series of laboratory-scale turbulent non-premixed jet flames with different Reynolds number (Sandia Flames B, C, and D) to further assess the models' performance.

  16. Effects of coal combustion and gasification upon lung structure and function. Quarterly progress report, March 12, 1981

    SciTech Connect

    Not Available

    1981-01-01

    The overall objective of the proposed research is to correlate both structural and functional alterations in cells and tissues of the lung brought about by exposure to fluidized bed combustion and fixed bed gasification effluents and reagent grade oxides of metals known to be associated with coal combustion and gasification.

  17. Nonlinear hydrodynamic and thermoacoustic oscillations of a bluff-body stabilised turbulent premixed flame

    NASA Astrophysics Data System (ADS)

    Lee, Chin Yik; Li, Larry Kin Bong; Juniper, Matthew P.; Cant, Robert Stewart

    2016-01-01

    Turbulent premixed flames often experience thermoacoustic instabilities when the combustion heat release rate is in phase with acoustic pressure fluctuations. Linear methods often assume a priori that oscillations are periodic and occur at a dominant frequency with a fixed amplitude. Such assumptions are not made when using nonlinear analysis. When an oscillation is fully saturated, nonlinear analysis can serve as a useful avenue to reveal flame behaviour far more elaborate than period-one limit cycles, including quasi-periodicity and chaos in hydrodynamically or thermoacoustically self-excited system. In this paper, the behaviour of a bluff-body stabilised turbulent premixed propane/air flame in a model jet-engine afterburner configuration is investigated using computational fluid dynamics. For the frequencies of interest in this investigation, an unsteady Reynolds-averaged Navier-Stokes approach is found to be appropriate. Combustion is represented using a modified laminar flamelet approach with an algebraic closure for the flame surface density. The results are validated by comparison with existing experimental data and with large eddy simulation, and the observed self-excited oscillations in pressure and heat release are studied using methods derived from dynamical systems theory. A systematic analysis is carried out by increasing the equivalence ratio of the reactant stream supplied to the premixed flame. A strong variation in the global flame structure is observed. The flame exhibits a self-excited hydrodynamic oscillation at low equivalence ratios, becomes steady as the equivalence ratio is increased to intermediate values, and again exhibits a self-excited thermoacoustic oscillation at higher equivalence ratios. Rich nonlinear behaviour is observed and the investigation demonstrates that turbulent premixed flames can exhibit complex dynamical behaviour including quasiperiodicity, limit cycles and period-two limit cycles due to the interactions of various

  18. Intermittent features of inertial particle distributions in turbulent premixed flames

    NASA Astrophysics Data System (ADS)

    Battista, F.; Picano, F.; Troiani, G.; Casciola, C. M.

    2011-12-01

    Clustering is widely observed in many turbulent flows, where it results from the inability of finite inertia particles to comply with the different time scales, which characterize a turbulent field. Depending on their inertia, particles are found to be instantaneously organized in clusters, whose size depends on the Kolmogorov-Stokes number and which presumably form as a consequence of particle ejection from persistent vortical structures. In reacting flows, the abrupt acceleration of the fluid across the thin flame front due to combustion adds new and unexpected features. The particles follow such acceleration with a certain time lag which, coupled with the flame front fluctuations, gives rise to an entirely different mechanism of cluster formation. As suggested in previous studies, a possible indicator of this preferential localization is the so-called clustering index, quantifying the departure of the actual particle arrangement from the Poissonian distribution. Most of the clustering is found in the flame brush region, where it cannot be explained by the standard arguments used in cold flows. Actually, the effect is significant also for very light particles, where the simple model we propose, based on the Bray-Moss-Libby formalism, is able to account for most of the deviation from the Poissonian. When the particle inertia increases, the effect becomes larger and it is found to persist well within the region of the burned gases. The observed clustering is confirmed by a more precise analysis in terms of a generalization of the radial distribution function to inhomogeneous, anisotropic flows. The results taken from a direct numerical simulation with single step kinetics favorably compare with experiments on a premixed Bunsen turbulent flame. The present findings are expected to be of some relevance for the plenty of applications dealing with particles in presence of combustion, e.g., liquid droplet swarms for combustion temperature control, soot dynamics, or

  19. Flame propagation in partially premixed conditions

    NASA Astrophysics Data System (ADS)

    Ruetsch, G.; Poinsot, T.; Veynante, D.; Trouvé, A.

    1996-11-01

    Turbulent flame propagation is studied under inhomogenously premixed conditions via data from direct numerical simulations. Departures from the premixed case are studied using four different configurations, ranging from one dimensional unsteady flames to turbulent three-dimensional simulations. Simulations are performed in these cases with various values of the mean equivalence ratio, fluctuations about the mean equivlalence ratio, correlation length scales, and probability denisty functions of the mixture composition. Propagation characteristics are described in terms of the flamelet approach, where the the main contribution of partial premixing on flame propagation is due to flame wrinkling relative to modification of the mean flamelet structure. This behavior is consistent over a broad range of conditions, with the exception being extreme departures from stoichiometric conditions where flamability limits are exceeded and flame quenching is observed.

  20. A coal-fired combustion system for industrial process heating applications. Quarterly technical progress report, October 1992--December 1992

    SciTech Connect

    Not Available

    1993-01-29

    This advanced combustion system research program is for the development of innovative coal-fired process heaters which can be used for high temperature melting, smelting and waste vitrification processes. The process heater concepts to be developed are based on advanced glass melting and ore smelting furnaces developed and patented by Vortec Corporation. The process heater systems to be developed have multiple use applications; however, the Phase III research effort is being focused on the development of a process heater system to be used for producing value added vitrified glass products from boiler/incinerator ashesand industrial wastes. The primary objective of the Phase III project is to develop and integrate all the system components, from fuel through total system controls, and then test the complete system in order to evaluate its potential marketability. During the current reporting period, a majority of the effort was spent relining the separator/reservoir and the cyclone melter. The relinings were completed, the cyclonemelter was reinstalled, and the test system was returned to operational status. The wet ESP was delivered and placed on its foundation. The focus during the upcoming months will be completing the integration ofthe wet ESP and conducting the first industrial proof-of-concept test. The other system modifications are well underway with the designs of the recuperator installation and the batch/coal feed system progressing smoothly. The program is still slightly behind the original schedule but it is anticipated that it will be back on schedule by the end of the year. The commercialization planning is continuing with the identification of seven potential near-term commercial demonstration opportunities.

  1. A coal-fired combustion system for industrial process heating applications. Quarterly technical progress report, July 1992--September 1992

    SciTech Connect

    Not Available

    1992-10-30

    This advanced combustion system research program is for the development of innovative coal-fired process heaters which can be used for high temperature melting, smelting and waste vitrification processes. The process heater concepts to be developed are based on advanced glass melting and ore smelting furnaces developed and patented by Vortec Corporation. The process heater systems to be developed have multiple use applications; however, the Phase III research effort is being focused on the development of a process heater system to be used for producing value added vitrified glass products from boiler/incinerator ashesand industrial wastes. ne primary objective of the Phase III project is to develop and integrate all the system components, from fuel through total system controls, and then test the complete system in order toevaluate its potential marketability. During the current reporting period, three preliminary coal-fired tests were successfully completed. These tests used industrial boiler flyash, sewer sludge ash, and waste glass collet as feedstocks. The coal-fired ash vitrification tests are considered near term potential commercial applications of the CMS technology. The waste glass cullet provided necessary dam on the effect of coal firing with respect to vitrified product oxidation state. Engineering and design activities in support of the Phase III proof of concept are continuing, and modifications to the existing test system configuration to allow performance of the proof-of-concept tests are continuing. The economic evaluation of commercial scale CMS processes is continuing. Preliminary designs for 15, 25, 100 and 400 ton/day systems are in progress. This dam will serve as input data to the life cycle cost analysis which will be-an integral part of the CMS commercialization plan.

  2. Colorimetric determination of selenium in mineral premixes .

    PubMed

    Hurlbut, J A; Burkepile, R G; Geisler, C A; Kijak, P J; Rummel, N G

    1997-01-01

    A method is described for determination of sodium selenite or sodium selenate in mineral-based premixes. It is based on the formation of intense-yellow piazselenol by Se(IV) and 3,3'-diaminobenzidine. Mineral premixes typically contain calcium carbonate as a base material and magnesium carbonate, silicon dioxide, and iron(III) oxide as minor components or additives. In this method, the premix is digested briefly in nitric acid, diluted with water, and filtered to remove any Iron(III) oxide. Ethylenediaminetetraacetic acid and HCl are added to the filtrate, which is heated to near boiling for 1 h to convert any selenate to selenite. After heating, the solution is buffered between pH 2 and 3 with NaOH and formic acid and treated with NH2OH and EDTA; any Se present forms a complex with 3,3'-diaminobenzidine at 60 degrees C. The solution is made basic with NH4OH, and the piazselenol is extracted into toluene. The absorbance of the complex in dried toluene is measured at 420 nm. The method was validated independently by 2 laboratories. Samples analyzed included calcium carbonate fortified with 100, 200, and 300 micrograms Se in the form of sodium selenite or sodium selenate, a calcium carbonate premix containing sodium selenite, a calcium carbonate premix containing sodium selenate, and a commercial premix; 5 replicates of each sample type were analyzed by each laboratory. Average recoveries ranged from 89 to 109% with coefficients of variation from 1.2 to 13.6%. PMID:9241835

  3. Progress Toward Affordable High Fidelity Combustion Simulations Using Filtered Density Functions for Hypersonic Flows in Complex Geometries

    NASA Technical Reports Server (NTRS)

    Drozda, Tomasz G.; Quinlan, Jesse R.; Pisciuneri, Patrick H.; Yilmaz, S. Levent

    2012-01-01

    Significant progress has been made in the development of subgrid scale (SGS) closures based on a filtered density function (FDF) for large eddy simulations (LES) of turbulent reacting flows. The FDF is the counterpart of the probability density function (PDF) method, which has proven effective in Reynolds averaged simulations (RAS). However, while systematic progress is being made advancing the FDF models for relatively simple flows and lab-scale flames, the application of these methods in complex geometries and high speed, wall-bounded flows with shocks remains a challenge. The key difficulties are the significant computational cost associated with solving the FDF transport equation and numerically stiff finite rate chemistry. For LES/FDF methods to make a more significant impact in practical applications a pragmatic approach must be taken that significantly reduces the computational cost while maintaining high modeling fidelity. An example of one such ongoing effort is at the NASA Langley Research Center, where the first generation FDF models, namely the scalar filtered mass density function (SFMDF) are being implemented into VULCAN, a production-quality RAS and LES solver widely used for design of high speed propulsion flowpaths. This effort leverages internal and external collaborations to reduce the overall computational cost of high fidelity simulations in VULCAN by: implementing high order methods that allow reduction in the total number of computational cells without loss in accuracy; implementing first generation of high fidelity scalar PDF/FDF models applicable to high-speed compressible flows; coupling RAS/PDF and LES/FDF into a hybrid framework to efficiently and accurately model the effects of combustion in the vicinity of the walls; developing efficient Lagrangian particle tracking algorithms to support robust solutions of the FDF equations for high speed flows; and utilizing finite rate chemistry parametrization, such as flamelet models, to reduce

  4. Chaos in an imperfectly premixed model combustor

    SciTech Connect

    Kabiraj, Lipika Saurabh, Aditya; Paschereit, Christian O.; Karimi, Nader; Sailor, Anna; Mastorakos, Epaminondas; Dowling, Ann P.

    2015-02-15

    This article reports nonlinear bifurcations observed in a laboratory scale, turbulent combustor operating under imperfectly premixed mode with global equivalence ratio as the control parameter. The results indicate that the dynamics of thermoacoustic instability correspond to quasi-periodic bifurcation to low-dimensional, deterministic chaos, a route that is common to a variety of dissipative nonlinear systems. The results support the recent identification of bifurcation scenarios in a laminar premixed flame combustor (Kabiraj et al., Chaos: Interdiscip. J. Nonlinear Sci. 22, 023129 (2012)) and extend the observation to a practically relevant combustor configuration.

  5. A coupled multi-block solution procedure for spray combustion in complex geometries

    NASA Technical Reports Server (NTRS)

    Chen, Kuo-Huey; Shuen, Jian-Shun

    1993-01-01

    Turbulent spray-combusting flow in complex geometries is presently treated by a coupled implicit procedure that employs finite-rate chemistry and real gas properties for combustion, as well as the stochastic separated model for spray and a multiblock treatment for complex geometries. Illustrative numerical tests conducted encompass a steady-state nonreacting backward-facing step flow, a premixed single-phase combustion flow, and spray combustion flow in a gas turbine combustor.

  6. Multiple mapping conditioning for flames with partial premixing

    SciTech Connect

    Kronenburg, A.; Cleary, M.J.

    2008-10-15

    Fully closed multiple mapping conditioning (MMC) is used to model partially premixed flames in homogeneous, isotropic decaying turbulence where the partial premixing is caused by local extinction and reignition phenomena. Two reference variables that represent mixing and reaction progress, such as mixture fraction and sensible enthalpy, are used to emulate turbulent scalar fluctuations. Local extinction is achieved by a priori coupling between scalar dissipation and temperature fluctuations via a correlation function that is based on the conditionally averaged sensible enthalpy at stoichiometric composition. The proposed model provides closures for the joint PDF of mixture fraction and sensible enthalpy, for the conditional variance equation of a reactive scalar, and for the doubly conditioned dissipation terms. Model results are compared with DNS in three flame cases with varying levels of local extinction, up to global extinction. The joint PDF predicted by MMC is in fair agreement with DNS. It constitutes, however, a clear improvement over conventional models using preassumed distribution functions for the PDFs. The doubly conditioned dissipation terms are modeled well and the results for all major chemical species are in good agreement with DNS. Predictions for intermediate species are also satisfactory. (author)

  7. Development of a lean premixed burner for hydrogen utilization

    SciTech Connect

    Keller, J.O.

    1996-10-01

    The long-term mandate of the hydrogen program is to develop the technologies needed to establish a hydrogen economy. Although a hydrogen fueled automobile has been established as a demonstration project, there are at least three other end use sectors that are recognized by the H{sub 2} program and that are addressed by this project. These end uses are: (1) power generation from stationary turbines, (2) generation of process heat or steam, and (3) commercial and residential direct use applications. Eliminating carbon from the fuel will remove carbon containing species from the emissions, however, NO{sub x} resulting from thermal NO production cannot be ignored. Thermal NO production is minimized by reducing the peak combustion temperature and the residence time at the peak temperature. NO can be reduced to extremely low levels (a few ppm) by operating sufficiently lean to reduce the peak combustion temperatures below 1700 to 1800 K. The objectives for this project are to: (1) develop an environmentally benign and safe burner operating on hydrogen in a lean premixed mode, (2) provide a facility in which fundamental investigations can be performed to support other programs.

  8. Analysis of non-premixed turbulent reacting flows

    NASA Technical Reports Server (NTRS)

    Leonard, Andy D.; Hill, James C.

    1987-01-01

    Studies of chemical reactions occurring in turbulent flows are important in the understanding of combustion and other applications. Current numerical methods are limited in their applications due to the numerical resolution required to completely capture all length scales, but, despite the fact that realistic combustion cannot be solved completely, numerical simulations can be used to give insight into the interaction between the processes of turbulence and chemical reaction. The objective was to investigate the effects of turbulent motion on the effects of chemical reaction to gain some insight on the interaction of turbulence, molecular diffusion, and chemical reaction to support modeling efforts. A direct turbulence simulation spectral code was modified to include the effects of chemical reaction and applied to an initial value problem of chemical reaction between non-premixed species. The influence of hydrodynamics on the instantaneous structure of the reaction was investigated. The local scalar dissipation rates and the local reaction rates were examined to determine the influence of vorticity or rate of strain on the reaction and the structure of the scalar field.

  9. Rayleigh-Taylor Instability in non-premixed reacting flames.

    NASA Astrophysics Data System (ADS)

    Attal, Nitesh; Ramaprabhu, Praveen

    2015-11-01

    The Rayleigh-Taylor instability (RTI) occurs at a perturbed interface between fluids of different densities when a light fluid pushes a heavier fluid. The mixing driven by RTI affects several physical phenomena, such as Inertial Confinement Fusion, Supernovae detonation, centrifugal combustors and liquid rocket engines. The RTI in such flows is often coupled with chemical/nuclear reactions that may form complex density stratifications in the form of flames or ablative layers. We investigate such a non-premixed fuel-air interface subject to a constant acceleration and developing under the influence of chemical reactions using high-resolution, Navier-Stokes simulations. The H2 fuel is diluted with N2 to vary the density difference across the interface in thermal equilibrium (at 1000K). The intervening layer between fuel and air is subject to exothermic combustion reactions to form a flame. Following combustion, initially unstable fuel-air interfaces at an Atwood number (At) <0.5, transform into stable (fuel-flame) and unstable (flame-air) interfaces. We report on interfaces (At = 0.2 and 0.6) with single wavelength, sinusoidal perturbations and a broadband spectrum of multimode perturbations.

  10. Stationary premixed flames in spherical and cylindrical geometries

    NASA Technical Reports Server (NTRS)

    Ronney, P. D.; Whaling, K. N.; Abbud-Madrid, A.; Gatto, J. L.; Pisowiscz, V. L.

    1994-01-01

    Stationary source-free spherical flames ('flame balls') in premixed combustible gases were studied by employing low-gravity (micro-g) environments in a drop tower and an aircraft flying parabolic trajectories to diminish the impact of buoyancy-induced convective flow. Flame balls were found in all mixture families tested when: (1) the Lewis number Le of the deficient reactant was sufficiently low; and (2) the compositions were sufficiently close to the flammability limits. Probably as a consequence of the reduction in buoyant convection, the flammability limits at micro-g were significantly more dilute than those at Earth gravity; for example, 3.35% H2 vs 4.0% H2 in lean H2-air mixtures. By comparison with analytical and computational models, it is inferred that the phenomenon is probably related to diffusive-thermal effects in low-Le mixtures in conjunction with flame-front curvature and radiative heat losses from the combustion products. The chemical reaction mechanism appears to play no qualitative role. In the aircraft experiments, the gravity levels (approximately equal 10(exp -2)g(sub 0)) were found to cause noticeable motion of flame balls due to buoyancy, which in turn influenced the behavior of flame balls. At these g levels, a new type of transient, nearly cylindrical flame structure, termed 'flame strings,' was observed.

  11. Torch ignition: Ideal for lean burn premixed-charge engines

    SciTech Connect

    Mavinahally, N.S. ); Assanis, D.N. ); Govinda Mallan, K.R.; Gopalakrishnan, K.V. )

    1994-10-01

    Sluggish flame initiation and propagation, and even potential misfiring, become major problems with lean-fueled, premixed-charge, spark-ignited engines. This work studies torch ignition as a means for improving combustion, fuel economy, and emissions of a retrofitted, large combustion chamber with nonideal spark plug location. A number of alternative configurations, employing different torch chamber designs, spark-plug locations, and materials, were tested under full-load and part-load conditions. Results indicate a considerable extension of the lean operating limit of the engine, especially under part-load conditions. In addition, torch ignition can lead to substantial thermal efficiency gains for either leaner or rich air-fuel ratios than the optimum for the conventional ignition system. On the richer side, in particular, the torch-ignited engine is capable of operating at maximum brake torque spark timings, rather than compromised, knock-limited spark timings used with conventional ignition. This translates into thermal efficiency improvements as high as 8% at an air-fuel ratio of 20:1 and full load.

  12. A ring stabilizer for lean premixed turbulent flames

    SciTech Connect

    Johnson, M.R.; Kostiuk, L.W.; Cheng, R.K.

    1998-08-01

    In previous experiments on conical flame behavior in microgravity, which were conducted in drop-towers and in airplanes, the use of a pilot flame was not an option. To permit combustion of stable lean premixed conical flames without a pilot, a ring stabilizer was developed. Although similar types of bluff-body stabilization have been used in the past, the ring stabilizer is somewhat unique. It is designed to fit inside the burner exit port and has demonstrated to be highly effective in stabilizing flames over a very wide range of conditions (including ultra-lean flames at high flow-rates) without adversely affecting flame emissions. Unlike a simple rod stabilizer or a stagnation flame system, the benefit of having the stabilizer conform to the burner port is that there is very little leakage of the unburned fuel. The purpose of this brief communication is to offer this simple and highly useful device to the combustion research community. Presented are highlights of a parametric study that measured the stabilization limits and pollutant emissions of several different rings, and demonstrated their potential for use in practical systems.

  13. Response of flame thickness and propagation speed under intense turbulence in spatially developing lean premixed methane–air jet flames

    DOE PAGES

    Sankaran, Ramanan; Hawkes, Evatt R.; Yoo, Chun Sang; Chen, Jacqueline H.

    2015-06-22

    Direct numerical simulations of three-dimensional spatially-developing turbulent Bunsen flames were performed at three different turbulence intensities. We performed these simulations using a reduced methane–air chemical mechanism which was specifically tailored for the lean premixed conditions simulated here. A planar-jet turbulent Bunsen flame configuration was used in which turbulent preheated methane–air mixture at 0.7 equivalence ratio issued through a central jet and was surrounded by a hot laminar coflow of burned products. The turbulence characteristics at the jet inflow were selected such that combustion occured in the thin reaction zones (TRZ) regime. At the lowest turbulence intensity, the conditions fall onmore » the boundary between the TRZ regime and the corrugated flamelet regime, and progressively moved further into the TRZ regime by increasing the turbulent intensity. The data from the three simulations was analyzed to understand the effect of turbulent stirring on the flame structure and thickness. Furthermore, statistical analysis of the data showed that the thermal preheat layer of the flame was thickened due to the action of turbulence, but the reaction zone was not significantly affected. A global and local analysis of the burning velocity of the flame was performed to compare the different flames. Detailed statistical averages of the flame speed were also obtained to study the spatial dependence of displacement speed and its correlation to strain rate and curvature.« less

  14. Response of flame thickness and propagation speed under intense turbulence in spatially developing lean premixed methane–air jet flames

    SciTech Connect

    Sankaran, Ramanan; Hawkes, Evatt R.; Yoo, Chun Sang; Chen, Jacqueline H.

    2015-06-22

    Direct numerical simulations of three-dimensional spatially-developing turbulent Bunsen flames were performed at three different turbulence intensities. We performed these simulations using a reduced methane–air chemical mechanism which was specifically tailored for the lean premixed conditions simulated here. A planar-jet turbulent Bunsen flame configuration was used in which turbulent preheated methane–air mixture at 0.7 equivalence ratio issued through a central jet and was surrounded by a hot laminar coflow of burned products. The turbulence characteristics at the jet inflow were selected such that combustion occured in the thin reaction zones (TRZ) regime. At the lowest turbulence intensity, the conditions fall on the boundary between the TRZ regime and the corrugated flamelet regime, and progressively moved further into the TRZ regime by increasing the turbulent intensity. The data from the three simulations was analyzed to understand the effect of turbulent stirring on the flame structure and thickness. Furthermore, statistical analysis of the data showed that the thermal preheat layer of the flame was thickened due to the action of turbulence, but the reaction zone was not significantly affected. A global and local analysis of the burning velocity of the flame was performed to compare the different flames. Detailed statistical averages of the flame speed were also obtained to study the spatial dependence of displacement speed and its correlation to strain rate and curvature.

  15. Pollutant Formation in Monodisperse Fuel Spray Combustion

    NASA Technical Reports Server (NTRS)

    Cernansky, N. P.; Sarv, H.

    1983-01-01

    The combustion of liquid sprays represents an extremely important class of combustion processes. In the transition region, encompassing droplet sizes in the range of 25-80 micron diameter, the mixing and evaporation processes are both incomplete at the flame front and burning occurs in a combined diffusive and premixed fashion. Under these conditions, the relative importance of heterogeneous and homogeneous effects in dominating the combustion process is switched and gives rise to a number of interesting phenomena. NO (sub x) formation in monodisperse spray combustion was investigated with the following specific objectives: (1) to quantitatively determine the effect of droplet size, number density, etc. on NO sub x formation in monodisperse fuel spray combustion; and (2) to isolate the important physical and chemical phenomena in NO sub x formation in these combustion systems.

  16. Catalytic combustion of residual fuels

    NASA Technical Reports Server (NTRS)

    Bulzan, D. L.; Tacina, R. R.

    1981-01-01

    A noble metal catalytic reactor was tested using two grades of petroleum derived residual fuels at specified inlet air temperatures, pressures, and reference velocities. Combustion efficiencies greater than 99.5 percent were obtained. Steady state operation of the catalytic reactor required inlet air temperatures of at least 800 K. At lower inlet air temperatures, upstream burning in the premixing zone occurred which was probably caused by fuel deposition and accumulation on the premixing zone walls. Increasing the inlet air temperature prevented this occurrence. Both residual fuels contained about 0.5 percent nitrogen by weight. NO sub x emissions ranged from 50 to 110 ppm by volume at 15 percent excess O2. Conversion of fuel-bound nitrogen to NO sub x ranged from 25 to 50 percent.

  17. Flowfield characterization of a piloted lean premixed injector by particle image velocimetry

    NASA Astrophysics Data System (ADS)

    Berdanier, Catherine G. P.

    Limiting atmospheric pollution, especially nitrous oxides, is an important endeavor for aviation technology companies. Technology-driving regulations from the International Civil Aviation Organization's (ICAO) Committee of Aviation Environmental Protection (CAEP) standards spur the combustion research and development community to find innovative engine technologies to decrease emissions in the coming years. As engine technologies are developed, testing is necessary to verify combustion models and expected flow patterns. Optical diagnostics provide a unique opportunity to visualize flowfields in complex practical combustor systems. For this thesis, Particle Image Velocimetry (PIV) was employed to characterize the flowfield in a piloted lean premixed injector under non-combusting conditions. Planes of PIV data were acquired at five spanwise locations and two streamwise locations, at two different pressure conditions in order to characterize the flowfields and structures throughout the optically accessible flowpath. Average velocity maps and time-resolved vector fields at these planes were analyzed for this thesis.

  18. Demonstration of a burner for the investigation of partially premixed low-temperature flames

    SciTech Connect

    Struckmeier, U.; Lucassen, A.; Kohse-Hoeinghaus, K.; Hansen, N.; Wada, T.; Peters, N.

    2010-10-15

    A burner, which stabilizes near-one-dimensional low-temperature flames at atmospheric pressure, was designed to access the combustion regime near 1500 K for quantitative species diagnostics. Combustion temperatures between 1300 and 1800 K in argon-diluted methane-oxygen flames were achieved by preheating the burner and adapting the inert gas flow. Mass spectrometry with electron ionization was used to determine mole fractions profiles of reactants, products, and intermediates. Combustion parameters were varied including stoichiometry, diluent mole fraction and preheat temperature. Mole fraction profiles resemble those taken in regular premixed flat flames. A number of C{sub 1}- and C{sub 2}-intermediates as well as some oxygenated species were identified. Higher-mass species (m/z > 42) were not detected in the low-temperature methane-oxygen flames which contain 90% argon in the cold gases. (author)

  19. Space Station Freedom combustion research

    NASA Technical Reports Server (NTRS)

    Faeth, G. M.

    1992-01-01

    Extended operations in microgravity, on board spacecraft like Space Station Freedom, provide both unusual opportunities and unusual challenges for combustion science. On the one hand, eliminating the intrusion of buoyancy provides a valuable new perspective for fundamental studies of combustion phenomena. On the other hand, however, the absence of buoyancy creates new hazards of fires and explosions that must be understood to assure safe manned space activities. These considerations - and the relevance of combustion science to problems of pollutants, energy utilization, waste incineration, power and propulsion systems, and fire and explosion hazards, among others - provide strong motivation for microgravity combustion research. The intrusion of buoyancy is a greater impediment to fundamental combustion studies than to most other areas of science. Combustion intrinsically heats gases with the resulting buoyant motion at normal gravity either preventing or vastly complicating measurements. Perversely, this limitation is most evident for fundamental laboratory experiments; few practical combustion phenomena are significantly affected by buoyancy. Thus, we have never observed the most fundamental combustion phenomena - laminar premixed and diffusion flames, heterogeneous flames of particles and surfaces, low-speed turbulent flames, etc. - without substantial buoyant disturbances. This precludes rational merging of theory, where buoyancy is of little interest, and experiments, that always are contaminated by buoyancy, which is the traditional path for developing most areas of science. The current microgravity combustion program seeks to rectify this deficiency using both ground-based and space-based facilities, with experiments involving space-based facilities including: laminar premixed flames, soot processes in laminar jet diffusion flames, structure of laminar and turbulent jet diffusion flames, solid surface combustion, one-dimensional smoldering, ignition and flame

  20. Stabilization of premixed flames on rotating Bunsen burners

    SciTech Connect

    Cha, J.M.; Sohrab, S.H.

    1996-09-01

    The effect of rotation on stabilization of methane-air premixed Bunsen flame sis experimentally investigated. Both the flame blowoff and flashback contours are determined in the fuel mole fraction versus Reynolds number plane (X{sub F}-Re) with the rotational Reynolds number Re{sub 4} as a parameter. It is found that rotation of the gas increases the flame stabilization area A{sub s} = A{sub B} {minus} A{sub F} defined as the difference between the flame blowoff A{sub B} and flashback A{sub F} areas in the (X{sub F}-Re) plane. The flame stabilization efficiency is defined as {eta}{sub s} = 1 {minus} A{sub F}/A{sub B} that approaches unity in either A{sub B} {yields} {infinity} or A{sub F} {yields} 0 limit. The experimental results suggest that rotation decreases the flame stabilization efficiency. However, rotation is found to substantially increase the flame stabilization coefficient defined as {beta}{sub s} = A{sub s}/A{sub st}, where A{sub st} is the stabilization area of the standard nonrotating burner. The parameters {eta}{sub s} and {beta}{sub s} may be useful in combustion technology for quantitative evaluation of the stabilization performance of different types of flame holders. In addition, the local hydrodynamics near the center of rotating Bunsen burner is simulated by investigating stabilization of planar laminar premixed flames on rotating porous disks with uniform surface velocity. Physical concepts concerning mechanisms of flame stabilization are discussed in terms of three important parameters namely the translational Reynolds number Re, the rotation Reynolds number Re{sub r}, and the fuel mole fraction X{sub F}. The results of the experimental findings are shown to be in accordance with prior theoretical investigation.

  1. Premixed-Gas Flame Propagation in Hele-Shaw Cells

    NASA Technical Reports Server (NTRS)

    Sharif, J.; Abid, M.; Ronney, P. D.

    1999-01-01

    It is well known that buoyancy and thermal expansion affect the propagation ra and shapes of premixed gas flames. The understanding of such effects is complicated by the large density ratio between the reactants and products, which induces a baroclinic production of vorticity due to misalignment of density and pressure gradients at the front, which in turn leads to a complicated multi-dimensional flame/flow interaction. The Hele-Shaw cell, i.e., the region between closely-spaced flat parallel plates, is probably the simplest system in which multi-dimensional convection is presents consequently, the behavior of fluids in this system has been studied extensively (Homsy, 1987). Probably the most important characteristic of Hele-Shaw flows is that when the Reynolds number based on gap width is sufficiently small, the Navier-Stokes equations averaged over the gap reduce to a linear relation, namely a Laplace equation for pressure (Darcy's law). In this work, flame propagation in Hele-Shaw cells is studied to obtain a better understanding of buoyancy and thermal expansion effects on premixed flames. This work is also relevant to the study of unburned hydrocarbon emissions produced by internal combustion engines since these emissions are largely a result of the partial burning or complete flame quenching in the narrow, annular gap called the "crevice volume" between the piston and cylinder walls (Heywood, 1988). A better understanding of how flames propagate in these volumes through experiments using Hele-Shaw cells could lead to identification of means to reduce these emissions.

  2. Combustion of dense streams of coal particles. Quarterly progress report No. 9, August 29, 1992--November 28, 1992

    SciTech Connect

    Annamalai, K.

    1992-12-31

    Ignition of the high volatile isolated coal particles in vitiated environment seems to occur heterogeneously at the leading edge of the particle. Volatiles are observed to be ejected upward as jets in the direction of the convective flow but only after heterogeneous ignition. The volatiles burn in the gas phase homogeneously and form a wake flame; a black inner zone (unburned volatile) is formed (see Fig.A.3 for many common characteristics of isolated flames).Intermittent volatile ignition and combustion are observed to occur during the combustion process for a few of the isolated particle combustion experiments on high volatile non-swelling coal. The medium volatile coal particles ignite faster than the high volatile coal; but the intermittent ignition is not observed. The low volatile isolated coal particles combust in shorter time. The isolated char particles ignite at the surface of the particle heterogeneously with little volatile ejected, yet are not sufficient to form a volatile flame, resulting in a subsequent heterogeneous combustion. A group flame is formed for the two-particle arrays at closer interparticle spacing (Fig.A.4). Also, intermittent ignition does not occur for the high volatile particles when the two particles are at farther distances which suggests that radiation interaction between the particles might be occurring. However this conclusion is purely speculative. The char arrays experience heterogeneous ignition at the leading edge; combustion proceeds heterogeneously.

  3. Coal Combustion Science quarterly progress report, January--March 1993. Task 1, Coal char combustion: Task 2,, Fate of mineral matter

    SciTech Connect

    Hardesty, D.R.; Hurt, R.H.; Baxter, L.L.

    1994-02-01

    The objective of this work is to obtain insights into the mechanisms of combustion, fragmentation, and final burnout, and to use the insights to aid in the interpretation of the quantitative data generated in Subtasks 1 and 2. The initial image sequences for Illinois No. 6 coal confirm the presence of an early near-extinction process (discussed in previous reports) and the asymptotic nature of the carbon burnout process. The technique also provided important new insights into the processes of particle fragmentation and reagglomeration at high burnout. During this quarter, chemical fractionation tests on coals pulverized to different sizes were completed. These data will help us to asses the accuracy of the fuels characterizations for the purpose of interpreting inorganic release during coal devolatilization. Chemical fractionation tests on mineral species are proceeding for the same purposes, but these are not yet completed.

  4. Effect of inlet temperature and pressure on emissions from a premixing gas turbine primary zone combustor

    NASA Technical Reports Server (NTRS)

    Roffe, G.

    1976-01-01

    Experiments were conducted to determine the performance of a premixing prevaporizing gas turbine primary zone combustor design over a range of combustor inlet temperatures from 700 to 1000 K and a range of inlet pressures from 40 to 240 N/sq cm. The 1 meter long combustor could be operated at pressures up to and including 120 N/sq cm without autoignition in the premixing duct or flashback from the stabilized combustion zone. Autoignition occurred in the mixer tube at the 240 N/sq cm pressure level with an entrance temperature of 830 K and a mixer residence time of 4 msec. Measured NOx level, combustion inefficiency, and hydrocarbon emission index correlated well with adiabatic flame temperature. The NOx levels varied from approximately 0.2 to 2.0 g NO2/kg fuel at combustion inefficiencies from 4 to 0.04 percent, depending upon adiabatic flame temperature and pressure. Measured NOx levels were sensitive to pressure. Tests were made at equivalence ratios ranging from 0.35 to 0.65. The overall total pressure drop for the configuration varied slightly with reference velocity and equivalence ratio, but never exceeded 3 percent.

  5. Blowoff characteristics of bluff-body stabilized conical premixed flames with upstream spatial mixture gradients and velocity oscillations

    SciTech Connect

    Chaudhuri, Swetaprovo; Cetegen, Baki M.

    2008-06-15

    This experimental study concerns determination of blowoff equivalence ratios for lean premixed conical flames for different mixture approach velocities ranging from 5 to 16 m/s in the presence of spatial mixture gradients and upstream velocity modulation. Conical flames were anchored on a disk-shaped bluff body that was attached to a central rod in the burner nozzle. A combustible propane-air mixture flowed through a converging axisymmetric nozzle with a concentric insert, allowing radial mixture variation by tailoring the composition in the inner and outer parts of the nozzle. The radial mixture profiles were characterized near the location of the flame holder by laser Rayleigh light scattering. Additionally, a loudspeaker at the nozzle base allowed introduction of periodic velocity oscillations with an amplitude of 9% of the mean flow velocity up to a frequency of 350 Hz. The flame blowoff equivalence ratio was experimentally determined by continuously lowering the fuel flow rates and determining the flame detachment point from the flame holder. Flame detachment was detected by a rapid reduction of CH* emission from the flame base imaged by a photomultiplier detector. It was found that the flame blowoff is preceded by progressive narrowing of the flame cone for the case of higher inner jet equivalence ratios. In this case, the fuel-lean outer flow cannot sustain combustion, and clearly this is not a good way of operating a combustor. Nevertheless, the overall blowoff equivalence ratio is reduced by inner stream fuel enrichment. A possible explanation for this behavior is given based on the radial extent of the variable-equivalence-ratio mixture burning near the flame stabilization region. Fuel enrichment in the outer flow was found to have no effect on blowoff as compared to the case of uniform mixture. The results were similar for the whole range of mean flow velocities and upstream excitation frequencies. (author)

  6. Prevaporization and premixing to obtain low oxides of nitrogen in gas turbine combustors

    NASA Technical Reports Server (NTRS)

    Roffe, G.; Ferri, A.

    1975-01-01

    Tests were conducted to determine the effectiveness of prevaporization and premixing in reducing the formation of oxides of nitrogen in a gas turbine type combustor using liquid JP-5 fuel at the supersonic cruise condition. The combustor inlet temperature was 833 K (1500 R) at a pressure of 4 atmospheres and a reference velocity of 46 m/sec (150 ft/sec). An order of magnitude reduction in nitric oxide emissions was achieved. Nitric oxide emission indices as low as 0.6 gm NO2/kg fuel were measured at an equivalence ratio of 0.29 with one percent combustion inefficiency without vitiation of the mixer stream.

  7. A multipurpose reduced chemical-kinetic mechanism for methanol combustion

    NASA Astrophysics Data System (ADS)

    Fernández-Tarrazo, Eduardo; Sánchez-Sanz, Mario; Sánchez, Antonio L.; Williams, Forman A.

    2016-07-01

    A multipurpose reduced chemical-kinetic mechanism for methanol combustion comprising 8 overall reactions and 11 reacting chemical species is presented. The development starts by investigating the minimum set of elementary reactions needed to describe methanol combustion with reasonable accuracy over a range of conditions of temperature, pressure, and composition of interest in combustion. Starting from a 27-step mechanism that has been previously tested and found to give accurate predictions of ignition processes for these conditions, it is determined that the addition of 11 elementary reactions taken from its basis (San Diego) mechanism extends the validity of the description to premixed-flame propagation, strain-induced extinction of non-premixed flames, and equilibrium composition and temperatures, giving results that compare favourably with experimental measurements and also with computations using the 247-step detailed San Diego mechanism involving 50 reactive species. Specifically, premixed-flame propagation velocities and extinction strain rates for non-premixed counterflow flames calculated with the 38-step mechanism show departures from experimental measurements and detailed-chemistry computations that are roughly on the order of 10%, comparable with expected experimental uncertainties. Similar accuracy is found in comparisons of autoignition times over the range considered, except at very high temperatures, under which conditions the computations tend to overpredict induction times for all of the chemistry descriptions tested. From this 38-step mechanism, the simplification is continued by introducing steady-state approximations for the intermediate species CH3, CH4, HCO, CH3O, CH2OH, and O, leading to an 8-step reduced mechanism that provides satisfactory accuracy for all conditions tested. The flame computations indicate that thermal diffusion has a negligible influence on methanol combustion in all cases considered and that a mixture-average species

  8. Use of laser-induced ionization to detect soot inception in premixed flames

    NASA Astrophysics Data System (ADS)

    Manzello, Samuel L.; Lee, Eui Ju; Mulholland, George W.

    2005-08-01

    Experimental measurements of laser-induced ionization were performed for ethene-air premixed flames operated near the soot inception point. Soot was ionized with a pulsed laser operated at 532 nm. The ionization signal was collected with a tungsten electrode located in the postflame region. Ionization signals were collected by use of both single-electrode and dual-electrode configurations. Earlier laser-induced- ionization studies focused on the use of a single biased electrode to generate the electric field, with the burner head serving as the path to ground. In many practical combustion systems, a path to ground is not readily available. To apply the laser-induced- ionization diagnostic to these geometries, a dual-electrode geometry must be employed. The influence of electrode configuration, flame equivalence ratio, and flame height on ionization signal detection was determined. The efficacy of the laser-induced-ionization diagnostic in detecting soot inception in the postflame region of a premixed flame by use of a dual-electrode configuration was investigated. Of the dual-electrode configurations tested, the dual-electrode geometry oriented parallel to the laser beam was observed to be most sensitive for detecting the soot inception point in a premixed flame.

  9. Use of laser-induced ionization to detect soot inception in premixed flames

    SciTech Connect

    Manzello, Samuel L.; Lee, Eui Ju; Mulholland, George W

    2005-08-20

    Experimental measurements of laser-induced ionization were performed for ethene-air premixed flames operated near the soot inception point. Soot was ionized with a pulsed laser operated at 532 nm. The ionization signal was collected with a tungsten electrode located in the postflame region. Ionization signals were collected by use of both single-electrode and dual-electrode configurations. Earlier laser-induced- ionization studies focused on the use of a single biased electrode to generate the electric field, with the burner head serving as the path to ground. In many practical combustion systems, a path to ground is not readily available. To apply the laser-induced- ionization diagnostic to these geometries, a dual-electrode geometry must be employed. The influence of electrode configuration, flame equivalence ratio, and flame height on ionization signal detection was determined. The efficacy of the laser-induced-ionization diagnostic in detecting soot inception in the postflame region of a premixed flame by use of a dual-electrode configuration was investigated. Of the dual-electrode configurations tested, the dual-electrode geometry oriented parallel to the laser beam was observed to be most sensitive for detecting the soot inception point in a premixed flame.

  10. How ''flat'' is the rich premixed flame produced by your McKenna burner?

    SciTech Connect

    Migliorini, F.; De Iuliis, S.; Cignoli, F.; Zizak, G.

    2008-05-15

    McKenna burners are widely used in the combustion community for producing ''flat'' premixed flames. These flames are considered as standards for the development and calibration of optical techniques. Rich premixed flames produced by McKenna burners are frequently investigated in order to understand soot formation processes both by optical and by sampling techniques. Measurements are normally performed along the axis of the flames, with a uniform distribution of temperature and species concentration assumed in the radial direction. In this work it is shown that the soot radial profiles of rich premixed ethylene-air flames produced by a McKenna burner with a stainless steel porous plug may be far from being ''flat.'' Soot is mainly distributed in an annular region and nonsoot fluorescing species are present in the core of the flames. This surprising result was verified under several working conditions. Furthermore, flames cannot be considered axial-symmetric but present a skewed soot distribution. Another McKenna burner with a bronze porous disk was used to produce flames of the same equivalence ratio and flows. These flames show a completely different soot radial profile, closer to the claimed flat distribution. These results cast doubts about the conclusions drawn in several studies on soot formation performed with a stainless steel McKenna burner. (author)

  11. A numerical investigation of the effects of imperfect premixing on flame propagation

    NASA Astrophysics Data System (ADS)

    Garrido-Lopez, David

    2005-07-01

    Gasoline direct-injection engines and lean-premixed prevaporized combustors have recently emerged as promising technologies for improving combustion efficiency and pollutant emission. In both applications, the time available for the mixing of fuel and oxidizer prior to combustion may be insufficient for the mixture to acquire a homogeneous composition, and this thesis addresses the propagation of premixed flames under such conditions. Previous numerical studies, owing to severe spatio-temporal limitations, have been unable to provide a clear picture of what to expect from the effects of imperfect premixing on turbulent flames, and have not found agreement with existing experimental data. In this study, direct numerical simulations (DNS) of flame propagation in inhomogeneous mixtures with imposed velocity fluctuations are carried out. To avoid aforementioned limitations and to account for important flame dynamics such as the hydrodynamic instability, a configuration that permits larger domains and longer times than previously accessed by DNS is employed. The simulated flows are unavoidably restricted to two dimensions. One-step chemistry and Fick's diffusion law are considered, along with unity Lewis number assumption. It is observed that relatively weak fluctuations in composition alone may lead to a large increase in flame wrinkling and propagation speed, consistent with experimental findings. The hydrodynamic instability caused by gas expansion is found to be responsible for such strong flame response. However, the impact of composition fluctuations diminishes as velocity fluctuations present become more intense, and eventually imperfect premixing ceases to affect the flame brush speed. This effect is explained based on the numerical results, and a criterion for the transition from one regime to the other is provided. It is also found that imperfect premixing always affects the structure of the flame brush. A gradual change in the composition of the unburnt

  12. Study on the Enhancement Effect of Dielectric Barrier Discharge on the Premixed Methane/Oxygen/Helium Flame Velocity

    NASA Astrophysics Data System (ADS)

    Mu, Haibao; Yu, Lin; Li, Ping; Tang, Chenglong; Wang, Jinhua; Zhang, Guanjun

    2015-12-01

    Recently, plasma-assisted combustion has become a potentially applicable technology in many combustion scenarios. In this paper, a dielectric barrier discharge (DBD) plasma generator is designed to explore the effect of plasma on the CH4 oxidation process, and several properties of combustion are considered. First, in the presence or absence of plasma discharge, physical appearance of the flame is examined and analyzed. Second, the flame propagation velocity is calculated by the flame front extracted from the imaging data with the Bunsen burner method. Finally, the main molecular components and their intensity variation in the flame and the plasma zones are identified with an emission spectrograph to analyze the effect of active species on the combustion process. We also discuss the possible kinetic regime of plasma-assisted combustion. Experimental results imply that plasma discharge applied to the premixed CH4/O2/He mixture significantly raises the flame speed with equivalence ratios ranging from 0.85 to 1.10, with the flame speed improved by 17% to 35%. It can be seen that plasma can improve methane oxidation efficiency in the premixed fuel/oxidizer, especially at a low equivalence ratio. supported by the Fundamental Research Funds for the Central Universities of China (No. xjj2013086), Natural Science Basic Research Plan in Shaanxi Province of China (No. 2014JQ7254) and National Natural Science Foundation of China (No. 51477135)

  13. Combustion of dense streams of coal particles. Quarterly progress report No. 12, May 29, 1993--August 28, 1993

    SciTech Connect

    Annamalai, K.

    1993-09-20

    Research continued on coal stream combustion. This report presents the results obtained from the gasification efficiency experiments by varying the (i) air fuel ratio of the coal cloud (ii) reaction zone height (residence time) and (iii) oxygen concentration. A brief discussion on the divergence of coal stream is presented.

  14. Toxic substances from coal combustion -- a comprehensive assessment. Quarterly technical progress report, 1 April 1996--30 June 1996

    SciTech Connect

    Bool, L.E. III; Senior, C.L.; Huggins, F.; Huffman, G.P.; Shah, N.

    1996-07-01

    Before electric utilities can plan or implement emissions minimization strategies for hazardous pollutants, they must have an accurate and site-specific means of predicting emissions in all effluent streams for the broad range of fuels and operating conditions commonly utilized. Development of a broadly applicable emissions model useful to utility planners first requires a sound understanding of the fundamental principles controlling the formation and partitioning of toxic species during coal combustion (specifically in Phase I, As, Se, Cr, and possibly Hg). PSI Technologies (PSIT) and its team members will achieve this objective through the development of an {open_quotes}Engineering Model{close_quotes} that accurately predicts the formation and partitioning of toxic species as a result of coal combustion. The {open_quotes}Toxics Partitioning Engineering Model{close_quotes} (ToPEM) will be applicable to all conditions including new fuels or blends, low-NO{sub x} combustion systems, and new power systems being advanced by DOE in the Combustion 2000 program. This report describes the mineralogy and chemical analysis of bituminous coal samples.

  15. A coal-fired combustion system for industrial process heating applications. Quarterly technical progress report, July 1994--September 1994

    SciTech Connect

    1994-12-01

    PETC has implemented a number of advanced combustion research projects that will lead to the establishment of a broad, commercially acceptable engineering data base for the advancement of coal as the fuel of choice for boilers, furnaces, and process heaters. Vortec Corporation`s Phase III development contract DE-AC22-91PC91161 for a {open_quotes}Coal-Fired Combustion System for Industrial Process Heating Applications{close_quotes} is a project funded under the DOE/PETC advanced combustion program. This advanced combustion system research program is for the development of innovative coal-fired process heaters which can be used for high temperature melting, smelting and waste vitrification processes. The process heater systems to be developed have multiple use applications; however, the Phase III research effort is being focused on the development of a process heater system to be used for producing value added vitrified glass products from boiler/incinerator ashes and industrial wastes. The primary objective of the Phase III project is to develop and integrate all the system components, from fuel through total system controls, and then test the complete system in order to evaluate its potential marketability.

  16. A coal-fired combustion system for industrial process heating applications. Quarterly technical progress report, October 1993--December 1993

    SciTech Connect

    1994-01-30

    PETC has implemented a number of advanced combustion research projects that will lead to the establishment of a broad, commercially acceptable engineering data base for the advancement of coal as the fuel of choice for boilers, furnaces, and process heaters. Vortec Corporation`s Phase III development contract DE-AC22-91PC91161 for a {open_quotes}Coal-Fired Combustion System for Industrial Process Heating Applications{close_quotes} is a project funded under the DOE/PETC advanced combustion program. This advanced combustion system research program is for the development of innovative coal-fired process heaters which can be used for high temperature melting, smelting and waste vitrification processes. The process heater systems to be developed have multiple use applications; however, the Phase III research effort is being focused on the development of a process heater system to be used for producing value added vitrified glass products from boiler/incinerator ashes and industrial wastes. The primary objective of the Phase III project is to develop and integrate all the system components, from fuel through total system controls, and then test the complete system in order to evaluate its potential marketability. During the past quarter, the major effort was completing the system modification installation designs, completing the TSCA ash testing, and conducting additional industry funded testing. Final detailed installation designs for the integrated test system configuration are being completed.

  17. Design, construction, operation, and evaluation of a prototype culm-combustion boiler/heater unit. Quarterly technical progress report, October 1-December 31, 1980

    SciTech Connect

    Not Available

    1981-02-01

    This report provides a summary of the work performed on the Prototype Culm Combustion Boiler/Heater Unit, Phase I - Engineering Design and Analysis and Phase II - Prototype Plant Construction during the period October 1, 1980 through December 31, 1980. The objectives of the program as well as the technical progress and problem areas encountered during the reporting period are presented. The final detail design effort was completed and the final design report submitted. Progress on procurement activity authorized by full Phase II release on March 20, 1980, is discussed. Following approval by DOE, a purchase order was placed with the Norflor Construction Corporation for the prototype plant construction which began in November. Construction of the access roadway installation of the electric power, sewer and water lines was completed during this reporting period. Boiler construction continued.

  18. Studies of Premixed Laminar and Turbulent Flames at Microgravity

    NASA Technical Reports Server (NTRS)

    Kwon, O. C.; Abid, M.; Porres, J.; Liu, J. B.; Ronney, P. D.; Struk, P. M.; Weiland, K. J.

    2003-01-01

    Several topics relating to premixed flame behavior at reduced gravity have been studied. These topics include: (1) flame balls; (2) flame structure and stability at low Lewis number; (3) experimental simulation of buoyancy effects in premixed flames using aqueous autocatalytic reactions; and (4) premixed flame propagation in Hele-Shaw cells. Because of space limitations, only topic (1) is discussed here, emphasizing results from experiments on the recent STS-107 Space Shuttle mission, along with numerical modeling efforts.

  19. Flame front configuration of turbulent premixed flames

    SciTech Connect

    Furukawa, Junichi; Maruta, Kaoru; Hirano, Toshisuke

    1998-02-01

    The present study is performed to explore dependence of the wrinkle scale of propane-air turbulent premixed flames on the characteristics of turbulence in the nonreacting flow, burner size, and mixture ratio. The wrinkle scales are examined and expressed in the frequency distribution of the radii of flame front curvatures. The average wrinkle scale depends not only on the characteristics of turbulence in the nonreacting flow but also on burner diameter and mixture ratio. The average wrinkle scale of a lean propane-air flame is larger than those of the near stoichiometric and rich flames. The smallest wrinkle scale of turbulent premixed flame is in the range of 0.75--1.0 mm, which is much larger than the Kolmogorov scale of turbulence in the nonreacting flow.

  20. Asymptotic expressions for turbulent burning velocity at the leading edge of a premixed flame brush and their validation by published measurement data

    NASA Astrophysics Data System (ADS)

    Lee, Jaeseo; Lee, Gwang G.; Huh, Kang Y.

    2014-12-01

    This paper presents validation of new analytical expressions for the turbulent burning velocity, ST, based on asymptotic behavior at the leading edge (LE) in turbulent premixed combustion. Reaction and density variation are assumed to be negligible at the LE to avoid the cold boundary difficulty in the statistically steady state. Good agreement is shown for the slopes, dST/du', with respect to Lc/δf at low turbulence, with both normalized by those of the reference cases. δf is the inverse of the maximum gradient of reaction progress variable through an unstretched laminar flame, and Lc is the characteristic length scale given as burner diameter or measured integral length scale. Comparison is made for thirty-five datasets involving different fuels, equivalence ratios, H2 fractions in fuel, pressures, and integral length scales from eight references [R. C. Aldredge et al., "Premixed-flame propagation in turbulent Taylor-Couette flow," Combust. Flame 115, 395 (1998); M. Lawes et al., "The turbulent burning velocity of iso-octane/air mixtures," Combust. Flame 159, 1949 (2012); H. Kido et al., "Influence of local flame displacement velocity on turbulent burning velocity," Proc. Combust. Inst. 29, 1855 (2002); J. Wang et al., "Correlation of turbulent burning velocity for syngas/air mixtures at high pressure up to 1.0 MPa," Exp. Therm. Fluid Sci. 50, 90 (2013); H. Kobayashi et al., "Experimental study on general correlation of turbulent burning velocity at high pressure," Proc. Combust. Inst. 27, 941 (1998); C. W. Chiu et al., "High-pressure hydrogen/carbon monoxide syngas turbulent burning velocities measured at constant turbulent Reynolds numbers," Int. J. Hydrogen Energy 37, 10935 (2012); P. Venkateswaran et al., "Pressure and fuel effects on turbulent consumption speeds of H2/CO blends," Proc. Combust. Inst. 34, 1527 (2013); M. Fairweather et al., "Turbulent burning rates of methane and methane-hydrogen mixtures," Combust. Flame 156, 780 (2009)]. The turbulent

  1. Effects of Buoyancy on Laminar and Turbulent Premixed V-Flame

    NASA Technical Reports Server (NTRS)

    Cheng, Robert K.; Bedat, Benoit

    1997-01-01

    Turbulent combustion occurs naturally in almost all combustion systems and involves complex dynamic coupling of chemical and fluid mechanical processes. It is considered as one of the most challenging combustion research problems today. Though buoyancy has little effect on power generating systems operating under high pressures (e.g., IC engines and turbines), flames in atmospheric burners and the operation of small to medium furnaces and boilers are profoundly affected by buoyancy. Changes in burner orientation impacts on their blow-off, flash-back and extinction limits, and their range of operation, burning rate, heat transfer, and emissions. Theoretically, buoyancy is often neglected in turbulent combustion models. Yet the modeling results are routinely compared with experiments of open laboratory flames that are obviously affected by buoyancy. This inconsistency is an obstacle to reconciling experiments and theories. Consequently, a fundamental understanding of the coupling between turbulent flames and buoyancy is significant to both turbulent combustion science and applications. The overall effect of buoyancy relates to the dynamic interaction between the flame and its surrounding, i.e., the so-called elliptical problem. The overall flame shape, its flowfield, stability, and mean and local burning rates are dictated by both upstream and downstream boundary conditions. In steady propagating premixed flames, buoyancy affects the products region downstream of the flame zone. These effects are manifested upstream through the mean and fluctuating pressure fields to influence flame stretch and flame wrinkling. Intuitively, the effects buoyancy should diminish with increasing flow momentum. This is the justification for excluding buoyancy in turbulent combustion models that treats high Reynolds number flows. The objectives of our experimental research program is to elucidate flame-buoyancy coupling processes in laminar and turbulent premixed flames, and to

  2. Lifted Partially Premixed Flames in Microgravity

    NASA Technical Reports Server (NTRS)

    Lock, Andrew J.; Ganguly, Ranjan; Puri, Ishwar K.; Aggarwal, Suesh K.; Hegde, Uday

    2004-01-01

    Lifted Double and Triple flames are established in the UIC-NASA Partially Premixed microgravity rig. The flames examined in this paper are established above a coannular burner because its axisymmetric geometry allows for future implementation of other non-intrusive optical diagnostic techniques easily. Both burner-attached stable flames and lifted flames are established at normal and microgravity conditions in the drop tower facility.

  3. Displacement speeds in turbulent premixed flame simulations

    SciTech Connect

    Day, Marcus S.; Shepherd, Ian G.; Bell, J.; Grcar, Joseph F.; Lijewski, Michael J.

    2007-07-01

    The theory of turbulent premixed flames is based on acharacterization of the flame as a discontinuous surface propagatingthrough the fluid. The displacement speed, defined as the local speed ofthe flame front normal to itself, relative to the unburned fluid,provides one characterization of the burning velocity. In this paper, weintroduce a geometric approach to computing displacement speed anddiscuss the efficacy of the displacement speed for characterizing aturbulent flame.

  4. Premixed Turbulent Flame Propagation in Microgravity

    NASA Technical Reports Server (NTRS)

    Menon, Suresh

    1999-01-01

    A combined numerical-experimental study has been carried out to investigate the structure and propagation characteristics of turbulent premixed flames with and without the influence of buoyancy. Experimentally, the premixed flame characteristics are studied in the wrinkled regime using a Couette flow facility and an isotropic flow facility in order to resolve the scale of flame wrinkling. Both facilities were chosen for their ability to achieve sustained turbulence at low Reynolds number. This implies that conventional diagnostics can be employed to resolve the smallest scales of wrinkling. The Couette facility was also built keeping in mind the constraints imposed by the drop tower requirements. Results showed that the flow in this Couette flow facility achieves full-developed turbulence at low Re and all turbulence statistics are in good agreement with past measurements on large-scale facilities. Premixed flame propagation studies were then carried out both using the isotropic box and the Couette facility. Flame imaging showed that fine scales of wrinkling occurs during flame propagation. Both cases in Ig showed significant buoyancy effect. To demonstrate that micro-g can remove this buoyancy effect, a small drop tower was built and drop experiments were conducted using the isotropic box. Results using the Couette facility confirmed the ability to carry out these unique reacting flow experiments at least in 1g. Drop experiments at NASA GRC were planned but were not completed due to termination of this project.

  5. Symposium (International) on Combustion, 20th, University of Michigan, Ann Arbor, MI, August 12-17, 1984, Proceedings

    NASA Technical Reports Server (NTRS)

    1985-01-01

    The present conference on combustion phenomena considers topics in automotive engine combustion, turbulent reacting flows, the modeling of practical combustion systems, reaction kinetics, combustion-generated particulates, combustion diagnostics, coal combustion process characteristics, fire-related phenomena, explosion/detonation phenomena, spray combustion, ignition/extinction, laminar flames, pollutant formation processes, practical combustor devices, and rocket propellant combustion. Attention is given to the contributions of combustion science to piston engine design, modeling and measurement techniques for turbulent combustion, the specific effects of energy, collisions, and transport processes in combustion chemistry kinetics, the formation of large molecules, particulates and ions in premixed hydrocarbon flames, the application of laser diagnostics to combustion systems, spark ignition energies for dust-air mixtures, the controlling mechanisms of flow-assisted flame spread, the ignition and combustion of coal-water slurries, spontaneous ignition of methane, turbulent and accelerating dust flames, and the temperature sensitivity of double base propellants.

  6. Successive laser ablation ignition of premixed methane/air mixtures.

    PubMed

    Bak, Moon Soo; Cappelli, Mark A

    2015-06-01

    Laser ablation has been used to study successive ignition in premixed methane/air mixtures under conditions in which the flow speed leads to flame blow-out. A range of laser pulse frequencies is experimentally mimicked by varying the time interval between two closely spaced laser pulses. Emission intensities from the laser ablation kernels are measured to qualitatively estimate laser energy coupling, and flame CH* chemiluminescence is recorded in a time-resolved manner to capture the flame evolution and propagation. A comparison of the measurements is made between the two successive breakdown ignition events. It is found that the formation of the subsequent ablation kernel is almost independent of the previous one, however, for the successive breakdowns, the first breakdown and its ensuing combustion created temporal regions of no energy coupling as they heat the gas and lower the density. Flame imaging shows that the second ablation event successfully produces another flame kernel and is capable of holding the flame-base even at pulse intervals where the second laser pulse cannot form a breakdown. This study demonstrates that successive ablation ignition can allow for the use of higher laser frequencies and enhanced flame stabilization than successive breakdown ignition. PMID:26072866

  7. Freely propagating open premixed turbulent flames stabilized by swirl

    SciTech Connect

    Chan, C.K.; Lau, K.S.; Chin, W.K.; Cheng, R.K.

    1991-12-01

    A novel means has been developed for using weak swirl to stabilize freely propagating open premixed turbulent flames (swirl numbers between 0.05 to 0.3). By injecting a small amount of air tangentially into the co-flow of a concentric burner, stationary flames can be maintained above the burner exit for a large range of mixture, turbulence and flow conditions. The absence of physical surfaces in the vicinity of the flame provides free access to laser diagnostics. Laser Doppler anemometry and laser Mie scattering measurements of four flames with and without incident turbulence show that their features are typical of wrinkled laminar flames. The most distinct characteristics is that flame stabilization does not rely on flow recirculation. Centrifugal force induced by swirl causes flow divergence, and the flame is maintained at where the local mass flux balances the burning rate. The flame speeds can be estimated based on the centerline velocity vector, which is locally normal to the flame brush. This flame geometry is the closest approximation to the 1-D planar flame for determining fundamental properties to advance turbulent combustion theories. 18 refs.

  8. Numerical simulation of premixed flame propagation in a closed tube

    NASA Astrophysics Data System (ADS)

    Kuzuu, Kazuto; Ishii, Katsuya; Kuwahara, Kunio

    1996-08-01

    Premixed flame propagation of methane-air mixture in a closed tube is estimated through a direct numerical simulation of the three-dimensional unsteady Navier-Stokes equations coupled with chemical reaction. In order to deal with a combusting flow, an extended version of the MAC method, which can be applied to a compressible flow with strong density variation, is employed as a numerical method. The chemical reaction is assumed to be an irreversible single step reaction between methane and oxygen. The chemical species are CH 4, O 2, N 2, CO 2, and H 2O. In this simulation, we reproduce a formation of a tulip flame in a closed tube during the flame propagation. Furthermore we estimate not only a two-dimensional shape but also a three-dimensional structure of the flame and flame-induced vortices, which cannot be observed in the experiments. The agreement between the calculated results and the experimental data is satisfactory, and we compare the phenomenon near the side wall with the one in the corner of the tube.

  9. Catalytic combustion with steam injection

    NASA Astrophysics Data System (ADS)

    Anderson, D. N.; Tacina, R. R.

    The effects of steam injection on (1) catalytic combustion performance, and (2) the tendency of residual fuel to burn in the premixing duct upstream of the catalytic reactor were determined. A petroleum residual, no. 2 diesel, and a blend of middle and heavy distillate coal derived fuels were tested. Fuel and steam were injected together into the preheated airflow entering a 12 cm diameter catalytic combustion test section. The inlet air velocity and pressure were constant at 10 m/s and 600 kPa, respectively. Steam flow rates were varied from 24 percent to 52 percent of the air flow rate. The resulting steam air mixture temperatures varied from 630 to 740 K. Combustion temperatures were in the range of 1200 to 1400 K. The steam had little effect on combustion efficiency or emissions. It was concluded that the steam acts as a diluent which has no adverse effect on catalytic combustion performance for no. 2 diesel and coal derived liquid fuels. Tests with the residual fuel showed that upstream burning could be eliminated with steam injection rates greater than 30 percent of the air flow rate, but inlet mixture temperatures were too low to permit stable catalytic combustion of this fuel.

  10. Catalytic combustion with steam injection

    NASA Technical Reports Server (NTRS)

    Anderson, D. N.; Tacina, R. R.

    1982-01-01

    The effects of steam injection on (1) catalytic combustion performance, and (2) the tendency of residual fuel to burn in the premixing duct upstream of the catalytic reactor were determined. A petroleum residual, no. 2 diesel, and a blend of middle and heavy distillate coal derived fuels were tested. Fuel and steam were injected together into the preheated airflow entering a 12 cm diameter catalytic combustion test section. The inlet air velocity and pressure were constant at 10 m/s and 600 kPa, respectively. Steam flow rates were varied from 24 percent to 52 percent of the air flow rate. The resulting steam air mixture temperatures varied from 630 to 740 K. Combustion temperatures were in the range of 1200 to 1400 K. The steam had little effect on combustion efficiency or emissions. It was concluded that the steam acts as a diluent which has no adverse effect on catalytic combustion performance for no. 2 diesel and coal derived liquid fuels. Tests with the residual fuel showed that upstream burning could be eliminated with steam injection rates greater than 30 percent of the air flow rate, but inlet mixture temperatures were too low to permit stable catalytic combustion of this fuel.

  11. Large-eddy simulation of combustion systems with convective heat-loss

    NASA Astrophysics Data System (ADS)

    Shunn, Lee

    Computer simulations have the potential to viably address the design challenges of modern combustion applications, provided that adequate models for the prediction of multiphysics processes can be developed. Heat transfer has particular significance in modeling because it directly affects thermal efficiencies and pollutant formation in combustion systems. Convective heat transfer from flame-wall interaction has received increased attention in aeronautical propulsion and power-generation applications where modern designs have trended towards more compact combustors with higher surface-to-volume ratios, and in diesel engines where enclosed volumes and cool walls provide ample conditions for thermal quenching. As intense flame-wall interactions can induce extremely large heat fluxes, their inclusion is important in computational models used to predict performance and design cooling systems. In the present work, a flamelet method is proposed for modeling turbulence/chemistry interactions in large-eddy simulations (LES) of non-premixed combustion systems with convective heat-losses. The new method is based on the flamelet/progress variable approach of Pierce & Moin (J. Fluid Mech. 2004, 504:73-97) and extends that work to include the effects of thermal-losses on the combustion chemistry. In the new model, chemical-state databases are constructed by solving one-dimensional diffusion/reaction equations which have been constrained by scaling the enthalpy of the system between the adiabatic state and a thermally-quenched reference state. The solutions are parameterized and tabulated as a function of the mapping variables: mixture fraction, reaction progress variable, and normalized enthalpy. The new model is applied to LES of non-premixed methane-air combustion in a coaxial-jet with isothermal wall-conditions to describe heat transfer to the confinement. The resulting velocity, species concentration, and temperature fields are compared to experimental measurements and to

  12. Theoretical and experimental studies of vortex breakdown in a lean, premixed swirl-stabilized combustor

    NASA Astrophysics Data System (ADS)

    Umeh, Chukwueloka O. U.

    Increasingly stringent emissions regulations on fossil fuel-burning combustors in land-based and aviation gas turbine engines has led engine manufacturers to turn to lean burning premixed combustors. In modern lean premixed gas turbine combustors, flame stabilization is achieved by the use of a high level of inlet swirl and an expansion into a larger chamber. This predisposes the inlet vortex flow to transition to a vortex breakdown state, which is characterized by a stagnation and recirculation zone near the exit plane of the inlet region. A compact, turbulent and highly mixed flame results. Although this breakdown phenomenon helps reduce emissions drastically compared to rich-burn engines, it also contributes to the formation of thermo-acoustic instabilities (or combustion dynamics), flashback and lean blow out, which hinder performance and in extreme cases, causes very expensive damage to the combustion system. Theoretical, computational and experimental studies of vortex breakdown in a finite length, axisymmetric chamber with a swirling inlet flow demonstrate that critical conditions for the first appearance of breakdown in the combustion chamber as well as in the combustor's inlet region govern the flow's behavior. These critical conditions are satisfied for both the average and the instantaneous behavior of the flow for ambient temperature, preheated and lean premixed reacting flows. Good agreement is found between the theoretical and numerical simulations, as well as the experimental results. Results show that these critical conditions, as well as the appearance, location, size and stability of the breakdown are affected by inlet airflow rate, inlet air temperature, flame temperature (in reacting flow), inlet tube length, dump plane configuration and chamber air leakage. In the presence of combustion, experimental results show that the existence of a breakdown zone, its shape, location and stability influence flame stabilization, combustion dynamics

  13. A coal-fired combustion system for industrial processing heating applications. Quarterly technical progress report, January 1995--March 1995

    SciTech Connect

    1995-04-01

    PETC has implemented a number of advanced combustion research projects that will lead to the establishment of a broad, commercially acceptable engineering data base for the advancement of coal as the fuel of choice for boilers, furnaces, and process heaters. Vortec Corporation`s Phase III development contract DE-AC22-91PC91161 for a {open_quotes}Coal-Fired Combustion System for Industrial Process Heating Applications{close_quotes} is a project funded under the DOE/PETC advanced combustion program. This advanced combustion system research program is for the development of innovative coal-fired process heaters which can be used for high temperature melting, smelting and waste vitrification processes. The process heater systems to be developed have multiple use applications; however, the Phase III research effort is being focused on the development of a process heater system to be used for producing value added vitrified glass products from boiler/incinerator ashes and industrial wastes. The primary objective of the Phase III project is to develop and integrate all the system components, from fuel through total system controls, and then test the complete system in order to evaluate its potential marketability. The test program consisted of one test run, with a duration of 100 hours at a nominal feed rate of 1000 lbs/hr. Throughout the test, the CMS was fired with coal and a coal by-product (i.e. coal-fired boiler fly ash) as the primary fuels. Natural gas was used as an auxiliary fuel as necessary to provide process trim. The feedstock consisted of a coal-fired utility boiler fly ash and dolomite and produced a stable, fully-reacted vitrified product. The fly ash, supplied by PENELEC, contained between 6 and 12% by weight of carbon because of the low NOx burners on the PENELEC boilers. Therefore, a substantial portion of the required thermal input came from the fly ash.

  14. A coal-fired combustion system for industrial process heating applications. Quarterly technical progress report, April 1992--June 1992

    SciTech Connect

    Not Available

    1992-09-03

    PETC has implemented a number of advanced combustion research projects that will lead to the establishment of a broad, commercially acceptable engineering data base for the advancement of coal as the fuel of choice for boilers, furnaces, and process heaters. Vortec Corporation`s Phase III development contract DE-AC22-91PC91161 for a ``Coal-Fired Combustion System for Industrial Process Heating Applications`` is project funded under the DOE/PETC advanced combustion program. This advanced combustion system research program is for the development of innovative coal-fired process heaters which can be used for high temperature melting, smelling and waste vitrification processes. The process heater concepts to be developed are based on advanced glass melting and ore smelting furnaces developed and patented by Vortec Corporation. The process heater systems to be developed have multiple use applications; however, the Phase III research effort is being focused on the development of a process heater system to be used for producing value added vitrified glass products from boiler/incinerator ashes and industrial wastes. The primary objective of the Phase III project is to develop and integrate all the system components, from fuel through total system controls, and then test the complete system in order to evaluate its potential marketability. During the current reporting period, approval of Vortec`s Environmental Assessment (EA) required under the National Environmental Policy Act (NEPA) was approved. The EA approval cycle took approximately 9 months. The preliminary test program which was being held in abeyance pending approval of the EA was initiated. Six preliminary test runs were successfully competed during the period. Engineering and design activities in support of the Phase III proof of concept are continuing, and modifications to the existing test system configuration to allow performance of the preliminary tests were completed.

  15. Resonance ionization detection of combustion radicals

    SciTech Connect

    Cool, T.A.

    1993-12-01

    Fundamental research on the combustion of halogenated organic compounds with emphasis on reaction pathways leading to the formation of chlorinated aromatic compounds and the development of continuous emission monitoring methods will assist in DOE efforts in the management and disposal of hazardous chemical wastes. Selective laser ionization techniques are used in this laboratory for the measurement of concentration profiles of radical intermediates in the combustion of chlorinated hydrocarbon flames. A new ultrasensitive detection technique, made possible with the advent of tunable VUV laser sources, enables the selective near-threshold photoionization of all radical intermediates in premixed hydrocarbon and chlorinated hydrocarbon flames.

  16. LES-Modeling of a Partially Premixed Flame using a Deconvolution Turbulence Closure

    NASA Astrophysics Data System (ADS)

    Wang, Qing; Wu, Hao; Ihme, Matthias

    2015-11-01

    The modeling of the turbulence/chemistry interaction in partially premixed and multi-stream combustion remains an outstanding issue. By extending a recently developed constrained minimum mean-square error deconvolution (CMMSED) method, to objective of this work is to develop a source-term closure for turbulent multi-stream combustion. In this method, the chemical source term is obtained from a three-stream flamelet model, and CMMSED is used as closure model, thereby eliminating the need for presumed PDF-modeling. The model is applied to LES of a piloted turbulent jet flame with inhomogeneous inlets, and simulation results are compared with experiments. Comparisons with presumed PDF-methods are performed, and issues regarding resolution and conservation of the CMMSED method are examined. The author would like to acknowledge the support of funding from Stanford Graduate Fellowship.

  17. Lean premixed flames for low NO{sub x} combustors

    SciTech Connect

    Sojka, P.; Tseng, L.; Bryjak, J.

    1995-10-01

    Gas turbines are being used throughout the world to generate electricity. Due to increasing fuel costs and environmental concerns, gas turbines must meet stringent performance requirements, demonstrating high thermal efficiencies and low pollutant emissions. In order for U.S. manufactured gas turbines to stay competitive, their NO{sub x} levels must be below 10 ppm and their thermal efficiencies should approach 60%. Current technology is being stretched to achieve these goals. The twin goals of high efficiency and low NO{sub x} emissions require extending the operating range of current gas turbines. Higher efficiency requires operation at higher pressures and temperatures. Lower NO{sub x} emissions requires lower flame temperatures. Lower flame temperatures can be achieved through partially to fully pre-mixed combustion. However, increased performance and lower emissions result in a set of competing goals. In order to achieve a successful compromise between high efficiency and low NO{sub x} emissions, advanced design tools must be developed. One key design tool is a computationally efficient, high pressure, turbulent flow, combustion model capable of predicting pollutant formation in an actual gas turbine. Its development is the goal of this program. Achieving this goal requires completion of three tasks. The first task is to develop a reduced chemical kinetics model describing N{sub O}x formation in natural gas-air systems. The second task is to develop a computationally efficient model that describes turbulence-chemistry interactions. The third task is to incorporate the reduced chemical kinetics and turbulence-chemistry interaction models into a commercially available flow solver and compare its predictions with experimental data obtained under carefully controlled conditions so that the accuracy of model predictions can be evaluated.

  18. A coal-fired combustion system for industrial process heating applications. Quarterly technical progress report, April 1993--June 1993

    SciTech Connect

    Not Available

    1993-07-30

    Vortec Corporation`s Phase III development contract DE-AC22-91PC91161 for a ``Coal-Fired Combustion System for Industrial Process Heating Applications`` is project funded under the DOE/PETC advanced combustion program. This advanced combustion system research program is for the development of innovative coal-fired process heaters which can be used for high temperature melting, smelting and waste vitrification processes. The process heater systems to be developed have multiple use applications; however, the Phase III research effort is being focused on the development of a process heater system to be used for producing value added vitrified glass products from boiler/incinerator ashes and industrial wastes. The primary objective of the Phase III project is to develop and integrate all the system components, from fuel through total system controls, and then test the complete system in order to evaluate its potential marketability. During the past quarter, the designs of the remaining major components of the integrated system were completed and the equipment was ordered. DOE has elected to modify the scope of the existing R&D program being conducted under this contract to include testing of a simulated TSCA incinerator ash. The modification will be in the form of an additional Task (Task 8 -- TSCA Ash Testing) to the original Statement of Work.

  19. Effect of flame-tube head structure on combustion chamber performance

    NASA Technical Reports Server (NTRS)

    Gu, Minqqi

    1986-01-01

    The experimental combustion performance of a premixed, pilot-type flame tube with various head structures is discussed. The test study covers an extensive area: efficiency of the combustion chamber, quality of the outlet temperature field, limit of the fuel-lean blowout, ignition performance at ground starting, and carbon deposition. As a result of these tests, a nozzle was found which fits the premixed pilot flame tube well. The use of this nozzle optimized the performance of the combustion chamber. The tested models had premixed pilot chambers with two types of air-film-cooling structures, six types of venturi-tube structures, and secondary fuel nozzles with two small spray-cone angles.

  20. Scalar fluctuations in turbulent combustion - An experimental study

    NASA Astrophysics Data System (ADS)

    Ballal, D. R.; Chen, T. H.; Yaney, P. P.

    1986-01-01

    Temperature and velocity fluctuations data were gathered for turbulent premixed combustion to evaluate a model for scalar transport and scalar dissipation. The data were collected using laser Raman spectroscopy and laser Doppler anemometry with a premixed CH4-air flame from a Bunsen burner. Mean temperature profiles were generated and the pdf's temperature fluctuations were calculated. A wrinkled laminar flame structure was noted in the reaction zone, where the scalar field was anisotropic and where the temperature fluctuations exhibited peak values. The Bray, Moss and Libby model (1985) was successful in predicting the temperature fluctuation intensity and the dissipation ratios, the latter reaching peak values in the flame tip region.

  1. Numerical study of shock-wave/boundary layer interactions in premixed hydrogen-air hypersonic flows

    NASA Technical Reports Server (NTRS)

    Yungster, Shaye

    1991-01-01

    A computational study of shock wave/boundary layer interactions involving premixed combustible gases, and the resulting combustion processes is presented. The analysis is carried out using a new fully implicit, total variation diminishing (TVD) code developed for solving the fully coupled Reynolds-averaged Navier-Stokes equations and species continuity equations in an efficient manner. To accelerate the convergence of the basic iterative procedure, this code is combined with vector extrapolation methods. The chemical nonequilibrium processes are simulated by means of a finite-rate chemistry model for hydrogen-air combustion. Several validation test cases are presented and the results compared with experimental data or with other computational results. The code is then applied to study shock wave/boundary layer interactions in a ram accelerator configuration. Results indicate a new combustion mechanism in which a shock wave induces combustion in the boundary layer, which then propagates outwards and downstream. At higher Mach numbers, spontaneous ignition in part of the boundary layer is observed, which eventually extends along the entire boundary layer at still higher values of the Mach number.

  2. Numerical study of shock-wave/boundary layer interactions in premixed hydrogen-air hypersonic flows

    NASA Technical Reports Server (NTRS)

    Yungster, Shaye

    1990-01-01

    A computational study of shock wave/boundary layer interactions involving premixed combustible gases, and the resulting combustion processes is presented. The analysis is carried out using a new fully implicit, total variation diminishing (TVD) code developed for solving the fully coupled Reynolds-averaged Navier-Stokes equations and species continuity equations in an efficient manner. To accelerate the convergence of the basic iterative procedure, this code is combined with vector extrapolation methods. The chemical nonequilibrium processes are simulated by means of a finite-rate chemistry model for hydrogen-air combustion. Several validation test cases are presented and the results compared with experimental data or with other computational results. The code is then applied to study shock wave/boundary layer interactions in a ram accelerator configuration. Results indicate a new combustion mechanism in which a shock wave induces combustion in the boundary layer, which then propagates outwards and downstream. At higher Mach numbers, spontaneous ignition in part of the boundary layer is observed, which eventually extends along the entire boundary layer at still higher values of the Mach number.

  3. Catalysis of propane oxidation and premixed propane-air flames

    NASA Astrophysics Data System (ADS)

    Wiswall, James T.

    Improvements in deriving energy from hydrocarbon fuels will have a large impact on our efforts to transition to sustainable and renewable energy resources. The hypothesis for this work is that catalysis can extend the useful operating conditions for hydrocarbon oxidation and combustion, improve device efficiencies, and reduce pollutants. Catalysis of propane oxidation and premixed propane-air flames are examined experimentally, using a stagnation-flow reactor to identify the important physical and chemical mechanisms over a range of flow catalyst, and temperature conditions. The propane oxidation studies consider five catalyst materials: platinum, palladium, SnO2, 90% SnO2 -- 10% Pt (by mass), and quartz. The volume fractions of CO2, O2, C 3H8, CO, NO and the electric power required to control the catalyst temperature quantify the activity of each catalyst for the equivalence ratios of φ = 0.67, 1.00, and 1.50, and over the catalyst temperature range 23-800°C. Quartz is used as a baseline and confirmed to be non-reactive at all conditions. 100% SnO2 has minimal reactivity. Platinum, palladium, and 90% SnO2 -- 10% Pt show similar trends and have the highest catalytic activity at φ = 1.50. Palladium and 90% SnO 2 -- 10% Pt show an increasing catalyst-activation temperature (Tsa) for decreasing φ, and platinum shows an approximately constant catalyst-activation temperature for decreasing φ (Tsa = 310°C). Of these the 90% SnO2 -- 10% Pt catalyst shows the lowest Tsa, occurring for the φ = 1.5 mixture (Tsa = 250°C). The studies of premixed propane-air flames consider platinum and quartz stagnation surfaces for fuel-mixture velocities from 0.6-1.6 m/s. Five flame structures are observed: cool core envelope, cone, envelope, disk and ring flames. The lean-extinction limit, disk-to-ring flame transition φ, and the disk-flame to stagnation-plane distance are reported. Platinum inhibits the ring flame structure. The lean-extinction limit and disk-flame to stagnation

  4. A coal-fired combustion system for industrial process heating applications. Quarterly technical progress report, October 1994--December 1994

    SciTech Connect

    1995-03-01

    PETC has implemented a number of advanced combustion research projects that will lead to the establishment of a broad, commercially acceptable engineering data base for the advancement of coal as the fuel of choice for boilers, furnaces, and process heaters. Vortec Corporation`s Phase III development contract DE-AC22-91PC91161 for a {open_quotes}Coal-Fired Combustion System for Industrial Process Heating Applications{close_quotes} is a project funded under the DOE/PETC advanced combustion program. This advanced combustion system research program is for the development of innovative coal-fired process heaters which can be used for high temperature melting, smelting and waste vitrification processes. The process heater systems to be developed have multiple use applications; however, the Phase III research effort is being focused on the development of a process heater system to be used for producing value added vitrified glass products from boiler/incinerator ashes and industrial wastes. The primary objective of the Phase III project is to develop and integrate all the system components, from fuel through total system controls, and then test the complete system in order to evaluate its potential marketability. During the past quarter, the major effort was concentrated on conducting the 100 hour demonstration test. The test was successfully conducted from September 12th through the 16th. The test program consisted of one test run, with a duration of 100 hours at a nominal feed rate of 1000 lbs/hr. Throughout the test, the CMS was fired with coal and a coal by-product (i.e. coal-fired boiler flyash) as the primary fuels. Natural gas was used as an auxiliary fuel as necessary to provide process trim. The feedstock consisted of a coal-fired utility boiler flyash and dolomite and produced a stable, fully-reacted vitrified product. The fly ash, supplied by PENELEC, contained between 6 and 12% by weight of carbon because of the low NO{sub x} burners on the PENELEC boilers.

  5. Effects of ambient conditions and fuel composition on combustion stability

    SciTech Connect

    Janus, M.C.; Richards, G.A.; Yip, M.J.; Robey, E.H.

    1997-04-01

    Recent regulations on NO, emissions are promoting the use of lean premix (LPM) combustion for industrial gas turbines. LPM combustors avoid locally stoichiometric combustion by premixing fuel and the air upstream of the reaction region, thereby eliminating the high temperatures that produce thermal NO.. Unfortunately, this style of combustor is prone to combustion oscillation. Significant pressure fluctuations can occur when variations in heat release periodically couple pressure to acoustic modes in the combustion chamber. These oscillations must be controlled because resulting vibration can shorten the life of engine hardware. Laboratory and engine field testing have shown that instability regimes can vary with environmental conditions. These observations prompted this study of the effects of ambient conditions and fuel composition on combustion stability. Tests are conducted on a sub-scale combustor burning natural gas, propane, and some hydrogen/hydrocarbon mixtures. A premix, swirl-stabilized fuel nozzle typical of industrial gas turbines is used. Experimental and numerical results describe how stability regions may shift as inlet air temperature, humidity, and fuel composition are altered. Results appear to indicate that shifting instability instability regimes are primarily caused by changes in reaction rate.

  6. TIME-VARYING FLAME IONIZATION SENSING APPLIED TO NATURAL GAS AND PROPANE BLENDS IN A PRESSURIZED LEAN PREMIXED (LPM) COMBUSTOR

    SciTech Connect

    D. L. Straub; B. T. Chorpening; E. D. Huckaby; J. D. Thornton; W. L. Fincham

    2008-06-13

    In-situ monitoring of combustion phenomena is a critical need for optimal operation and control of advanced gas turbine combustion systems. The concept described in this paper is based on naturally occurring flame ionization processes that accompany the combustion of hydrocarbon fuels. Previous work has shown that flame ionization techniques may be applied to detect flashback, lean blowout, and some aspects of thermo-acoustic combustion instabilities. Previous work has focused on application of DC electric fields. By application of time-varying electric fields, significant improvements to sensor capabilities have been observed. These data have been collected in a lean premixed combustion test rig operating at 0.51-0.76 MPa (5-7.5 atm) with air preheated to 588 K (600°F). Five percent of the total fuel flow is injected through the centerbody tip as a diffusion pilot. The fuel composition is varied independently by blending approximately 5% (volume) propane with the pipeline natural gas. The reference velocity through the premixing annulus is kept constant for all conditions at a nominal value of 70 m/s. The fuel-air equivalence ratio is varied independently from 0.46 – 0.58. Relative to the DC field version, the time-varying combustion control and diagnostic sensor (TV-CCADS) shows a significant improvement in the correlation between the measured flame ionization current and local fuel-air equivalence ratio. In testing with different fuel compositions, the triangle wave data show the most distinct change in flame ionization current in response to an increase in propane content. Continued development of this sensor technology will improve the capability to control advanced gas turbine combustion systems, and help address issues associated with variations in fuel supplies.

  7. Fuel gas combustion research at METC

    SciTech Connect

    Norton, T.S.

    1995-06-01

    The in-house combustion research program at METC is an integral part of many METC activities, providing support to METC product teams, project managers, and external industrial and university partners. While the majority of in-house combustion research in recent years has been focussed on the lean premixed combustion of natural gas fuel for Advanced Turbine Systems (ATS) applications, increasing emphasis is being placed on issues of syngas combustion, as the time approaches when the ATS and coal-fired power systems programs will reach convergence. When the METC syngas generator is built in 1996, METC will have the unique combination of mid-scale pressurized experimental facilities, a continuous syngas supply with variable ammonia loading, and a team of people with expertise in low-emissions combustion, chemical kinetics, combustion modeling, combustion diagnostics, and the control of combustion instabilities. These will enable us to investigate such issues as the effects of pressure, temperature, and fuel gas composition on the rate of conversion of fuel nitrogen to NOx, and on combustion instabilities in a variety of combustor designs.

  8. Kinetic measurements on elementary fossil fuel combustion reactions over wide temperatures ranges. Progress report, December 1, 1990--November 30, 1991

    SciTech Connect

    Fontijin, A.

    1992-01-01

    The goals of this work are to provide accurate data on the temperature dependence of the kinetics of elementary combustion reactions (i) for use by combustion modelers, and (ii) to gain a better fundamental understanding of, and hence predictive ability for, the chemistry involved. Experimental measurements are made using the pseudo-static HTP (high-temperature photochemistry) technique. This approach allows observations on single reactions in the 300 to 1800 K temperature range to be made. Typical total (bath gas) pressures are in the 100 to 1000 mbar range. Ground-state O and H atoms are produced by flash or excimer laser photolysis of suitable precursors (O{sub 2}, CO{sub 2}, SO{sub 2}, NH{sub 3}). The relative atom concentrations are monitored by resonance fluorescence pumped by a cw microwave discharge flow lamp. The molecular reactant-in-excess is introduced through a cooled inlet. Adequate time for mixing, 0.1 to 10 s, between this inlet and the photolysis/observation zone is achieved by using slow flows (typically less than 20 cm s{sup {minus}1}). Results are reported for: O-Atom Reactions with the Four Isomeric Butenes, H + HCl {yields} H{sub 2} + Cl, and the O-atom 1,3-butadiene reaction.

  9. A coal-fired combustion system for industrial process heating applications. Quarterly technical progress report, July 1993--September 1993

    SciTech Connect

    Not Available

    1994-01-30

    The Pittsburgh Energy Technology Center (PETC) of the US Department of Energy awarded Vortec Corporation this Phase III contract (No. DE-AC22-91PC91161) for the development of {open_quotes}A Coal-Fired Combustion System for Industrial Process Heating Applications{close_quotes}. The effective contrast start date was September 3, 1991. The contract period of performance is 36 months. This advanced combustion system research program is for the development of innovative coal-fired process heaters which can be used for high temperature melting, smelting and waste vitrification processes. The process heater systems to be developed have multiple use applications; however, the Phase III research effort is being focused on the development of a process heater system to be used for producing value added vitrified glass products from boiler/incinerator ashes and industrial wastes. The primary objective of the Phase III project is to develop and integrate all the system components, from fuel through total system controls, and then test the complete system in order to evaluate its potential marketability. Final detailed installation designs for the integrated test system configuration are being completed. The equipment is being fabricated and deliveries have begun. The industry funded testing consisted of vitrifying Spent Aluminum Potliner (SPL) which is a listed hazardous waste. This testing has verified that SPL can be vitrified into a safe recyclable glass product.

  10. Premixed rapid-setting calcium phosphate composites for bone repair.

    PubMed

    Carey, Lisa E; Xu, Hockin H K; Simon, Carl G; Takagi, Shozo; Chow, Laurence C

    2005-08-01

    Although calcium phosphate cement (CPC) is promising for bone repair, its clinical use requires on site powder-liquid mixing. To shorten surgical time and improve graft properties, it is desirable to develop premixed CPC in which the paste remains stable during storage and hardens only after placement into the defect. The objective of this study was to develop premixed CPC with rapid setting when immersed in a physiological solution. Premixed CPCs were formulated using the following approach: Premixed CPC = CPC powder + nonaqueous liquid + gelling agent + hardening accelerator. Three premixed CPCs were developed: CPC-monocalcium phosphate monohydrate (MCPM), CPC-chitosan, and CPC-tartaric. Setting time for these new premixed CPCs ranged from 5.3 to 7.9 min, significantly faster than 61.7 min for a premixed control CPC reported previously (p < 0.05). SEM revealed the formation of nano-sized needle-like hydroxyapatite crystals after 1 d immersion and crystal growth after 7 d. Diametral tensile strength for premixed CPCs at 7 d ranged from 2.8 to 6.4 MPa, comparable to reported strengths for cancellous bone and sintered porous hydroxyapatite implants. Osteoblast cells attained a normal polygonal morphology on CPC-MCPM and CPC-chitosan with cytoplasmic extensions adhering to the nano-hydroxyapatite crystals. In summary, fast-setting premixed CPCs were developed to avoid the powder-liquid mixing in surgery. The pastes hardened rapidly once immersed in physiological solution and formed hydroxyapatite. The cements had strengths matching those of cancellous bone and sintered porous hydroxyapatite and non-cytotoxicity similar to conventional non-premixed CPC.

  11. Premixed rapid-setting calcium phosphate composites for bone repair✩

    PubMed Central

    Carey, Lisa E.; Xu, Hockin H.K.; Simon, Carl G.; Takagi, Shozo; Chow, Laurence C.

    2009-01-01

    Although calcium phosphate cement (CPC) is promising for bone repair, its clinical use requires on site powder–liquid mixing. To shorten surgical time and improve graft properties, it is desirable to develop premixed CPC in which the paste remains stable during storage and hardens only after placement into the defect. The objective of this study was to develop premixed CPC with rapid setting when immersed in a physiological solution. Premixed CPCs were formulated using the following approach: Premixed CPC = CPC powder+nonaqueous liquid+gelling agent+hardening accelerator. Three premixed CPCs were developed: CPC–monocalcium phosphate monohydrate (MCPM), CPC–chitosan, and CPC–tartaric. Setting time for these new premixed CPCs ranged from 5.3 to 7.9 min, significantly faster than 61.7 min for a premixed control CPC reported previously (p<05). SEM revealed the formation of nano-sized needle-like hydroxyapatite crystals after 1 d immersion and crystal growth after 7 d. Diametral tensile strength for premixed CPCs at 7 d ranged from 2.8 to 6.4 MPa, comparable to reported strengths for cancellous bone and sintered porous hydroxyapatite implants. Osteoblast cells attained a normal polygonal morphology on CPC–MCPM and CPC–chitosan with cytoplasmic extensions adhering to the nano-hydroxyapatite crystals. In summary, fast-setting premixed CPCs were developed to avoid the powder–liquid mixing in surgery. The pastes hardened rapidly once immersed in physiological solution and formed hydroxyapatite. The cements had strengths matching those of cancellous bone and sintered porous hydroxyapatite and non-cytotoxicity similar to conventional non-premixed CPC. PMID:15769536

  12. Understanding and predicting soot generation in turbulent non-premixed jet flames.

    SciTech Connect

    Wang, Hai; Kook, Sanghoon; Doom, Jeffrey; Oefelein, Joseph Charles; Zhang, Jiayao; Shaddix, Christopher R.; Schefer, Robert W.; Pickett, Lyle M.

    2010-10-01

    This report documents the results of a project funded by DoD's Strategic Environmental Research and Development Program (SERDP) on the science behind development of predictive models for soot emission from gas turbine engines. Measurements of soot formation were performed in laminar flat premixed flames and turbulent non-premixed jet flames at 1 atm pressure and in turbulent liquid spray flames under representative conditions for takeoff in a gas turbine engine. The laminar flames and open jet flames used both ethylene and a prevaporized JP-8 surrogate fuel composed of n-dodecane and m-xylene. The pressurized turbulent jet flame measurements used the JP-8 surrogate fuel and compared its combustion and sooting characteristics to a world-average JP-8 fuel sample. The pressurized jet flame measurements demonstrated that the surrogate was representative of JP-8, with a somewhat higher tendency to soot formation. The premixed flame measurements revealed that flame temperature has a strong impact on the rate of soot nucleation and particle coagulation, but little sensitivity in the overall trends was found with different fuels. An extensive array of non-intrusive optical and laser-based measurements was performed in turbulent non-premixed jet flames established on specially designed piloted burners. Soot concentration data was collected throughout the flames, together with instantaneous images showing the relationship between soot and the OH radical and soot and PAH. A detailed chemical kinetic mechanism for ethylene combustion, including fuel-rich chemistry and benzene formation steps, was compiled, validated, and reduced. The reduced ethylene mechanism was incorporated into a high-fidelity LES code, together with a moment-based soot model and models for thermal radiation, to evaluate the ability of the chemistry and soot models to predict soot formation in the jet diffusion flame. The LES results highlight the importance of including an optically-thick radiation model

  13. Numerical analysis of bipropellant combustion in orbit maneuvering vehicle thrust chamber

    NASA Technical Reports Server (NTRS)

    Chiu, H. H.; Jiang, T. L.; Krebsback, A. N.; Gross, K. W.

    1990-01-01

    The combustion and aerodynamic processes of liquid-liquid bipropellant; monomethylhydrazine and nitrogen tetroxide in the combustion chamber of a variable thrust engine (VTE) have been examined to assess the flow structure, combustion characteristics, and wall heat transfer under the simulated engine operations at two power levels. The Generalized Elliptic Multi-phase flow with Chemical reaction, Heat transfer and Interfacial Processes (GEM-CHIP) code and the Bipropellant Combustion (BICOMB) code, which is the GEMCHIP algorithm reformulated in the frame work of a body fitted coordinate system, have been used for the numerical study. Combustion flow structure with non-premixed type injection that simulates the impingement type injector is predicted and the results are compared with that of the premixed injector.

  14. Progression in sulfur isotopic compositions from coal to fly ash: Examples from single-source combustion in Indiana

    USGS Publications Warehouse

    Yaofa, Jiang; Elswick, E.R.; Mastalerz, Maria

    2008-01-01

    Sulfur occurs in multiple mineral forms in coals, and its fate in coal combustion is still not well understood. The sulfur isotopic composition of coal from two coal mines in Indiana and fly ash from two power plants that use these coals were studied using geological and geochemical methods. The two coal beds are Middle Pennsylvanian in age; one seam is the low-sulfur ( 5%) Springfield Coal Member of the Petersburg Formation. Both seams have ash contents of approximately 11%. Fly-ash samples were collected at various points in the ash-collection system in the two plants. The results show notable difference in ??34S for sulfur species within and between the low-sulfur and high-sulfur coal. The ??34S values for all sulfur species are exclusively positive in the low-sulfur Danville coal, whereas the ??34S values for sulfate, pyritic, and organic sulfur are both positive and negative in the high-sulfur Springfield coal. Each coal exhibits a distinct pattern of stratigraphic variation in sulfur isotopic composition. Overall, the ??34S for sulfur species values increase up the section in the low-sulfur Danville coal, whereas they show a decrease up the vertical section in the high-sulfur Springfield coal. Based on the evolution of ??34S for sulfur species, it is suggested that there was influence of seawater on peat swamp, with two marine incursions occurring during peat accumulation of the high-sulfur Springfield coal. Therefore, bacterial sulfate reduction played a key role in converting sulfate into hydrogen sulfide, sulfide minerals, and elemental sulfur. The differences in ??34S between sulfate sulfur and pyritic sulfur is very small between individual benches of both coals, implying that some oxidation occurred during deposition or postdeposition. The ??34S values for fly ash from the high-sulfur Springfield coal (averaging 9.7???) are greatly enriched in 34S relative to those in the parent coal (averaging 2.2???). This indicates a fractionation of sulfur isotopes

  15. Large-eddy simulation of supercritical fluid flow and combustion

    NASA Astrophysics Data System (ADS)

    Huo, Hongfa

    predicted heat flux profile agrees very well with the experimental data. The steady flamelet model and the flamelet/progress-variable have been used to study the LOX/methane flame stabilized by a splitter plate. Results show that the flame is always anchored in the recirculation zone that is immediately after the splitter plate. Turbulence is not strong enough to extinguish the non-premixed flame. The flame stabilization is found to be achieved through the recirculation zone and the vortex shedding processes in the near field of the splitter plate. The flamelet-progress-variable case further confirms that the artificially quenched flame can be re-established as long as the quenching distance is within the mean recirculation zone. (Abstract shortened by UMI.)

  16. Modeling complex chemical effects in turbulent nonpremixed combustion

    NASA Technical Reports Server (NTRS)

    Smith, Nigel S. A.

    1995-01-01

    Virtually all of the energy derived from the consumption of combustibles occurs in systems which utilize turbulent fluid motion. Since combustion is largely related to the mixing of fluids and mixing processes are orders of magnitude more rapid when enhanced by turbulent motion, efficiency criteria dictate that chemically powered devices necessarily involve fluid turbulence. Where combustion occurs concurrently with mixing at an interface between two reactive fluid bodies, this mode of combustion is called nonpremixed combustion. This is distinct from premixed combustion where flame-fronts propagate into a homogeneous mixture of reactants. These two modes are limiting cases in the range of temporal lag between mixing of reactants and the onset of reaction. Nonpremixed combustion occurs where this lag tends to zero, while premixed combustion occurs where this lag tends to infinity. Many combustion processes are hybrids of these two extremes with finite non-zero lag times. Turbulent nonpremixed combustion is important from a practical standpoint because it occurs in gas fired boilers, furnaces, waste incinerators, diesel engines, gas turbine combustors, and afterburners etc. To a large extent, past development of these practical systems involved an empirical methodology. Presently, efficiency standards and emission regulations are being further tightened (Correa 1993), and empiricism has had to give way to more fundamental research in order to understand and effectively model practical combustion processes (Pope 1991). A key element in effective modeling of turbulent combustion is making use of a sufficiently detailed chemical kinetic mechanism. The prediction of pollutant emission such as oxides of nitrogen (NO(x)) and sulphur (SO(x)) unburned hydrocarbons, and particulates demands the use of detailed chemical mechanisms. It is essential that practical models for turbulent nonpremixed combustion are capable of handling large numbers of 'stiff' chemical species

  17. Prediction of Combustion Stability and Flashback in Turbines with High-Hydrogen Fuel

    SciTech Connect

    Lieuwen, Tim; Santavicca, Dom; Yang, Vigor

    2012-03-31

    During the duration of this sponsorship, we broadened our understanding of combustion instabilities through both analytical and experimental work. Predictive models were developed for flame response to transverse acoustic instabilities and for quantifying how a turbulent flame responds to velocity and fuel/air ratio forcing. Analysis was performed on the key instability mechanisms controlling heat release response for flames over a wide range of instability frequencies. Importantly, work was done closely with industrial partners to transition existing models into internal instability prediction codes. Experimentally, the forced response of hydrogen-enriched natural gas/air premixed and partially premixed flames were measured. The response of a lean premixed flame was investigated, subjected to velocity, equivalence ratio, and both forcing mechanisms simultaneously. In addition, important physical mechanisms controlling the response of partially premixed flames to inlet velocity and equivalence ratio oscillations were analyzed. This final technical report summarizes our findings and major publications stemming from this program.

  18. Combustion of pulverized coal in vortex structures. Quarterly progress report No. 6, January 1, 1995--March 31, 1995

    SciTech Connect

    Gollahalli, S.R.

    1995-03-01

    This sixth quarterly report describes the activities and accomplishments of the research team at the University of Oklahoma, Norman, Oklahoma, related to the project entitled ``Combustion of Pulverized Coal in Vortex Structures`` during the period January 1, 1995 to March 31, 1995. The work performed in this quarter consisted of the following four tasks: (1) design and fabrication of a computer-driven traversing mechanism for traversing LDV transmitter and receiving optics, (2) color schlieren photography, (3) presenting a report in the panel-review meeting in Pittsburgh, (4) installation of additional safety devices in response to the letter of Dr. Sean Plasynski, and (5) streamwise velocity measurement in the isothermal heterogeneous shear layer with nonreacting particles using LDV. In the next quarter, we plan to continue this work with heated shear layers in which particles undergo pyrolysis. Flow visualization and mean velocity field measurement instrumentation will continue as the major experimental techniques.

  19. Transient change in the shape of premixed burner flame with the superposition of pulsed dielectric barrier discharge

    NASA Astrophysics Data System (ADS)

    Zaima, Kazunori; Sasaki, Koichi

    2016-08-01

    We investigated the transient phenomena in a premixed burner flame with the superposition of a pulsed dielectric barrier discharge (DBD). The length of the flame was shortened by the superposition of DBD, indicating the activation of combustion chemical reactions with the help of the plasma. In addition, we observed the modulation of the top position of the unburned gas region and the formations of local minimums in the axial distribution of the optical emission intensity of OH. These experimental results reveal the oscillation of the rates of combustion chemical reactions as a response to the activation by pulsed DBD. The cycle of the oscillation was 0.18–0.2 ms, which could be understood as the eigenfrequency of the plasma-assisted combustion reaction system.

  20. Transient change in the shape of premixed burner flame with the superposition of pulsed dielectric barrier discharge

    NASA Astrophysics Data System (ADS)

    Zaima, Kazunori; Sasaki, Koichi

    2016-08-01

    We investigated the transient phenomena in a premixed burner flame with the superposition of a pulsed dielectric barrier discharge (DBD). The length of the flame was shortened by the superposition of DBD, indicating the activation of combustion chemical reactions with the help of the plasma. In addition, we observed the modulation of the top position of the unburned gas region and the formations of local minimums in the axial distribution of the optical emission intensity of OH. These experimental results reveal the oscillation of the rates of combustion chemical reactions as a response to the activation by pulsed DBD. The cycle of the oscillation was 0.18-0.2 ms, which could be understood as the eigenfrequency of the plasma-assisted combustion reaction system.

  1. Rayleigh/Raman/LIF measurements in a turbulent lean premixed combustor

    SciTech Connect

    Nandula, S.P.; Pitz, R.W.; Barlow, R.S.

    1995-10-01

    Much of the industrial electrical generation capability being added worldwide is gas-turbine engine based and is fueled by natural gas. These gas-turbine engines use lean premixed (LP) combustion to meet the strict NO{sub x} emission standards, while maintaining acceptable levels of CO. In conventional, diffusion flame gas turbine combustors, large amount of NO{sub x} forms in the hot stoichiometric zones via the Zeldovich (thermal) mechanism. Hence, lean premixed combustors are rapidly becoming the norm, since they are specifically designed to avoid these hot stoichiometric zones and the associated thermal NO, However, considerable research and development are still required to reduce the NO{sub x} levels (25-40 ppmvd adjusted to 15% O{sub 2} with the current technology), to the projected goal of under 10 ppmvd by the turn of the century. Achieving this objective would require extensive experiments in LP natural gas (or CH{sub 4}) flames for understanding the combustion phenomena underlying the formation of the exhaust pollutants. Although LP combustion is an effective way to control NO{sub x}, the downside is that it increases the CO emissions. The formation and destruction of the pollutants (NO{sub x} and CO) are strongly affected by the fluid mechanics, the finite-rate chemistry, and their (turbulence-chemistry) interactions. Hence, a thorough understanding of these interactions is vital for controlling and reducing the pollutant emissions. The present research is contributing to this goal by providing a detailed nonintrusive laser based data set with good spatial and temporal resolutions of the pollutants (NO and CO) along with the major species, temperature, and OH. The measurements reported in this work, along with the existing velocity data on a turbulent LP combustor burning CH{sub 4}, would provide insight into the turbulence-chemistry interactions and their effect on pollutant formation.

  2. Active control for turbulent premixed flame simulations

    SciTech Connect

    Bell, John B.; Day, Marcus S.; Grcar, Joseph F.; Lijewski, Michael J.

    2004-03-26

    Many turbulent premixed flames of practical interest are statistically stationary. They occur in combustors that have anchoring mechanisms to prevent blow-off and flashback. The stabilization devices often introduce a level of geometric complexity that is prohibitive for detailed computational studies of turbulent flame dynamics. As a result, typical detailed simulations are performed in simplified model configurations such as decaying isotropic turbulence or inflowing turbulence. In these configurations, the turbulence seen by the flame either decays or, in the latter case, increases as the flame accelerates toward the turbulent inflow. This limits the duration of the eddy evolutions experienced by the flame at a given level of turbulent intensity, so that statistically valid observations cannot be made. In this paper, we apply a feedback control to computationally stabilize an otherwise unstable turbulent premixed flame in two dimensions. For the simulations, we specify turbulent in flow conditions and dynamically adjust the integrated fueling rate to control the mean location of the flame in the domain. We outline the numerical procedure, and illustrate the behavior of the control algorithm. We use the simulations to study the propagation and the local chemical variability of turbulent flame chemistry.

  3. Numerical prediction of turbulent flame stability in premixed/prevaporized (HSCT) combustors

    NASA Technical Reports Server (NTRS)

    Winowich, Nicholas S.

    1990-01-01

    A numerical analysis of combustion instabilities that induce flashback in a lean, premixed, prevaporized dump combustor is performed. KIVA-II, a finite volume CFD code for the modeling of transient, multidimensional, chemically reactive flows, serves as the principal analytical tool. The experiment of Proctor and T'ien is used as a reference for developing the computational model. An experimentally derived combustion instability mechanism is presented on the basis of the observations of Proctor and T'ien and other investigators of instabilities in low speed (M less than 0.1) dump combustors. The analysis comprises two independent procedures that begin from a calculated stable flame: The first is a linear increase of the equivalence ratio and the second is the linear decrease of the inflow velocity. The objective is to observe changes in the aerothermochemical features of the flow field prior to flashback. It was found that only the linear increase of the equivalence ratio elicits a calculated flashback result. Though this result did not exhibit large scale coherent vortices in the turbulent shear layer coincident with a flame flickering mode as was observed experimentally, there were interesting acoustic effects which were resolved quite well in the calculation. A discussion of the k-e turbulence model used by KIVA-II is prompted by the absence of combustion instabilities in the model as the inflow velocity is linearly decreased. Finally, recommendations are made for further numerical analysis that may improve correlation with experimentally observed combustion instabilities.

  4. Fuel Flexible Combustion Systems for High-Efficiency Utilization of Opportunity Fuels in Gas Turbines

    SciTech Connect

    Venkatesan, Krishna

    2011-11-30

    The purpose of this program was to develop low-emissions, efficient fuel-flexible combustion technology which enables operation of a given gas turbine on a wider range of opportunity fuels that lie outside of current natural gas-centered fuel specifications. The program encompasses a selection of important, representative fuels of opportunity for gas turbines with widely varying fundamental properties of combustion. The research program covers conceptual and detailed combustor design, fabrication, and testing of retrofitable and/or novel fuel-flexible gas turbine combustor hardware, specifically advanced fuel nozzle technology, at full-scale gas turbine combustor conditions. This project was performed over the period of October 2008 through September 2011 under Cooperative Agreement DE-FC26-08NT05868 for the U.S. Department of Energy/National Energy Technology Laboratory (USDOE/NETL) entitled "Fuel Flexible Combustion Systems for High-Efficiency Utilization of Opportunity Fuels in Gas Turbines". The overall objective of this program was met with great success. GE was able to successfully demonstrate the operability of two fuel-flexible combustion nozzles over a wide range of opportunity fuels at heavy-duty gas turbine conditions while meeting emissions goals. The GE MS6000B ("6B") gas turbine engine was chosen as the target platform for new fuel-flexible premixer development. Comprehensive conceptual design and analysis of new fuel-flexible premixing nozzles were undertaken. Gas turbine cycle models and detailed flow network models of the combustor provide the premixer conditions (temperature, pressure, pressure drops, velocities, and air flow splits) and illustrate the impact of widely varying fuel flow rates on the combustor. Detailed chemical kinetic mechanisms were employed to compare some fundamental combustion characteristics of the target fuels, including flame speeds and lean blow-out behavior. Perfectly premixed combustion experiments were conducted to

  5. Combustion of pulverized coal in vortex structures. Quarterly progress report No. 2, January 1, 1994--March 31, 1994

    SciTech Connect

    Gollahalli, S.R.

    1994-04-01

    This second quarterly report describes the activities and accomplishments of the research team at the University of Oklahoma, Norman, Oklahoma, related to the project entitled ``Combustion of Pulverized Coal in Vortex Structures`` during the period January 1, 1994 to March 31, 1994. The construction of the experimental facility for generating two-dimensional shear layers containing vortex structures has been completed. Preliminary shake-down test of the test facility were conducted for debugging and fine-tuning. A smoke generator was constructed for smoke-visualization of shear layers. Direct photographs of smoke flow patterns of the interfacial region of the mixing layers have been taken. Mean velocity profiles in the direction normal to the tunnel stream direction have been measured with a hot-wire anemometer for different ratios of the initial velocities of the mixing streams. In the next quarter, we plan to conduct schlieren flow visualization of the shear layer, fabricate the particulate feeding system, and measure the velocity field as a function of the particulate concentration in one of the streams.

  6. Blowoff dynamics of bluff body stabilized turbulent premixed flames

    SciTech Connect

    Chaudhuri, Swetaprovo; Kostka, Stanislav; Renfro, Michael W.; Cetegen, Baki M.

    2010-04-15

    This article concerns the flame dynamics of a bluff body stabilized turbulent premixed flame as it approaches lean blowoff. Time resolved chemiluminescence imaging along with simultaneous particle image velocimetry and OH planar laser-induced fluorescence were utilized in an axisymmetric bluff body stabilized, propane-air flame to determine the sequence of events leading to blowoff and provide a quantitative analysis of the experimental results. It was found that as lean blowoff is approached by reduction of equivalence ratio, flame speed decreases and the flame shape progressively changes from a conical to a columnar shape. For a stably burning conical flame away from blowoff, the flame front envelopes the shear layer vortices. Near blowoff, the columnar flame front and shear layer vortices overlap to induce high local stretch rates that exceed the extinction stretch rates instantaneously and in the mean, resulting in local flame extinction along the shear layers. Following shear layer extinction, fresh reactants can pass through the shear layers to react within the recirculation zone with all other parts of the flame extinguished. This flame kernel within the recirculation zone may survive for a few milliseconds and can reignite the shear layers such that the entire flame is reestablished for a short period. This extinction and reignition event can happen several times before final blowoff which occurs when the flame kernel fails to reignite the shear layers and ultimately leads to total flame extinguishment. (author)

  7. EXPERIMENTAL AND MODELING STUDY OF PREMIXED LAMINAR FLAMES OF ETHANOL AND METHANE

    PubMed Central

    Tran, Luc-Sy; Glaude, Pierre-Alexandre; Fournet, René; Battin-Leclerc, Frédérique

    2013-01-01

    To better understand the chemistry of the combustion of ethanol, the structure of five low pressure laminar premixed flames has been investigated: a pure methane flame (φ=1), three pure ethanol flames (φ=0.7, 1.0, and 1.3), and an ethanol/methane mixture flames (φ=1). The flames have been stabilized on a burner at a pressure of 6.7 kPa using argon as dilutant, with a gas velocity at the burner of 64.3 cm/s at 333 K. The results consist of mole fraction profiles of 20 species measured as a function of the height above the burner by probe sampling followed by online gas chromatography analyses. A mechanism for the oxidation of ethanol was proposed. The reactions of ethanol and acetaldehyde were updated and include recent theoretical calculations while that of ethenol, dimethyl ether, acetone, and propanal were added in the mechanism. This mechanism was also tested against experimental results available in the literature for laminar burning velocities and laminar premixed flame where ethenol was detected. The main reaction pathways of consumption of ethanol are analyzed. The effect of the branching ratios of reaction C2H5OH+OH→Products+H2O is also discussed. PMID:23712124

  8. Direct spectral/hp element simulation of piloted jet non-premixed flames

    NASA Astrophysics Data System (ADS)

    Nastase, Cristian R.

    2004-11-01

    The spectral/hp element method is used for direct numerical simulation (DNS) of piloted non premixed methane jet flames. This method combines the accuracy of spectral methods with versatility of finite element methods, and allows accurate simulations of complex flows on structured and unstructured grids. Here, the methodology is extended for simulation of multi-species, reactive flows using the discontinuous Galerkin formulation. Parallel computation is performed via MPI standards coupled with a domain decomposition methodology. The overall computational scheme allows for an efficient partitioning of the flow configuration. Tests performed with up to 64 processors show quasi-linear parallel performance and scalability. The flame configurations are similar to the piloted jet non-premixed flame considered at the Combustion Research Facility at the Sandia National Laboratories. For a momentum dominated flame, the simulated results portray many of the features observed experimentally. This pertains to both the spatial and the compositional structures of the flow. For a buoyancy controlled flame (at elevated gravity levels), the results indicate an increase in both the turbulence levels and flow acceleration. Departure from equilibrium, including localized extinction is observed on a significant portion of this flame.

  9. Chemical kinetic considerations for postflame synthesis of carbon nanotubes in premixed flames using a support catalyst

    SciTech Connect

    Gopinath, Prarthana; Gore, Jay

    2007-11-15

    Multiwalled carbon nanotubes (MWCNTs) on a grid supported cobalt nanocatalyst were grown, by exposing it to combustion gases from ethylene/air rich premixed flames. Ten equivalence ratios ({phi}) were investigated, as follows: 1.37, 1.44, 1.47, 1.50, 1.55, 1.57, 1.62, 1.75, 1.82, and 1.91. MWCNT growth could be observed for the range of equivalence ratios between 1.45 and 1.75, with the best yield restricted to the range 1.5-1.6. A one-dimensional premixed flame code with a postflame heat loss model, including detailed chemistry, was used to estimate the gas phase chemical composition that favors MWCNT growth. The results of the calculations show that the mixture, including the water gas shift reaction, is not even in partial chemical equilibrium. Therefore, past discussions of compositional parameters that relate to optimum carbon nanotube (CNT) growth are revised to include chemical kinetic effects. Specifically, rapid departures of the water gas shift reaction from partial equilibrium and changes in mole fraction ratios of unburned C{sub 2} hydrocarbons to hydrogen correlate well with experimentally observed CNT yields. (author)

  10. Large eddy simulation of soot formation in a turbulent non-premixed jet flame

    SciTech Connect

    El-Asrag, Hossam; Menon, Suresh

    2009-02-15

    A recently developed subgrid model for soot dynamics [H. El-Asrag, T. Lu, C.K. Law, S. Menon, Combust. Flame 150 (2007) 108-126] is used to study the soot formation in a non-premixed turbulent flame. The model allows coupling between reaction, diffusion and soot (including soot diffusion and thermophoretic forces) processes in the subgrid domain without requiring ad hoc filtering or model parameter adjustments. The combined model includes the entire process, from the initial phase, when the soot nucleus diameter is much smaller than the mean free path, to the final phase, after coagulation and aggregation, where it can be considered in the continuum regime. A relatively detailed but reduced kinetics for ethylene-air is used to simulate an experimentally studied non-premixed ethylene/air jet diffusion flame. Acetylene is used as a soot precursor species. The soot volume fraction order of magnitude, the location of its maxima, and the soot particle size distribution are all captured reasonably. Along the centerline, an initial region dominated by nucleation and surface growth is established followed by an oxidation region. The diffusion effect is found to be most important in the nucleation regime, while the thermophoretic forces become more influential downstream of the potential core in the oxidation zone. The particle size distribution shows a log-normal distribution in the nucleation region, and a more Gaussian like distribution further downstream. Limitations of the current approach and possible solution strategies are also discussed. (author)

  11. A fluidized bed selective emitter system driven by a non-premixed burner

    NASA Astrophysics Data System (ADS)

    Ortabasi, U.; Lund, K. O.; Seshadri, K.

    1996-02-01

    One of the key priorities in the development of Thermophotovoltaic power technology is a highly efficient heat-source/emitter system that is robust and stable. This paper describes a tightly coupled burner/selective emitter combination that integrates two novel concepts that are now under development: A fluidized bed emitter that consists of hollow, submillimeter spheres as the sources of radiant energy and a non-premixed, self regulating burner. The rationale behind the proposed system is to combine the unique intrinsic features of both concepts to provide the TPV community with an enabling technology. The fluidized bed provides excellent heat transfer, temperature uniformity, high radiant power density, reduced substrate and combustion background, robustness, thermal shock resistance, minimal contamination, and long operational life. The paper discusses a fluidized bed system that consists of selectively emitting, hollow Ho-YAG spheres with 500 micron diameter and 10-100 micron shell thickness operating at 1500 K. Key issues related to heat transfer and radiation transport in the fluidized bed are analyzed. The collective emitter efficiency and power density of a fluidized bed are discussed. The non-premixed burner achieves very high temperatures, has a low emission in toxic byproducts, provides self regulating stability, eliminates flashback hazards, and is operable with hydrogen. The paper concludes with a description of a complete fluidized bed TPV system including an elliptic/parabolic transfer optics and a photovoltaic cavity converter that boosts the flux density received by the photovoltaic cells.

  12. OH-Planar Fluorescence Measurements of Pressurized, Hydrogen Premixed Flames in the SimVal Combustor

    SciTech Connect

    Strakey, P.A.; Woodruff, S.D.; Williams, T.C.; Schefer, R.W.

    2008-07-01

    Planar laser-induced fluorescence measurements of the hydroxyl radical in lean, premixed natural gas flames augmented with hydrogen are presented. The experiments were conducted in the Simulation Validation combustor at the National Energy Technology Laboratory at operating pressures from 1 to 8 atmospheres. The data, which were collected in a combustor with well-controlled boundary conditions, are intended to be used for validating computational fluid dynamics models under conditions directly relevant to land-based gas turbine engines. The images, which show significant effects of hydrogen on local flame quenching, are discussed in terms of a turbulent premixed combustion regime and nondimensional parameters such as Karlovitz number. Pressure was found to thin the OH region, but only had a secondary effect on overall flame shape compared with the effects of hydrogen addition, which was found to decrease local quenching and shorten the turbulent flame brush. A method to process the individual images based on local gradients of fluorescence intensity is proposed, and results are presented. Finally, the results of several large eddy simulations are presented and compared with the experimental data in an effort to understand the issues related to model validation, especially for simulations that do not include OH as an intermediate species.

  13. Large eddy simulation and laser diagnostic studies on a low swirl stratified premixed flame

    SciTech Connect

    Nogenmyr, K.-J.; Bai, X.S.; Fureby, C.; Petersson, P.; Collin, R.; Linne, M.

    2008-11-15

    This paper presents numerical simulations and laser diagnostic experiments of a swirling lean premixed methane/air flame with an aim to compare different Large Eddy Simulations (LES) models for reactive flows. An atmospheric-pressure laboratory swirl burner has been developed wherein lean premixed methane/air is injected in an unconfined low-speed flow of air. The flame is stabilized above the burner rim in a moderate swirl flow, triggering weak vortex breakdown in the downstream direction. Both stereoscopic (3-component) PIV and 2-component PIV are used to investigate the flow. Filtered Rayleigh scattering is used to examine the temperature field in the leading flame front. Acetone-Planar Laser Induced Fluorescence (PLIF) is applied to examine the fuel distribution. The experimental data are used to assess two different LES models; one based on level-set G-equation and flamelet chemistry, and the other based on finite rate chemistry with reduced kinetics. The two LES models treat the chemistry differently, which results in different predictions of the flame dynamic behavior and statistics. Yet, great similarity of flame structures was predicted by both models. The LES and experimental data reveal several intrinsic features of the low swirl flame such as the W-shape at the leading front, the highly wrinkled fronts in the shear layers, and the existence of extinction holes in the trailing edge of the flame. The effect of combustion models, the numerical solvers and boundary conditions on the flame and flow predictions was systematically examined. (author)

  14. Large eddy simulation and laser diagnostic studies on a low swirl stratified premixed flame

    SciTech Connect

    Nogenmyr, K.-J.; Bai, X.S.; Fureby, C.; Petersson, P.; Collin, R.; Linne, M.

    2009-01-15

    This paper presents numerical simulations and laser diagnostic experiments of a swirling lean premixed methane/air flame with an aim to compare different Large Eddy Simulations (LES) models for reactive flows. An atmospheric-pressure laboratory swirl burner has been developed wherein lean premixed methane/air is injected in an unconfined low-speed flow of air. The flame is stabilized above the burner rim in a moderate swirl flow, triggering weak vortex breakdown in the downstream direction. Both stereoscopic (3-component) PIV and 2-component PIV are used to investigate the flow. Filtered Rayleigh scattering is used to examine the temperature field in the leading flame front. Acetone-Planar Laser Induced Fluorescence (PLIF) is applied to examine the fuel distribution. The experimental data are used to assess two different LES models; one based on level-set G-equation and flamelet chemistry, and the other based on finite rate chemistry with reduced kinetics. The two LES models treat the chemistry differently, which results in different predictions of the flame dynamic behavior and statistics. Yet, great similarity of flame structures was predicted by both models. The LES and experimental data reveal several intrinsic features of the low swirl flame such as the W-shape at the leading front, the highly wrinkled fronts in the shear layers, and the existence of extinction holes in the trailing edge of the flame. The effect of combustion models, the numerical solvers and boundary conditions on the flame and flow predictions was systematically examined. (author)

  15. Effect of turbulence characteristics on local flame structure of H2 air premixed flames

    NASA Astrophysics Data System (ADS)

    Nada, Y.; Tanahashi, M.; Miyauchi, T.

    2004-04-01

    Direct numerical simulations (DNS) of turbulent premixed flames are conducted to investigate effects of turbulence characteristics on the local flame structure. A detailed kinetic mechanism including 12 reactive species and 27 elementary reactions is used to represent the H2-air reaction in turbulence. Numerical conditions of DNS can be classified into a wrinkled-flamelets regime, a corrugated-flamelets regime and thin reaction zones near the boundary of Karlovitz number Ka=1.0 of the turbulent-combustion diagram. For all cases, the distribution of heat-release rate shows a three-dimensionally connected sheet-like feature, even though the heat-release rate highly fluctuates along the flamefront. The heat-release rate tends to increase at the flamefronts that are convex towards the burnt side. For the turbulent premixed flames in the corrugated-flamelets regime, the handgrip structure is produced by the intrusion of the coherent fine-scale eddy into the flame and the heat-release rate in this structure increases up to 1.2 times of that of a laminar flame. In the wrinkled-flamelets regime, the spire-like structure of the flamefront is created due to the coherent fine-scale eddies in turbulence. By identifying flame elements in turbulence, their statistical characteristics are also discussed. This article was chosen from Selected Proceedings of the Third International Symposium on Turbulence and Shear Flow Phenomena (Sendai, Japan, 24-27 June 2003) ed N Kasagi et al.

  16. A coal-fired combustion system for industrial process heating applications. Quarterly technical progress report, July 1993--September 1993

    SciTech Connect

    Not Available

    1993-10-30

    This advanced combustion system research program is for the development of innovative coal-fired process heaters which can be used for high temperature melting, smelting and waste vitrification processes. The process heater systems to be developed have multiple use applications; however, the Phase 3 research effort is being focused on the development of a process heater system to be used for producing value added vitrified glass products from boiler/incinerator ashes and industrial wastes. The primary objective of the Phase 3 project is to develop and integrate all the system components, from fuel through total system controls, and then test the complete system in order to evaluate its potential marketability. During the past quarter, the major effort was completing some of the system modification installation designs, completing industry funded testing, developing a surrogate TSCA ash composition, and completing the TSCA ash Test Plan. The installation designs will be used for the equipment modifications planned for the end of CY 93. The industry funded testing consisted of vitrifying Spent Aluminum Potliner (SPL) which is a listed hazardous waste. This testing has verified that SPL can be vitrified into a safe, recyclable glass product. Some results from this testing are provided in Section 2.2.1. The surrogate TSCA ash composition was developed with input from various DOE laboratories and subcontractors. The surrogate ash consists of a mixture of MSW fly ash and bottom ash spiked with heavy metal contaminants. The levels of metal additives are sufficient to ascertain the partitioning of the contaminants between the glass and effluent flow streams. Details of the surrogate composition and the planned testing is provided in Section 4.2.2.

  17. Premixed flames in closed cylindrical tubes

    NASA Astrophysics Data System (ADS)

    Metzener, Philippe; Matalon, Moshe

    2001-09-01

    We consider the propagation of a premixed flame, as a two-dimensional sheet separating unburned gas from burned products, in a closed cylindrical tube. A nonlinear evolution equation, that describes the motion of the flame front as a function of its mean position, is derived. The equation contains a destabilizing term that results from the gas motion induced by thermal expansion and has a memory term associated with vorticity generation. Numerical solutions of this equation indicate that, when diffusion is stabilizing, the flame evolves into a non-planar form whose shape, and its associated symmetry properties, are determined by the Markstein parameter, and by the initial data. In particular, we observe the development of convex axisymmetric or non-axisymmetric flames, tulip flames and cellular flames.

  18. In vitro and in vivo carcinogenesis of metals and their coumpounds produced by coal combustion. Progress report

    SciTech Connect

    Costa, M.

    1982-04-08

    Research progress in the following areas is reported. The phagocytosis activity and induction of cell transformation by a number of particulate metal compounds in tissue culture systems (crystalline or amorphous NiS, CoS, CuS, and CdS) have been examined. The induction of DNA strand breaks by various water soluble and insoluble metal compounds was demonstrated. It has been found that the surface charge of a particle has a direct influence on whether it will be phagocytosed and this property ultimately affects its carcinogenic ability. The ability of nickel compounds to interact and bind with DNA, RNA and protein was investigated. (ACR)

  19. Implementation of Premixed Equilibrium Chemistry Capability in OVERFLOW

    NASA Technical Reports Server (NTRS)

    Olsen, Mike E.; Liu, Yen; Vinokur, M.; Olsen, Tom

    2004-01-01

    An implementation of premixed equilibrium chemistry has been completed for the OVERFLOW code, a chimera capable, complex geometry flow code widely used to predict transonic flowfields. The implementation builds on the computational efficiency and geometric generality of the solver.

  20. Implementation of Premixed Equilibrium Chemistry Capability in OVERFLOW

    NASA Technical Reports Server (NTRS)

    Olsen, M. E.; Liu, Y.; Vinokur, M.; Olsen, T.

    2003-01-01

    An implementation of premixed equilibrium chemistry has been completed for the OVERFLOW code, a chimera capable, complex geometry flow code widely used to predict transonic flowfields. The implementation builds on the computational efficiency and geometric generality of the solver.

  1. Structure of the Soot Growth Region of Laminar Premixer Methane/Oxygen Flames

    NASA Technical Reports Server (NTRS)

    Xu, F.; Faeth, G. M.

    1999-01-01

    Soot is a dominant feature of hydrocarbon/air flames, affecting their reaction mechanisms and structure. As a result, soot processes affect capabilities for computational combustion as well as predictions of flame radiation and pollution emissions. Motivated by these observations, the present investigation extended past work on soot growth in laminar premixed flames, seeking to evaluate model predictions of flame structure. Xu et al. report direct measurements of soot residence times, soot concentrations, soot structure, gas temperatures and gas compositions for premixed flames similar to those studied by Harris and Weiner and Ramer et al. respectively. It was found that predictions of major stable gas species concentrations based on mechanisms of Leung and Lindstedt and Frenklach and coworkers, were in good agreement with the measurements. The results were also used to evaluate the hydrogen-abstraction/carbon-addition (HACA) soot growth mechanisms of Frenklach and coworkers and Colket and Hall. It was found that these mechanisms were effective using quite reasonable correlations for the steric factors appearing in the theories. The successful evaluation of the HACA mechanism of soot growth in Refs. 1 and 2 is encouraging but one aspect of this evaluation is a concern. In particular, H-atom concentrations play a crucial role in the HACA mechanism and it was necessary to estimate these concentrations because they were not measured directly. These estimates were made assuming local thermodynamic equilibrium between H, and H based on measured temperatures and H2 concentrations and the equilibrium constant data of Kee et al.. This approach was justified by the flame structure predictions; nevertheless, direct evaluation of equilibrium estimates of H-atom concentrations in the soot growth regions of laminar premixed flames is needed to provide more convincing proof of this behavior. Thus, the objective of the present investigation was to complete new measurements of the

  2. Subgrid Combustion Modeling for the Next Generation National Combustion Code

    NASA Technical Reports Server (NTRS)

    Menon, Suresh; Sankaran, Vaidyanathan; Stone, Christopher

    2003-01-01

    In the first year of this research, a subgrid turbulent mixing and combustion methodology developed earlier at Georgia Tech has been provided to researchers at NASA/GRC for incorporation into the next generation National Combustion Code (called NCCLES hereafter). A key feature of this approach is that scalar mixing and combustion processes are simulated within the LES grid using a stochastic 1D model. The subgrid simulation approach recovers locally molecular diffusion and reaction kinetics exactly without requiring closure and thus, provides an attractive feature to simulate complex, highly turbulent reacting flows of interest. Data acquisition algorithms and statistical analysis strategies and routines to analyze NCCLES results have also been provided to NASA/GRC. The overall goal of this research is to systematically develop and implement LES capability into the current NCC. For this purpose, issues regarding initialization and running LES are also addressed in the collaborative effort. In parallel to this technology transfer effort (that is continuously on going), research has also been underway at Georgia Tech to enhance the LES capability to tackle more complex flows. In particular, subgrid scalar mixing and combustion method has been evaluated in three distinctly different flow field in order to demonstrate its generality: (a) Flame-Turbulence Interactions using premixed combustion, (b) Spatially evolving supersonic mixing layers, and (c) Temporal single and two-phase mixing layers. The configurations chosen are such that they can be implemented in NCCLES and used to evaluate the ability of the new code. Future development and validation will be in spray combustion in gas turbine engine and supersonic scalar mixing.

  3. Non-premixed flame-turbulence interaction in compressible turbulent flow

    SciTech Connect

    Livescu, D.; Madnia, C. K.

    2002-01-01

    Nonpremixed turbulent reacting flows are intrinsically difficult to model due to the strong coupling between turbulent motions and reaction. The large amount of heat released by a typical hydrocarbon flame leads to significant modifications of the thermodynamic variables and the molecular transport coefficients and thus alters the fluid dynamics. Additionally, in nonpremixed combustion, the flame has a complex spatial structure. Localized expansions and contractions occur, enhancing the dilatational motions. Therefore, the compressibility of the flow and the heat release are intimately related. However, fundamental studies of the role of compressibility on the scalar mixing and reaction are scarce. In this paper they present results concerning the fundamental aspects of the interaction between non-premixed flame and compressible turbulence.

  4. Propagation of a premixed flame in a divided-chamber combustor

    NASA Technical Reports Server (NTRS)

    Cattolica, R. J.; Barr, P. K.; Mansour, N. N.

    1987-01-01

    The propagation of premixed ethylene-air mixtures (of 0.5, 0.525, 0.55, and 0.65 equivalence ratios) in a divided-chamber combustor was investigated. The vessel, divided by a small cylindrical prechamber, had optical access (for laser-schlieren videography) and was instrumented by a pressure transducer. For the Reynolds numbers of 1870, 2300, and 2830, the observed spatial development of the laminar flames showed that the flame position and shape could be scaled by a characteristic time, based on the burned gas flame speed and the length of the prechamber. Above a Reynolds number of 4330, this scaling breaks down the appearance of Kelvin-Helmholtz instabilities. The observed flame propagation was compared with predictions obtained with a numerical model of flame propagation. The calculated spatial and temporal development of the flame in the main combustion chamber agreed with the experimental observations only for the lowest Reynolds number (1870).

  5. Effect of flameholder pressure drop on emissions and performance of premixed-prevaporized combustors

    NASA Technical Reports Server (NTRS)

    Duerr, R. A.; Lyons, V. J.

    1983-01-01

    Parametric tests were conducted to determine the effects of flameholder pressure drop on the emissions and performance of lean premixed-prevaporized combustors. A conical flameholder mounted in a diverging duct was tested with two values of flameholder blockage. Emissions of nitrogen oxides, carbon monoxide, carbon dioxide, and unburned hydrocarbons were measured for combustor entrance conditions of 600 to 800 K air temperature, 0.3 MPa to 0.5 MPa pressure, and 20 m/sec to 35 m/sec reference velocity. Jet A fuel was injected at flow rates corresponding to an equivalence ratio range from 0.8 down to the lean stability limit. Emission results for the high-blockage flameholder were a substantial improvement over the low-blockage emission results. A correlation of combustion efficiency with flameholder pressure drop was developed for pressure drops less than 9 percent.

  6. Dynamics of premixed flames in a narrow channel with a step-wise wall temperature

    SciTech Connect

    Kurdyumov, Vadim N.; Pizza, Gianmarco; Frouzakis, Christos E.; Mantzaras, John

    2009-11-15

    The effect of channel height, inflow velocity and wall temperature on the dynamics and stability of unity Lewis number premixed flames in channels with specified wall temperature is investigated with steady and transient numerical simulations using a two-dimensional thermo-diffusive model. The simplified model is capable of capturing many of the transitions and the combustion modes observed experimentally and in direct numerical simulations in micro- and meso-scale channels, and indicates that the thermal flame/wall interaction is the mechanism leading to the observed flame instabilities. Finally, an ad-hoc one-dimensional model based on the flame-sheet approximation is tested in its capacity to reproduce some of the flame dynamics of the two-dimensional thermo-diffusive model. (author)

  7. Fourth International Microgravity Combustion Workshop

    NASA Technical Reports Server (NTRS)

    Sacksteder, Kurt R. (Compiler)

    1997-01-01

    This Conference Publication contains 84 papers presented at the Fourth International Microgravity Combustion Workshop held in Cleveland, Ohio, from May 19 to 21, 1997. The purpose of the workshop was twofold: to exchange information about the progress and promise of combustion science in microgravity and to provide a forum to discuss which areas in microgravity combustion science need to be expanded profitably and which should be included in upcoming NASA Research Announcements (NRA).

  8. Study and modeling of finite rate chemistry effects in turbulent non-premixed flames

    NASA Technical Reports Server (NTRS)

    Vervisch, Luc

    1993-01-01

    The development of numerical models that reflect some of the most important features of turbulent reacting flows requires information about the behavior of key quantities in well defined combustion regimes. In turbulent flames, the coupling between turbulent and chemical processes is so strong that it is extremely difficult to isolate the role played by one individual physical phenomenon. Direct numerical simulation (hereafter DNS) allows us to study in detail the turbulence-chemistry interaction in some restricted but completely defined situations. Globally, non-premixed flames are controlled by two limiting regimes: the fast chemistry case, where the turbulent flame can be pictured as a random distribution of local chemical equilibrium problems; and the slow chemistry case, where the chemistry integrates in time the turbulent fluctuations. The Damkoehler number, ratio of a mechanical time scale to chemical time scale, is used to distinguish between these regimes. Today most of the industrial computer codes are able to perform predictions in the hypothesis of local equilibrium chemistry using a presumed shape for the probability density function (pdt) of the conserved scalar. However, the finite rate chemistry situation is of great interest because industrial burners usually generate regimes in which, at some points, the flame is undergoing local extinction or at least non-equilibrium situations. Moreover, this variety of situations strongly influences the production of pollutants. To quantify finite rate chemistry effect, the interaction between a non-premixed flame and a free decaying turbulence is studied using DNS. The attention is focused on the dynamic of extinction, and an attempt is made to quantify the effect of the reaction on the small scale mixing process. The unequal diffusivity effect is also addressed. Finally, a simple turbulent combustion model based on the DNS observations and tractable in real flow configurations is proposed.

  9. Design, construction, operation, and evaluation of a prototype culm combustion boiler/heater unit. Quarterly technical progress report, October 1-December 21, 1981

    SciTech Connect

    Not Available

    1982-01-01

    This report provides a summary of the work performed on the Prototype Culm Combustion Boiler/Heater Unit, Phase I - Engineering Design and Analysis, Phase II - Prototype Plant Construction and Phase III - Start-Up and Operation during the period October 1, 1981 through December 31, 1981. The objectives of the program as well as the technical progress and problem areas encountered during the reporting period are presented. Seven shakedown tests were run. Start-up and shakedown testing was completed. Four parametric tests were run. Performance data are presented with the exception of boiler efficiency which will be reported once chemical analyses are completed. Total boiler operation time through the end of this quarter - 1225 h, 50 min; operating time on culm and culm/limestone - 682 h, 43 min. Inspection revealed no problems with boiler tube wear. Sulfur capture greater than 94% was demonstrated (design is 88%). A turndown of better than 4 to 1 was shown (design is 2.5 to 1). Computer control of most of the loops has been successful and manual control was also demonstrated.

  10. Formation and Combustion of Smoke in Laminar Flames

    NASA Technical Reports Server (NTRS)

    Schalla, Rose L; Clark, Thomas P; Mcdonald, Glen E

    1954-01-01

    The nature and formation of smoke and its combustion were investigated. Smoke, which consist of tiny mesomorphous crystals tightly packed into popcorn-ball-like particles that agglomerate to give filaments, was found to contain about 5 percent of the hydrogen originally present in the fuel. Factors affecting smoke formation were studied in both diffusion flames and premixed Bunsen flames. It is suggested that smoking tendency increases with increasing stability of the carbon skeleton of the molecule, as determined by relative bond strength.

  11. Combustion noise

    NASA Technical Reports Server (NTRS)

    Strahle, W. C.

    1977-01-01

    A review of the subject of combustion generated noise is presented. Combustion noise is an important noise source in industrial furnaces and process heaters, turbopropulsion and gas turbine systems, flaring operations, Diesel engines, and rocket engines. The state-of-the-art in combustion noise importance, understanding, prediction and scaling is presented for these systems. The fundamentals and available theories of combustion noise are given. Controversies in the field are discussed and recommendations for future research are made.

  12. Particle cloud combustion in reduced gravity

    NASA Technical Reports Server (NTRS)

    Berlad, A. L.

    1988-01-01

    The prinicipal objectives of this microgravity experiment program are to obtain flame propagation rate and flame extinction limit data for several important premixed, quiescent particle cloud combustion systems under near zero-gravity conditions. The data resulting from these experiments are needed for utilization with currently available and tractable flame propagation and extinction theory. These data are also expected to provide standards for the evaluation of fire hazards in particle suspensions in both Earth-based and space-based applications. Both terrestrial and space-based fire safety criteria require the identification of the critical concentrations of particulate fuels and inerts at the flame extinction conditions.

  13. Turbulence measurements and observations of turbulent premixed flames at elevated pressures up to 3.0 MPa

    SciTech Connect

    Kobayashi, Hideaki; Maruta, Kaoru; Niioka, Takashi; Nakashima, Teppei; Tamura, Takashi

    1997-01-01

    In order to explore the characteristics of turbulence and turbulent premixed flames in a high-pressure environment, a nozzle-type burner with a turbulence generator was installed in a high-pressure chamber. Turbulence measurements and combustion experiments were conducted with the chamber pressure up to 3.0 MPa. Methane-air mixtures were used for the combustion experiments and confirmed that the turbulent premixed flames were successfully stabilized. Flame observations were made using instantaneous Schlieren photographs and high-speed laser tomography. Turbulence measurements were conducted using a hot-wire anemometer installed in the high-pressure chamber. It was found that the scales of turbulence generated by perforated plates at elevated pressure are smaller than those at atmospheric pressure. From flame observations, the following features of the flames at elevated pressure were found: (1) wrinkles structures of the flames become very fine and complex, and the cusps become sharp as pressure rises; (2) the flamelet breaks at many points of the flames and the scales of broken flamelets become small; (3) small-scale parts of the flame front convex to the unburned mixture frequently occur and move quickly to the unburned side. The effects of ambient pressure on turbulence characteristics and possible mechanisms which produce the wrinkled structure of the fine scales and generate flame front disturbances in the high-pressure environment are discussed.

  14. Flame front geometry in premixed turbulent flames

    SciTech Connect

    Shepherd, I.G. ); Ashurst, W.T. )

    1991-12-01

    Experimental and numerical determinations of flame front curvature and orientation in premixed turbulent flames are presented. The experimental data is obtained from planar, cross sectional images of stagnation point flames at high Damkoehler number. A direct numerical simulation of a constant energy flow is combined with a zero-thickness, constant density flame model to provide the numerical results. The computational domain is a 32{sup 3} cube with periodic boundary conditions. The two-dimensional curvature distributions of the experiments and numerical simulations compare well at similar q{prime}/S{sub L} values with means close to zero and marked negative skewness. At higher turbulence levels the simulations show that the distributions become symmetric about zero. These features are also found in the three dimensional distributions of curvature. The simulations support assumptions which make it possible to determine the mean direction cosines from the experimental data. This leads to a reduction of 12% in the estimated flame surface area density in the middle of the flame brush. 18 refs.

  15. Real-Time Combustion Controls and Diagnostics Sensors (CCADS)

    SciTech Connect

    Thornton, J.D.; Richard, G.A.; Dodrill, K.A.; Nutter, R.S. Jr; Straub, D.

    2005-05-03

    The present invention is directed to an apparatus for the monitoring of the combustion process within a combustion system. The apparatus comprises; a combustion system, a means for supplying fuel and an oxidizer, a device for igniting the fuel and oxidizer in order to initiate combustion, and a sensor for determining the current conducted by the combustion process. The combustion system comprises a fuel nozzle and an outer shell attached to the combustion nozzle. The outer shell defines a combustion chamber. Preferably the nozzle is a lean premix fuel nozzle (LPN). Fuel and an oxidizer are provided to the fuel nozzle at separate rates. The fuel and oxidizer are ignited. A sensor positioned within the combustion system comprising at least two electrodes in spaced-apart relationship from one another. At least a portion of the combustion process or flame is between the first and second electrodes. A voltage is applied between the first and second electrodes and the magnitude of resulting current between the first and second electrodes is determined.

  16. Real-time combustion controls and diagnostics sensors (CCADS)

    DOEpatents

    Thornton, Jimmy D.; Richards, George A.; Dodrill, Keith A.; Nutter, Jr., Roy S.; Straub, Douglas

    2005-05-03

    The present invention is directed to an apparatus for the monitoring of the combustion process within a combustion system. The apparatus comprises; a combustion system, a means for supplying fuel and an oxidizer, a device for igniting the fuel and oxidizer in order to initiate combustion, and a sensor for determining the current conducted by the combustion process. The combustion system comprises a fuel nozzle and an outer shell attached to the combustion nozzle. The outer shell defines a combustion chamber. Preferably the nozzle is a lean premix fuel nozzle (LPN). Fuel and an oxidizer are provided to the fuel nozzle at separate rates. The fuel and oxidizer are ignited. A sensor positioned within the combustion system comprising at least two electrodes in spaced-apart relationship from one another. At least a portion of the combustion process or flame is between the first and second electrodes. A voltage is applied between the first and second electrodes and the magnitude of resulting current between the first and second electrodes is determined.

  17. Time-dependent Computational Studies of Premixed Flames in Microgravity

    NASA Technical Reports Server (NTRS)

    Kailasanath, K.; Patnaik, Gopal; Oran, Elaine S.

    1993-01-01

    This report describes the research performed at the Center for Reactive Flow and Dynamical Systems in the Laboratory for Computational Physics and Fluid Dynamics, at the Naval Research Laboratory, in support of NASA Microgravity Science and Applications Program. The primary focus of this research is on investigating fundamental questions concerning the propagation and extinction of premixed flames in earth gravity and in microgravity environments. Our approach is to use detailed time-dependent, multispecies, numerical models as tools to simulate flames in different gravity environments. The models include a detailed chemical kinetics mechanism consisting of elementary reactions among the eight reactive species involved in hydrogen combustion, coupled to algorithms for convection, thermal conduction, viscosity, molecular and thermal diffusion, and external forces. The external force, gravity, can be put in any direction relative to flame propagation and can have a range of values. Recently more advanced wall boundary conditions such as isothermal and no-slip have been added to the model. This enables the simulation of flames propagating in more practical systems than before. We have used the numerical simulations to investigate the effects of heat losses and buoyancy forces on the structure and stability of flames, to help resolve fundamental questions on the existence of flammability limits when there are no external losses or buoyancy forces in the system, to understand the interaction between the various processes leading to flame instabilities and extinguishment, and to study the dynamics of cell formation and splitting. Our studies have been able to bring out the differences between upward- and downward-propagating flames and predict the zero-gravity behavior of these flames. The simulations have also highlighted the dominant role of wall heat losses in the case of downward-propagating flames. The simulations have been able to qualitatively predict the

  18. Characteristics of Non-Premixed Turbulent Flames in Microgravity

    NASA Technical Reports Server (NTRS)

    Hegde, U.; Yuan, Z. G.; Stocker, D. P.; Bahadori, M. Y.

    2001-01-01

    This project is concerned with the characteristics of turbulent hydrocarbon (primarily propane) gas-jet diffusion flames in microgravity. A microgravity environment provides the opportunity to study the structure of turbulent diffusion flames under momentum-dominated conditions (large Froude number) at moderate Reynolds number which is a combination not achievable in normal gravity. This paper summarizes progress made since the last workshop. Primarily, the features of flame radiation from microgravity turbulent jet diffusion flames in a reduced gravity environment are described. Tests were conducted for non-premixed, nitrogen diluted propane flames burning in quiescent air in the NASA Glenn 5.18 Second Zero Gravity Facility. Measured flame radiation from wedge-shaped, axial slices of the flame are compared for microgravity and normal gravity flames. Results from numerical computations of the flame using a k-e model for the turbulence are also presented to show the effects of flame radiation on the thermal field. Flame radiation is an important quantity that is impacted by buoyancy as has been shown in previous studies by the authors and also by Urban et al. It was found that jet diffusion flames burning under microgravity conditions have significantly higher radiative loss (about five to seven times higher) compared to their normal gravity counterparts because of larger flame size in microgravity and larger convective heat loss fraction from the flame in normal gravity. These studies, however, were confined to laminar flames. For the case of turbulent flames, the flame radiation is a function of time and both the time-averaged and time-dependent components are of interest. In this paper, attention is focused primarily on the time-averaged level of the radiation but the turbulent structure of the flame is also assessed from considerations of the radiation power spectra.

  19. Fundamental characterization of alternative fuel effects in continuous combustion systems. Summary technical progress report, 1 February 1980-31 March 1981

    SciTech Connect

    Kowalik, R.M.; Ruth, L.A.; Edelman, R.B.; Wong, E.; Farmer, R.C.

    1981-05-01

    Recent efforts under this contract have involved (1) investigations of soot production phenomena in gas phase jet-stirred combustors, (2) preliminary experiments concerning the effects of liquid spray fuel injection on soot production in jet-stirred combustors, (3) development and shakedown of ER and E's new Variable Pressure Jet-Stirred Combustor, and (4) continued development of SAI's quasi-global chemical kinetic model of hydrocarbon combustion/soot production processes. Progress in each of these subject areas, including experimental results from the first two areas, detailed descriptions of the Variable Pressure Jet-Stirred Combustor and the present quasi-global model, and brief outlooks on future experimental and modeling efforts are discussed. Results from the gas phase jet-stirred combustor studies provide information regarding a possible soot formation mechanism change at 1800/sup 0/K, the appropriateness of a separate sooting category for 1-methylnaphthalene and other multiring aromatics, the identification of unburned hydrocarbons in the exhaust gases, and the dependencies of soot properties on combustor operating conditions. The liquid fuel spray experiments provide data which relate liquid spray soot yields to fuel type, overall equivalence ratio, atomizing air flow rate, and combustor temperature. Of particular significance is the temperature dependence of the soot yield, which was found to be exactly opposite previous trends obtained in gas phase jet-stirred combustors. The description of the Variable Pressure Jet-Stirred Combustor includes the actual combustor, its versatile air and fuel supply systems, and associated instrumentation and diagnostics. The quasi-global model description contains tentative reaction mechanisms and rate constants and comparisons of model calculations with experimental data.

  20. 21 CFR 170.60 - Nitrites and/or nitrates in curing premixes.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 3 2014-04-01 2014-04-01 false Nitrites and/or nitrates in curing premixes. 170... nitrates in curing premixes. (a) Nitrites and/or nitrates are food additives when combined in curing... nitrates, when packaged separately from flavoring and seasoning in curing premixes, may continue to be...

  1. Conditional statistics in a turbulent premixed flame derived from direct numerical simulation

    NASA Technical Reports Server (NTRS)

    Mantel, Thierry; Bilger, Robert W.

    1994-01-01

    The objective of this paper is to briefly introduce conditional moment closure (CMC) methods for premixed systems and to derive the transport equation for the conditional species mass fraction conditioned on the progress variable based on the enthalpy. Our statistical analysis will be based on the 3-D DNS database of Trouve and Poinsot available at the Center for Turbulence Research. The initial conditions and characteristics (turbulence, thermo-diffusive properties) as well as the numerical method utilized in the DNS of Trouve and Poinsot are presented, and some details concerning our statistical analysis are also given. From the analysis of DNS results, the effects of the position in the flame brush, of the Damkoehler and Lewis numbers on the conditional mean scalar dissipation, and conditional mean velocity are presented and discussed. Information concerning unconditional turbulent fluxes are also presented. The anomaly found in previous studies of counter-gradient diffusion for the turbulent flux of the progress variable is investigated.

  2. Characterization of degeneration process in combustion instability based on dynamical systems theory.

    PubMed

    Gotoda, Hiroshi; Okuno, Yuta; Hayashi, Kenta; Tachibana, Shigeru

    2015-11-01

    We present a detailed study on the characterization of the degeneration process in combustion instability based on dynamical systems theory. We deal with combustion instability in a lean premixed-type gas-turbine model combustor, one of the fundamentally and practically important combustion systems. The dynamic behavior of combustion instability in close proximity to lean blowout is dominated by a stochastic process and transits to periodic oscillations created by thermoacoustic combustion oscillations via chaos with increasing equivalence ratio [Chaos 21, 013124 (2011); Chaos 22, 043128 (2012)]. Thermoacoustic combustion oscillations degenerate with a further increase in the equivalence ratio, and the dynamic behavior leads to chaotic fluctuations via quasiperiodic oscillations. The concept of dynamical systems theory presented here allows us to clarify the nonlinear characteristics hidden in complex combustion dynamics.

  3. Characterization of degeneration process in combustion instability based on dynamical systems theory.

    PubMed

    Gotoda, Hiroshi; Okuno, Yuta; Hayashi, Kenta; Tachibana, Shigeru

    2015-11-01

    We present a detailed study on the characterization of the degeneration process in combustion instability based on dynamical systems theory. We deal with combustion instability in a lean premixed-type gas-turbine model combustor, one of the fundamentally and practically important combustion systems. The dynamic behavior of combustion instability in close proximity to lean blowout is dominated by a stochastic process and transits to periodic oscillations created by thermoacoustic combustion oscillations via chaos with increasing equivalence ratio [Chaos 21, 013124 (2011); Chaos 22, 043128 (2012)]. Thermoacoustic combustion oscillations degenerate with a further increase in the equivalence ratio, and the dynamic behavior leads to chaotic fluctuations via quasiperiodic oscillations. The concept of dynamical systems theory presented here allows us to clarify the nonlinear characteristics hidden in complex combustion dynamics. PMID:26651761

  4. Evaluation of an unsteady flamelet progress variable model for autoignition and flame development in compositionally stratified mixtures

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, Saumyadip; Abraham, John

    2012-07-01

    The unsteady flamelet progress variable (UFPV) model has been proposed by Pitsch and Ihme ["An unsteady/flamelet progress variable method for LES of nonpremixed turbulent combustion," AIAA Paper No. 2005-557, 2005] for modeling the averaged/filtered chemistry source terms in Reynolds averaged simulations and large eddy simulations of reacting non-premixed combustion. In the UFPV model, a look-up table of source terms is generated as a function of mixture fraction Z, scalar dissipation rate χ, and progress variable C by solving the unsteady flamelet equations. The assumption is that the unsteady flamelet represents the evolution of the reacting mixing layer in the non-premixed flame. We assess the accuracy of the model in predicting autoignition and flame development in compositionally stratified n-heptane/air mixtures using direct numerical simulations (DNS). The focus in this work is primarily on the assessment of accuracy of the probability density functions (PDFs) employed for obtaining averaged source terms. The performance of commonly employed presumed functions, such as the dirac-delta distribution function, the β distribution function, and statistically most likely distribution (SMLD) approach in approximating the shapes of the PDFs of the reactive and the conserved scalars is evaluated. For unimodal distributions, it is observed that functions that need two-moment information, e.g., the β distribution function and the SMLD approach with two-moment closure, are able to reasonably approximate the actual PDF. As the distribution becomes multimodal, higher moment information is required. Differences are observed between the ignition trends obtained from DNS and those predicted by the look-up table, especially for smaller gradients where the flamelet assumption becomes less applicable. The formulation assumes that the shape of the χ(Z) profile can be modeled by an error function which remains unchanged in the presence of heat release. We show that this

  5. Annular fuel and air co-flow premixer

    DOEpatents

    Stevenson, Christian Xavier; Melton, Patrick Benedict; York, William David

    2013-10-15

    Disclosed is a premixer for a combustor including an annular outer shell and an annular inner shell. The inner shell defines an inner flow channel inside of the inner shell and is located to define an outer flow channel between the outer shell and the inner shell. A fuel discharge annulus is located between the outer flow channel and the inner flow channel and is configured to inject a fuel flow into a mixing area in a direction substantially parallel to an outer airflow through the outer flow channel and an inner flow through the inner flow channel. Further disclosed are a combustor including a plurality of premixers and a method of premixing air and fuel in a combustor.

  6. Laminar Premixed and Diffusion Flames (Ground-Based Study)

    NASA Technical Reports Server (NTRS)

    Dai, Z.; El-Leathy, A. M.; Lin, K.-C.; Sunderland, P. B.; Xu, F.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2000-01-01

    Ground-based studies of soot processes in laminar flames proceeded in two phases, considering laminar premixed flames and laminar diffusion flames, in turn. The test arrangement for laminar premixed flames involved round flat flame burners directed vertically upward at atmospheric pressure. The test arrangement for laminar jet diffusion flames involved a round fuel port directed vertically upward with various hydrocarbon fuels burning at atmospheric pressure in air. In both cases, coflow was used to prevent flame oscillations and measurements were limited to the flame axes. The measurements were sufficient to resolve soot nucleation, growth and oxidation rates, as well as the properties of the environment needed to evaluate mechanisms of these processes. The experimental methods used were also designed to maintain capabilities for experimental methods used in corresponding space-based experiments. This section of the report will be limited to consideration of flame structure for both premixed and diffusion flames.

  7. Innovative Clean Coal Technology (ICCT): 500 MW demonstration of advanced wall-fired combustion techniques for the reduction of nitrogen oxide (NO{sub x}) emissions from coal-fired boilers. Technical progress report, Second quarter 1992

    SciTech Connect

    Not Available

    1992-08-24

    This quarterly report discusses the technical progress of an Innovative Clean Coal Technology (ICCT) demonstration of advanced wall-fired combustion techniques for the reduction of nitrogen oxide (No{sub x}) emissions from coal-fired boilers. The project is being conducted at Georgia Power Company`s Plant Hammond Unit 4 located near Rome, Georgia. The primary goal of this project is the characterization of the low NO{sub x} combustion equipment through the collection and analysis of long-term emissions data. A target of achieving fifty percent NO{sub x} reduction using combustion modifications has been established for the project. The project provides a stepwise retrofit of an advanced overfire air (AOFA) system followed by low NO{sub x} burners (LNB). During each test phase of the project, diagnostic, performance, long-term, and verification testing will be performed. These tests are used to quantify the NO{sub x} reductions of each technology and evaluate the effects of those reductions on other combustion parameters such as particulate characteristics and boiler efficiency.

  8. Simulating Combustion

    NASA Astrophysics Data System (ADS)

    Merker, G.; Schwarz, C.; Stiesch, G.; Otto, F.

    The content spans from simple thermodynamics of the combustion engine to complex models for the description of the air/fuel mixture, ignition, combustion and pollutant formation considering the engine periphery of petrol and diesel engines. Thus the emphasis of the book is on the simulation models and how they are applicable for the development of modern combustion engines. Computers can be used as the engineers testbench following the rules and recommendations described here.

  9. Acoustic radiation from weakly wrinkled premixed flames

    SciTech Connect

    Lieuwen, Tim; Mohan, Sripathi; Rajaram, Rajesh; Preetham,

    2006-01-01

    This paper describes a theoretical analysis of acoustic radiation from weakly wrinkled (i.e., u'/S{sub L}<1) premixed flames. Specifically, it determines the transfer function relating the spectrum of the acoustic pressure oscillations, P'({omega}), to that of the turbulent velocity fluctuations in the approach flow, U'({omega}). In the weakly wrinkled limit, this transfer function is local in frequency space; i.e., velocity fluctuations at a frequency {omega} distort the flame and generate sound at the same frequency. This transfer function primarily depends upon the flame Strouhal number St (based on mean flow velocity and flame length) and the correlation length, {lambda}, of the flow fluctuations. For cases where the ratio of the correlation length and duct radius {lambda}/a>>1, the acoustic pressure and turbulent velocity power spectra are related by P'({omega})-{omega}{sup 2}U'({omega}) and P'({omega})-U'({omega}) for St<<1 and St>>1, respectively. For cases where {lambda}/a<<1, the transfer functions take the form P'({omega})-{omega}{sup 2}({lambda}/a){sup 2}U'({omega}) and P'({omega})-{omega}{sup 2}({lambda}/a){sup 2}({psi}-{delta}ln({lambda}/a))U'({omega}) for St<<1 and St>>1, respectively, where (PS) and {delta} are constants. The latter result demonstrates that this transfer function does not exhibit a simple power law relationship in the high frequency region of the spectra. The simultaneous dependence of this pressure-velocity transfer function upon the Strouhal number and correlation length suggests a mechanism for the experimentally observed maximum in acoustic spectra and provides some insight into the controversy in the literature over how this peak should scale with the flame Strouhal number.

  10. Two-stage combustion for reducing pollutant emissions from gas turbine combustors

    NASA Technical Reports Server (NTRS)

    Clayton, R. M.; Lewis, D. H.

    1981-01-01

    Combustion and emission results are presented for a premix combustor fueled with admixtures of JP5 with neat H2 and of JP5 with simulated partial-oxidation product gas. The combustor was operated with inlet-air state conditions typical of cruise power for high performance aviation engines. Ultralow NOx, CO and HC emissions and extended lean burning limits were achieved simultaneously. Laboratory scale studies of the non-catalyzed rich-burning characteristics of several paraffin-series hydrocarbon fuels and of JP5 showed sooting limits at equivalence ratios of about 2.0 and that in order to achieve very rich sootless burning it is necessary to premix the reactants thoroughly and to use high levels of air preheat. The application of two-stage combustion for the reduction of fuel NOx was reviewed. An experimental combustor designed and constructed for two-stage combustion experiments is described.

  11. A Study of Strain Rate Effects for Turbulent Premixed Flames with Application to LES of a Gas Turbine Combustor Model

    DOE PAGES

    Kemenov, Konstantin A.; Calhoon, William H.

    2015-03-24

    Large-scale strain rate field, a resolved quantity which is easily computable in large-eddy simulations (LES), could have profound effects on the premixed flame properties by altering the turbulent flame speed and inducing local extinction. The role of the resolved strain rate has been investigated in a posterior LES study of GE lean premixed dry low NOx emissions LM6000 gas turbine combustor model. A novel approach which is based on the coupling of the lineareddy model with a one-dimensional counter-flow solver has been applied to obtain the parameterizations of the resolved premixed flame properties in terms of the reactive progress variable,more » the local strain rate measure, and local Reynolds and Karlovitz numbers. The strain rate effects have been analyzed by comparing LES statistics for several models of the turbulent flame speed, i.e, with and without accounting for the local strain rate effects, with available experimental data. The sensitivity of the simulation results to the inflow velocity conditions as well as the grid resolution have been also studied. Overall, the results suggest the necessity to represent the strain rate effects accurately in order to improve LES modeling of the turbulent flame speed.« less

  12. A Study of Strain Rate Effects for Turbulent Premixed Flames with Application to LES of a Gas Turbine Combustor Model

    SciTech Connect

    Kemenov, Konstantin A.; Calhoon, William H.

    2015-03-24

    Large-scale strain rate field, a resolved quantity which is easily computable in large-eddy simulations (LES), could have profound effects on the premixed flame properties by altering the turbulent flame speed and inducing local extinction. The role of the resolved strain rate has been investigated in a posterior LES study of GE lean premixed dry low NOx emissions LM6000 gas turbine combustor model. A novel approach which is based on the coupling of the lineareddy model with a one-dimensional counter-flow solver has been applied to obtain the parameterizations of the resolved premixed flame properties in terms of the reactive progress variable, the local strain rate measure, and local Reynolds and Karlovitz numbers. The strain rate effects have been analyzed by comparing LES statistics for several models of the turbulent flame speed, i.e, with and without accounting for the local strain rate effects, with available experimental data. The sensitivity of the simulation results to the inflow velocity conditions as well as the grid resolution have been also studied. Overall, the results suggest the necessity to represent the strain rate effects accurately in order to improve LES modeling of the turbulent flame speed.

  13. Natural Gas for Advanced Dual-Fuel Combustion Strategies

    NASA Astrophysics Data System (ADS)

    Walker, Nicholas Ryan

    Natural gas fuels represent the next evolution of low-carbon energy feedstocks powering human activity worldwide. The internal combustion engine, the energy conversion device widely used by society for more than one century, is capable of utilizing advanced combustion strategies in pursuit of ultra-high efficiency and ultra-low emissions. Yet many emerging advanced combustion strategies depend upon traditional petroleum-based fuels for their operation. In this research the use of natural gas, namely methane, is applied to both conventional and advanced dual-fuel combustion strategies. In the first part of this work both computational and experimental studies are undertaken to examine the viability of utilizing methane as the premixed low reactivity fuel in reactivity controlled compression ignition, a leading advanced dual-fuel combustion strategy. As a result, methane is shown to be capable of significantly extending the load limits for dual-fuel reactivity controlled compression ignition in both light- and heavy-duty engines. In the second part of this work heavy-duty single-cylinder engine experiments are performed to research the performance of both conventional dual-fuel (diesel pilot ignition) and advanced dual-fuel (reactivity controlled compression ignition) combustion strategies using methane as the premixed low reactivity fuel. Both strategies are strongly influenced by equivalence ratio; diesel pilot ignition offers best performance at higher equivalence ratios and higher premixed methane ratios, whereas reactivity controlled compression ignition offers superior performance at lower equivalence ratios and lower premixed methane ratios. In the third part of this work experiments are performed in order to determine the dominant mode of heat release for both dual-fuel combustion strategies. By studying the dual-fuel homogeneous charge compression ignition and single-fuel spark ignition, strategies representative of autoignition and flame propagation

  14. Large-Eddy Simulations of Turbulent Premixed Bunsen Flames at Different Turbulence Levels

    NASA Astrophysics Data System (ADS)

    Duchampde Lageneste, Laurent; Pitsch, Heinz

    2002-11-01

    In a recent study we have formulated a level-set method based on the G-equation for Large-Eddy Simulation (LES) of premixed turbulent combustion and applied the model successfully in a simulation of the turbulent Bunsen flame,F3, experimentally investigated by Chen et al. (1996). This flame is nominally in the thin reaction zones regime. As a further validation of the model and to demonstrate the benefits of LES in turbulent combustion modeling, in the present work, we report on an LES of the F2-flame from the same series of experiments, which has a higher turbulence level and hence a higher Karlovitz number. This flame is still in the thin reaction zones regime, but locally reveals regions burning in the broken reaction zones regime. Results from the simulation will be compared with experimental data for temperature and axial velocity. The experimental data shows substantial differences between flames F2 and F3, which is well described by the simulation. Flame F2, for instance, shows an almost linear increase of the flame brush thickness with downstream distance from the nozzle, whereas flame F3 shows almost constant flame brush thickness.

  15. Direct numerical simulation of non-premixed flame-wall interactions

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Trouvé, A.

    2005-01-01

    The overall objective of this paper is to illustrate how detailed numerical modelling may be used to bring basic information on fundamental problems in combustion science. We consider in the following the interaction of non-premixed flames with cold solid wall surfaces. Flame-wall interactions are an important feature in many combustion systems, that result in significant changes in the flame and wall dynamics: the flame strength is reduced near cold wall surfaces, leading possibly to (partial or total) quenching, while the gassolid heat flux takes peak values at flame contact. The questions of turbulent fuel-air-temperature mixing, flame extinction and wall surface heat transfer are here studied using direct numerical simulation (DNS). The DNS configuration corresponds to an ethylene-air diffusion flame stabilized in the near-wall region of a chemically-inert solid surface. Simulations are performed with adiabatic or isothermal wall boundary conditions, and with different turbulence intensities. The simulations feature flame extinction events resulting from excessive wall cooling, and convective heat transfer up to 90 kW/m2. The structure of the simulated wall flames is studied in terms of a classical mass mixing variable, i.e. the fuel-airbased mixture fraction, and a less familiar heat loss variable, i.e. the excess enthalpy variable, introduced to provide a measure of non-adiabatic behavior due to wall cooling.

  16. Measurements of fuel mixture fraction oscillations of a turbulent jet non-premixed flame

    SciTech Connect

    Kanga, D.M.; Fernandez, V.; Culick, F.E.C.; Ratner, A.

    2009-01-15

    This work describes new type of combustion instability for which the 3-way coupling between mixing, flame heat release, and acoustics is modified by local buoyancy effects. Measurements of fuel mixture fraction are made for a non-premixed jet flame in a combustion chamber to assess the dynamics of mixing under imposed acoustic oscillations (22-55 Hz). Infrared laser absorption and phase resolved acetone-planar laser induced fluorescence are used to measure the fuel mixture fraction and then the degree of fuel/air mixing is calculated by determining the unmixedness. Results show acoustic excitation causes oscillations in the degree of fuel/air mixing at the driving frequency, which results in oscillatory flame behavior. This oscillatory flame behavior couples to the buoyancy and this in turn affects the mixing. Results also show that the mixing becomes less effective when the excitation frequency is increased or when the flame is present, compared to the non-reacting case. This work describes a key coupling mechanism that occurs when buoyancy is a significant factor in the flow field. (author)

  17. Premixed silane-oxygen-nitrogen flames

    SciTech Connect

    Tokuhashi, K.; Horiguchi, S.; Uranco, Y.; Iwasaka, M.; Ohtani, H.; Kondo, S. )

    1990-10-01

    The burning velocities of lean premised silane-oxygen-nitrogen flames were measured in the silane and oxygen concentration ranges from 1.6% to 2.9% and from 4% to 24%, respectively. Combustion product analyses and flame temperature measurements were also carried out. The burning velocity of a silane-air flame is around 55 cm/ at a silane concentration of 2%. For lean mixtures, when the oxygen concentration is reduced, dependence of burning velocity upon silane concentration decreases but does not significantly affect the flame temperature. For extremely lean flames, the degree of hydrogen production increase with decreasing silane, although silane is consumed almost completely. On the other hand, if the silane concentration exceeds stoichiometric, the burning velocity increases gradually with increasing silane concentration. In that case, silane as well as oxygen are consumed completely and, at the same time, hydrogen rather than water production becomes dominant. The mechanism of silane combustion is discussed, based on numerical calculations, where the mechanism used in the calculation is assembled by analogy of silane to methane combustion.

  18. The effect of insulated combustion chamber surfaces on direct-injected diesel engine performance, emissions, and combustion

    NASA Technical Reports Server (NTRS)

    Dickey, Daniel W.; Vinyard, Shannon; Keribar, Rifat

    1988-01-01

    The combustion chamber of a single-cylinder, direct-injected diesel engine was insulated with ceramic coatings to determine the effect of low heat rejection (LHR) operation on engine performance, emissions, and combustion. In comparison to the baseline cooled engine, the LHR engine had lower thermal efficiency, with higher smoke, particulate, and full load carbon monoxide emissions. The unburned hydrocarbon emissions were reduced across the load range. The nitrous oxide emissions increased at some part-load conditions and were reduced slightly at full loads. The poor LHR engine performance was attributed to degraded combustion characterized by less premixed burning, lower heat release rates, and longer combustion duration compared to the baseline cooled engine.

  19. Study of Unsteady, Sphere-Driven, Shock-Induced Combustion for Application to Hypervelocity Airbreathing Propulsion

    NASA Technical Reports Server (NTRS)

    Axdahl, Erik; Kumar, Ajay; Wilhite, Alan

    2011-01-01

    A premixed, shock-induced combustion engine has been proposed in the past as a viable option for operating in the Mach 10 to 15 range in a single stage to orbit vehicle. In this approach, a shock is used to initiate combustion in a premixed fuel/air mixture. Apparent advantages over a conventional scramjet engine include a shorter combustor that, in turn, results in reduced weight and heating loads. There are a number of technical challenges that must be understood and resolved for a practical system: premixing of fuel and air upstream of the combustor without premature combustion, understanding and control of instabilities of the shock-induced combustion front, ability to produce sufficient thrust, and the ability to operate over a range of Mach numbers. This study evaluated the stability of the shock-induced combustion front in a model problem of a sphere traveling in a fuel/air mixture at high Mach numbers. A new, rapid analysis method was developed and applied to study such flows. In this method the axisymmetric, body-centric Navier-Stokes equations were expanded about the stagnation streamline of a sphere using the local similarity hypothesis in order to reduce the axisymmetric equations to a quasi-1D set of equations. These reduced sets of equations were solved in the stagnation region for a number of flow conditions in a premixed, hydrogen/air mixture. Predictions from the quasi-1D analysis showed very similar stable or unstable behavior of the shock-induced combustion front as compared to experimental studies and higher-fidelity computational results. This rapid analysis tool could be used in parametric studies to investigate effects of fuel rich/lean mixtures, non-uniformity in mixing, contaminants in the mixture, and different chemistry models.

  20. Effects of Lewis number on vorticity and enstrophy transport in turbulent premixed flames

    NASA Astrophysics Data System (ADS)

    Chakraborty, Nilanjan; Konstantinou, Ilias; Lipatnikov, Andrei

    2016-01-01

    The effects of Lewis number Le on both vorticity and enstrophy transport within the flame brush have been analysed using direct numerical simulation data of freely propagating statistically planar turbulent premixed flames, representing the thin reaction zone regime of premixed turbulent combustion. In the simulations, Le was ranged from 0.34 to 1.2 by keeping the laminar flame speed, thermal thickness, Damköhler, Karlovitz, and Reynolds numbers unchanged. The enstrophy has been shown to decay significantly from the unburned to the burned gas side of the flame brush in the Le ≈ 1.0 flames. However, a considerable amount of enstrophy generation within the flame brush has been observed for the Le = 0.34 case and a similar qualitative behaviour has been observed in a much smaller extent for the Le = 0.6 case. The vorticity components have been shown to exhibit anisotropic behaviour within the flame brush, and the extent of anisotropy increases with decreasing Le. The baroclinic torque term has been shown to be principally responsible for this anisotropic behaviour. The vortex stretching and viscous dissipation terms have been found to be the leading order contributors to the enstrophy transport for all cases, but the baroclinic torque and the sink term due to dilatation play increasingly important role for flames with decreasing Le. Furthermore, the correlation between the fluctuations of enstrophy and dilatation rate has been shown to play an important role in determining the material derivative of enstrophy based on the mean flow in the case of a low Le.

  1. An experimental and numerical study on the stability and propagation of laminar premixed flames

    NASA Astrophysics Data System (ADS)

    Vagelopoulos, Christina Maria

    The laminar flame speed is a very important property of laminar premixed flames, especially for the validation of chemical kinetics and modeling of turbulent combustion. The counterflow technique is one of the best approaches for the experimental determination of this property because it allows for the establishment of planar, nearly adiabatic, steady, quasi-one dimensional flames that are subjected to well-defined aerodynamic strain rate. However non-linear effects as the strain rate goes to zero lead to overprediction of the laminar flame speed. In the present study these non-linear effects were investigated experimentally and numerically and significant overprediction was verified, particularly for weakly-burning hydrogen/air flames. Subsequently effort was made to establish and study flame properties at a very-low strain rate regime and qualitative and quantitative conclusions were drawn for the stability of the flame surface subjected to very low aerodynamic strain rate, coupled with the effect of gravity and preferential diffusion. A new experimental technique was developed, based on the observation that if a laminar premixed flame undergoes a transition from planar to Bunsen the strain rate changes from positive to negative values and a near-zero strain-rate regime is established. Flame speed measurements were conducted by using LDV for this regime; the flame speed measured is the true laminar flame speed and this is the first time that this property is directly and experimentally measured. Particle Streak velocimetry was developed to evaluate the strain-rates for near-zero strain-rate regime. The laminar flame speed was measured for atmospheric methane/air, ethane/air and propane/air mixtures for the whole range of equivalence ratios; the new data are lower when compared to previous ones and the overprediction is at the order of 15%.

  2. Laser ablation plasma-assisted stabilization of premixed methane/air flame

    NASA Astrophysics Data System (ADS)

    Li, Xiaohui; Yu, Yang; Peng, Jiangbo; Yu, Xin; Fan, Rongwei; Sun, Rui; Chen, Deying

    2016-01-01

    Laser ablation plasma has been applied to assist stabilization of premixed methane/air flames with a flow speed up to 15.3 m/s. The ablation plasma was generated using the 50 Hz, 1064 nm output of a Nd:YAG laser onto a tantalum slab. With the ablation plasma, the stabilization equivalence ratio has been extended to the fuel-leaner end and the blow off limits have been enhanced by from 3.6- to 14.8-folds for flames which can stabilize without the plasma. The laser pulse energy required for flameholding was reduced to 10 mJ, a 64 % reduction compared with that of gas breakdown plasma, which will ease the demand for high-power lasers for high-frequency plasma generation. The temporal evolutions of the flame kernels following the ablation plasma were investigated using the OH* chemiluminescence imaging approach, and the flame propagation speed ( v f) was measured from the flame kernel evolutions. With the ablation plasma, the v f with flow speed of 4.7-9.0 m/s and equivalence ratio of 1.4 has been enhanced from 0.175 m/s of laminar premixed methane/air flame to 2.79-4.52 and 1.59-5.46 m/s, respectively, in the early and late time following the ablation plasma. The increase in the combustion radical concentrations by the ablation plasma was thought to be responsible for the v f enhancement and the resulted flame stabilization.

  3. Near field flow structure of isothermal swirling flows and reacting non-premixed swirling flames

    SciTech Connect

    Olivani, Andrea; Solero, Giulio; Cozzi, Fabio; Coghe, Aldo

    2007-04-15

    Two confined lean non-premixed swirl-stabilized flame typologies were investigated in order to achieve detailed information on the thermal and aerodynamic field in the close vicinity of the burner throat and provide correlation with the exhaust emissions. Previous finding indicated the generation of a partially premixed flame with radial fuel injection and a purely diffusive flame with co-axial injection in a swirling co-flow. In the present work, the experimental study is reported which has been conducted on a straight exit laboratory burner with no quarl cone, fuelled by natural gas and air, and fired vertically upwards with the flame stabilized at the end of two concentric pipes with the annulus supplying swirled air and the central pipe delivering the fuel. Two fuel injection typologies, co-axial and radial (i.e., transverse), leading to different mixing mechanisms, have been characterized through different techniques: particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) for a comprehensive analysis of the velocity field, still photography for the detection of flame front and main visible features, and thermocouples for the temperature distribution. Isothermal flow conditions have been included in the experimental investigation to provide a basic picture of the flow field and to comprehend the modifications induced by the combustion process. The results indicated that, although the global mixing process and the main flame structure are governed by the swirl motion imparted to the air stream, the two different fuel injection methodologies play an important role on mixture formation and flame stabilization in the primary mixing zone. Particularly, it has been found that, in case of axial injection, the turbulent interaction between the central fuel jet and the backflow generated by the swirl can induce an intermittent fuel penetration in the recirculated hot products and the formation of a central sooting luminous plume, a phenomenon totally

  4. The effect of temperature on soot properties in premixed methane flames

    SciTech Connect

    Alfe, M.; Apicella, B.; Tregrossi, A.; Ciajolo, A.; Rouzaud, J.-N.

    2010-10-15

    The effect of flame temperature on soot properties was studied in premixed methane/oxygen flames burning at a constant mixture composition (C/O = 0.60, {phi} = 2.4) and different cold-gas flow velocities (4 and 5 cm s{sup -1}). Temperature and concentration profiles of stable gases and condensed phases combustion products were measured along the flame axis. It was found that the high flame temperature conditions cause a larger decomposition of methane into hydrogen and C{sub 2}-C{sub 4} hydrocarbons, thereby reducing the formation of benzene and condensed phases including condensed species and soot. Soot properties were studied by UV-Visible absorption spectroscopy, thermogravimetry and H/C elemental analysis. A description of soot nanostructural organization was also performed by means of high-resolution transmission electron microscopy. Different properties and nanostructures were found to develop in the soot, depending on the temperature and on soot aging associated. Soot dehydrogenation occurred to a larger extent in the high flame temperature conditions. As soot dehydrogenates the mass absorption coefficients of soot exhibited an increasing trend along the flame axis. However, mature soot retained a relatively high H/C ratio and low absorption coefficients with respect to other less hydrogenated fuels even in high temperature conditions. This indicates that the aromatization/dehydrogenation of soot in premixed flames is more dependent on the fuel characteristics rather than on the flame temperature. Generally, it was assessed that mature soot produced from diverse hydrocarbon fuels with similar flame temperatures and flame types possess a different chemical composition and structure. To this regard the H/C atomic ratio and mass absorption coefficients appeared to be signatures of soot properties and structural evolution. (author)

  5. Hydrocarbon Fouling of SCR during PCCI combustion

    SciTech Connect

    Prikhodko, Vitaly Y; Pihl, Josh A; Lewis Sr, Samuel Arthur; Parks, II, James E

    2012-01-01

    The combination of advanced combustion with advanced selective catalytic reduction (SCR) catalyst formulations was studied in the work presented here to determine the impact of the unique hydrocarbon (HC) emissions from premixed charge compression ignition (PCCI) combustion on SCR performance. Catalyst core samples cut from full size commercial Fe- and Cu-zeolite SCR catalysts were exposed to a slipstream of raw engine exhaust from a 1.9-liter 4-cylinder diesel engine operating in conventional and PCCI combustion modes. The zeolites which form the basis of these catalysts are different with the Cu-based catalyst made on a chabazite zeolite which las smaller pore structures relative to the Fe-based catalyst. Subsequent to exposure, bench flow reactor characterization of performance and hydrocarbon release and oxidation enabled evaluation of overall impacts from the engine exhaust. The Fe-zeolite NOX conversion efficiency was significantly degraded, especially at low temperatures (<250 C), after the catalyst was exposed to the raw engine exhaust. The degradation of the Fe-zeolite performance was similar for both combustion modes. The Cu-zeolite showed better tolerance to HC fouling at low temperatures compared to the Fe-zeolite but PCCI exhaust had a more significant impact than the exhaust from conventional combustion on the NOX conversion efficiency. Furthermore, chemical analysis of the hydrocarbons trapped on the SCR cores was conducted to better determine chemistry specific effects.

  6. Effects of fuel cetane number on the structure of diesel spray combustion: An accelerated Eulerian stochastic fields method

    NASA Astrophysics Data System (ADS)

    Jangi, Mehdi; Lucchini, Tommaso; Gong, Cheng; Bai, Xue-Song

    2015-09-01

    An Eulerian stochastic fields (ESF) method accelerated with the chemistry coordinate mapping (CCM) approach for modelling spray combustion is formulated, and applied to model diesel combustion in a constant volume vessel. In ESF-CCM, the thermodynamic states of the discretised stochastic fields are mapped into a low-dimensional phase space. Integration of the chemical stiff ODEs is performed in the phase space and the results are mapped back to the physical domain. After validating the ESF-CCM, the method is used to investigate the effects of fuel cetane number on the structure of diesel spray combustion. It is shown that, depending of the fuel cetane number, liftoff length is varied, which can lead to a change in combustion mode from classical diesel spray combustion to fuel-lean premixed burned combustion. Spray combustion with a shorter liftoff length exhibits the characteristics of the classical conceptual diesel combustion model proposed by Dec in 1997 (http://dx.doi.org/10.4271/970873), whereas in a case with a lower cetane number the liftoff length is much larger and the spray combustion probably occurs in a fuel-lean-premixed mode of combustion. Nevertheless, the transport budget at the liftoff location shows that stabilisation at all cetane numbers is governed primarily by the auto-ignition process.

  7. Invited Review: A review of deterministic effects in cyclic variability of internal combustion engines

    DOE PAGES

    Finney, Charles E.; Kaul, Brian C.; Daw, C. Stuart; Wagner, Robert M.; Edwards, K. Dean; Green, Johney B.

    2015-02-18

    Here we review developments in the understanding of cycle to cycle variability in internal combustion engines, with a focus on spark-ignited and premixed combustion conditions. Much of the research on cyclic variability has focused on stochastic aspects, that is, features that can be modeled as inherently random with no short term predictability. In some cases, models of this type appear to work very well at describing experimental observations, but the lack of predictability limits control options. Also, even when the statistical properties of the stochastic variations are known, it can be very difficult to discern their underlying physical causes andmore » thus mitigate them. Some recent studies have demonstrated that under some conditions, cyclic combustion variations can have a relatively high degree of low dimensional deterministic structure, which implies some degree of predictability and potential for real time control. These deterministic effects are typically more pronounced near critical stability limits (e.g. near tipping points associated with ignition or flame propagation) such during highly dilute fueling or near the onset of homogeneous charge compression ignition. We review recent progress in experimental and analytical characterization of cyclic variability where low dimensional, deterministic effects have been observed. We describe some theories about the sources of these dynamical features and discuss prospects for interactive control and improved engine designs. In conclusion, taken as a whole, the research summarized here implies that the deterministic component of cyclic variability will become a pivotal issue (and potential opportunity) as engine manufacturers strive to meet aggressive emissions and fuel economy regulations in the coming decades.« less

  8. Invited Review: A review of deterministic effects in cyclic variability of internal combustion engines

    SciTech Connect

    Finney, Charles E.; Kaul, Brian C.; Daw, C. Stuart; Wagner, Robert M.; Edwards, K. Dean; Green, Johney B.

    2015-02-18

    Here we review developments in the understanding of cycle to cycle variability in internal combustion engines, with a focus on spark-ignited and premixed combustion conditions. Much of the research on cyclic variability has focused on stochastic aspects, that is, features that can be modeled as inherently random with no short term predictability. In some cases, models of this type appear to work very well at describing experimental observations, but the lack of predictability limits control options. Also, even when the statistical properties of the stochastic variations are known, it can be very difficult to discern their underlying physical causes and thus mitigate them. Some recent studies have demonstrated that under some conditions, cyclic combustion variations can have a relatively high degree of low dimensional deterministic structure, which implies some degree of predictability and potential for real time control. These deterministic effects are typically more pronounced near critical stability limits (e.g. near tipping points associated with ignition or flame propagation) such during highly dilute fueling or near the onset of homogeneous charge compression ignition. We review recent progress in experimental and analytical characterization of cyclic variability where low dimensional, deterministic effects have been observed. We describe some theories about the sources of these dynamical features and discuss prospects for interactive control and improved engine designs. In conclusion, taken as a whole, the research summarized here implies that the deterministic component of cyclic variability will become a pivotal issue (and potential opportunity) as engine manufacturers strive to meet aggressive emissions and fuel economy regulations in the coming decades.

  9. Characterization of degeneration process in thermo-acoustic combustion instability using dynamical systems theory

    NASA Astrophysics Data System (ADS)

    Hayashi, Kenta; Gotoda, Hiroshi; Okuno, Yuta; Tachibana, Shigeru; Tokyo University of Science Collaboration; Japan Aerospace Exploration Agency Collaboration

    2015-11-01

    We have experimentally investigated the degeneration process of combustion instability in a lean premixed gas-turbine model combustor on the basis of dynamical systems theory. Our previous study reported that with increasing the equivalence ratio, the dynamical behavior of combustion state close to lean blowout transits from stochastic fluctuations to periodic thermoacoustic combustion oscillations via low-dimensional chaotic oscillations. The further increase in the equivalence ratio gives rise to the quasi-periodic oscillations and the subsequent chaotic oscillations with small amplitudes. The route to chaotic oscillations is quantitatively shown by the use of nonlinear time series analysis involving the color recurrence plots, permutation entropy and local predictor.

  10. Vorticity transformation in high Karlovitz number premixed flames

    NASA Astrophysics Data System (ADS)

    Bobbitt, Brock; Lapointe, Simon; Blanquart, Guillaume

    2016-01-01

    To better understand the two-way coupling between turbulence and chemistry, the changes in turbulence characteristics through a premixed flame are investigated. Specifically, this study focuses on vorticity, ω, which is characteristic of the smallest length and time scales of turbulence, analyzing its behavior within and across high Karlovitz number (Ka) premixed flames. This is accomplished through a series of direct numerical simulations (DNS) of premixed n-heptane/air flames, modeled with a 35-species finite-rate chemical mechanism, whose conditions span a wide range of unburnt Karlovitz numbers and flame density ratios. The behavior of the terms in the enstrophy, ω2 = ω ṡ ω, transport equation is analyzed, and a scaling is proposed for each term. The resulting normalized enstrophy transport equation involves only a small set of parameters. Specifically, the theoretical analysis and DNS results support that, at high Karlovitz number, enstrophy transport obtains a balance of the viscous dissipation and production/vortex stretching terms. It is shown that, as a result, vorticity scales in the same manner as in homogeneous, isotropic turbulence within and across the flame, namely, scaling with the inverse of the Kolmogorov time scale, τη. As τη is a function only of the viscosity and dissipation rate, this work supports the validity of Kolmogorov's first similarity hypothesis in premixed turbulent flames for sufficiently high Ka numbers. Results are unaffected by the transport model, chemical model, turbulent Reynolds number, and finally the physical configuration.

  11. Characterization of Reactivity Controlled Compression Ignition (RCCI) Using Premixed Gasoline and Direct-Injected Gasoline with a Cetane Improver on a Multi-Cylinder Engine

    SciTech Connect

    Dempsey, Adam B.; Curran, Scott; Reitz, Rolf D.

    2015-04-14

    The focus of the present paper was to characterize Reactivity Controlled Compression Ignition (RCCI) using a single-fuel approach of gasoline and gasoline mixed with a commercially available cetane improver on a multi-cylinder engine. RCCI was achieved by port-injecting a certification grade 96 research octane gasoline and direct-injecting the same gasoline mixed with various levels of a cetane improver, 2-ethylhexyl nitrate (EHN). The EHN volume percentages investigated in the direct-injected fuel were 10, 5, and 2.5%. The combustion phasing controllability and emissions of the different fueling combinations were characterized at 2300 rpm and 4.2 bar brake mean effective pressure over a variety of parametric investigations including direct injection timing, premixed gasoline percentage, and intake temperature. Comparisons were made to gasoline/diesel RCCI operation on the same engine platform at nominally the same operating condition. The experiments were conducted on a modern four cylinder light-duty diesel engine that was modified with a port-fuel injection system while maintaining the stock direct injection fuel system. The pistons were modified for highly premixed operation and feature an open shallow bowl design. The results indicate that the authority to control the combustion phasing through the fuel delivery strategy (e.g., direct injection timing or premixed gasoline percentage) is not a strong function of the EHN concentration in the direct-injected fuel. It was also observed that NOx emissions are a strong function of the global EHN concentration in-cylinder and the combustion phasing. Finally, in general, NOx emissions are significantly elevated for gasoline/gasoline+EHN operation compared with gasoline/diesel RCCI operation at a given operating condition.

  12. Characterization of Reactivity Controlled Compression Ignition (RCCI) Using Premixed Gasoline and Direct-Injected Gasoline with a Cetane Improver on a Multi-Cylinder Engine

    DOE PAGES

    Dempsey, Adam B.; Curran, Scott; Reitz, Rolf D.

    2015-04-14

    The focus of the present paper was to characterize Reactivity Controlled Compression Ignition (RCCI) using a single-fuel approach of gasoline and gasoline mixed with a commercially available cetane improver on a multi-cylinder engine. RCCI was achieved by port-injecting a certification grade 96 research octane gasoline and direct-injecting the same gasoline mixed with various levels of a cetane improver, 2-ethylhexyl nitrate (EHN). The EHN volume percentages investigated in the direct-injected fuel were 10, 5, and 2.5%. The combustion phasing controllability and emissions of the different fueling combinations were characterized at 2300 rpm and 4.2 bar brake mean effective pressure over amore » variety of parametric investigations including direct injection timing, premixed gasoline percentage, and intake temperature. Comparisons were made to gasoline/diesel RCCI operation on the same engine platform at nominally the same operating condition. The experiments were conducted on a modern four cylinder light-duty diesel engine that was modified with a port-fuel injection system while maintaining the stock direct injection fuel system. The pistons were modified for highly premixed operation and feature an open shallow bowl design. The results indicate that the authority to control the combustion phasing through the fuel delivery strategy (e.g., direct injection timing or premixed gasoline percentage) is not a strong function of the EHN concentration in the direct-injected fuel. It was also observed that NOx emissions are a strong function of the global EHN concentration in-cylinder and the combustion phasing. Finally, in general, NOx emissions are significantly elevated for gasoline/gasoline+EHN operation compared with gasoline/diesel RCCI operation at a given operating condition.« less

  13. Symposium /International/ on Combustion, 17th, Leeds University, Leeds, England, August 20-25, 1978, Proceedings

    NASA Technical Reports Server (NTRS)

    1979-01-01

    The Symposium focused on deflagration to detonation transition, coal combustion, turbulent-combustion interactions, kinetics, furnace combustion, inhibition and ignition, flame structure and chemistry, combustion studies, measurement techniques, fire and explosion, engine combustion, soot, and propellants and explosives. Papers were presented on numerical modeling of the deflagration-to-detonation transition, the interaction between turbulence and combustion, turbulent flame propagation in premixed gases, spray evaporation in recirculating flow, dissociation of nitric oxide in shock waves, pollutant emissions from partially mixed turbulent flames, energy transfer and quenching rates of laser-pumped electronically excited alkalis in flames, a study of flammability limits using counterflow flames, the unified theory of explosions with fuel consumption, and the dynamics and radiant intensity of large hydrogen flames.

  14. Development and testing of commercial-scale, coal-fired combustion systems, Phase 3. Technical progress report, April 1991--June 1991

    SciTech Connect

    Not Available

    1991-12-31

    The US Department of Energy`s Pittsburgh Energy Technology Center (PETC) is actively pursuing the development and testing of coal-fired combustion systems for residential, commercial, and industrial market sectors. In response, MTCI initiated the development of a new combustor technology based on the principle of pulse combustion under the sponsorship of PETC (Contract No. AC22-83PC60419). The initial pulse combustor development program was conducted in three phases (MTCI, Development of a Pulsed Coal Combustor Fired with CWM, Phase III Final Report, DOE Contract No. AC22-83PC60419, November 1986). Phase I included a review of the prior art in the area of pulse combustion and the development of pulse combustor design concepts. It led to the conclusion that pulse combustors offer technical and base-of-operation advantages over conventional burners and also indicated favorable economics for replacement of oil- and gas-fired equipment.

  15. Development and testing of commercial-scale, coal-fired combustion systems: Phase 3. Technical progress report, January 1992--March 1992

    SciTech Connect

    Not Available

    1992-08-01

    The US Department of Energy`s Pittsburgh Energy Technology Center (PETC) is actively pursuing the development and testing of coal-fired combustion systems for residential, commercial, and industrial market sectors. In response, MTCI initiated the development of a new combustor technology based on the principle of pulse combustion under the sponsorship of PETC (Contract No. AC22-83PC60419). The initial pulse combustor development program was conducted in three phases (MTCI, Development of a Pulsed Coal Combustor Fired with CWM, Phase III Final Report, DOE Contract No. AC22-83PC60419, November 1986). Phase I included a review of the prior art in the area of pulse combustion and the development of pulse combustor design concepts. It led to the conclusion that pulse combustors offer technical and base-of-operation advantages over conventional burners and also indicated favorable economics for replacement of oil- and gas-fired equipment.

  16. Dynamics of the flame surface area in turbulent nonpremixed combustion

    SciTech Connect

    Kollmann, W.; Chen, J.H.

    1994-01-01

    The dynamic equation for the total surface area of level surfaces is developed based on a theorem of geometric measure theory and its relation to other versions of the equation is established. The mixture fraction, a quantity which is relevant to non-premixed combustion, is used to define the level surfaces. The level surface corresponding to its stoichiometric value is defined as the flame surface. It is shown that the evolution of the surface properties is determined by the rate-of-strain generated by the motion of the fluid, coupled with molecular diffusion and source terms of the scalar variable defining the level surface. DNS results obtained for a low-Reynolds number turbulent non-premixed flame are used to evaluate the effects of strain rate and scalar dynamics on the surface area of level surfaces.

  17. Quantifying real-gas effects on a laminar n-dodecane - air premixed flame

    NASA Astrophysics Data System (ADS)

    Gopal, Abishek; Yellapantula, Shashank; Larsson, Johan

    2015-11-01

    With the increasing demand for higher efficiencies in aircraft gas-turbine engines, there has been a progressive march towards high pressure-ratio cycles. Under these conditions, the aviation fuel, Jet A, is injected into the combustor at supercritical pressures. In this work, we study and quantify the effects of transcriticality on a 1D freely propagating laminar n-dodecane - air premixed flame. The impact of the constitutive state relations arising from the Ideal Gas equation of state(EOS) and Peng-Robinson EOS on flame structure and propagation is presented. The effects of real-gas models of transport properties, such as viscosity on laminar flame speed, are also presented.

  18. Combustion physics

    NASA Astrophysics Data System (ADS)

    Jones, A. R.

    1985-11-01

    Over 90% of our energy comes from combustion. By the year 2000 the figure will still be 80%, even allowing for nuclear and alternative energy sources. There are many familiar examples of combustion use, both domestic and industrial. These range from the Bunsen burner to large flares, from small combustion chambers, such as those in car engines, to industrial furnaces for steel manufacture or the generation of megawatts of electricity. There are also fires and explosions. The bountiful energy release from combustion, however, brings its problems, prominent among which are diminishing fuel resources and pollution. Combustion science is directed towards finding ways of improving efficiency and reducing pollution. One may ask, since combustion is a chemical reaction, why physics is involved: the answer is in three parts. First, chemicals cannot react unless they come together. In most flames the fuel and air are initially separate. The chemical reaction in the gas phase is very fast compared with the rate of mixing. Thus, once the fuel and air are mixed the reaction can be considered to occur instantaneously and fluid mechanics limits the rate of burning. Secondly, thermodynamics and heat transfer determine the thermal properties of the combustion products. Heat transfer also plays a role by preheating the reactants and is essential to extracting useful work. Fluid mechanics is relevant if work is to be performed directly, as in a turbine. Finally, physical methods, including electric probes, acoustics, optics, spectroscopy and pyrometry, are used to examine flames. The article is concerned mainly with how physics is used to improve the efficiency of combustion.

  19. Flammability of Heterogeneously Combusting Metals

    NASA Technical Reports Server (NTRS)

    Jones, Peter D.

    1998-01-01

    Most engineering materials, including some metals, most notably aluminum, burn in homogeneous combustion. 'Homogeneous' refers to both the fuel and the oxidizer being in the same phase, which is usually gaseous. The fuel and oxidizer are well mixed in the combustion reaction zone, and heat is released according to some relation like q(sub c) = delta H(sub c)c[((rho/rho(sub 0))]exp a)(exp -E(sub c)/RT), Eq. (1) where the pressure exponent a is usually close to unity. As long as there is enough heat released, combustion is sustained. It is useful to conceive of a threshold pressure beyond which there is sufficient heat to keep the temperature high enough to sustain combustion, and beneath which the heat is so low that temperature drains away and the combustion is extinguished. Some materials burn in heterogeneous combustion, in which the fuel and oxidizer are in different phases. These include iron and nickel based alloys, which burn in the liquid phase with gaseous oxygen. Heterogeneous combustion takes place on the surface of the material (fuel). Products of combustion may appear as a solid slag (oxide) which progressively covers the fuel. Propagation of the combustion melts and exposes fresh fuel. Heterogeneous combustion heat release also follows the general form of Eq.(1), except that the pressure exponent a tends to be much less than 1. Therefore, the increase in heat release with increasing pressure is not as dramatic as it is in homogeneous combustion. Although the concept of a threshold pressure still holds in heterogeneous combustion, the threshold is more difficult to identify experimentally, and pressure itself becomes less important relative to the heat transfer paths extant in any specific application. However, the constants C, a, and E(sub c) may still be identified by suitable data reduction from heterogeneous combustion experiments, and may be applied in a heat transfer model to judge the flammability of a material in any particular actual

  20. Computational study of lean premixed turbulent flames using RANSPDF and LESPDF methods

    NASA Astrophysics Data System (ADS)

    Rowinski, David H.; Pope, Stephen B.

    2013-08-01

    A computational study is performed on a series of four piloted, lean, premixed turbulent jet flames. These flames use the Sydney Piloted Premixed Jet Burner (PPJB), and with jet velocities of 50, 100, 150 and 200 m/s are denoted PM150, PM1100, PM1150 and PM1200, respectively. Calculations are performed using the RANSPDF and LESPDF methodologies, with different treatments of molecular diffusion, with detailed chemistry and flamelet-based chemistry modelling, and using different imposed boundary conditions. The sensitivities of the calculations to these different aspects of the modelling are compared and discussed. Comparisons are made to experimental data and to previously-performed calculations. It is found that, given suitable boundary conditions and treatment of molecular diffusion, excellent agreement between the calculations and experimental measurements of the mean and variance fields can be achieved for PM150 and PM1100. The application of a recently developed implementation of molecular diffusion results in a large improvement in the computed variance fields in the LESPDF calculations. The inclusion of differential diffusion in the LESPDF calculations provides insight on the behaviour in the near-field region of the jet, but its effects are found to be confined to this region and to the species CO, OH and H2. A major discrepancy observed in many previous calculations of these flames is an overprediction of reaction progress in PM1150 and PM1200, and this discrepancy is also observed in the LESPDF calculations; however, a parametric study of the LESPDF mixing model reveals that, with a sufficiently large mixing frequency, calculations of these two flames are capable of yielding improved reaction progress in good qualitative agreement with the mean and RMS scalar measurements up to an x/D of 30. Lastly, the merits of each computational methodology are discussed in light of their computational costs.

  1. Numerical prediction of radiative heat transfer in reciprocating superadiabatic combustion in porous media.

    PubMed

    Du, Liming; Xie, Maozhao

    2011-06-01

    A numerical study of Reciprocating Superadiabatic Combustion of Premixed gases in porous media (hereafter, referred to as RSCP) is performed. In this system the transient combustion of methane-air mixture is stabilized in a porous media combustor by periodically switching flow directions. The mass, momentum, energy and species conservation equations are solved using a two-dimensional control volume method. Local thermal non-equilibrium between the gas and the solid phases is considered by solving separate energy equations for the two phases and coupling them through a convective heat transfer coefficient. The porous media is assumed to emit, absorb and isotropically scatter radiation. The influences of the dominating operating parameters, such as filtration velocity, equivalence ratio and half cycle on the temperature profile, heat release rate, radiant flux, radiant efficiency and combustion efficiency are discussed. The results show that coupling calculating of flow field, combustion reaction and volume radiation of the optically thick media is successively achieved and heat radiation plays an important role in the overall performance of the burner. The temperature profile inside the RSCP combustor has a typical trapezoidal shape and the profile of radiation flux is similar to sinusoidal shape. Compared with the conventional premixed combustion in porous medium, combustion behavior in RSCP combustor is superior, such as better thermal structure and higher radiation efficiency and combustion efficiency.

  2. Laser diagnostics of plasma assisted combustion

    NASA Astrophysics Data System (ADS)

    Rao, Xing

    In this study, a microwave re-entrant cavity discharge system and a direct current (DC) plasmatron are used to investigate flame enhancement and nitric oxide (NO) formation using laser and optical diagnostics. The uniqueness of this study lies in the direct coupling concept, a novel highly efficient strategy used here for the first time. To investigate combustion dynamics of direct microwave coupled combustion, an atmospheric high-Q re-entrant cavity applicator is used to couple microwave (2.45 GHz) electromagnetic energy directly into the reaction zone of a premixed laminar methane-oxygen flame using a compact torch. When microwave energy increases, a transition from electric field enhancement to microwave plasma discharge is observed. At 6 to 10 Watts, ionization and eventually break-down occurs. 2-D laser induced fluorescence (LIF) imaging of hydroxyl radicals (OH) and carbon monoxide (CO) is conducted in the reaction zone over this transition, as well as spectrally resolved flame emission measurements. These measurements serve to monitor excited state species and derive rotational temperatures using OH chemiluminescence for a range of equivalence ratios (both rich and lean) and total flow rates. Combustion dynamics is also investigated for plasma enhanced methane-air flames in premixed and nonpremixed configurations using a transient arc DC plasmatron. Results for OH and CO PLIF also indicate the differences in stability mechanism, and energy consumption for premixed and nonpremixed modes. It is shown that both configurations are significantly influenced by in-situ fuel reforming at higher plasma powers. Parametric studies are conducted in a plasma assisted methane/air premixed flame for quantitative NO production using a DC plasmatron with PLIF imaging. Quantitative measurements of NO are reported as a function of gas flow rate (20 to 50 SCFH), plasma power (100 to 900 mA, 150 to 750 W) and equivalence ratio (0.7 to 1.3). NO PLIF images and single point NO

  3. Combustion characteristics and influential factors of isooctane active-thermal atmosphere combustion assisted by two-stage reaction of n-heptane

    SciTech Connect

    Lu, Xingcai; Ji, Libin; Ma, Junjun; Zhou, Xiaoxin; Huang, Zhen

    2011-02-15

    This paper presents an experimental study on the isooctane active-thermal atmosphere combustion (ATAC) which is assisted by two-stage reaction of n-heptane. The active-thermal atmosphere is created by low- and high-temperature reactions of n-heptane which is injected at intake port, and isooctane is directly injected into combustion chamber near the top dead center. The effects of isooctane injection timing, active-thermal atmosphere intensity, overall equivalence ratio, and premixed ratio on combustion characteristics and emissions are investigated. The experimental results reveal that, the isooctane ignition and combustion can be classified to thermal atmosphere combustion, active atmosphere combustion, and active-thermal atmosphere combustion respectively according to the extent of n-heptane oxidation as well as effects of isooctane quenching and charge cooling. n-Heptane equivalence ratio, isooctane equivalence ratio and isooctane delivery advance angle are major control parameters. In one combustion cycle, the isooctane ignited and burned after those of n-heptane, and then this combustion phenomenon can also be named as dual-fuel sequential combustion (DFSC). The ignition timing of the overall combustion event is mainly determined by n-heptane equivalence ratio and can be controlled in flexibility by simultaneously adjusting isooctane equivalence ratio. The isooctane ignition regime, overall thermal efficiency, and NO{sub x} emissions show strong sensitivity to the fuel delivery advance angle between 20 CA BTDC and 25 CA BTDC. (author)

  4. Manifold methods for methane combustion

    SciTech Connect

    Yang, B.; Pope, S.B.

    1995-10-01

    Great progresses have been made in combustion research, especially, the computation of laminar flames and the probability density function (PDF) method in turbulent combustion. For one-dimensional laminar flames, by considering the transport mechanism, the detailed chemical kinetic mechanism and the interactions between these two basic processes, today it is a routine matter to calculate flame velocities, extinction, ignition, temperature, and species distributions from the governing equations. Results are in good agreement with those obtained for experiments. However, for turbulent combustion, because of the complexities of turbulent flow, chemical reactions, and the interaction between them, in the foreseeable future, it is impossible to calculate the combustion flow field by directly integrating the basic governing equations. So averaging and modeling are necessary in turbulent combustion studies. Averaging, on one hand, simplifies turbulent combustion calculations, on the other hand, it introduces the infamous closure problems, especially the closure problem with chemical reaction terms. Since in PDF calculations of turbulent combustion, the averages of the chemical reaction terms can be calculated, PDF methods overcome the closure problem with the reaction terms. It has been shown that the PDF method is a most promising method to calculate turbulent combustion. PDF methods have been successfully employed to calculate laboratory turbulent flames: they can predict phenomena such as super equilibrium radical levels, and local extinction. Because of these advantages, PDF methods are becoming used increasingly in industry combustor codes.

  5. Microgravity Combustion Science: 1995 Program Update

    NASA Technical Reports Server (NTRS)

    Ross, Howard D. (Editor); Gokoglu, Suleyman A. (Editor); Friedman, Robert (Editor)

    1995-01-01

    Microgravity greatly benefits the study of fundamental combustion processes. In this environment, buoyancy-induced flow is nearly eliminated, weak or normally obscured forces and flows can be isolated, gravitational settling or sedimentation is nearly eliminated, and temporal and spatial scales can be expanded. This document reviews the state of knowledge in microgravity combustion science with the emphasis on NASA-sponsored developments in the current period of 1992 to early 1995. The subjects cover basic research in gaseous premixed and diffusion-flame systems, flame structure and sooting, liquid droplets and pools, and solid-surface ignition and flame spread. They also cover applied research in combustion synthesis of ceramic-metal composites, advanced diagnostic instrumentation, and on-orbit fire safety. The review promotes continuing research by describing the opportunities for Principal Investigator participation through the NASA Research Announcement program and the available NASA Lewis Research Center ground-based facilities and spaceflight accommodations. This review is compiled by the members and associates of the NASA Lewis Microgravity Combustion Branch, and it serves as an update of two previous overview reports.

  6. Reynolds number effects in combustion noise

    NASA Technical Reports Server (NTRS)

    Seshan, P. K.

    1981-01-01

    Acoustic emission spectra have been obtained for non-premixed turbulent combustion from two small diameter laboratory gas burners, two commercial gas burners and a large gas burner in the firebox of a Babcock-Wilcox Boiler (50,000 lb steam/hr). The changes in burner size and firing rate represent changes in Reynolds number and changes in air/fuel ratio represent departure from stoichiometric proportions. The combustion efficiency was measured independently through gas analysis. The acoustic spectra obtained from the various burners exhibit a persistent shape over the Reynolds number range of 8200-82,000. The spectra were analyzed for identification of a predictable frequency domain that is most responsive to, and readily correlated with, combustion efficiency. A simple parameter (consisting of the ratio of the average acoustic power output in the most responsive frequency bandwidth to the acoustic power level of the loudest frequency) is proposed whose value increases significantly and unmistakably as combustion efficiency approaches 100%. The dependence of the most responsive frequency domain on the various Reynolds numbers associated with turbulent jets is discussed.

  7. Innovative Clean Coal Technology (ICCT): 500 MW demonstration of advanced wall-fired combustion techniques for the reduction of nitrogen oxide (NO{sub x}) emissions from coal-fired boilers. Technical progress report: First quarter 1993

    SciTech Connect

    Not Available

    1993-12-31

    This quarterly report discusses the technical progress of an Innovative Clean Coal Technology (ICCT) demonstration being conducted at Georgia Power Company`s Plant Hammond Unit 4 located near Rome, Georgia. The primary goal of this project is the characterization of the low NO{sub x} combustion equipment through the collection and analysis of long-term emissions data. A target of achieving fifty percent NO{sub x} reduction using combustion modifications has been established for the project. The project provides a stepwise retrofit of an advanced overfire air (AOFA) system followed by low NO{sub x} burners (LNB). During each test phase of the project, diagnostic, performance, long-term, and verification testing will be performed. These tests are used to quantify the NO{sub x} reductions of each technology and evaluate the effects of those reductions on other combustion parameters such as particulate characteristics and boiler efficiency. During this quarter, long-term testing of the LNB + AOFA configuration continued and no parametric testing was performed. Further full-load optimization of the LNB + AOFA system began on March 30, 1993. Following completion of this optimization, comprehensive testing in this configuration will be performed including diagnostic, performance, verification, long-term, and chemical emissions testing. These tests are scheduled to start in May 1993 and continue through August 1993. Preliminary engineering and procurement are progressing on the Advanced Low NOx Digital Controls scope addition to the wall-fired project. The primary activities during this quarter include (1) refinement of the input/output lists, (2) procurement of the distributed digital control system, (3) configuration training, and (4) revision of schedule to accommodate project approval cycle and change in unit outage dates.

  8. Nitric oxide formation in a lean, premixed-prevaporized jet A/air flame tube: An experimental and analytical study

    NASA Technical Reports Server (NTRS)

    Lee, Chi-Ming; Bianco, Jean; Deur, John M.; Ghorashi, Bahman

    1992-01-01

    An experimental and analytical study was performed on a lean, premixed-prevaporized Jet A/air flame tube. The NO(x) emissions were measured in a flame tube apparatus at inlet temperatures ranging from 755 to 866 K (900 to 1100 F), pressures from 10 to 15 atm, and equivalence ratios from 0.37 to 0.62. The data were then used in regressing an equation to predict the NO(x) production levels in combustors of similar design. Through an evaluation of parameters it was found that NO(x) is dependent on adiabatic flame temperature and combustion residence time, yet independent of pressure and inlet air temperature for the range of conditions studied. This equation was then applied to experimental data that were obtained from the literature, and a good correlation was achieved.

  9. High-Speed Tomographic PIV Measurements of Strain Rate Properties in Turbulent Partially-Premixed Jet Flames

    NASA Astrophysics Data System (ADS)

    Coriton, Bruno; Frank, Jonathan H.

    2014-11-01

    The effects of combustion on the strain rate field in turbulent jets were studied using 10 kHz tomographic particle image velocimetry (TPIV). Measurements were performed in a series of turbulent partially-premixed jet flames with increasing jet Reynolds numbers and increasing probabilities of localized extinction. Properties of the strain rate were analyzed including the relative ratios of principal strain rates, the preferential alignment of the principal strain rates with vorticity, and the strain rate clustering and intermittency. Comparisons with measurements in turbulent air jets revealed the effects of heat release on the structure and dynamics of the strain rate field. This material is based upon work supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences.

  10. Investigation of shock-induced combustion past blunt projectiles

    NASA Technical Reports Server (NTRS)

    Ahuja, J. K.; Tiwari, S. N.

    1996-01-01

    A numerical study is conducted to simulate shock-induced combustion in premixed hydrogen-air mixtures at various free-stream conditions and parameters. Two-dimensional axisymmetric, reacting viscous flow over blunt projectiles is computed to study shock-induced combustion at Mach 5.11 and Mach 6.46 in hydrogen-air mixture. A seven-species, seven reactions finite rate hydrogen-air chemical reaction mechanism is used combined with a finite-difference, shock-fitting method to solve the complete set of Navier-Stokes and species conservation equations. The study has allowed an improved understanding of the physics of shock-induced combustion over blunt projectiles and the numerical results can now be explained more readily with one-dimensional wave-interaction model.

  11. Combustion characteristics in the transition region of liquid fuel sprays

    NASA Technical Reports Server (NTRS)

    Cernansky, N. P.; Namer, I.; Tidona, R. J.

    1984-01-01

    A number of important effects were observed in the droplet size transition region in spray combustion systems. In this region, where the mechanism of flame propagation is transformed from diffusive to premixed dominated combustion, the following effects have been observed: (1) maxima in burning velocity; (2) extension of flammability limits; (3) minima in ignition energy; and (4) minima in NO(x) formation. Unfortunately, because of differences in experimental facilities and limitations in the ranges of experimental data, a unified description of these transition region effects is not available at this time. Consequently, a fundamental experimental investigation was initiated to study the effect of droplet size, size distribution, and operating parameters on these transition region phenomena in a single well controlled spray combustion facility.

  12. High-temperature oxidation chemistry of n-butanol--experiments in low-pressure premixed flames and detailed kinetic modeling.

    PubMed

    Hansen, N; Harper, M R; Green, W H

    2011-12-01

    An automated reaction mechanism generator is used to develop a predictive, comprehensive reaction mechanism for the high-temperature oxidation chemistry of n-butanol. This new kinetic model is an advancement of an earlier model, which had been extensively tested against earlier experimental data (Harper et al., Combust. Flame, 2011, 158, 16-41). In this study, the model's predictive capabilities are improved by targeting isomer-resolved quantitative mole fraction profiles of flame species in low-pressure flames. To this end, a total of three burner-stabilized premixed flames are isomer-selectively analyzed by flame-sampling molecular-beam time-of-flight mass spectrometry using photoionization by tunable vacuum-ultraviolet synchrotron radiation. For most species, the newly developed chemical kinetic model is capable of accurately reproducing the experimental trends in these flames. The results clearly indicate that n-butanol is mainly consumed by H-atom abstraction with H, O, and OH, forming predominantly the α-C(4)H(9)O radical (CH(3)CH(2)CH(2)˙CHOH). Fission of C-C bonds in n-butanol is only predicted to be significant in a similar, but hotter flame studied by Oßwald et al. (Combust. Flame, 2011, 158, 2-15). The water-elimination reaction to 1-butene is found to be of no importance under the premixed conditions studied here. The initially formed isomeric C(4)H(9)O radicals are predicted to further oxidize by reacting with H and O(2) or to decompose to smaller fragments via β-scission. Enols are detected experimentally, with their importance being overpredicted by the model. PMID:21993635

  13. Aerodynamic properties of turbulent combustion fields

    NASA Technical Reports Server (NTRS)

    Hsiao, C. C.; Oppenheim, A. K.

    1985-01-01

    Flow fields involving turbulent flames in premixed gases under a variety of conditions are modeled by the use of a numerical technique based on the random vortex method to solve the Navier-Stokes equations and a flame propagation algorithm to trace the motion of the front and implement the Huygens principle, both due to Chorin. A successive over-relaxation hybrid method is applied to solve the Euler equation for flows in an arbitrarily shaped domain. The method of images, conformal transformation, and the integral-equation technique are also used to treat flows in special cases, according to their particular requirements. Salient features of turbulent flame propagation in premixed gases are interpreted by relating them to the aerodynamic properties of the flow field. Included among them is the well-known cellular structure of flames stabilized by bluff bodies, as well as the formation of the characteristic tulip shape of flames propagating in ducts. In its rudimentary form, the mechanism of propagation of a turbulent flame is shown to consist of: (1) rotary motion of eddies at the flame front, (2) self-advancement of the front at an appropriate normal burning speed, and (3) dynamic effects of expansion due to exothermicity of the combustion reaction. An idealized model is used to illustrate these fundamental mechanisms and to investigate basic aerodynamic features of flames in premixed gases. The case of a confined flame stabilized behind a rearward-facing step is given particular care and attention. Solutions are shown to be in satisfactory agreement with experimental results, especially with respect to global properties such as the average velocity profiles and reattachment length.

  14. Partially Premixed Flame (PPF) Research for Fire Safety

    NASA Technical Reports Server (NTRS)

    Puri, Ishwar K.; Aggarwal, Suresh K.; Lock, Andrew J.; Hegde, Uday

    2004-01-01

    Incipient fires typically occur after the partial premixing of fuel and oxidizer. The mixing of product species into the fuel/oxidizer mixture influences flame stabilization and fire spread. Therefore, it is important to characterize the impact of different levels of fuel/oxidizer/product mixing on flame stabilization, liftoff and extinguishment under different gravity conditions. With regard to fire protection, the agent concentration required to achieve flame suppression is an important consideration. The initial stage of an unwanted fire in a microgravity environment will depend on the level of partial premixing and the local conditions such as air currents generated by the fire itself and any forced ventilation (that influence agent and product mixing into the fire). The motivation of our investigation is to characterize these impacts in a systematic and fundamental manner.

  15. Premixing quality and flame stability: A theoretical and experimental study

    NASA Technical Reports Server (NTRS)

    Radhakrishnan, K.; Heywood, J. B.; Tabaczynski, R. J.

    1979-01-01

    Models for predicting flame ignition and blowout in a combustor primary zone are presented. A correlation for the blowoff velocity of premixed turbulent flames is developed using the basic quantities of turbulent flow, and the laminar flame speed. A statistical model employing a Monte Carlo calculation procedure is developed to account for nonuniformities in a combustor primary zone. An overall kinetic rate equation is used to describe the fuel oxidation process. The model is used to predict the lean ignition and blow out limits of premixed turbulent flames; the effects of mixture nonuniformity on the lean ignition limit are explored using an assumed distribution of fuel-air ratios. Data on the effects of variations in inlet temperature, reference velocity and mixture uniformity on the lean ignition and blowout limits of gaseous propane-air flames are presented.

  16. The application of a probabilistic particle model for turbulent combustion modelling in combustors. (German Title: Die Anwendung eines probabilistischen Partikelmodells für die Modellierung der turbulenten Verbrennung in Brennkammern)

    NASA Astrophysics Data System (ADS)

    Aumeier, Thomas

    2011-12-01

    The modeling of combustion phenomena in turbulent flows is an important requirement to calculate the effects on the underlying flow field and thus to use the results for design studies and optimization processes in technical applications. Complex chemical systems arise due to the large amount of species participating in combustion reactions as well as multiple reaction paths which are represented by a set of reaction equations. These systems have to be solved with suitable numerical techniques and must consider the influence of turbulence in the mean transport equations, respectively. Compared to the time scales in the flow, chemical reactions occur on a more expanded range of time at a molecular level. This effect reflects in the formulation of the equations for the calculation of chemical reaction rates, which are given in a Lagrangian formulation and therefore only depends on time. In practical cases specific combustion models are used depending on the combustion regime which is associated within an application. In this thesis a combustion model for turbulence chemistry interactions is presented, which can be used, independently of the combustion regime, for both diffusion and premixed flames as well as for partially premixed flames in realistic combustors. With the aid of the model the mean chemical source terms can be coupled to the species transport equations and the energy equation of the commercial CFD - solver FLUENT®. This is done within the solver by a user-friendly interface, the so-called User Defined Functions (UDF). Transport equations for each specie progressing in the chemical reactions are solved and its source terms are calculated with the aid of a detailed reaction mechanism. In the presented model the calculation of the mean values is performed by coupling a Lagrangian solution procedure with an Eulerian finite volume solver. A very large amount of individual particles are considered where for each particle additional Lagrangian equations

  17. Combustion system for hybrid solar fossil fuel receiver

    DOEpatents

    Mehos, Mark S.; Anselmo, Kenneth M.; Moreno, James B.; Andraka, Charles E.; Rawlinson, K. Scott; Corey, John; Bohn, Mark S.

    2004-05-25

    A combustion system for a hybrid solar receiver comprises a pre-mixer which combines air and fuel to form an air-fuel mixture. The mixture is introduced tangentially into a cooling jacket. A burner plenum is fluidically connected to the cooling jacket such that the burner plenum and the cooling jacket are arranged in thermal contact with one another. The air-fuel mixture flows through the cooling jacket cooling the burner plenum to reduce pre-ignition of the air-fuel mixture in the burner plenum. A combustion chamber is operatively associated with and open to the burner plenum to receive the air-fuel mixture from the burner plenum. An igniter is operatively positioned in the combustion chamber to combust the air-fuel mixture, releasing heat. A recuperator is operatively associated with the burner plenum and the combustion chamber and pre-heats the air-fuel mixture in the burner plenum with heat from the combustion chamber. A heat-exchanger is operatively associated and in thermal contact with the combustion chamber. The heat-exchanger provides heat for the hybrid solar receiver.

  18. The 3rd International Microgravity Combustion Workshop

    NASA Technical Reports Server (NTRS)

    Ross, Howard D. (Compiler)

    1995-01-01

    This Conference Publication contains 71 papers presented at the Third International Microgravity Combustion Workshop held in Cleveland, Ohio, from April 11 to 13, 1995. The purpose of the workshop was twofold: to exchange information about the progress and promise of combustion science in microgravity and to provide a forum to discuss which areas in microgravity combustion science need to be expanded profitably and which should be included in upcoming NASA Research Announcements (NRA).

  19. The Second International Microgravity Combustion Workshop

    NASA Technical Reports Server (NTRS)

    1993-01-01

    This CP contains 40 papers presented at the Second International Microgravity Combustion Workshop held in Cleveland, OH, from September 15 to 17, 1992. The purpose of the workshop was twofold: to exchange information about the progress and promise of combustion science in microgravity and to provide a forum to discuss which areas in microgravity combustion science need to be expanded profitably and which should be included in upcoming NASA Research Announcements (NRA).

  20. Coal-water slurry fuel combustion testing in an oil-fired industrial boiler. Semiannual technical progress report, February 15--August 15, 1996

    SciTech Connect

    Miller, B.G.; Scaroni, A.W.

    1997-06-03

    The project consists of four phases: (1) design, permitting, and test planning, (2) construction and start up, (3) demonstration and evaluation (1,000-hour demonstration), and (4) expanded demonstration and evaluation (installing a CWSF preparation circuit, performing baseline tests firing No. 6 fuel oil, and conducting additional CWSF testing). The boiler testing and evaluation will determine if the CWSF combustion characteristics, heat release rate, fouling and slagging behavior, corrosion and erosion tendencies, and fuel transport, storage, and handling characteristics can be accommodated in a boiler system designed to fire heavy fuel oil. In addition, the proof-of-concept demonstration will generate data to determine how the properties of a CWSF and its parent coal affect boiler performance. The economic factors associated with retrofitting boilers is also evaluated. The first three phases have been completed and the combustion performance of the burner that was provided with the boiler did not meet performance goals. A maximum coal combustion efficiency of 95% (compared to a target of 98%) was achieved and natural gas cofiring (15% of the total thermal input) was necessary to maintain a stable flame. Consequently, the first demonstration was terminated after 500 hours. The second CWSF demonstration (Phase 4) was conducted with a proven coal-designed burner. Prior to starting the second demonstration, a CWSF preparation circuit was constructed to provide flexibility in CWSF production. The circuit initially installed involved single-stage grinding. A regrind circuit was recently installed and was evaluated. A burner was installed from ABB Combustion Engineering (ABB/CE) and was used to generate baseline data firing No. 6 fuel oil and fire CWSF. A temporary storage system for No. 6 fuel oil was installed and modifications to the existing CWSF handling and preheating system were made to accommodate No. 6 oil.

  1. Burning Questions in Gravity-Dependent Combustion Science

    NASA Technical Reports Server (NTRS)

    Urban, David; Chiaramonte, Francis P.

    2012-01-01

    Building upon a long history of spaceflight and ground based research, NASA's Combustion Science program has accumulated a significant body of accomplishments on the ISS. Historically, NASAs low-gravity combustion research program has sought: to provide a more complete understanding of the fundamental controlling processes in combustion by identifying simpler one-dimensional systems to eliminate the complex interactions between the buoyant flow and the energy feedback to the reaction zone to provide realistic simulation of the fire risk in manned spacecraft and to enable practical simulation of the gravitational environment experienced by reacting systems in future spacecraft. Over the past two decades, low-gravity combustion research has focused primarily on increasing our understanding of fundamental combustion processes (e.g. droplet combustion, soot, flame spread, smoldering, and gas-jet flames). This research program was highly successful and was aided by synergistic programs in Europe and in Japan. Overall improvements were made in our ability to model droplet combustion in spray combustors (e.g. jet engines), predict flame spread, predict soot production, and detect and prevent spacecraft fires. These results provided a unique dataset that supports both an active research discipline and also spacecraft fire safety for current and future spacecraft. These experiments have been conducted using the Combustion Integrated Rack (CIR), the Microgravity Science Glovebox and the Express Rack. In this paper, we provide an overview of the earlier space shuttle experiments, the recent ISS combustion experiments in addition to the studies planned for the future. Experiments in combustion include topics such as droplet combustion, gaseous diffusion flames, solid fuels, premixed flame studies, fire safety, and super critical oxidation processes.

  2. Comparison of Flamelet Models with the Transported Mass Fraction Approach for Supersonic Combustion

    NASA Astrophysics Data System (ADS)

    Li, Wenhai; Alabi, Ken; Ladeinde, Foluso

    2015-11-01

    In this study, two fully compressible RANS, LES, and combined RANS/LES flow solvers - AEROFLO and VULCAN, both of which were originally developed by the United States Department of Defense but have since been significantly enhanced and commercialized by our organization, are used to investigate the accuracy of flamelet-based approach when employed to model supersonic combustion. The flamelet results from both codes are assessed relative to solutions obtained by solving the transport equations for the mass fractions - which is also supported by one of the codes, and making familiar assumptions about the closure of the reaction rate. The studies are carried out in the flamelet regime, and the numerical procedures are based on high-order schemes, which are also used to solve the level-set and mixture fraction transport equations used to study, respectively, premixed and non-premixed combustion. The effects of supersonic Mach numbers on the results are discussed.

  3. A Two-dimensional Cartesian and Axisymmetric Study of Combustion-acoustic Interaction

    NASA Technical Reports Server (NTRS)

    Hood, Caroline; Frendi, Abdelkader

    2006-01-01

    This paper describes a study of a lean premixed (LP) methane-air combustion wave in a two-dimensional Cartesian and axisymmetric coordinate system. Lean premixed combustors provide low emission and high efficiency; however, they are susceptible to combustion instabilities. The present study focuses on the behavior of the flame as it interacts with an external acoustic disturbance. It was found that the flame oscillations increase as the disturbance amplitude is increased. Furthermore, when the frequency of the disturbance is at resonance with a chamber frequency, the instabilities increase. For the axisymmetric geometry, the flame is found to be more unstable compared to the Cartesian case. In some cases, these instabilities were severe and led to flame extinction. In the axisymmetric case, several passive control devices were tested to assess their effectiveness. It is found that an acoustic cavity is better able at controlling the pressure fluctuations in the chamber.

  4. Biofuels combustion.

    PubMed

    Westbrook, Charles K

    2013-01-01

    This review describes major features of current research in renewable fuels derived from plants and from fatty acids. Recent and ongoing fundamental studies of biofuel molecular structure, oxidation reactions, and biofuel chemical properties are reviewed, in addition to combustion applications of biofuels in the major types of engines in which biofuels are used. Biofuels and their combustion are compared with combustion features of conventional petroleum-based fuels. Two main classes of biofuels are described, those consisting of small, primarily alcohol, fuels (particularly ethanol, n-butanol, and iso-pentanol) that are used primarily to replace or supplement gasoline and those derived from fatty acids and used primarily to replace or supplement conventional diesel fuels. Research efforts on so-called second- and third-generation biofuels are discussed briefly.

  5. Bubble Combustion

    NASA Technical Reports Server (NTRS)

    Corrigan, Jackie

    2004-01-01

    A method of energy production that is capable of low pollutant emissions is fundamental to one of the four pillars of NASA s Aeronautics Blueprint: Revolutionary Vehicles. Bubble combustion, a new engine technology currently being developed at Glenn Research Center promises to provide low emissions combustion in support of NASA s vision under the Emissions Element because it generates power, while minimizing the production of carbon dioxide (CO2) and nitrous oxides (NOx), both known to be Greenhouse gases. and allows the use of alternative fuels such as corn oil, low-grade fuels, and even used motor oil. Bubble combustion is analogous to the inverse of spray combustion: the difference between bubble and spray combustion is that spray combustion is spraying a liquid in to a gas to form droplets, whereas bubble combustion involves injecting a gas into a liquid to form gaseous bubbles. In bubble combustion, the process for the ignition of the bubbles takes place on a time scale of less than a nanosecond and begins with acoustic waves perturbing each bubble. This perturbation causes the local pressure to drop below the vapor pressure of the liquid thus producing cavitation in which the bubble diameter grows, and upon reversal of the oscillating pressure field, the bubble then collapses rapidly with the aid of the high surface tension forces acting on the wall of the bubble. The rapid and violent collapse causes the temperatures inside the bubbles to soar as a result of adiabatic heating. As the temperatures rise, the gaseous contents of the bubble ignite with the bubble itself serving as its own combustion chamber. After ignition, this is the time in the bubble s life cycle where power is generated, and CO2, and NOx among other species, are produced. However, the pollutants CO2 and NOx are absorbed into the surrounding liquid. The importance of bubble combustion is that it generates power using a simple and compact device. We conducted a parametric study using CAVCHEM

  6. Biofuels combustion*

    DOE PAGES

    Westbrook, Charles K.

    2013-01-04

    This review describes major features of current research in renewable fuels derived from plants and from fatty acids. Recent and ongoing fundamental studies of biofuel molecular structure, oxidation reactions, and biofuel chemical properties are reviewed, in addition to combustion applications of biofuels in the major types of engines in which biofuels are used. Biofuels and their combustion are compared with combustion features of conventional petroleum-based fuels. Two main classes of biofuels are described, those consisting of small, primarily alcohol, fuels (particularly ethanol, n-butanol, and iso-pentanol) that are used primarily to replace or supplement gasoline and those derived from fatty acidsmore » and used primarily to replace or supplement conventional diesel fuels. As a result, research efforts on so-called second- and third-generation biofuels are discussed briefly.« less

  7. Biofuels combustion*

    SciTech Connect

    Westbrook, Charles K.

    2013-01-04

    This review describes major features of current research in renewable fuels derived from plants and from fatty acids. Recent and ongoing fundamental studies of biofuel molecular structure, oxidation reactions, and biofuel chemical properties are reviewed, in addition to combustion applications of biofuels in the major types of engines in which biofuels are used. Biofuels and their combustion are compared with combustion features of conventional petroleum-based fuels. Two main classes of biofuels are described, those consisting of small, primarily alcohol, fuels (particularly ethanol, n-butanol, and iso-pentanol) that are used primarily to replace or supplement gasoline and those derived from fatty acids and used primarily to replace or supplement conventional diesel fuels. As a result, research efforts on so-called second- and third-generation biofuels are discussed briefly.

  8. Biofuels Combustion

    NASA Astrophysics Data System (ADS)

    Westbrook, Charles K.

    2013-04-01

    This review describes major features of current research in renewable fuels derived from plants and from fatty acids. Recent and ongoing fundamental studies of biofuel molecular structure, oxidation reactions, and biofuel chemical properties are reviewed, in addition to combustion applications of biofuels in the major types of engines in which biofuels are used. Biofuels and their combustion are compared with combustion features of conventional petroleum-based fuels. Two main classes of biofuels are described, those consisting of small, primarily alcohol, fuels (particularly ethanol, n-butanol, and iso-pentanol) that are used primarily to replace or supplement gasoline and those derived from fatty acids and used primarily to replace or supplement conventional diesel fuels. Research efforts on so-called second- and third-generation biofuels are discussed briefly.

  9. Combustion characterization of coal fines recovered from the handling plant. Quarterly technical progress report No. 2, January 1, 1995--March 31, 1995

    SciTech Connect

    Houshang, Masudi

    1995-04-01

    The main goal of this research project is to evaluate the combustion characteristics of the slurry fuels prepared from the recovered coal fines and plant coal fines. A specific study will include the combustion behavior, flame stability, ash behavior and emissions of SO{sub x}, NO{sub x} and particulate in a well insulated laboratory scale furnace in which the residence time and temperature history of the burning particles are similar to that of utility boiler furnace at 750,000 Btu/hr input and 20% excess air. The slurry fuel will be prepared at 60% solid to match the generic slurry properties, i.e., viscosity less than 500 cp, 100% of particles passing through 100 mesh and 80-90% of solid particles passing through 200 mesh. The coal blend is prepared using a mix of 15% effluent recovered coal and 85% plant fines. Combustion characteristics of the slurry fuels is determined at three different firing rates 750K, 625K, 500K Btu/hr. Finally a comparison of the results is made to determine the advantages of coal water slurry fuel over the plant coal blended form.

  10. Basic combustion and pollutant-formation processes for pulverized fuels. Quarterly technical progress report No. 4, 1 July 1981-30 September 1981

    SciTech Connect

    Germane, G.J.; Smoot, L.D.

    1981-10-15

    This contract study of basic combustion and pollutant formation processes for pulverized solid fossil fuels includes coal-water mixtures and chars derived from coal pyrolysis, liquefaction or gasification processes. The factors that affect the physical properties of coal-water mixtures (CWM) have been identified and characterization tests initiated to determine how these variables (e.g., solids loading, particle size, particle size distribution, additives) affect the coal slurries. A bench-scale apparatus consisting of a pressure vessel and an atomizing nozzle was designed and is being fabricated. This apparatus will assist in the development of handling and atomization techniques for the combustion tests. It will also aid in comparing viscosities of slurries of different solids loadings and coal types. Chars were obtained for characterization tests. A series of potential tests to characterize the chars was identified. Grading and sizing of the chars was begun as well as elemental analysis. Samples of the chars were sent to Phillips for CO/sub 2/ reactivity tests to be performed. Coding for incorporation of swirling flows into the two-dimensional coal combustion model (PCGC-2) was completed. Debugging was initiated and sample computations are performed for a gaseous, isothermal system for low swirl numbers. Convergence problems were encountered when attempts were made to complete runs at higher swirl numbers.

  11. The Effects of Fuel Stratification and Heat Release Rate Shaping in Reactivity Controlled Compression Ignition (RCCI) Combustion

    NASA Astrophysics Data System (ADS)

    DelVescovo, Dan A.

    Low temperature combustion strategies have demonstrated high thermal efficiency with low emissions of pollutants, including oxides of nitrogen and particulate matter. One such combustion strategy, called Reactivity Controlled Compression Ignition (RCCI), which involves the port injection of a low reactivity fuel such as gasoline, ethanol, or natural gas, and a direct injection of a high reactivity fuel, such as diesel, has demonstrated excellent control over the heat release event due to the introduction of in-cylinder stratification of equivalence ratio and reactivity. The RCCI strategy is inherently fuel flexible, however the direct injection strategy needs to be tailored to the combination of premixed and direct injected fuels. Experimental results demonstrate that, when comparing different premixed fuels, matching combustion phasing with premixed mass percentage or SOI timing is not sufficient to retain baseline efficiency and emissions results. If the bulk characteristics of the heat release event can be matched, however, then the efficiency and emissions can be maintained. A 0-D methodology for predicting the required fuel stratification for a desired heat release for kinetically-controlled stratified-charge combustion strategies is proposed and validated with 3-D reacting and non-reacting CFD simulations performed with KIVA3Vr2 in this work. Various heat release rate shapes, phasing, duration, and premixed and DI fuel chemistries are explored using this analysis. This methodology provides a means by which the combustion process of a stratified-charge, kinetically-controlled combustion strategy could be optimized for any fuel combination, assuming that the fuel chemistry is well characterized.

  12. Effects of Radiative and Diffusive Transport Processes on Premixed Flames near Flammability Limits

    NASA Technical Reports Server (NTRS)

    Abbud-Madrid, Angel; Ronney, Paul D.

    1991-01-01

    A study of the mechanisms of flammability limits and the dynamics of flame extinguishment in premixed gas flames is described, a novel feature of which is the use of diluent gases having a wide range of radiative and diffusive transport properties. This feature enables an assessment of the importance of volumetric heat losses and Lewis number effects on these mechanisms. Additionally, effects of flame dynamics and flame front curvature are studied by employing spherically expanding flames obtained in a microgravity environment whereby natural convection is eliminated. New diagnostics include chamber pressure measurements and the first reported species concentration measurements in a microgravity combustion experiment. The limit mechanisms and extinguishment phenomena are found to be strongly influenced by the combined effects of radiant heat loss, Lewis number and flame curvature. Two new and as yet not well understood phenomena are reported: 'double flames' in rich H2-O2-CO2 mixtures and an 'inverse flammability region' in rich C3H8-O2-CO2 mixtures.

  13. Analysis of the electric currents in 1D premixed flames under applied voltages

    NASA Astrophysics Data System (ADS)

    Han, Jie; Belhi, Memdouh; Bisetti, Fabrizio; Casey, Tiernan; Im, Hong G.; Chen, Jyh-Yuan

    2015-11-01

    Studying electric currents in flames has practical aspects such as the determination of the ionic structure of a flame, the analysis of the flame behavior under an electric field and the use of flame electric properties for combustion diagnostics. This study proposes a simplified model to compute the electric currents in lean-to-stoichiometric 1D premixed flames under applied voltages. The Navier-Stokes equations coupled with transport equations for neutral and charged species along with a Poisson equation for the electric potential are solved. The model reproduces qualitatively the voltage-current characteristic found experimentally. The sensitivity of the electric currents to the applied voltage, equivalence ratio, and pressure is studied and the key parameters affecting the saturation current are determined. Results show that the saturation current is controlled by the amount of charged species created by the chemi-ionization reaction. We found that the recombination rate of electrons with cations and transport coefficients of charged species are the most important parameters affecting the voltage at witch saturation occurs. Analytical formulas for the voltage-current characteristic and the potential of saturation are developed and used to explain the obtained results.

  14. Quasi-steady stages in the process of premixed flame acceleration in narrow channels

    NASA Astrophysics Data System (ADS)

    Valiev, D. M.; Bychkov, V.; Akkerman, V.; Eriksson, L.-E.; Law, C. K.

    2013-09-01

    The present paper addresses the phenomenon of spontaneous acceleration of a premixed flame front propagating in micro-channels, with subsequent deflagration-to-detonation transition. It has recently been shown experimentally [M. Wu, M. Burke, S. Son, and R. Yetter, Proc. Combust. Inst. 31, 2429 (2007)], 10.1016/j.proci.2006.08.098, computationally [D. Valiev, V. Bychkov, V. Akkerman, and L.-E. Eriksson, Phys. Rev. E 80, 036317 (2009)], 10.1103/PhysRevE.80.036317, and analytically [V. Bychkov, V. Akkerman, D. Valiev, and C. K. Law, Phys. Rev. E 81, 026309 (2010)], 10.1103/PhysRevE.81.026309 that the flame acceleration undergoes different stages, from an initial exponential regime to quasi-steady fast deflagration with saturated velocity. The present work focuses on the final saturation stages in the process of flame acceleration, when the flame propagates with supersonic velocity with respect to the channel walls. It is shown that an intermediate stage may occur during acceleration with quasi-steady velocity, noticeably below the Chapman-Jouguet deflagration speed. The intermediate stage is followed by additional flame acceleration and subsequent saturation to the Chapman-Jouguet deflagration regime. We elucidate the intermediate stage by the joint effect of gas pre-compression ahead of the flame front and the hydraulic resistance. The additional acceleration is related to viscous heating at the channel walls, being of key importance at the final stages. The possibility of explosion triggering is also demonstrated.

  15. Lagrangian Fluid Element Tracking and Estimation of Local Displacement Speeds in Turbulent Premixed Flames

    NASA Astrophysics Data System (ADS)

    Ramji, Sarah Ann

    Improved understanding of turbulence-flame interactions in premixed combustion can be achieved using fully 3D time-resolved multi-kHz multi-scalar experimental measurements. These interactions may be represented by the evolution of various Lagrangian quantities described by theoretical Lagrangian Fluid Elements (LFEs). The data used in this work came from two experimental campaigns that used simultaneous T-PIV and OH/CH2O PLIF, at Sandia National Labs and the Air Force Research Lab at Wright-Patterson. In this thesis, an algorithm to accurately track LFEs through this 4D experimental space has been developed and verified by cross-correlation with the T-PIV seed particle fields. A novel method to measure the local instantaneous displacement speed in 3D has been developed, using this algorithm to track control masses of fluid that interact with the flame front. Statistics of the displacement speed have been presented, and the effects of local turbulence and flame topological properties on the displacement speed have been studied.

  16. An experimental and kinetic investigation of premixed furan/oxygen/argon flames

    PubMed Central

    Tian, Zhenyu; Yuan, Tao; Fournet, Rene; Glaude, Pierre-Alexandre; Sirjean, Baptiste; Battin-Leclerc, Frédérique; Zhang, Kuiwen; Qi, Fei

    2013-01-01

    The detailed chemical structures of three low-pressure (35 Torr) premixed laminar furan/oxygen/argon flames with equivalence ratios of 1.4, 1.8 and 2.2 have been investigated by using tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam mass spectrometry. About 40 combustion species including hydrocarbons and oxygenated intermediates have been identified by measurements of photoionization efficiency spectra. Mole fraction profiles of the flame species including reactants, intermediates and products have been determined by scanning burner position with some selected photon energies near ionization thresholds. Flame temperatures have been measured by a Pt-6%Rh/Pt-30%Rh thermocouple. A new mechanism involving 206 species and 1368 reactions has been proposed whose predictions are in reasonable agreement with measured species profiles for the three investigated flames. Rate-of-production and sensitivity analyses have been performed to track the key reaction paths governing furan consumption for different equivalence ratios. Both experimental and modeling results indicate that few aromatics could be formed in these flames. Furthermore, the current model has been validated against previous pyrolysis results of the literature obtained behind shock waves and the agreement is reasonable as well. PMID:23814311

  17. Aromatic and polycyclic aromatic hydrocarbon formation in a laminar premixed n-butane flame

    SciTech Connect

    Marinov, N.M.; Pitz, W.J.; Westbrook, C.K.; Vincitore, A.M.; Castaldi, M.J.; Senkan, S.M.; Melius, C.F.

    1998-07-01

    Experimental and detailed chemical kinetic modeling work has been performed to investigate aromatic and polycyclic aromatic hydrocarbon (PAH) formation pathways in a premixed, rich, sooting, n-butane-oxygen-argon burner stabilized flame. An atmospheric pressure, laminar flat flame operated at an equivalence ratio of 2.6 was used to acquire experimental data for model validation. Gas composition analysis was conducted by an on-line gas chromatograph/mass spectrometer technique. Measurements were made in the main reaction and post-reaction zones for a number of low molecular weight species, aliphatics, aromatics, and polycyclic aromatic hydrocarbons (PAHs) ranging from two to five-fused aromatic rings. Reaction flux and sensitivity analysis were used to help identify the important reaction sequences leading to aromatic and PAH growth and destruction in the n-butane flame. Reaction flux analysis showed the propargyl recombination reaction was the dominant pathway to benzene formation. The consumption of propargyl by H atoms was shown to limit propargyl, benzene, and naphthalene formation in flames as exhibited by the large negative sensitivity coefficients. Naphthalene and phenanthrene production was shown to be plausibly formed through reactions involving resonantly stabilized cyclopentadienyl and indenyl radicals. Many of the low molecular weight aliphatics, combustion by-products, aromatics, branched aromatics, and PAHs were fairly well simulated by the model. Additional work is required to understand the formation mechanisms of phenyl acetylene, pyrene, and fluoranthene in the n-butane flame. 73 refs.

  18. Large Eddy Simulations of Colorless Distributed Combustion Systems

    NASA Astrophysics Data System (ADS)

    Abdulrahman, Husam F.; Jaberi, Farhad; Gupta, Ashwani

    2014-11-01

    Development of efficient and low-emission colorless distributed combustion (CDC) systems for gas turbine applications require careful examination of the role of various flow and combustion parameters. Numerical simulations of CDC in a laboratory-scale combustor have been conducted to carefully examine the effects of these parameters on the CDC. The computational model is based on a hybrid modeling approach combining large eddy simulation (LES) with the filtered mass density function (FMDF) equations, solved with high order numerical methods and complex chemical kinetics. The simulated combustor operates based on the principle of high temperature air combustion (HiTAC) and has shown to significantly reduce the NOx, and CO emissions while improving the reaction pattern factor and stability without using any flame stabilizer and with low pressure drop and noise. The focus of the current work is to investigate the mixing of air and hydrocarbon fuels and the non-premixed and premixed reactions within the combustor by the LES/FMDF with the reduced chemical kinetic mechanisms for the same flow conditions and configurations investigated experimentally. The main goal is to develop better CDC with higher mixing and efficiency, ultra-low emission levels and optimum residence time. The computational results establish the consistency and the reliability of LES/FMDF and its Lagrangian-Eulerian numerical methodology.

  19. Detection and control of combustion instability based on the concept of dynamical system theory

    NASA Astrophysics Data System (ADS)

    Gotoda, Hiroshi; Shinoda, Yuta; Kobayashi, Masaki; Okuno, Yuta; Tachibana, Shigeru

    2014-02-01

    We propose an online method of detecting combustion instability based on the concept of dynamical system theory, including the characterization of the dynamic behavior of combustion instability. As an important case study relevant to combustion instability encountered in fundamental and practical combustion systems, we deal with the combustion dynamics close to lean blowout (LBO) in a premixed gas-turbine model combustor. The relatively regular pressure fluctuations generated by thermoacoustic oscillations transit to low-dimensional intermittent chaos owing to the intermittent appearance of burst with decreasing equivalence ratio. The translation error, which is characterized by quantifying the degree of parallelism of trajectories in the phase space, can be used as a control variable to prevent LBO.

  20. Study of shock-induced combustion using an implicit TVD scheme

    NASA Technical Reports Server (NTRS)

    Yungster, Shayne

    1992-01-01

    The supersonic combustion flowfields associated with various hypersonic propulsion systems, such as the ram accelerator, the oblique detonation wave engine, and the scramjet, are being investigated using a new computational fluid dynamics (CFD) code. The code solves the fully coupled Reynolds-averaged Navier-Stokes equations and species continuity equations in an efficient manner. It employs an iterative method and a second order differencing scheme to improve computational efficiency. The code is currently being applied to study shock wave/boundary layer interactions in premixed combustible gases, and to investigate the ram accelerator concept. Results obtained for a ram accelerator configuration indicate a new combustion mechanism in which a shock wave induces combustion in the boundary layer, which then propagates outward and downstream. The combustion process creates a high pressure region over the back of the projectile resulting in a net positive thrust forward.