Science.gov

Sample records for laminar diffusion flames

  1. Burning Laminar Jet Diffusion Flame

    NASA Technical Reports Server (NTRS)

    2003-01-01

    Study of the downlink data from the Laminar Soot Processes (LSP) experiment quickly resulted in discovery of a new mechanism of flame extinction caused by radiation of soot. Scientists found that the flames emit soot sooner than expected. These findings have direct impact on spacecraft fire safety, as well as the theories predicting the formation of soot -- which is a major factor as a pollutant and in the spread of unwanted fires. This sequence was taken July 15, 1997, MET:14/10:34 (approximate) and shows the ignition and extinction of this flame. LSP investigated fundamental questions regarding soot, a solid byproduct of the combustion of hydrocarbon fuels. The experiment was performed using a laminar jet diffusion flame, which is created by simply flowing fuel -- like ethylene or propane -- through a nozzle and igniting it, much like a butane cigarette lighter. The LSP principal investigator was Gerard Faeth, University of Michigan, Arn Arbor. The experiment was part of the space research investigations conducted during the Microgravity Science Laboratory-1R mission (STS-94, July 1-17 1997). LSP results led to a reflight for extended investigations on the STS-107 research mission in January 2003. Advanced combustion experiments will be a part of investigations planned for the International Space Station. (518KB, 20-second MPEG, screen 160 x 120 pixels; downlinked video, higher quality not available) A still JPG composite of this movie is available at http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0300182.html.

  2. Laminar Jet Diffusion Flame Burning

    NASA Technical Reports Server (NTRS)

    2003-01-01

    Study of the downlink data from the Laminar Soot Processes (LSP) experiment quickly resulted in discovery of a new mechanism of flame extinction caused by radiation of soot. Scientists found that the flames emit soot sooner than expected. These findings have direct impact on spacecraft fire safety, as well as the theories predicting the formation of soot -- which is a major factor as a pollutant and in the spread of unwanted fires. This sequence, using propane fuel, was taken STS-94, July 4 1997, MET:2/05:30 (approximate). LSP investigated fundamental questions regarding soot, a solid byproduct of the combustion of hydrocarbon fuels. The experiment was performed using a laminar jet diffusion flame, which is created by simply flowing fuel-like ethylene or propane -- through a nozzle and igniting it, much like a butane cigarette lighter. The LSP principal investigator was Gerard Faeth, University of Michigan, Arn Arbor. The experiment was part of the space research investigations conducted during the Microgravity Science Laboratory-1R mission (STS-94, July 1-17 1997). LSP results led to a reflight for extended investigations on the STS-107 research mission in January 2003. Advanced combustion experiments will be a part of investigations planned for the International Space Station. (983KB, 9-second MPEG, screen 320 x 240 pixels; downlinked video, higher quality not available) A still JPG composite of this movie is available at http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0300184.html.

  3. Flow/Soot-Formation Interactions in Nonbuoyant Laminar Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Dai, Z.; Lin, K.-C.; Sunderland, P. B.; Xu, F.; Faeth, G. M.

    2002-01-01

    This is the final report of a research program considering interactions between flow and soot properties within laminar diffusion flames. Laminar diffusion flames were considered because they provide model flame systems that are far more tractable for theoretical and experimental studies than more practical turbulent diffusion flames. In particular, understanding the transport and chemical reaction processes of laminar flames is a necessary precursor to understanding these processes in practical turbulent flames and many aspects of laminar diffusion flames have direct relevance to turbulent diffusion flames through application of the widely recognized laminar flamelet concept of turbulent diffusion flames. The investigation was divided into three phases, considering the shapes of nonbuoyant round laminar jet diffusion flames in still air, the shapes of nonbuoyant round laminar jet diffusion flames in coflowing air, and the hydrodynamic suppression of soot formation in laminar diffusion flames.

  4. Flame height measurement of laminar inverse diffusion flames.

    SciTech Connect

    Shaddix, Christopher R.; Williams, Timothy C.; Blevins, Linda Gail; Mikofski, Mark A.

    2005-09-01

    Flame heights of co-flowing cylindrical ethylene-air and methane-air laminar inverse diffusion flames were measured. The luminous flame height was found to be greater than the height of the reaction zone determined by planar laser-induced fluorescence (PLIF) of hydroxyl radicals (OH) because of luminous soot above the reaction zone. However, the location of the peak luminous signals along the centerline agreed very well with the OH flame height. Flame height predictions using Roper's analysis for circular port burners agreed with measured reaction zone heights when using values for the characteristic diffusion coefficient and/or diffusion temperature somewhat different from those recommended by Roper. The fact that Roper's analysis applies to inverse diffusion flames is evidence that inverse diffusion flames are similar in structure to normal diffusion flames.

  5. Flame height measurement of laminar inverse diffusion flames

    SciTech Connect

    Mikofski, Mark A.; Williams, Timothy C.; Shaddix, Christopher R.; Blevins, Linda G.

    2006-07-15

    Flame heights of co-flowing cylindrical ethylene-air and methane-air laminar inverse diffusion flames were measured. The luminous flame height was found to be greater than the height of the reaction zone determined by planar laser-induced fluorescence (PLIF) of hydroxyl radicals (OH) because of luminous soot above the reaction zone. However, the location of the peak luminous signals along the centerline agreed very well with the OH flame height. Flame height predictions using Roper's analysis for circular port burners agreed with measured reaction zone heights when using values for the characteristic diffusion coefficient and/or diffusion temperature somewhat different from those recommended by Roper. The fact that Roper's analysis applies to inverse diffusion flames is evidence that inverse diffusion flames are similar in structure to normal diffusion flames. (author)

  6. Flame Shapes of Nonbuoyant Laminar Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Xu, F.; Dai, Z.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z. G. (Technical Monitor)

    2001-01-01

    The shapes (flame-sheet and luminous-flame boundaries) of steady nonbuoyant round hydrocarbon-fueled laminar-jet diffusion flames in still and coflowing air were studied both experimentally and theoretically. Flame-sheet shapes were measured from photographs using a CH optical filter to distinguish flame-sheet boundaries in the presence of blue CO2 and OH emissions and yellow continuum radiation from soot. Present experimental conditions included acetylene-, methane-, propane-, and ethylene-fueled flames having initial reactant temperatures of 300 K, ambient pressures of 4-50 kPa, jet exit Reynolds number of 3-54, initial air/fuel velocity ratios of 0-9 and luminous flame lengths of 5-55 mm; earlier measurements for propylene- and 1,3-butadiene-fueled flames for similar conditions were considered as well. Nonbuoyant flames in still air were observed at micro-gravity conditions; essentially nonbuoyant flames in coflowing air were observed at small pressures to control effects of buoyancy. Predictions of luminous flame boundaries from soot luminosity were limited to laminar smokepoint conditions, whereas predictions of flame-sheet boundaries ranged from soot-free to smokepoint conditions. Flame-shape predictions were based on simplified analyses using the boundary layer approximations along with empirical parameters to distinguish flame-sheet and luminous flame (at the laminar smoke point) boundaries. The comparison between measurements and predictions was remarkably good and showed that both flame-sheet and luminous-flame lengths are primarily controlled by fuel flow rates with lengths in coflowing air approaching 2/3 lengths in still air as coflowing air velocities are increased. Finally, luminous flame lengths at laminar smoke-point conditions were roughly twice as long as flame-sheet lengths at comparable conditions due to the presence of luminous soot particles in the fuel-lean region of the flames.

  7. Flame Shapes of Nonbuoyant Laminar Jet Diffusion Flames. Appendix K

    NASA Technical Reports Server (NTRS)

    Xu, F.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2000-01-01

    The shapes (flame-sheet and luminous-flame boundaries) of steady nonbuoyant round hydrocarbon-fueled laminar-jet diffusion flames in still and coflowing air were studied both experimentally and theoretically. Flame-sheet shapes were measured from photographs using a CH optical filter to distinguish flame-sheet boundaries in the presence of blue C02 and OH emissions and yellow continuum radiation from soot. Present experimental conditions included acetylene-, methane-, propane-, and ethylene-fueled flames having initial reactant temperatures of 300 K, ambient pressures of 4-50 kPa, jet exit Reynolds number of 3-54, initial air/fuel velocity ratios of 0-9 and luminous flame lengths of 5-55 mm; earlier measurements for propylene- and 1,3-butadiene-fueled flames for similar conditions were considered as well. Nonbuoyant flames in still air were observed at micro-gravity conditions; essentially nonbuoyant flames in coflowing air were observed at small pressures to control effects of buoyancy. Predictions of luminous flame boundaries from soot luminosity were limited to laminar smoke-point conditions, whereas predictions of flame-sheet boundaries ranged from soot-free to smoke-point conditions. Flame-shape predictions were based on simplified analyses using the boundary layer approximations along with empirical parameters to distinguish flame-sheet and luminous-flame (at the laminar smoke point) boundaries. The comparison between measurements and predictions was remarkably good and showed that both flame-sheet and luminous-flame lengths are primarily controlled by fuel flow rates with lengths in coflowing air approaching 2/3 lengths in still air as coflowing air velocities are increased. Finally, luminous flame lengths at laminar smoke-point conditions were roughly twice as long as flame-sheet lengths at comparable conditions due to the presence of luminous soot particles in the fuel-lean region of the flames.

  8. Structure of laminar sooting inverse diffusion flames

    SciTech Connect

    Mikofski, Mark A.; Fernandez-Pello, A. Carlos; Williams, Timothy C.; Shaddix, Christopher R.; Blevins, Linda G.

    2007-06-15

    The flame structure of laminar inverse diffusion flames (IDFs) was studied to gain insight into soot formation and growth in underventilated combustion. Both ethylene-air and methane-air IDFs were examined, fuel flow rates were kept constant for all flames of each fuel type, and airflow rates were varied to observe the effect on flame structure and soot formation. Planar laser-induced fluorescence of hydroxyl radicals (OH PLIF) and polycyclic aromatic hydrocarbons (PAH PLIF), planar laser-induced incandescence of soot (soot PLII), and thermocouple-determined gas temperatures were used to draw conclusions about flame structure and soot formation. Flickering, caused by buoyancy-induced vortices, was evident above and outside the flames. The distances between the OH, PAH, and soot zones were similar in IDFs and normal diffusion flames (NDFs), but the locations of those zones were inverted in IDFs relative to NDFs. Peak OH PLIF coincided with peak temperature and marked the flame front. Soot appeared outside the flame front, corresponding to temperatures around the minimum soot formation temperature of 1300 K. PAHs appeared outside the soot layer, with characteristic temperature depending on the wavelength detection band. PAHs and soot began to appear at a constant axial position for each fuel, independent of the rate of air flow. PAH formation either preceded or coincided with soot formation, indicating that PAHs are important components in soot formation. Soot growth continued for some time downstream of the flame, at temperatures below the inception temperature, probably through reaction with PAHs. (author)

  9. Velocity profiles in laminar diffusion flames

    NASA Technical Reports Server (NTRS)

    Lyons, Valerie J.; Margle, Janice M.

    1986-01-01

    Velocity profiles in vertical laminar diffusion flames were measured by using laser Doppler velocimetry (LDV). Four fuels were used: n-heptane, iso-octane, cyclohexane, and ethyl alcohol. The velocity profiles were similar for all the fuels, although there were some differences in the peak velocities. The data compared favorably with the theoretical velocity predictions. The differences could be attributed to errors in experimental positioning and in the prediction of temperature profiles. Error in the predicted temperature profiles are probably due to the difficulty in predicting the radiative heat losses from the flame.

  10. 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.

  11. Laminar Diffusion Flame Studies (Ground- and Space-Based Studies)

    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

    Laminar diffusion flames are of interest because they provide model flame systems that are far more tractable for analysis and experiments than more practical turbulent diffusion flames. Certainly, understanding flame processes within laminar diffusion flames must precede understanding these processes in more complex turbulent diffusion flames. In addition, many properties of laminar diffusion flames are directly relevant to turbulent diffusion flames using laminar flamelet concepts. Laminar jet diffusion flame shapes (luminous flame boundaries) have been of particular interest since the classical study of Burke and Schumann because they are a simple nonintrusive measurement that is convenient for evaluating flame structure predictions. Thus, consideration of laminar flame shapes is undertaken in the following, emphasizing conditions where effects of gravity are small, due to the importance of such conditions to practical applications. Another class of interesting properties of laminar diffusion flames are their laminar soot and smoke point properties (i.e., the flame length, fuel flow rate, characteristic residence time, etc., at the onset of soot appearance in the flame (the soot point) and the onset of soot emissions from the flame (the smoke point)). These are useful observable soot properties of nonpremixed flames because they provide a convenient means to rate several aspects of flame sooting properties: the relative propensity of various fuels to produce soot in flames; the relative effects of fuel structure, fuel dilution, flame temperature and ambient pressure on the soot appearance and emission properties of flames; the relative levels of continuum radiation from soot in flames; and effects of the intrusion of gravity (or buoyant motion) on emissions of soot from flames. An important motivation to define conditions for soot emissions is that observations of laminar jet diffusion flames in critical environments, e.g., space shuttle and space station

  12. Shapes of Buoyant and Nonbuoyant Methane Laminar Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Sunderland, Peter B.; Yuan, Zeng-Guang; Urban, David L.

    1997-01-01

    Laminar gas jet diffusion flames represent a fundamental combustion configuration. Their study has contributed to numerous advances in combustion, including the development of analytical and computational combustion tools. Laminar jet flames are pertinent also to turbulent flames by use of the laminar flamelet concept. Investigations into the shapes of noncoflowing microgravity laminar jet diffusion flames have primarily been pursued in the NASA Lewis 2.2-second drop tower, by Cochran and coworkers and by Bahadori and coworkers. These studies were generally conducted at atmospheric pressure; they involved soot-containing flames and reported luminosity lengths and widths instead of the flame-sheet dimensions which are of Greater value to theory evaluation and development. The seminal model of laminar diffusion flames is that of Burke and Schumann, who solved the conservation of momentum equation for a jet flame in a coflowing ambient by assuming the velocity of fuel, oxidizer and products to be constant throughout. Roper and coworkers improved upon this model by allowing for axial variations of velocity and found flame shape to be independent of coflow velocity. Roper's suggestion that flame height should be independent of gravity level is not supported by past or present observations. Other models have been presented by Klajn and Oppenheim, Markstein and De Ris, Villermaux and Durox, and Li et al. The common result of all these models (except in the buoyant regime) is that flame height is proportional to fuel mass flowrate, with flame width proving much more difficult to predict. Most existing flame models have been compared with shapes of flames containing soot, which is known to obscure the weak blue emission of flame sheets. The present work involves measurements of laminar gas jet diffusion flame shapes. Flame images have been obtained for buoyant and nonbuoyant methane flames burning in quiescent air at various fuel flow-rates, burner diameters and ambient

  13. Analytical Study of Gravity Effects on Laminar Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Edelman, R. B.; Fortune, O.; Weilerstein, G.

    1972-01-01

    A mathematical model is presented for the description of axisymmetric laminar-jet diffusion flames. The analysis includes the effects of inertia, viscosity, diffusion, gravity and combustion. These mechanisms are coupled in a boundary layer type formulation and solutions are obtained by an explicit finite difference technique. A dimensional analysis shows that the maximum flame width radius, velocity and thermodynamic state characterize the flame structure. Comparisons with experimental data showed excellent agreement for normal gravity flames and fair agreement for steady state low Reynolds number zero gravity flames. Kinetics effects and radiation are shown to be the primary mechanisms responsible for this discrepancy. Additional factors are discussed including elipticity and transient effects.

  14. Structure and Early Soot Oxidation Properties of Laminar Diffusion Flames

    NASA Technical Reports Server (NTRS)

    El-Leathy, A. M.; Xu, F.; Faeth, G. M.

    2001-01-01

    Soot is an important unsolved problem of combustion science because it is present in most hydrocarbon-fueled flames and current understanding of the reactive and physical properties of soot in flame environments is limited. This lack of understanding affects progress toward developing reliable predictions of flame radiation properties, reliable predictions of flame pollutant emission properties and reliable methods of computational combustion, among others. Motivated by these observations, the present investigation extended past studies of soot formation in this laboratory, to consider soot oxidation in laminar diffusion flames using similar methods. Early work showed that O2 was responsible for soot oxidation in high temperature O2-rich environments. Subsequent work in high temperature flame environments having small O2 concentrations, however, showed that soot oxidation rates substantially exceeded estimates based on the classical O2 oxidation rates of Nagle and Strickland-Constable and suggests that radicals such as O and OH might be strong contributors to soot oxidation for such conditions. Neoh et al. subsequently made observations in premixed flames, supported by later work, that showed that OH was responsible for soot oxidation at these conditions with a very reasonable collision efficiency of 0.13. Subsequent studies in diffusion flames, however, were not in agreement with the premixed flame studies: they agreed that OH played a dominant role in soot oxidation in flames, but found collision efficiencies that varied with flame conditions and were not in good agreement with each other or with Neoh et al. One explanation for these discrepancies is that optical scattering and extinction properties were used to infer soot structure properties for the studies that have not been very successful for representing the optical properties of soot. Whatever the source of the problem, however, these differences among observations of soot oxidation in premixed and

  15. Flame and Soot Boundaries of Laminar Jet Diffusion Flames. Appendix A

    NASA Technical Reports Server (NTRS)

    Xu, F.; Dai, Z.; Faeth, G. M.; Yuan, Z.-G. (Technical Monitor); Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2002-01-01

    The shapes (flame-sheet and luminous-flame boundaries) or steady weakly buoyant round hydrocarbon-fueled laminar-jet diffusion flames in still and coflowing air were studied both experimentally and theoretically. Flame-sheet shapes were measured from photographs using a CH optical filter to distinguish flame-sheet boundaries in the presence of blue CO2 and OH emissions and yellow continuum radiation from soot. Present experimental conditions included acetylene-, methane-, propane-, and ethylene-fueled flames having initial reactant temperatures of 300 K. ambient pressures of 4-50 kPa, jet-exit Reynolds numbers of 3-54, initial air/fuel velocity ratios of 0-9, and luminous flame lengths of 5-55 mm; earlier measurements for propylene- and 1,3-butadiene-fueled flames for similar conditions were considered as well. Nonbuoyant flames in still air were observed at microgravity conditions; essentially nonbuoyant flames in coflowing air were observed at small pressures to control effects of buoyancy. Predictions of luminous flame boundaries from soot luminosity were limited to laminar smoke-point conditions, whereas predictions of flame-sheet boundaries ranged from soot-free to smoke-point conditions. Flame-shape predictions were based on simplified analyses using the boundary-layer approximations along with empirical parameters to distinguish flame-sheet and luminous-flame (at the laminar smoke point) boundaries. The comparison between measurements and predictions was remarkably good and showed that both flame-sheet and luminous-flame lengths are primarily controlled by fuel flow rates with lengths in coflowing air approaching 2/3 of the lengths in still air as coflowing air velocities are increased. Finally, luminous flame lengths at laminar smoke-point conditions were roughly twice as long as flame-sheet lengths at comparable conditions because of the presence of luminous soot particles in the fuel-lean region of the flames.

  16. Buoyancy induced extinction of laminar gas jet diffusion flames

    NASA Technical Reports Server (NTRS)

    Altenkirch, R. A.; Eichhorn, R.; Brancic, A. B.

    1977-01-01

    The behavior of laminar gas jet diffusion flames subjected to elevated gravity in order to investigate the role of buoyancy in such flames has been studied experimentally. Higher than earth normal gravity was achieved using a 1.83 m diameter centrifuge. Methane, ethane, propane and hydrogen air flames were stabilized at the exit of small tubular burners ranging in size from .05 to .21 cm in diameter. The experimental arrangement was such that the flames were burnt vertically upward. Following a shortening of the flame and a decrease in luminosity with increasing gravity level, further increases in gravity caused the hydrocarbon flames to separate from the rim and eventually extinguish. The extinction gravity levels appear to correlate with the parameter g alpha (u)/S to the 3rd (u), which should be a constant for buoyancy controlled extinction. This parameter is developed by a rudimentary analysis of the heat loss from the premixed stabilizing flame in the lifted flame base. When the loss is excessive, the flame is extinguished.

  17. A theoretical study of a laminar diffusion flame

    NASA Technical Reports Server (NTRS)

    Frair, K. L.

    1978-01-01

    Theoretical models of an axisymmetric laminar diffusion flame are discussed, with an emphasis on the behavior of such flames at increasing pressures. The flame-sheet or Burke-Schumann model (in terms of Bessel functions) and various boundary layer numerical solutions are presented and their results compared with experimental data. The most promising theoretical model combines the numerical flow field solution of the Patankar-Spalding computer code with the Pratt-Wormeck chemical reaction subroutine. The flame shapes for pressures of 1, 5, 10, 20, and 50 atmospheres were computed and agree remarkably well with experimental data. There is a noticeable shape change with pressure, believed to be a result of buoyancy effects. The chemical concentration profiles do not exhibit much dependence on pressure, a reflection of the fact that only one chemical mechanism was utilized at all pressures.

  18. Structure of confined laminar spray diffusion flames: Numerical investigation

    NASA Technical Reports Server (NTRS)

    Mawid, M. A.; Bulzan, D. L.; Aggarwal, S. K.

    1993-01-01

    The structure of confined laminar spray diffusion flames is investigated numerically by solving the gas-phase conservation equations for mass species, continuity, momentum, and energy and the liquid-phase equations for droplet position, velocity, size, and temperature. A one-step global reaction scheme along with six equilibrium reactions are employed to model the flame chemistry. Monodisperse as well as polydisperse sprays are considered. The numerical results demonstrate that liquid spray flames substantially differ from gaseous flames in their structure, i.e., temperature, concentration, and velocity fields, shape, and dimensions under the same conditions. Spray flames are predicted to be taller and narrower than their counterpart gaseous ones and their shapes are almost cylindrical. This is in agreement with experimental observations. The numerical computations also show that the use of the equilibrium reactions with the one-step reaction scheme decreases the flame temperature compared to the one-step reaction scheme without the equilibrium reactions and more importantly increases the surface area of the flame zone due to a phenomenon termed 'equilibrium broadening.' The spray flames also possess a finite thickness with minimal overlap of the fuel and oxygen species. A case for which a fuel-mixture consisting of 20 to 80 percent gas-liquid by mass is introduced into the combustor is also investigated and compared with predictions using only gaseous or liquid fuel.

  19. Suppression of Soot Formation and Shapes of Laminar Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Xu, F.; Dai, Z.; Faeth, G. M.

    2001-01-01

    Laminar nonpremixed (diffusion) flames are of interest because they provide model flame systems that are far more tractable for analysis and experiments than practical turbulent flames. In addition, many properties of laminar diffusion flames are directly relevant to turbulent diffusion flames using laminar flamelet concepts. Finally, laminar diffusion flame shapes have been of interest since the classical study of Burke and Schumann because they involve a simple nonintrusive measurement that is convenient for evaluating flame shape predictions. Motivated by these observations, the shapes of round hydrocarbon-fueled laminar jet diffusion flames were considered, emphasizing conditions where effects of buoyancy are small because most practical flames are not buoyant. Earlier studies of shapes of hydrocarbon-fueled nonbuoyant laminar jet diffusion flames considered combustion in still air and have shown that flames at the laminar smoke point are roughly twice as long as corresponding soot-free (blue) flames and have developed simple ways to estimate their shapes. Corresponding studies of hydrocarbon-fueled weakly-buoyant laminar jet diffusion flames in coflowing air have also been reported. These studies were limited to soot-containing flames at laminar smoke point conditions and also developed simple ways to estimate their shapes but the behavior of corresponding soot-free flames has not been addressed. This is unfortunate because ways of selecting flame flow properties to reduce soot concentrations are of great interest; in addition, soot-free flames are fundamentally important because they are much more computationally tractable than corresponding soot-containing flames. Thus, the objectives of the present investigation were to observe the shapes of weakly-buoyant laminar jet diffusion flames at both soot-free and smoke point conditions and to use the results to evaluate simplified flame shape models. The present discussion is brief.

  20. Structure and Soot Properties of Non-Buoyant Laminar Round-Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Mortazavi, Saeed; Sunderland, Peter B.; Jurng, Jongsoo; Faeth, Gerard M.

    1993-01-01

    The structure and soot properties of nonbuoyant laminar diffusion flames are being studied experimentally and theoretically in order to better understand the soot and thermal radiation emissions from luminous flames. The measurements involve weakly-buoyant flames at low pressure in normal gravity (ng) and nonbuoyant flames at normal pressures in microgravity (micro g). The objectives of the present investigation are to study the differences of soot properties between nonbuoyant and buoyant diffusion flames, and to evaluate predictions based on the laminar flamelet approach.

  1. CoFlame: A refined and validated numerical algorithm for modeling sooting laminar coflow diffusion flames

    NASA Astrophysics Data System (ADS)

    Eaves, Nick A.; Zhang, Qingan; Liu, Fengshan; Guo, Hongsheng; Dworkin, Seth B.; Thomson, Murray J.

    2016-10-01

    Mitigation of soot emissions from combustion devices is a global concern. For example, recent EURO 6 regulations for vehicles have placed stringent limits on soot emissions. In order to allow design engineers to achieve the goal of reduced soot emissions, they must have the tools to so. Due to the complex nature of soot formation, which includes growth and oxidation, detailed numerical models are required to gain fundamental insights into the mechanisms of soot formation. A detailed description of the CoFlame FORTRAN code which models sooting laminar coflow diffusion flames is given. The code solves axial and radial velocity, temperature, species conservation, and soot aggregate and primary particle number density equations. The sectional particle dynamics model includes nucleation, PAH condensation and HACA surface growth, surface oxidation, coagulation, fragmentation, particle diffusion, and thermophoresis. The code utilizes a distributed memory parallelization scheme with strip-domain decomposition. The public release of the CoFlame code, which has been refined in terms of coding structure, to the research community accompanies this paper. CoFlame is validated against experimental data for reattachment length in an axi-symmetric pipe with a sudden expansion, and ethylene-air and methane-air diffusion flames for multiple soot morphological parameters and gas-phase species. Finally, the parallel performance and computational costs of the code is investigated. Catalogue identifier: AFAU_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AFAU_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public License, version 3 No. of lines in distributed program, including test data, etc.: 94964 No. of bytes in distributed program, including test data, etc.: 6242986 Distribution format: tar.gz Programming language: Fortran 90, MPI. (Requires an Intel compiler). Computer: Workstations

  2. Shapes of Nonbuoyant Round Luminous Hydrocarbon/Air Laminar Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Lin, K.-C.; Faeth, G. M.; Sunderland, P. B.; Urban, D. L.; Yuan, Z.-G.

    1999-01-01

    The shapes (luminous flame boundaries) of round luminous nonbuoyant soot-containing hydrocarbon/air laminar jet diffusion flames at microgravity were found from color video images obtained on orbit in the Space Shuttle Columbia. Test conditions included ethylene- and propane-fueled flames burning in still air at an ambient temperature of 300 K, ambient pressures of 35-130 kPa, initial jet diameters of 1.6 and 2.7 mm, and jet exit Reynolds numbers of 45-170. Present test times were 100-200 s and yielded steady axisymmetric flames that were close to the laminar smoke point (including flames both emitting and not emitting soot) with luminous flame lengths of 15-63 mm. The present soot-containing flames had larger luminous flame lengths than earlier ground-based observations having similar burner configurations: 40% larger than the luminous flame lengths of soot-containing low gravity flames observed using an aircraft (KC-135) facility due to reduced effects of accelerative disturbances and unsteadiness; roughly twice as large as the luminous flame lengths of soot-containing normal gravity flames due to the absence of effects of buoyant mixing and roughly twice as large as the luminous flame lengths of soot-free low gravity flames observed using drop tower facilities due to the presence of soot luminosity and possible reduced effects of unsteadiness. Simplified expressions to estimate the luminous flame boundaries of round nonbuoyant laminar jet diffusion flames were obtained from the classical analysis of Spalding (1979); this approach provided Successful Correlations of flame shapes for both soot-free and soot-containing flames, except when the soot-containing flames were in the opened-tip configuration that is reached at fuel flow rates near and greater than the laminar smoke point fuel flow rate.

  3. Laser-saturated fluorescence measurements in laminar sooting diffusion flames

    NASA Technical Reports Server (NTRS)

    Wey, Changlie

    1993-01-01

    The hydroxyl radical is known to be one of the most important intermediate species in the combustion processes. The hydroxyl radical has also been considered a dominant oxidizer of soot particles in flames. In this investigation the hydroxyl concentration profiles in sooting diffusion flames were measured by the laser-saturated fluorescence (LSF) method. The temperature distributions in the flames were measured by the two-line LSF technique and by thermocouple. In the sooting region the OH fluorescence was too weak to make accurate temperature measurements. The hydroxyl fluorescence profiles for all four flames presented herein show that the OH fluorescence intensities peaked near the flame front. The OH fluorescence intensity dropped sharply toward the dark region of the flame and continued declining to the sooting region. The OH fluorescence profiles also indicate that the OH fluorescence decreased with increasing height in the flames for all flames investigated. Varying the oxidizer composition resulted in a corresponding variation in the maximum OH concentration and the flame temperature. Furthermore, it appears that the maximum OH concentration for each flame increased with increasing flame temperature.

  4. Experiments on Diffusion Flame Structure of a Laminar Vortex Ring

    NASA Technical Reports Server (NTRS)

    Chen, Shin-Juh; Dahm, Werner J. A.

    1999-01-01

    The study of flame-vortex interactions provides one of the means to better understand turbulent combustion, and allows for canonical configurations that contain the fundamental elements found in turbulent flames, These include concentrated vorticity, entrainment and mixing, strain and nonequilibrium phenomena, diffusion and differential diffusion, partial premixing and diluent effects, and heat release effects. In flame- vortex configurations, these fundamental elements can be studied under more controlled conditions than is possible in direct investigations of turbulent flames. Since the paper of Marble, the problem of the flame-vortex interaction has received considerable attention theoretically, numerically and experimentally. Several configurations exist for study of the premixed flame/vortex ring interaction but more limited results have been obtained to date for the diffusion flame/vortex ring case. The setup of Chen and Dahm, which is conceptually similar to that of Karagozian and Manda and Karagozian, Suganuma and Strom where the ring is composed of fuel and air and combustion begins during the ring formation process, is used in the current study. However, it is essential to conduct the experiments in microgravity to remove the asymmetries caused by buoyancy and thus obtain highly symmetric and repeatable interactions. In previous studies it was found that the flame structure of the vortex ring was similar to that obtained analytically by Karagozian and Manda. Dilution of propane with nitrogen led mainly to a reduction in flame luminosities, flame burnout times were affected by both fuel volumes and amount of dilution, and a simple model of the burnout times was developed. In this paper, a discussion on reacting ring displacement and flame burnout time will be given, and the flame structures of vortex rings containing ethane and air will be compared to those of propane reacting in air.

  5. Smoke-Point Properties of Non-Buoyant Round Laminar Jet Diffusion Flames. Appendix J

    NASA Technical Reports Server (NTRS)

    Urban, D. L.; Yuan, Z.-G.; Sunderland, P. B.; Lin, K.-C.; Dai, Z.; Faeth, G. M.

    2000-01-01

    The laminar smoke-point properties of non-buoyant round laminar jet diffusion flames were studied emphasizing results from long-duration (100-230 s) experiments at microgravity carried out in orbit aboard the space shuttle Columbia. Experimental conditions included ethylene- and propane-fueled flames burning in still air at an ambient temperature of 300 K, pressures of 35-130 kPa, jet exit diameters of 1.6 and 2.7 mm, jet exit velocities of 170-690 mm/s, jet exit Reynolds numbers of 46-172, characteristic flame residence times of 40-302 ms, and luminous flame lengths of 15-63 mm. Contrary to the normal-gravity laminar smoke point, in microgravity, the onset of laminar smoke-point conditions involved two flame configurations: closed-tip flames with soot emissions along the flame axis and open-tip flames with soot emissions from an annular ring about the flame axis. Open-tip flames were observed at large characteristic flame residence times with the onset of soot emissions associated with radiative quenching near the flame tip: nevertheless, unified correlations of laminar smoke-point properties were obtained that included both flame configurations. Flame lengths at laminar smoke-point conditions were well correlated in terms of a corrected fuel flow rate suggested by a simplified analysis of flame shape. The present steady and non-buoyant flames emitted soot more readily than non-buoyant flames in earlier tests using ground-based microgravity facilities and than buoyant flames at normal gravity, as a result of reduced effects of unsteadiness, flame disturbances, and buoyant motion. For example, present measurements of laminar smoke-point flame lengths at comparable conditions were up to 2.3 times shorter than ground-based microgravity measurements and up to 6.4 times shorter than buoyant flame measurements. Finally, present laminar smoke-point flame lengths were roughly inversely proportional to pressure to a degree that is a somewhat smaller than observed during

  6. Smoke-Point Properties of Nonbuoyant Round Laminar Jet Diffusion Flames. Appendix B

    NASA Technical Reports Server (NTRS)

    Urban, D. L.; Yuan, Z.-G.; Sunderland, P. B.; Lin, K.-C.; Dai, Z.; Faeth, G. M.; Ross, H. D. (Technical Monitor)

    2000-01-01

    The laminar smoke-point properties of non-buoyant round laminar jet diffusion flames were studied emphasizing results from long-duration (100-230 s) experiments at microgravity carried out in orbit aboard the space shuttle Columbia. Experimental conditions included ethylene- and propane-fueled flames burning in still air at an ambient temperature of 300 K, pressures of 35-130 kPa, jet exit diameters of 1.6 and 2.7 mm, jet exit velocities of 170-690 mm/s, jet exit Reynolds numbers of 46-172, characteristic flame residence times of 40-302 ms, and luminous flame lengths of 15-63 mm. Contrary to the normal-gravity laminar smoke point, in microgravity the onset of laminar smoke-point conditions involved two flame configurations: closed-tip flames with soot emissions along the flame axis and open-tip flames with soot emissions from an annular ring about the flame axis. Open-tip flames were observed at large characteristic flame residence times with the onset of soot emissions associated with radiative quenching near the flame tip: nevertheless, unified correlations of laminar smoke-point properties were obtained that included both flame configurations. Flame lengths at laminar smoke-point conditions were well correlated in terms of a corrected fuel flow rate suggested by a simplified analysis of flame shape. The present steady and nonbuoyant flames emitted soot more readily than non-buoyant flames in earlier tests using ground-based microgravity facilities and than buoyant flames at normal gravity, as a result of reduced effects of unsteadiness, flame disturbances, and buoyant motion. For example, present measurements of laminar smokepoint flame lengths at comparable conditions were up to 2.3 times shorter than ground-based microgravity measurements and up to 6.4 times shorter than buoyant flame measurements. Finally, present laminar smoke-point flame lengths were roughly inversely proportional to pressure to a degree that is a somewhat smaller than observed during

  7. Flow/Soot-Formation Interactions in Nonbuoyant Laminar Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Dai, Z.; Faeth, G. M.

    1999-01-01

    Nonpremixed (diffusion) flames are attractive for practical applications because they avoid the stability, autoignition, flashback, etc. problems of premixed flames. Unfortunately, soot formation in practical hydrocarbon-fueled diffusion flames reduces their attractiveness due to widely-recognized public health and combustor durability problems of soot emissions. For example, more deaths are attributed to the emission of soot (15,000-60,000 deaths annually in the U.S. alone) than any other combustion-generated pollutant. In addition, continuum radiation from soot-containing flames is the principle heat load to combustor components and is mainly responsible for engine durability problems of aircraft and gas turbine engines. As a result, there is considerable interest in controlling both soot concentrations within flames and soot emissions from flames. Thus, the objective of the present investigation is to study ways to control soot formation in diffusion flames by manipulating the mixing process between the fuel and oxidant streams. In order to prevent the intrusion of gravity from masking flow properties that reduce soot formation in practical flames (where effects of gravity are small), methods developed during past work will be exploited to minimize effects of buoyant motion.

  8. Hydrodynamic Suppression of Soot Formation in Laminar Coflowing Jet Diffusion Flames. Appendix C

    NASA Technical Reports Server (NTRS)

    Dai, Z.; Faeth, G. M.; Yuan, Z.-G. (Technical Monitor); Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2000-01-01

    Effects of flow (hydrodynamic) properties on limiting conditions for soot-free laminar non-premixed hydrocarbon/air flames (called laminar soot-point conditions) were studied, emphasizing non-buoyant laminar coflowing jet diffusion flames. Effects of air/fuel-stream velocity ratios were of particular interest; therefore, the experiments were carried out at reduced pressures to minimize effects of flow acceleration due to the intrusion of buoyancy. Test conditions included reactant temperatures of 300 K; ambient pressures of 3.7-49 8 kPa; methane-, acetylene-, ethylene-, propane-, and methane-fueled flames burning in coflowing air with fuel-port diameters of 1.7, 3.2, and 6.4 mm, fuel jet Reynolds numbers of 18-121; air coflow velocities of 0-6 m/s; and air/fuel-stream velocity ratios of 0.003-70. Measurements included laminar soot-point flame lengths, laminar soot-point fuel flow rates, and laminar liftoff conditions. The measurements show that laminar soot-point flame lengths and fuel flow rates can be increased, broadening the range of fuel flow rates where the flames remain soot free, by increasing air/fuel-stream velocity ratios. The mechanism of this effect involves the magnitude and direction of flow velocities relative to the flame sheet where increased air/fuel-stream velocity ratios cause progressive reduction of flame residence times in the fuel-rich soot-formation region. The range of soot-free conditions is limited by both liftoff, particularly at low pressures, and the intrusion of effects of buoyancy on effective air/fuel-stream velocity ratios, particularly at high pressures. Effective correlations of laminar soot- and smoke-point flame lengths were also found in terms of a corrected fuel flow rate parameter, based on simplified analysis of laminar jet diffusion flame structure. The results show that laminar smoke-point flame lengths in coflowing air environments are roughly twice as long as soot-free (blue) flames under comparable conditions due to

  9. Soot Formation in Laminar Acetylene/Air Diffusion Flames at Atmospheric Pressure. Appendix J

    NASA Technical Reports Server (NTRS)

    Xu, F.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2001-01-01

    The flame structure and soot-formation (soot nucleation and growth) properties of axisymmetric laminar coflowing jet diffusion flames were studied experimentally. Test conditions involved acetylene-nitrogen jets burning in coflowing air at atmospheric pressure. Measurements were limited to the axes of the flames and included soot concentrations, soot temperatures, soot structure, major gas species concentrations, radical species (H, OH, and O) concentrations, and gas velocities. The results show that as distance increases along the axes of the flames, detectable soot formation begins when significant H concentrations are present, and ends when acetylene concentrations become small. Species potentially associated with soot oxidation--O2, CO2, H2O, O, and OH-are present throughout the soot-formation region so that soot formation and oxidation proceed at the same time. Strong rates of soot growth compared to soot nucleation early in the soot-formation process, combined with increased rates of soot nucleation and oxidation as soot formation proceeds, causes primary soot particle diameters to reach a maximum relatively early in the soot-formation process. Aggregation of primary soot particles proceeds, however, until the final stages of soot oxidation. Present measurements of soot growth (corrected for soot oxidation) in laminar diffusion flames were consistent with earlier measurements of soot growth in laminar premixed flames and exhibited encouraging agreement with existing hydrogen-abstraction/carbon-addition (HACA) soot growth mechanisms in the literature that were developed based on measurements within laminar premixed flames. Measured primary soot particle nucleation rates in the present laminar diffusion flames also were consistent with corresponding rates measured in laminar premixed flames and yielded a crude correlation in terms of acetylene and H concentrations and the temperature.

  10. Soot Formation in Laminar Acetylene/Air Diffusion Flames at Atmospheric Pressure. Appendix C

    NASA Technical Reports Server (NTRS)

    Xu, F.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2000-01-01

    The flame structure and soot-formation (soot nucleation and growth) properties of axisymmetric laminar coflowing jet diffusion flames were studied experimentally. Test conditions involved acetylene-nitrogen jets burning in coflowing air at atmospheric pressure. Measurements were limited to the axes of the flames and included soot concentrations, soot temperatures, soot structure, major gas species concentrations, radical species (H, OH, and O) concentrations, and gas velocities. The results show that as distance increases along the axes of the flames, detectable soot formation begins when significant H concentrations are present, and ends when acetylene concentrations become small. Species potentially associated with soot oxidation-O2, CO2, H2O, O, and OH-are present throughout the soot-formation region so that soot formation and oxidation proceed at the same time. Strong rates of soot growth compared to soot nucleation early in the soot-formation process, combined with increased rates of soot nucleation and oxidation as soot formation proceeds, causes primary soot particle diameters to reach a maximum relatively early in the soot-formation process. Aggregation of primary soot particles proceeds, however, until the final stages of soot oxidation. Present measurements of soot growth (corrected for soot oxidation) in laminar diffusion flames were consistent with earlier measurements of soot growth in laminar premixed flames and exhibited encouraging agreement with existing hydrogen-abstraction/carbon-addition (HACA) soot growth mechanisms in the literature that were developed based on measurements within laminar premixed flames. Measured primary soot particle nucleation rates in the present laminar diffusion flames also were consistent with corresponding rates measured in laminar premixed flames and yielded a crude correlation in terms of acetylene and H concentrations and the temperature.

  11. Soot Formation in Laminar Acetylene/Air Diffusion Flames at Atmospheric Pressure. Appendix H

    NASA Technical Reports Server (NTRS)

    Xu, F.; Faeth, G. M.; Yuan, Z.-G. (Technical Monitor); Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2001-01-01

    The flame structure and soot-formation (soot nucleation and growth) properties of axisymmetric laminar coflowing jet diffusion flames were studied experimentally. Test conditions involved acetylene-nitrogen jets burning in coflowing air at atmospheric pressure. Measurements were limited to the axes of the flames and included soot concentrations, soot temperatures, soot structure, major gas species concentrations, radical species (H, OH, and O) concentrations, and gas velocities. The results show that as distance increases along the axes of the flames, detectable soot formation begins when significant H concentrations are present, and ends when acetylene concentrations become small. Species potentially associated with soot oxidation-O2, CO2, H2O, O, and OH-are present throughout the soot-formation region so that soot formation and oxidation proceed at the same time. Strong rates of soot growth compared to soot nucleation early in the soot-formation process, combined with increased rates of soot nucleation and oxidation as soot formation proceeds, causes primary soot particle diameters to reach a maximum relatively early in the soot-formation process. Aggregation of primary soot particles proceeds, however, until the final stages of soot oxidation. Present measurements of soot growth (corrected for soot oxidation) in laminar diffusion flames were consistent with earlier measurements of soot growth in laminar premixed flames and exhibited encouraging agreement with existing hydrogen-abstraction/carbon-addition (HACA) soot growth mechanisms in the literature that were developed based on measurements within laminar premixed flames. Measured primary soot particle nucleation rates in the present laminar diffusion flames also were consistent with corresponding rates measured in laminar premixed flames and yielded a crude correlation in terms of acetylene and H concentrations and the temperature.

  12. Effects of Buoyancy on Laminar, Transitional, and Turbulent Gas Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Bahadori, M. Yousef; Stocker, Dennis P.; Vaughan, David F.; Zhou, Liming; Edelman, Raymond B.

    1993-01-01

    Gas jet diffusion flames have been a subject of research for many years. However, a better understanding of the physical and chemical phenomena occurring in these flames is still needed, and, while the effects of gravity on the burning process have been observed, the basic mechanisms responsible for these changes have yet to be determined. The fundamental mechanisms that control the combustion process are in general coupled and quite complicated. These include mixing, radiation, kinetics, soot formation and disposition, inertia, diffusion, and viscous effects. In order to understand the mechanisms controlling a fire, laboratory-scale laminar and turbulent gas-jet diffusion flames have been extensively studied, which have provided important information in relation to the physico-chemical processes occurring in flames. However, turbulent flames are not fully understood and their understanding requires more fundamental studies of laminar diffusion flames in which the interplay of transport phenomena and chemical kinetics is more tractable. But even this basic, relatively simple flame is not completely characterized in relation to soot formation, radiation, diffusion, and kinetics. Therefore, gaining an understanding of laminar flames is essential to the understanding of turbulent flames, and particularly fires, in which the same basic phenomena occur. In order to improve and verify the theoretical models essential to the interpretation of data, the complexity and degree of coupling of the controlling mechanisms must be reduced. If gravity is isolated, the complication of buoyancy-induced convection would be removed from the problem. In addition, buoyant convection in normal gravity masks the effects of other controlling parameters on the flame. Therefore, the combination of normal-gravity and microgravity data would provide the information, both theoretical and experimental, to improve our understanding of diffusion flames in general, and the effects of gravity on the

  13. Gaseous Species Measurements of Alternative Jet Fuels in Sooting Laminar Coflow Diffusion Flames

    NASA Astrophysics Data System (ADS)

    Zabeti, Parham

    The gaseous species concentration of Jet A-1, GTL, CTL and a blend of 80 vol.% GTL and 20 vol.% hexanol jet fuels in laminar coflow diffusion flames have been measured and studied. These species are carbon monoxide, carbon dioxide, oxygen, methane, ethane, ethylene, propylene, and acetylene. Benzene and propyne concentrations were also detected in CTL flames. 1-Butene has been quantified for the blend of GTL and hexanol flame. The detailed experimental setup has been described and results from different flames are compared. The CO is produced in a same amount in all the flames. The CTL flame had the largest and GTL/hexanol flame had lowest CO2 concentrations. The results indicate that GTL and GTL hexanol blend flames produce similar concentrations for all the measured hydrocarbon species and have the highest concentration among all the jet fuels. The experimental results from Jet A-1 fuel are also compared with numerical studies by Saffaripour et al .

  14. Soret transport, unequal diffusivity, and dilution effects on laminar diffusion flame temperatures and positions

    SciTech Connect

    Arias-Zugasti, Manuel; Rosner, Daniel E.

    2008-04-15

    Since, according to ideal gas kinetic theory, Ludwig-Soret species transport (temperature-gradient-driven mass transport) must be simultaneously included along with nonunity Lewis numbers [D.E. Rosner, R.S. Israel, B. La Mantia, Combust. Flame 123 (2000) 547-560], we formally consider here the influence of both effects on laminar, counterflow gaseous diffusion flames in the thin flame limit. Our deliberately idealized theoretical analysis includes cases of steady/unsteady, strained/unstrained flames and formally permits the prediction of trends for the combustion of either light or heavy fuel vapors in O{sub 2}-containing streams. Our results suggest that, in cases of low- or high-molecular-weight gaseous fuels, Ludwig-Soret transport can itself introduce significant shifts in flame position and flame temperature, compared to results of the same mathematical model neglecting Soret fuel-vapor transport but including only nonunity fuel Lewis numbers. These systematic shifts (which in specific cases may have to be supplemented by additional corrections due to variable thermophysical properties) are expected to have important consequences for NO{sub x} production and/or infrared radiation emission. (author)

  15. Shapes of Nonbuoyant Round Luminous Laminar-Jet Diffusion Flames in Coflowing Air. Appendix F

    NASA Technical Reports Server (NTRS)

    Lin, K.-C.; Faeth, G. M.; Urban, David L. (Technical Monitor)

    2000-01-01

    The shapes (luminous flame boundaries) of steady nonbuoyant round luminous hydrocarbon-fueled laminar-jet diffusion flames in coflowing air were studied both experimentally and theoretically. Flame shapes were measured from photographs of flames burning at low pressures in order to minimize the effects of buoyancy. Test conditions involved acetylene-, propylene. and 1,3-butadiene-fueled flames having initial reactant temperatures of 300 K, ambient pressures of 19-50 kPa, jet-exit Reynolds numbers of 18-121, and initial air/fuel velocity ratios of 0.22-32.45 to yield luminous flame lengths of 21-198 mm. The present flames were close to the laminar smoke point but were not soot emitting. Simple expressions to estimate the shapes of nonbuoyant laminar-jet diffusion flames in coflow were found by extending an earlier analysis of Mahalingam et al. These formulas provided a good correlation of present measurements except near the burner exit where self-similar approximations used in the simplified analysis are no longer appropriate.

  16. On the structure of gaseous confined laminar diffusion flames: Numerical investigation

    NASA Technical Reports Server (NTRS)

    Mawid, M. A.; Bulzan, D. L.; Aggarwal, S. K.

    1993-01-01

    The structure and characteristics of gaseous confined laminar diffusion flames are investigated by numerically solving the time-dependent two-dimensional axisymmetric conservation equations. The numerical model accounts for the important chemical and physical processes involved, including axial diffusion, viscous effects, radial convection, and finite-rate chemistry. The numerical results clearly show that the flame has a finite thickness and leakage of fuel vapor into the flame zone is possible. The effect of heat release is found to induce some radial flow. Predicted flame shape and dimensions are compared to the classical Burke-Schumann flame. The numerically calculated flame is observed to be about 15 percent taller and 5 percent narrower than that of the Burke-Schumann solution under the same conditions.

  17. Soot Surface Growth in Laminar Hydrocarbon/Air Diffusion Flames. Appendix J

    NASA Technical Reports Server (NTRS)

    El-Leathy, A. M.; Xu, F.; Kim, C. H.; Faeth, G. M.; Yuan, Z.-G. (Technical Monitor); Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2003-01-01

    The structure and soot surface growth properties of round laminar jet diffusion flames were studied experimentally. Measurements were made along the axes of ethylene-, propylene-propane- and acetylene-benzene-fueled flames burning in coflowing air at atmospheric pressure with the reactants at normal temperature. The measurements included soot structure, soot concentrations, soot temperatures, major gas species concentrations, some radial species (H, OH and 0) concentrations, and gas velocities. These measurements yielded the local flame properties that are thought to affect soot surface growth as well as local soot surface growth rates. When present results were combined with similar earlier observations of acetylene-fueled laminar jet diffusion flames, the results suggested that soot surface growth involved decomposition of the original fuel to form acetylene and H, which were the main reactants for soot surface growth, and that the main effect of the parent fuel on soot surface growth involved its yield of acetylene and H for present test conditions. Thus, as the distance increased along the axes of the flames, soot formation (which was dominated by soot surface growth) began near the cool core of the flow once acetylene and H appeared together and ended near the flame sheet when acetylene disappeared. Species mainly responsible for soot oxidation - OH and 02 were present throughout the soot formation region so that soot surface growth and oxidation proceeded at the same time. Present measurements of soot surface growth rates (corrected for soot surface oxidation) in laminar jet diffusion flames were consistent with earlier measurements of soot surface growth rates in laminar premixed flames and exhibited good agreement with existing Hydrogen-Abstraction/Carbon-Addition (HACA) soot surface growth mechanisms in the literature with steric factors in these mechanisms having values on the order of unity, as anticipated.

  18. Soot Surface Growth in Laminar Hydrocarbon/Air Diffusion Flames. Appendix B

    NASA Technical Reports Server (NTRS)

    El-Leathy, A. M.; Xu, F.; Kim, C. H.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2001-01-01

    The structure and soot surface growth properties of round laminar jet diffusion flames were studied experimentally. Measurements were made along the axes of ethylene-, propylene-propane- and acetylene-benzene-fueled flames burning in coflowing air at atmospheric pressure with the reactants at normal temperature. The measurements included soot structure, soot concentrations, soot temperatures, major gas species concentrations, some radial species (H, OH and O) concentrations, and gas velocities. These measurements yielded the local flame properties that are thought to affect soot surface growth as well as local soot surface growth rates. When present results were combined with similar earlier observations of acetylene-fueled laminar jet diffusion flames, the results suggested that soot surface growth involved decomposition of the original fuel to form acetylene and H, which were the main reactants for soot surface growth, and that the main effect of the parent fuel on soot surface growth involved its yield of acetylene and H for present test conditions. Thus, as the distance increased along the axes of the flames, soot formation (which was dominated by soot surface growth) began near the cool core of the flow once acetylene and H appeared together and ended near the flame sheet when acetylene disappeared. Species mainly responsible for soot oxidation - OH and O2 were present throughout the soot formation region so that soot surface growth and oxidation proceeded at the same time. Present measurements of soot surface growth rates (corrected for soot surface oxidation) in laminar jet diffusion flames were consistent with earlier measurements of soot surface growth rates in laminar premixed flames and exhibited good agreement with existing Hydrogen-Abstraction/Carbon-Addition (HACA) soot surface growth mechanisms in the literature with steric factors in these mechanisms having values on the order of unity, as anticipated.

  19. Multigrid methods for numerical simulation of laminar diffusion flames

    NASA Technical Reports Server (NTRS)

    Liu, C.; Liu, Z.; Mccormick, S.

    1993-01-01

    This paper documents the result of a computational study of multigrid methods for numerical simulation of 2D diffusion flames. The focus is on a simplified combustion model, which is assumed to be a single step, infinitely fast and irreversible chemical reaction with five species (C3H8, O2, N2, CO2 and H2O). A fully-implicit second-order hybrid scheme is developed on a staggered grid, which is stretched in the streamwise coordinate direction. A full approximation multigrid scheme (FAS) based on line distributive relaxation is developed as a fast solver for the algebraic equations arising at each time step. Convergence of the process for the simplified model problem is more than two-orders of magnitude faster than other iterative methods, and the computational results show good grid convergence, with second-order accuracy, as well as qualitatively agreement with the results of other researchers.

  20. Numerical simulation of the laminar diffusion flame in a simplified burner

    SciTech Connect

    Cloutman, L.D.

    1995-11-08

    The laminar ethylene-air diffusion fame in a simple laboratory burner was simulated with the COYOTE reactive flow program. This program predicts the flow field, transport, and chemistry for the purposes of code validation and providing physical understanding of the processes occurring in the flame. We show the results of numerical experiments to test the importance of several physical effects, including gravity, radiation, and differential diffusion. The computational results compare favorably with the experimental measurements.

  1. Effects of Fuel Preheat on Soot Formation in Microgravity Laminar Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Konsur, Bogdan; Megaridis, Constantine M.; Griffin, DeVon W.

    1997-01-01

    Nonbuoyant flames offer themselves as an attractive and promising platform to gain a better understanding of soot mechanisms. The effects of buoyancy can be eliminated temporarily in drop towers which sustain brief intervals of reduced gravity-typically lower than 10(exp -3)g- extending up to several seconds at a time. Microgravity facilities have been employed to show that nonbuoyant flames are longer, wider and sootier than their normal-gravity counterparts. Sunderland et al. recently verified the existence of smoke point in laminar nonbuoyant flames. As reported, microgravity flames operating above their smoke point displayed a blunt tip and much broader soot-containing regimes in comparison to their buoyant counterparts. Mortazavi et al. established that residence times in microgravity laminar jet diffusion flames with Re=0(100) tend to be proportional to burner diameter and inversely proportional to burner exit velocity. This offers the capability to alter residence times in nonbuoyant laminar jet diffusion flames when varying the burner exit diameters and velocities. Megaridis et al. presented a quantitative definition of the soot-field structure within laminar microgravity jet diffusion flames which operated well above their smoke point. The experimental methodology involved a full-field laser-light extinction technique and jet diffusion flames of nitrogen-diluted (50% vol.) acetylene fuel burning in quiescent air at atmospheric pressure. The work was conducted at the 2.2s drop tower of the NASA Lewis Research Center (NASA-LeRC). Parallel work on 1-g flames was also presented in (6) to facilitate comparisons on the effect of gravity on the soot fields. As reported, the soot spatial distributions in 0-g flames did not change in a detectable manner after 1s within a typical 2.2s experiment. During that period, the soot field was shown to sustain a pronounced annular structure throughout the luminous nonbuoyant-flame zone. The maximum soot volume fraction

  2. Numerical simulation of the laminar diffusion flame in a simplified burner. Revision 1

    SciTech Connect

    Cloutman, L.D.

    1996-02-01

    The laminar ethylene-air diffusion flame in a simple laboratory burner was simulated with the COYOTE reactive flow program. This program predicts the flow field, transport, and chemistry for the purposes of code validation and providing physical understanding of the processes occurring in the flame. The authors show the results of numerical experiments to test the importance of several physical phenomena, including gravity, radiation, and differential diffusion. The computational results compare favorably with the experimental measurements, and all three phenomena are important to accurate simulations.

  3. A Numerical and Experimental Study of Coflow Laminar Diffusion Flames: Effects of Gravity and Inlet Velocity

    NASA Technical Reports Server (NTRS)

    Cao, S.; Bennett, B. A. V.; Ma, B.; Giassi, D.; Stocker, D. P.; Takahashi, F.; Long, M. B.; Smooke, M. D.

    2015-01-01

    In this work, the influence of gravity, fuel dilution, and inlet velocity on the structure, stabilization, and sooting behavior of laminar coflow methane-air diffusion flames was investigated both computationally and experimentally. A series of flames measured in the Structure and Liftoff in Combustion Experiment (SLICE) was assessed numerically under microgravity and normal gravity conditions with the fuel stream CH4 mole fraction ranging from 0.4 to 1.0. Computationally, the MC-Smooth vorticity-velocity formulation of the governing equations was employed to describe the reactive gaseous mixture; the soot evolution process was considered as a classical aerosol dynamics problem and was represented by the sectional aerosol equations. Since each flame is axisymmetric, a two-dimensional computational domain was employed, where the grid on the axisymmetric domain was a nonuniform tensor product mesh. The governing equations and boundary conditions were discretized on the mesh by a nine-point finite difference stencil, with the convective terms approximated by a monotonic upwind scheme and all other derivatives approximated by centered differences. The resulting set of fully coupled, strongly nonlinear equations was solved simultaneously using a damped, modified Newton's method and a nested Bi-CGSTAB linear algebra solver. Experimentally, the flame shape, size, lift-off height, and soot temperature were determined by flame emission images recorded by a digital camera, and the soot volume fraction was quantified through an absolute light calibration using a thermocouple. For a broad spectrum of flames in microgravity and normal gravity, the computed and measured flame quantities (e.g., temperature profile, flame shape, lift-off height, and soot volume fraction) were first compared to assess the accuracy of the numerical model. After its validity was established, the influence of gravity, fuel dilution, and inlet velocity on the structure, stabilization, and sooting

  4. Models And Experiments Of Laminar Diffusion Flames In Non-Uniform Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Baker, J.; Varagani, R.; Saito, K.

    2003-01-01

    Non-uniform magnetic fields affect laminar diffusion flames as a result of the paramagnetic and diamagnetic properties of the products and reactants. Paramagnetism is the weak attraction to a magnetic field a material exhibits as a result of permanent magnetic dipole moments in the atoms of the material. Diamagnetism is the weak repulsion to a magnetic field exhibited by a material due to the lack of permanent magnetic dipole moments in the atoms of a material. The forces associated with paramagnetic and diamagnetism are several orders of magnitude less than the forces associated with the more familiar ferromagnetism. A typical example of a paramagnetic gas is oxygen while hydrocarbon fuels and products of combustion are almost always diamagnetic. The fact that magnets can affect flame behavior has been recognized for more than one hundred years. Early speculation was that such behavior was due to the magnetic interaction with the ionized gases associated with a flame. Using a scaling analysis, it was later shown that for laminar diffusion flames the magnetic field/ionized gas interaction was insignificant to the paramagnetic and diamagnetic influences. In this effort, the focus has been on examining laminar diffusion slot flames in the presence of non-uniform upward decreasing magnetic fields produced using permanent magnets. The principal reason for choosing slot flames was mathematical models of such flames show an explicit dependence on gravitational body forces, in the buoyancy-controlled regime, and an applied magnetic field would also impose a body force. In addition, the behavior of such flames was more easily visualized while maintaining the symmetry of the two-dimensional problem whereas it would have been impossible to obtain a symmetric magnetic field around a circular flame and still visually record the flame height and shape along the burner axis. The motivation for choosing permanent magnets to produce the magnetic fields was the assumption that

  5. Numerical Simulation of an Enclosed Laminar Jet Diffusion Flame in Microgravity Environment: Comparison with ELF Data

    NASA Technical Reports Server (NTRS)

    Jia, Kezhong; Venuturumilli, Rajasekhar; Ryan, Brandon J.; Chen, Lea-Der

    2001-01-01

    been some research on the stability of laminar flames, but most studies have focused on turbulent flames. It is also well known that the airflow around the fuel jet can significantly alter the lift off, reattachment and blow out of the jet diffusion flame. Buoyant convection is sufficiently strong in 1-g flames that it can dominate the flow-field, even at the burner rim. In normal-gravity testing, it is very difficult to delineate the effects of the forced airflow from those of the buoyancy-induced flow. Comparison of normal-gravity and microgravity flames provides clear indication of the influence of forced and buoyant flows on the flame stability. The overall goal of the Enclosed Laminar Flames (ELF) investigation (STS-87/USMP-4 Space Shuttle mission, November to December 1997) is to improve our understanding of the effects of buoyant convection on the structure and stability of co-flow diffusion flame, e.g., see http://zeta.lerc.nasa.gov/expr/elf.htm. The ELF hardware meets the experiment hardware limit of the 35-liter interior volume of the glovebox working area, and the 180x220-mm dimensions of the main door. The ELF experiment module is a miniature, fan-driven wind tunnel, equipped with a gas supply system. A 1.5-mm diameter nozzle is located on the duct's flow axis. The cross section of the duct is nominally a 76-mm square with rounded corners. The forced air velocity can be varied from about 0.2 to 0.9 m/s. The fuel flow can be set as high as 3 std. cubic centimeter (cc) per second, which corresponds to a nozzle exit velocity of up to 1.70 m/s. The ELF hardware and experimental procedure are discussed in detail in Brooker et al. The 1-g test results are repeated in several experiments following the STS-87 Mission. The ELF study is also relevant to practical systems because the momentum-dominated behavior of turbulent flames can be achieved in laminar flames in microgravity. The specific objectives of this paper are to evaluate the use reduced model for

  6. Aerodynamics of Laminar Flames

    NASA Astrophysics Data System (ADS)

    Law, Chung K.

    2000-11-01

    The presentation will review recent advances in the understanding of the structure, dynamics, and geometry of stretched, nonequidiffusive, laminar premixed flames, as exemplified by the unsteady propagation of wrinkled flames in nonuniform flow fields. It is first shown that by considering the effects of aerodynamic stretch on the flame structure, and by allowing for mixture nonequidiffusion, the flame responses, especially the flame propagation speed, can be quantitatively as well as qualitatively modified from the idealized planar limit. Subsequently, by treating the flame as a level surface propagating with the stretch-affected flame speed, problems of increasing complexity are presented to illustrate various features of flame propagation. The illustration first treats the flame as a structureless surface propagating into a constant-density combustible with a constant velocity * the laminar flame speed, and demonstrates the phenomena of cusp formation and volumetric burning rate augmentation through flame wrinkling. By using the stretch-affected flame speed, we then describe the phenomena of cusp broadening as well as tip opening of the Bunsen flame. Finally, by allowing for the density jump across the flame surface, a unified dispersion relation is derived for the intrinsic hydrodynamic, body-force, and nonequidiffusive modes of flame

  7. Soot Oxidation in Laminar Hydrocarbon/Air Diffusion Flames at Atmospheric Pressure. Appendix D

    NASA Technical Reports Server (NTRS)

    Xu, F.; El-Leathy, A. M.; Faeth, G. M.

    2000-01-01

    Soot oxidation was studied experimentally in laminar hydrocarbon/air diffusion flames at atmospheric pressure. Measurements were carried out along the axes of round jets burning in coflowing air considering acetylene, ethylene, proplyene and propane as fuels. Measurements were limited to the initial stages of soot oxidation (carbon consumption less than 70%) where soot oxidation mainly occurs at the surface of primary soot particles. The following properties were measured as a function of distance above the burner exit: soot concentrations by deconvoluted laser extinction, soot temperatures by deconvoluted multiline emission, soot structure by thermophoretic sampling and analysis using Transmission Electron Microscopy (TEM), concentrations of stable major gas species (N2, H2O, H2, 02, CO, CO2, CH4, C2H2, C2H4, C2H6, C3H6, and C3H8) by sampling and gas chromatography, concentrations of some radical species (H, OH, O) by the deconvoluted Li/LiOH atomic absorption technique and flow velocities by laser velocimetry. It was found that soot surface oxidation rates are not particularly affected by fuel type for laminar diffusion flames and are described reasonably well by the OH surface oxidation mechanism with a collision efficiency of 0.10, (standard deviation of 0.07) with no significant effect of fuel type in this behavior; these findings are in good agreement with the classical laminar premixed flame measurements of Neoh et al. Finally, direct rates of surface oxidation by O2 were small compared to OH oxidation for present conditions, based on estimated O2 oxidation rates due to Nagle and Strickland-Constable, because soot oxidation was completed near the flame sheet where O2 concentrations were less than 1.2% by volume.

  8. Optical determination of incipient soot particle concentrations in ethene laminar diffusion flames.

    SciTech Connect

    Gupta, S. B.; Santoro, R. J.

    1999-07-06

    Recent studies in premixed flames have shown the existence of ''transparent particles.'' These particles, 2 nm in size and in high number densities are considered to be a phase transitional between the gas phase PAH species and particulate soot. In the present study, various optical diagnostics were evaluated for measuring the concentration of these particles in situ, Through such evaluations, a technique using extinction at two wavelengths was found to be ideal. While employing such a technique, the volume fractions of these particles in an ethene laminar diffusion flame were measured. Low in the flame, these particles were found to be concentrated in the fuel rich core, while at higher locations, they could be found with appreciable volume fractions even in the soot laden regions. Having given due consideration for the errors due to uncertainties in the optical constants, we report the existence of these particles in an ethene flame with volume fractions comparable to those of soot. Also, similar measurements performed in a low sooting ethene/methanol flame show the concentration of these particles to be of the same order of magnitude as in a pure ethene flame.

  9. Structure and Soot Properties of Nonbuoyant Ethylene/Air Laminar Jet Diffusion Flames. Appendix I

    NASA Technical Reports Server (NTRS)

    Urban, D. L.; Yuan, Z.-G.; Sunderland, P. B.; Linteris, G. T.; Voss, J. E.; Lin, K.-C.; Dai, Z.; Sun, K.; Faeth, G. M.; Ross, Howard D. (Technical Monitor)

    2000-01-01

    The structure and soot properties of round, soot-emitting, nonbuoyant, laminar jet diffusion flames are described, based on long-duration (175-230/s) experiments at microgravity carried out on orbit In the Space Shuttle Columbia. Experiments] conditions included ethylene-fueled flames burning in still air at nominal pressures of 50 and 100 kPa and an ambient temperature of 300 K with luminous Annie lengths of 49-64 mm. Measurements included luminous flame shapes using color video imaging, soot concentration (volume fraction) distributions using deconvoluted laser extinction imaging, soot temperature distributions using deconvoluted multiline emission imaging, gas temperature distributions at fuel-lean (plume) conditions using thermocouple probes, not structure distributions using thermophoretic sampling and analysis by transmission electron microscopy, and flame radiation using a radiometer. The present flames were larger, and emitted soot men readily, than comparable observed during ground-based microgravity experiments due to closer approach to steady conditions resulting from the longer test times and the reduced gravitational disturbances of the space-based experiments.

  10. Effects of pressure on the mechanisms of soot formation and oxidation in laminar diffusion flames

    NASA Astrophysics Data System (ADS)

    Kim, Chul Han

    Soot processes within flames fueled with hydrocarbons are important because they affect the durability and performance of propulsion systems, the danger associated with unwanted fires, the pollutant and particulate emissions of combustion processes, local and global environments and the potential for developing computational combustion. The objective of the current work was to improve understanding of the processes controlling soot formation in combustion systems over a broad range of pressure conditions. The flame and soot structure, including primary soot particle nucleation, soot particle surface growth and oxidation properties, of round laminar diffusion flames were studied experimentally at pressures of 0.1-8.0 atm. Acetylene-nitrogen mixtures were used at pressures from 0.1 to 1.0 atm (in air coflow). Ethylene-helium mixtures were used at pressures from 1.0 to 8.0 atm (in oxygen/helium coflow). Soot concentrations, soot temperatures, soot structure, concentrations of major stable gas species, concentrations of radical species (H, OH, O), and flow velocities were measured along the axis of each flame studied. The data were analyzed to determine local soot surface growth, oxidation and nucleation rates, as well as local flame properties that are thought to affect these rates. The measurements of soot surface growth rates were consistent with earlier measurements in laminar premixed and diffusion flames involving a variety of hydrocarbons at atmospheric pressure. In addition, the growth rates from all the available flames were in good agreement with each other and with existing hydrogen-abstraction/carbon-addition (HACA) soot surface growth mechanisms available in the literature. Measurements of soot surface oxidation rates were consistent with earlier measurements, and the oxidation rates from all available flame data could be explained by reaction with OH; supplemented to only a minor degree by direct soot surface oxidation by O2. A simplified method to

  11. Quantitative Measurements of Electronically Excited CH Concentration in Normal Gravity and Microgravity Coflow Laminar Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Giassi, D.; Cao, S.; Stocker, D. P.; Takahashi, F.; Bennett, B. A. V.; Smooke, M. D.; Long, M. B.

    2015-01-01

    With the conclusion of the SLICE campaign aboard the ISS in 2012, a large amount of data was made available for the analysis of the effect of microgravity on laminar coflow diffusion flames. Previous work focused on the study of sooty flames in microgravity as well as the ability of numerical models to predict its formation in a simplified buoyancy-free environment. The current work shifts the investigation to soot-free flames, putting an emphasis on the chemiluminescence emission from electronically excited CH (CH*). This radical species is of significant interest in combustion studies: it has been shown that the electronically excited CH spatial distribution is indicative of the flame front position and, given the relatively simple diagnostic involved with its measurement, several works have been done trying to understand the ability of electronically excited CH chemiluminescence to predict the total and local flame heat release rate. In this work, a subset of the SLICE nitrogen-diluted methane flames has been considered, and the effect of fuel and coflow velocity on electronically excited CH concentration is discussed and compared with both normal gravity results and numerical simulations. Experimentally, the spectral characterization of the DSLR color camera used to acquire the flame images allowed the signal collected by the blue channel to be considered representative of the electronically excited CH emission centered around 431 nm. Due to the axisymmetric flame structure, an Abel deconvolution of the line-of-sight chemiluminescence was used to obtain the radial intensity profile and, thanks to an absolute light intensity calibration, a quantification of the electronically excited CH concentration was possible. Results show that, in microgravity, the maximum flame electronically excited CH concentration increases with the coflow velocity, but it is weakly dependent on the fuel velocity; normal gravity flames, if not lifted, tend to follow the same trend

  12. Quantitative Measurements of CH* Concentration in Normal Gravity and Microgravity Coflow Laminar Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Giassi, D.; Cao, S.; Stocker, D. P.; Takahashi, F.; Bennett, B. A.; Smooke, M. D.; Long, M. B.

    2015-01-01

    With the conclusion of the SLICE campaign aboard the ISS in 2012, a large amount of data was made available for the analysis of the effect of microgravity on laminar coflow diffusion flames. Previous work focused on the study of sooty flames in microgravity as well as the ability of numerical models to predict its formation in a simplified buoyancy-free environment. The current work shifts the investigation to soot-free flames, putting an emphasis on the chemiluminescence emission from electronically excited CH (CH*). This radical species is of significant interest in combustion studies: it has been shown that the CH* spatial distribution is indicative of the flame front position and, given the relatively simple diagnostic involved with its measurement, several works have been done trying to understand the ability of CH* chemiluminescence to predict the total and local flame heat release rate. In this work, a subset of the SLICE nitrogen-diluted methane flames has been considered, and the effect of fuel and coflow velocity on CH* concentration is discussed and compared with both normal gravity results and numerical simulations. Experimentally, the spectral characterization of the DSLR color camera used to acquire the flame images allowed the signal collected by the blue channel to be considered representative of the CH* emission centered around 431 nm. Due to the axisymmetric flame structure, an Abel deconvolution of the line-of-sight chemiluminescence was used to obtain the radial intensity profile and, thanks to an absolute light intensity calibration, a quantification of the CH* concentration was possible. Results show that, in microgravity, the maximum flame CH* concentration increases with the coflow velocity, but it is weakly dependent on the fuel velocity; normal gravity flames, if not lifted, tend to follow the same trend, albeit with different peak concentrations. Comparisons with numerical simulations display reasonably good agreement between measured and

  13. Soot formation and temperature field structure in laminar propane-air diffusion flames at elevated pressures

    SciTech Connect

    Bento, Decio S.; Guelder, OEmer L.; Thomson, Kevin A.

    2006-06-15

    The effect of pressure on soot formation and the structure of the temperature field was studied in coflow propane-air laminar diffusion flames over the pressure range of 0.1 to 0.73 MPa in a high-pressure combustion chamber. The fuel flow rate was selected so that the soot was completely oxidized within the visible flame and the flame was stable at all pressures. Spectral soot emission was used to measure radially resolved soot volume fraction and soot temperature as a function of pressure. Additional soot volume fraction measurements were made at selected heights using line-of-sight light attenuation. Soot concentration values from these two techniques agreed to within 30% and both methods exhibited similar trends in the spatial distribution of soot concentration. Maximum line-of-sight soot concentration along the flame centerline scaled with pressure; the pressure exponent was about 1.4 for pressures between 0.2 and 0.73 MPa. Peak carbon conversion to soot, defined as the percentage of fuel carbon content converted to soot, also followed a power-law dependence on pressure, where the pressure exponent was near to unity for pressures between 0.2 and 0.73 MPa. Soot temperature measurements indicated that the overall temperatures decreased with increasing pressure; however, the temperature gradients increased with increasing pressure. (author)

  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. Laminar round jet diffusion flame buoyant instabilities: Study on the disappearance of varicose structures at ultra-low Froude number

    SciTech Connect

    Boulanger, Joan

    2010-04-15

    At very low Froude number, buoyancy instabilities of round laminar jet diffusion flames disappear (except for small tip oscillations referred to as flickering) and those flames look stable and smooth. This study examines the contributions of the different phenomena in the flow dynamics that may explain this effect. It is observed that, at ultra-low Froude/Reynolds numbers, the material influenced by buoyancy is the plume of the flame and not the flame itself (reaction zone) that is short. Therefore, the vorticity creation zone does not profit from the reaction neighbourhood promoting a sharp gradient of density. Expansion and stretch are also important as they push vorticity creation terms more inside the flame and closer to the burner rim compared to moderate Froude flames. In these latter, the vorticity is continuously created around the flame reaction zone, along its developed height and closer to the vertical direction (in average). (author)

  16. Implementation of REDIM reduced chemistry to model an axisymmetric laminar diffusion methane-air flame

    NASA Astrophysics Data System (ADS)

    Henrique de Almeida Konzen, Pedro; Richter, Thomas; Riedel, Uwe; Maas, Ulrich

    2011-06-01

    The goal of this work is to analyze the use of automatically reduced chemistry by the Reaction-Diffusion Manifold (REDIM) method in simulating axisymmetric laminar coflow diffusion flames. Detailed chemical kinetic models are usually computationally prohibitive for simulating complex reacting flows, and therefore reduced models are required. Automatic reduction model approaches usually exploit the natural multi-scale structure of combustion systems. The novel REDIM approach applies the concept of invariant manifolds to treat also the influence of the transport processes on the reduced model, which overcomes a fundamental problem of model reduction in neglecting the coupling of molecular transport with thermochemical processes. We have considered a previously well studied atmospheric pressure nitrogen-diluted methane-air flame as a test case to validate the methodology presented here. First, one-dimensional and two-dimensional REDIMs were computed and tabulated in lookup tables. Then, the full set of governing equations are projected on the REDIM and implemented in the object-oriented C++ Gascoigne code with a new add-on library to deal with the REDIM tables. The projected set of governing equations have been discretized by the Finite Element Method (FEM) and solved by a GMRES iteration preconditioned by a geometric multigrid method. Local grid refinement, adaptive mesh and parallelization are applied to ensure efficiency and precision. The numerical results obtained using the REDIM approach have shown very good agreement with detailed numerical simulations and experimental data.

  17. Experimental and Computational Study fo CH, CH*, and OH* in an Axisymmetric Laminar Diffusion Flame

    NASA Technical Reports Server (NTRS)

    Walsh, K. T.

    1998-01-01

    In this study, we extend the results of previous combined numerical and experimental investigations of an axisymmetric laminar diffusion flame in which difference Raman spectroscopy, laser-induced fluorescence (LIF), and a multidimensional flame model were used to generate profiles of the temperature and major and minor species. A procedure is outlined by which the number densities of ground-state CH (X(sup 2)II) excited-state CH (A(sup 2)Delta, denoted CH*), and excited-state OH (A(sup 2)Sigma, denoted OH*) are measured and modeled. CH* and OH* number densities are deconvoluted from line-of-sight flame-emission measurements. Ground-state CH is measured using linear LIF. The computations are done with GRI Mech 2.11 as well as an alternate hydrocarbon mechanism. In both cases, additional reactions for the production and consumption of CH* and OH* are added from recent kinetic studies. Collisional quenching and spontaneous emission are responsible for the de-excitation of the excited-state radicals. As with our previous investigations, GRI Mech 2.11 continues to produce very good agreement with the overall flame length observed in the experiments, while significantly under predicting the flame lift-off height. The alternate kinetic scheme is much more accurate in predicting lift-off height but overpredicts the over-all flame length. Ground-state CH profiles predicted with GRI Mech 2.11 are in excellent agreement with the corresponding measurements, regarding both spatial distribution and absolute concentration (measured at 4 ppm) of the CH radical. Calculations of the excited-state species show reasonable agreement with the measurements as far as spatial distribution and overall characteristics are concerned. For OH*, the measured peak mole fraction, 1.3 x 10(exp -8), compared well with computed peaks, while the measured peak level for CH*, 2 x 10(exp -9), was severely underpredicted by both kinetic schemes, indicating that the formation and destruction kinetics

  18. Effect of CF3H and CF3Br on laminar diffusion flames in normal and microgravity

    NASA Technical Reports Server (NTRS)

    Vanderwege, B. A.; Bush, Michael T.; Hochgreb, Simone; Linteris, Gregory T.

    1995-01-01

    Chemical inhibition of diffusion flames through addition of halogenated inhibitors is a problem of significant practical and scientific interest. Extensive studies on diffusion flames in microgravity have shown that these flames have significantly different characteristics than those under normal gravity. However, the mechanisms through which inhibitors reach the reaction zone to suppress combustion in diffusion flames and the effectiveness of these compounds under reduced gravity have yet to be investigated. This study reports preliminary results of investigations on the behavior of laminar jet diffusion flames upon the addition of bromotrifluoromethane (CF3Br) and trifluoromethane (CF3H) to the surroundings under normal and microgravity conditions. The results show that the flame structure in microgravity is significantly different from that under normal gravity conditions, and more importantly, that conditions for flame stability are less stringent under microgravity. Experiments show that flames that cannot be stabilized under normal gravity are quite stable under microgravity conditions. In addition, normal gravity experiments at reduced pressure (low buoyancy) did not reproduce the structure or stability limits of inhibited flames in microgravity.

  19. Soot Surface Oxidation in Laminar Hydrocarbon/Air Diffusion Flames at Atmospheric Pressure. Appendix I

    NASA Technical Reports Server (NTRS)

    Xu, F.; El-Leathy, A. M.; Kim, C. H.; Faeth, G. M.; Yuan, Z.-G. (Technical Monitor); Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2003-01-01

    Soot surface oxidation was studied experimentally in laminar hydrocarbon/air diffusion flames at atmospheric pressure. Measurements were carried out along the axes of round fuel jets burning in coflowing dry air considering acetylene-nitrogen, ethylene, propyiene-nitrogen, propane and acetylene-benzene-nitrogen in the fuel stream. Measurements were limited to the initial stages of soot oxidation (carbon consumption less than 70%) where soot oxidation occurs at the surface of primary soot particles. The following properties were measured as a function of distance above the burner exit: soot concentrations by deconvoluted laser extinction, soot temperatures by deconvoluted multiline emission, soot structure by thermophoretic sampling and analysis using Transmission Electron Microscopy (TEM), concentrations of major stable gas species (N2, H2O, H2, O2, CO, CO2, CH4, C2H2, C2H6, C3H6, C3H8, and C6H6) by sampling and gas chromatography, concentrations of some radical species (H, OH, O) by deconvoluted Li/LiOH atomic absorption and flow velocities by laser velocimetry. For present test conditions, it was found that soot surface oxidation rates were not affected by fuel type, that direct rates of soot surface oxidation by O2 estimated from Nagle and Strickland-Constable (1962) were small compared to observed soot surface oxidation rates because soot surface oxidation was completed near the flame sheet where O2 concentrations were less than 3% by volume, and that soot surface oxidation rates were described by the OH soot surface oxidation mechanism with a collision efficiency of 0.14 and an uncertainty (95% confidence) of +/- 0.04 when allowing for direct soot surface oxidation by O2, which is in reasonably good agreement with earlier observations of soot surface oxidation rates in both premixed and diffusion flames at atmospheric pressure.

  20. Modeling soot formation and burnout in a high temperature laminar diffusion flame burning under oxygen-enriched conditions

    SciTech Connect

    Moss, J.B.; Stewart, C.D.; Young, K.J.

    1995-06-01

    A simplified model of soot formation, based on a laminar flamelet approach and developed, in earlier studies, with a view to subsequent turbulent flame prediction, is extended to include oxidation. The model is evaluated against detailed measurements in a two-dimensional laminar diffusion flame on a Wolfhard-Parker burner. The freestream compositions are modified to raise the stoichiometric condition ({zeta}{sub st} = 0.475), thereby adjusting the flame shape to make the burn-out regime readily accessible to measurement and to substantially raise the temperature levels throughout the flame--peak measured temperature was {approximately} 2,550 K. These temperatures are more relevant to many practical systems than those typically realized in small-scale laminar flame experiments and therefore provide some insight into the extrapolation necessary for practical application. The principal oxidizing species is shown to be the hydroxyl radical, introduced into the prediction from a flamelet calculation as a function of the mixture fraction, the characteristic scalar variable for the complete composition field. The simplified representation of sooting processes in terms of volume fraction and number density is then readily adapted to incorporate soot oxidation and is shown to satisfactorily embrace the enhanced temperature range.

  1. An Analytical Model for Non-Uniform Magnetic Field Effects on Two-Dimensional Laminar Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Calvert, M. E.; Baker, J.; Saito, K.; VanderWal, R. L.

    2001-01-01

    In 1846, Michael Faraday found that permanent magnets could cause candle flames to deform into equatorial disks. He believed that the change in flame shape was caused by the presence of charged particles within the flames interacting with the magnetic fields. Later researchers found that the interaction between the flame ions and the magnetic fields were much too small to cause the flame deflection. Through a force analysis, von Engel and Cozens showed that the change in the flame shape could be attributed to the diamagnetic flame gases in the paramagnetic atmosphere. Paramagnetism occurs in materials composed of atoms with permanent magnetic dipole moments. In the presence of magnetic field gradients, the atoms align with the magnetic field and are drawn into the direction of increasing magnetic field. Diamagnetism occurs when atoms have no net magnetic dipole moment. In the presence of magnetic gradient fields, diamagnetic substances are repelled towards areas of decreasing magnetism. Oxygen is an example of a paramagnetic substance. Nitrogen, carbon monoxide and dioxide, and most hydrocarbon fuels are examples of diamagnetic substances. In order to evaluate the usefulness of these magnets in altering flame behavior, a study has been undertaken to develop an analytical model to describe the change in the flame length of a laminar diffusion jet in the presence of a nonuniform magnetic field.

  2. Holographic Interferometry and Laminar Jet Diffusion Flames in the Presence of Non-Uniform Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Baker, J.; Calvert, M. E.; Saito, K.; VanderWal, R.

    2001-01-01

    Magnetic fields impact combustion processes in a manner analogous to that of buoyancy, i.e., as a body force. It is well known that in a terrestrial environment buoyancy is one of the principal transport mechanisms associated with diffusion flame behavior. Unfortunately, in a terrestrial environment it is difficult if not impossible to isolate flame behavior due magnetic fields from the behavior associated with buoyancy. A micro-, or reduced, gravity environment is ideally suited for studying the impact of magnetic fields on diffusion flames due to the decreased impact of buoyancy on flame behavior.

  3. A numerical study of soot aggregate formation in a laminar coflow diffusion flame

    SciTech Connect

    Zhang, Q.; Thomson, M.J.; Guo, H.; Liu, F.; Smallwood, G.J.

    2009-03-15

    Soot aggregate formation in a two-dimensional laminar coflow ethylene/air diffusion flame is studied with a pyrene-based soot model, a detailed sectional aerosol dynamics model, and a detailed radiation model. The chemical kinetic mechanism describes polycyclic aromatic hydrocarbon formation up to pyrene, the dimerization of which is assumed to lead to soot nucleation. The growth and oxidation of soot particles are characterized by the HACA surface mechanism and pyrene-soot surface condensation. The mass range of the solid soot phase is divided into thirty-five discrete sections and two equations are solved in each section to model the formation of the fractal-like soot aggregates. The coagulation model is improved by implementing the aggregate coagulation efficiency. Several physical processes that may cause sub-unitary aggregate coagulation efficiency are discussed. Their effects on aggregate structure are numerically investigated. The average number of primary soot particles per soot aggregate n{sub p} is found to be a strong function of the aggregate coagulation efficiency. Compared to the available experimental data, n{sub p} is well reproduced with a constant 20% aggregate coagulation efficiency. The predicted axial velocity, OH mole fraction, and C{sub 2}H{sub 2} mole fraction are validated against experimental data in the literature. Reasonable agreements are obtained. Finally, a sensitivity study of the effects of particle coalescence on soot volume fraction and soot aggregate nanostructure is conducted using a coalescence cutoff diameter method. (author)

  4. Understanding soot particle size evolution in laminar ethylene/air diffusion flames using novel soot coalescence models

    NASA Astrophysics Data System (ADS)

    Veshkini, Armin; Dworkin, Seth B.; Thomson, Murray J.

    2016-07-01

    Two coalescence models based on different merging mechanisms are introduced. The effects of the soot coalescence process on soot particle diameter predictions are studied using a detailed sectional aerosol dynamic model. The models are applied to a laminar ethylene/air diffusion flame, and comparisons are made with experimental data to validate the models. The implementation of coalescence models significantly improves the agreement of prediction of particle diameters with the experimental data. Sensitivity of the soot prediction to the coalescence parameters is analysed. Finally, an update to the coalescence model based on experimental observations of soot particles in the flame oxidation regions has been introduced to improve its predicting capabilities.

  5. Experimental and Numerical Studies for Soot Formation in Laminar Coflow Diffusion Flames of Jet A-1 and Synthetic Jet Fuels

    NASA Astrophysics Data System (ADS)

    Saffaripour, Meghdad

    In the present doctoral thesis, fundamental experimental and numerical studies are conducted for the laminar, atmospheric pressure, sooting, coflow diffusion flames of Jet A-1 and synthetic jet fuels. The first part of this thesis presents a comparative experimental study for Jet A-1, which is a widely used petroleum-based fuel, and four synthetically produced alternative jet fuels. The main goals of this part of the thesis are to compare the soot emission levels of the alternative fuels to those of a standard fuel, Jet A-1, and to determine the effect of fuel chemical composition on soot formation characteristics. To achieve these goals, experimental measurements are constructed and performed for flame temperature, soot concentration, soot particle size, and soot aggregate structure in the flames of pre-vaporized jet fuels. The results show that a considerable reduction in soot production, compared to the standard fuel, can be obtained by using synthetic fuels which will help in addressing future regulations. A strong correlation between the aromatic content of the fuels and the soot concentration levels in the flames is observed. The second part of this thesis presents the development and experimental validation of a fully-coupled soot formation model for laminar coflow jet fuel diffusion flames. The model is coupled to a detailed kinetic mechanism to predict the chemical structure of the flames and soot precursor concentrations. This model also provides information on size and morphology of soot particles. The flames of a three-component surrogate for Jet A-1, a three-component surrogate for a synthetic jet fuel, and pure n-decane are simulated using this model. Concentrations of major gaseous species and flame temperatures are well predicted by the model. Soot volume fractions are predicted reasonably well everywhere in the flame, except near the flame centerline where soot concentrations are underpredicted by a factor of up to five. There is an excellent

  6. The Effects of Buoyancy and Dilution on the Structure and Lift-Off of Coflow Laminar Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Walsh, Kevin T.; Long, Marshall B.; Smooke, Mitchell D.

    1999-01-01

    The ability to predict the coupled effects of complex transport phenomena with detailed chemical kinetics in diffusion flames is critical in the modeling of turbulent reacting flows and in understanding the processes by which soot formation and radiative transfer take place. In addition, an understanding of those factors that affect flame extinction in diffusion flames is critical in the suppression of fires and in improving engine efficiency. A goal of this work is to bring to microgravity flame studies the detailed experimental and numerical tools that have been used to study ground-based systems. This will lead to a more detailed understanding of the interaction of convection, diffusion and chemistry in a nonbuoyant environment. To better understand these phenomena, experimental and computational studies of a coflow laminar diffusion flame have been carried out. To date, these studies have focused on a single set of flow conditions, in which a nitrogen-diluted methane fuel stream (65% methane by volume) was surrounded by an air coflow, with exit velocities matched at 35 cm/s. Of particular interest is the change in flame shape due to the absence of buoyant forces, as well as the amount of diluent in the fuel stream and the coflow velocity. As a sensitive marker of changes in the flame shape, the number densities of excited-state CH (A(exp 2 delta) denoted CH*), and excited-state OH (A(exp 2 sigma, denoted OH*) are measured. CH* and OH* number densities are deconvoluted from line-of-sight chemiluminescence measurements made on the NASA KC135 reduced-gravity aircraft. Measured signal levels are calibrated, post-flight, with Rayleigh scattering. In extending the study to microgravity conditions, improvements to the computational model have been made and new calculations performed for a range of gravity conditions. In addition, modifications to the experimental approach were required as a consequence of the constraints imposed by existing microgravity facilities

  7. State Relationships of Laminar Permanently-Blue Opposed-Jet Hydrocarbon-Fueled Diffusion Flames. Appendix D

    NASA Technical Reports Server (NTRS)

    Lin, K.-C.; Faeth, G. M.; Urban, D. L. (Technical Monitor)

    2000-01-01

    The structure and state relationships of laminar soot-free (permanently-blue) diffusion flames at various strain rates were studied experimentally using an opposed-jet configuration, motivated by the importance of soot-free hydrocarbon-fueled diffusion flames for many practical applications. Measurements of gas velocities, temperatures and compositions were carried out along the stagnation stream line. Flame conditions studied included propylene- and 1,3-butadiene-fueled opposed-jet diffusion flames having a stoichiometric mixture fractions of 0.7 and strain rates of 60-240 s (exp -1) at normal temperature and pressure. It was found that oxygen leakage to fuel-rich conditions and carbon monoxide leakage to fuel-lean conditions both increased as strain rates increased. Furthermore, increased strain rates caused increased fuel concentrations near the flame sheet, decreased peak gas temperatures, and decreased concentrations of carbon dioxide and water vapor throughout the flames. State relationships for major gas species and gas temperatures for these flames were found to exist over broad ranges of strain rates. In addition, current measurements, as well as previous measurements and predictions of ethylene-fueled permanently-blue diffusion flames, all having a stoichiometric mixture fraction of 0.7, were combined to establish generalized state relationships for permanently-blue diffusion flames for this stoichiometric mixture fraction. The combined measurements and predictions support relatively universal generalized state relationships for N2, CO2, H2O and fuel over a broad range of strain rates and fuel types. State relationships for O2 in the fuel-rich region, and for CO in the fuel-lean region, however, are functions of strain rate and fuel type. State relationships for H2 and temperature exhibit less universality, mainly due to the increased experimental uncertainties for these variables. The existence of state relationships for soot-free hydrocarbon

  8. Flame Structure and Scalar Properties in Microgravity Laminar Fires

    NASA Technical Reports Server (NTRS)

    Feikema, D. A.; Lim, J.; Sivathanu, Y.

    2006-01-01

    Recent results from microgravity combustion experiments conducted in the Zero Gravity Facility (ZGF) 5.18 second drop tower are reported. Emission mid-infrared spectroscopy measurements have been completed to quantitatively determine the flame temperature, water and carbon dioxide vapor concentrations, radiative emissive power, and soot concentrations in a microgravity laminar ethylene/air flame. The ethylene/air laminar flame conditions are similar to previously reported experiments including the Flight Project, Laminar Soot Processes (LSP). Soot concentrations and gas temperatures are in reasonable agreement with similar results available in the literature. However, soot concentrations and flame structure dramatically change in long duration microgravity laminar diffusion flames as demonstrated in this paper.

  9. The Effects of Buoyancy and Dilution on the Structure and Lift-off of Coflow Laminar Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Walsh, Kevin T.; Long, Marshall B.; Smooke, Mitchell D.

    1999-01-01

    The ability to predict the coupled effects of complex transport phenomena with detailed chemical kinetics in diffusion flames is critical in the modeling of turbulent reacting flows and in understanding the processes by which soot formation and radiative transfer take place. In addition, an understanding of the factors that affect flame extinction in diffusion flames is critical in the suppression of fires and in improving engine efficiency. The goal of our characterizations of coflow laminar diffusion flames is to bring to microgravity the multidimensional diagnostic tools available in normal gravity, and in so doing provide a broader understanding of the successes and limitations of current combustion models. This will lead to a more detailed understanding of the interaction of convection, diffusion and chemistry in both buoyant and nonbuoyant environments. As a sensitive marker of changes in the flame shape, the number densities of excited-state CH (A(exp 2)delta, denoted CH*), and excited-state OH (A(exp 2)Sigma, denoted OH*) are measured in mu-g and normal gravity. Two-dimensional CH* and OH* number densities are deconvoluted from line-of-sight chemiluminescence measurements made on the NASA KC-135 reduced-gravity aircraft. Measured signal levels are calibrated, post-flight, with Rayleigh scattering. Although CH* and OH* kinetics are not well understood, the CH*, OH*, and ground-state CH distributions are spatially coincident in the flame anchoring region. Therefore, the ground-state CH distribution, which is easily computed, and the readily measured CH*/OH* distributions can be used to provide a consistent and convenient way of measuring lift-off height and flame shape in the diffusion flame under investigation. Given that the fuel composition affects flame chemistry and that buoyancy influences the velocity profile of the flow, we have the opportunity to computationally and experimentally study the roles of fluids and chemistry. In performing this

  10. Laminar flame speeds of moist syngas mixtures

    SciTech Connect

    Das, Apurba K.; Kumar, Kamal; Sung, Chih-Jen

    2011-02-15

    This work experimentally investigates the effect of the presence of water vapor on the laminar flame speeds of moist syngas/air mixtures using the counterflow twin-flame configuration. The experimental results presented here are for fuel lean syngas mixtures with molar percentage of hydrogen in the hydrogen and carbon monoxide mixture varying from 5% to 100%, for an unburned mixture temperature of 323 K, and under atmospheric pressure. At a given equivalence ratio, the effect of varying amount of water vapor addition on the measured laminar flame speed is demonstrated. The experimental laminar flame speeds are also compared with computed values using chemical kinetic mechanisms reported in the literature. It is found that laminar flame speed varies non-monotonically with addition of water for the carbon monoxide rich mixtures. It first increases with increasing amount of water addition, reaches a maximum value, and then decreases. An integrated reaction path analysis is further conducted to understand the controlling mechanism responsible for the non-monotonic variation in laminar flame speed due to water addition. On the other hand, for higher values of H{sub 2}/CO ratio the laminar flame speed monotonically decreases with increasing water addition. It is shown that the competition between the chemical and thermal effects of water addition leads to the observed response. Furthermore, reaction rate sensitivity analysis as well as binary diffusion coefficient sensitivity analysis are conducted to identify the possible sources of discrepancy between the experimental and predicted values. The sensitivity results indicate that the reaction rate constant of H{sub 2}+OH = H{sub 2}O+H is worth revisiting and refinement of binary diffusion coefficient data of N{sub 2}-H{sub 2}O, N{sub 2}-H{sub 2}, and H{sub 2}-H{sub 2}O pairs can be considered. (author)

  11. Numerical investigation of the effect of signal trapping on soot measurements using LII in laminar coflow diffusion flames

    NASA Astrophysics Data System (ADS)

    Liu, F.; Thomson, K. A.; Smallwood, G. J.

    2009-09-01

    Laser-induced incandescence has been rapidly developed into a powerful diagnostic technique for measurements of soot in many applications. The incandescence intensity generated by laser-heated soot particles at the measurement location suffers the signal trapping effect caused by absorption and scattering by soot particles present between the measurement location and the detector. The signal trapping effect was numerically investigated in soot measurements using both a 2D LII setup and the corresponding point LII setup at detection wavelengths of 400 and 780 nm in a laminar coflow ethylene/air flame. The radiative properties of aggregated soot particles were calculated using the Rayleigh-Debye-Gans polydisperse fractal aggregate theory. The radiative transfer equation in emitting, absorbing, and scattering media was solved using the discrete-ordinates method. The radiation intensity along an arbitrary direction was obtained using the infinitely small weight technique. The contribution of scattering to signal trapping was found to be negligible in atmospheric laminar diffusion flames. When uncorrected LII intensities are used to determine soot particle temperature and the soot volume fraction, the errors are smaller in 2D LII setup where soot particles are excited by a laser sheet. The simple Beer-Lambert exponential attenuation relationship holds in LII applications to axisymmetric flames as long as the effective extinction coefficient is adequately defined.

  12. Supercritical and subcritical combustion of LOX with hydrogen in an axisymmetric laminar diffusion flame

    SciTech Connect

    Yang, A.S.; Kuo, K.K.; Hsieh, W.H.

    1994-12-31

    Combustion of liquid oxygen (LOX) with H{sub 2} under super- and subcritical conditions was studied both theoretically and experimentally. In the theoretical work, a comprehensive model was formulated and solved numerically to simulate combustion processes of LOX, supplied from a circular tube at its rate of consumption, with ambient hydrogen gas flowing parallel to the axial direction of LOX-supplying tube. The model was based on the conservation equations for a multicomponent system, with consideration of gravitational body force, solubility of ambient gases in liquid, and variable thermophysical properties. A fugacity-based multicomponent thermodynamic analysis with quantum-gas mixing rules was carried out to characterize the solubility of ambient gas the LOX surface. A stable onion-shaped LOX/H{sub 2}/He diffusion flame was achieved at a pressure of 30 atm. The calculated flame shape agreed well with the shape of the observed luminous flame. Under a supercritical combustion situation at 68 atm, the calculated flame shape exhibited a pearlike contour. From the simulation results, it was found that two counter-rotating vortex structures existed in the flame region due mainly to the combustion-induced baroclinic torque as well as buoyancy-induced flow acceleration and entrainment of the surrounding H{sub 2}/He mixture. From the comparison of calculated results using the flame-sheet model and those based upon equilibrium calculations, the flame-sheet model was found to be able to predict the location of the flame front as well as distributions of temperatures, velocity, and major constituent species with reasonable accuracy.

  13. Experimental Methodology for Estimation of Local Heat Fluxes and Burning Rates in Steady Laminar Boundary Layer Diffusion Flames.

    PubMed

    Singh, Ajay V; Gollner, Michael J

    2016-01-01

    Modeling the realistic burning behavior of condensed-phase fuels has remained out of reach, in part because of an inability to resolve the complex interactions occurring at the interface between gas-phase flames and condensed-phase fuels. The current research provides a technique to explore the dynamic relationship between a combustible condensed fuel surface and gas-phase flames in laminar boundary layers. Experiments have previously been conducted in both forced and free convective environments over both solid and liquid fuels. A unique methodology, based on the Reynolds Analogy, was used to estimate local mass burning rates and flame heat fluxes for these laminar boundary layer diffusion flames utilizing local temperature gradients at the fuel surface. Local mass burning rates and convective and radiative heat feedback from the flames were measured in both the pyrolysis and plume regions by using temperature gradients mapped near the wall by a two-axis traverse system. These experiments are time-consuming and can be challenging to design as the condensed fuel surface burns steadily for only a limited period of time following ignition. The temperature profiles near the fuel surface need to be mapped during steady burning of a condensed fuel surface at a very high spatial resolution in order to capture reasonable estimates of local temperature gradients. Careful corrections for radiative heat losses from the thermocouples are also essential for accurate measurements. For these reasons, the whole experimental setup needs to be automated with a computer-controlled traverse mechanism, eliminating most errors due to positioning of a micro-thermocouple. An outline of steps to reproducibly capture near-wall temperature gradients and use them to assess local burning rates and heat fluxes is provided. PMID:27285827

  14. Experimental Methodology for Estimation of Local Heat Fluxes and Burning Rates in Steady Laminar Boundary Layer Diffusion Flames

    PubMed Central

    Singh, Ajay V.; Gollner, Michael J.

    2016-01-01

    Modeling the realistic burning behavior of condensed-phase fuels has remained out of reach, in part because of an inability to resolve the complex interactions occurring at the interface between gas-phase flames and condensed-phase fuels. The current research provides a technique to explore the dynamic relationship between a combustible condensed fuel surface and gas-phase flames in laminar boundary layers. Experiments have previously been conducted in both forced and free convective environments over both solid and liquid fuels. A unique methodology, based on the Reynolds Analogy, was used to estimate local mass burning rates and flame heat fluxes for these laminar boundary layer diffusion flames utilizing local temperature gradients at the fuel surface. Local mass burning rates and convective and radiative heat feedback from the flames were measured in both the pyrolysis and plume regions by using temperature gradients mapped near the wall by a two-axis traverse system. These experiments are time-consuming and can be challenging to design as the condensed fuel surface burns steadily for only a limited period of time following ignition. The temperature profiles near the fuel surface need to be mapped during steady burning of a condensed fuel surface at a very high spatial resolution in order to capture reasonable estimates of local temperature gradients. Careful corrections for radiative heat losses from the thermocouples are also essential for accurate measurements. For these reasons, the whole experimental setup needs to be automated with a computer-controlled traverse mechanism, eliminating most errors due to positioning of a micro-thermocouple. An outline of steps to reproducibly capture near-wall temperature gradients and use them to assess local burning rates and heat fluxes is provided. PMID:27285827

  15. Laminar Soot Processes Experiment Shedding Light on Flame Radiation

    NASA Technical Reports Server (NTRS)

    Urban, David L.

    1998-01-01

    The Laminar Soot Processes (LSP) experiment investigated soot processes in nonturbulent, round gas jet diffusion flames in still air. The soot processes within these flames are relevant to practical combustion in aircraft propulsion systems, diesel engines, and furnaces. However, for the LSP experiment, the flames were slowed and spread out to allow measurements that are not tractable for practical, Earth-bound flames.

  16. The interaction between soot and NO formation in a laminar axisymmetric coflow ethylene/air diffusion flame

    SciTech Connect

    Guo, Hongsheng; Smallwood, Gregory J.

    2007-04-15

    The interaction between soot and NO formation in a laminar axisymmetric coflow ethylene/air diffusion flame was investigated by numerical simulation. A detailed gas-phase reaction scheme and a simplified soot model were employed. The results show that the formation of NO has little effect on that of soot. However, the formation of soot in the flame significantly suppresses the formation of NO. The peak NO concentration and NO emission index are reduced by 28 and 46%, respectively, due to the formation of soot. The influence of soot on NO formation is caused by not only the radiation-induced thermal effect, but also the reaction-induced chemical effect. Relatively the thermal effect is more significant, causing 25 and 38% reduction, respectively, in peak NO concentration and NO emission index. The chemical effect is caused by the competition for acetylene (C{sub 2}H{sub 2}) between soot and NO formation. The formation of soot consumes acetylene in the flame and thus lowers the formation rate of radical CH. This reduces the reaction rate of CH + N{sub 2} = HCN + N, which is the rate-limiting step of the prompt NO formation route, the dominant route in the studied flame. (author)

  17. Investigation of in-flame soot optical properties in laminar coflow diffusion flames using thermophoretic particle sampling and spectral light extinction

    NASA Astrophysics Data System (ADS)

    Kempema, Nathan J.; Ma, Bin; Long, Marshall B.

    2016-09-01

    Soot optical properties are essential to the noninvasive study of the in-flame evolution of soot particles since they allow quantitative interpretation of optical diagnostics. Such experimental data are critical for comparison to results from computational models and soot sub-models. In this study, the thermophoretic sampling particle diagnostic (TSPD) technique is applied along with data from a previous spectrally resolved line-of-sight light attenuation experiment to determine the soot volume fraction and absorption function. The TSPD technique is applied in a flame stabilized on the Yale burner, and the soot scattering-to-absorption ratio is calculated using the Rayleigh-Debye-Gans theory for fractal aggregates and morphology information from a previous sampling experiment. The soot absorption function is determined as a function of wavelength and found to be in excellent agreement with previous in-flame measurements of the soot absorption function in coflow laminar diffusion flames. Two-dimensional maps of the soot dispersion exponent are calculated and show that the soot absorption function may have a positive or negative exponential wavelength dependence depending on the in-flame location. Finally, the wavelength dependence of the soot absorption function is related to the ratio of soot absorption functions, as would be found using two-excitation-wavelength laser-induced incandescence.

  18. Determination of soot scattering coefficient from extinction and three-angle scattering in a laminar diffusion flame

    SciTech Connect

    Iyer, Suresh S.; Litzinger, Thomas A.; Lee, Seong-Young; Santoro, Robert J.

    2007-04-15

    The total scattering coefficient is determined from three multiangle scattering measurements at different heights above the burner in a nonsooting laminar ethylene diffusion flame. The local extinction coefficient is determined from multichord extinction measurements. The above analysis quantifies the contribution from scattering to extinction without knowledge of the soot primary particle diameter or the morphology of the aggregates, and the absorption coefficient can now be determined. The primary particle diameter, the number density of primary particles, the average number of primary particles in an aggregate, and the width of the lognormal distribution function for the number of primary particles in an aggregate are calculated using the absorption coefficient and assumed constant values for the fractal dimension, the fractal prefactor, and the complex refractive index for soot. The values for the primary particle diameter obtained from the in situ measurements in this study compare well with those obtained from transmission electron microscopic measurements of thermophoretically sampled soot aggregates in a previous study at all heights in the diffusion flame, while the calculated soot structure parameters compare well with previous studies only at heights between 30 and 50 mm above the burner. (author)

  19. Triple flame structure and diffusion flame stabilization

    NASA Technical Reports Server (NTRS)

    Veynante, D.; Vervisch, L.; Poinsot, T.; Linan, A.; Ruetsch, G.

    1994-01-01

    The stabilization of diffusion flames is studied using asymptotic techniques and numerical tools. The configuration studied corresponds to parallel streams of cold oxidizer and fuel initially separated by a splitter plate. It is shown that stabilization of a diffusion flame may only occur in this situation by two processes. First, the flame may be stabilized behind the flame holder in the wake of the splitter plate. For this case, numerical simulations confirm scalings previously predicted by asymptotic analysis. Second, the flame may be lifted. In this case a triple flame is found at longer distances downstream of the flame holder. The structure and propagation speed of this flame are studied by using an actively controlled numerical technique in which the triple flame is tracked in its own reference frame. It is then possible to investigate the triple flame structure and velocity. It is shown, as suggested from asymptotic analysis, that heat release may induce displacement speeds of the triple flame larger than the laminar flame speed corresponding to the stoichiometric conditions prevailing in the mixture approaching the triple flame. In addition to studying the characteristics of triple flames in a uniform flow, their resistance to turbulence is investigated by subjecting triple flames to different vortical configurations.

  20. Fuel Preheat Effects on Soot-Field Structure in Laminar Gas Jet Diffusion Flames Burning in 0-g and 1-g

    NASA Technical Reports Server (NTRS)

    Konsur, Bogdan; Megaridis, Constantine M.; Griffin, Devon W.

    1999-01-01

    An experimental investigation conducted at the 2.2-s drop tower of the NASA Lewis Research Center is presented to quantify the influence of moderate fuel preheat on soot-field structure within 0-g laminar gas jet diffusion flames. Parallel work in 1-g is also presented to delineate the effect of elevated fuel temperatures on soot-field structure in buoyant flames. The experimental methodology implements jet diffusion flames of nitrogen-diluted acetylene fuel burning in quiescent air at atmospheric pressure. Fuel preheat of approximately 100 K in the 0-g laminar jet diffusion flames is found to reduce soot loadings in the annular region, but causes an increase in soot volume fractions at the centerline. In addition, fuel preheat reduces the radial extent of the soot field in 0-g. In 1-g, the same fuel preheat levels have a more moderated influence on soot loadings in the annular region, but are also seen to enhance soot concentrations near the axis low in the flame. The increased soot loadings near the flame centerline, as caused by fuel preheat, are consistent with the hypothesis that preheat levels of approximately 100 K enhance fuel pyrolysis rates. The results show that the growth stage of particles transported along the soot annulus is shortened both in 1-g and 0-g when elevated fuel temperatures are used.

  1. Scale-Invariant Forms of Conservation Equations in Reactive Fields and a Modified Hydro-Thermo-Diffusive Theory of Laminar Flames

    NASA Technical Reports Server (NTRS)

    Sohrab, Siavash H.; Piltch, Nancy (Technical Monitor)

    2000-01-01

    A scale-invariant model of statistical mechanics is applied to present invariant forms of mass, energy, linear, and angular momentum conservation equations in reactive fields. The resulting conservation equations at molecular-dynamic scale are solved by the method of large activation energy asymptotics to describe the hydro-thermo-diffusive structure of laminar premixed flames. The predicted temperature and velocity profiles are in agreement with the observations. Also, with realistic physico-chemical properties and chemical-kinetic parameters for a single-step overall combustion of stoichiometric methane-air premixed flame, the laminar flame propagation velocity of 42.1 cm/s is calculated in agreement with the experimental value.

  2. Measurement of the spatially distributed temperature and soot loadings in a laminar diffusion flame using a Cone-Beam Tomography technique

    NASA Astrophysics Data System (ADS)

    Zhao, Huayong; Williams, Ben; Stone, Richard

    2014-01-01

    A new low-cost optical diagnostic technique, called Cone Beam Tomographic Three Colour Spectrometry (CBT-TCS), has been developed to measure the planar distributions of temperature, soot particle size, and soot volume fraction in a co-flow axi-symmetric laminar diffusion flame. The image of a flame is recorded by a colour camera, and then by using colour interpolation and applying a cone beam tomography algorithm, a colour map can be reconstructed that corresponds to a diametral plane. Look-up tables calculated using Planck's law and different scattering models are then employed to deduce the temperature, approximate average soot particle size and soot volume fraction in each voxel (volumetric pixel). A sensitivity analysis of the look-up tables shows that the results have a high temperature resolution but a relatively low soot particle size resolution. The assumptions underlying the technique are discussed in detail. Sample data from an ethylene laminar diffusion flame are compared with data in the literature for similar flames. The comparison shows very consistent temperature and soot volume fraction profiles. Further analysis indicates that the difference seen in comparison with published results are within the measurement uncertainties. This methodology is ready to be applied to measure 3D data by capturing multiple flame images from different angles for non-axisymmetric flame.

  3. Turbulent forced diffusion flames

    SciTech Connect

    Arpaci, V.S.; Li, C.Y.

    1995-07-01

    It is the purpose of this study to introduce a turbulent microscale appropriate for forced diffusion flames and to propose models for fuel consumption and skin friction in terms of this scale. The study consists of four sections. Following the introduction, Section 2 recapitulates the laminar theories of reacting boundary layers in terms of dimensional arguments and proposes models for fuel consumption and skin friction. Section 3 extends these arguments by introducing a microscale appropriate for turbulent flames and, in terms of this scale, develops models for fuel consumption and skin friction, correlates the experimental data on skin friction, and Section 4 concludes the study.

  4. A Computational and Experimental Study of Coflow Laminar Methane/Air Diffusion Flames: Effects of Fuel Dilution, Inlet Velocity, and Gravity

    NASA Technical Reports Server (NTRS)

    Cao, S.; Ma, B.; Bennett, B. A. V.; Giassi, D.; Stocker, D. P.; Takahashi, F.; Long, M. B.; Smooke, M. D.

    2014-01-01

    The influences of fuel dilution, inlet velocity, and gravity on the shape and structure of laminar coflow CH4-air diffusion flames were investigated computationally and experimentally. A series of nitrogen-diluted flames measured in the Structure and Liftoff in Combustion Experiment (SLICE) on board the International Space Station was assessed numerically under microgravity (mu g) and normal gravity (1g) conditions with CH4 mole fraction ranging from 0.4 to 1.0 and average inlet velocity ranging from 23 to 90 cm/s. Computationally, the MC-Smooth vorticity-velocity formulation was employed to describe the reactive gaseous mixture, and soot evolution was modeled by sectional aerosol equations. The governing equations and boundary conditions were discretized on a two-dimensional computational domain by finite differences, and the resulting set of fully coupled, strongly nonlinear equations was solved simultaneously at all points using a damped, modified Newton's method. Experimentally, flame shape and soot temperature were determined by flame emission images recorded by a digital color camera. Very good agreement between computation and measurement was obtained, and the conclusions were as follows. (1) Buoyant and nonbuoyant luminous flame lengths are proportional to the mass flow rate of the fuel mixture; computed and measured nonbuoyant flames are noticeably longer than their 1g counterparts; the effect of fuel dilution on flame shape (i.e., flame length and flame radius) is negligible when the flame shape is normalized by the methane flow rate. (2) Buoyancy-induced reduction of the flame radius through radially inward convection near the flame front is demonstrated. (3) Buoyant and nonbuoyant flame structure is mainly controlled by the fuel mass flow rate, and the effects from fuel dilution and inlet velocity are secondary.

  5. Structure and Soot Properties of Nonbuoyant Ethylene/Air Laminar Jet Diffusion Flames. Appendix E; Repr. from AIAA Journal, v. 36 p 1346-1360

    NASA Technical Reports Server (NTRS)

    Urban, D. L.; Yuan, Z.-G.; Sunderland, P. B.; Linteris, G. T.; Voss, J. E.; Lin, K.-C.; Dai, Z.; Sun, K.; Faeth, G. M.; Ross, Howard D. (Technical Monitor)

    2001-01-01

    The structure and soot properties of round, soot-emitting, nonbuoyant, laminar jet diffusion flames are described, based on long-duration (175-230-s) experiments at microgravity carried out on orbit in the Space Shuttle Columbia. Experimental conditions included ethylene-fueled flames burning in still air at nominal pressures of 50 and 100 kPa and an ambient temperature of 300 K with luminous flame lengths of 49-64 mm Measurements included luminous flame shapes using color video imaging soot concentration (volume fraction) distributions using deconvoluted laser extinction imaging, soot temperature distributions using deconvoluted multiline emission imaging, gas temperature distributions at fuel-lean (plume) conditions using thermocouple probes, soot structure distributions using thermophoretic sampling and analysis by transmission electron microscopy, and flame radiation using a radiometer.The present flames were larger, and emitted soot more readily, than comparable flames observed during ground-based microgravity experiments due to closer approach to steady conditions resulting from the longer test times and the reduced gravitational disturbances of the space-based experiments.

  6. A Series of Laminar Jet Flame

    NASA Technical Reports Server (NTRS)

    2003-01-01

    Study of the downlink data from the Laminar Soot Processes (LSP) experiment quickly resulted in discovery of a new mechanism of flame extinction caused by radiation of soot. Scientists found that the flames emit soot sooner than expected. These findings have direct impact on spacecraft fire safety, as well as the theories predicting the formation of soot -- which is a major factor as a pollutant and in the spread of unwanted fires. This sequence, using propane fuel, was taken STS-94, July 4 1997, MET:2/05:30 (approximate). LSP investigated fundamental questions regarding soot, a solid byproduct of the combustion of hydrocarbon fuels. The experiment was performed using a laminar jet diffusion flame, which is created by simply flowing fuel-like ethylene or propane -- through a nozzle and igniting it, much like a butane cigarette lighter. The LSP principal investigator was Gerard Faeth, University of Michigan, Arn Arbor. The experiment was part of the space research investigations conducted during the Microgravity Science Laboratory-1R mission (STS-94, July 1-17 1997). LSP results led to a reflight for extended investigations on the STS-107 research mission in January 2003. Advanced combustion experiments will be a part of investigations planned for the International Space Station. (249KB JPEG, 1350 x 1524 pixels; downlinked video, higher quality not available) The MPG from which this composite was made is available at http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0300185.html.

  7. Implementation of two-equation soot flamelet models for laminar diffusion flames

    SciTech Connect

    Carbonell, D.; Oliva, A.; Perez-Segarra, C.D.

    2009-03-15

    The two-equation soot model proposed by Leung et al. [K.M. Leung, R.P. Lindstedt, W.P. Jones, Combust. Flame 87 (1991) 289-305] has been derived in the mixture fraction space. The model has been implemented using both Interactive and Non-Interactive flamelet strategies. An Extended Enthalpy Defect Flamelet Model (E-EDFM) which uses a flamelet library obtained neglecting the soot formation is proposed as a Non-Interactive method. The Lagrangian Flamelet Model (LFM) is used to represent the Interactive models. This model uses direct values of soot mass fraction from flamelet calculations. An Extended version (E-LFM) of this model is also suggested in which soot mass fraction reaction rates are used from flamelet calculations. Results presented in this work show that the E-EDFM predict acceptable results. However, it overpredicts the soot volume fraction due to the inability of this model to couple the soot and gas-phase mechanisms. It has been demonstrated that the LFM is not able to predict accurately the soot volume fraction. On the other hand, the extended version proposed here has been shown to be very accurate. The different flamelet mathematical formulations have been tested and compared using well verified reference calculations obtained solving the set of the Full Transport Equations (FTE) in the physical space. (author)

  8. Measurement of distributions of temperature and wavelength-dependent emissivity of a laminar diffusion flame using hyper-spectral imaging technique

    NASA Astrophysics Data System (ADS)

    Liu, Huawei; Zheng, Shu; Zhou, Huaichun; Qi, Chaobo

    2016-02-01

    A generalized method to estimate a two-dimensional (2D) distribution of temperature and wavelength-dependent emissivity in a sooty flame with spectroscopic radiation intensities is proposed in this paper. The method adopts a Newton-type iterative method to solve the unknown coefficients in the polynomial relationship between the emissivity and the wavelength, as well as the unknown temperature. Polynomial functions with increasing order are examined, and final results are determined as the result converges. Numerical simulation on a fictitious flame with wavelength-dependent absorption coefficients shows a good performance with relative errors less than 0.5% in the average temperature. What’s more, a hyper-spectral imaging device is introduced to measure an ethylene/air laminar diffusion flame with the proposed method. The proper order for the polynomial function is selected to be 2, because every one order increase in the polynomial function will only bring in a temperature variation smaller than 20 K. For the ethylene laminar diffusion flame with 194 ml min-1 C2H4 and 284 L min-1 air studied in this paper, the 2D distribution of average temperature estimated along the line of sight is similar to, but smoother than that of the local temperature given in references, and the 2D distribution of emissivity shows a cumulative effect of the absorption coefficient along the line of sight. It also shows that emissivity of the flame decreases as the wavelength increases. The emissivity under wavelength 400 nm is about 2.5 times as much as that under wavelength 1000 nm for a typical line-of-sight in the flame, with the same trend for the absorption coefficient of soot varied with the wavelength.

  9. On the effect of carbon monoxide addition on soot formation in a laminar ethylene/air coflow diffusion flame

    SciTech Connect

    Guo, Hongsheng; Thomson, Kevin A.; Smallwood, Gregory J.

    2009-06-15

    The effect of carbon monoxide addition on soot formation in an ethylene/air diffusion flame is investigated by experiment and detailed numerical simulation. The paper focuses on the chemical effect of carbon monoxide addition by comparing the results of carbon monoxide and nitrogen diluted flames. Both experiment and simulation show that although overall the addition of carbon monoxide monotonically reduces the formation of soot, the chemical effect promotes the formation of soot in an ethylene/air diffusion flame. The further analysis of the details of the numerical result suggests that the chemical effect of carbon monoxide addition may be caused by the modifications to the flame temperature, soot surface growth and oxidation reactions. Flame temperature increases relative to a nitrogen diluted flame, which results in a higher surface growth rate, when carbon monoxide is added. Furthermore, the addition of carbon monoxide increases the concentration of H radical owing to the intensified forward rate of the reaction CO + OH = CO{sub 2} + H and therefore increases the surface growth reaction rates. The addition of carbon monoxide also slows the oxidation rate of soot because the same reaction CO + OH = CO{sub 2} + H results in a lower concentration of OH. (author)

  10. Experimental study on thermophoretic deposition of soot particles in laminar diffusion flames along a solid wall in microgravity

    SciTech Connect

    Choi, Jae-Hyuk; Chung, Suk Ho; Fujita, Osamu; Tsuiki, Takafumi; Kim, Junhong

    2008-09-15

    Soot deposition process in diffusion flames along a solid wall has been investigated experimentally under a microgravity environment. An ethylene (C{sub 2}H{sub 4}) diffusion flame was formed around a cylindrical rod-burner with the surrounding air velocities of V{sub a} = 2.5, 5, and 10 cm/s, the oxygen concentration of 35%, and the burner wall temperature of 300 K. A laser extinction method was adopted to measure the distribution of soot volume fraction. The experiments determined the trace of maximum soot concentration together with the relative distance of the trace of flame. Results showed that the distance was about 2-5 mm. As the surrounding air velocity increased, the region of the soot particle distribution moved closer to the burner wall. The soot particles near the flame zone tended to move away from the flame zone because of the thermophoretic force and to concentrate at a certain narrow region inside the flame. Because of the simultaneous effects of convection and the thermophoresis, soot particles finally adhered to the burner wall. It has been found that there existed an optimal air velocity for the early deposition of soot on the furnace wall. (author)

  11. Experimental determination of the velocity and strain rate field in a laminar H2/Air counter-flow diffusion flame via LDA

    NASA Technical Reports Server (NTRS)

    Yeo, S. H.; Dancey, C. L.

    1991-01-01

    Measurements of the axial and radial components of velocity on the air side of stagnation in an axisymmetric H2/Air laminar counter-flow diffusion flame are reported. Results include the two-dimensional velocity field and computed velocity gradients (strain rates) along the stagnation streamline at two 'characteristic' strain rates, below the extinction limit. The measurements generally verify the modeling assumptions appropriate to the model of Kee et al. (1988). The 'traditional' potential flow model is not consistent with the measured results.

  12. Structure and Soot Formation Properties of Laminar Flames

    NASA Technical Reports Server (NTRS)

    El-Leathy, A. M.; Xu, F.; Faeth, G. M.

    2001-01-01

    Soot formation within hydrocarbon-fueled flames is an important unresolved problem of combustion science for several reasons: soot emissions are responsible for more deaths than any other combustion-generated pollutant, thermal loads due to continuum radiation from soot limit the durability of combustors, thermal radiation from soot is mainly responsible for the growth and spread of unwanted fires, carbon monoxide emissions associated with soot emissions are responsible for most fire deaths, and limited understanding of soot processes in flames is a major impediment to the development of computational combustion. Motivated by these observations, soot processes within laminar premixed and nonpremixed (diffusion) flames are being studied during this investigation. The study is limited to laminar flames due to their experimental and computational tractability, noting the relevance of these results to practical flames through laminar flamelet concepts. Nonbuoyant flames are emphasized because buoyancy affects soot processes in laminar diffusion flames whereas effects of buoyancy are small for most practical flames. This study involves both ground- and space-based experiments, however, the following discussion will be limited to ground-based experiments because no space-based experiments were carried out during the report period. The objective of this work was to complete measurements in both premixed and nonpremixed flames in order to gain a better understanding of the structure of the soot-containing region and processes of soot nucleation and surface growth in these environments, with the latter information to be used to develop reliable ways of predicting soot properties in practical flames. The present discussion is brief, more details about the portions of the investigation considered here can be found in refs. 8-13.

  13. Radiation-affected laminar flame quenching

    SciTech Connect

    Arpaci, V.S.; Tabaczynski, R.J.

    1984-08-01

    A radiation number describing all effects of radiation (emission, absorption, and scattering) near a wall is introduced. The increase in the Peclet number characterizing the flame quench distance and the decrease in flame temperature are shown in terms of this radiation number. Finally, the above considerations have made it possible to qualitatively show that the contribution of radiation to the heat transfer and the laminar flame quenching in small diesel engines can be as much as 35 percent. 27 references.

  14. A numerical study of laminar flames propagating in stratified mixtures

    NASA Astrophysics Data System (ADS)

    Zhang, Jiacheng

    Numerical simulations are carried out to study the structure and speed of laminar flames propagating in compositionally and thermally stratified fuel-air mixtures. The study is motivated by the need to understand the physics of flame propagation in stratified-charge engines and model it. The specific question of interest in this work is: how does the structure and speed of the flame in the stratified mixture differ from that of the flame in a corresponding homogeneous mixture at the same equivalence ratio, temperature, and pressure? The studies are carried out in hydrogen-air, methane-air, and n-heptane-air mixtures. A 30-species 184-step skeletal mechanism is employed for methane oxidation, a 9-species 21-step mechanism for hydrogen oxidation, and a 37-species 56-step skeletal mechanism for n-heptane oxidation. Flame speed and structure are compared with corresponding values for homogeneous mixtures. For compositionally stratified mixtures, as shown in prior experimental work, the numerical results suggest that when the flame propagates from a richer mixture to a leaner mixture, the flame speed is faster than the corresponding speed in the homogeneous mixture. This is caused by enhanced diffusion of heat and species from the richer mixture to the leaner mixture. In fact, the effects become more pronounced in leaner mixtures. Not surprisingly, the stratification gradient influences the results with shallower gradients showing less effect. The controlling role that diffusion plays is further assessed and confirmed by studying the effect of a unity Lewis number assumption in the hydrogen/air mixtures. Furthermore, the effect of stratification becomes less important when using methane or n-heptane as fuel. The laminar flame speed in a thermally stratified mixture is similar to the laminar flame speed in homogeneous mixture at corresponding unburned temperature. Theoretical analysis is performed and the ratio of extra thermal diffusion rate to flame heat release rate

  15. Flame Radiation, Structure, and Scalar Properties in Microgravity Laminar Fires

    NASA Technical Reports Server (NTRS)

    Feikema, Douglas; Lim, Jongmook; Sivathanu, Yudaya

    2007-01-01

    Results from microgravity combustion experiments conducted in the Zero Gravity Research Facility (ZGF) 5.18 second drop facility are reported. The results quantify flame radiation, structure, and scalar properties during the early phase of a microgravity fire. Emission mid-infrared spectroscopy measurements have been completed to quantitatively determine the flame temperature, water and carbon dioxide vapor concentrations, radiative emissive power, and soot concentrations in microgravity laminar methane/air, ethylene/nitrogen/air and ethylene/air jet flames. The measured peak mole fractions for water vapor and carbon dioxide are found to be in agreement with state relationship predictions for hydrocarbon/air combustion. The ethylene/air laminar flame conditions are similar to previously reported results including those from the flight project, Laminar Soot Processes (LSP). Soot concentrations and gas temperatures are in reasonable agreement with similar results available in the literature. However, soot concentrations and flame structure dramatically change in long-duration microgravity laminar diffusion flames as demonstrated in this report.

  16. The Structure and Stability of Laminar Flames

    NASA Technical Reports Server (NTRS)

    Buckmaster, John

    1993-01-01

    This review paper on the structure and stability of laminar flames considers such phenomena as heterogeneous mixtures, acoustic instabilities, flame balls and related phenomena, radiation effects, the iodate oxidation of arsenous acid and 'liquid flame fronts', approximate kinetic mechanisms and asymptotic approximations, and tribrachial or triple flames. The topics examined here indicate three themes that may play an important role in laminar flame theory in the coming years: microgravity experiments, kinetic modeling, and turbulence modeling. In the discussion of microgravity experiments it is pointed out that access to drop towers, the Space Shuttle and, in due course, the Space Station Freedom will encourage the development of experiments well designed to isolate the fundamental physics of combustion.

  17. Ignition and structure of a laminar diffusion flame in a compressible mixing layer with finite rate chemistry

    NASA Technical Reports Server (NTRS)

    Grosch, C. E.; Jackson, T. L.

    1991-01-01

    The ignition and structure of a reacting compressible mixing layer is considered using finite rate chemistry lying between two streams of reactants with different freestream speeds and temperatures. Numerical integration of the governing equations show that the structure of the reacting flow can be quite complicated depending on the magnitude of the Zeldovich number. An analysis of both the ignition a diffusion flame regimes is presented using a combination of large Zeldovich number asymptotics and numerics. This allows to analyze the behavior of these regimes as a function of the parameters of the problem.

  18. Ignition and structure of a laminar diffusion flame in a compressible mixing layer with finite rate chemistry

    NASA Technical Reports Server (NTRS)

    Grosch, C. E.; Jackson, T. L.

    1991-01-01

    The ignition and structure of a reacting compressible mixing layer is considered using finite rate chemistry lying between two streams of reactants with different freestream speeds and temperatures. Numerical integration of the governing equations show that the structure of the reacting flow can be quite complicated depending on the magnitude of the Zeldovich number. An analysis of both the ignition and diffusion flame regimes is presented using a combination of large Zeldovich number asymptotics and numerics. This allows to analyze the behavior of these regimes as a function of the parameters of the problem.

  19. Development of PIV for Microgravity Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Greenberg, Paul S.; Wernet, Mark P.; Yanis, William; Urban, David L.; Sunderland, Peter B.

    2003-01-01

    Results are presented from the application of Particle Image Velocimetry(PIV) to the overfire region of a laminar gas jet diffusion flame in normal gravity. A methane flame burning in air at 0.98 bar was considered. The apparatus demonstrated here is packaged in a drop rig designed for use in the 2.2 second drop tower.

  20. Numerical and experimental study of an axisymmetric coflow laminar methane-air diffusion flame at pressures between 5 and 40 atmospheres

    SciTech Connect

    Liu, Fengshan; Thomson, Kevin A.; Guo, Hongsheng; Smallwood, Gregory J.

    2006-08-15

    A numerical and experimental study of an axisymmetric coflow laminar methane-air diffusion flame at pressures between 5 and 40 atm was conducted to investigate the effect of pressure on the flame structure and soot formation characteristics. Experimental work was carried out in a new high-pressure combustion chamber described in a recent study [K.A. Thomson, O.L. Gulder, E.J. Weckman, R.A. Fraser, G.J. Smallwood, D.R. Snelling, Combust. Flame 140 (2005) 222-232]. Radially resolved soot volume fraction was experimentally measured using both spectral soot emission and line-of-sight attenuation techniques. Numerically, the elliptic governing equations were solved in axisymmetric cylindrical coordinates using the finite volume method. Detailed gas-phase chemistry and complex thermal and transport properties were employed in the numerical calculations. The soot model employed in this study accounts for soot nucleation and surface growth using a semiempirical acetylene-based global soot model with oxidation of soot by O{sub 2}, OH, and O taken into account. Radiative heat transfer was calculated using the discrete-ordinates method and a nine-band nongray radiative property model. Two soot surface growth submodels were investigated and the predicted pressure dependence of soot yield was compared with available experimental data. The experiment, the numerical model, and a simplified theoretical analysis found that the visible flame diameter decreases with pressure as P{sub a}{sup -0.5}. The flame-diameter-integrated soot volume fraction increases with pressure as P{sub a}{sup 1.3} between 5 and 20 atm. The assumption of a square root dependence of the soot surface growth rate on the soot particle surface area predicts the pressure dependence of soot yield in good agreement with the experimental observation. On the other hand, the assumption of linear dependence of the soot surface growth rate on the soot surface area predicts a much faster increase in the soot yield with

  1. Laminar flame propagation in a stratified charge

    NASA Astrophysics Data System (ADS)

    Ra, Youngchul

    The propagation of laminar flame from a rich or stoichiometric mixture to a lean mixture in a stratified methane-air charge was investigated experimentally and numerically. Emphasis was on the understanding of the flame behavior in the transition region; in particular, on the mechanism of burning velocity enhancement in this region. In the experimental setup, mixtures of two different equivalence ratios were separated by a soap bubble in a spherical constant volume combustion vessel. The richer mixture inside the bubble was ignited by a focused laser beam. The flame development was observed by Schlieren technique and flame speeds were measured by heat release analysis of the pressure data. An one-dimensional, time- dependant numerical simulation of the flame propagation in a charge with step-stratification was used to interpret the experimental results. Both the experimental and numerical studies showed that the instantaneous flame speed depended on the previous flame history. Thus a `strong' (with mixture equivalence ratio close to stoichiometric) flame can sustain propagation into finite regions of substantially lean equivalence ratio. Both thermal and chemical effects were crucial for explaining the mechanism of the flame speed enhancement in the transition period. Because of the presence of this `back- support' effect, the usual concept of specifying the burning velocity as a function of the end gas state is inadequate for a stratified charge. A simple correlation for instantaneous flame velocity based on the local burned gas temperature is developed. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253- 1690.)

  2. Laminar dust flames in a reduced-gravity environment

    NASA Astrophysics Data System (ADS)

    Goroshin, Samuel; Tang, Francois-David; Higgins, Andrew J.; Lee, John H. S.

    2011-04-01

    The propagation of laminar dust flames in suspensions of iron in gaseous oxidizers was studied in a low-gravity environment onboard a parabolic flight aircraft. The reduction of buoyancy-induced convective flows and particle settling permitted the measurement of fundamental combustion parameters, such as the burning velocity and the flame quenching distance over a wide range of particle sizes and in different gaseous mixtures. Experimentally measured flame speeds and quenching distances were found in good agreement with theoretical predictions of a simplified analytical model that assumes particles burning in a diffusive mode. However, the comparison of flame speeds in oxygen-argon and oxygen-helium iron suspensions indicates the possibility that fine micron-sized particles burn in the kinetic mode. Furthermore, when the particle spacing is large compared to the scale of the reaction zone, a theoretical analysis suggests the existence of a new so-called discrete flame propagation regime. Discrete flames are strongly dependent on particle density fluctuations and demonstrate directed percolation behavior near flame propagation limits. The experimental observation of discrete flames in particle suspensions will require low levels of gravity over extended periods available only on orbital platforms.

  3. Diffusion Flame Stabilization

    NASA Technical Reports Server (NTRS)

    Takahashi, Fumiaki; Katta, V. R.

    2006-01-01

    Diffusion flames are commonly used for industrial burners in furnaces and flares. Oxygen/fuel burners are usually diffusion burners, primarily for safety reasons, to prevent flashback and explosion in a potentially dangerous system. Furthermore, in most fires, condensed materials pyrolyze, vaporize, and burn in air as diffusion flames. As a result of the interaction of a diffusion flame with burner or condensed-fuel surfaces, a quenched space is formed, thus leaving a diffusion flame edge, which plays an important role in flame holding in combustion systems and fire spread through condensed fuels. Despite a long history of jet diffusion flame studies, lifting/blowoff mechanisms have not yet been fully understood, compared to those of premixed flames. In this study, the structure and stability of diffusion flames of gaseous hydrocarbon fuels in coflowing air at normal earth gravity have been investigated experimentally and computationally. Measurements of the critical mean jet velocity (U(sub jc)) of methane, ethane, or propane at lifting or blowoff were made as a function of the coflowing air velocity (U(sub a)) using a tube burner (i.d.: 2.87 mm). By using a computational fluid dynamics code with 33 species and 112 elementary reaction steps, the internal chemical-kinetic structures of the stabilizing region of methane and propane flames were investigated. A peak reactivity spot, i.e., reaction kernel, is formed in the flame stabilizing region due to back-diffusion of heat and radical species against an oxygen-rich incoming flow, thus holding the trailing diffusion flame. The simulated flame base moved downstream under flow conditions close to the measured stability limit.

  4. Diffusion Flame Stabilization

    NASA Technical Reports Server (NTRS)

    Takahashi, Fumiaki; Katta, Viswanath R.

    2007-01-01

    Diffusion flames are commonly used for industrial burners in furnaces and flares. Oxygen/fuel burners are usually diffusion burners, primarily for safety reasons, to prevent flashback and explosion in a potentially dangerous system. Furthermore, in most fires, condensed materials pyrolyze, vaporize, and burn in air as diffusion flames. As a result of the interaction of a diffusion flame with burner or condensed-fuel surfaces, a quenched space is formed, thus leaving a diffusion flame edge, which plays an important role in flame holding in combustion systems and fire spread through condensed fuels. Despite a long history of jet diffusion flame studies, lifting/blowoff mechanisms have not yet been fully understood, compared to those of premixed flames. In this study, the structure and stability of diffusion flames of gaseous hydrocarbon fuels in coflowing air at normal earth gravity have been investigated experimentally and computationally. Measurements of the critical mean jet velocity (U(sub jc)) of methane, ethane, or propane at lifting or blowoff were made as a function of the coflowing air velocity (U(sub a)) using a tube burner (i.d.: 2.87 mm) (Fig. 1, left). By using a computational fluid dynamics code with 33 species and 112 elementary reaction steps, the internal chemical-kinetic structures of the stabilizing region of methane and propane flames were investigated (Fig. 1, right). A peak reactivity spot, i.e., reaction kernel, is formed in the flame stabilizing region due to back-diffusion of heat and radical species against an oxygen-rich incoming flow, thus holding the trailing diffusion flame. The simulated flame base moved downstream under flow conditions close to the measured stability limit.

  5. Transitional Gas Jet Diffusion Flames in Microgravity

    NASA Technical Reports Server (NTRS)

    Agrawal, Ajay K.; Alammar, Khalid; Gollahalli, S. R.; Griffin, DeVon (Technical Monitor)

    2000-01-01

    Drop tower experiments were performed to identify buoyancy effects in transitional hydrogen gas jet diffusion flames. Quantitative rainbow schlieren deflectometry was utilized to optically visualize the flame and to measure oxygen concentration in the laminar portion of the flame. Test conditions consisted of atmospheric pressure flames burning in quiescent air. Fuel from a 0.3mm inside diameter tube injector was issued at jet exit Reynolds numbers (Re) of 1300 to 1700. Helium mole percentage in the fuel was varied from 0 to 40%. Significant effects of buoyancy were observed in near field of the flame even-though the fuel jets were momentum-dominated. Results show an increase of breakpoint length in microgravity. Data suggest that transitional flames in earth-gravity at Re<1300 might become laminar in microgravity.

  6. Use of laser-induced spark for studying ignition stability and unburned hydrogen escaping from laminar diluted hydrogen diffusion jet flames

    NASA Astrophysics Data System (ADS)

    Phuoc, Tran X.; Chen, Ruey-Hung

    2007-08-01

    Ignition and unburned hydrogen escaping from hydrogen jet diffusion flames diluted with nitrogen up to 70% were experimentally studied. The successful ignition locations were about 2/3 of the flame length above the jet exit for undiluted flames and moved much closer to the exit for diluted flames. For higher levels of dilution or higher flow rates, there existed a region within which a diluted hydrogen diffusion flame can be ignited and burns with a stable liftoff height. This is contrary to previous findings that pure and diluted hydrogen jet diffusion cannot achieve a stable lifted flame configuration. With liftoff, the flame is noisy and short with significant amount of unburned hydrogen escaping into the product gases. If ignition is initiated below this region, the flame propagates upstream quickly and attaches to the burner rim. Results from measurements of unburned hydrogen in the combustion products showed that the amount of unburned hydrogen increased as the nitrogen dilution level was increased. Thus, hydrogen diffusion flame diluted with nitrogen cannot burn completely.

  7. Two-dimensional stability of laminar flames

    NASA Technical Reports Server (NTRS)

    Mukunda, H. S.; Drummond, J. Philip

    1992-01-01

    The stability of laminar flames was studied numerically and the dependence of stability on finite rate chemistry with low activation energy and variable thermodynamic and transport properties was addressed. The calculations show that activation energy and details of chemistry play a minor role in altering the linear neutral stability results from asymptotic analysis. Variable specific heat makes a marginal change to the stability; variable transport properties, on the other hand, tend to substantially enhance the stability from a critical wave number of about 0.50 to 0.20. Also, the effects of variable properties tend to nullify the effects of nonunity Lewis number. When the Lewis number of a single species is different from unity, as is true in a hydrogen-air premixed flame, the stability results remain close to that of unity Lewis number.

  8. 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%.

  9. Absolute, spatially resolved, in situ CO profiles in atmospheric laminar counter-flow diffusion flames using 2.3 μm TDLAS

    NASA Astrophysics Data System (ADS)

    Wagner, Steven; Klein, Moritz; Kathrotia, Trupti; Riedel, Uwe; Kissel, Thilo; Dreizler, Andreas; Ebert, Volker

    2012-11-01

    We developed a new, spatially traversing, direct tunable diode laser absorption spectrometer (TDLAS) for quantitative, calibration-free, and spatially resolved in situ measurements of CO profiles in atmospheric, laminar, non-premixed CH4/air model flames stabilized at a Tsuji counter-flow burner. The spectrometer employed a carefully characterized, room temperature distributed feedback diode laser to detect the R20 line of CO near 2,313 nm (4,324.4 cm-1), which allows to minimize spectral CH4 interference and detect CO even in very fuel-rich zones of the flame. The burner head was traversed through the 0.5 mm diameter laser beam in order to derive spatially resolved CO profiles in the only 60-mm wide CH4/air flame. Our multiple Voigt line Levenberg-Marquardt fitting algorithm and the use of highly efficient optical disturbance correction algorithms for treating transmission and background emission fluctuations as well as careful fringe interference suppression permitted to achieve a fractional optical resolution of up to 2.4 × 10-4 OD (1σ) in the flame ( T up to 1,965 K). Highly accurate, spatially resolved, absolute gas temperature profiles, needed to compute mole fraction and correct for spectroscopic temperature dependencies, were determined with a spatial resolution of 65 μm using ro-vibrational N2-CARS (Coherent anti-Stokes Raman spectroscopy). With this setup we achieved temperature-dependent CO detection limits at the R20 line of 250-2,000 ppmv at peak CO concentrations of up to 4 vol.%. This permitted local CO detection with signal to noise ratios of more than 77. The CO TDLAS spectrometer was then used to determine absolute, spatially resolved in situ CO concentrations in the Tsuji flame, investigate the strain dependence of the CO Profiles and favorably compare the results to a new flame-chemistry model.

  10. Unsteady planar diffusion flames: Ignition, travel, burnout

    NASA Technical Reports Server (NTRS)

    Fendell, F.; Wu, F.

    1995-01-01

    In microgravity, a thin planar diffusion flame is created and thenceforth travels so that the flame is situated at all times at an interface at which the hydrogen and oxygen meet in stoichiometric proportion. If the initial amount of hydrogen is deficient relative to the initial amount of oxygen, then the planar flame will travel further and further into the half volume initially containing hydrogen, until the hydrogen is (virtually) fully depleted. Of course, when the amount of residual hydrogen becomes small, the diffusion flame is neither vigorous nor thin; in practice, the flame is extinguished before the hydrogen is fully depleted, owing to the finite rate of the actual chemical-kinetic mechanism. The rate of travel of the hydrogen-air diffusion flame is much slower than the rate of laminar flame propagation through a hydrogen-air mixture. This slow travel facilitates diagnostic detection of the flame position as a function of time, but the slow travel also means that the time to burnout (extinction) probably far exceeds the testing time (typically, a few seconds) available in earth-sited facilities for microgravity-environment experiments. We undertake an analysis to predict (1) the position and temperature of the diffusion flame as a function of time, (2) the time at which extinction of the diffusion flame occurs, and (3) the thickness of quench layers formed on side walls (i.e., on lateral boundaries, with normal vectors parallel to the diffusion-flame plane), and whether, prior to extinction, water vapor formed by burning will condense on these cold walls.

  11. 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.

  12. 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.

  13. The effects of gravity on wrinkled laminar flames

    SciTech Connect

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

    1992-09-01

    Laminar and turbulent conical Bunsen type flames were used. The study compares results from normal gravity with the burner in an up-right orientation (+g), the burner inverted (-g), and in microgravity ({mu}g) by using the NASA Lewis drop tower facility. The primary diagnostic is a laser schlieren system and some LDA measurements were taken for the +g condition to measure the flow field. The +g laminar flame experiences a large amount of instabilities and results in an unsteady flame tip; cause is torroidal vortex rolling up between products and stagnate surrounding air. Comparison between LDA measurements in reactants and schlieren images shows that velocity fluctuation are induced at the same frequency as the roll up vortices are formed. This pumping of the reactant stream by the product/air interface instability in the +g case is also observed in the turbulent flames. In the -g arrangement the product/air interface is stable so there is no large pumping of the flame tip. At low flow rates the -g flames have flattened tips, but at higher flow rates they become conical in shape. When both flames. appear conical, the -g flames are longer for the same flow rate. In {mu}g the larger instabilities in the flame no longer exist as the product/air interface is believed to become stable. The laminar flames in {mu}g still show small instabilities over the entire flame.

  14. The effects of gravity on wrinkled laminar flames

    SciTech Connect

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

    1992-09-01

    Laminar and turbulent conical Bunsen type flames were used. The study compares results from normal gravity with the burner in an up-right orientation (+g), the burner inverted (-g), and in microgravity ([mu]g) by using the NASA Lewis drop tower facility. The primary diagnostic is a laser schlieren system and some LDA measurements were taken for the +g condition to measure the flow field. The +g laminar flame experiences a large amount of instabilities and results in an unsteady flame tip; cause is torroidal vortex rolling up between products and stagnate surrounding air. Comparison between LDA measurements in reactants and schlieren images shows that velocity fluctuation are induced at the same frequency as the roll up vortices are formed. This pumping of the reactant stream by the product/air interface instability in the +g case is also observed in the turbulent flames. In the -g arrangement the product/air interface is stable so there is no large pumping of the flame tip. At low flow rates the -g flames have flattened tips, but at higher flow rates they become conical in shape. When both flames. appear conical, the -g flames are longer for the same flow rate. In [mu]g the larger instabilities in the flame no longer exist as the product/air interface is believed to become stable. The laminar flames in [mu]g still show small instabilities over the entire flame.

  15. Nonlinear effects in the extraction of laminar flame speeds from expanding spherical flames

    SciTech Connect

    Kelley, A.P.; Law, C.K.

    2009-09-15

    Various factors affecting the determination of laminar flames speeds from outwardly propagating spherical flames in a constant-pressure combustion chamber were considered, with emphasis on the nonlinear variation of the stretched flame speed to the flame stretch rate, and the associated need to nonlinearly extrapolate the stretched flame speed to yield an accurate determination of the laminar flame speed and Markstein length. Experiments were conducted for lean and rich n-butane/air flames at 1atm initial pressure, demonstrating the complex and nonlinear nature of the dynamics of flame evolution, and the strong influences of the ignition transient and chamber confinement during the initial and final periods of the flame propagation, respectively. These experimental data were analyzed using the nonlinear relation between the stretched flame speed and stretch rate, yielding laminar flame speeds that agree well with data determined from alternate flame configurations. It is further suggested that the fidelity in the extraction of the laminar flame speed from expanding spherical flames can be facilitated by using small ignition energy and a large combustion chamber. (author)

  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. The coupling of conical wrinkled laminar flames with gravity

    SciTech Connect

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

    1995-10-01

    This work explores the influences that gravity has on conical premixed laminar and mildly turbulent flames (i.e., wrinkled laminar flames). The approach is to compare overall flame characteristics in normal (+g) reverse ({minus}g), and micro-gravity ({micro}g). Laser schlieren is the principal diagnostic for the {micro}g experiments. Laboratory investigation of +g and {minus}g flames also include two components laser doppler anemometry. The results obtained in a wide range of flow, mixture and turbulence conditions show that gravity has a profound effect on the lean stabilization limits, features of the flowfield, and mean flame heights. in +g and {micro}g do not flicker. analysis of the flame flickering frequencies produces in an empirical relationship St*{sup 2}/Ri = 0.0018 Re{sup 2/3} (where St*, Ri, and Re are, respectively, the Strouhal number normalized by the heat release ratio, the Richardson number, and the Reynolds number). This correlation would be useful for theoretical prediction of buoyancy induced flame instabilities. Comparison of mean flame heights shows that +g, {minus}g, {micro}g flame properties do not converge with increased flow momentum. Velocity measurements in laminar flames show that in +g, the flow generated by the rising products plum is almost non-divergent, slightly turbulent and unstable. In {minus}g, the flow becomes divergent but is stable and non-turbulent in the region surrounding the flame cone. The change from a nondivergent to divergent flow field seems to account for the differences in the observed mean flame heights. The schlieren images and the velocity measurements in +g and {minus}g also provide some insight into the overall flowfield features of {micro}g flames.

  18. Laminar burning velocities and flame instabilities of butanol isomers-air mixtures

    SciTech Connect

    Gu, Xiaolei; Huang, Zuohua; Wu, Si; Li, Qianqian

    2010-12-15

    Laminar burning velocities and flame instabilities of the butanol-air premixed flames and its isomers are investigated using the spherically expanding flame with central ignition at initial temperature of 428 K and initial pressures of 0.10 MPa, 0.25 MPa, 0.50 MPa and 0.75 MPa. Laminar burning velocities and sensitivity factor of n-butanol-air mixtures are computed using a newly developed kinetic mechanism. Unstretched laminar burning velocity, adiabatic temperature, Lewis number, Markstein length, critical flame radius and Peclet number are obtained over a wide range of equivalence ratios. Effect of molecular structure on laminar burning velocity of the isomers of butanol is analyzed from the aspect of C-H bond dissociation energy. Study indicates that although adiabatic flame temperatures of the isomers of butanol are the same, laminar burning velocities give an obvious difference among the isomers of butanol. This indicates that molecular structure has a large influence on laminar burning velocities of the isomers of butanol. Branching (-CH3) will decrease laminar burning velocity. Hydroxyl functional group (-OH) attaching to the terminal carbon atoms gives higher laminar burning velocity compared to that attaching to the inner carbon atoms. Calculated dissociation bond energies show that terminal C-H bonds have larger bond energies than that of inner C-H bonds. n-Butanol, no branching and with hydroxyl functional group (-OH) attaching to the terminal carbon atom, gives the largest laminar burning velocity. tert-Butanol, with highly branching and hydroxyl functional group (-OH) attaching to the inner carbon atom, gives the lowest laminar burning velocity. Laminar burning velocities of iso-butanol and sec-butanol are between those of n-butanol and tert-butanol. The instant of transition to cellularity is experimentally determined for the isomers of butanol and subsequently interpreted on the basis of hydrodynamic and diffusion-thermal instabilities. Little effect

  19. 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.

  20. On the extraction of laminar flame speed and Markstein length from outwardly propagating spherical flames

    SciTech Connect

    Chen, Zheng

    2011-02-15

    Large discrepancies among the laminar flame speeds and Markstein lengths of methane/air mixtures measured by different researchers using the same constant-pressure spherical flame method are observed. As an effort to reduce these discrepancies, one linear model (LM, the stretched flame speed changes linearly with the stretch rate) and two non-linear models (NM I and NM II, the stretched flame speed changes non-linearly with the stretch rate) for extracting the laminar flame speed and Markstein length from propagating spherical flames are investigated. The accuracy and performance of the LM, NM I, and NM II are found to strongly depend on the Lewis number. It is demonstrated that NM I is the most accurate for mixtures with large Lewis number (positive Markstein length) while NM II is the most accurate for mixtures with small Lewis number (negative Markstein length). Therefore, in order to get accurate laminar flame speed and Markstein length from spherical flame experiments, different non-linear models should be used for different mixtures. The validity of the theoretical results is further demonstrated by numerical and experimental studies. The results of this study can be used directly in spherical flame experiments measuring the laminar flame speed and Markstein length. (author)

  1. Numerical Study of Buoyancy and Differential Diffusion Effects on the Structure and Dynamics of Triple Flames

    NASA Technical Reports Server (NTRS)

    Chen, J. -Y.; Echekki, T.

    1999-01-01

    Triple flames arise in a number of practical configurations where fuel and oxidizer are partially premixed, such as in the base of a lifted jet flame. Past experimental studies, theoretical analyses, and numerical modeling of triple flames suggested the potential role of triple flames in stabilizing turbulent flames and in promoting flame propagation. From recent numerical simulations of laminar triple flames, a strong influence of differential diffusion among species and heat on the triple flame structure has been gradually appreciated. This paper reports preliminary numerical results on the influence of gravity and differential diffusion effects on the structure and dynamics of triple flames with a one-step global irreversible chemistry model.

  2. Effects of Buoyancy on Lean Premixed V-Flames Part I: Laminar and Turblent Flame Structure

    NASA Technical Reports Server (NTRS)

    Cheng, Robert K.; Bedat, Benoit; Kostiuk, Larry W.

    1998-01-01

    Laser schlieren and planar laser-induced fluorescence techniques have been used to investigate laminar and turbulent v-flames in +g, -g, and micro g under flow conditions that span the regimes of momentum domination (Ri < 0. 1) and buoyancy domination (Ri > 0.1). Overall flame features shown by schlieren indicate that buoyancy dominates the entire flow field for conditions close to Ri = 1. With decreasing Ri, buoyancy effects are observed only in the far-field regions. Analyses of the mean flame angles demonstrate that laminar and turbulent flames do not have similar responses to buoyancy. Difference in the laminar +g and -g flame angles decrease with Ri (i.e., increasing Re) and converge to the microgravity flame angle at the momentum limit (Ri - 0). This is consistent with the notion that the effects of buoyancy diminish with increasing flow momentum. The +g and -g turbulent flame angles, however, do not converge at Ri = 0. As shown by OH-PLIF images, the inconsistency in +g and -g turbulent flame angles is associated with the differences in flame wrinkles. Turbulent flame wrinkles evolve more slowly in +g than in -g. The difference in flame wrinkle structures, however, cannot be explained in terms of buoyancy effects on flame instability mechanisms. It seems to be associated with the field effects of buoyancy that stretches the turbulent flame brushes in +g and compresses the flame brush in -g. Flame wrinkling offers a mechanism through which the flame responds to the field effects of buoyancy despite increasing flow momentum. These observations point to the need to include both upstream and downstream contributions in theoretical analysis of flame turbulence interactions.

  3. Soot Formation in Purely-Curved Premixed Flames and Laminar Flame Speeds of Soot-Forming Flames

    NASA Technical Reports Server (NTRS)

    Buchanan, Thomas; Wang, Hai

    2005-01-01

    The research addressed here is a collaborative project between University of Delaware and Case Western Reserve University. There are two basic and related scientific objectives. First, we wish to demonstrate the suitability of spherical/cylindrical, laminar, premixed flames in the fundamental study of the chemical and physical processes of soot formation. Our reasoning is that the flame standoff distance in spherical/cylindrical flames under microgravity can be substantially larger than that in a flat burner-stabilized flame. Therefore the spherical/cylindrical flame is expected to give better spatial resolution to probe the soot inception and growth chemistry than flat flames. Second, we wish to examine the feasibility of determining the laminar flame speed of soot forming flames. Our basic assumption is that under the adiabatic condition (in the absence of conductive heat loss), the amount and dynamics of soot formed in the flame is unique for a given fuel/air mixture. The laminar flame speed can be rigorously defined as long as the radiative heat loss can be determined. This laminar flame speed characterizes the flame soot formation and dynamics in addition to the heat release rate. The research involves two integral parts: experiments of spherical and cylindrical sooting flames in microgravity (CWRU), and the computational counterpart (UD) that aims to simulate sooting laminar flames, and the sooting limits of near adiabatic flames. The computations work is described in this report, followed by a summary of the accomplishments achieved to date. Details of the microgra+ experiments will be discussed in a separate, final report prepared by the co-PI, Professor C-J. Sung of CWRU. Here only a brief discussion of these experiments will be given.

  4. Extinction of turbulent diffusion flames by Kolmogorov microscale turbulence

    SciTech Connect

    Yoshida, A.; Igarashi, T.; Kotani, Y.

    1997-06-01

    The effects of turbulent straining on the structure and response of cylindrical diffusion flames were studied experimentally by using the counterflow flame configuration formed in the forward stagnation region of a porous cylinder from which propane or methane was ejected. From the shadowgraphs, it was found that the turbulence caused large-scale distortions with small amplitude on a diffusion flame which had a locally laminar structure. The time-averaged flame thickness was three times as large as the laminar flame. The turbulent flow field was measured in detail by a hot-wire anemometer. The temperature profiles were determined as functions of the applied strain rate by using a fine-wire thermocouple the thermal inertia of which was compensated electrically. The total strain rate applied to the flame was decomposed into the bulk strain rate induced by the mean flow velocity gradient and the turbulent strain rate which was modelled. In the present study, the latter was modelled by the reciprocal of the Kolmogorov time scale. The total strain rate at which the turbulent diffusion flame was extinguished coincided with the critical velocity gradient at which the extinction of a laminar flame occurred. With the increase of the total strain rate, the turbulent diffusion flame became thinner, and the maximum mean temperature gradually decreased due to the decrease of the maximum temperature within the laminar flamelet. On the other hand, the maximum rms fluctuating temperature was rather insensitive to the total strain rate over a wide range of total strain rates. However, close to extinction, nonreactive holes appeared intermittently in the flame along the stagnation line established in the forward stagnation region of the porous cylinder. These holes led to an abrupt increase in the maximum rms fluctuating temperature and, also, a decrease in the maximum mean temperature very close to the state of extinction.

  5. Polydisperse spray diffusion flames in oscillating flow

    NASA Astrophysics Data System (ADS)

    Greenberg, Jerrold Barry; Katoshevski, David

    2016-03-01

    The phenomenon of droplet clustering or grouping found when a spray of droplets is moving in an oscillating host flow field is investigated for the case of a polydisperse spray that fuels a laminar co-flow diffusion flame. A mathematical solution is developed for the liquid phase based on use of small Stokes numbers for size sections into which the polydisperse spray size distribution is divided. Droplet clustering in the oscillatory flow field is accounted for by constructing a special model for the sectional vaporization Damkohler numbers in accordance with droplet size. Combining this with a formal solution for a gas phase Schvab-Zel'dovich variable yields the means whereby flame dynamics can be described. Results calculated from this solution demonstrate that preferential droplet size behaviour (with smaller droplets tending to cluster to a greater extent and reduce the vaporization Damkohler number more than larger ones) can have a major impact on the flame dynamics through local droplet enrichment with attendant consequences on the production of fuel vapour. The dynamics of the sort of flame (over- or under-ventilated) and the occurrence of flame pinching leading to multiple flame sheets are altered under these circumstances. However, potential control of the actual initial spray polydispersity may reduce the intensity of such effects.

  6. Soot Formation in Laminar Premixed Methane/Oxygen Flames at Atmospheric Pressure

    NASA Technical Reports Server (NTRS)

    Xu, F.; Lin, K.-C.; Faeth, G. M.

    1998-01-01

    Flame structure and soot formation were studied within soot-containing laminar premixed mc1hane/oxygen flames at atmospheric pressure. The following measurements were made: soot volume fractions by laser extinction, soot temperatures by multiline emission, gas temperatures (where soot was absent) by corrected fine-wire thermocouples, soot structure by thermophoretic sampling and transmission electron microscope (TEM), major gas species concentrations by sampling and gas chromatography, and gas velocities by laser velocimetry. Present measurements of gas species concentrations were in reasonably good agreement with earlier measurements due to Ramer et al. as well as predictions based on the detailed mechanisms of Frenklach and co-workers and Leung and Lindstedt: the predictions also suggest that H atom concentrations are in local thermodynamic equilibrium throughout the soot formation region. Using this information, it was found that measured soot surface growth rates could be correlated successfully by predictions based on the hydrogen-abstraction/carbon-addition (HACA) mechanisms of both Frenklach and co-workers and Colket and Hall, extending an earlier assessment of these mechanisms for premixed ethylene/air flames to conditions having larger H/C ratios and acetylene concentrations. Measured primary soot particle nucleation rates were somewhat lower than the earlier observations for laminar premixed ethylene/air flames and were significantly lower than corresponding rates in laminar diffusion flames. for reasons that still must be explained.

  7. Soot Formation in Laminar Premixed Methane/Oxygen Flames at Atmospheric Pressure. Appendix H

    NASA Technical Reports Server (NTRS)

    Xu, F.; Lin, K.-C.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2001-01-01

    Flame structure and soot formation were studied within soot-containing laminar premixed methanefoxygen flames at atmospheric pressure. The following measurements were made: soot volume fractions by laser extinction, soot temperatures by multiline emission, gas temperatures (where soot was absent) by corrected fine-wire thermocouples, soot structure by thermophoretic sampling and transmission electron microscope (TEM), major gas species concentrations by sampling and gas chromatography, and gas velocities by laser velocimetry. Present measurements of gas species concentrations were in reasonably good agreement with earlier measurements due to Ramer et al. as well as predictions based on the detailed mechanisms of Frenklach and co-workers and Leung and Lindstedt; the predictions also suggest that H atom concentrations are in local thermodynamic equilibrium throughout the soot formation region. Using this information, it was found that measured soot surface growth rates could be correlated successfully by predictions based on the hydrogenabstraction/carbon-addition (HACA) mechanisms of both Frenklach and co-workers and Colket and Hall, extending an earlier assessment of these mechanisms for premixed ethylene/air flames to conditions having larger H/C ratios and acetylene concentrations. Measured primary soot particle nucleation rates were somewhat lower than the earlier observations for laminar premixed ethylene/air flames and were significantly lower than corresponding rates in laminar diffusion flames, for reasons that still must be explained.

  8. Computatonal and experimental study of laminar flames

    SciTech Connect

    Smooke, M.D.; Long, M.B.

    1993-12-01

    This research has centered on an investigation of the effects of complex chemistry and detailed transport on the structure and extinction of hydrocarbon flames in counterflow, cylindrical and coflowing axisymmetric configurations. The authors have pursued both computational and experimental aspects of the research in parallel. The computational work has focused on the application of accurate and efficient numerical methods for the solution of the one and two-dimensional nonlinear boundary value problems describing the various reacting systems. Detailed experimental measurements were performed on axisymmetric coflow flames using two-dimensional imaging techniques. In particular, spontaneous Raman scattering and laser induced fluorescence were used to measure the temperature, major and minor species profiles.

  9. High pressure flame system for pollution studies with results for methane-air diffusion flames

    NASA Technical Reports Server (NTRS)

    Miller, I. M.; Maahs, H. G.

    1977-01-01

    A high pressure flame system was designed and constructed for studying nitrogen oxide formation in fuel air combustion. Its advantages and limitations were demonstrated by tests with a confined laminar methane air diffusion flame over the pressure range from 1 to 50 atm. The methane issued from a 3.06 mm diameter port concentrically into a stream of air contained within a 20.5 mm diameter chimney. As the combustion pressure is increased, the flame changes in shape from wide and convex to slender and concave, and there is a marked increase in the amount of luminous carbon. The height of the flame changes only moderately with pressure.

  10. Iron/soot interaction in a laminar ethylene nonpremixed flame

    SciTech Connect

    Zhang, J.; Megaridis, C.M.

    1994-12-31

    A laminar, coannular, ethylene/air nonpremixed flame doped with ferrocene additive is employed to address the fundamental question of how iron becomes incorporated into the carbonaceous soot phase, thus interfering with the soot formation processes. The structure and chemical composition of individual aggregates are characterized with respect to flame coordinates via a combination of thermophoretic sampling, transmission electron microscopy, and energy dispersive spectrometry. Soot aggregate microstructure clearly reveals iron occlusion, as well as stratification of soot layers over the occluded phase. The study provides physical evidence that the soot and iron compounds combine in the flame to form a hybrid (inhomogeneous) particulate phase. The reported observations are consistent with the hypothesis that ferrocene decomposes early in the combustion process and before the onset of soot particle inception, thus forming a fine aerosol for the subsequent deposition of carbonaceous substances. Examination of a series of inhomogeneous soot aggregates shows that the flame aerosol composition varies with flame coordinates. In particular, aggregates transported in the soot annulus near the luminous flame front are primarily composed of carbon and oxygen, with traces of iron finely dispersed through the aggregate matrix. On the other hand, carbonaceous soot transported at low heights and near the flame axis contains iron in its elemental form. Finally, soot aggregates in all other areas of the flame contain both iron and oxygen, thus implying the possible presence of iron oxides within the carbonaceous matrix.

  11. Scaling of turbulent flame speed for expanding flames with Markstein diffusion considerations.

    PubMed

    Chaudhuri, Swetaprovo; Wu, Fujia; Law, Chung K

    2013-09-01

    In this paper we clarify the role of Markstein diffusivity, which is the product of the planar laminar flame speed and the Markstein length, on the turbulent flame speed and its scaling, based on experimental measurements on constant-pressure expanding turbulent flames. Turbulent flame propagation data are presented for premixed flames of mixtures of hydrogen, methane, ethylene, n-butane, and dimethyl ether with air, in near-isotropic turbulence in a dual-chamber, fan-stirred vessel. For each individual fuel-air mixture presented in this work and the recently published iso-octane data from Leeds, normalized turbulent flame speed data of individual fuel-air mixtures approximately follow a Re_{T,f}^{0.5} scaling, for which the average radius is the length scale and thermal diffusivity is the transport property of the turbulence Reynolds number. At a given Re_{T,f}^{}, it is experimentally observed that the normalized turbulent flame speed decreases with increasing Markstein number, which could be explained by considering Markstein diffusivity as the leading dissipation mechanism for the large wave number flame surface fluctuations. Consequently, by replacing thermal diffusivity with the Markstein diffusivity in the turbulence Reynolds number definition above, it is found that normalized turbulent flame speeds could be scaled by Re_{T,M}^{0.5} irrespective of the fuel, equivalence ratio, pressure, and turbulence intensity for positive Markstein number flames. PMID:24125342

  12. Scaling of turbulent flame speed for expanding flames with Markstein diffusion considerations.

    PubMed

    Chaudhuri, Swetaprovo; Wu, Fujia; Law, Chung K

    2013-09-01

    In this paper we clarify the role of Markstein diffusivity, which is the product of the planar laminar flame speed and the Markstein length, on the turbulent flame speed and its scaling, based on experimental measurements on constant-pressure expanding turbulent flames. Turbulent flame propagation data are presented for premixed flames of mixtures of hydrogen, methane, ethylene, n-butane, and dimethyl ether with air, in near-isotropic turbulence in a dual-chamber, fan-stirred vessel. For each individual fuel-air mixture presented in this work and the recently published iso-octane data from Leeds, normalized turbulent flame speed data of individual fuel-air mixtures approximately follow a Re_{T,f}^{0.5} scaling, for which the average radius is the length scale and thermal diffusivity is the transport property of the turbulence Reynolds number. At a given Re_{T,f}^{}, it is experimentally observed that the normalized turbulent flame speed decreases with increasing Markstein number, which could be explained by considering Markstein diffusivity as the leading dissipation mechanism for the large wave number flame surface fluctuations. Consequently, by replacing thermal diffusivity with the Markstein diffusivity in the turbulence Reynolds number definition above, it is found that normalized turbulent flame speeds could be scaled by Re_{T,M}^{0.5} irrespective of the fuel, equivalence ratio, pressure, and turbulence intensity for positive Markstein number flames.

  13. Scaling of turbulent flame speed for expanding flames with Markstein diffusion considerations

    NASA Astrophysics Data System (ADS)

    Chaudhuri, Swetaprovo; Wu, Fujia; Law, Chung K.

    2013-09-01

    In this paper we clarify the role of Markstein diffusivity, which is the product of the planar laminar flame speed and the Markstein length, on the turbulent flame speed and its scaling, based on experimental measurements on constant-pressure expanding turbulent flames. Turbulent flame propagation data are presented for premixed flames of mixtures of hydrogen, methane, ethylene, n-butane, and dimethyl ether with air, in near-isotropic turbulence in a dual-chamber, fan-stirred vessel. For each individual fuel-air mixture presented in this work and the recently published iso-octane data from Leeds, normalized turbulent flame speed data of individual fuel-air mixtures approximately follow a ReT,f0.5 scaling, for which the average radius is the length scale and thermal diffusivity is the transport property of the turbulence Reynolds number. At a given ReT,f, it is experimentally observed that the normalized turbulent flame speed decreases with increasing Markstein number, which could be explained by considering Markstein diffusivity as the leading dissipation mechanism for the large wave number flame surface fluctuations. Consequently, by replacing thermal diffusivity with the Markstein diffusivity in the turbulence Reynolds number definition above, it is found that normalized turbulent flame speeds could be scaled by ReT,M0.5 irrespective of the fuel, equivalence ratio, pressure, and turbulence intensity for positive Markstein number flames.

  14. Computational and experimental study of laminar flames

    SciTech Connect

    Smooke, Mitchell

    2015-05-29

    During the past three years, our research has centered on an investigation of the effects of complex chemistry and detailed transport on the structure and extinction of hydrocarbon flames in coflowing axisymmetric configurations. We have pursued both computational and experimental aspects of the research in parallel on both steady-state and time-dependent systems. The computational work has focused on the application of accurate and efficient numerical methods for the solution of the steady-state and time-dependent boundary value problems describing the various reacting systems. Detailed experimental measurements were performed on axisymmetric coflow flames using two-dimensional imaging techniques. Previously, spontaneous Raman scattering, chemiluminescence, and laser-induced fluorescence were used to measure the temperature, major and minor species profiles. Particle image velocimetry (PIV) has been used to investigate velocity distributions and for calibration of time-varying flames. Laser-induced incandescence (LII) with an extinction calibration was used to determine soot volume fractions, while soot surface temperatures were measured with three-color optical pyrometry using a color digital camera. A blackbody calibration of the camera allows for determination of soot volume fraction as well, which can be compared with the LII measurements. More recently, we have concentrated on a detailed characterization of soot using a variety of techniques including time-resolved LII (TiRe-LII) for soot primary particles sizes, multi-angle light scattering (MALS) for soot radius of gyration, and spectrally-resolved line of sight attenuation (spec-LOSA). Combining the information from all of these soot measurements can be used to determine the soot optical properties, which are observed to vary significantly depending on spatial location and fuel dilution. Our goal has been to obtain a more fundamental understanding of the important fluid dynamic and chemical interactions in

  15. Further experiments on the stability of laminar and turbulent hydrogen-air flames at reduced pressures

    NASA Technical Reports Server (NTRS)

    Fine, Burton

    1957-01-01

    Stability limits for laminar and turbulent hydrogen-air burner flames were measured as a function of pressure, burner diameter, and composition. On the basis of a simple flame model, turbulent flashback involved a smaller effective penetration distance than laminar flashback. No current theoretical treatment predicts the observed pressure and diameter dependence of laminar and turbulent blowoff.

  16. Dynamic response of a pulsed Burke-Schumann diffusion flame

    NASA Technical Reports Server (NTRS)

    Sheu, Jyh-Cherng; Stocker, Dennis P.; Chen, Lea-Der

    1995-01-01

    Turbulent flames are often envisioned as an ensemble of random vortices interacting with the combustion process. A better understanding of the vortex-flame interactions therefore would be useful in improving the modeling of turbulent diffusion flames. Substantial simplification may be made by investigating controlled interactions in a laminar flame, as opposed to random interactions in a turbulent flame. The general goals of the research project are to improve our understanding of (1) the influence of buoyancy on co-flow diffusion flames and (2) the effects of buoyancy on vortex-flame interactions in co-flow diffusion flames. As a first step toward objective (2), we conducted a joint experimental and numerical investigation of the vortex-flame interaction. Vortices were produced by mechanically pulsing the fuel flow at a low frequency, e.g., 10 Hz. Experiments were conducted using a nonflickering Burke-Schumann flame in both microgravity (mu-g) and normal gravity (1g) as a means of varying the buoyant force without modification of the pressure (i.e., density). The effects of buoyant convection may then be determined by a comparison of the mu-g and 1g results. The mu-g results may also reveal the important mechanisms which are masked or overwhelmed by buoyant convection in 1g. A numerical investigation was conducted using a validated, time-accurate numerical code to study the underlying physics during the flame interaction and to assist the interpretation of the experimental results.

  17. An experimental investigation of an acoustically excited laminar premixed flame

    SciTech Connect

    Kartheekeyan, S.; Chakravarthy, S.R.

    2006-08-15

    A two-dimensional laminar premixed flame is stabilized over a burner in a confined duct and is subjected to external acoustic forcing from the downstream end. The equivalence ratio of the flame is 0.7. The flame is stabilized in the central slot of a three-slotted burner. The strength of the shear layer of the cold reactive mixture through the central slot is controlled by the flow rate of cold nitrogen gas through the side slots. The frequency range of acoustic excitation is 400-1200 Hz, and the amplitude levels are such that the acoustic velocity is less than the mean flow velocity of the reactants. Time-averaged chemiluminescence images of the perturbed flame front display time-mean changes as compared to the unperturbed flame shape at certain excitation frequencies. Prominent changes to the flame front are in the form of stretching or shrinkage, asymmetric development of its shape, increased/preferential lift-off of one or both of the stabilization points of the flame, and nearly random three-dimensional fluctuations over large time scales under some conditions. The oscillations of the shear layer and the response of the confined jet of the hot products to the acoustic forcing, such as asymmetric flow development and jet spreading, are found to be responsible for the observed mean changes in the flame shape. A distinct low-frequency component ({approx}60-90 Hz) relative to the excitation frequency is observed in the fluctuations of the chemiluminescent intensity in the flame under most conditions. It is observed that fluctuations in the flame area predominantly contribute to the origin of the low-frequency component. This is primarily due to the rollup of vortices and the generation of enthalpy waves at the burner lip. Both of these processes are excited at the externally imposed acoustic time scale, but convect/propagate downstream at the flow time scale, which is much larger. (author)

  18. Laminar flame acceleration by neon enrichment in white dwarf supernovae

    NASA Astrophysics Data System (ADS)

    Chamulak, David; Brown, Edward F.; Timmes, Francis X.

    We explore how the laminar flame speed of degenerate C/O thermonuclear burning during a type Ia supernova depends on the composition of the white dwarf. Type Ia supernovae are currently the premier standard candle for measuring distances to redshift 1.6. The currently favored scenario for this supernovae is the thermonuclear incineration of a C/O white dwarf. Recent observations suggest that there may be more than one population of progenitor, and it has been suggested the peak luminosity may depend on the composition of the progenitor white dwarf. Of particular interest is 22 Ne, which is formed from CNO elements during core He burning of the progenitor star and therefore reflects the metallicity of the progenitor. We find that the laminar flame speed of a C/O mixture increases linearly with the abundance of 22 Ne when the abundance of 22 Ne is small. The faster and narrower laminar flame enlarges the lengthscale at which turbulent eddies can disrupt the burn. As a result, the addition of 22 Ne might lower the density at which a transition to distributed burning occurs.

  19. Soot Aerosol Properties in Laminar Soot-Emitting Microgravity Nonpremixed Flames

    NASA Technical Reports Server (NTRS)

    Konsur, Bogdan; Megaridis, Constantine M.; Griffin, Devon W.

    1999-01-01

    The spatial distributions and morphological properties of the soot aerosol are examined experimentally in a series of 0-g laminar gas-jet nonpremixed flames. The methodology deploys round jet diffusion flames of nitrogen-diluted acetylene fuel burning in quiescent air at atmospheric pressure. Full-field laser-light extinction is utilized to determine transient soot spatial distributions within the flames. Thermophoretic sampling is employed in conjunction with transmission electron microscopy to define soot microstructure within the soot-emitting 0-g flames. The microgravity tests indicate that the 0-g flames attain a quasi-steady state roughly 0.7 s after ignition, and sustain their annular structure even beyond their luminous flame tip. The measured peak soot volume fractions show a complex dependence on burner exit conditions, and decrease in a nonlinear fashion with decreasing characteristic flow residence times. Fuel preheat by approximately 140 K appears to accelerate the formation of soot near the flame axis via enhanced fuel pyrolysis rates. The increased soot presence caused by the elevated fuel injection temperatures triggers higher flame radiative losses, which may account for the premature suppression of soot growth observed along the annular region of preheated-fuel flames. Electron micrographs of soot aggregates collected in 0-g reveal the presence of soot precursor particles near the symmetry axis at midflame height, The observations also verify that soot primary particle sizes are nearly uniform among aggregates present at the same flame location, but vary considerably with radius at a fixed distance from the burner. The maximum primary size in 0-g is found to be by 40% larger than in 1-g, under the same burner exit conditions. Estimates of the number concentration of primary particles and surface area of soot particulate phase per unit volume of the combustion gases are also made for selected in-flame locations.

  20. 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.

  1. Effects of Buoyancy in Hydrogen Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Agrawal, A. K.; Al-Ammar, K.; Gollahalli, S. R.; Griffin, D. W.

    1999-01-01

    This project was carried out to understand the effects of heat release and buoyancy on the flame structure of diffusion flames. Experiments were conducted at atmospheric pressure in both normal gravity and microgravity conditions in the NASA LeRC 2.2 s drop tower. Experiments were also conducted in a variable pressure combustion facility in normal gravity to scale buoyancy and thus, to supplement the drop tower experiments. Pure H2 or H2 mixed with He was used as the jet fluid to avoid the complexities associated with soot formation. Fuel jet burning in quiescent air was visualized and quantified by the Rainbow Schlieren Deflectometry (RSD) to obtain scalar profiles (temperature, oxygen concentration) within the flame. Burner tube diameter (d) was varied from 0.3 to 1.19 mm producing jet exit Reynolds numbers ranging from 40 to 1900, and generating flames encompassing laminar and transitional (laminar to turbulent) flow structure. Some experiments were also complemented with the CFD analysis. In a previous paper, we have presented details of the RSD technique, comparison of computed and measured scalar distributions, and effects of buoyancy on laminar and transitional H2 gas-jet diffusion flames. Results obtained from the RSD technique, variable pressure combustion chamber, and theoretical models have been published. Subsequently, we have developed a new drop rig with improved optical and image acquisition. In this set up, the schlieren images are acquired in real time and stored digitally in RAM of an onboard computer. This paper deals with laminar diffusion flames of pure H2 in normal and microgravity.

  2. Effects of soot formation on shape of a nonpremixed laminar flame established in a shear boundary layer in microgravity

    NASA Astrophysics Data System (ADS)

    Y Wang, H.; Merino, J. L. F.; Dagaut, P.

    2011-12-01

    A numerical study was performed to give a quantitative description of a heavily sooting, nonpremixed laminar flame established in a shear boundary layer in microgravity. Controlling mechanisms of three dimensional flow, combustion, soot and radiation are coupled. Soot volume fraction were predicted by using three approaches, referred respectively to as the fuel, acetylene and PAH inception models. It is found that the PAH inception model, which is based on the formation of two and three-ringed aromatic species, reproduces correctly the experimental data from a laminar ethylene diffusion flame. The PAH inception model serves later to better understand flame quenching, flame stand-off distance and soot formation as a function of the dimensionless volume coefficient, defined as Cq = VF/Vox where VF is the fuel injection velocity, and Vox air stream velocity. The present experiments showed that a blue unstable flame, negligible radiative feedback, may change to a yellow stable flame, significant radiative loss with an increase of Cq; this experimental trend was numerically reproduced. The flame quenching occurs at the trailing edge due to radiative heat loss which is significantly amplified by increasing VF or decreasing Vox, favouring soot formation. Along a semi-infinite fuel zone, the ratio, df/db, where df is the flame standoff distance, and db the boundary layer thickness, converges towards a constant value of 1.2, while soot resides always within the boundary layer far away from the flame sheet.

  3. The structure and stability of the laminar counter-flow partially premixed methane/air triple flame

    SciTech Connect

    Lockett, R.D.; Boulanger, B.; Harding, S.C.; Greenhalgh, D.A.

    1999-10-01

    The flame stability map defining the regime of existence of a counter-flowing laminar partially premixed methane-air triple flame has been determined using OH planar laser-induced fluorescence (PLIF). The stability limits were determined through the observation of flame merging and flame extinction, a function of rich and lean equivalence ratios, and mean axial strain rate. Relatively quantitative OH species profiles and Rayleigh scattering profiles have been measured for three flame conditions. Axial flow velocity profiles, and nozzle exit velocity profiles have been determined for two of the three conditions using 1-D laser Doppler velocimetry (LDV). The diffusion flame extinction axial velocity profile has been measured, and the local extinction axial strain rate has been determined to be 710 s{sup {minus}1}.

  4. Soot Formation in Laminar Premixed Ethylene/Air Flames at Atmospheric Pressure. Appendix G

    NASA Technical Reports Server (NTRS)

    Xu, F.; Sunderland, P. B.; Faeth, G. M.; Urban, D. L. (Technical Monitor)

    2001-01-01

    Soot formation was studied within laminar premixed ethylene/air flames (C/O ratios of 0.78-0.98) stabilized on a flat-flame burner operating at atmospheric pressure. Measurements included soot volume fractions by both laser extinction and gravimetric methods, temperatures by multiline emission, soot structure by thermophoretic sampling and transmission electron microscopy, major gas species concentrations by sampling and gas chromatography, concentrations of condensable hydrocarbons by gravimetric sampling. and velocities by laser velocimetry. These data were used to find soot surface growth rates and primary soot particle nucleation rates along the axes of the flames. Present measurements of soot surface growth rates were correlated successfully by predictions based on typical hydrogen-abstraction/carbon-addition (HACA) mechanisms of Frenklach and co-workers and Colket and Hall. These results suavest that reduced soot surface growth rates with increasing residence time seen in the present and other similar flames were mainly caused by reduced rates of surface activation due to reduced H atom concentrations as temperatures decrease as a result of radiative heat losses. Primary soot particle nucleation rates exhibited variations with temperature and acetylene concentrations that were similar to recent observations for diffusion flames; however, nucleation rates in the premixed flames were significantly lower than in, the diffusion flames for reasons that still must be explained. Finally, predictions of yields of major gas species based on mechanisms from both Frenklach and co-workers and Leung and Lindstedt were in good agreement with present measurements and suggest that H atom concentrations (relevant to HACA mechanisms) approximate estimates based on local thermodynamic equilibrium in the present flames.

  5. Effects of buoyancy on gas jet diffusion flames

    NASA Technical Reports Server (NTRS)

    Bahadori, M. Yousef; Edelman, Raymond B.

    1993-01-01

    The objective of this effort was to gain a better understanding of the fundamental phenomena involved in laminar gas jet diffusion flames in the absence of buoyancy by studying the transient phenomena of ignition and flame development, (quasi-) steady-state flame characteristics, soot effects, radiation, and, if any, extinction phenomena. This involved measurements of flame size and development, as well as temperature and radiation. Additionally, flame behavior, color, and luminosity were observed and recorded. The tests quantified the effects of Reynolds number, nozzle size, fuel reactivity and type, oxygen concentration, and pressure on flame characteristics. Analytical and numerical modeling efforts were also performed. Methane and propane flames were studied in the 2.2 Second Drop Tower and the 5.18-Second Zero-Gravity Facility of NASA LeRC. In addition, a preliminary series of tests were conducted in the KC-135 research aircraft. Both micro-gravity and normal-gravity flames were studied in this program. The results have provided unique and new information on the behavior and characteristics of gas jet diffusion flames in micro-gravity environments.

  6. FORMATION OF POLYCYCLIC AROMATIC HYDROCARBONS IN AN ATMOSPHERIC PRESSURE ETHYLENE DIFFUSION FLAME. (R825412)

    EPA Science Inventory

    Abstract

    The microstructure of an atmospheric pressure, counterflow, sooting, flat, laminar ethylene diffusion flame has been studied experimentally by withdrawing samples from within the flame using a heated quartz microprobe coupled to an online gas chromatograph/mas...

  7. Effect of cylindrical confinement on the determination of laminar flame speeds using outwardly propagating flames

    SciTech Connect

    Burke, Michael P.; Chen, Zheng; Ju, Yiguang; Dryer, Frederick L.

    2009-04-15

    The effect of nonspherical (i.e. cylindrical) bomb geometry on the evolution of outwardly propagating flames and the determination of laminar flame speeds using the conventional constant-pressure technique is investigated experimentally and theoretically. The cylindrical chamber boundary modifies the propagation rate through the interaction of the wall with the flow induced by thermal expansion across the flame (even with constant pressure), which leads to significant distortion of the flame surface for large flame radii. These departures from the unconfined case, especially the resulting nonzero burned gas velocities, can lead to significant errors in flame speeds calculated using the conventional assumptions, especially for large flame radii. For example, at a flame radius of 0.5 times the wall radius, the flame speed calculated neglecting confinement effects can be low by {proportional_to}15% (even with constant pressure). A methodology to estimate the effect of nonzero burned gas velocities on the measured flame speed in cylindrical chambers is presented. Modeling and experiments indicate that the effect of confinement can be neglected for flame radii less than 0.3 times the wall radius while still achieving acceptable accuracy (within 3%). The methodology is applied to correct the flame speed for nonzero burned gas speeds, in order to extend the range of flame radii useful for flame speed measurements. Under the proposed scaling, the burned gas speed can be well approximated as a function of only flame radius for a given chamber geometry - i.e. the correction function need only be determined once for an apparatus and then it can be used for any mixture. Results indicate that the flow correction can be used to extract flame speeds for flame radii up to 0.5 times the wall radius with somewhat larger, yet still acceptable uncertainties for the cases studied. Flow-corrected burning velocities are measured for hydrogen and syngas mixtures at atmospheric and

  8. On the dynamics of flame edges in diffusion-flame/vortex interactions

    SciTech Connect

    Hermanns, Miguel; Linan, Amable; Vera, Marcos

    2007-04-15

    We analyze the local flame extinction and reignition of a counterflow diffusion flame perturbed by a laminar vortex ring. Local flame extinction leads to the appearance of flame edges separating the burning and extinguished regions of the distorted mixing layer. The dynamics of these edges is modeled based on previous numerical results, with heat release effects fully taken into account, which provide the propagation velocity of triple and edge flames in terms of the upstream unperturbed value of the scalar dissipation. The temporal evolution of the mixing layer is determined using the classical mixture fraction approach, with both unsteady and curvature effects taken into account. Although variable density effects play an important role in exothermic reacting mixing layers, in this paper the description of the mixing layer is carried out using the constant density approximation, leading to a simplified analytical description of the flow field. The mathematical model reveals the relevant nondimensional parameters governing diffusion-flame/vortex interactions and provides the parameter range for the more relevant regime of local flame extinction followed by reignition via flame edges. Despite the simplicity of the model, the results show very good agreement with previously published experimental results. (author)

  9. Radiation from Gas-Jet Diffusion Flames in Microgravity Environments

    NASA Technical Reports Server (NTRS)

    Bahadori, M. Yousef; Edelman, Raymond B.; Sotos, Raymond G.; Stocker, Dennis P.

    1991-01-01

    This paper presents the first demonstration of quantitative flame-radiation measurement in microgravity environments, with the objective of studying the influences and characteristics of radiative transfer on the behavior of gas-jet diffusion flames with possible application to spacecraft fire detection. Laminar diffusion flames of propane, burning in quiescent air at atmospheric pressure, are studied in the 5.18-Second Zero-Gravity Facility of NASA Lewis Research Center. Radiation from these flames is measured using a wide-view angle, thermopile-detector radiometer, and comparisons are made with normal-gravity flames. The results show that the radiation level is significantly higher in microgravity compared to normal-gravity environments due to larger flame size, enhanced soot formation, and entrapment of combustion products in the vicinity of the flame. These effects are the consequences of the removal of buoyancy which makes diffusion the dominant mechanism of transport. The results show that longer test times may be needed to reach steady state in microgravity environments.

  10. Numerical Simulation And Experimental Investigation Of The Lift-Off And Blowout Of Enclosed Laminar Flames

    NASA Technical Reports Server (NTRS)

    Venuturmilli, Rajasekhar; Zhang, Yong; Chen, Lea-Der

    2003-01-01

    Enclosed flames are found in many industrial applications such as power plants, gas-turbine combustors and jet engine afterburners. A better understanding of the burner stability limits can lead to development of combustion systems that extend the lean and rich limits of combustor operations. This paper reports a fundamental study of the stability limits of co-flow laminar jet diffusion flames. A numerical study was conducted that used an adaptive mesh refinement scheme in the calculation. Experiments were conducted in two test rigs with two different fuels and diluted with three inert species. The numerical stability limits were compared with microgravity experimental data. Additional normal-gravity experimental results were also presented.

  11. Oxygen and Fuel Jet Diffusion Flame Studies in Microgravity Motivated by Spacecraft Oxygen Storage Fire Safety

    NASA Technical Reports Server (NTRS)

    Sunderland, P. B.; Yuan, Z.-G.; Krishnan, S. S.; Abshire, J. M.; Gore, J. P.

    2003-01-01

    Owing to the absence of past work involving flames similar to the Mir fire namely oxygen-enhanced, inverse gas-jet diffusion flames in microgravity the objectives of this work are as follows: 1. Observe the effects of enhanced oxygen conditions on laminar jet diffusion flames with ethane fuel. 2. Consider both earth gravity and microgravity. 3. Examine both normal and inverse flames. 4. Compare the measured flame lengths and widths with calibrated predictions of several flame shape models. This study expands on the work of Hwang and Gore which emphasized radiative emissions from oxygen-enhanced inverse flames in earth gravity, and Sunderland et al. which emphasized the shapes of normal and inverse oxygen-enhanced gas-jet diffusion flames in microgravity.

  12. Computation of Steady and Unsteady Laminar Flames: Theory

    NASA Technical Reports Server (NTRS)

    Hagstrom, Thomas; Radhakrishnan, Krishnan; Zhou, Ruhai

    1999-01-01

    In this paper we describe the numerical analysis underlying our efforts to develop an accurate and reliable code for simulating flame propagation using complex physical and chemical models. We discuss our spatial and temporal discretization schemes, which in our current implementations range in order from two to six. In space we use staggered meshes to define discrete divergence and gradient operators, allowing us to approximate complex diffusion operators while maintaining ellipticity. Our temporal discretization is based on the use of preconditioning to produce a highly efficient linearly implicit method with good stability properties. High order for time accurate simulations is obtained through the use of extrapolation or deferred correction procedures. We also discuss our techniques for computing stationary flames. The primary issue here is the automatic generation of initial approximations for the application of Newton's method. We use a novel time-stepping procedure, which allows the dynamic updating of the flame speed and forces the flame front towards a specified location. Numerical experiments are presented, primarily for the stationary flame problem. These illustrate the reliability of our techniques, and the dependence of the results on various code parameters.

  13. Physical characterization of laminar spray flames in the pressure range 0.1-0.9 MPa

    SciTech Connect

    Russo, Stefano; Gomez, Alessandro

    2006-04-15

    An experimental study is reported on the physical characterization of the structure of ethanol/argon/oxygen coflow laminar spray diffusion flames in the pressure range 0.1-0.9 MPa. Diagnostic techniques include phase Doppler anemometry to measure the droplet size distribution and the axial and radial velocity components of the droplets. The gas-phase velocity is determined using measurements from the smallest (low Stokes number) droplets and is corrected for thermophoretic effects. Temperature information is obtained using thin-film pyrometry combined with an infrared camera. All flames present a cold inner core, in which little or no vaporization takes place, surrounded by an envelope flame buried in a thermal boundary layer, where most of the droplet evaporation occurs. The thickness of this thermal boundary layer scales with the inverse of the Peclet number. Especially near the base of the flame, photographic evidence of streaks, which in some case even reveal the presence of soot, suggests that some droplets survive the common envelope flame and burn isolated on the oxidizer side in a mixed regime of internal/external group combustion. The reconstruction of the entire droplet vaporization history confirms this evidence quantitatively. A criterion for droplet survival beyond the envelope flame based on the critical value of a suitably defined vaporization Damkohler number is proposed. The scaling and self-similar behavior of the investigated flames suggest that a mixed regime is established, with a momentum-controlled cold core and a buoyancy-controlled high-temperature boundary layer, the thickness of which varies significantly with pressure, as expected from Peclet number scaling. The growth of this layer and the thickness of the vaporization region are reduced at pressures above atmospheric because of density effects on thermal diffusivity. Some aspects of the design of the combustion chamber and of the atomizer system are discussed in detail since they are

  14. Buoyancy Effects on Flow Transition in Hydrogen Gas Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Albers, Burt W.; Agrawal, Ajay K.; Griffin, DeVon (Technical Monitor)

    2000-01-01

    Experiments were performed in earth-gravity to determine how buoyancy affected transition from laminar to turbulent flow in hydrogen gas jet diffusion flames. The jet exit Froude number characterizing buoyancy in the flame was varied from 1.65 x 10(exp 5) to 1.14 x 10(exp 8) by varying the operating pressure and/or burner inside diameter. Laminar fuel jet was discharged vertically into ambient air flowing through a combustion chamber. Flame characteristics were observed using rainbow schlieren deflectometry, a line-of-site optical diagnostic technique. Results show that the breakpoint length for a given jet exit Reynolds number increased with increasing Froude number. Data suggest that buoyant transitional flames might become laminar in the absence of gravity. The schlieren technique was shown as effective in quantifying the flame characteristics.

  15. Oscillatory Extinction Of Spherical Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Law, C. K.; Yoo, S. W.; Christianson, E. W.

    2003-01-01

    Since extinction has been observed in an oscillatory manner in Le greater than 1 premixed flames, it is not unreasonable to expect that extinction could occur in an unsteady manner for diffusion flames. Indeed, near-limit oscillations have been observed experimentally under microgravity conditions for both candle flames and droplet flames. Furthermore, the analysis of Cheatham and Matalon on the unsteady behavior of diffusion flames with heat loss, identified an oscillatory regime which could be triggered by either a sufficiently large Lewis number (even without heat loss) or an appreciable heat loss (even for Le=1). In light of these recent understanding, the present investigation aims to provide a well-controlled experiment that can unambiguously demonstrate the oscillation of diffusion flames near both the transport- and radiation-induced limits. That is, since candle and jet flames are stabilized through flame segments that are fundamentally premixed in nature, and since premixed flames are prone to oscillate, there is the possibility that the observed oscillation of these bulk diffusion flames could be triggered and sustained by the oscillation of the premixed flame segments. Concerning the observed oscillatory droplet extinction, it is well-known that gas-phase oscillation in heterogeneous burning can be induced by and is thereby coupled with condensed-phase unsteadiness. Consequently, a convincing experiment on diffusion flame oscillation must exclude any ingredients of premixed flames and other sources that may either oscillate themselves or promote the oscillation of the diffusion flame. The present experiment on burner-generated spherical flames with a constant reactant supply endeavored to accomplish this goal. The results are further compared with those from computational simulation for further understanding and quantification of the flame dynamics and extinction.

  16. Structure and Stability of Burke-Schumann Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Lee, Yong G.; Chen, Lea-Der; Brooker, John E.; Stocker, Dennis P.

    1997-01-01

    The general goal of this NASA Grant is twofold: to improve our understanding of (1) the influence of buoyancy on the stability and structure of Burke-Schumann type diffusion flames, and (2) the effects of buoyancy on vortex-flame interactions in co-flow diffusion flames. A numerical code with a higher order accuracy for spatial discretization is developed in this project for simulation of time-dependent diffusion flames by Sheu and Sheu and Chen, and an extended reduced mechanism is incorporated for prediction of methane oxidation and NO(x)(NO, NO2, and N2O) formation and emission from methane Burke-Schumann diffusion flame (BSDF) as reported in Sheu, and Sheu and Chen. Initial investigation of vortex and flame interaction within the context of fast chemistry is reported. Experiments are conducted in reduced pressure to study the lift-off and stabilization of methane-fueled BSDF in reduced buoyancy environments due to reduced pressure. Measurements of temperature and species concentrations are made in normal and reduced pressure environments to study the effects of buoyancy on the structure of BSDF, and will be reported in this paper. To study the buoyancy effects on the lift-off and stabilization of methane-fueled jet diffusion flames in coflowing air, a glovebox investigation, Enclosed Laminar Flames (ELF), has been proposed and approved for space-based testing on the fourth United States Microgravity Payload (USMP-4) mission, scheduled for October 1997. A brief description of the ELF investigation is also presented.

  17. 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

  18. Soot and Radiation Measurements in Microgravity Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Ku, Jerry C.

    1996-01-01

    The subject of soot formation and radiation heat transfer in microgravity jet diffusion flames is important not only for the understanding of fundamental transport processes involved but also for providing findings relevant to spacecraft fire safety and soot emissions and radiant heat loads of combustors used in air-breathing propulsion systems. Our objectives are to measure and model soot volume fraction, temperature, and radiative heat fluxes in microgravity jet diffusion flames. For this four-year project, we have successfully completed three tasks, which have resulted in new research methodologies and original results. First is the implementation of a thermophoretic soot sampling technique for measuring particle size and aggregate morphology in drop-tower and other reduced gravity experiments. In those laminar flames studied, we found that microgravity soot aggregates typically consist of more primary particles and primary particles are larger in size than those under normal gravity. Comparisons based on data obtained from limited samples show that the soot aggregate's fractal dimension varies within +/- 20% of its typical value of 1.75, with no clear trends between normal and reduced gravity conditions. Second is the development and implementation of a new imaging absorption technique. By properly expanding and spatially-filtering the laser beam to image the flame absorption on a CCD camera and applying numerical smoothing procedures, this technique is capable of measuring instantaneous full-field soot volume fractions. Results from this technique have shown the significant differences in local soot volume fraction, smoking point, and flame shape between normal and reduced gravity flames. We observed that some laminar flames become open-tipped and smoking under microgravity. The third task we completed is the development of a computer program which integrates and couples flame structure, soot formation, and flame radiation analyses together. We found good

  19. 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.

  20. Radiant Extinction of Gaseous Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Berhan, Sean; Atreya, Arvind; Everest, David; Sacksteder, Kurt R.

    1999-01-01

    The absence of buoyancy-induced flows in microgravity (mu-g) and the resulting increase in the reactant residence time significantly alters the fundamentals of many combustion processes. Substantial differences between normal gravity (ng) and mu-g flames have been reported in experiments on candle flames, flame spread over solids, droplet combustion, and others. These differences are more basic than just in the visible flame shape. Longer residence times and higher concentration of combustion products in the flame zone create a thermochemical environment that changes the flame chemistry and the heat and mass transfer processes. Processes such as flame radiation, that are often ignored in ng, become very important and sometimes even controlling. Furthermore, microgravity conditions considerably enhance flame radiation by: (1) the build-up of combustion products in the high-temperature reaction zone which increases the gas radiation; and (2) longer residence times make conditions appropriate for substantial amounts of soot to form which is also responsible for radiative heat loss. Thus, it is anticipated that radiative heat loss may eventually extinguish the "weak" (low burning rate per unit flame area) mu-g diffusion flame. Yet, space shuttle experiments on candle flames show that in an infinite ambient atmosphere, the hemispherical candle flame in mu-g will burn indefinitely. This may be because of the coupling between the fuel production rate and the flame via the heat-feedback mechanism for candle flames, flames over solids and fuel droplet flames. Thus, to focus only on the gas-phase phenomena leading to radiative extinction, aerodynamically stabilized gaseous diffusion flames are examined. This enables independent control of the fuel flow rate to help identify conditions under which radiative extinction occurs. Also, spherical geometry is chosen for the mu-g experiments and modeling because: (1) It reduces the complexity by making the problem one

  1. Unsteady Spherical Diffusion Flames in Microgravity

    NASA Technical Reports Server (NTRS)

    Atreya, Arvind; Berhan, S.; Chernovsky, M.; Sacksteder, Kurt R.

    2001-01-01

    The absence of buoyancy-induced flows in microgravity (mu-g) and the resulting increase in the reactant residence time significantly alters the fundamentals of many combustion processes. Substantial differences between normal gravity (ng) and (mu-g) flames have been reported in experiments on candle flames, flame spread over solids, droplet combustion, and others. These differences are more basic than just in the visible flame shape. Longer residence times and higher concentration of combustion products in the flame zone create a thermochemical environment that changes the flame chemistry and the heat and mass transfer processes. Processes such as flame radiation, that are often ignored in ng, become very important and sometimes even controlling. Furthermore, microgravity conditions considerably enhance flame radiation by: (i) the build-up of combustion products in the high-temperature reaction zone which increases the gas radiation, and (ii) longer residence times make conditions appropriate for substantial amounts of soot to form which is also responsible for radiative heat loss. Thus, it is anticipated that radiative heat loss may eventually extinguish the "weak" (low burning rate per unit flame area) mu-g diffusion flame. Yet, space shuttle experiments on candle flames show that in an infinite ambient atmosphere, the hemispherical candle flame in mu-g will burn indefinitely. This may be because of the coupling between the fuel production rate and the flame via the heat-feedback mechanism for candle flames, flames over solids and fuel droplet flames. Thus, to focus only on the gas-phase phenomena leading to radiative extinction, aerodynamically stabilized gaseous diffusion flames are examined. This enables independent control of the fuel flow rate to help identify conditions under which radiative extinction occurs. Also, spherical geometry is chosen for the mu-g experiments and modeling because: (i) It reduces the complexity by making the problem one

  2. Radiant Extinction Of Gaseous Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Berhan, S.; Chernovsky, M.; Atreya, A.; Baum, Howard R.; Sacksteder, Kurt R.

    2003-01-01

    The absence of buoyancy-induced flows in microgravity (mu:g) and the resulting increase in the reactant residence time significantly alters the fundamentals of many combustion processes. Substantial differences between normal gravity (ng) and :g flames have been reported in experiments on candle flames [1, 2], flame spread over solids [3, 4], droplet combustion [5,6], and others. These differences are more basic than just in the visible flame shape. Longer residence times and higher concentration of combustion products in the flame zone create a thermochemical environment that changes the flame chemistry and the heat and mass transfer processes. Processes such as flame radiation, that are often ignored in ng, become very important and sometimes even controlling. Furthermore, microgravity conditions considerably enhance flame radiation by: (i) the build-up of combustion products in the high-temperature reaction zone which increases the gas radiation, and (ii) longer residence times make conditions appropriate for substantial amounts of soot to form which is also responsible for radiative heat loss. Thus, it is anticipated that radiative heat loss may eventually extinguish the Aweak@ (low burning rate per unit flame area) :g diffusion flame. Yet, space shuttle experiments on candle flames show that in an infinite ambient atmosphere, the hemispherical candle flame in :g will burn indefinitely [1]. This may be because of the coupling between the fuel production rate and the flame via the heat-feedback mechanism for candle flames, flames over solids and fuel droplet flames. Thus, to focus only on the gas-phase phenomena leading to radiative extinction, aerodynamically stabilized gaseous diffusion flames are examined. This enables independent control of the fuel flow rate to help identify conditions under which radiative extinction occurs. Also, spherical geometry is chosen for the :g experiments and modeling because: (i) It reduces the complexity by making the problem

  3. Experimental study of Markstein number effects on laminar flamelet velocity in turbulent premixed flames

    SciTech Connect

    Weiss, M.; Zarzalis, N.; Suntz, R.

    2008-09-15

    Effects of turbulent flame stretch on mean local laminar burning velocity of flamelets, u{sub n}, were investigated experimentally in an explosion vessel at normal temperature and pressure. In this context, the wrinkling, A{sub t}/A{sub l}, and the burning velocity, u{sub t}, of turbulent flames were measured simultaneously. With the flamelet assumption the mean local laminar burning velocity of flamelets, u{sub n}=u{sub t} x (A{sub t}/A{sub l}){sup -1}, was calculated for different turbulence intensities. The results were compared to the influence of stretch on spherically expanding laminar flames. For spherically expanding laminar flames the stretched laminar burning velocity, u{sub n}, varied linearly with the Karlovitz stretch factor, yielding Markstein numbers that depend on the mixture composition. Six different mixtures with positive and negative Markstein numbers were investigated. The measurements of the mean local laminar burning velocity of turbulent flamelets were used to derive an efficiency parameter, I, which reflects the impact of the Markstein number and turbulent flame stretch - expressed by the turbulent Karlovitz stretch factor - on the local laminar burning velocity of flamelets. The results showed that the efficiency is reduced with increasing turbulence intensity and the reduction can be correlated to unsteady effects. (author)

  4. Radiant extinction of gaseous diffusion flames

    NASA Technical Reports Server (NTRS)

    Atreya, Arvind; Agrawal, Sanjay; Shamim, Tariq; Pickett, Kent; Sacksteder, Kurt R.; Baum, Howard R.

    1995-01-01

    The absence of buoyancy-induced flows in microgravity significantly alters the fundamentals of many combustion processes. Substantial differences between normal-gravity and microgravity flames have been reported during droplet combustion, flame spread over solids, candle flames, and others. These differences are more basic than just in the visible flame shape. Longer residence time and higher concentration of combustion products create a thermochemical environment which changes the flame chemistry. Processes such as flame radiation, that are often ignored under normal gravity, become very important and sometimes even controlling. This is particularly true for conditions at extinction of a microgravity diffusion flame. Under normal-gravity, the buoyant flow, which may be characterized by the strain rate, assists the diffusion process to transport the fuel and oxidizer to the combustion zone and remove the hot combustion products from it. These are essential functions for the survival of the flame which needs fuel and oxidizer. Thus, as the strain rate is increased, the diffusion flame which is 'weak' (reduced burning rate per unit flame area) at low strain rates is initially 'strengthened' and eventually it may be 'blown-out'. Most of the previous research on diffusion flame extinction has been conducted at the high strain rate 'blow-off' limit. The literature substantially lacks information on low strain rate, radiation-induced, extinction of diffusion flames. At the low strain rates encountered in microgravity, flame radiation is enhanced due to: (1) build-up of combustion products in the flame zone which increases the gas radiation, and (2) low strain rates provide sufficient residence time for substantial amounts of soot to form which further increases the flame radiation. It is expected that this radiative heat loss will extinguish the already 'weak' diffusion flame under certain conditions. Identifying these conditions (ambient atmosphere, fuel flow rate, fuel

  5. Turbulent Flame Processes Via Diffusion Flame-Vortex Ring Interactions

    NASA Technical Reports Server (NTRS)

    Dahm, Werner J. A.; Chen, Shin-Juh; Silver, Joel A.; Piltch, Nancy D.; VanderWal, Randall L.

    2001-01-01

    Flame-vortex interactions are canonical configurations that can be used to study the underlying processes occurring in turbulent reacting flows. This configuration contains many of the fundamental aspects of the coupling between fluid dynamics and combustion that could be investigated with more controllable conditions than are possible under direct investigations of turbulent flames. Diffusion flame-vortex ring interaction contains many of the fundamental elements of flow, transport, combustion, and soot processes found in turbulent diffusion flames. Some of these elements include concentrated vorticity, entrainment and mixing, strain and nonequilibrium phenomena, diffusion and differential diffusion, partial premixing and diluent effects, soot formation and oxidation, and heat release effects. Such simplified flowfield allows the complex processes to be examined more closely and yet preserving the physical processes present in turbulent reacting flows. Furthermore, experimental results from the study of flame-vortex interactions are useful for the validation of numerical simulations and more importantly to deepen our understanding of the fundamental processes present in reacting flows. Experimental and numerical results obtained under microgravity conditions of the diffusion flame-vortex ring interaction are summarized in this paper. Results are obtained using techniques that include Flame Luminosity Imaging (FLI), Laser Soot-Mie Scattering (LSMS), Computational Fluid Dynamics and Combustion (CFDC), and Diode Laser Spectroscopy/Iterative Temperature with Assumed Chemistry (DLS/ITAC).

  6. Soot formation and radiation in turbulent jet diffusion flames under normal and reduced gravity conditions

    NASA Technical Reports Server (NTRS)

    Ku, Jerry C.; Tong, LI; Sun, Jun; Greenberg, Paul S.; Griffin, Devon W.

    1993-01-01

    Most practical combustion processes, as well as fires and explosions, exhibit some characteristics of turbulent diffusion flames. For hydrocarbon fuels, the presence of soot particles significantly increases the level of radiative heat transfer from flames. In some cases, flame radiation can reach up to 75 percent of the heat release by combustion. Laminar diffusion flame results show that radiation becomes stronger under reduced gravity conditions. Therefore, detailed soot formation and radiation must be included in the flame structure analysis. A study of sooting turbulent diffusion flames under reduced-gravity conditions will not only provide necessary information for such practical issues as spacecraft fire safety, but also develop better understanding of fundamentals for diffusion combustion. In this paper, a summary of the work to date and of future plans is reported.

  7. Explosion bomb measurements of ethanol-air laminar gaseous flame characteristics at pressures up to 1.4 MPa

    SciTech Connect

    Bradley, D.; Lawes, M.; Mansour, M.S.

    2009-07-15

    The principal burning characteristics of a laminar flame comprise the fuel vapour pressure, the laminar burning velocity, ignition delay times, Markstein numbers for strain rate and curvature, the stretch rates for the onset of flame instabilities and of flame extinction for different mixtures. With the exception of ignition delay times, measurements of these are reported and discussed for ethanol-air mixtures. The measurements were in a spherical explosion bomb, with central ignition, in the regime of a developed stable, flame between that of an under or over-driven ignition and that of an unstable flame. Pressures ranged from 0.1 to 1.4 MPa, temperatures from 300 to 393 K, and equivalence ratios were between 0.7 and 1.5. It was important to ensure the relatively large volume of ethanol in rich mixtures at high pressures was fully evaporated. The maximum pressure for the measurements was the highest compatible with the maximum safe working pressure of the bomb. Many of the flames soon became unstable, due to Darrieus-Landau and thermo-diffusive instabilities. This effect increased with pressure and the flame wrinkling arising from the instabilities enhanced the flame speed. Both the critical Peclet number and the, more rational, associated critical Karlovitz stretch factor were evaluated at the onset of the instability. With increasing pressure, the onset of flame instability occurred earlier. The measured values of burning velocity are expressed in terms of their variations with temperature and pressure, and these are compared with those obtained by other researchers. Some comparisons are made with the corresponding properties for iso-octane-air mixtures. (author)

  8. High-pressure soot formation and diffusion flame extinction characteristics of gaseous and liquid fuels

    NASA Astrophysics Data System (ADS)

    Karatas, Ahmet Emre

    High-pressure soot formation and flame stability characteristics were studied experimentally in laminar diffusion flames. For the former, radially resolved soot volume fraction and temperature profiles were measured in axisymmetric co-flow laminar diffusion flames of pre-vaporized n-heptane-air, undiluted ethylene-air, and nitrogen and carbon dioxide diluted ethylene-air at elevated pressures. Abel inversion was used to re-construct radially resolved data from the line-of-sight spectral soot emission measurements. For the latter, flame extinction strain rate was measured in counterflow laminar diffusion flames of C1-4 alcohols and hydrocarbon fuels of n-heptane, n-octane, iso-octane, toluene, Jet-A, and biodiesel. The luminous flame height, as marked by visible soot radiation, of the nitrogen- and helium-diluted n-heptane and nitrogen- and carbon dioxide-diluted ethylene flames stayed constant at all pressures. In pure ethylene flames, flame heights initially increased with pressure, but changed little above 5 atm. The maximum soot yield as a function of pressure in nitrogen-diluted n-heptane diffusion flames indicate that n-heptane flames are slightly more sensitive to pressure than gaseous alkane hydrocarbon flames at least up to 7 atm. Ethylene's maximum soot volume fractions were much higher than those of ethane and n-heptane diluted with nitrogen (fuel to nitrogen mass flow ratio is about 0.5). Pressure dependence of the peak carbon conversion to soot, defined as the percentage of fuel's carbon content converted to soot, was assessed and compared to previous measurements with other gaseous fuels. Maximum soot volume fractions were consistently lower in carbon dioxide-diluted flames between 5 and 15 atm but approached similar values to those in nitrogen-diluted flames at 20 atm. This observation implies that the chemical soot suppression effect of carbon dioxide, previously demonstrated at atmospheric pressure, is also present at elevated pressures up to 15 atm

  9. Numerical investigations of gaseous spherical diffusion flames

    NASA Astrophysics Data System (ADS)

    Lecoustre, Vivien R.

    Spherical diffusion flames have several unique characteristics that make them attractive from experimental and theoretical perspectives. They can be modeled with one spatial dimension, which frees computational resources for detailed chemistry, transport, and radiative loss models. This dissertation is a numerical study of two classes of spherical diffusion flames: hydrogen micro-diffusion flames, emphasizing kinetic extinction, and ethylene diffusion flames, emphasizing sooting limits. The flames were modeled using a one-dimensional, time-accurate diffusion flame code with detailed chemistry and transport. Radiative losses from products were modeled using a detailed absorption/emission statistical narrow band model and the discrete ordinates method. During this work the code has been enhanced by the implementation of a soot formation/oxidation model using the method of moments. Hydrogen micro-diffusion flames were studied experimentally and numerically. The experiments involved gas jets of hydrogen. At their quenching limits, these flames had heat release rates of 0.46 and 0.25 W in air and in oxygen, respectively. These are the weakest flames ever observed. The modeling results confirmed the quenching limits and revealed high rates of reactant leakage near the limits. The effects of the burner size and mass flow rate were predicted to have a significant impact on the flame chemistry and species distribution profiles, favoring kinetic extinction. Spherical ethylene diffusion flames at their sooting limits were also examined. Seventeen normal and inverse spherical flames were considered. Initially sooty, these flames were experimentally observed to reach their sooting limits 2 s after ignition. Structure of the flames at 2 s was considered, with an emphasis on the relationships among local temperature, carbon to oxygen atom ratio (C/O), and scalar dissipation rate. A critical C/O ratio was identified, along with two different sooting limit regimes. Diffusion flames

  10. Effect of pressure on structure and NO sub X formation in CO-air diffusion flames

    NASA Technical Reports Server (NTRS)

    Maahs, H. G.; Miller, I. M.

    1979-01-01

    A study was made of nitric oxide formation in a laminar CO-air diffusion flame over a pressure range from 1 to 50 atm. The carbon monoxide (CO) issued from a 3.06 mm diameter port coaxially into a coflowing stream of air confined within a 20.5 mm diameter chimney. Nitric oxide concentrations from the flame were measured at two carbon monoxide (fuel) flow rates: 73 standard cubic/min and 146 sccm. Comparison of the present data with data in the literature for a methane-air diffusion flame shows that for flames of comparable flame height (8 to 10 mm) and pseudoequivalence ratio (0.162), the molar emission index of a CO-air flame is significantly greater than that of a methane-air flame.

  11. Modeling of hydrogen-air diffusion flame

    NASA Technical Reports Server (NTRS)

    Isaac, K. M.

    1989-01-01

    An analytical and computational study of opposed jet diffusion flame for the purpose of understanding the effects of contaminants in the reactants and thermal diffusion of light species on extinction and reignition of diffusion flames is in progress. The methodologies that have been attempted so far are described. Results using a simple, one-step reaction for the hydrogen-air counterflow diffusion flame are presented. These results show the correct trends in the profiles of chemical species and temperature. The extinction limit can be clearly seen in the plot of temperature vs. Damkohler number.

  12. 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.

  13. Modeling of hydrogen-air diffusion flame

    NASA Technical Reports Server (NTRS)

    Isaac, K. M.

    1988-01-01

    Work performed during the first six months of the project duration for NASA Grant (NAG-1-861) is reported. An analytical and computational study of opposed jet diffusion flame for the purpose of understanding the effects of contaminants in the reactants and thermal diffusion of light species on extinction and reignition of diffusion flames is in progress. The methodologies attempted so far are described.

  14. 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.

  15. Reaction Kernel Structure of a Slot Jet Diffusion Flame in Microgravity

    NASA Technical Reports Server (NTRS)

    Takahashi, F.; Katta, V. R.

    2001-01-01

    Diffusion flame stabilization in normal earth gravity (1 g) has long been a fundamental research subject in combustion. Local flame-flow phenomena, including heat and species transport and chemical reactions, around the flame base in the vicinity of condensed surfaces control flame stabilization and fire spreading processes. Therefore, gravity plays an important role in the subject topic because buoyancy induces flow in the flame zone, thus increasing the convective (and diffusive) oxygen transport into the flame zone and, in turn, reaction rates. Recent computations show that a peak reactivity (heat-release or oxygen-consumption rate) spot, or reaction kernel, is formed in the flame base by back-diffusion and reactions of radical species in the incoming oxygen-abundant flow at relatively low temperatures (about 1550 K). Quasi-linear correlations were found between the peak heat-release or oxygen-consumption rate and the velocity at the reaction kernel for cases including both jet and flat-plate diffusion flames in airflow. The reaction kernel provides a stationary ignition source to incoming reactants, sustains combustion, and thus stabilizes the trailing diffusion flame. In a quiescent microgravity environment, no buoyancy-induced flow exits and thus purely diffusive transport controls the reaction rates. Flame stabilization mechanisms in such purely diffusion-controlled regime remain largely unstudied. Therefore, it will be a rigorous test for the reaction kernel correlation if it can be extended toward zero velocity conditions in the purely diffusion-controlled regime. The objectives of this study are to reveal the structure of the flame-stabilizing region of a two-dimensional (2D) laminar jet diffusion flame in microgravity and develop a unified diffusion flame stabilization mechanism. This paper reports the recent progress in the computation and experiment performed in microgravity.

  16. Ammonia conversion and NOx formation in laminar coflowing nonpremixed methane-air flames

    SciTech Connect

    Sullivan, Neal; Jensen, Anker; Glarborg, Peter; Day, Marcus S.; Grcar, Joseph F.; Bell, John B.; Pope, Christopher J.; Kee, Robert J.

    2002-01-07

    This paper reports on a combined experimental and modeling investigation of NOx formation in nitrogen-diluted laminar methane diffusion flames seeded with ammonia. The methane-ammonia mixture is a surrogate for biomass fuels which contain significant fuel-bound nitrogen. The experiments use flue-gas sampling to measure the concentration of stable species in the exhaust gas, including NO, O2, CO, and CO2. The computations evolve a two-dimensional low Mach number model using a solution-adaptive projection algorithm to capture fine-scale features of the flame. The model includes detailed thermodynamics and chemical kinetics, differential diffusion, buoyancy, and radiative losses. The model shows good agreement with the measurements over the full range of experimental NH3 seeding amounts. As more NH3 is added, a greater percentage is converted to N2 rather than to NO. The simulation results are further analyzed to trace the changes in NO formation mechanisms with increasing amounts of ammonia in the fuel.

  17. NO sub x destruction in diffusion flame environments

    SciTech Connect

    Wendt, J.O.L.; Lin, W.C.; Mwabe, P.

    1991-07-31

    This research is concerned with reburning, which is an NO{sub x} abatement technique involving the injection of secondary fuel into the post flame of a furnace. The specific objectives of this research are to determine whether heterogeneities inherent in diffusion flame environments can be exploited to achieve greater reductions in NO than can be achieved in premixed systems. The research project described here is but a first step to explore this question, and should be viewed more as a screening study rather than as completed research, the results of which are completely understood. The problem was attacked through both experimentation and theoretical modeling. Experiments employed a bench scale, laminar, counter-flow, diffusion flame, which was designed to simulate the stretched diffusion flamelets that arise at the interface between turbulent fuel and oxidant jets. Data gathered were of two types. First, NO destruction from the integral system was investigated through parametric studies in which only inlet and outlet species and flows were measured. Three different experimental configurations were examined, under a wide range of operating conditions, with emphasis on reburning under overall fuel lean conditions. Second, in order to gain insight into the observed phenomena, detailed axial profiles of major and minor species were measured for one configurations. Theoretical modeling consisted of computer simulations which attempt to describe the experimental configuration as an infinitely wide flat flame. This yielded predictions of axial profiles but was not readily adaptable for (integral) predictions of total NO destroyed in our flame. The model employed detailed chemical reactions, and was also used to determine regimes in which ignition occurs under diffusion flame conditions. 30 refs., 31 figs., 19 tabs.

  18. Analysis of the flamelet concept in the numerical simulation of laminar partially premixed flames

    SciTech Connect

    Consul, R.; Oliva, A.; Perez-Segarra, C.D.; Carbonell, D.; de Goey, L.P.H.

    2008-04-15

    The aim of this work is to analyze the application of flamelet models based on the mixture fraction variable and its dissipation rate to the numerical simulation of partially premixed flames. Although the main application of these models is the computation of turbulent flames, this work focuses on the performance of flamelet concept in laminar flame simulations removing, in this way, turbulence closure interactions. A well-known coflow methane/air laminar flame is selected. Five levels of premixing are taken into account from an equivalence ratio {phi}={infinity} (nonpremixed) to {phi}=2.464. Results obtained using the flamelet approaches are compared to data obtained from the detailed solution of the complete transport equations using primitive variables. Numerical simulations of a counterflow flame are also presented to support the discussion of the results. Special emphasis is given to the analysis of the scalar dissipation rate modeling. (author)

  19. Carbon Monoxide and Soot Formation in Inverse Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Blevins, L. G.; Mulholland, G. W.; Davis, R. W.

    1999-01-01

    The objective of this project is to study carbon monoxide (CO) and soot formation in laminar, inverse diffusion flames (IDFs). The IDF is used because it is a special case of underventilated combustion. The microgravity environment is crucial for this study because buoyancy-induced instabilities impede systematic variation of IDF operating conditions in normal gravity. The project described in this paper is just beginning, and no results are available. Hence, the goals of this paper are to establish the motivation for the research, to review the IDF literature, and to briefly introduce the experimental and computational plan for the research.

  20. Pulsed Turbulent Diffusion Flames in a Coflow

    NASA Astrophysics Data System (ADS)

    Usowicz, James E.; Hermanson, James C.; Johari, Hamid

    2000-11-01

    Fully modulated diffusion flames were studied experimentally in a co-flow combustor using unheated ethylene fuel at atmospheric pressure. A fast solenoid valve was used to fully modulate (completely shut-off) the fuel flow. The fuel was released from a 2 mm diameter nozzle with injection times ranging from 2 to 750 ms. The jet exit Reynolds number was 2000 to 10,000 with a co-flow air velocity of up to 0.02 times the jet exit velocity. Establishing the effects of co-flow for the small nozzle and short injection times is required for future tests of pulsed flames under microgravity conditions. The very short injection times resulted in compact, burning puffs. The compact puffs had a mean flame length as little as 20flame for the same Reynolds number. As the injection time and fuel volume increased, elongated flames resembling starting jets resulted with a flame length comparable to that of a steady flame. For short injection times, the addition of an air co-flow resulted in an increase in flame length of nearly 50flames with longer injection times was correspondingly smaller. The effects of interaction of successive pulses on the flame length were most pronounced for the compact puffs. The emissions of unburned hydrocarbon and NOx from the pulsed flames were examined.

  1. 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.

  2. Conditions for a split diffusion flame

    SciTech Connect

    Hertzberg, J.R.

    1997-05-01

    An unusual phenomenon has been observed in a methane jet diffusion flame subjected to axial acoustic forcing. At specific excitation frequencies and amplitudes, the driven flame splits into a central jet and one or two side jets. The splitting is accompanied by a partial detachment of the flame from the nozzle exit, a shortening of the flame by a factor of 2, and a change from the common yellow color of soot radiation to a clear blue flame. Such a phenomenon may be useful for the control of soot production or product species. The splitting is intermittent in time, bifurcating between the split flame and an ordinary single jet diffusion flame. The experiment consists of an unconfined axisymmetric methane jet formed by a short length of 0.4 cm diameter pipe. The pipe is connected to a large plenum surrounding a bass reflex loudspeaker enclosure that provides the excitation. Conditions producing split and bifurcated flames are presented. The drive frequencies required to cause bifurcation correspond to the first two peaks in the system`s frequency response curve. Bifurcating behavior was observed at a wide range of flow rates, ranging from very small flames of Reynolds number 240 up to turbulent lift-off, at Re = 1,000, based on the inner pipe diameter. It was not sensitive to nozzle length, but the details of the nozzle tip, such as orifice or pipe geometry, can affect the frequency range.

  3. Nonpremixed ignition, laminar flame propagation, and mechanism reduction of n-butanol, iso-butanol, and methyl butanoate

    SciTech Connect

    Lu, Wei; Kelley, A. P.; Law, C. K.

    2011-01-01

    The non-premixed ignition temperature of n-butanol (CH{sub 3}CH{sub 2}CH{sub 2}CH{sub 2}OH), iso-butanol ((CH{sub 3}){sub 2}CHCH{sub 2}OH) and methyl butanoate (CH{sub 3}CH{sub 2}CH{sub 2}COOCH{sub 3}) was measured in a liquid pool assembly by heated oxidizer in a stagnation flow for system pressures of 1 and 3 atm. In addition, the stretch-corrected laminar flame speeds of mixtures of air–n-butanol/iso-butanol/methyl butanoate were determined from the outwardly propagating spherical flame at initial pressures of up to 2 atm, for an extensive range of equivalence ratio. The ignition temperature and laminar flame speeds of n-butanol and methyl butanoate were computationally simulated with three recently developed kinetic mechanisms in the literature. Dominant reaction pathways to ignition and flame propagation were identified and discussed through a chemical explosive mode analysis (CEMA) and sensitivity analysis. The detailed models were further reduced through a series of systematic strategies. The reduced mechanisms provided excellent agreement in both homogeneous and diffusive combustion environments and greatly improved the computation efficiency.

  4. Edge Diffusion Flame Propagation and Stabilization Studied

    NASA Technical Reports Server (NTRS)

    Takahashi, Fumiaki; Katta, Viswanath R.

    2004-01-01

    In most practical combustion systems or fires, fuel and air are initially unmixed, thus forming diffusion flames. As a result of flame-surface interactions, the diffusion flame often forms an edge, which may attach to burner walls, spread over condensed fuel surfaces, jump to another location through the fuel-air mixture formed, or extinguish by destabilization (blowoff). Flame holding in combustors is necessary to achieve design performance and safe operation of the system. Fires aboard spacecraft behave differently from those on Earth because of the absence of buoyancy in microgravity. This ongoing in-house flame-stability research at the NASA Glenn Research Center is important in spacecraft fire safety and Earth-bound combustion systems.

  5. Interaction between a laminar flame and its self-generated flow

    SciTech Connect

    Dunn-Rankin, D.

    1985-04-01

    The interaction between a premixed laminar flame and its self-generated flow is experimentally studied in a closed duct. A laser Doppler anemometer measures two components of the enclosed gas velocity during the flame propagation. High-speed schlieren cinematography is used to observe changes in flame shape and location. Pressure records correlate with the qualitative schlieren movies and help quantify the progress of the combustion process. A one-dimensional model accurately predicts the unburned gas motion. The flow in the burned gas is rotational because of vorticity generated from flow deflection through the curved flame front. The density difference between the burned and unburned gas requires a velocity jump at the flame front to maintain continuity of mass flux. The measured velocity jump corresponds to this predicted value. A large flame cusp, called a ''tulip'' flame, appears during the flame propagation. Flame instability, pressure wave/flame interaction, and large scale circulation in the unburned gas are suggested explanation for the ''tulip'' flame. Velocity measurements of this work show that no large scale circulation exists in the unburned gas. The onset of the ''tulip'' process coincides with the quench of part of the flame at the sidewalls of the combustion vessel. The velocity decrease in the unburned gas and the curved flame shape at the time of quench combine to generate a vortex in the burned gas. The vortex remains in the proximity of the flame and modifies the flame shape and unburned gas field such that the flame cusp or ''tulip'' is formed.

  6. 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

  7. Study of Buoyancy Effects in Diffusion Flames Using Rainbow Schlieren Deflectometry

    NASA Technical Reports Server (NTRS)

    Agrawal, Ajay K.; Gollahalli, Subramanyam R.; Griffin, DeVon

    1997-01-01

    Diffusion flames are extensively encountered in many domestic and industrial processes. Even after many decades of research, a complete understanding of the diffusion flame structure is not available. The structure and properties of the flames are governed by the mixing (laminar or turbulent), chemical kinetics, radiation and soot processes. Another important phenomenon that affects flame structure in normal gravity is buoyancy. The presence of buoyancy has long hindered the rational understanding of many combustion processes. In gas jet diffusion flames, buoyancy affects the structure of the shear layer, the development of fluid instabilities, and formation of the coherent structures in the near nozzle region of the gas jets. The buoyancy driven instabilities generate vorticial structures outside the flame resulting in flame flicker. The vortices also strongly interact with the small-scale structures in the jet shear layer. This affects the transitional and turbulence characteristics of the flame. For a fundamental understanding of diffusion flames it is essential to isolate the effects of buoyancy. This is the primary goal of the experiments conducted in microgravity. Previous investigations, have shown dramatic differences between the jet flames in microgravity and normal gravity. It has been observed that flames in microgravity are taller and more sooty than in normal gravity. The fuels used in these experiments were primarily hydrocarbons. In the absence of buoyancy the soot resides near the flame region, which adversely affects the entrainment of reactants. It is very important to eliminate the interference of soot on flame characteristics in microgravity. The present work, therefore, focuses on the changes in the flame structure due to buoyancy without the added complexities of heterogeneous reactions. Clean burning hydrogen is used as the fuel to avoid soot formation and minimize radiative losses. Because of the low luminosity of hydrogen flames, we use

  8. Study on combustion of gasoline/MTBE in laminar flame with synchrotron radiation.

    PubMed

    Yao, Chunde; Li, Jing; Li, Qi; Huang, Chaoqun; Wei, Lixia; Wang, Jing; Tian, Zhenyu; Li, Yuyang; Qi, Fei

    2007-05-01

    Synchrotron radiation offers important advantages with the use of tunable vacuum ultraviolet (VUV) lasers for molecular beam sampling mass spectrometry (MBMS). These advantages include superior signal-to-noise, soft ionization, and access to photon energies outside the limited tuning ranges of current VUV laser sources. Combining MBMS with tunable synchrotron radiation photoionization, two similar types of fuels, gasoline/oxygen and gasoline/MTBE/oxygen in low-pressure premixed laminar flame were investigated. Photoionization efficiency (PIE) measurements were used to identify the intermediates isomers within flame. The two combustion processes are discussed by comparing the intermediates and their spatial profiles within the two kinds of flame mentioned above.

  9. Laminar Soot Processes

    NASA Technical Reports Server (NTRS)

    Lin, K. -C.; Dai, Z.; Faeth, G. M.

    1999-01-01

    Soot formation within hydrocarbon-fueled flames is an important unresolved problem of combustion science for several reasons: soot emissions are responsible for more deaths than any other combustion pollutant, thermal loads due to continuum radiation from soot limit the durability of combustors, thermal radiation from soot is mainly responsible for the growth and spread of unwanted fires, carbon monoxide associated with soot emissions is responsible for most fire deaths, and limited understanding of soot processes is a major impediment to the development of computational combustion. Thus, soot processes within laminar nonpremixed (diffusion) flames are being studied, emphasizing space-based experiments at microgravity. The study is limited to laminar flames due to their experimental and computational tractability, noting the relevance of these results to practical flames through laminar flamelet concepts. The microgravity environment is emphasized because buoyancy affects soot processes in laminar diffusion flames whereas effects of buoyancy are small for most practical flames. Results discussed here were obtained from experiments carried out on two flights of the Space Shuttle Columbia. After a brief discussion of experimental methods, results found thus far are described, including soot concentration measurements, laminar flame shapes, laminar smoke points and flame structure. The present discussion is brief.

  10. An experimental study of the structure of laminar premixed flames of ethanol/methane/oxygen/argon

    PubMed Central

    Tran, L.S.; Glaude, P.A.; Battin-Leclerc, F.

    2013-01-01

    The structures of three laminar premixed stoichiometric flames at low pressure (6.7 kPa): a pure methane flame, a pure ethanol flame and a methane flame doped by 30% of ethanol, have been investigated and compared. The results consist of concentration profiles of methane, ethanol, O2, Ar, CO, CO2, H2O, H2, C2H6, C2H4, C2H2, C3H8, C3H6, p-C3H4, a-C3H4, CH2O, CH3HCO, measured as a function of the height above the burner by probe sampling followed by on-line gas chromatography analyses. Flame temperature profiles have been also obtained using a PtRh (6%)-PtRh (30%) type B thermocouple. The similarities and differences between the three flames were analyzed. The results show that, in these three flames, the concentration of the C2 intermediates is much larger than that of the C3 species. In general, mole fraction of all intermediate species in the pure ethanol flame is the largest, followed by the doped flame, and finally the pure methane flame. PMID:24092946

  11. Numerical investigation of steady laminar flame propagation in a circular tube

    SciTech Connect

    Lee, S.T.; Chien, C.H. . Dept. of Mechanical Engineering)

    1994-12-01

    The steady propagation of a premixed laminar flame in circular tubes with adiabatic wall and isothermal wall is numerically investigated in the present study. It is assumed that the flow is axisymmetric and the flame chemistry is modeled by an one-step overall reaction which simulates the reaction of a lean methane-air mixture. The numerical results show that the flame propagating steadily in a tube can take two distinct shapes: tulip shape and mushroom shape. It is found that, in a insulated tube, the tulip-shaped flame is a more robust manifestation than the mushroom-shaped flame, and is the primary mode of the solutions. The opposite is true in a tube with isothermal wall. The effect of the gravity along the tube axis is also studied. It is found that the gravity not only modifies the flame speed, it also affects the flame shape. For example, under zero-gravity, only tulip-shaped flame can be found in a small tube with adiabatic wall, but under the normal gravitational force, both mushroom-shaped flame and tulip-shaped flame exist.

  12. 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.

  13. 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

  14. Effects of Flame Structure and Hydrodynamics on Soot Particle Inception and Flame Extinction in Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Axelbaum, R. L.; Chen, R.; Sunderland, P. B.; Urban, D. L.; Liu, S.; Chao, B. H.

    2001-01-01

    This paper summarizes recent studies of the effects of stoichiometric mixture fraction (structure) and hydrodynamics on soot particle inception and flame extinction in diffusion flames. Microgravity experiments are uniquely suited for these studies because, unlike normal gravity experiments, they allow structural and hydrodynamic effects to be independently studied. As part of this recent flight definition program, microgravity studies have been performed in the 2.2 second drop tower. Normal gravity counterflow studies also have been employed and analytical and numerical models have been developed. A goal of this program is to develop sufficient understanding of the effects of flame structure that flames can be "designed" to specifications - consequently, the program name Flame Design. In other words, if a soot-free, strong, low temperature flame is required, can one produce such a flame by designing its structure? Certainly, as in any design, there will be constraints imposed by the properties of the available "materials." For hydrocarbon combustion, the base materials are fuel and air. Additives could be considered, but for this work only fuel, oxygen and nitrogen are considered. Also, the structure of these flames is "designed" by varying the stoichiometric mixture fraction. Following this line of reasoning, the studies described are aimed at developing the understanding of flame structure that is needed to allow for optimum design.

  15. A comparison of transport algorithms for premixed, laminar steady state flames

    NASA Technical Reports Server (NTRS)

    Coffee, T. P.; Heimerl, J. M.

    1980-01-01

    The effects of different methods of approximating multispecies transport phenomena in models of premixed, laminar, steady state flames were studied. Five approximation methods that span a wide range of computational complexity were developed. Identical data for individual species properties were used for each method. Each approximation method is employed in the numerical solution of a set of five H2-02-N2 flames. For each flame the computed species and temperature profiles, as well as the computed flame speeds, are found to be very nearly independent of the approximation method used. This does not indicate that transport phenomena are unimportant, but rather that the selection of the input values for the individual species transport properties is more important than the selection of the method used to approximate the multispecies transport. Based on these results, a sixth approximation method was developed that is computationally efficient and provides results extremely close to the most sophisticated and precise method used.

  16. Linear and non-linear forced response of a conical, ducted, laminar premixed flame

    SciTech Connect

    Karimi, Nader; Brear, Michael J.; Jin, Seong-Ho; Monty, Jason P.

    2009-11-15

    This paper presents an experimental study on the dynamics of a ducted, conical, laminar premixed flame subjected to acoustic excitation of varying amplitudes. The flame transfer function is measured over a range of forcing frequencies and equivalence ratios. In keeping with previous works, the measured flame transfer function is in good agreement with that predicted by linear kinematic theory at low amplitudes of acoustic velocity excitation. However, a systematic departure from linear behaviour is observed as the amplitude of the velocity forcing upstream of the flame increases. This non-linearity is mostly in the phase of the transfer function and manifests itself as a roughly constant phase at high forcing amplitude. Nonetheless, as predicted by non-linear kinematic arguments, the response always remains close to linear at low forcing frequencies, regardless of the forcing amplitude. The origin of this phase behaviour is then sought through optical data post-processing. (author)

  17. Experiments and numerical simulation on the laminar flame speeds of dichloromethane and trichloromethane

    SciTech Connect

    Leylegian, J.C.; Zhu, D.L.; Law, C.K.; Wang, H.

    1998-08-01

    The laminar flame speeds of blends of dichloromethane and trichloromethane with methane in air at room temperature and atmospheric pressure were experimentally determined using the counterflow twin-flame technique, varying both the amount of chlorinated compound in the fuel and the equivalence ratio of the unburned mixture. A detailed kinetic model previously employed for simulation of chloromethane combustion was expanded to include the oxidation kinetics of dichloromethane and trichloromethane. Numerical simulation shows that the expanded kinetic model predicted the flame speeds to within 3 cm/s of the measured values. Carbon flux and sensitivity analyses indicate that the reaction kinetics of the methane flame doped with chlorinated methanes are qualitatively similar, despite the variation in the chlorinated methane fuel structure.

  18. Soot suppression by ferrocene in laminar ethylene/air nonpremixed flames

    SciTech Connect

    Zhang, J.; Megaridis, C.M.

    1996-06-01

    An experimental investigation is presented on the origin of the soot suppressing role of ferrocene additive in laminar, coannular, ethylene/air nonpremixed flames. The conditions examined involve laminar flames operating above and below their smoke point. In-flame diagnostics are employed to discern the interaction between the soot matrix and additive combustion products. The data presented in a previous study, as produced by thermophoretic sampling, transmission electron microscopy and high-resolution microanalysis techniques, are supplemented by soot volume fraction, temperature, and soot primary size measurements to unravel the mechanisms through which ferrocene combustion products influence soot formation processes. Furthermore, Z-contrast scanning/transmission electron microscopy is used to examine the over-fire aerosol and, in turn, provide insight on the fine-scale dispersion of iron fragments within the carbonaceous soot matrix. It is shown that ferrocene seeding of the fuel stream accelerates the particular inception mechanisms, but does not influence soot loadings when soot growth is dominant. Ferrocene is also found to enhance soot oxidation rates near the flame terminus. It is concluded that the fine-scale incorporation of iron compounds within the soot matrix is a primary factor for the soot suppressing role of ferrocene in nonpremixed flames.

  19. Analytic modeling of a spray diffusion flame

    NASA Technical Reports Server (NTRS)

    Harsha, P. T.; Edelman, R. B.

    1984-01-01

    A detailed model for a spray diffusion flame is described. The model is based on the boundary layer form of the equations of motion, with droplet transport accounted for using a discretized droplet size distribution function. Interphase transport of mass and energy are accounted for, with a flame-sheet model used to describe the combustion process on a droplet scale. Near dynamic equilibrium is assumed for the description of droplet transport; droplets can diffuse relative to the gas phase. Gas-phase mixing is accounted for using a two-equation turbulence model; buoyancy effects are included, with a temperature fluctuation equation used to account for buoyancy effects on turbulence structure. Thermal radiation from gas-phase CO2 and H2O is included. Gas-phase chemical kinetics are modeled using a 20-reaction, 10-species version of the advanced quasi-global chemical kinetics formulation. Results are compared with data for a vaporizing Freon spray and a pentane spray flame. It is shown that the computational approach provides a reasonably valid picture of the overall development of a spray diffusion flame, and, furthermore, provides a useful tool for the parametric examination of the spray combustion process.

  20. A multi-probe thermophoretic soot sampling system for high-pressure diffusion flames.

    PubMed

    Vargas, Alex M; Gülder, Ömer L

    2016-05-01

    Optical diagnostics and physical probing of the soot processes in high pressure combustion pose challenges that are not faced in atmospheric flames. One of the preferred methods of studying soot in atmospheric flames is in situ thermophoretic sampling followed by transmission electron microscopy imaging and analysis for soot sizing and morphology. The application of this method of sampling to high pressures has been held back by various operational and mechanical problems. In this work, we describe a rotating disk multi-probe thermophoretic soot sampling system, driven by a microstepping stepper motor, fitted into a high-pressure chamber capable of producing sooting laminar diffusion flames up to 100 atm. Innovative aspects of the sampling system design include an easy and precise control of the sampling time down to 2.6 ms, avoidance of the drawbacks of the pneumatic drivers used in conventional thermophoretic sampling systems, and the capability to collect ten consecutive samples in a single experimental run. Proof of principle experiments were performed using this system in a laminar diffusion flame of methane, and primary soot diameter distributions at various pressures up to 10 atm were determined. High-speed images of the flame during thermophoretic sampling were recorded to assess the influence of probe intrusion on the flow field of the flame.

  1. A multi-probe thermophoretic soot sampling system for high-pressure diffusion flames.

    PubMed

    Vargas, Alex M; Gülder, Ömer L

    2016-05-01

    Optical diagnostics and physical probing of the soot processes in high pressure combustion pose challenges that are not faced in atmospheric flames. One of the preferred methods of studying soot in atmospheric flames is in situ thermophoretic sampling followed by transmission electron microscopy imaging and analysis for soot sizing and morphology. The application of this method of sampling to high pressures has been held back by various operational and mechanical problems. In this work, we describe a rotating disk multi-probe thermophoretic soot sampling system, driven by a microstepping stepper motor, fitted into a high-pressure chamber capable of producing sooting laminar diffusion flames up to 100 atm. Innovative aspects of the sampling system design include an easy and precise control of the sampling time down to 2.6 ms, avoidance of the drawbacks of the pneumatic drivers used in conventional thermophoretic sampling systems, and the capability to collect ten consecutive samples in a single experimental run. Proof of principle experiments were performed using this system in a laminar diffusion flame of methane, and primary soot diameter distributions at various pressures up to 10 atm were determined. High-speed images of the flame during thermophoretic sampling were recorded to assess the influence of probe intrusion on the flow field of the flame. PMID:27250464

  2. A multi-probe thermophoretic soot sampling system for high-pressure diffusion flames

    NASA Astrophysics Data System (ADS)

    Vargas, Alex M.; Gülder, Ömer L.

    2016-05-01

    Optical diagnostics and physical probing of the soot processes in high pressure combustion pose challenges that are not faced in atmospheric flames. One of the preferred methods of studying soot in atmospheric flames is in situ thermophoretic sampling followed by transmission electron microscopy imaging and analysis for soot sizing and morphology. The application of this method of sampling to high pressures has been held back by various operational and mechanical problems. In this work, we describe a rotating disk multi-probe thermophoretic soot sampling system, driven by a microstepping stepper motor, fitted into a high-pressure chamber capable of producing sooting laminar diffusion flames up to 100 atm. Innovative aspects of the sampling system design include an easy and precise control of the sampling time down to 2.6 ms, avoidance of the drawbacks of the pneumatic drivers used in conventional thermophoretic sampling systems, and the capability to collect ten consecutive samples in a single experimental run. Proof of principle experiments were performed using this system in a laminar diffusion flame of methane, and primary soot diameter distributions at various pressures up to 10 atm were determined. High-speed images of the flame during thermophoretic sampling were recorded to assess the influence of probe intrusion on the flow field of the flame.

  3. On the structure, propagation, and stabilization of laminar premixed flames. Final report

    SciTech Connect

    Law, Chung K.

    1999-07-01

    The primary objective of the funded program was to qualitatively understand and quantitatively determine the structure and dynamics of laminar premixed flames. The investigation was conducted using laser-based experimentation, computational simulation with detailed chemistry and transport, and activation energy asymptotic analysis. Highlights of accomplishments were discussed in the annual reports submitted to the program monitor for this project. Details are reported in the thirty journal publications cited in the journal article list which is the major component of this final report.

  4. Soot formation and temperature structure in small methane-oxygen diffusion flames at subcritical and supercritical pressures

    SciTech Connect

    Joo, Hyun I.; Guelder, Oemer L.

    2010-06-15

    An experimental study was conducted to examine the characteristics of laminar methane-oxygen diffusion flames up to 100 atmospheres. The influence of pressure on soot formation and on the structure of the temperature field was investigated over the pressure range of 10-90 atmospheres in a high-pressure combustion chamber using a non-intrusive, line-of-sight spectral soot emission diagnostic technique. Two distinct zones characterized the appearance of a methane and pure oxygen diffusion flame: an inner luminous zone similar to the methane-air diffusion flames, and an outer diffusion flame zone which is mostly blue. The flame height, marked by the visible soot radiation emission, was reduced by over 50% over the pressure range of 10-100 atmospheres. Between 10 and 40 atmospheres, the soot levels increased with increasing pressure; however, above 40 atmospheres the soot concentrations decreased with increasing pressure. (author)

  5. Fan Beam Emission Tomography for Estimating Scalar Properties in Laminar Flames

    NASA Technical Reports Server (NTRS)

    Lim, Jongmook; Sivathanu, Yudaya; Feikema, Douglas

    2003-01-01

    A new method of estimating temperatures and gas species concentrations (CO2 and H2O) in a laminar flame is reported. The path-integrated, spectral radiation intensities emitted from a laminar flame at multiple wavelengths and view angles are calculated using a narrow band radiation model. Synthetic data, in the form of radial profiles of temperature and gas concentrations, are used in these calculations. The calculations mimic measurements that would theoretically be obtained using a mid-infrared spectrometer with a scanner. The path integrated spectral radiation intensities are deconvoluted using a maximum likelihood estimation method in conjunction with an iterative scheme. The deconvolution algorithm accounts for the self-absorption of radiation by the intervening gases, and provides the local temperature and gas species concentrations. The deconvoluted temperatures and gas concentrations are compared with the synthetic data used for calculating the spectral radiation intensities. The deconvoluted temperatures and gas species concentrations are within 0.5 % of the synthetic data. The deconvolution algorithm is expected to provide combustion researchers with an easy method of obtaining the radial profiles of major gas species concentrations and temperatures in laminar flames non-intrusively using a mid-infrared spectrometer with a scanner.

  6. Modelling thermal radiation in buoyant turbulent diffusion flames

    NASA Astrophysics Data System (ADS)

    Consalvi, J. L.; Demarco, R.; Fuentes, A.

    2012-10-01

    This work focuses on the numerical modelling of radiative heat transfer in laboratory-scale buoyant turbulent diffusion flames. Spectral gas and soot radiation is modelled by using the Full-Spectrum Correlated-k (FSCK) method. Turbulence-Radiation Interactions (TRI) are taken into account by considering the Optically-Thin Fluctuation Approximation (OTFA), the resulting time-averaged Radiative Transfer Equation (RTE) being solved by the Finite Volume Method (FVM). Emission TRIs and the mean absorption coefficient are then closed by using a presumed probability density function (pdf) of the mixture fraction. The mean gas flow field is modelled by the Favre-averaged Navier-Stokes (FANS) equation set closed by a buoyancy-modified k-ɛ model with algebraic stress/flux models (ASM/AFM), the Steady Laminar Flamelet (SLF) model coupled with a presumed pdf approach to account for Turbulence-Chemistry Interactions, and an acetylene-based semi-empirical two-equation soot model. Two sets of experimental pool fire data are used for validation: propane pool fires 0.3 m in diameter with Heat Release Rates (HRR) of 15, 22 and 37 kW and methane pool fires 0.38 m in diameter with HRRs of 34 and 176 kW. Predicted flame structures, radiant fractions, and radiative heat fluxes on surrounding surfaces are found in satisfactory agreement with available experimental data across all the flames. In addition further computations indicate that, for the present flames, the gray approximation can be applied for soot with a minor influence on the results, resulting in a substantial gain in Computer Processing Unit (CPU) time when the FSCK is used to treat gas radiation.

  7. Fullerenes, PAH, Carbon Nanostructures, and Soot in Low Pressure Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Grieco, William J.; Lafleur, Arthur L.; Rainey, Lenore C.; Taghizadeh, Koli; VanderSande, John B.; Howard, Jack B.

    1997-01-01

    The formation of fullerenes C60 and C7O is known to occur in premixed laminar benzene/oxygen/argon flames operated at reduced pressures. High resolution transmission electron microscopy (HRTEM) images of material collected from these flames has identified a variety of multishelled nanotubes and fullerene 'onions' as well as some trigonous structures. These fullerenes and nanostructures resemble the material that results from commercial fullerene production systems using graphite vaporization. As a result, combustion is an interesting method for fullerenes synthesis. If commercial scale operation is to be considered, the use of diffusion flames might be safer and less cumbersome than premixed flames. However, it is not known whether diffusion flames produce the types and yields of fullerenes obtained from premixed benzene/oxygen flames. Therefore, the formation of fullerenes and carbon nanostructures, as well as polycyclic aromatic hydrocarbons (PAH) and soot, in acetylene and benzene diffusion flames is being studied using high performance liquid chromatography (HPLC) and high resolution transmission electron microscopy (HRTEM).

  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. A Computational Investigation of Sooting Limits of Spherical Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Lecoustre, V. R.; Chao, B. H.; Sunderland, P. B.; Urban, D. L.; Stocker, D. P.; Axelbaum, R. L.

    2007-01-01

    Limiting conditions for soot particle inception in spherical diffusion flames were investigated numerically. The flames were modeled using a one-dimensional, time accurate diffusion flame code with detailed chemistry and transport and an optically thick radiation model. Seventeen normal and inverse flames were considered, covering a wide range of stoichiometric mixture fraction, adiabatic flame temperature, and residence time. These flames were previously observed to reach their sooting limits after 2 s of microgravity. Sooting-limit diffusion flames with residence times longer than 200 ms were found to have temperatures near 1190 K where C/O = 0.6, whereas flames with shorter residence times required increased temperatures. Acetylene was found to be a reasonable surrogate for soot precursor species in these flames, having peak mole fractions of about 0.01.

  10. 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

  11. A detailed kinetic modeling study of aromatics formation in laminar premixed acetylene and ethylene flames

    SciTech Connect

    Wang, H.; Frenklach, M.

    1997-07-01

    A computational study was performed for the formation and growth of polycyclic aromatic hydrocarbons (PAHs) in laminar premixed acetylene and ethylene flames. A new detailed reaction mechanism describing fuel pyrolysis and oxidation, benzene formation, and PAH mass growth and oxidation is presented and critically tested. It is shown that the reaction model predicts reasonably well the concentration profiles of major and intermediate species and aromatic molecules in a number of acetylene and ethylene flames reported in the literature. It is demonstrated that reactions of n-C{sub 4}H{sub x} + C{sub 2}H{sub 2} leading to the formation of one-ring aromatics are as important as the propargyl recombination, and hence must be included in kinetic modeling of PAH formation in hydrocarbon flames. It is further demonstrated that the mass growth of PAHs can be accounted for by the previously proposed H-abstraction-C{sub 2}H{sub 2}-addiction mechanism.

  12. Liftoff and blowoff of a diffusion flame between parallel streams of fuel and air

    SciTech Connect

    Fernandez-Tarrazo, Eduardo; Vera, Marcos; Linan, Amable

    2006-01-01

    A numerical analysis is presented to describe the liftoff and blowoff of a diffusion flame in the mixing layer between two parallel streams of fuel (mainly methane diluted with nitrogen) and air emerging from porous walls. The analysis, which takes into account the effects of thermal expansion, assumes a one-step overall Arrhenius reaction, where the activation energy E is allowed to vary to reproduce the variations of the planar flame propagation velocity with the equivalence ratio. First, we describe the steady flame-front structure when stabilized close to the porous wall (attached flame regime). Then, we analyze the case where the flame front is located far away from the porous wall, at a distance x{sub f}' such that, upstream of the flame front, the mixing layer has a self-similar structure (lifted flame regime). For steady lifted flames, the results, given here in the case when the fuel and air streams are injected with the same velocity, relate U{sub f}'/S{sub L}, the front velocity (relative to the upstream flow) measured with the planar stoichiometric flame velocity, with the Damkohler number D{sub m}=({delta}{sub m}/{delta}{sub L}){sup 2}, based on the thickness, {delta}{sub m}, of the nonreacting mixing layer at the flame-front position and the laminar flame thickness, {delta}{sub L}. For large values of D{sub m}, the results, presented here for a wide range of dilutions of the fuel stream, provide values of the front propagation velocity that are in good agreement with previous experimental results, yielding well-defined conditions for blowoff. The calculated flame-front velocity can also be used to describe the transient flame-front dynamics after ignition by an external energy source.

  13. Detailed modeling analysis for soot formation and radiation in microgravity gas jet diffusion flames

    NASA Technical Reports Server (NTRS)

    Ku, Jerry C.; Tong, LI; Greenberg, Paul S.

    1995-01-01

    Radiation heat transfer in combustion systems has been receiving increasing interest. In the case of hydrocarbon fuels, a significant portion of the radiation comes from soot particles, justifying the need for detailed soot formation model and radiation transfer calculations. For laminar gas jet diffusion flames, results from this project (4/1/91 8/22/95) and another NASA study show that flame shape, soot concentration, and radiation heat fluxes are substantially different under microgravity conditions. Our emphasis is on including detailed soot transport models and a detailed solution for radiation heat transfer, and on coupling them with the flame structure calculations. In this paper, we will discuss the following three specific areas: (1) Comparing two existing soot formation models, and identifying possible improvements; (2) A simple yet reasonably accurate approach to calculating total radiative properties and/or fluxes over the spectral range; and (3) Investigating the convergence of iterations between the flame structure solver and the radiation heat transfer solver.

  14. A comparison of the structures of lean and rich axisymmetric laminar Bunsen flames: application of local rectangular refinement solution-adaptive gridding

    NASA Astrophysics Data System (ADS)

    Bennett, Beth Anne V.; Fielding, Joseph; Mauro, Richard J.; Long, Marshall B.; Smooke, Mitchell D.

    1999-12-01

    Axisymmetric laminar methane-air Bunsen flames are computed for two equivalence ratios: lean (icons/Journals/Common/Phi" ALT="Phi" ALIGN="TOP"/> = 0.776), in which the traditional Bunsen cone forms above the burner; and rich (icons/Journals/Common/Phi" ALT="Phi" ALIGN="TOP"/> = 1.243), in which the premixed Bunsen cone is accompanied by a diffusion flame halo located further downstream. Because the extremely large gradients at premixed flame fronts greatly exceed those in diffusion flames, their resolution requires a more sophisticated adaptive numerical method than those ordinarily applied to diffusion flames. The local rectangular refinement (LRR) solution-adaptive gridding method produces robust unstructured rectangular grids, utilizes multiple-scale finite-difference discretizations, and incorporates Newton's method to solve elliptic partial differential equation systems simultaneously. The LRR method is applied to the vorticity-velocity formulation of the fully elliptic governing equations, in conjunction with detailed chemistry, multicomponent transport and an optically-thin radiation model. The computed lean flame is lifted above the burner, and this liftoff is verified experimentally. For both lean and rich flames, grid spacing greatly influences the Bunsen cone's position, which only stabilizes with adequate refinement. In the rich configuration, the oxygen-free region above the Bunsen cone inhibits the complete decay of CH4, thus indirectly initiating the diffusion flame halo where CO oxidizes to CO2. In general, the results computed by the LRR method agree quite well with those obtained on equivalently refined conventional grids, yet the former require less than half the computational resources.

  15. The effects of unsteady hydrodynamics on soot formation in a counterflow diffusion flame

    NASA Astrophysics Data System (ADS)

    Riggen-Decroix, Michele Elaine

    Currently, there is an increased interest in reducing soot emissions from combustors, because environmental regulations are requiring dramatic reductions in particulate emissions. Most practical, large scale combustion processes rely on turbulent diffusion flames. These same combustors, which bum hydrocarbon fuels, are also well known for their high soot emissions. The study of chemical processes, such as soot formation, in a turbulent diffusion flame is complicated by the unsteady multi-dimensional flowfield, complex hydrocarbon chemistry, and the interaction between the flowfield and chemistry. Flamelet theory simplifies the analysis of a turbulent diffusion flames by treating the flame as an ensemble of strained, laminar, one dimensional flamelets which can be described by two variables. Counterflow diffusion flames exhibit many characteristics of flamelets. Currently, researchers assume flamelets respond in a quasi-steady manner to the unsteady strain rates in the real turbulent diffusion flame. However, this assumption has not been verified by experiments. This research involved a series of experiments designed to investigate a flamelet's response to unsteady strain rates by quantitatively measuring soot concentrations in an oscillating propane-air counterflow diffusion flame using the non-intrusive laser induced incandescence (LII) technique. These spatially and temporally resolved measurements were made as a function of initial steady strain rate, forcing frequency, and forcing amplitude of the strain rate fluctuation. Also, laser Doppler velocimetry was used to measure the unsteady strain rate imposed on the flame. The results of this study showed that low frequency oscillations always increased the maximum soot concentration. At high initial strain rates, the soot formation process became insensitive to the strain rate fluctuation. At low initial strain rates, the maximum soot concentration was reduced by up to 90% with high frequency high amplitude

  16. Gas phase radiative effects in diffusion flames

    NASA Astrophysics Data System (ADS)

    Bedir, Hasan

    Several radiation models are evaluated for a stagnation point diffusion flame of a solid fuel in terms of accuracy and computational time. Narrowband, wideband, spectral line weighted sum of gray gases (SLWSGG), and gray gas models are included in the comparison. Radiative heat flux predictions by the nongray narrowband, wideband, and SLWSGG models are found to be in good agreement with each other, whereas the gray gas models are found to be inaccurate. The narrowband model, the most complex among the models evaluated, is then applied first to a solid fuel and second to a pure gaseous diffusion flame. A polymethylmethacrylate (PMMA) diffusion flame in a stagnation point geometry is solved with the narrowband model with COsb2, Hsb2O, and MMA vapor included in participating species. A detailed account of the emission and absorption from these species as well as the radiative heat fluxes are given as a function of the stretch rate. It is found that at low stretch rate the importance of radiation is increased due to an increase in the optical thickness, and a decrease in the conductive heat flux. Results show that COsb2 is the biggest emitter and absorber in the flame, MMA vapor is the second and Hsb2O is the least important. A pure gaseous flame in an opposed jet configuration is solved with the narrowband radiation model with CO as the fuel, and Osb2 as the oxidizer. Detailed. chemical kinetics and transport are incorporated into the combustion model with the use of the CHEMKIN and TRANSPORT software packages. The governing equations are solved with a modified version of the OPPDIF code. Dry and wet CO flames as well as COsb2 dilution are studied. Comparison of the results with and without the consideration of radiation reveals that the radiation is important for the whole flammable range of dry CO flames and for the low stretch rates of wet flames. Without the consideration of radiation the temperature and the species mole fractions (especially of minor species

  17. Effects of CO addition on the characteristics of laminar premixed CH{sub 4}/air opposed-jet flames

    SciTech Connect

    Wu, C.-Y.; Chao, Y.-C.; Chen, C.-P.; Ho, C.-T.; Cheng, T.S.

    2009-02-15

    The effects of CO addition on the characteristics of premixed CH{sub 4}/air opposed-jet flames are investigated experimentally and numerically. Experimental measurements and numerical simulations of the flame front position, temperature, and velocity are performed in stoichiometric CH{sub 4}/CO/air opposed-jet flames with various CO contents in the fuel. Thermocouple is used for the determination of flame temperature, velocity measurement is made using particle image velocimetry (PIV), and the flame front position is measured by direct photograph as well as with laser-induced predissociative fluorescence (LIPF) of OH imaging techniques. The laminar burning velocity is calculated using the PREMIX code of Chemkin collection 3.5. The flame structures of the premixed stoichiometric CH{sub 4}/CO/air opposed-jet flames are simulated using the OPPDIF package with GRI-Mech 3.0 chemical kinetic mechanisms and detailed transport properties. The measured flame front position, temperature, and velocity of the stoichiometric CH{sub 4}/CO/air flames are closely predicted by the numerical calculations. Detailed analysis of the calculated chemical kinetic structures reveals that as the CO content in the fuel is increased from 0% to 80%, CO oxidation (R99) increases significantly and contributes to a significant level of heat-release rate. It is also shown that the laminar burning velocity reaches a maximum value (57.5 cm/s) at the condition of 80% of CO in the fuel. Based on the results of sensitivity analysis, the chemistry of CO consumption shifts to the dry oxidation kinetics when CO content is further increased over 80%. Comparison between the results of computed laminar burning velocity, flame temperature, CO consumption rate, and sensitivity analysis reveals that the effect of CO addition on the laminar burning velocity of the stoichiometric CH{sub 4}/CO/air flames is due mostly to the transition of the dominant chemical kinetic steps. (author)

  18. A comparison of experimental results of soot production in laminar premixed flames

    NASA Astrophysics Data System (ADS)

    Caetano, Nattan R.; Soares, Diego; Nunes, Roger P.; Pereira, Fernando M.; Smith Schneider, Paulo; Vielmo, Horácio A.; van der Laan, Flávio Tadeu

    2015-05-01

    Soot emission has been the focus of numerous studies due to the numerous applications in industry, as well as the harmful effects caused to the environment. Thus, the purpose of this work is to analyze the soot formation in a flat flame burner using premixed compressed natural gas and air, where these quasi-adiabatic flames have one-dimensional characteristics. The measurements were performed applying the light extinction technique. The air/fuel equivalence ratiowas varied to assess the soot volume fractions for different flame configurations. Soot production along the flamewas also analyzed by measurements at different heights in relation to the burner surface. Results indicate that soot volume fraction increases with the equivalence ratio. The higher regions of the flamewere analyzed in order to map the soot distribution on these flames. The results are incorporated into the experimental database for measurement techniques calibration and for computational models validation of soot formation in methane premixed laminar flames, where the equivalence ratio ranging from 1.5 up to 8.

  19. Effect of a uniform electric field on soot in laminar premixed ethylene/air flames

    SciTech Connect

    Wang, Y.; Yao, Q.; Nathan, G.J.; Alwahabi, Z.T.; King, K.D.; Ho, K.

    2010-07-15

    The effect of a nominally uniform electric field on the initially uniform distribution of soot has been assessed for laminar premixed ethylene/air flames from a McKenna burner. An electrophoretic influence on charged soot particles was measured through changes to the deposition rate of soot on the McKenna plug, using laser extinction (LE). Soot volume fraction was measured in situ using laser-induced incandescence (LII). Particle size and morphologies were assessed through ex situ transmission electron microscopy (TEM) using thermophoretic sampling particle diagnostics (TSPD). The results show that the majority of these soot particles are positively charged. The presence of a negatively charged plug was found to decrease the particle residence times in the flame and to influence the formation and oxidation progress. A positively charged plug has the opposite effect. The effect on soot volume fraction, particles size and morphology with electric field strength is also reported. Flame stability was also found to be affected by the presence of the electric field, with the balance of the electrophoretic force and drag force controlling the transition to unstable flame flicker. The presence of charged species generated by the flame was found to reduce the dielectric field strength to one seventh that of air. (author)

  20. Structure of the Soot Growth Region of Laminar Premixed Methane/Oxygen Flames. Appendix I

    NASA Technical Reports Server (NTRS)

    Xu, F.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2001-01-01

    The structure of the soot growth region of laminar premixed methane/oxygen flames (fuel-equivalence ratios of 1.60-2.77) was studied both experimentally and computationally. Measurements were carried out in flames stabilized on a flat flame burner operated at standard temperature and pressure, and included velocities by laser velocimetry, soot volume fractions by laser extinction, soot temperatures by multiline emission, gas temperatures (where soot was absent) by corrected fine-wire thermocouples, major gas species concentrations by sampling and gas chromatography, and hydrogen atom concentrations by the Li/LiOH technique in conjunction with atomic absorption to find the proportion of free lithium in the flames. The measured concentrations of major gas species were in reasonably good agreement with predictions based on the detailed mechanisms of Leung and Lindstedt, and Frenklach and coworkers. The measurements also confirmed predictions of both these mechanisms that H-atom concentrations are in local thermodynamic equilibrium throughout the soot growth region even through the concentrations of major gas species are not. Thus, present findings support recent evaluations of the hydrogen-abstraction/carbon-addition (HACA) soot growth mechanism in similar flames, where the approximation that H-atom concentrations were in local thermodynamic equilibrium was adopted, based on predictions using the two mechanisms, due to the absence of direct H-atom concentration measurements.

  1. Structure of Soot Growth Region of Laminar Premixed Methane/Oxygen Flames. Appendix B

    NASA Technical Reports Server (NTRS)

    Xu, F.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2000-01-01

    The structure of the soot growth region of laminar premixed methane/oxygen flames (fuel-equivalence ratios of 1.60 - 2.77) was studied both experimentally and computationally. Measurements were carried out in flames stabilized on a flat flame burner operated at standard temperature and pressure, and included velocities by laser velocimetry, soot volume fractions by laser extinction, soot temperatures by multiline emission, gas temperatures (where soot was absent) by corrected fine-wire thermocouples, major gas species concentrations by sampling and gas chromatography, and hydrogen atom concentrations by the Li/LiOH technique in conjunction with atomic absorption to find the proportion of free lithium in the flames. The measured concentrations of major gas species were in reasonably good agreement with predictions based on the detailed mechanisms of Leung and Lindstedt, and Frenklach and coworkers. The measurements also confirmed predictions of both these mechanisms that H-atom concentrations are in local thermodynamic equilibrium throughout the soot growth region even through the concentrations of major gas species are not. Thus, present findings support recent evaluations of the hydrogen-abstraction/carbon-addition (HACA) soot growth mechanism in similar flames, where the approximation that H-atom concentrations were in local thermodynamic equilibrium was adopted, based on predictions using the two mechanisms, due to the absence of direct H-atom concentration measurements.

  2. Structure of the Soot Growth Region of Laminar Premixed Methane/Oxygen Flames. Appendix G

    NASA Technical Reports Server (NTRS)

    Xu, F.; Faeth, G. M.; Yuan, Z.-G. (Technical Monitor); Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2000-01-01

    The structure of the soot growth region of laminar premixed methane/oxygen flames (fuel-equivalence ratios of 1.60-2.77) was studied both experimentally and computationally. Measurements were carried out in flames stabilized on a flat flame burner operated at standard temperature and pressure, and included velocities by laser velocimetry, soot volume fractions by laser extinction, soot temperatures by multiline emission, gas temperatures (where soot was absent) by corrected fine-wire thermocouples, major gas species concentrations by sampling and gas chromatography, and hydrogen atom concentrations by the Li/LiOH technique in conjunction with atomic absorption to find the proportion of free lithium in the flames. The measured concentrations of major gas species were in reasonably good agreement with predictions based on the detailed mechanisms of Leung and Lindstedt, and Frenklach and coworkers. The measurements also confirmed predictions of both these mechanisms that H-atom concentrations are in local thermodynamic equilibrium throughout the soot growth region even through the concentrations of major gas species are not. Thus, present findings support recent evaluations of the hydrogen-abstraction/carbon-addition (HACA) soot growth mechanism in similar flames, where the approximation that H-atom concentrations were in local thermodynamic equilibrium was adopted, based on predictions using the two mechanisms, due to the absence of direct H-atom concentration measurements.

  3. 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.

  4. Strain-induced extinction of hydrogen-air counterflow diffusion flames - Effects of steam, CO2, N2, and O2 additives to air

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Northam, G. B.; Wilson, L. G.

    1992-01-01

    A fundamental study was performed using axisymmetric nozzle and tubular opposed jet burners to measure the effects of laminar plug flow and parabolic input velocity profiles on the extinction limits of H2-air counterflow diffusion flames. Extinction limits were quantified by 'flame strength', (average axial air jet velocity) at blowoff of the central flame. The effects of key air contaminants, on the extinction limits, are characterized and analyzed relative to utilization of combustion contaminated vitiated air in high enthalpy supersonic test facilities.

  5. Soot formation, transport, and radiation in unsteady diffusion flames : LDRD final report.

    SciTech Connect

    Suo-Anttila, Jill Marie; Williams, Timothy C.; Shaddix, Christopher R.; Jensen, Kirk A.; Blevins, Linda Gail; Kearney, Sean Patrick; Schefer, Robert W.

    2004-10-01

    Fires pose the dominant risk to the safety and security of nuclear weapons, nuclear transport containers, and DOE and DoD facilities. The thermal hazard from these fires primarily results from radiant emission from high-temperature flame soot. Therefore, it is necessary to understand the local transport and chemical phenomena that determine the distributions of soot concentration, optical properties, and temperature in order to develop and validate constitutive models for large-scale, high-fidelity fire simulations. This report summarizes the findings of a Laboratory Directed Research and Development (LDRD) project devoted to obtaining the critical experimental information needed to develop such constitutive models. A combination of laser diagnostics and extractive measurement techniques have been employed in both steady and pulsed laminar diffusion flames of methane, ethylene, and JP-8 surrogate burning in air. For methane and ethylene, both slot and coannular flame geometries were investigated, as well as normal and inverse diffusion flame geometries. For the JP-8 surrogate, coannular normal diffusion flames were investigated. Soot concentrations, polycyclic aromatic hydrocarbon (PAH) laser-induced fluorescence (LIF) signals, hydroxyl radical (OH) LIF, acetylene and water vapor concentrations, soot zone temperatures, and the velocity field were all successfully measured in both steady and unsteady versions of these various flames. In addition, measurements were made of the soot microstructure, soot dimensionless extinction coefficient (&), and the local radiant heat flux. Taken together, these measurements comprise a unique, extensive database for future development and validation of models of soot formation, transport, and radiation.

  6. Instabilities of diffusion flames near extinction

    NASA Astrophysics Data System (ADS)

    Papas, Paul; Rais, Redha M.; Monkewitz, Peter A.; Tomboulides, Ananias G.

    2003-12-01

    The linear spatio-temporal stability of a diffusion flame, represented by a simplified one-dimensional model, located in a mixing layer is investigated. The analysis focuses on recently discovered `heat release' or combustion modes reported for flames near the extinction limit, i.e. for low Damköhler number. Numerical simulations of the two-dimensional linearized impulse response are performed to uncover the convective versus absolute nature of these combustion modes. To complement these two-dimensional simulations, the convective absolute transitions of these modes are confirmed with spatio-temporal linear stability calculations. The effects of initial reactant temperature, flow shear Reynolds number, as well as low fuel Lewis number, are explored. In addition to the Kelvin Helmholtz mode, the generalized model predicts a variety of instabilities near the extinction state, such as travelling and stationary cellular modes, zero wavenumber instabilities or `pulsations', and coupled hydrodynamic-combustion modes. The results elucidate the fundamental destabilizing mechanisms for these near-extinction flames and their relationship to previous work.

  7. Experimental investigation of stabilization mechanisms in turbulent, lifted jet diffusion flames

    SciTech Connect

    Su, L.K.; Sun, O.S.; Mungal, M.G.

    2006-02-01

    Simultaneous planar-laser induced fluorescence (PLIF) and particle image velocimetry (PIV) provide a comprehensive view of the molecular mixing and velocity fields in the stabilization region of turbulent, lifted jet diffusion flames. The Mie scattering medium for PIV is a glycerol-water fog, which evaporates at elevated temperatures and allows inference of the location of the high-temperature interface at the flame base. The jet Reynolds numbers vary from 4400 to 10,700. The mixing and velocity fields upstream of the flame base evolve consistently with nonreacting jet scaling. Conditional statistics of the fuel mole fraction at the instantaneous high-temperature interface show that the flame stabilization point does not generally correspond to the most upstream point on the interface (called here the leading point), because the mixture there is typically too lean to support combustion. Instead, the flame stabilization point lies toward the jet centerline relative to the leading point. Conditional axial velocity statistics indicate that the mean axial velocity at the flame front is {approx}1.8S{sub L}, where S{sub L} is the stoichiometric laminar flame speed. The data also permit determination of the scalar dissipation rates, {chi}, with the results indicating that {chi} values near the high-temperature interfaces do not typically exceed the quenching value. Thus, the flame stabilization process is more consistent with theories based on partial fuel-air premixing than with those dependent on diffusion flame quenching. We propose a description of flame stabilization that depends on the large-scale organization of the mixing field. (author)

  8. Electric fields effect on liftoff and blowoff of nonpremixed laminar jet flames in a coflow

    SciTech Connect

    Kim, M.K.; Ryu, S.K.; Won, S.H.; Chung, S.H.

    2010-01-15

    The stabilization characteristics of liftoff and blowoff in nonpremixed laminar jet flames in a coflow have been investigated experimentally for propane fuel by applying AC and DC electric fields to the fuel nozzle with a single-electrode configuration. The liftoff and blowoff velocities have been measured by varying the applied voltage and frequency of AC and the voltage and the polarity of DC. The result showed that the AC electric fields extended the stabilization regime of nozzle-attached flame in terms of jet velocity. As the applied AC voltage increased, the nozzle-attached flame was maintained even over the blowout velocity without having electric fields. In such a case, a blowoff occurred directly without experiencing a lifted flame. While for the DC cases, the influence on liftoff was minimal. There existed three different regimes depending on the applied AC voltage. In the low voltage regime, the nozzle-detachment velocity of either liftoff or blowoff increased linearly with the applied voltage, while nonlinearly with the AC frequency. In the intermediate voltage regime, the detachment velocity decreased with the applied voltage and reasonably independent of the AC frequency. At the high voltage regime, the detachment was significantly influenced by the generation of discharges. (author)

  9. Application of Shear Plate Interferometry to Jet Diffusion Flame Temperature Measurements

    NASA Technical Reports Server (NTRS)

    VanDerWege, Brad A.; OBrien, Chris J.; Hochgreb, Simone

    1997-01-01

    The recent ban on the production of bromotrifluoromethane (CF3Br) because of its high stratospheric ozone depletion potential has led to interest in finding alternative agents for fire extinguishing applications. Some of the promising alternatives are fluorinated hydrocarbons. A clear understanding of the effects of CF3Br and alternative chemical suppressants on diffusion flames is therefore necessary in the selection of alternative suppressants for use in normal and microgravity. The flame inhibition effects of halogen compounds have been studied extensively in premixed systems. The effect of addition of halocarbons (carbon-halogen compounds) to diffusion flames has been studied experimentally in coflow configurations and in counterflow gaseous and liquid-pool flames. Halogenated compounds are believed to inhibit combustion by scavenging hydrogen radicals to form the relatively unreactive compound HF, or through a catalytic recombination cycle involving HBr to form H2. Comparisons between halogens show that bromine inhibition is significantly more effective than chlorine or fluorine. Although fluorinated compounds are only slightly more effective inhibitors on a mass basis than nitrogen, they are more effective on a volume basis and are easily stored in liquid form. The objectives of this study are (a) to determine the stability limits of laminar jet diffusion flames with respect to inhibitor concentration in both normal and microgravity, and (b) to investigate the structure of halocarbon-inhibited flames. In the initial phase of this project, visual diagnostics were used to observe the structure and behavior of normal and microgravity flames. The initial observations showed significant changes in the structure of the flames with the addition of halocarbons to the surrounding environment, as discussed below. Furthermore, the study established that the flames are more stable relative to the addition of halocarbons in microgravity than in normal gravity. Visual

  10. Numerical investigation of flame-vortex interactions in laminar cross-flow non-premixed flames in the presence of bluff bodies

    NASA Astrophysics Data System (ADS)

    Kozhumal Shijin, Puthiyaparambath; Raghavan, Vasudevan; Babu, Viswanathan

    2016-07-01

    Flame stabilisation in a combustor having vortices generated by flame holding devices constitutes an interesting fundamental problem. The presence of vortices in many practical combustors ranging from industrial burners to high speed propulsion systems induces vortex-flame interactions and complex stabilisation conditions. The scenario becomes more complex if the flame sustains after separating itself from the flame holder. In a recent study [P.K. Shijin, S.S. Sundaram, V. Raghavan, and V. Babu, Numerical investigation of laminar cross-flow non-premixed flames in the presence of a bluff-body, Combust. Theory Model. 18, 2014, pp. 692-710], the authors reported details of the regimes of flame stabilisation of non-premixed laminar flames established in a cross-flow combustor in the presence of a square cylinder. In that, the separated flame has been shown to be three dimensional and highly unsteady. Such separated flames are investigated further in the present study. Flame-vortex interactions in separated methane-air cross flow flames established behind three bluff bodies, namely a square cylinder, an isosceles triangular cylinder and a half V-gutter, have been analysed in detail. The mixing process in the reactive flow has been explained using streamlines of species velocities of CH4 and O2. The time histories of z-vorticity, net heat release rate and temperature are analysed to reveal the close relationship between z-vorticity and net heat release rate spectra. Two distinct fluctuating layers are visible in the proper orthogonal decomposition and discrete Fourier transform of OH mass fraction data. The upper fluctuating layer observed in the OH field correlates well with that of temperature. A detailed investigation of the characteristics of OH transport has also been carried out to show the interactions between factors affecting fluid dynamics and chemical kinetics that cause multiple fluctuating layers in the OH.

  11. Unlocking the Keys to Vortex/Flame Interactions in Turbulent Gas-Jet Diffusion Flames--Dynamic Behavior Explored on the Space Shuttle

    NASA Technical Reports Server (NTRS)

    Stocker, Dennis P.

    1999-01-01

    Most combustion processes in industrial applications (e.g., furnaces and engines) and in nature (e.g., forest fires) are turbulent. A better understanding of turbulent combustion could lead to improved combustor design, with enhanced efficiency and reduced emissions. Despite its importance, turbulent combustion is poorly understood because of its complexity. The rapidly changing and random behavior of such flames currently prevents detailed analysis, whether experimentally or computationally. However, it is possible to learn about the fundamental behavior of turbulent flames by exploring the controlled interaction of steady laminar flames and artificially induced flow vortices. These interactions are an inherent part of turbulent flames, and understanding them is essential to the characterization of turbulent combustion. Well-controlled and defined experiments of vortex interaction with laminar flames are not possible in normal gravity because of the interference of buoyancy- (i.e., gravity) induced vortices. Therefore, a joint microgravity study was established by researchers from the Science and Technology Development Corp. and the NASA Lewis Research Center. The experimental study culminated in the conduct of the Turbulent Gas-Jet Diffusion Flames (TGDF) Experiment on the STS-87 space shuttle mission in November 1997. The fully automated hardware, shown in photo, was designed and built at Lewis. During the mission, the experiment was housed in a Get Away Special (GAS) canister in the cargo bay.

  12. Flame Oscillations In Non-Premixed Systems Diffusion Flames and Edge-Flames

    NASA Technical Reports Server (NTRS)

    Matalon, Moshe

    2003-01-01

    Diffusive-thermal instabilities are well known features of premixed and diffusion flames. In one of its form the instability appears as spontaneous oscillations. In premixed systems oscillations are predicted to occur when the effective Lewis number, defined as the ratio of the thermal diffusivity of the mixture to the mass diffusivity of the deficient component, is sufficiently larger than one. Oscillations would therefore occur in mixtures that are deficient in the less mobile reactant, namely in lean hydrocarbon-air or rich hydrogen-air mixtures. The theoretical predictions summarized above are in general agreement with experimental results; see for example [5] where a jet configuration was used and experiments were conducted for various inert-diluted propane and methane flames burning in inert-diluted oxygen. Nitrogen, argon and SF6 were used as inert in order to produce conditions of substantially different Lewis numbers and mixture strength. In accord with the predicted trend, it was found that oscillations arise at near extinction conditions, that for oscillations to occur it suffices that one of the two Lewis numbers be sufficiently large, and that oscillations are more likely to be observed when is relatively large.

  13. Soot Oxidation in Hydrocarbon/Air Diffusion Flames at Atmospheric Pressure. Appendix K

    NASA Technical Reports Server (NTRS)

    Xu, F.; El-Leathy, A. M.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2001-01-01

    Soot oxidation was studied experimentally in laminar hydrocarbon/air diffusion flames at atmospheric pressure. Measurements were carried out along the axes of round jets burning in coflowing air considering acetylene, ethylene, propylene and propane as fuels. Measurements were limited to the initial stages of soot oxidation (carbon consumption less than 70%) where soot oxidation mainly occurs at the surface of primary soot particles. The following properties were measured as a function of distance above the burner exit: soot concentrations by deconvoluted laser extinction, soot temperatures by deconvoluted multiline emission, soot structure by thermophoretic sampling and analysis using Transmission Electron Microscopy (TEM), concentrations of stable major gas species (N2, H2O, H2, O2, CO, CO2, CH4, C2H2,C2H4, C2H6, C3H6, and C3H8) by sampling and gas chromatography, concentrations of some radical species (H, OH, O) by the deconvoluted Li/LiOH atomic absorption technique and flow velocities by laser velocimetry. It was found that soot surface oxidation rates are not particularly affected by fuel type for laminar diffusion flames and are described reasonably well by the OH surface oxidation mechanism with a collision efficiency of 0.10, (standard deviation of 0.07) with no significant effect of fuel type in this behavior; these findings are in good agreement with the classical laminar premixed flame measurements of Neoh et al. Finally, direct rates of surface oxidation by O2 were small compared to OH oxidation for present conditions, based on estimated O2 oxidation rates due to Nagle and Strickland-Constable (1962), because soot oxidation was completed near the flame sheet where O2 concentrations were less than 1.2% by volume.

  14. Laser imaging of chemistry-flowfield interactions: Enhanced soot formation in time-varying diffusion flames

    SciTech Connect

    Harrington, J.E.; Shaddix, C.R.; Smyth, K.C.

    1994-12-31

    Models of detailed flame chemistry and soot formation are based upon experimental results obtained in steady, laminar flames. For successful application of these descriptions to turbulent combustion, it is instructive to test predictions against measurements in time-varying flowfields. This paper reports the use of optical methods to examine soot production and oxidation processes in a co-flowing, axisymmetric CH{sub 4}/air diffusion flame in which the fuel flow rate is acoustically forced to create a time-varying flowfield. For a particular forcing condition in which tip clipping occurs (0.75 V loudspeaker excitation), elastic scattering of vertically polarized light from the soot particles increases by nearly an order of magnitude with respect to that observed for a steady flame with the same mean fuel flow rate. The visible flame luminosity and laser-induced fluorescence attributed to polycyclic aromatic hydrocarbons (PAH) are also enhanced. Peak soot volume fractions, as measured by time-resolved laser extinction/tomography at 632.8 and 454.5 nm and calibrated laser-induced incandescence (LII), show a factor of 4--5 enhancement in this flickering flame. The LII method is found to track the soot volume fraction closely and to give better signal-to-noise than the extinction measurements in both the steady and time-varying flowfields. A Mie analysis suggests that most of the enhanced soot production results from the formation of larger particles in the time-varying flowfield.

  15. Effects of Lewis Number on Temperatures of Spherical Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Santa, K. J.; Sun, Z.; Chao, B. H.; Sunderland, P. B.; Axelbaum, R. I.; Urban, D. L.; Stocker, D. P.

    2007-01-01

    Spherical diffusion flames supported on a porous sphere were studied numerically and experimentally. Experiments were performed in 2.2 s and 5.2 s microgravity facilities. Numerical results were obtained from a Chemkin-based program. The program simulates flow from a porous sphere into a quiescent environment, yields both steady-state and transient results, and accounts for optically thick gas-phase radiation. The low flow velocities and long residence times in these diffusion flames lead to enhanced radiative and diffusive effects. Despite similar adiabatic flame temperatures, the measured and predicted temperatures varied by as much as 700 K. The temperature reduction correlates with flame size but characteristic flow times and, importantly, Lewis number also influence temperature. The numerical results show that the ambient gas Lewis number would have a strong effect on flame temperature if the flames were steady and nonradiating. For example, a 10% decrease in Lewis number would increase the steady-state flame temperature by 200 K. However, for these transient, radiating flames the effect of Lewis number is small. Transient predictions of flame sizes are larger than those observed in microgravity experiments. Close agreement could not be obtained without either increasing the model s thermal and mass diffusion properties by 30% or reducing mass flow rate by 25%.

  16. Effect of ferrocene on soot in a prevaporized iso-octane/air diffusion flame

    SciTech Connect

    Bonczyk, P.A. )

    1991-12-01

    This paper reports on ferrocene, or dicyclopentadienyl iron ((C{sub 5}H{sub 5}){sub 2}Fe) which is an organometallic compound of proven, considerable importance in relation to the control of soot resulting from the combustion of hydrocarbon fuels. Ferrocene as a fuel additive has been observed to suppress soot in oil-fired boilers and furnaces, jet engines, poly (vinyl chloride) combustion, acetylene pyrolysis, and laboratory-scale diffusion flames. This study of a well-defined laminar diffusion flame applies several complementary diagnostic approaches to clarify ferrocene's influence on soot particulates, their precursors, and flame temperature. Unlike most past work, the additive's intervention was evaluated with spatial precision throughout the luminous zone of the flame. To this end, light scattering measurements were made in order to determine the effect of ferrocene on particulate size, number density, and volume fraction. Sampling of the flame with a quartz microprobe was done as well to search for the perturbation of soot precursor and other gas-phase species by the additive; sample concentrations were analyzed via conventional gas chromatography.

  17. Experimental and numerical investigation of laminar flame speeds of hydrogen/carbon monoxide/carbon dioxide/nitrogen mixtures

    NASA Astrophysics Data System (ADS)

    Natarajan, Jayaprakash

    Coal derived synthetic gas (syngas) fuel is a promising solution for today's increasing demand for clean and reliable power. Syngas fuels are primarily mixtures of H2 and CO, often with large amounts of diluents such as N2, CO2, and H2O. The specific composition depends upon the fuel source and gasification technique. This requires gas turbine designers to develop fuel flexible combustors capable of operating with high conversion efficiency while maintaining low emissions for a wide range of syngas tact mixtures. Design tools often used in combustor development require data on various fundamental gas combustion properties. For example, laminar flame speed is often an input as it has a significant impact upon the size and static stability of the combustor. Moreover it serves as a good validation parameter for leading kinetic models used for detailed combustion simulations. Thus the primary objective of this thesis is measurement of laminar flame speeds of syngas fuel mixtures at conditions relevant to ground-power gas turbines. To accomplish this goal, two flame speed measurement approaches were developed: a Bunsen flame approach modified to use the reaction zone area in order to reduce the influence of flame curvature on the measured flame speed and a stagnation flame approach employing a rounded bluff body. The modified Bunsen flame approach was validated against stretch-corrected approaches over a range of fuels and test conditions; the agreement is very good (less than 10% difference). Using the two measurement approaches, extensive flame speed information were obtained for lean syngas mixtures at a range of conditions: (1) 5 to 100% H2 in the H2/CO fuel mixture; (2) 300-700 K preheat temperature; (3) 1 to 15 atm pressure, and (4) 0-70% dilution with CO2 or N2. The second objective of this thesis is to use the flame speed data to validate leading kinetic mechanisms for syngas combustion. Comparisons of the experimental flame speeds to those predicted using

  18. Enhancement of a laminar premixed methane/oxygen/nitrogen flame speed using femtosecond-laser-induced plasma

    SciTech Connect

    Yu Xin; Peng Jiangbo; Yi Yachao; Zhao Yongpeng; Chen Deying; Yu Junhua; Yang Peng; Sun Rui

    2010-07-05

    We first investigate the effects of femtosecond-laser-induced plasma on the flame speed of a laminar premixed methane/oxygen/nitrogen flame with a wide range of the equivalence ratios (0.8-1.05) at atmospheric pressure. It is experimentally found that the flame speed increases 20.5% at equivalence ratios 1.05. The self-emission spectra from the flame and the plasma are studied and an efficient production of active radicals under the action of femtosecond (fs)-laser pulses has been observed. Based on the experimental data obtained, the presence of oxygen atom and hydrocarbon radicals is suggested to be a key factor enhancing flame speed.

  19. Laminar Soot Processes (LSP) Experiment: Findings From Space Flight Measurements

    NASA Technical Reports Server (NTRS)

    Sunderland, P. B.; Urban, D. L.; Yuan, Z. G.; Aalburg, C.; Diez, F. J.; Faeth, G. M.

    2003-01-01

    The present experimental study of soot processes in hydrocarbon-fueled laminar nonbuoyant and nonpremixed (diffusion) flames at microgravity within a spacecraft was motivated by the relevance of soot to the performance of power and propulsion systems, to the hazards of unwanted fires, and to the emission of combustion-generated pollutants. Soot processes in turbulent flames are of greatest practical interest, however, direct study of turbulent flames is not tractable because the unsteadiness and distortion of turbulent flames limit available residence times and spatial resolution within regions where soot processes are important. Thus, laminar diffusion flames are generally used to provide more tractable model flame systems to study processes relevant to turbulent diffusion flames, justified by the known similarities of gas-phase processes in laminar and turbulent diffusion flames, based on the widely-accepted laminar flamelet concept of turbulent flames. Unfortunately, laminar diffusion flames at normal gravity are affected by buoyancy due to their relatively small flow velocities and, as discussed next, they do not have the same utility for simulating the soot processes as they do for simulating the gas phase processes of turbulent flames.

  20. The multispecies modeling of the premixed, laminar steady-state ozone flame

    NASA Technical Reports Server (NTRS)

    Heimerl, J. M.; Coffee, T. P.

    1980-01-01

    Species dependent kinetic, transport and thermodynamic coefficients were employed in a one dimensional model of the premixed, laminar, steady state ozone flame. Convenient expressions for these coefficients are reported. They are based on independent measurements, no arbitrary parameters are used. The governing equations are solved using a relaxation technique and the partial differential equation package, PDECOL. Species and temperature profiles and the burning velocities are found over the range of initial ozone mole fraction of 0.25 to 1.00. The computed burning velocities are no more than 30% greater than the measurements of Streng and Grosses. Comparison with the computed results of Warnatz shows agreement within + or - 12%, even though quite different expressions for some of the kinetic coefficients were used. These differences are most obvious in the atomic oxygen and temperature profiles at an initial ozone mole fraction of unity.

  1. Radiative Extinction of Gaseous Spherical Diffusion Flames in Microgravity

    NASA Technical Reports Server (NTRS)

    Santa, K. J.; Chao, B. H.; Sunderland, P. B.; Urban, D. L.; Stocker, D. P.; Axelbaum, R. L.

    2007-01-01

    Radiative extinction of spherical diffusion flames was investigated experimentally and numerically. The experiments involved microgravity spherical diffusion flames burning ethylene and propane at 0.98 bar. Both normal (fuel flowing into oxidizer) and inverse (oxidizer flowing into fuel) flames were studied, with nitrogen supplied to either the fuel or the oxygen. Flame conditions were chosen to ensure that the flames extinguished within the 2.2 s of available test time; thus extinction occurred during unsteady flame conditions. Diagnostics included color video and thin-filament pyrometry. The computations, which simulated flow from a porous sphere into a quiescent environment, included detailed chemistry, transport and radiation, and yielded transient results. Radiative extinction was observed experimentally and simulated numerically. Extinction time, peak temperature, and radiative loss fraction were found to be independent of flow rate except at very low flow rates. Radiative heat loss was dominated by the combustion products downstream of the flame and was found to scale with flame surface area, not volume. For large transient flames the heat release rate also scaled with surface area and thus the radiative loss fraction was largely independent of flow rate. Peak temperatures at extinction onset were about 1100 K, which is significantly lower than for kinetic extinction. One observation of this work is that while radiative heat losses can drive transient extinction, this is not because radiative losses are increasing with time (flame size) but rather because the heat release rate is falling off as the temperature drops.

  2. Experimental and Numerical Study of Ammonium Perchlorate Counterflow Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Smooke, M. D.; Yetter, R. A.; Parr, T. P.; Hanson-Parr, D. M.; Tanoff, M. A.

    1999-01-01

    Many solid rocket propellants are based on a composite mixture of ammonium perchlorate (AP) oxidizer and polymeric binder fuels. In these propellants, complex three-dimensional diffusion flame structures between the AP and binder decomposition products, dependent upon the length scales of the heterogeneous mixture, drive the combustion via heat transfer back to the surface. Changing the AP crystal size changes the burn rate of such propellants. Large AP crystals are governed by the cooler AP self-deflagration flame and burn slowly, while small AP crystals are governed more by the hot diffusion flame with the binder and burn faster. This allows control of composite propellant ballistic properties via particle size variation. Previous measurements on these diffusion flames in the planar two-dimensional sandwich configuration yielded insight into controlling flame structure, but there are several drawbacks that make comparison with modeling difficult. First, the flames are two-dimensional and this makes modeling much more complex computationally than with one-dimensional problems, such as RDX self- and laser-supported deflagration. In addition, little is known about the nature, concentration, and evolution rates of the gaseous chemical species produced by the various binders as they decompose. This makes comparison with models quite difficult. Alternatively, counterflow flames provide an excellent geometric configuration within which AP/binder diffusion flames can be studied both experimentally and computationally.

  3. Combustion rate limits of hydrogen plus hydrocarbon fuel: Air diffusion flames from an opposed jet burner technique

    NASA Technical Reports Server (NTRS)

    Pellett, Gerald L.; Guerra, Rosemary; Wilson, Lloyd G.; Reeves, Ronald N.; Northam, G. Burton

    1987-01-01

    Combustion of H2/hydrocarbon (HC) fuel mixtures may be considered in certain volume-limited supersonic airbreathing propulsion applications. Effects of HC addition to H2 were evaluated, using a recent argon-bathed, coaxial, tubular opposed jet burner (OJB) technique to measure the extinction limits of counterflow diffusion flames. The OJB flames were formed by a laminar jet of (N2 and/or HC)-diluted H2 mixture opposed by a similar jet of air at ambient conditions. The OJB data, derived from respective binary mixtures of H2 and methane, ethylene, or propane HCs, were used to characterize BLOWOFF and RESTORE. BLOWOFF is a sudden breaking of the dish-shaped OJB flame to a stable torus or ring shape, and RESTORE marks sudden restoration of the central flame by radial inward flame propagation. BLOWOFF is a measure of kinetically-limited flame reactivity/speed under highly stretched, but relatively ideal impingement flow conditions. RESTORE measures inward radial flame propagation rate, which is sensitive to ignition processes in the cool central core. It is concluded that relatively small molar amounts of added HC greatly reduce the reactivity characteristics of counterflow hydrogen-air diffusion flames, for ambient initial conditions.

  4. Numerical modeling of NO formation in laminar Bunsen flames -- A flamelet approach

    SciTech Connect

    Chou, C.P.; Chen, J.Y.; Yam, C.G.; Marx, K.D.

    1998-08-01

    Based on the flamelet concept, a numerical model has been developed for fast predictions of NO{sub x} and CO emissions from laminar flames. The model is applied to studying NO formation in the secondary nonpremixed flame zone of fuel-rich methane Bunsen flames. By solving the steady-state flamelet equations with the detailed GR12.1 methane-air mechanism, a flamelet library is generated containing thermochemical information for a range of scalar dissipation rates at the ambient pressure condition. Modeling of NO formation is made by solving its conservation equation with chemical source term evaluated based on flamelet library using the extended Zeldovich mechanism and NO reburning reactions. The optically-thin radiation heat transfer model is used to explore the potential effect of heat loss on thermal NO formation. The numerical scheme solves the two-dimensional Navier-Stokes equations as well as three additional equations: the mixture fraction, the NO mass fraction, and the enthalpy deficit due to radiative heat loss. With an established flamelet library, typical computing times are about 5 hours per calculation on a DEC-3000 300LX workstation. The predicted mixing field, radial temperature profiles, and NO distributions compare favorably with recent experimental data obtained by Nguyen et al. The dependence of NO{sub x} emission on equivalence ratio is studied numerically and the predictions are found to agree reasonably well with the measurements by Muss. The computed results show a decreasing trend of NO{sub x} emission with the equivalence ratio but an increasing trend in the CO emission index. By examining this trade-off between NO{sub x} and CO, an optimal equivalence ratio of 1.4 is found to yield the lowest combined emission.

  5. Rich premixed laminar methane flames doped by light unsaturated hydrocarbons. II. 1,3-Butadiene

    SciTech Connect

    Gueniche, H.A.; Glaude, P.A.; Fournet, R.; Battin-Leclerc, F.

    2007-10-15

    In line with the study presented in Part I of this paper, the structure of a rich premixed laminar methane flame doped with 1,3-butadiene has been investigated. The flame contains 20.7% (molar) of methane, 31.4% of oxygen, and 3.3% of 1,3-butadiene, corresponding to an equivalence ratio of 1.8, and a C{sub 4}H{sub 6}/CH{sub 4} ratio of 16%. The flame has been stabilized on a burner at a pressure of 6.7 kPa using argon as dilutant, with a gas velocity at the burner of 36 cm/s at 333 K. The temperature ranged from 600 K close to the burner up to 2150 K. Quantified species included the usual methane C{sub 0}-C{sub 2} combustion products and 1,3-butadiene, but also propyne, allene, propene, propane, 1,2-butadiene, butynes, vinylacetylene, diacetylene, 1,3-pentadiene, 2-methyl-1,3-butadiene (isoprene), 1-pentene, 3-methyl-1-butene, benzene, and toluene. To model these new results, some improvements have been made to a mechanism previously developed in our laboratory for the reactions of C{sub 3}-C{sub 4} unsaturated hydrocarbons. The main reaction pathways of consumption of 1,3-butadiene and of formation of C{sub 6} aromatic species have been derived from flow rate analyses. In this case, the C{sub 4} route to benzene formation plays an important role in comparison to the C{sub 3} pathway. (author)

  6. Soot precursor measurements in benzene and hexane diffusion flames

    SciTech Connect

    Kobayashi, Y.; Furuhata, T.; Amagai, K.; Arai, M.

    2008-08-15

    To clarify the mechanism of soot formation in diffusion flames of liquid fuels, measurements of soot and its precursors were carried out. Sooting diffusion flames formed by a small pool combustion equipment system were used for this purpose. Benzene and hexane were used as typical aromatic and paraffin fuels. A laser-induced fluorescence (LIF) method was used to obtain spatial distributions of polycyclic aromatic hydrocarbons (PAHs), which are considered as soot particles. Spatial distributions of soot in test flames were measured by a laser-induced incandescence (LII) method. Soot diameter was estimated from the temporal change of LII intensity. A region of transition from PAHs to soot was defined from the results of LIF and LII. Flame temperatures, PAH species, and soot diameters in this transition region were investigated for both benzene and hexane flames. The results show that though the flame structures of benzene and hexane were different, the temperature in the PAHs-soot transition region of the benzene flame was similar to that of the hexane flame. Furthermore, the relationship between the PAH concentrations measured by gas chromatography in both flames and the PAH distributions obtained from LIF are discussed. It was found that PAHs with smaller molecular mass, such as benzene and toluene, remained in both the PAHs-soot transition and sooting regions, and it is thought that molecules heavier than pyrene are the leading candidates for soot precursor formation. (author)

  7. Lateral Diffusion of Bedload Transport under Laminar Flow

    NASA Astrophysics Data System (ADS)

    Ortiz, C. P.; Houssais, M.; Purohit, P. K.; Durian, D. J.; Jerolmack, D. J.

    2014-12-01

    Lateral sediment transport is a key momentum-exchange mechanism to model equilibrium channel geometry and channel bar evolution. We study sediment transport from a statistical mechanical point of view akin to Furbish et al. 2012. This approach holds promise for linking grain-scale motion to macroscopic transport, but there are few data to definitively develop and test such models. We study an experimental model river, composed of monodisperse acrylic spheres dispersed in silicon oil, driven by a layer of fluid under steady shear. We choose to drive fluid flow in the laminar regime (Re < 1) to suppress fluid turbulence and isolate granular and bed structure controls. We use a refractive-index-matched laser scanning technique to observe the motion of particles at the surface of the bed as well as the particle dynamics below the surface. We study how the probability distribution of displacements varies as a function of distance from the bed surface and as a function of distance to the channel center. In the streamwise direction, in agreement with Furbish et al. 2012, we find that the dynamics can be decomposed into an advection and a diffusion term. In the lateral direction, we find a competition between diffusion and an elastic-like interaction with the bed. We study this lateral stochastic process and find a need to introduce two parameters to quantify this competition. The first parameter describes the tendency for particles to reside near the center of the channel and the second parameter describes the kinetic energy distribution of the particles. We study how the requisite averaging scales and ensemble sizes to achieve statistically convergent parameters, and we explore how these parameters depend on the driving rate.

  8. The Effects of Flame Structure on Extinction of CH4-O2-N2 Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Du, J.; Axelbaum, R. L.; Gokoglu, S. (Technical Monitor)

    1996-01-01

    The effects of flame structure on the extinction limits of CH4-O2-N2 counterflow diffusion flames were investigated experimentally and numerically by varying the stoichiometric mixture fraction Z(sub st), Z(sub st) was varied by varying free-stream concentrations, while the adiabatic flame temperature T(sub ad) was held fixed by maintaining a fixed amount of nitrogen at the flame. Z(sub st) was varied between 0.055 (methane-air flame) and 0.78 (diluted- methane-oxygen flame). The experimental results yielded an extinction strain rate K(sub ext) of 375/s for the methane-air flame, increasing monotonically to 1042/s for the diluted-methane-oxygen flame. Numerical results with a 58-step Cl mechanism yielded 494/s and 1488/s, respectively. The increase in K(sub ext) with Z(sub st) for a fixed T(sub ad) is explained by the shift in the O2 profile toward the region of maximum temperature and the subsequent increase in rates for chain-branching reactions. The flame temperature at extinction reached a minimum at Z(sub st) = 0.65, where it was 200 C lower than that of the methane-air flame. This significant increase in resistance to extinction is seen to correspond to the condition in which the OH and O production zones are centered on the location of maximum temperature.

  9. Effects of water-contaminated air on blowoff limits of opposed jet hydrogen-air diffusion flames

    NASA Technical Reports Server (NTRS)

    Pellett, Gerald L.; Jentzen, Marilyn E.; Wilson, Lloyd G.; Northam, G. Burton

    1988-01-01

    The effects of water-contaminated air on the extinction and flame restoration of the central portion of N2-diluted H2 versus air counterflow diffusion flames are investigated using a coaxial tubular opposed jet burner. The results show that the replacement of N2 contaminant in air by water on a mole for mole basis decreases the maximum sustainable H2 mass flow, just prior to extinction, of the flame. This result contrasts strongly with the analogous substitution of water for N2 in a relatively hot premixed H2-O2-N2 flame, which was shown by Koroll and Mulpuru (1986) to lead to a significant, kinetically controlled increase in laminar burning velocity.

  10. Flame Design: A Novel Approach Developed to Produce Clean, Efficient Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Axelbaum, Richard L.; Urban, David L.; Sunderland, Peter B.; Chao, Beei-Huan

    2000-01-01

    Soot formation and flame extinction are vital concerns in the combustion of fossil fuels. In particular, soot is responsible for pollutant emissions, and extinction can cause inefficient or unstable burning. Normal-gravity experiments have demonstrated that flames can be designed to improve both characteristics by redirecting some or all of the nitrogen from the oxidizer into the fuel. Such nitrogen exchange can produce permanently blue flames, which are soot free under all possible flame conditions. Furthermore, this approach can lead to stronger, extinction-resistant flames. Past investigations of nitrogen exchange were unable to identify the physical mechanisms responsible for its benefits because these mechanisms cannot be isolated when normal-gravity flames are studied. In contrast, the Diffusion Flame Extinction and Soot Inception (DESI) experiment considers spherical flames, where nearly perfect spherical symmetry affords new levels of control. Because of buoyancy, spherical flames cannot be created in Earth s gravity. DESI was conceived by principal investigator Professor R.L. Axelbaum of Washington University in St. Louis. Tests to date have utilized the 2.2-Second Drop Tower at the NASA Glenn Research Center at Lewis Field. The experiment is slated for testing aboard the International Space Station in a few years. Two mechanisms have been proposed to explain the connection between nitrogen exchange and permanently blue flames. These are the structure (chemical effects) and hydrodynamics (flow direction and speed). In normal-gravity flames, the structure and hydrodynamics are coupled, since nitrogen exchange simultaneously modifies both. Spherical microgravity flames, on the other hand, allow independent control of these factors. Specifically, structure can be modified via nitrogen exchange, and flow direction can be reversed by swapping the ambient and burner-feed gases. In DESI, these variations can be accomplished without changing the theoretical flame

  11. Determination, correlation, and mechanistic interpretation of effects of hydrogen addition on laminar flame speeds of hydrocarbon–air mixtures

    SciTech Connect

    Tang, C. L.; Huang, Z. H.; Law, C. K.

    2010-08-30

    The stretch-affected propagation speeds of expanding spherical flames of n-butane–air mixtures with hydrogen addition were measured at atmospheric pressure and subsequently processed through a nonlinear regression analysis to yield the stretch-free laminar flame speeds. Based on a hydrogen addition parameter (RH) and an effective fuel equivalence ratio (ΦF), these laminar flame speeds were found to increase almost linearly with RH, for ΦF between 0.6 and 1.4 and RHRH from 0 to 0.5, with the slope of the variation assuming a minimum around stoichiometry. These experimental results also agree well with computed values using a detailed reaction mechanism. Furthermore, a mechanistic investigation aided by sensitivity analysis identified that kinetic effects through the global activation energy, followed by thermal effects through the adiabatic flame temperature, have the most influence on the increase in the flame speeds and the associated linear variation with RH due to hydrogen addition. Nonequidiffusion effects due to the high mobility of hydrogen, through the global Lewis number, have the least influence. Further calculations for methane, ethene, and propane as the fuel showed similar behavior, leading to possible generalization of the phenomena and correlation.

  12. Saturated fluorescence measurements of the hydroxyl radical in laminar high-pressure flames

    NASA Technical Reports Server (NTRS)

    Carter, Campbell D.; King, Galen B.; Laurendeau, Normand M.

    1990-01-01

    The efficacy of laser saturated fluorescence (LSF) for OH concentration measurements in high pressure flames was studied theoretically and experimentally. Using a numerical model describing the interaction of hydroxyl with nonuniform laser excitation, the effect of pressure on the validity of the balanced cross-rate model was studied along with the sensitivity of the depopulation of the laser-coupled levels to the ratio of rate coefficients describing: (1) electronic quenching to (sup 2) Sigma (+) (v double prime greater than 0), and (2) vibrational relaxation from v double prime greater than 0 to v double prime = 0. At sufficiently high pressures and near-saturated conditions, the total population of the laser-coupled levels reaches an asymptotic value, which is insensitive to the degree of saturation. When the ratio of electronic quenching to vibrational relaxation is small and the rate of coefficients for rotational transfer in the ground and excited electronic states are nearly the same, the balanced cross-rate model remains a good approximation for all pressures. When the above ratio is large, depopulation of the laser-coupled levels becomes significant at high pressures, and thus the balanced cross-rate model no longer holds. Under these conditions, however, knowledge of the depletion of the laser-coupled levels can be used to correct the model. A combustion facility for operation up to 20 atm was developed to allow LSF measurements of OH in high pressure flames. Using this facility, partial saturation in laminar high pressure (less than or equal to 12.3 atm) C2H6/O2/N2 flames was achieved. To evaluate the limits of the balanced cross-rate model, absorption and calibrated LSF measurements at 3.1 and 6.1 atm were compared. The fluorescence voltages were calibrated with absorption measurements in an atmospheric flame and corrected for their finite sensitivity to quenching with: (1) estimated quenching rate coefficients, and (2) an in situ measurement from a

  13. Theoretical and Numerical Investigation of Radiative Extinction of Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Ray, Anjan

    1996-01-01

    The influence of soot radiation on diffusion flames was investigated using both analytical and numerical techniques. Soot generated in diffusion flames dominate the flame radiation over gaseous combustion products and can significantly lower the temperature of the flame. In low gravity situations there can be significant accumulation of soot and combustion products in the vicinity of the primary reaction zone owing to the absence of any convective buoyant flow. Such situations may result in substantial suppression of chemical activities in a flame, and the possibility of a radiative extinction may also be anticipated. The purpose of this work was to not only investigate the possibility of radiative extinction of a diffusion flame but also to qualitatively and quantitatively analyze the influence of soot radiation on a diffusion flame. In this study, first a hypothetical radiative loss profile of the form of a sech(sup 2) was assumed to influence a pure diffusion flame. It was observed that the reaction zone can, under certain circumstances, move through the radiative loss zone and locate itself on the fuel side of the loss zone contrary to our initial postulate. On increasing the intensity and/or width of the loss zone it was possible to extinguish the flame, and extinction plots were generated. In the presence of a convective flow, however, the movement of the temperature and reaction rate peaks indicated that the flame behavior is more complicated compared to a pure diffusional flame. A comprehensive model of soot formation, oxidation and radiation was used in a more involved analysis. The soot model of Syed, Stewart and Moss was used for soot nucleation and growth and the model of Nagle and Strickland-Constable was used for soot oxidation. The soot radiation was considered in the optically thin limit. An analysis of the flame structure revealed that the radiative loss term is countered both by the reaction term and the diffusion term. The essential balance for

  14. Planar Strain-Rate-Free Diffusion Flames: Initiation, Properties, and Extinction

    NASA Technical Reports Server (NTRS)

    Fendell, Francis; Gokoglu, Suleyman; Rungaldier, Harald; Schultz, Donald

    1999-01-01

    An effectively strain-rate-free diffusion flame constitutes the most vigorous laminar combustion of initially unmixed reactive gases. Such a diffusion flame is characterized by a relatively long residence time and by a relatively large characteristic length scale. If such a flame were also planar, providing high symmetry, it would be particularly suitable for experimental and theoretical investigations of key combustion phenomena, such as multicomponent diffusion, chemical kinetics, and soot inception, growth, and oxidation. Unfortunately, a planar strain-rate-free diffusion flame is highly disrupted in earth-gravity (e.g., in a counterflow-diffusion-flame apparatus) because of the very rapid onset (approx. 100 ms) of gravity-induced instability. Accordingly, a specially dedicated apparatus was designed, fabricated, and initially checked out for the examination of a planar strain-rate-free diffusion flame in microgravity. Such a diffusion flame may be formed within a hollowed-out squat container (initially configured as 25 cm x 25 cm x 9 cm), with isothermal, noncatalytic, impervious walls. At test initiation, a thin metallic sheet (approx. 1 mm in thickness) that separates the internal volume into two equal portions, each of dimensions 25 cm x 25 cm x 4.5 cm, is withdrawn, by uniform translation (approx. 50 cm/s) in its own plane, through a tightly fitting slit in one side wall. Thereupon, diluted fuel vapor (initially confined to one half-volume of the container) gains access to diluted oxygen (initially with the same pressure, density, and temperature as the fuel, but initially confined to the other half-volume). After a brief delay (approx. 10 ms), to permit limited but sufficient-for-flammability diffusional interpenetration of fuel vapor and oxidizer, burning is initiated by discharge of a line igniter, located along that side wall from which the trailing edge of the separator withdraws. The ignition spawns a triple-flame propagation across the 25 cm x 25 cm

  15. Laminar Soot Processes (LSP)

    NASA Technical Reports Server (NTRS)

    Dai, Z.; El-Leathy, A. M.; Kim, C. H.; Krishnan, S. S.; Lin, K.-C.; Xu, F.; Faeth, G. M.

    2002-01-01

    This is the final report of a research program considering the structure and the soot surface reaction properties of laminar nonpremixed (diffusion) flames. The study was limited to ground-based measurements of buoyant laminar jet diffusion flames at pressures of 0.1-1.0 atm. The motivation for the research is that soot formation in flames is a major unresolved problem of combustion science that influences the pollutant emissions, durability and performance of power and propulsion systems, as well as the potential for developing computational combustion. The investigation was divided into two phases considering the structure of laminar soot-containing diffusion flames and the soot surface reaction properties (soot surface growth and oxidation) of these flames, in turn. The first phase of the research addressed flame and soot structure properties of buoyant laminar jet diffusion flames at various pressures. The measurements showed that H, OH and O radical concentrations were generally in superequilibrium concentrations at atmospheric pressure but tended toward subequilibrium concentrations as pressures decreased. The measurements indicated that the original fuel decomposed into more robust compounds at elevated temperatures, such as acetylene (unless the original fuel was acetylene) and H, which are the major reactants for soot surface growth, and that the main effect of the parent fuel on soot surface growth involved its yield of acetylene and H for present test conditions. The second phase of the research addressed soot surface reaction properties, e.g., soot surface growth and surface oxidation. It was found that soot surface growth rates in both laminar premixed and diffusion flames were in good agreement, that these rates were relatively independent of fuel type, and that these rates could be correlated by the Hydrogen-Abstraction/Carbon-Addition (HACA) mechanisms of Colket and Hall (1994), Frenklach et al. (1990,1994), and Kazakov et al. (1995). It was also

  16. Dynamics and Structure of Dusty Reacting Flows: Inert Particles in Strained, Laminar, Premixed Flames

    NASA Technical Reports Server (NTRS)

    Egolfopoulos, Fokion N.; Campbell, Charles S.; Wu, Ming-Shin (Technical Monitor)

    1999-01-01

    A detailed numerical study was conducted on the dynamics and thermal response of inert spherical particles in strained, laminar, premixed hydrogen/air flames. The modeling included the solution of the steady conservation equations for both the gas and particle phases along and around the stagnation streamline of an opposed-jet configuration, and the use of detailed descriptions of chemical kinetics and molecular transport. For the gas phase, the equations of mass, momentum, energy, and species are considered, while for the particle phase, the model is based on conservation equations of the particle momentum balance in the axial and radial direction, the particle number density, and the particle thermal energy equation. The particle momentum equation includes the forces as induced by drag, thermophoresis, and gravity. The particle thermal energy equation includes the convective/conductive heat exchange between the two phases, as well as radiation emission and absorption by the particle. A one-point continuation method is also included in the code that allows for the description of turning points, typical of ignition and extinction behavior. As expected, results showed that the particle velocity can be substantially different than the gas phase velocity, especially in the presence of large temperature gradients and large strain rates. Large particles were also found to cross the gas stagnation plane, stagnate, and eventually reverse as a result of the opposing gas phase velocity. It was also shown that the particle number density varies substantially throughout the flowfield, as a result of the straining of the flow and the thermal expansion. Finally, for increased values of the particle number density, substantial flame cooling to extinction states and modification of the gas phase fluid mechanics were observed. As also expected, the effect of gravity was shown to be important for low convective velocities and heavy particles. Under such conditions, simulations

  17. Dynamics and Structure of Dusty Reacting Flows: Inert Particles in Strained, Laminar, Premixed Flames

    NASA Technical Reports Server (NTRS)

    Egolfopoulos, Fokion N.; Campbell, Charles S.

    1999-01-01

    A detailed numerical study was conducted on the dynamics and thermal response of inert, spherical particles in strained, laminar, premixed hydrogen/air flames. The modeling included the solution of the steady conservation equations for both the gas and particle phases along and around the stagnation streamline of an opposed-jet configuration, and the use of detailed descriptions of chemical kinetics and molecular transport, For the gas phase, the equations of mass, momentum, energy, and species are considered, while for the particle phase, the model is based on conservation equations of the particle momentum balance in the axial and radial direction, the particle number density, and the particle thermal energy equation. The particle momentum equation includes the forces as induced by drag, thermophoresis, and gravity. The particle thermal energy equation includes the convective/conductive heat exchange between the two phases, as well as radiation emission and absorption by the particle. A one-point continuation method is also included in the code that allows for the description of turning points, typical of ignition and extinction behavior. As expected, results showed that the particle velocity can be substantially different than the gas phase velocity, especially in the presence of large temperature gradients and large strain rates. Large particles were also found to cross the gas stagnation plane, stagnate, and eventually reverse as a result of the opposing gas phase velocity. It was also shown that the particle number density varies substantially throughout the flowfield, as a result of the straining of the flow and the thermal expansion. Finally, for increased values of the particle number density, substantial flame cooling to extinction states and modification of the gas phase fluid mechanics were observed. As also expected, the effect of gravity was shown to be important for low convective velocities and heavy particles. Under such conditions, simulations

  18. Flow characterization of diffusion flame oscillations using particle image velocimetry

    NASA Astrophysics Data System (ADS)

    Yilmaz, Nadir; Lucero, Ralph E.; Donaldson, A. Burl; Gill, Walt

    2009-04-01

    Particle image velocimetry (PIV) was used to measure velocity fields inside and around oscillating methane-air diffusion flames with a slot fuel orifice. PIV provided velocity and directional information of the flow field comprised of both the flame and air. From this, information on flow paths of entrained air into the flame were obtained and visualized. These show that at low fuel flow rates for which the oscillations were strongest, the responsible mechanism for the oscillating flow appeared to be the repetitive occurrence of flame quenching. PIV findings indicated that quenching appears to be associated primarily with air entrainment. Velocity was found to be considerably larger in regions where quenching occurred. The shedding of vortices in the shear layer occurs immediately outside the boundary of the flame envelope and was speculated to be the primary driving force for air entrainment.

  19. Gravity effects on stability and flickering motion of diffusion flames

    NASA Astrophysics Data System (ADS)

    Yilmaz, Nadir; Lucero, Ralph E.; Donaldson, A. Burl; Gill, Walt

    2009-01-01

    Particle image velocimetry (PIV) was used to measure velocity fields inside and around oscillating methane-air diffusion flames with a slot fuel orifice. PIV provided velocity and directional information of the flow field comprised of both the flame and air. From this, information on flow paths of entrained air into the flame were obtained and visualized. These show that at low fuel flow rates for which the oscillations were strongest, the responsible mechanism for the oscillating flow appeared to be the repetitive occurrence of flame quenching. PIV findings indicated that quenching appears to be associated primarily with air entrainment. Velocity was found to be considerably larger in regions where quenching occurred. The shedding of vortices in the shear layer occurs immediately outside the boundary of the flame envelope and was speculated to be the primary driving force for air entrainment.

  20. Chaotic map models of soot fluctuations in turbulent diffusion flames

    SciTech Connect

    Mukerji, S.; McDonough, J.M.; Menguec, M.P.; Manickavasagam, S.; Chung, S.

    1998-10-01

    In this paper, the authors introduce a methodology to characterize time-dependent soot volume fraction fluctuations in turbulent diffusion flames via chaotic maps. The approach is based on the hypothesis that fluctuations of properties in turbulent flames are deterministic in nature, rather than statistical. The objective is to develop models of these fluctuations to be used in comprehensive algorithms to study the nature of turbulent flames and the interaction of turbulence with radiation. To this end the authors measured the time series of soot scattering coefficient in an ethylene diffusion flame from light scattering experiments and fit these data to linear combinations of chaotic maps of the unit interval. Both time series and power spectra can be modeled with reasonable accuracy in this way.

  1. Extinction of low-stretched diffusion flame in microgravity

    SciTech Connect

    Maruta, Kaoru; Yoshida, Masaharu; Guo, Hongsheng; Ju, Yiguang; Niioka, Takashi

    1998-01-01

    Extinction of counterflow diffusion flames of air and methane diluted with nitrogen is studied by drop tower experiments and numerical calculation using detailed chemistry and transport properties. Radiative heat loss from the flame zone is taken into consideration. Experimental results identified two kinds of extinction at the same fuel concentration, that is, in addition to the widely known stretch extinction, another type of extinction is observed when the stretch rate is sufficiently low. Consequently, plots of stretch rates versus fuel concentration limits exhibit a C-shaped extinction curve. Numerical calculation including radiative heat loss from the flame zone qualitatively agreed with the experimental results and indicated that the mechanism of counterflow diffusion flame extinction at low stretch rates was radiative heat loss.

  2. Counterflow diffusion flame synthesis of ceramic oxide powders

    DOEpatents

    Katz, J.L.; Miquel, P.F.

    1997-07-22

    Ceramic oxide powders and methods for their preparation are revealed. Ceramic oxide powders are obtained using a flame process whereby one or more precursors of ceramic oxides are introduced into a counterflow diffusion flame burner wherein the precursors are converted into ceramic oxide powders. The nature of the ceramic oxide powder produced is determined by process conditions. The morphology, particle size, and crystalline form of the ceramic oxide powders may be varied by the temperature of the flame, the precursor concentration ratio, the gas stream and the gas velocity. 24 figs.

  3. Counterflow diffusion flame synthesis of ceramic oxide powders

    DOEpatents

    Katz, Joseph L.; Miquel, Philippe F.

    1997-01-01

    Ceramic oxide powders and methods for their preparation are revealed. Ceramic oxide powders are obtained using a flame process whereby one or more precursors of ceramic oxides are introduced into a counterflow diffusion flame burner wherein the precursors are converted into ceramic oxide powders. The nature of the ceramic oxide powder produced is determined by process conditions. The morphology, particle size, and crystalline form of the ceramic oxide powders may be varied by the temperature of the flame, the precursor concentration ratio, the gas stream and the gas velocity.

  4. A study of hydrogen diffusion flames using PDF turbulence model

    NASA Technical Reports Server (NTRS)

    Hsu, Andrew T.

    1991-01-01

    The application of probability density function (pdf) turbulence models is addressed in this work. For the purpose of accurate prediction of turbulent combustion, an algorithm that combines a conventional CFD flow solver with the Monte Carlo simulation of the pdf evolution equation has been developed. The algorithm has been validated using experimental data for a heated turbulent plane jet. The study of H2-F2 diffusion flames has been carried out using this algorithm. Numerical results compared favorably with experimental data. The computuations show that the flame center shifts as the equivalence ratio changes, and that for the same equivalence ratio, similarity solutions for flames exist.

  5. A study of hydrogen diffusion flames using PDF turbulence model

    NASA Technical Reports Server (NTRS)

    Hsu, Andrew T.

    1991-01-01

    The application of probability density function (pdf) turbulence models is addressed. For the purpose of accurate prediction of turbulent combustion, an algorithm that combines a conventional computational fluid dynamic (CFD) flow solver with the Monte Carlo simulation of the pdf evolution equation was developed. The algorithm was validated using experimental data for a heated turbulent plane jet. The study of H2-F2 diffusion flames was carried out using this algorithm. Numerical results compared favorably with experimental data. The computations show that the flame center shifts as the equivalence ratio changes, and that for the same equivalence ratio, similarity solutions for flames exist.

  6. A model of particulate and species formation applied to laminar, nonpremixed flames for three aliphatic-hydrocarbon fuels

    SciTech Connect

    D'Anna, A.; Kent, J.H.

    2008-03-15

    A detailed kinetic mechanism is developed that includes aromatic growth and particulate formation. The model includes reaction pathways leading to the formation of nanosized particles and their coagulation and growth to larger soot particles using a sectional approach for the particle phase. It is tested against literature data of species concentrations and particulate measurements in nonpremixed laminar flames of methane, ethylene, and butene. Reasonably good predictions of gas and particle-phase concentrations and particle sizes are obtained without any change to the kinetic scheme for the different fuels. The model predicts the low concentration of particulates in the methane flame (about 0.5 ppm) and the higher concentration of soot in the ethylene and butene flames (near 10 ppm). Model predictions show that in the methane flame small precursor particles dominate the particulate loading, whereas soot is the major component in ethylene and butene flames, in accordance with the experimental data. The driving factors in the model responsible for the quite different soot predictions in the ethylene and butene flames compared with the methane flame are benzene and acetylene concentrations, which are higher in the ethylene and butene flames. Soot loadings in the ethylene flame are sensitive to the acetylene soot growth reaction, whereas particle inception rates are linked to benzene in the model. A coagulation model is used to obtain collision efficiencies for some of the particle reactions, and tests show that the modeled results are not particularly sensitive to coagulation at the rates used in our model. Soot oxidation rates are not high enough to correctly predict burnout, and this aspect of the model needs further attention. (author)

  7. Diffusion Flame Tip Instabilities of a Wide Sample in Microgravity

    NASA Technical Reports Server (NTRS)

    Oravecz, Lisa; Wichman, Indrek

    1999-01-01

    This work is a study of diffusion flame tip instabilities of a wide thermally thin sample in a microgravity environment. The purpose of this work is to determine the thermodiffusive and hydrodynamic instability mechanisms which cause a spreading diffusion flame to become corrugated and later fragment into smaller separate flames that we call flamelets. These thermodiffusive and hydrodynamic mechanisms are prominent forces in the near limit because buoyancy is quashed in the microgravity environment. A fundamental knowledge of the underlying mechanisms controlling the extinction limit of a diffusion flame can be applied to any real world device involving a spreading diffusion flame as well as fire safety applications on earth and in space. Our work, which combines microgravity experiments, theoretical models, and numerical computation, is a joint effort between NASA and Michigan State University. Experiments in the 2.2 second drop tower at NASA Lewis Research Center in the Microgravity Combustion Branch have been a preliminary step in locating a region where these instabilities are prevalent. These positive results will be discussed as well as the second phase of our project and future plans and recommendations.

  8. Dynamics of Diffusion Flames in von Karman Swirling Flows Studied

    NASA Technical Reports Server (NTRS)

    Nayagam, Vedha; Williams, Forman A.

    2002-01-01

    Von Karman swirling flow is generated by the viscous pumping action of a solid disk spinning in a quiescent fluid media. When this spinning disk is ignited in an oxidizing environment, a flat diffusion flame is established adjacent to the disk, embedded in the boundary layer (see the preceding illustration). For this geometry, the conservation equations reduce to a system of ordinary differential equations, enabling researchers to carry out detailed theoretical models to study the effects of varying strain on the dynamics of diffusion flames. Experimentally, the spinning disk burner provides an ideal configuration to precisely control the strain rates over a wide range. Our original motivation at the NASA Glenn Research Center to study these flames arose from a need to understand the flammability characteristics of solid fuels in microgravity where slow, subbuoyant flows can exist, producing very small strain rates. In a recent work (ref. 1), we showed that the flammability boundaries are wider and the minimum oxygen index (below which flames cannot be sustained) is lower for the von Karman flow configuration in comparison to a stagnation-point flow. Adding a small forced convection to the swirling flow pushes the flame into regions of higher strain and, thereby, decreases the range of flammable strain rates. Experiments using downward facing, polymethylmethacrylate (PMMA) disks spinning in air revealed that, close to the extinction boundaries, the flat diffusion flame breaks up into rotating spiral flames (refs. 2 and 3). Remarkably, the dynamics of these spiral flame edges exhibit a number of similarities to spirals observed in biological systems, such as the electric pulses in cardiac muscles and the aggregation of slime-mold amoeba. The tail of the spiral rotates rigidly while the tip executes a compound, meandering motion sometimes observed in Belousov-Zhabotinskii reactions.

  9. Flame-in-gas-shield and miniature diffusion flame hydride atomizers for atomic fluorescence spectrometry: optimization and comparison

    NASA Astrophysics Data System (ADS)

    Marschner, Karel; Musil, Stanislav; Dědina, Jiří

    2015-07-01

    A detailed optimization of relevant experimental parameters of two hydride atomizers for atomic fluorescence spectrometry: flame-in-gas-shield atomizer with a two-channel shielding unit and a standard atomizer for atomic fluorescence spectrometry, miniature diffusion flame, was performed. Arsine, generated by the reaction with NaBH4 in a flow injection arrangement, was chosen as the model hydride. Analytical characteristics of both the atomizers (sensitivity, noise, limits of detection) were compared. Under optimum conditions sensitivity obtained with flame-in-gas-shield atomizer was approximately twice higher than with miniature diffusion flame. The additional advantage of flame-in-gas-shield atomizer is significantly lower flame emission resulting in a better signal to noise ratio. The resulting arsenic limits of detection for miniature diffusion flame and flame-in-gas-shield atomizer were 3.8 ng l- 1 and 1.0 ng l- 1, respectively.

  10. Measurements and Modeling of Soot Formation and Radiation in Microgravity Jet Diffusion Flames. Volume 4

    NASA Technical Reports Server (NTRS)

    Ku, Jerry C.; Tong, Li; Greenberg, Paul S.

    1996-01-01

    This is a computational and experimental study for soot formation and radiative heat transfer in jet diffusion flames under normal gravity (1-g) and microgravity (0-g) conditions. Instantaneous soot volume fraction maps are measured using a full-field imaging absorption technique developed by the authors. A compact, self-contained drop rig is used for microgravity experiments in the 2.2-second drop tower facility at NASA Lewis Research Center. On modeling, we have coupled flame structure and soot formation models with detailed radiation transfer calculations. Favre-averaged boundary layer equations with a k-e-g turbulence model are used to predict the flow field, and a conserved scalar approach with an assumed Beta-pdf are used to predict gaseous species mole fraction. Scalar transport equations are used to describe soot volume fraction and number density distributions, with formation and oxidation terms modeled by one-step rate equations and thermophoretic effects included. An energy equation is included to couple flame structure and radiation analyses through iterations, neglecting turbulence-radiation interactions. The YIX solution for a finite cylindrical enclosure is used for radiative heat transfer calculations. The spectral absorption coefficient for soot aggregates is calculated from the Rayleigh solution using complex refractive index data from a Drude- Lorentz model. The exponential-wide-band model is used to calculate the spectral absorption coefficient for H20 and C02. It is shown that when compared to results from true spectral integration, the Rosseland mean absorption coefficient can provide reasonably accurate predictions for the type of flames studied. The soot formation model proposed by Moss, Syed, and Stewart seems to produce better fits to experimental data and more physically sound than the simpler model by Khan et al. Predicted soot volume fraction and temperature results agree well with published data for a normal gravity co-flow laminar

  11. Effects of H2O, CO2, and N2 Air Contaminants on Critical Airside Strain Rates for Extinction of Hydrogen-Air Counterflow Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Wilson, L. G.; Northam, G. B.; Guerra, Rosemary

    1989-01-01

    Coaxial tubular opposed jet burners (OJB) were used to form dish shaped counterflow diffusion flames (CFDF), centered by opposing laminar jets of H2, N2 and both clean and contaminated air (O2/N2 mixtures) in an argon bath at 1 atm. Jet velocities for flame extinction and restoration limits are shown versus wide ranges of contaminant and O2 concentrations in the air jet, and also input H2 concentration. Blowoff, a sudden breaking of CFDF to a stable ring shape, occurs in highly stretched stagnation flows and is generally believed to measure kinetically limited flame reactivity. Restore, a sudden restoration of central flame, is a relatively new phenomenon which exhibits a H2 dependent hysteresis from Blowoff. For 25 percent O2 air mixtures, mole for mole replacement of 25 percent N2 contaminant by steam increased U(air) or flame strength at Blowoff by about 5 percent. This result is consistent with laminar burning velocity results from analogous substitution of steam for N2 in a premixed stoichiometric H2-O2-N2 (or steam) flame, shown by Koroll and Mulpuru to promote a 10 percent increase in experimental and calculated laminar burning velocity, due to enhanced third body efficiency of water in: H + O2 + M yields HO2 + M. When the OJB results were compared with Liu and MacFarlane's experimental laminar burning velocity of premixed stoichiometric H2 + air + steam, a crossover occurred, i.e., steam enhanced OJB flame strength at extinction relative to laminar burning velocity.

  12. Effect of fuel composition and differential diffusion on flame stabilization in reacting syngas jets in turbulent cross-flow

    DOE PAGES

    Minamoto, Yuki; Kolla, Hemanth; Grout, Ray W.; Gruber, Andrea; Chen, Jacqueline H.

    2015-07-24

    Here, three-dimensional direct numerical simulation results of a transverse syngas fuel jet in turbulent cross-flow of air are analyzed to study the influence of varying volume fractions of CO relative to H2 in the fuel composition on the near field flame stabilization. The mean flame stabilizes at a similar location for CO-lean and CO-rich cases despite the trend suggested by their laminar flame speed, which is higher for the CO-lean condition. To identify local mixtures having favorable mixture conditions for flame stabilization, explosive zones are defined using a chemical explosive mode timescale. The explosive zones related to flame stabilization aremore » located in relatively low velocity regions. The explosive zones are characterized by excess hydrogen transported solely by differential diffusion, in the absence of intense turbulent mixing or scalar dissipation rate. The conditional averages show that differential diffusion is negatively correlated with turbulent mixing. Moreover, the local turbulent Reynolds number is insufficient to estimate the magnitude of the differential diffusion effect. Alternatively, the Karlovitz number provides a better indicator of the importance of differential diffusion. A comparison of the variations of differential diffusion, turbulent mixing, heat release rate and probability of encountering explosive zones demonstrates that differential diffusion predominantly plays an important role for mixture preparation and initiation of chemical reactions, closely followed by intense chemical reactions sustained by sufficient downstream turbulent mixing. The mechanism by which differential diffusion contributes to mixture preparation is investigated using the Takeno Flame Index. The mean Flame Index, based on the combined fuel species, shows that the overall extent of premixing is not intense in the upstream regions. However, the Flame Index computed based on individual contribution of H2 or CO species reveals that hydrogen

  13. Effect of fuel composition and differential diffusion on flame stabilization in reacting syngas jets in turbulent cross-flow

    SciTech Connect

    Minamoto, Yuki; Kolla, Hemanth; Grout, Ray W.; Gruber, Andrea; Chen, Jacqueline H.

    2015-07-24

    Here, three-dimensional direct numerical simulation results of a transverse syngas fuel jet in turbulent cross-flow of air are analyzed to study the influence of varying volume fractions of CO relative to H2 in the fuel composition on the near field flame stabilization. The mean flame stabilizes at a similar location for CO-lean and CO-rich cases despite the trend suggested by their laminar flame speed, which is higher for the CO-lean condition. To identify local mixtures having favorable mixture conditions for flame stabilization, explosive zones are defined using a chemical explosive mode timescale. The explosive zones related to flame stabilization are located in relatively low velocity regions. The explosive zones are characterized by excess hydrogen transported solely by differential diffusion, in the absence of intense turbulent mixing or scalar dissipation rate. The conditional averages show that differential diffusion is negatively correlated with turbulent mixing. Moreover, the local turbulent Reynolds number is insufficient to estimate the magnitude of the differential diffusion effect. Alternatively, the Karlovitz number provides a better indicator of the importance of differential diffusion. A comparison of the variations of differential diffusion, turbulent mixing, heat release rate and probability of encountering explosive zones demonstrates that differential diffusion predominantly plays an important role for mixture preparation and initiation of chemical reactions, closely followed by intense chemical reactions sustained by sufficient downstream turbulent mixing. The mechanism by which differential diffusion contributes to mixture preparation is investigated using the Takeno Flame Index. The mean Flame Index, based on the combined fuel species, shows that the overall extent of premixing is not intense in the upstream regions. However, the Flame Index computed based on individual contribution of H2 or CO species reveals that

  14. Response analysis of a laminar premixed M-flame to flow perturbations using a linearized compressible Navier-Stokes solver

    SciTech Connect

    Blanchard, M.; Schuller, T.; Sipp, D.; Schmid, P. J.

    2015-04-15

    The response of a laminar premixed methane-air flame subjected to flow perturbations around a steady state is examined experimentally and using a linearized compressible Navier-Stokes solver with a one-step chemistry mechanism to describe combustion. The unperturbed flame takes an M-shape stabilized both by a central bluff body and by the external rim of a cylindrical nozzle. This base flow is computed by a nonlinear direct simulation of the steady reacting flow, and the flame topology is shown to qualitatively correspond to experiments conducted under comparable conditions. The flame is then subjected to acoustic disturbances produced at different locations in the numerical domain, and its response is examined using the linearized solver. This linear numerical model then allows the componentwise investigation of the effects of flow disturbances on unsteady combustion and the feedback from the flame on the unsteady flow field. It is shown that a wrinkled reaction layer produces hydrodynamic disturbances in the fresh reactant flow field that superimpose on the acoustic field. This phenomenon, observed in several experiments, is fully interpreted here. The additional perturbations convected by the mean flow stem from the feedback of the perturbed flame sheet dynamics onto the flow field by a mechanism similar to that of a perturbed vortex sheet. The different regimes where this mechanism prevails are investigated by examining the phase and group velocities of flow disturbances along an axis oriented along the main direction of the flow in the fresh reactant flow field. It is shown that this mechanism dominates the low-frequency response of the wrinkled shape taken by the flame and, in particular, that it fully determines the dynamics of the flame tip from where the bulk of noise is radiated.

  15. Buoyancy Effects in Fully-Modulated, Turbulent Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Hermanson, J. C.; Johari, H.; Ghaem-Maghami, E.; Stocker, D. P.; Hegde, U. G.; Page, K. L.

    2003-01-01

    Pulsed combustion appears to have the potential to provide for rapid fuel/air mixing, compact and economical combustors, and reduced exhaust emissions. The objective of this experiment (PuFF, for Pulsed-Fully Flames) is to increase the fundamental understanding of the fuel/air mixing and combustion behavior of pulsed, turbulent diffusion flames by conducting experiments in microgravity. In this research the fuel jet is fully-modulated (i.e., completely shut off between pulses) by an externally controlled valve system. This gives rise to drastic modification of the combustion and flow characteristics of flames, leading to enhanced fuel/air mixing compared to acoustically excited or partially-modulated jets. Normal-gravity experiments suggest that the fully-modulated technique also has the potential for producing turbulent jet flames significantly more compact than steady flames with no increase in exhaust emissions. The technique also simplifies the combustion process by avoiding the acoustic forcing generally present in pulsed combustors. Fundamental issues addressed in this experiment include the impact of buoyancy on the structure and flame length, temperatures, radiation, and emissions of fully-modulated flames.

  16. Buoyant Low Stretch Diffusion Flames Beneath Cylindrical PMMA Samples

    NASA Technical Reports Server (NTRS)

    Olson, S. L.; Tien, J. S.

    1999-01-01

    A unique new way to study low gravity flames in normal gravity has been developed. To study flame structure and extinction characteristics in low stretch environments, a normal gravity low-stretch diffusion flame is generated using a cylindrical PMMA sample of varying large radii. Burning rates, visible flame thickness, visible flame standoff distance, temperature profiles in the solid and gas, and radiative loss from the system were measured. A transition from the blowoff side of the flammability map to the quenching side of the flammability map is observed at approximately 6-7/ sec, as determined by curvefits to the non-monotonic trends in peak temperatures, solid and gas-phase temperature gradients, and non-dimensional standoff distances. A surface energy balance reveals that the fraction of heat transfer from the flame that is lost to in-depth conduction and surface radiation increases with decreasing stretch until quenching extinction is observed. This is primarily due to decreased heat transfer from the flame, while the magnitude of the losses remains the same. A unique local extinction flamelet phenomena and associated pre-extinction oscillations are observed at very low stretch. An ultimate quenching extinction limit is found at low stretch with sufficiently high induced heat losses.

  17. Strain-Rate-Free Diffusion Flames: Initiation, Properties, and Quenching

    NASA Technical Reports Server (NTRS)

    Fendell, Francis; Rungaldier, Harald; Gokoglu, Suleyman; Schultz, Donald

    1997-01-01

    For about a half century, the stabilization of a steady planar deflagration on a heat-sink-type flat-flame burner has been of extraordinary service for the theoretical modeling and diagnostic probing of combusting gaseous mixtures. However, most engineering devices and most unwanted fire involve the burning of initially unmixed reactants. The most vigorous burning of initially separated gaseous fuel and oxidizer is the diffusion flame. In this useful idealization (limiting case), the reactants are converted to product at a mathematically thin interface, so no interpenetration of fuel and oxidizer occurs. This limit is of practical importance because it often characterizes the condition of optimal performance (and sometimes environmentally objectionable operation) of a combustor. A steady planar diffusion flame is most closely approached in the laboratory in the counterflow apparatus. The utility of this simple-strain-rate flow for the modeling and probing of diffusion flames was noted by Pandya and Weinberg 35 years ago, though only in the last decade or so has its use become internationally common place. However, typically, as the strain rate a is reduced below about 20 cm(exp -1), and the diffusion-flame limit (reaction rate much faster than the flow rate) is approached, the burning is observed to become unstable in earth gravity. The advantageous steady planar flow is not available in the diffusion-flame limit in earth gravity. This is unfortunate because the typical spatial scale in a counterflow is (k/a)(sup 1/2), where k denotes a characteristic diffusion coefficient; thus, the length scale becomes large, and the reacting flow is particularly amenable to diagnostic probing, as the diffusion-flame limit is approached. The disruption of planar symmetry is owing the fact that, as the strain rate a decreases, the residence time (l/a) of the throughput in the counterflow burner increases. Observationally, when the residence time exceeds about 50 msec, the

  18. Agglomeration of soot particles in diffusion flames under microgravity

    SciTech Connect

    Ito, H.; Fujita, O.; Ito, K.

    1994-11-01

    Experiments have been conducted to investigate the behavior of soot particles in diffusion flames under microgravity conditions using a 490-m drop shaft (10-s microgravity duration) in Hokkaido, Japan. Flames from the combustion of paper sheets and butane jet diffusion flames are observed under microgravity. The oxygen concentration of the surroundings, the butane flow rate,and the burner diameter are varied as experimental parameters. The generated soot particles are sampled under microgravity and observed using scanning electron and transmission electron microscopes. The flames with a residual convection or forced convection are also observed to examine the influence of flow field on soot particle generation under microgravity. From these results, it is found that a number of large luminous spots appear in diffusion flames under microgravity. From the observation of TEM images, the luminous spots are the result of agglomerated soot particles and the growth of their diameters to a discernible level. The diameter of the agglomerated particles measure about 0.1 mm, 200 to 500 times as large as those generated under normal gravity. It is suggested that these large soot particles are generated in the limited areas where the conditions for the formation of these particles, such as gas velocity (residence time) and oxygen concentration, are satisfied.

  19. A detailed kinetic modeling study of toluene oxidation in a premixed laminar flame

    SciTech Connect

    Tian, Z; Pitz, W J; Fournet, R; Glaude, P; Battin-Leclerc, F

    2009-12-18

    An improved chemical kinetic model for the toluene oxidation based on experimental data obtained in a premixed laminar low-pressure flame with vacuum ultraviolet (VUV) photoionization and molecular beam mass spectrometry (MBMS) techniques has been proposed. The present mechanism consists of 273 species up to chrysene and 1740 reactions. The rate constants of reactions of toluene, decomposition, reaction with oxygen, ipso-additions and metatheses with abstraction of phenylic H-atom are updated; new pathways of C{sub 4} + C{sub 2} species giving benzene and fulvene are added. Based on the experimental observations, combustion intermediates such as fulvenallene, naphtol, methylnaphthalene, acenaphthylene, 2-ethynylnaphthalene, phenanthrene, anthracene, 1-methylphenanthrene, pyrene and chrysene are involved in the present mechanism. The final toluene model leads to an overall satisfactory agreement between the experimentally observed and predicted mole fraction profiles for the major products and most combustion intermediates. The toluene depletion is governed by metathese giving benzyl radicals, ipso-addition forming benzene and metatheses leading to C{sub 6}H{sub 4}CH{sub 3} radicals. A sensitivity analysis indicates that the unimolecular decomposition via the cleavage of a C-H bond has a strong inhibiting effect, while decomposition via C-C bond breaking, ipso-addition of H-atom to toluene, decomposition of benzyl radicals and reactions related to C{sub 6}H{sub 4}CH{sub 3} radicals have promoting effect for the consumption of toluene. Moreover, flow rate analysis is performed to illustrate the formation pathways of mono- and polycyclic aromatics.

  20. A simple reaction-rate model for turbulent diffusion flames

    NASA Technical Reports Server (NTRS)

    Bangert, L. H.

    1975-01-01

    A simple reaction rate model is proposed for turbulent diffusion flames in which the reaction rate is proportional to the turbulence mixing rate. The reaction rate is also dependent on the mean mass fraction and the mean square fluctuation of mass fraction of each reactant. Calculations are compared with experimental data and are generally successful in predicting the measured quantities.

  1. MAGNETIC TRANSPORT ON THE SOLAR ATMOSPHERE BY LAMINAR AND TURBULENT AMBIPOLAR DIFFUSION

    SciTech Connect

    Hiraki, Y.; Krishan, V.; Masuda, S.

    2010-09-10

    The lower solar atmosphere consists of partially ionized turbulent plasmas harboring velocity field, magnetic field, and current density fluctuations. The correlations among these small-scale fluctuations give rise to large-scale flows and magnetic fields which decisively affect all transport processes. The three-fluid system consisting of electrons, ions, and neutral particles supports nonideal effects such as the Hall effect and ambipolar diffusion. Here, we study magnetic transport by the laminar- and turbulent-scale ambipolar diffusion processes using a simple model of the magnetic induction equation. Based on a linear analysis of the induction equation, we perform a one-dimensional numerical simulation to study the laminar ambipolar effect on medium-scale magnetic field structures. The nonlinearity of the laminar ambipolar diffusion creates magnetic structures with sharp gradients in the scale of hundreds of kilometers. We expect that these can be amenable to processes such as magnetic reconnection and energy release therefrom for heating and flaring of the solar plasma. Analyzing the characteristic timescales of these processes, we find that the turbulent diffusion timescale is smaller by several orders of magnitude than the laminar diffusion timescale. The effect of the modeled turbulent ambipolar diffusion on the obtained field structures is briefly discussed.

  2. Interaction of a laminar flame with its self-generated flow during constant volume combustion

    SciTech Connect

    Dunn-Rankin, D.; Sawyer, R.F.

    1985-02-01

    The formation of cusp shaped or ''tulip'' flames during closed tube flame propagation has been recorded by combustion researchers for nearly sixty years. Flame instability, pressure wave/flame interaction, and large scale circulation in the unburned gas have been suggested as explanations for the ''tulip'' flame phenomenon, but the cause of the ''tulip'' flame has not been conclusively determined. This work uses laser Doppler anemometer measurements of the flow field during flame propagation in a closed tube to describe the combustion generated flow and to support a fluid mechanical explanation for the ''tulip'' flame formation. The flame behaves as a fluid mechanical discontinuity which deflects the velocity of the gas passing through it. As the flame quenches at the side walls of the combustion vessel, the flow deflection generates a vortex in the burned gas. The vortex remains in the proximity of the flame and modifies the unburned gas field such that the flame propagates more quickly near the wall than at the center. The discrepancy in propagation rates leads to the ''tulip'' flame.

  3. Diffusion flame extinction in slow convenctive flow under microgravity environment

    NASA Technical Reports Server (NTRS)

    Chen, C. H.

    1986-01-01

    A theoretical analysis is presented to study the extinction characteristics of a diffusion flame near the leading edge of a thin fuel plate in slow, forced convective flows in a microgravity environment. The mathematical model includes two-dimensional Navier-Stokes momentum, energy and species equations with one-step overall chemical reaction using second-order finite rate Arrhenius kinetics. Radiant heat loss on the fuel plate is applied in the model as it is the dominant mechanism for flame extinguishment in the small convective flow regime. A parametric study based on the variation of convective flow velocity, which varies the Damkohler number (Da), and the surface radiant heat loss parameter (S) simultaneously, is given. An extinction limit is found in the regime of slow convective flow when the rate of radiant heat loss from fuel surface outweighs the rate of heat generation due to combustion. The transition from existent envelope flame to extinguishment consists of gradual flame contraction in the opposed flow direction together with flame temperature reduction as the convective flow velocity decreases continuously until the extinction limit is reached. A case of flame structure subjected to surface radiant heat loss is also presented and discussed.

  4. Diffusion flame extinction in slow convection flow under microgravity environment

    NASA Technical Reports Server (NTRS)

    Chen, Chiun-Hsun

    1986-01-01

    A theoretical analysis is presented to study the extinction characteristics of a diffusion flame near the leading edge of a thin fuel plate in slow, forced convective flows in a microgravity environment. The mathematical model includes two-dimensional Navier-Stokes momentum, energy and species equations with one-step overall chemical reaction using second-order finite rate Arrhenius kinetics. Radiant heat loss on the fuel plate is applied in the model as it is the dominant mechanism for flame extinguishment in the small convective flow regime. A parametric study based on the variation of convective flow velocity, which varies the Damkchler number (Da), and the surface radiant heat loss parameter (S) simultaneously, is given. An extinction limit is found in the regime of slow convective flow when the rate of radiant heat loss from fuel surface outweighs the rate of heat generation due to combustion. The transition from existent envelope flame to extinguishment consists of gradual flame contraction in the opposed flow direction together with flame temperature reduction as the convective flow velocity decreases continuously until the extinction limit is reached. A case of flame structure subjected to surface radiant heat loss is also presented and discussed.

  5. Preflame zone structure and main features of fuel conversion in atmospheric pressure premixed laminar hydrocarbon flames

    SciTech Connect

    Ksandopulo, G.I.

    1995-08-25

    This report describes the structure study of the premixed hydrocarbon-oxidizer Bunsen flames burning at the atmospheric pressure and also the ones with some inhibitors added. Studies were performed on hexane, propane, methane, acetylene, and hexene flames.

  6. Blue nano titania made in diffusion flames.

    PubMed

    Teleki, Alexandra; Pratsinis, Sotiris E

    2009-05-21

    Blue titanium suboxide nanoparticles (including Magneli phases) were formed directly without any post-processing or addition of dopants by combustion of titanium-tetra-isopropoxide (TTIP) vapor at atmospheric pressure. Particle size, phase composition, rutile and anatase crystal sizes as well as the blue coloration were controlled by rapid quenching of the flame with a critical flow nozzle placed at various heights above the burner. The particles showed a broad absorption in the near-infrared region and retained their blue color upon storage in ambient atmosphere. A high concentration of paramagnetic Ti3+ centres was found in the substoichiometric particles by electron paramagnetic resonance (EPR) spectroscopy. Furthermore particles with controlled band gap energy from 3.2 to 3.6 eV were made by controlling the burner-nozzle-distance from 10 to 1 cm, respectively. The color robustness and extent of suboxidation could be further enhanced by co-oxidation of TTIP with hexamethyldisiloxane in the flame resulting in SiO2-coated titanium suboxide particles. The process is cost-effective and green while the particles produced can replace traditional blue colored, cobalt-containing pigments. PMID:19421486

  7. A Detailed Chemical Kinetic Reaction Mechanism for Oxidation of Four Small Alkyl Esters in Laminar Premixed Flames

    SciTech Connect

    Westbrook, C K; Pitz, W J; Westmoreland, P R; Dryer, F L; Chaos, M; Osswald, P; Kohse-Hoinghaus, K; Cool, T A; Wang, J; Yang, B; Hansen, N; Kasper, T

    2008-02-08

    A detailed chemical kinetic reaction mechanism has been developed for a group of four small alkyl ester fuels, consisting of methyl formate, methyl acetate, ethyl formate and ethyl acetate. This mechanism is validated by comparisons between computed results and recently measured intermediate species mole fractions in fuel-rich, low pressure, premixed laminar flames. The model development employs a principle of similarity of functional groups in constraining the H atom abstraction and unimolecular decomposition reactions in each of these fuels. As a result, the reaction mechanism and formalism for mechanism development are suitable for extension to larger oxygenated hydrocarbon fuels, together with an improved kinetic understanding of the structure and chemical kinetics of alkyl ester fuels that can be extended to biodiesel fuels. Variations in concentrations of intermediate species levels in these flames are traced to differences in the molecular structure of the fuel molecules.

  8. A diffuse interface Lox/hydrogen transcritical flame model

    NASA Astrophysics Data System (ADS)

    Gaillard, Pierre; Giovangigli, Vincent; Matuszewski, Lionel

    2016-05-01

    We present a diffuse-interface all-pressure flame model that transitions smoothly between subcritical and supercritical conditions. The model involves a non-equilibrium liquid/gas diffuse interface of van der Waals/Korteweg type embedded into a non-ideal multicomponent reactive fluid. The multicomponent transport fluxes are evaluated in their thermodynamic form in order to avoid singularities at thermodynamic mechanical stability limits. The model also takes into account condensing liquid water in order to avoid thermodynamic chemical instabilities. The resulting equations are used to investigate the interface between cold dense and hot light oxygen as well as the structure of diffusion flames between cold dense oxygen and gaseous-like hydrogen at all pressures, either subcritical or supercritical.

  9. Effects of non-unity Lewis numbers in diffusion flames

    NASA Technical Reports Server (NTRS)

    Linan, A.; Orlandi, P.; Verzicco, R.; Higuera, F. J.

    1994-01-01

    The purpose of this work is to carry out direct numerical simulations of diffusion controlled combustion with non-unity Lewis numbers for the reactants and products, thus accounting for the differential diffusion effects of the temperature and concentration fields. We use a formulation based on combining the conservation equations in a way to eliminate the reaction terms similar to the method used by Burke and Schumann (1928) for unity Lewis numbers. We present calculations for an axisymmetric fuel jet and for a planar, time evolving mixing layer, leaving out the effects of thermal expansion and variations of the transport coefficients due to the heat release. Our results show that the front of the flame shifts toward the fuel or oxygen sides owing to the effect of the differential diffusion and that the location of maximum temperature may not coincide with the flame. The dependence of the distribution of the reaction products on their Lewis number has been investigated.

  10. In situ TDLAS measurement of absolute acetylene concentration profiles in a non-premixed laminar counter-flow flame

    NASA Astrophysics Data System (ADS)

    Wagner, S.; Klein, M.; Kathrotia, T.; Riedel, U.; Kissel, T.; Dreizler, A.; Ebert, V.

    2012-06-01

    Acetylene (C2H2), as an important precursor for chemiluminescence species, is a key to understand, simulate and model the chemiluminescence and the related reaction paths. Hence we developed a high resolution spectrometer based on direct Tunable Diode Laser Absorption Spectroscopy (TDLAS) allowing the first quantitative, calibration-free and spatially resolved in situ C2H2 measurement in an atmospheric non-premixed counter-flow flame supported on a Tsuji burner. A fiber-coupled distributed feedback diode laser near 1535 nm was used to measure several absolute C2H2 concentration profiles (peak concentrations up to 9700 ppm) in a laminar non-premixed CH4/air flame ( T up to 1950 K) supported on a modified Tsuji counter-flow burner with N2 purge slots to minimize end flames. We achieve a fractional optical resolution of up to 5×10-5 OD (1 σ) in the flame, resulting in temperature-dependent acetylene detection limits for the P17e line at 6513 cm-1 of up to 2.1 ppmṡm. Absolute C2H2 concentration profiles were obtained by translating the burner through the laser beam using a DC motor with 100 μm step widths. Intercomparisons of the experimental C2H2 profiles with simulations using our new hydrocarbon oxidation mechanisms show excellent agreement in position, shape and in the absolute C2H2 values.

  11. Appearance and stability of a laminar conical premixed flame subjected to an acoustic perturbation

    SciTech Connect

    Bourehla, A.; Baillot, F.

    1998-08-01

    The paper describes an experimental study of quad-conical premixed air/methane flames vibrating under periodic fluctuations of the upstream flow. The flow field and the flame were characterized by an LDV system and image processing. The flow velocity fluctuations were created by an acoustic perturbation with a frequency between 20 and 1000 Hz and a perturbation intensity, defined as the ratio of the rms amplitude of the flow velocity fluctuations to the mean velocity at the exit of the burner, ranging from 0 to 150%. In the perturbation plane (frequency and intensity), a chart is established that shows the configurations assumed by the flame in response to the acoustic perturbation. Three configurations were studied. The wrinkled flame configuration exhibits a flame with undulations symmetrical about the vertical axis and vibrating at the perturbation frequency. This work completes previous studies. In particular, a critical value of the frequency is found. Above this acoustic amplitudes of deformation are damped at the front, which is unaffected by the wrinkling. The subharmonic flame configuration exhibits a flame whose front oscillates with half the perturbation frequency, symmetrical or not, about the burner centerline. The asymmetrical flame is composed of two half-fronts moving in opposition. This instability on Bunsen burners has never previously been observed or predicted. The chaotic flame configuration characterizes a flame not necessarily attached to the burner that exhibits a disordered geometry that leads to aperiodicity of its motion.

  12. Features of the propagation of laminar spherical flames initiated by a spark discharge in mixtures of methane, pentane, and hydrogen with air at atmospheric pressure

    NASA Astrophysics Data System (ADS)

    Rubtsov, N. M.; Seplyarskii, B. S.; Troshin, K. Ya.; Chernysh, V. I.; Tsvetkov, G. I.

    2011-10-01

    Using high-speed digital color cinematography, we studied the propagation of a laminar spherical flame in stoichiometric mixtures of hydrogen, methane, and pentane with air in the presence of additives at atmospheric pressure in constant-volume reactors, and derived quantitative data on the time of formation of a stable flame front. Cellular flames caused by gas-dynamic instability attributable to convective flows arising during the afterburning of gas were observed in hydrocarbon-air stoichiometric mixtures diluted with inert additives. It was found that the effect of additives of carbon dioxide and argon (>10%) and minor additives of CCl4 on the combustion of hydrocarbons, and of propylene on the combustion of hydrogen-rich mixtures, lead to periods of delay in the development of a laminar spherical flame; in addition, additives of propylene promote the combustion of hydrogen poor mixtures.

  13. A counterflow diffusion flame study of branched octane isomers

    SciTech Connect

    Sarathy, S. Mani; Niemann, Ulrich; Yeung, Coleman; Gehmlich, Ryan; Westrbrook, Charles K.; Plomer, Max; Luo, Zhaoyu; Mehl, Marco; Pitz, William J.; Seshadri, Kalyanasundaram; Thomson, Murray J.; Lu, Tianfeng

    2012-09-25

    Conventional petroleum, Fischer–Tropsch (FT), and other alternative hydrocarbon fuels typically contain a high concentration of lightly methylated iso-alkanes. However, until recently little work has been done on this important class of hydrocarbon components. In order to better understand the combustion characteristics of real fuels, this study presents new experimental data for 3-methylheptane and 2,5-dimethylhexane in counterflow diffusion flames. This new dataset includes flame ignition, extinction, and speciation profiles. The high temperature oxidation of these fuels has been modeled using an extended transport database and a high temperature skeletal chemical kinetic model. The skeletal model is generated from a detailed model reduced using the directed relation graph with expert knowledge (DRG-X) methodology. The proposed skeletal model contains sufficient chemical fidelity to accurately predict the experimental speciation data in flames. The predictions are compared to elucidate the effects of number and location of the methyl substitutions. The location is found to have little effect on ignition and extinction in these counterflow diffusion flames. However, increasing the number of methyl substitutions was found to inhibit ignition and promote extinction. Chemical kinetic modelling simulations were used to correlate a fuel’s extinction propensity with its ability to populate the H radical concentration. In conclusion, species composition measurements indicate that the location and number of methyl substitutions was found to particularly affect the amount and type of alkenes observed.

  14. A counterflow diffusion flame study of branched octane isomers

    DOE PAGES

    Sarathy, S. Mani; Niemann, Ulrich; Yeung, Coleman; Gehmlich, Ryan; Westrbrook, Charles K.; Plomer, Max; Luo, Zhaoyu; Mehl, Marco; Pitz, William J.; Seshadri, Kalyanasundaram; et al

    2012-09-25

    Conventional petroleum, Fischer–Tropsch (FT), and other alternative hydrocarbon fuels typically contain a high concentration of lightly methylated iso-alkanes. However, until recently little work has been done on this important class of hydrocarbon components. In order to better understand the combustion characteristics of real fuels, this study presents new experimental data for 3-methylheptane and 2,5-dimethylhexane in counterflow diffusion flames. This new dataset includes flame ignition, extinction, and speciation profiles. The high temperature oxidation of these fuels has been modeled using an extended transport database and a high temperature skeletal chemical kinetic model. The skeletal model is generated from a detailed modelmore » reduced using the directed relation graph with expert knowledge (DRG-X) methodology. The proposed skeletal model contains sufficient chemical fidelity to accurately predict the experimental speciation data in flames. The predictions are compared to elucidate the effects of number and location of the methyl substitutions. The location is found to have little effect on ignition and extinction in these counterflow diffusion flames. However, increasing the number of methyl substitutions was found to inhibit ignition and promote extinction. Chemical kinetic modelling simulations were used to correlate a fuel’s extinction propensity with its ability to populate the H radical concentration. In conclusion, species composition measurements indicate that the location and number of methyl substitutions was found to particularly affect the amount and type of alkenes observed.« less

  15. An experimental investigation of the interaction between a Karman vortex street and a premixed laminar flame

    NASA Astrophysics Data System (ADS)

    Namer, I.

    1980-12-01

    The interaction of a premixed C2H4-air flame with a Karman vortex street was studied. Laser Doppler anemometry was used for velocity measurements and Rayleigh scattering was used to measure total gas density. A reference hot wire was used to enable phase-locked ensemble averaging to be performed on the data. The velocity measurements for vortex shedding cylinder Reynolds numbers indicated that the vortex street and, hence, the flow field upstream of the flame is deflected by the flame. This is due to the pressure drop across the flame which is necessary to accelerate the flow behind the flame. The vortices were not observed behind the flame. The combination of dilation and increased dissipation consumed the vortices. Density statistics obtained from Rayleigh scattering measurements were compared with predictions by the Bray-Moss-Libby (B-M-L) model which neglects intermediate states. Density fluctuations were overpredicted by the B-M-L model by a small amount.

  16. Charge-induced secondary atomization in diffusion flames of electrostatic sprays

    NASA Technical Reports Server (NTRS)

    Gomez, Alessandro; Chen, Gung

    1994-01-01

    The combustion of electrostatic sprays of heptane in laminar counterflow diffusion flames was experimentally studied by measuring droplet size and velocity distributions, as well as the gas-phase temperature. A detailed examination of the evolution of droplet size distribution as droplets approach the flame shows that, if substantial evaporation occurs before droplets interact with the flame, an initially monodisperse size distribution becomes bimodal. A secondary sharp peak in the size histogram develops in correspondence of diameters about one order of magnitude smaller than the mean. No evaporation mechanism can account for the development of such bimodality, that can be explained only in terms of a disintegration of droplets into finer fragments of size much smaller than that of the parent. Other evidence in support of this interpretation is offered by the measurements of droplet size-velocity correlation and velocity component distributions, showing that, as a consequence of the ejection process, the droplets responsible for the secondary peak have velocities uncorrelated with the mean flow. The fission is induced by the electric charge. When a droplet evaporates, in fact, the electric charge density on the droplet surface increases while the droplet shrinks, until the so-called Rayleigh limit is reached at which point the repulsion of electric charges overcomes the surface tension cohesive force, ultimately leading to a disintegraton into finer fragments. We report on the first observation of such fissions in combustion environments. If, on the other hand, insufficient evaporation has occurred before droplets enter the high temperature region, there appears to be no significant evidence of bimodality in their size distribution. In this case, in fact, the concentration of flame chemi-ions or, in the case of positively charged droplets, electrons may be sufficient for them to neutralize the charge on the droplets and to prevent disruption.

  17. Effects of Inert Dust Clouds on the Extinction of Strained, Laminar Flames at Normal and Micro Gravity

    NASA Technical Reports Server (NTRS)

    Andac, M. Gurhan; Egolfopoulos, Fokion N.; Campbell, Charles S.; Lauvergne, Romain; Wu, Ming-Shin (Technical Monitor)

    2000-01-01

    A combined experimental and detailed numerical study was conducted on the interaction between chemically inert solid particles and strained, atmospheric methane/air and propane/air laminar flames, both premixed and non-premixed. Experimentally, the opposed jet configuration was used with the addition of a particle seeder capable of operating in conditions of varying gravity. The particle seeding system was calibrated under both normal and micro gravity and a noticeable gravitational effect was observed. Flame extinction experiments were conducted at normal gravity by seeding inert particles at various number densities and sizes into the reacting gas phase. Experimental data were taken for 20 and 37 (mu) nickel alloy and 25 and 60 (mu) aluminum oxide particles. The experiments were simulated by solving along the stagnation streamline the conservation equations of mass, momentum, energy, and species conservation for both phases, with detailed descriptions of chemical kinetics, molecular transport, and thermal radiation. The experimental data were compared with numerical simulations, and insight was provided into the effects on extinction of the fuel type, equivalence ratio, flame configuration, strain rate. particle type. particle size. particle mass, delivery rate. the orientation of particle injection with respect to the flame and gravity. It was found that for the same injected solid mass, larger particles can result in more effective flame cooling compared to smaller particles, despite the fact that equivalent masses of the larger particles have smaller total surface area to volume ratio. This counter-intuitive finding resulted from the fact that the heat exchange between the two phases is controlled by the synergistic effect of the total contact area and the temperature difference between the two phases. Results also demonstrate that meaningful scaling of interactions between the two phases may not be possible due to the complexity of the couplings between the

  18. Application of superplastically formed and diffusion bonded aluminum to a laminar flow control leading edge

    NASA Technical Reports Server (NTRS)

    Goodyear, M. D.

    1987-01-01

    NASA sponsored the Aircraft Energy Efficiency (ACEE) program in 1976 to develop technologies to improve fuel efficiency. Laminar flow control was one such technology. Two approaches for achieving laminar flow were designed and manufactured under NASA sponsored programs: the perforated skin concept used at McDonnell Douglas and the slotted design used at Lockheed-Georgia. Both achieved laminar flow, with the slotted design to a lesser degree (JetStar flight test program). The latter design had several fabrication problems concerning springback and adhesive flow clogging the air flow passages. The Lockheed-Georgia Company accomplishments is documented in designing and fabricating a small section of a leading edge article addressing a simpler fabrication method to overcome the previous program's manufacturing problems, i.e., design and fabrication using advanced technologies such as diffusion bonding of aluminum, which has not been used on aerospace structures to date, and the superplastic forming of aluminum.

  19. Effects of H2O, CO2, and N2 air contaminants on critical airside strain rates for extinction of hydrogen-air counterflow diffusion flames

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Northam, G. B.; Wilson, L. G.; Guerra, Rosemary

    1989-01-01

    Dish-shaped counterflow diffusion flames centered by opposing laminar jets of H2 and clean and contaminant O2/N2 mixtures in an argon bath at 1 atm were used to study the effects of contaminants on critical airside strain. The jet velocities for both flame extinction and restoration are found for a wide range of contaminant and O2 concentrations in the air jet. The tests are also conducted for a variety of input H2 concentrations. The results are compared with those from several other studies.

  20. Numerical analysis of entropy generation in a turbulent diffusion flame

    NASA Astrophysics Data System (ADS)

    Bouras, F.; Khaldi, F.

    2016-01-01

    Thermodynamic irreversibilities generated by the combustion process are evaluated and analyzed numerically. The numerical simulation is performed for a reference case study for which experimental data are available in the literature: diffusion flame properties in a common burner configuration are studied by the Fluent software with the standard k-ɛ turbulence model and two-step chemical reaction. The study quantifies the contribution of each mechanism to entropy generation, i.e., friction, heat conduction, species diffusion, and chemical reaction. The chemical reaction and heat conduction are found to be the major sources of entropy production. Preheating of air reduces thermodynamic irreversibilities within the combustor.

  1. A new apparatus for study of pressure-dependent laminar premixed flames with vacuum ultraviolet photoionization mass spectrometry

    NASA Astrophysics Data System (ADS)

    Zhou, Z. Y.; Wang, Y.; Tang, X. F.; Wu, W. H.; Qi, F.

    2013-01-01

    We report a home-made combustion apparatus for study of pressure-dependent laminar premixed flames with tunable vacuum ultraviolet photoionization mass spectrometry. The instrument consists of a flame chamber, a photoionization chamber with a single-stage sampling system, an ion transfer/storage system, and an orthogonal-acceleration reflectron time-of-flight mass spectrometer. Preliminary results of fuel-rich C2H4/O2/Ar flames at pressures of 30, 150, and 760 Torr have been obtained with this instrument. Compared to previous instruments [T. A. Cool, A. McIlroy, F. Qi, P. R. Westmoreland, L. Poisson, D. S. Peterka, and M. Ahmed, Rev. Sci. Instrum. 76, 094102 (2005), 10.1063/1.2010307; F. Qi, R. Yang, B. Yang, C. Q. Huang, L. X. Wei, J. Wang, L. S. Sheng, and Y. W. Zhang, Rev. Sci. Instrum. 77, 084101 (2006)], 10.1063/1.2234855, performances of the new apparatus have higher mass resolution (˜3500 at m/z = 40), better detection limit (<1 ppm), and broader dynamic range (better than 5 order of magnitude).

  2. Soot Aerosol Properties in Laminar Soot-Emitting Microgravity Nonpremixed Flames

    NASA Technical Reports Server (NTRS)

    Konsur, Bogdan; Megaridis, Constantine M.; Griffin, Devon W.

    1999-01-01

    The 0-g flame soot measurements reported in previous studies are extended by adding new 0-g data for different fuel flow rates and burner diameters. The new flame conditions allow more conclusive comparisons regarding the effect of characteristic flow residence times on soot field structure, the influence of fuel preheat on fuel pyrolysis rates near the flame centerline, and the premature cessation of soot growth along the soot annulus in 0-g when the fuel is preheated. The paper also reports on the implementation of thermophoretic soot sampling in a specific 0-g flame featuring burner exit velocities typical of buoyant flames and presents quantitative data on the radial variation of soot microstructure at a fixed height above the burner mouth.

  3. Velocity Fields of Axisymmetric Hydrogen-Air Counterflow Diffusion Flames from LDV, PIV, and Numerical Computation

    NASA Technical Reports Server (NTRS)

    Pellett, Gerald L.; Wilson, Lloyd G.; Humphreys, William M., Jr.; Bartram, Scott M.; Gartrell, Luther R.; Isaac, K. M.

    1995-01-01

    Laminar fuel-air counterflow diffusion flames (CFDFs) were studied using axisymmetric convergent-nozzle and straight-tube opposed jet burners (OJBs). The subject diagnostics were used to probe a systematic set of H2/N2-air CFDFs over wide ranges of fuel input (22 to 100% Ha), and input axial strain rate (130 to 1700 Us) just upstream of the airside edge, for both plug-flow and parabolic input velocity profiles. Laser Doppler Velocimetry (LDV) was applied along the centerline of seeded air flows from a convergent nozzle OJB (7.2 mm i.d.), and Particle Imaging Velocimetry (PIV) was applied on the entire airside of both nozzle and tube OJBs (7 and 5 mm i.d.) to characterize global velocity structure. Data are compared to numerical results from a one-dimensional (1-D) CFDF code based on a stream function solution for a potential flow input boundary condition. Axial strain rate inputs at the airside edge of nozzle-OJB flows, using LDV and PIV, were consistent with 1-D impingement theory, and supported earlier diagnostic studies. The LDV results also characterized a heat-release hump. Radial strain rates in the flame substantially exceeded 1-D numerical predictions. Whereas the 1-D model closely predicted the max I min axial velocity ratio in the hot layer, it overpredicted its thickness. The results also support previously measured effects of plug-flow and parabolic input strain rates on CFDF extinction limits. Finally, the submillimeter-scale LDV and PIV diagnostics were tested under severe conditions, which reinforced their use with subcentimeter OJB tools to assess effects of aerodynamic strain, and fueVair composition, on laminar CFDF properties, including extinction.

  4. Effects of C/O Ratio and Temperature on Sooting Limits of Spherical Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Lecoustre, V. R.; Sunderland, P. B.; Chao, B. H.; Urban, D. L.; Stocker, D. P.; Axelbaum, R. L.

    2008-01-01

    Limiting conditions for soot particle inception in spherical diffusion flames were investigated numerically. The flames were modeled using a one-dimensional, time accurate diffusion flame code with detailed chemistry and transport and an optically thick radiation model. Seventeen normal and inverse flames were considered, covering a wide range of stoichiometric mixture fraction, adiabatic flame temperature, residence time and scalar dissipation rate. These flames were previously observed to reach their sooting limits after 2 s of microgravity. Sooting-limit diffusion flames with scalar dissipation rate lower than 2/s were found to have temperatures near 1400 K where C/O = 0.51, whereas flames with greater scalar dissipation rate required increased temperatures. This finding was valid across a broad range of fuel and oxidizer compositions and convection directions.

  5. Numerical investigation of the shape of a laminar flame in a channel

    SciTech Connect

    Makhviladze, G.M.; Melikhov, V.I.; Sivashinskii, G.I.

    1994-11-01

    The method of numerical integration of the nonstationary two-dimensional equations describing the essentially subsonic motions of a reacting gas is used to investigate the characteristics of the shape and structure of the flame from propagating in a plane closed channel. It is shown that at fairly high Reynolds numbers a two-humped front shape ({open_quotes}tulip{close_quotes}), caused by the development of hydrodynamic flame instability, is formed.

  6. Soot oxidation and agglomeration modeling in a microgravity diffusion flame

    SciTech Connect

    Ezekoye, O.A.; Zhang, Z.

    1997-07-01

    The global evolution of a microgravity diffusion flame is detailed. Gas species evolution is computed using a reduced finite rate chemical mechanism. Soot evolution is computed using various combinations of existing soot mechanisms. Radiative transfer is coupled to the soot and gas phase chemistry processes using a P1 spherical harmonics radiation model. The soot agglomeration model was examined to note the dependence of soot growth and oxidation processes on soot surface area predictions. For limiting cases where agglomeration was excluded from the soot evolution model, soot primary particle sizes and number concentrations were calculated, and the number of primary particles per aggregate was inferred. These computations are compared with experimental results for microgravity and nonbuoyant flame conditions.

  7. Dynamic Weakening (Extinction) of Simple Hydrocarbon-air Counterflow Diffusion Flames by Oscillatory Inflows

    NASA Technical Reports Server (NTRS)

    Pellett, G.; Kabaria, A.; Panigrahi, B.; Sammons, K.; Convery, J.; Wilson, L.

    2005-01-01

    This study of laminar non-premixed HC-air flames used an Oscillatory-input Opposed Jet Burner (OOJB) system developed from a previously well-characterized 7.2-mm Pyrex-nozzle OJB system. Over 600 dynamic Flame Strength (FS) measurements were obtained on unanchored (free-floating) laminar Counterflow Diffusion Flames (CFDF's). Flames were stabilized using plug inflows having steady-plus-sinusoidal axial velocities of varied magnitude, frequency, f, up to 1600 Hz, and phase angle from 0 (most data) to 360 degrees. Dynamic FS is defined as the maximum average air input velocity (U(sub air), at nozzle exit) a CFDF can sustain before strain-induced extinction occurs due to prescribed oscillatory peak-to-peak velocity inputs superimposed on steady inputs. Initially, dynamic flame extinction data were obtained at low f, and were supported by 25-120 Hz Hot-Wire cold-flow velocity data at nozzle exits. Later, expanded extinction data were supported by 4-1600 Hz Probe Microphone (PM) pk/pk P data at nozzle exits. The PM data were first obtained without flows, and later with cold stagnating flows, which better represent speaker-diaphragm dynamics during runs. The PM approach enabled characterizations of Dynamic Flame Weakening (DFW) of CFDF's from 8 to 1600 Hz. DFW was defined as % decrease in FS per Pascal of pk/pk P oscillation, namely, DFW = - 100 d(U(sub air) / U(sub air),0Hz) / d(pkpk P). The linear normalization with respect to acoustic pressure magnitude (and steady state (SS) FS) led to a DFW unaffected by strong internal resonances. For the C2H4/N2-air system, from 8 to 20 Hz, DFW is constant at 8.52 plus or minus 0.20 (% weakening)/Pa. This reflects a quasi-steady flame response to an acoustically induced dU(sub air)/dP. Also, it is surprisingly independent of C2H4/N2 mole fraction due to normalization by SS FS. From 20 to approximately 150 Hz, the C2H4/N2 air-flames weakened progressively less, with an inflection at approximately 70 Hz, and became asymptotically

  8. Kinetic Effects of Aromatic Molecular Structures on Diffusion Flame Extinction

    SciTech Connect

    Won, Sang Hee; Dooley, S.; Dryer, F. L.; Ju, Yiguang

    2011-01-01

    Kinetic effects of aromatic molecular structures for jet fuel surrogates on the extinction of diffusion flames have been investigated experimentally and numerically in the counterflow configuration for toluene, n-propylbenzene, 1,2,4-trimethylbenzene, and 1,3,5-trimethylbenzene. Quantitative measurement of OH concentration for aromatic fuels was conducted by directly measuring the quenching rate from the emission lifetimes of OH planar laser induced fluorescence (LIF). The kinetic models for toluene and 1,2,4-trimethylbenzene were validated against the measurements of extinction strain rates and LIF measurements. A semi-detailed n-propylbenzene kinetic model was developed and tested. The experimental results showed that the extinction limits are ranked from highest to lowest as n-propylbenzene, toluene, 1,2,4-trimethylbenzene, and 1,3,5-trimethylbenzene. The present models for toluene and n-propylbenzene agree reasonably well with the measurements, whereas the model for 1,2,4-trimethylbenzene under-estimates extinction limits. Kinetic pathways of OH production and consumption were analyzed to investigate the impact of fuel fragmentation on OH formation. It was found that, for fuels with different molecular structures, the fuel decomposition pathways and their propagation into the formation of radical pool play an important role to determine the extinction limits of diffusion flames. Furthermore, OH concentrations were found to be representative of the entire radical pool concentration, the balance between chain branching and propagation/termination reactions and the balance between heat production from the reaction zone and heat losses to the fuel and oxidizer sides. Finally, a proposed “OH index,” was defined to demonstrate a linear correlation between extinction strain rate and OH index and fuel mole fraction, suggesting that the diffusion flame extinctions for the tested aromatic fuels can be determined by the capability of a fuel to establish a radical pool

  9. Properties of turbulence in natural gas-oxygen diffusion flames

    SciTech Connect

    Sautet, J.C.; Ditaranto, M. ); Samaniego, J.M.; Charon, O. )

    1999-07-01

    Measurements of turbulent flow field velocities, including first and second order velocity moments and the shear stress are carried out by laser Doppler velocimetry in five different, 25 kW, turbulent natural gas-oxygen diffusion flames. The mean flow behavior is described including the velocity half value radius as well as centerline velocity. Mean radial velocity profiles are fitted by a Gaussian function. According to the initial momentum ratio, different jet dynamic behaviors are pointed out by the description of the fluctuating velocity field.

  10. Effects of repetitive pulsing on multi-kHz planar laser-induced incandescence imaging in laminar and turbulent flames

    DOE PAGES

    Michael, James B.; Venkateswaran, Prabhakar; Shaddix, Christopher R.; Meyer, Terrence R.

    2015-04-08

    Planar laser-induced incandescence (LII) imaging is reported at repetition rates up to 100 kHz using a burst-mode laser system to enable studies of soot formation dynamics in highly turbulent flames. Furthermore, to quantify the accuracy and uncertainty of relative soot volume fraction measurements, the temporal evolution of the LII field in laminar and turbulent flames is examined at various laser operating conditions. Under high-speed repetitive probing, it is found that LII signals are sensitive to changes in soot physical characteristics when operating at high laser fluences within the soot vaporization regime. For these laser conditions, strong planar LII signals aremore » observed at measurement rates up to 100 kHz but are primarily useful for qualitative tracking of soot structure dynamics. However, LII signals collected at lower fluences allow sequential planar measurements of the relative soot volume fraction with a sufficient signal-to-noise ratio at repetition rates of 10–50 kHz. Finally, guidelines for identifying and avoiding the onset of repetitive probe effects in the LII signals are discussed, along with other potential sources of measurement error and uncertainty.« less

  11. Effects of repetitive pulsing on multi-kHz planar laser-induced incandescence imaging in laminar and turbulent flames

    SciTech Connect

    Michael, James B.; Venkateswaran, Prabhakar; Shaddix, Christopher R.; Meyer, Terrence R.

    2015-04-08

    Planar laser-induced incandescence (LII) imaging is reported at repetition rates up to 100 kHz using a burst-mode laser system to enable studies of soot formation dynamics in highly turbulent flames. Furthermore, to quantify the accuracy and uncertainty of relative soot volume fraction measurements, the temporal evolution of the LII field in laminar and turbulent flames is examined at various laser operating conditions. Under high-speed repetitive probing, it is found that LII signals are sensitive to changes in soot physical characteristics when operating at high laser fluences within the soot vaporization regime. For these laser conditions, strong planar LII signals are observed at measurement rates up to 100 kHz but are primarily useful for qualitative tracking of soot structure dynamics. However, LII signals collected at lower fluences allow sequential planar measurements of the relative soot volume fraction with a sufficient signal-to-noise ratio at repetition rates of 10–50 kHz. Finally, guidelines for identifying and avoiding the onset of repetitive probe effects in the LII signals are discussed, along with other potential sources of measurement error and uncertainty.

  12. Studies of Flame Structure in Microgravity

    NASA Technical Reports Server (NTRS)

    Law, C. K.; Sung, C. J.; Zhu, D. L.

    1997-01-01

    The present research endeavor is concerned with gaining fundamental understanding of the configuration, structure, and dynamics of laminar premixed and diffusion flames under conditions of negligible effects of gravity. Of particular interest is the potential to establish and hence study the properties of spherically- and cylindrically-symmetric flames and their response to external forces not related to gravity. For example, in an earlier experimental study of the burner-stabilized cylindrical premixed flames, the possibility of flame stabilization through flow divergence was established, while the resulting one-dimensional, adiabatic, stretchless flame also allowed an accurate means of determining the laminar flame speeds of combustible mixtures. We have recently extended our studies of the flame structure in microgravity along the following directions: (1) Analysis of the dynamics of spherical premixed flames; (2) Analysis of the spreading of cylindrical diffusion flames; (3) Experimental observation of an interesting dual luminous zone structure of a steady-state, microbuoyancy, spherical diffusion flame of air burning in a hydrogen/methane mixture environment, and its subsequent quantification through computational simulation with detailed chemistry and transport; (4) Experimental quantification of the unsteady growth of a spherical diffusion flame; and (5) Computational simulation of stretched, diffusionally-imbalanced premixed flames near and beyond the conventional limits of flammability, and the substantiation of the concept of extended limits of flammability. Motivation and results of these investigations are individually discussed.

  13. Laminar Soot Processes (Lsp) Experiment: Findings From Ground-Based Measurements

    NASA Technical Reports Server (NTRS)

    Kim, C. H.; El-Leathy, A. M.; Faeth, G. M.; Xu, F.

    2003-01-01

    Processes of soot formation and oxidation must be understood in order to achieve reliable computational combustion calculations for nonpremixed (diffusion) flames involving hydrocarbon fuels. Motivated by this observation, the present investigation extended earlier work on soot formation and oxidation in laminar jet ethylene/air and methane/oxygen premixed and acetylene-nitrogen/air diffusion flames at atmospheric pressure in this laboratory, emphasizing soot surface growth and early soot surface oxidation in laminar diffusion flames fueled with a variety of hydrocarbons at pressures in the range 0.1 - 1.0 atm.

  14. Apparatus for studying premixed laminar flames using mass spectrometry and fiber-optic spectrometry

    NASA Astrophysics Data System (ADS)

    Olsson, Jim O.; Andersson, Lars L.; Lenner, Magnus; Simonson, Margaret

    1990-03-01

    An integrated flat-flame/ microprobe sampling quadrupole mass spectrometer system, complemented by optical spectrometry based on optical fibers, is presented. The short microprobe sampling line (total 25 cm) is directly connected to an open ion source closely flanked by two nude cryopumps (900 l/s) yielding a background pressure of 10-9 Torr and a sampling pressure of about 10-5 Torr. Due to this improved microprobe system, mass spectrometry can be used for analysis of stable species (including fuel, O2, H2O, CO2, CO, and Ar) with less disturbance of the sample than with a conventional microprobe with a back pressure of about 1 Torr. Optical spectrometry is used for the study of emission from important radical species (such as C2, CH, and OH). The system is proposed as a complement to more conventional flat-flame/MBMS systems in which the sampling cone can effect the experimental system. Details are provided concerning the configuration of the whole system ranging from gas delivery to data evaluation. Test data are presented for a 16% methanol/68% oxygen/16% argon flame studied at a pressure of 40 Torr, to elucidate the special features of this system.

  15. Effects of differential diffusion on the flame structure of oxygen enhanced turbulent non-premixed jet flames

    NASA Astrophysics Data System (ADS)

    Dietzsch, Felix; Gauding, Michael; Hasse, Christian

    2014-11-01

    By means of Direct Numerical Simulation we have investigated the influence of differential diffusion for non-premixed oxygen-enhanced turbulent flames. Oxygen-enhanced conversion usually yields higher amounts of H2 as compared to conventional air combustion. It is well known that H2 as a very diffusive species leads to differential diffusion effects. In addition to the diffusive transport mixing processes are also often controlled by turbulent transport. Previous investigations of a turbulent CH4/H2 oxygen-enhanced jet flame have shown that in mixture fraction space it is important to distinguish between regions of equal diffusivities and detailed transport. These findings are of particular interest when performing Large-Eddy simulations applying a flamelet approach. Using this approach a LES study was performed of the aforementioned flame considering differential diffusion. Therefore, flamelet equations including differential diffusion via non-unity constant Lewis numbers were solved. However, this study showed that keeping the non-unity Lewis numbers constant, is not sufficient to capture the diffusion phenomena in this particular flame. Direct Numerical Simulations have been conducted in order to investigate how Lewis numbers are affected in mixture fraction space. Computer resources for this project have been provided by the Gauss Centre for Supercomputing/Leibniz Supercomputing Centre under Grant: pr83xa.

  16. A Role of the Reaction Kernel in Propagation and Stabilization of Edge Diffusion Flames of C1-C3 Hydrocarbons

    NASA Technical Reports Server (NTRS)

    Takahashi, Fumiaki; Katta, Viswanath R.

    2003-01-01

    Diffusion flame stabilization is of essential importance in both Earth-bound combustion systems and spacecraft fire safety. Local extinction, re-ignition, and propagation processes may occur as a result of interactions between the flame zone and vortices or fire-extinguishing agents. By using a computational fluid dynamics code with a detailed chemistry model for methane combustion, the authors have revealed the chemical kinetic structure of the stabilizing region of both jet and flat-plate diffusion flames, predicted the flame stability limit, and proposed diffusion flame attachment and detachment mechanisms in normal and microgravity. Because of the unique geometry of the edge of diffusion flames, radical back-diffusion against the oxygen-rich entrainment dramatically enhanced chain reactions, thus forming a peak reactivity spot, i.e., reaction kernel, responsible for flame holding. The new results have been obtained for the edge diffusion flame propagation and attached flame structure using various C1-C3 hydrocarbons.

  17. Extremely weak hydrogen flames

    SciTech Connect

    Lecoustre, V.R.; Sunderland, P.B.; Chao, B.H.; Axelbaum, R.L.

    2010-11-15

    Hydrogen jet diffusion flames were observed near their quenching limits. These involved downward laminar flow of hydrogen from a stainless steel hypodermic tube with an inside diameter of 0.15 mm. Near their quenching limits these flames had hydrogen flow rates of 3.9 and 2.1 {mu}g/s in air and oxygen, respectively. Assuming complete combustion, the associated heat release rates are 0.46 and 0.25 W. To the authors' knowledge, these are the weakest self-sustaining steady flames ever observed. (author)

  18. Numerical simulation and sensitivity analysis of detailed soot particle size distribution in laminar premixed ethylene flames

    SciTech Connect

    Singh, Jasdeep; Patterson, Robert I.A.; Kraft, Markus; Wang, Hai

    2006-04-15

    In this paper, the prediction of a soot model [J. Appel, H. Bockhorn, M. Frenklach, Combust. Flame 121 (2000) 122-136] is compared to a recently published set of highly detailed soot particle size distributions [B. Zhao, Z. Yang, Z. Li, M.V. Johnston, H. Wang, Proc. Combust. Inst. 30 (2005)]. A stochastic approach is used to obtain soot particle size distributions (PSDs). The key features of the measured and simulated particle size distributions are identified and used as a simple way of comparing PSDs. The sensitivity of the soot PSDs to the parameters defining parts of the soot model, such as soot inception, particle and PAH collision efficiency and enhancement, and surface activity is investigated. Incepting soot particle size is found to have a very significant effect on the small-size end of the PSDs, especially the position of the trough for a bimodal soot PSDs. A new model for the decay in the surface activity is proposed in which the activity of the soot particle depends only on the history of that particle and the local temperature in the flame. This is a first attempt to use local flame variables to define the surface aging which has major impact on the prediction of the large-size end of the PSDs. Using these modifications to the soot model it is possible to improve the agreement between some of the points of interest in the simulated and measured PSDs. The paper achieves the task to help advance the soot models to predict soot PSD in addition to soot volume fraction and number density, which has been the focus of the literature. (author)

  19. Buoyancy Effects in Strongly-Pulsed, Turbulent Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Hermanson, J. C.; Johari, H.; Ghaem-Maghami, E.; Stocker, D. P.; Hegde, U. G.

    2004-01-01

    The objective of this experiment is to better understand the combustion behavior of pulsed, turbulent diffusion flames by conducting experiments in microgravity. The fuel jet is fully-modulated (i.e., completely shut off between pulses) by an externally controlled valve system leading to enhanced fuel/air mixing compared to acoustically excited or partially-modulated jets. Experiments are conducted both in laboratories at UW and WPI and in the GRC 2.2s Drop Tower. A single fuel nozzle with diameter d = 2 mm is centered in a combustor 20 20 cm in cross section and 67 cm in height. The gaseous fuel flow (ethylene or a 50/50 ethylene/nitrogen mixture by volume) is fully-modulated by a fast-response solenoid valve with injection times from tau = 4 to tau = 300 ms. The nominal Reynolds number based on the fuel velocity during injection, U(sub jet), is 5,000. A slow oxidizer co-flow properly ventilates the flame and an electrically heated wire loop serves as a continuous ignition source. Diagnostic techniques include video imaging, fine-wire thermocouples and thermopile radiometers, and gas sampling and standard emissions instruments (the last in the laboratory only).

  20. Buoyancy Effects in Strongly-pulsed, Turbulent Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Hermanson, J. C.; Johari, H.; Ghaem-Maghami, E.; Stocker, D. P.; Hegde, U. G.

    2004-01-01

    The objective of this experiment is to better understand the combustion behavior of pulsed, turbulent diffusion flames by conducting experiments in microgravity. The fuel jet is fully-modulated (i.e., completely shut off between pulses) by an externally controlled valve system leading to enhanced fuel/air mixing compared to acoustically excited or partially-modulated jets. Experiments are conducted both in laboratories at UW and WPI and in the GRC 2.2s Drop Tower. A single fuel nozzle with diameter d = 2 mm is centered in a combustor 20 x 20 cm in cross section and 67 cm in height. The gaseous fuel flow (ethylene or a 50/50 ethylene/nitrogen mixture by volume) is fully-modulated by a fast-response solenoid valve with injection times from tau = 4 to tau = 300 ms. The nominal Reynolds number based on the fuel velocity during injection, U(sub jet), is 5,000. A slow oxidizer co-flow properly ventilates the flame and an electrically heated wire loop serves as a continuous ignition source. Diagnostic techniques include video imaging, fine-wire thermocouples and thermopile radiometers, and gas sampling and standard emissions instruments (the last in the laboratory only).

  1. Analysis of opposed-jet hydrogen-air counter flow diffusion flame

    NASA Technical Reports Server (NTRS)

    Ho, Y. H.; Isaac, K. M.; Pellett, G. L.; Northam, G. B.

    1991-01-01

    An opposed-jet counterflow diffusion-flame configuration is considered for the analysis of a nitrogen-diluted hydrogen-air diffusion flame. A boundary-layer similarity solution is employed in order to reduce the governing equations to a set of equations in one independent variable. The equation set is written in the time-dependent form and solved by the finite-volume time-marching technique. This model uses detailed chemistry and accounts for the variations of Prandtl number and Lewis number as well as the effect of thermal diffusion on the flame. It is noted that a one-step model can predict several features of the flame, while the detailed-chemistry model can be used for fine-tuning the results. The present results indicate that thermal diffusion has negligible effect on the characteristics of the flame.

  2. Counterflow diffusion flames of hydrogen, and hydrogen plus methane, ethylene, propane, and silane vs. air - Strain rates at extinction

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Northam, G. Burton; Wilson, L. G.

    1991-01-01

    Five coaxial tubular opposed jet burners (OJBs) with tube diameter D(T) of 1.8-10 mm and 5 mm conical nozzles were used to form dish-shaped counterflow diffusion flames centered by opposing laminar jets of nitrogen and hydrocarbon-diluted H2 versus air in an argon-purged chamber at 1 atm. Area-averaged air jet velocities at blowoff of the central flame, U(air), characterized extinction of the airside flame as functions of input H2 concentration on the fuelside. A master plot of extensive U(air) data at blowoff versus D(T) shows that U(air) varies linearly with D(T). This and other data sets are used to find that nozzle OJB results for U(air)/diameter average 4.24 + or - 0.28 times larger than tubular OJB results for the same fuel compositions. Critical radial velocity gradients consistent with one-dimensional stagnation point boundary theory and with plug flow inputs are estimated. The results compare favorably with published numerical results based only on potential flow.

  3. An Experimental and Theoretical Study of Radiative Extinction of Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Atreya, Arvind; Wichman, Indrek; Guenther, Mark; Ray, Anjan; Agrawal, Sanjay

    1993-01-01

    In a recent paper on 'Observations of candle flames under various atmospheres in microgravity' by Ross et al., it was found that for the same atmosphere, the burning rate per unit wick surface area and the flame temperature were considerably reduced in microgravity as compared with normal gravity. Also, the flame (spherical in microgravity) was much thicker and further removed from the wick. It thus appears that the flame becomes 'weaker' in microgravity due to the absence of buoyancy generated flow which serves to transport the oxidizer to the combustion zone and remove the hot combustion products from it. The buoyant flow, which may be characterized by the strain rate, assists the diffusion process to execute these essential functions for the survival of the flame. Thus, the diffusion flame is 'weak' at very low strain rates and as the strain rate increases the flame is initially 'strengthened' and eventually it may be 'blown out'. The computed flammability boundaries of T'ien show that such a reversal in material flammability occurs at strain rates around 5 sec. At very low or zero strain rates, flame radiation is expected to considerably affect this 'weak' diffusion flame because: (1) the concentration of combustion products which participate in gas radiation is high in the flame zone; and (2) low strain rates provide sufficient residence time for substantial amounts of soot to form which is usually responsible for a major portion of the radiative heat loss. We anticipate that flame radiation will eventually extinguish this flame. Thus, the objective of this project is to perform an experimental and theoretical investigation of radiation-induced extinction of diffusion flames under microgravity conditions. This is important for spacecraft fire safety.

  4. Theoretical analysis of molecular diffusion in pressure-driven laminar flow in microfluidic channels.

    PubMed Central

    Kamholz, A E; Yager, P

    2001-01-01

    The T-sensor is a microfluidic analytical device that operates at low Reynolds numbers to ensure entirely laminar flow. Diffusion of molecules between streams flowing side by side may be observed directly. The pressure-driven velocity profile in the duct-shaped device influences diffusive transport in ways that affect the use of the T-sensor to measure molecular properties. The primary effect is a position-dependent variation in the extent of diffusion that occurs due to the distribution of residence time among different fluid laminae. A more detailed characterization reveals that resultant secondary concentration gradients yield variations in the scaling behavior between diffusive displacement and elapsed time in different regions of the channel. In this study, the time-dependent evolution of analyte distribution has been quantified using a combination of one- and two-dimensional models. The results include an accurate portrayal of the shape of the interdiffusion region in a representative T-sensor assay, calculation of the diffusive scaling law across the width of the channel, and quantification of artifacts that occur when making diffusion coefficient measurements in the T-sensor. PMID:11159391

  5. Pattern Formation in Diffusion Flames Embedded in von Karman Swirling Flows

    NASA Technical Reports Server (NTRS)

    Nayagam, Vedha

    2006-01-01

    Pattern formation is observed in nature in many so-called excitable systems that can support wave propagation. It is well-known in the field of combustion that premixed flames can exhibit patterns through differential diffusion mechanism between heat and mass. However, in the case of diffusion flames where fuel and oxidizer are separated initially there have been only a few observations of pattern formation. It is generally perceived that since diffusion flames do not possess an inherent propagation speed they are static and do not form patterns. But in diffusion flames close to their extinction local quenching can occur and produce flame edges which can propagate along stoichiometric surfaces. Recently, we reported experimental observations of rotating spiral flame edges during near-limit combustion of a downward-facing polymethylmethacrylate disk spinning in quiescent air. These spiral flames, though short-lived, exhibited many similarities to patterns commonly found in quiescent excitable media including compound tip meandering motion. Flame disks that grow or shrink with time depending on the rotational speed and in-depth heat loss history of the fuel disk have also been reported. One of the limitations of studying flame patterns with solid fuels is that steady-state conditions cannot be achieved in air at normal atmospheric pressure for experimentally reasonable fuel thickness. As a means to reproduce the flame patterns observed earlier with solid fuels, but under steady-state conditions, we have designed and built a rotating, porous-disk burner through which gaseous fuels can be injected and burned as diffusion flames. The rotating porous disk generates a flow of air toward the disk by a viscous pumping action, generating what is called the von K rm n boundary layer which is of constant thickness over the entire burner disk. In this note we present a map of the various dynamic flame patterns observed during the combustion of methane in air as a function of

  6. Ignition and Unburned Hydrogen Escaping from Hydrogen Diffusion Jet Flame Diluted with Nitrogen

    SciTech Connect

    Tran, P.X.; Soong, Yee

    2007-07-01

    Ignition and unburned hydrogen escaping from hydrogen jet diffusion flames diluted with nitrogen up to 70% were experimentally studied. The successful ignition locations were about 2/3 of the flame length above the jet exit for undiluted flames and moved much closer to the exit for diluted flames. For higher levels of dilution or higher flow rates, there existed a region within which a diluted hydrogen diffusion flame can be ignited and burns with a stable liftoff height. This is contrary to previous findings that pure and diluted hydrogen jet diffusion cannot achieve a stable lifted flame configuration. With liftoff, the flame is noisy and short with significant amount of unburned hydrogen escaping into the product gases. If ignition is initiated below this region, the flame propagates upstream quickly and attaches to the burner rim. Results from measurements of unburned hydrogen in the combustion products showed that the amount of unburned hydrogen increased as the nitrogen dilution level was increased. Thus, hydrogen diffusion flame diluted with nitrogen cannot burn completely.

  7. The interaction of high-speed turbulence with flames: Global properties and internal flame structure

    SciTech Connect

    Poludnenko, A.Y.; Oran, E.S.

    2010-05-15

    We study the dynamics and properties of a turbulent flame, formed in the presence of subsonic, high-speed, homogeneous, isotropic Kolmogorov-type turbulence in an unconfined system. Direct numerical simulations are performed with Athena-RFX, a massively parallel, fully compressible, high-order, dimensionally unsplit, reactive flow code. A simplified reaction-diffusion model represents a stoichiometric H{sub 2}-air mixture. The system being modeled represents turbulent combustion with the Damkoehler number Da=0.05 and with the turbulent velocity at the energy injection scale 30 times larger than the laminar flame speed. The simulations show that flame interaction with high-speed turbulence forms a steadily propagating turbulent flame with a flame brush width approximately twice the energy injection scale and a speed four times the laminar flame speed. A method for reconstructing the internal flame structure is described and used to show that the turbulent flame consists of tightly folded flamelets. The reaction zone structure of these is virtually identical to that of the planar laminar flame, while the preheat zone is broadened by approximately a factor of two. Consequently, the system evolution represents turbulent combustion in the thin reaction zone regime. The turbulent cascade fails to penetrate the internal flame structure, and thus the action of small-scale turbulence is suppressed throughout most of the flame. Finally, our results suggest that for stoichiometric H{sub 2}-air mixtures, any substantial flame broadening by the action of turbulence cannot be expected in all subsonic regimes. (author)

  8. An Experimental and Theoretical Study of Radiative Extinction of Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Wichman, Indrek S.

    1993-01-01

    The objective of this work is to investigate the radiation-induced rich extinction limits for diffusion flames. Radiative extinction is caused by the formation of particulates (e.g., soot) that drain chemical energy from the flame. We examine (mu)g conditions because there is a strong reason to believe that radiation-induced rich-limit extinction is not possible under normal-gravity conditions. In normal- g, the hot particulates formed in the fuel-rich flames are swept upward by buoyancy, out of the flame to the region above it, where their influence on the flame is negligible. However, in (mu)g the particulates remain in the flame vicinity, creating a strong energy sink that can, under suitable conditions, cause flame extinction.

  9. Effects of Structure and Hydrodynamics on the Sooting Behavior of Spherical Microgravity Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Sunderland, P. B.; Axelbaum, Richard L.; Urban, D. L.

    2000-01-01

    We have examined the sooting behavior of spherical microgravity diffusion flames burning ethylene at atmospheric pressure in the NASA Glenn 2.2-second drop tower. In a novel application of microgravity, spherical flames allowed convection across the flame to be either from fuel to oxidizer or from oxidizer to fuel. Thus, microgravity flames are uniquely capable of allowing independent variation of convection direction across the flame and stoichiometric mixture fraction, Z(sub st). This allowed us to determine the dominant mechanism responsible for the phenomenon of permanently-blue diffusion flames -- flames that remain blue as strain rate approaches zero. Stoichiometric mixture fraction was varied by changing inert concentrations such that adiabatic flame temperature did not change. At low and high Z(sub st) nitrogen was supplied with the oxidizer and the fuel, respectively. For the present flames, structure (Z(sub st)) was found to have a profound effect on soot production. Soot-free conditions were observed at high Z(sub st) (Z(sub st) = 0.78) and sooting conditions were observed at low Z(sub st) (Z(sub st) = 0.064) regardless of the direction of convection. Convection direction was found to have a lesser impact on soot inception, with formation being suppressed when convection at the flame sheet was directed towards the oxidizer.

  10. Transient Evolution of a Planar Diffusion Flame Aft of a Translating Flat Plate

    NASA Technical Reports Server (NTRS)

    Gokoglu, Suleyman A.

    2003-01-01

    The high degree of spatial symmetry of a planar diffusion flame affords great simplifications for experimental and modeling studies of gaseous fuel combustion. Particularly, in a microgravity environment, where buoyancy effects are negligible, an effectively strain-rate-free, vigorous flame may be obtained. Such a flame can also provide long residence times and large length scales for practical probing of flame structures and soot processes. This 2-D numerical study explores the feasibility of establishing such a planar diffusion flame in an enclosed container utilizing a realistic test protocol for a microgravity experiment. Fuel and oxygen mixtures, initially segregated into two half-volumes of a squat rectangular container by a thin separator, are ignited as soon as a flammable mixture is formed in the wake of the separator withdrawn in the centerplane. A triple-flame ensues that propagates behind the trailing edge of the separator. The results of calculations show that the mechanically- and thermally-induced convection decays in about two seconds. The establishment of a planar diffusion flame after this period seems feasible in the central region of the container with sufficient quantities of reactants left over for subsequent studies. An analysis of the flame initiation and formation process suggests how the feasibility of creating such a flame can be further improved.

  11. Homogeneous nucleation rate measurements of 1-butanol in helium: a comparative study of a thermal diffusion cloud chamber and a laminar flow diffusion chamber.

    PubMed

    Brus, David; Hyvärinen, Antti-Pekka; Zdímal, Vladimír; Lihavainen, Heikki

    2005-06-01

    Isothermal homogeneous nucleation rates of 1-butanol were measured both in a thermal diffusion cloud chamber and in a laminar flow diffusion chamber built recently at the Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, Prague, Czech Republic. The chosen system 1-butanol-helium can be studied reasonably well in both devices, in the overlapping range of temperatures. The results were compared with those found in the literature and those measured by Lihavainen in a laminar flow diffusion chamber of a similar design. The same isotherms measured with the thermal diffusion cloud chamber occur at highest saturation ratios of the three devices. Isotherms measured with the two laminar flow diffusion chambers are reasonably close together; the measurements by Lihavainen occur at lowest saturation ratios. The temperature dependences observed were similar in all three devices. The molecular content of critical clusters was calculated using the nucleation theorem and compared with the Kelvin equation. Both laminar flow diffusion chambers provided very similar sizes slightly above the Kelvin equation, whereas the thermal diffusion cloud chamber suggests critical cluster sizes significantly smaller. The results found elsewhere in the literature were in reasonable agreement with our results.

  12. Homogeneous nucleation rate measurements of 1-butanol in helium: a comparative study of a thermal diffusion cloud chamber and a laminar flow diffusion chamber.

    PubMed

    Brus, David; Hyvärinen, Antti-Pekka; Zdímal, Vladimír; Lihavainen, Heikki

    2005-06-01

    Isothermal homogeneous nucleation rates of 1-butanol were measured both in a thermal diffusion cloud chamber and in a laminar flow diffusion chamber built recently at the Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, Prague, Czech Republic. The chosen system 1-butanol-helium can be studied reasonably well in both devices, in the overlapping range of temperatures. The results were compared with those found in the literature and those measured by Lihavainen in a laminar flow diffusion chamber of a similar design. The same isotherms measured with the thermal diffusion cloud chamber occur at highest saturation ratios of the three devices. Isotherms measured with the two laminar flow diffusion chambers are reasonably close together; the measurements by Lihavainen occur at lowest saturation ratios. The temperature dependences observed were similar in all three devices. The molecular content of critical clusters was calculated using the nucleation theorem and compared with the Kelvin equation. Both laminar flow diffusion chambers provided very similar sizes slightly above the Kelvin equation, whereas the thermal diffusion cloud chamber suggests critical cluster sizes significantly smaller. The results found elsewhere in the literature were in reasonable agreement with our results. PMID:15974753

  13. Flame Structure and Emissions of Strongly-Pulsed Turbulent Diffusion Flames with Swirl

    NASA Astrophysics Data System (ADS)

    Liao, Ying-Hao

    This work studies the turbulent flame structure, the reaction-zone structure and the exhaust emissions of strongly-pulsed, non-premixed flames with co-flow swirl. The fuel injection is controlled by strongly-pulsing the fuel flow by a fast-response solenoid valve such that the fuel flow is completely shut off between pulses. This control strategy allows the fuel injection to be controlled over a wide range of operating conditions, allowing the flame structure to range from isolated fully-modulated puffs to interacting puffs to steady flames. The swirl level is controlled by varying the ratio of the volumetric flow rate of the tangential air to that of the axial air. For strongly-pulsed flames, both with and without swirl, the flame geometry is strongly impacted by the injection time. Flames appear to exhibit compact, puff-like structures for short injection times, while elongated flames, similar in behaviors to steady flames, occur for long injection times. The flames with swirl are found to be shorter for the same fuel injection conditions. The separation/interaction level between flame puffs in these flames is essentially governed by the jet-off time. The separation between flame puffs decreases as swirl is imposed, consistent with the decrease in flame puff celerity due to swirl. The decreased flame length and flame puff celerity are consistent with an increased rate of air entrainment due to swirl. The highest levels of CO emissions are generally found for compact, isolated flame puffs, consistent with the rapid quenching due to rapid dilution with excess air. The imposition of swirl generally results in a decrease in CO levels, suggesting more rapid and complete fuel/air mixing by imposing swirl in the co-flow stream. The levels of NO emissions for most cases are generally below the steady-flame value. The NO levels become comparable to the steady-flame value for sufficiently short jet-off time. The swirled co-flow air can, in some cases, increase the NO

  14. Flame Propagation in Low-Intensity Turbulence under Microgravity Conditions

    NASA Technical Reports Server (NTRS)

    Aldredge, R. C.

    2001-01-01

    The goal of the research is to understand the influences of the hydrodynamic instability on premixed-flame propagation. It is known that coupling between flame and flow-field dynamics in association with the hydrodynamic instability may lead to flame-generated turbulence, flame acceleration and enhancement of burning rates. As a result of such hydrodynamic coupling the transition from initially planar or wrinkled laminar flames to fast turbulent flames or detonations is possible, even when diffusive-thermal effects associated with non-unity reactant Lewis numbers are not destabilizing. It is important to identify methods of suppressing the hydrodynamic instability so as to insure fire safety, particularly in space.

  15. TRAJECTORY AND INCINERATION OF ROGUE DROPLETS IN A TURBULENT DIFFUSION FLAME

    EPA Science Inventory

    The trajectory and incineration efficiency of individual droplet streams of a fuel mixture injected into a swirling gas turbulent diffusion flame were measured as a function of droplet size, droplet velocity, interdroplet spacing, and droplet injection angle. Additional experimen...

  16. Growth of a diffusion flame in the field of a vortex

    NASA Technical Reports Server (NTRS)

    Marble, F. E.

    1985-01-01

    In the present study of the growth of a diffusion flame in the field of a vortex, the motion in the core is converted into a solid body rotation. The flame extension and distortion kinematics are presented, and the effect of the local flow field on local flame structure is analyzed in detail. The combustion field is found to consist of a totally reacted core region whose radius is time-dependent, and an external flame region which consists of a pair of spiral arms that extend at large radii toward their original positions on the horizontal axis. Two similarity rules are formulated which are independent of kinematic viscosity.

  17. The Extinction of Low Strain Rate Diffusion Flames by a Suppressant

    NASA Technical Reports Server (NTRS)

    Hamins, A.; Yang, J.; Puri, I. K.

    1999-01-01

    This paper describes plans for an experimental and computational study on the structure and extinction of low strain rate diffusion flames by a suppressant added to the oxidizer stream. Stable low strain rate flames will be established through ground based reduced gravity experiments using the 2.2 s drop tower. A variety of agents will be investigated, including both physically and chemically acting agents (He, N2, CO2, and CF3Br) for flames burning methane and propane. A computational model of flame structure and extinction will be modified to include radiative losses, which is thought to be a significant heat loss mechanism at low strain rates.

  18. Ignition time of hydrogen-air diffusion flames

    NASA Astrophysics Data System (ADS)

    Sánchez, Antonio L.; Fernández-Tarrazo, Eduardo; Boivin, Pierre; Liñán, Amable; Williams, Forman A.

    2012-11-01

    The ignition time of hydrogen-air diffusion flames is a quantity of utmost interest in a large number of applications, with implications regarding the viability of supersonic combustion and the safe operation of gas turbines. The underlying chemistry and the associated ignition history are very different depending on the initial temperature and pressure. This article addresses conditions that place the system above the so-called second explosion limit, as is typically the case in SCRAMJET operation, so that a branched-chain explosion characterizes the ignition process. The roles of local radical accumulation, molecular transport, and chemical reaction in nonpremixed ignition are clarified by considering the temporal evolution of an unstrained mixing layer formed between two semi-infinite spaces of hydrogen and air. The problem is formulated in terms of a radical-pool mass fraction, whose evolution in time is studied with a WKB expansion that exploits the disparity of chemical time scales present in the problem, leading to an explicit expression for the ignition time. The applicability of the analytical results for obtaining predictions of ignition distances in supersonic-combustion applications is also considered.

  19. Effects of Coaxial Air on Nitrogen-Diluted Hydrogen Jet Diffusion Flame Length and NOx Emission

    SciTech Connect

    Weiland, N.T.; Chen, R.-H.; Strakey, P.A.

    2007-10-01

    Turbulent nitrogen-diluted hydrogen jet diffusion flames with high velocity coaxial air flows are investigated for their NOx emission levels. This study is motivated by the DOE turbine program’s goal of achieving 2 ppm dry low NOx from turbine combustors running on nitrogen-diluted high-hydrogen fuels. In this study, effects of coaxial air velocity and momentum are varied while maintaining low overall equivalence ratios to eliminate the effects of recirculation of combustion products on flame lengths, flame temperatures, and resulting NOx emission levels. The nature of flame length and NOx emission scaling relationships are found to vary, depending on whether the combined fuel and coaxial air jet is fuel-rich or fuel-lean. In the absence of differential diffusion effects, flame lengths agree well with predicted trends, and NOx emissions levels are shown to decrease with increasing coaxial air velocity, as expected. Normalizing the NOx emission index with a flame residence time reveals some interesting trends, and indicates that a global flame strain based on the difference between the fuel and coaxial air velocities, as is traditionally used, is not a viable parameter for scaling the normalized NOx emissions of coaxial air jet diffusion flames.

  20. Observations of Methane and Ethylene Diffusion Flames Stabilized Around a Blowing Porous Sphere Under Microgravity Conditions

    NASA Technical Reports Server (NTRS)

    Atreya, Arvind; Agrawal, Sanjay; Sacksteder, Kurt; Baum, Howard R.

    1994-01-01

    This paper presents the experimental and theoretical results for expanding methane and ethylene diffusion flames in microgravity. A small porous sphere made from a low-density and low-heat-capacity insulating material was used to uniformly supply fuel at a constant rate to the expanding diffusion flame. A theoretical model which includes soot and gas radiation is formulated but only the problem pertaining to the transient expansion of the flame is solved by assuming constant pressure infinitely fast one-step ideal gas reaction and unity Lewis number. This is a first step toward quantifying the effect of soot and gas radiation on these flames. The theoretically calculated expansion rate is in good agreement with the experimental results. Both experimental and theoretical results show that as the flame radius increases, the flame expansion process becomes diffusion controlled and the flame radius grows as gamma t. Theoretical calculations also show that for a constant fuel mass injection rate a quasi-steady state is developed in the region surrounded by the flame and the mass flow rate at any location inside this region equals the mass injection rate.

  1. Thermal Characteristics and Structure of Fully-Modulated, Turbulent Diffusion Flames in Microgravity

    NASA Technical Reports Server (NTRS)

    Hermanson, J. C.; Johari, H.; Stocker, D. P.; Hegde, U. G.

    2003-01-01

    Turbulent jet diffusion flames are studied in microgravity and normal gravity under fully-modulated conditions for a range of injection times and a 50% duty cycle. Diluted ethylene was injected through a 2-mm nozzle at a Reynolds number of 5,000 into an open duct, with a slow oxidizer co-flow. Microgravity tests are conducted in NASA's 2.2 Second Drop Tower. Flames with short injection times and high duty cycle exhibit a marked increase in the ensemble-averaged flame length due to the removal of buoyancy. The cycle-averaged centerline temperature profile reveals higher temperatures in the microgravity flames, especially at the flame tip where the difference is about 200 K. In addition, the cycle-averaged measurements of flame radiation were about 30% to 60% greater in microgravity than in normal gravity.

  2. Turbulent structure and emissions of strongly-pulsed jet diffusion flames

    NASA Astrophysics Data System (ADS)

    Fregeau, Mathieu

    -pulsed flames was not strongly impacted by buoyancy. This lack of sensitivity to buoyancy was consistent with offsetting changes in flame puff celerity and time to burnout for the microgravity versus normal-gravity cases. The emissions of CO and NO were examined in the vicinity of the visible flame tip and at the combustor exit for strongly-pulsed flames. The highest exhaust-point emission indices of CO for compact, isolated puffs were as much as a factor of six higher than those of elongated flames with longer injection times. The amount of CO decreased substantially with a decreased amount of flame puff interaction. The higher CO levels for pulsed flames with the shortest injection times were consistent with quenching due to the very rapid mixing and dilution with excess air for the most compact flame puffs. The injection time for which steady-flame emission levels were attained was comparable to the injection time for which the visible flame length approached the flame length of steady flames. The CO emissions, for a given fuelling rate, were strongly dependent on both the injection time and jet-off time for a jet-on fraction less than approximately 50%. The NO levels were generally proportional to the fuelling rate. This work indicates that there are specific combinations of injection time and jet-off time that considerably change the fuel/air mixing, resulting in emissions comparable to those of the steady flame while the flame length is significantly shorter. This points the potential utility of the strongly-pulsed injection technique in the development of compact, low emissions combustors involving turbulent diffusion flames. (Abstract shortened by UMI.)

  3. Characteristics of Gaseous Diffusion Flames with High Temperature Combustion Air in Microgravity

    NASA Technical Reports Server (NTRS)

    Ghaderi, M.; Gupta, A. K.

    2003-01-01

    The characteristics of gaseous diffusion flames have been obtained using high temperature combustion air under microgravity conditions. The time resolved flame images under free fall microgravity conditions were obtained from the video images obtained. The tests results reported here were conducted using propane as the fuel and about 1000 C combustion air. The burner included a 0.686 mm diameter central fuel jet injected into the surrounding high temperature combustion air. The fuel jet exit Reynolds number was 63. Several measurements were taken at different air preheats and fuel jet exit Reynolds number. The resulting hybrid color flame was found to be blue at the base of the flame followed by a yellow color flame. The length and width of flame during the entire free fall conditions has been examined. Also the relative flame length and width for blue and yellow portion of the flame has been examined under microgravity conditions. The results show that the flame length decreases and width increases with high air preheats in microgravity condition. In microgravity conditions the flame length is larger with normal temperature combustion air than high temperature air.

  4. Diffusion flame analysis of twin plane jets via a kinetic theory approach

    NASA Astrophysics Data System (ADS)

    Chuang, Shu-Hao; Hong, Zuu-Chang

    1991-07-01

    Diffusion flame solutions of twin plane jets based on a turbulent kinetic theory due to Chung and a Green function method by Hong are presented. The chemical reaction between fuel and oxidizer is assumed to be one-step, ne-direction and infinitely fast. The solutions are obtained by direct integration over a constructed probability density function in velocity space. The probability density functions of reactants in transverse velocity space, species mass fraction distributions, turbulent transport of momentum and heat, temperature distributions and flame structure are also considered in this paper. The diffusion flame phenomena of the twin plane jets show that the interaction between the two jets is a dominant factor.

  5. Experimental and Chemical Kinetics Study of the Effects of Halon 1211 (CF2BrCl) on the Laminar Flame Speed and Ignition of Light Hydrocarbons.

    PubMed

    Mathieu, Olivier; Keesee, Charles; Gregoire, Claire; Petersen, Eric L

    2015-07-16

    In this study, the effect of Halon 1211 (CF2BrCl) on the ignition delay time and laminar flame speed of CH4, C2H4, and C3H8 were investigated experimentally for the first time. The results showed that the effects of Halon 1211 on the ignition delay time are strongly dependent on the hydrocarbon: the ignition delay time of CH4 is significantly decreased by Halon 1211 addition, while a significant increase in the ignition delay time was observed with C2H4 for the lowest temperatures investigated. Ignition delay times for C3H8 were slightly increased, mostly on the low-temperature side and for the fuel-rich case. A significant reduction in the laminar flame speed was observed for all of the fuels. A tentative chemical kinetics model was assembled from existing models and completed with reactions that have been determined in the literature or estimated when necessary. The experimental results were reproduced satisfactorily by the model, and a chemical analysis showed that most of the effects of Halon 1211 on the ignition delay times of C2H4 and C3H8 are due to the consumption of H radical through the reaction HBr + H ⇄ Br + H2. In the case of methane, the CF2 radical promotes the formation of H via CF2 + CH3 ⇄ CH2:CF2 + H, which then promotes the branching reaction H + O2 ⇄ OH + O. The laminar flame speed results can be explained using catalytic cycles involving Br atoms that are similar to those reported in the literature for CF3Br. This study exhibits the need for a better estimation of the chlorine atom chemistry during the combustion of hydrocarbons in the presence of fire suppressants.

  6. Fuel structure and pressure effects on the formation of soot particles in diffusion flames. Annual technical report, 15 January 1988-15 January 1989

    SciTech Connect

    Santoro, R.J.

    1989-02-15

    Studies emphasizing the effects of fuel molecular structure on soot formation processes in laminar-diffusion flames were investigated. Particular attention was given to the particle inception and surface growth processes for a series of fuels. Studies of butane, 1-butene, and 1,3 butadiene have revealed that fuel structure strongly affects the soot-particle-inception process. However, subsequent surface-growth processes are largely determined by the available surface area. Thus, the surface growth process is independent of the fuel molecular structure following the initial particle-inception stage. Studies of the particle-inception region indicate that increased soot formation is strongly correlated with visible-fluorescence measurements attributed to large polynuclear aromatic hydrocarbon species in the flame.

  7. A lean methane premixed laminar flame doped with components of diesel fuel part III: Indane and comparison between n-butylbenzene, n-propylcyclohexane and indane

    SciTech Connect

    Pousse, E.; Tian, Z.Y.; Glaude, P.A.; Fournet, R.; Battin-Leclerc, F.

    2010-07-15

    To better understand the chemistry of the combustion of components of diesel fuel, the structure of a laminar lean premixed methane flame doped with indane has been investigated. The inlet gases contained 7.1% (molar) of methane, 36.8% of oxygen and 0.9% of indane corresponding to an equivalence ratio of 0.67 and a ratio C{sub 10}H{sub 14}/CH{sub 4} of 12.8%. The flame has been stabilized on a burner at a pressure of 6.7 kPa (50 Torr) using argon as diluent, with a gas velocity at the burner of 49.1 cm s{sup -1} at 333 K. Quantified species included the usual methane C{sub 0}-C{sub 2} combustion products, but also 16 C{sub 3}-C{sub 5} non-aromatic hydrocarbons, 6 C{sub 1}-C{sub 3} non-aromatic oxygenated compounds, as well as 22 aromatic products, namely benzene, toluene, xylenes, phenylacetylene, ethylbenzene, styrene, propenylbenzene, allylbenzene, n-propylbenzene, methylstyrenes, ethyltoluenes, trimethylbenzenes, n-butylbenzene, dimethylethylbenzene, indene, methylindenes, methylindane, benzocyclobutene, naphthalene, phenol, benzaldehyde, and benzofuran. A new mechanism for the oxidation of indane was proposed whose predictions were in satisfactory agreement with measured species profiles in both flames and jet-stirred reactor experiments. The main reaction pathways of consumption of indane have been derived from flow rate analyses in the two types of reactors. A comparison of the effect of the addition of three components of diesel fuel, namely indane, n-butylbenzene and n-propylcyclohexane (parts I and II of this series of paper), on the structure of a laminar lean premixed methane flame is also presented. (author)

  8. 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.

  9. Effect of Swirl on Flickering Motion of Diffusion Flame

    NASA Astrophysics Data System (ADS)

    Gotoda, Hiroshi; Hoo Chuah, Keng; Kushida, Genichiro

    2006-11-01

    The buoyancy-induced oscillation is referred to as the so-called flame flickering and its dynamics are important when revealing mechanism of flame oscillations encountered in some combustion systems. Many aspects of flame oscillation / buoyancy coupling have been extensively explored, but the effect of swirling flow on buoyancy-induced flame flickering has yet to be elucidated. The purpose of the present study is to investigate how the buoyancy-induced flame flickering motion is altered by swirl, using a rotating Bunsen burner. The rotating burner tube (Diameter of the burner tube D0 is 10 mm) is vertically supported by bearings, and rotated by a DC motor through a pulley and belt unit. The fuel injection velocity U (= volume flow rate / cross-sectional area of the burner tube) is varied from 0.1 to 0.3 m/s. The rotational speed of the burner tube N is varied up to 2000 rpm. Variations in the flame motion, oscillation frequency, and flame height as a function of burner rotation rate are presented in detail.

  10. Numerical Study of Buoyancy and Different Diffusion Effects on the Structure and Dynamics of Triple Flames

    NASA Technical Reports Server (NTRS)

    Chen, Jyh-Yuan; Echekki, Tarek

    2001-01-01

    Numerical simulations of 2-D triple flames under gravity force have been implemented to identify the effects of gravity on triple flame structure and propagation properties and to understand the mechanisms of instabilities resulting from both heat release and buoyancy effects. A wide range of gravity conditions, heat release, and mixing widths for a scalar mixing layer are computed for downward-propagating (in the same direction with the gravity vector) and upward-propagating (in the opposite direction of the gravity vector) triple flames. Results of numerical simulations show that gravity strongly affects the triple flame speed through its contribution to the overall flow field. A simple analytical model for the triple flame speed, which accounts for both buoyancy and heat release, is developed. Comparisons of the proposed model with the numerical results for a wide range of gravity, heat release and mixing width conditions, yield very good agreement. The analysis shows that under neutral diffusion, downward propagation reduces the triple flame speed, while upward propagation enhances it. For the former condition, a critical Froude number may be evaluated, which corresponds to a vanishing triple flame speed. Downward-propagating triple flames at relatively strong gravity effects have exhibited instabilities. These instabilities are generated without any artificial forcing of the flow. Instead disturbances are initiated by minute round-off errors in the numerical simulations, and subsequently amplified by instabilities. A linear stability analysis on mean profiles of stable triple flame configurations have been performed to identify the most amplified frequency in spatially developed flows. The eigenfunction equations obtained from the linearized disturbance equations are solved using the shooting method. The linear stability analysis yields reasonably good agreements with the observed frequencies of the unstable triple flames. The frequencies and amplitudes of

  11. Soot topography in a planar diffusion flame wrapped by a line vortex

    SciTech Connect

    Cetegen, B.M.; Basu, S.

    2006-09-15

    An experimental study of the interaction of a planar diffusion flame with a line vortex is presented. A planar diffusion flame is established between two coflowing, equal velocity streams of acetylene diluted with nitrogen and air. A line vortex is generated on demand by momentarily pulsing one of the flow streams by way of electromagnetic actuation of a piston in the flow apparatus. The flame-vortex interactions are diagnosed by planar laser-induced incandescence for soot yield and by particle image velocimetry for vortex flow characterization. The results show that soot formation and distribution are influenced by the reactant streams from which vortices are initiated. The vortices interacting with the flame from the air side produce more soot and soot is distributed in and around the vortex core in diffuse layers. In contrast, topography of soot in vortices interacting from the fuel side is such that soot is confined to thinner layers around the vortex core which does not contain any soot. The flame curvature is found to influence the local soot production with the flame regions convex to the fuel side containing more soot locally. It is also found that the overall soot yield is less sensitive to the vortex strength and is of lower magnitude when vortex is spun from the fuel side. The knowledge of this type of asymmetry in soot yield in flame-vortex interactions is useful for combustion engineering and design of practical devices. (author)

  12. Spherical Ethylene/Air Diffusion Flames Subject to Concentric DC Electric Field in Microgravity

    NASA Technical Reports Server (NTRS)

    Yuan, Z. -G.; Hegde, U.; Faeth, G. M.

    2001-01-01

    It is well known that microgravity conditions, by eliminating buoyant flow, enable many combustion phenomena to be observed that are not possible to observe at normal gravity. One example is the spherical diffusion flame surrounding a porous spherical burner. The present paper demonstrates that by superimposing a spherical electrical field on such a flame, the flame remains spherical so that we can study the interaction between the electric field and flame in a one-dimensional fashion. Flames are susceptible to electric fields that are much weaker than the breakdown field of the flame gases owing to the presence of ions generated in the high temperature flame reaction zone. These ions and the electric current of the moving ions, in turn, significantly change the distribution of the electric field. Thus, to understand the interplay between the electric field and the flame is challenging. Numerous experimental studies of the effect of electric fields on flames have been reported. Unfortunately, they were all involved in complex geometries of both the flow field and the electric field, which hinders detailed study of the phenomena. In a one-dimensional domain, however, the electric field, the flow field, the thermal field and the chemical species field are all co-linear. Thus the problem is greatly simplified and becomes more tractable.

  13. Standard and high-throughput microfluidic disposables based on laminar fluid diffusion interfaces

    NASA Astrophysics Data System (ADS)

    Weigl, Bernhard H.; Morris, Chris; Kesler, Natasa; Battrell, Fred; Bardell, Ron L.

    2002-06-01

    Laminar Fluid Diffusion Interfaces are generated when tow or more streams flow in parallel in a microfluidic structure. This technology can be used for diffusion-based separation and detection applications, for example: DNA desalting, the extraction of small proteins from whole-blood samples, and the detection of various constituents in while blood. Additional applications are the establishment of stable concentration gradients, and the exposure of chemical constituents or biological particles to these concentration gradients, enabling the uniform and controlled exposure of cells to lysing agents, allowing the differentiation of cells by their sensitivity to specific agents in an on-chip cytometer coupled directly to the lysing structure. We have developed integrated systems using machine-controlled disposable cartridges and passive self-contained disposable cards including particle separators, flow cytometers, valves, detection channels, mixers, and diluters that are used in a hematology analyzer, stand-alone blood plasma separators, and a variety of chemical and biological assays. Microfluidic arrays compatible with common well-plate formats have been designed for high-throughout toxicology screening applications. All these devices were manufactured using Micronics' unique rapid-prototyping process yielding low-cost plastic disposable microfluidic chips.

  14. Mechanisms and enhancement of flame stabilization

    SciTech Connect

    Law, C.K.

    1993-01-01

    During the reporting period, useful contributions have been made in understanding the structure of laminar premixed and diffusion flames, with emphasis on the influence of aerodynamics and chemical kinetics. These contributions include (1) derivation of the missing closure condition for the activation energy asymptotic analysis of premixed flames, (2) identification of a dual extinction mode for radiation-affected flames, (3) formulation of a unified theory of fundamental flammability limits, and (4) demonstration that flame stabilization can be achieved in the absence of heat loss. These investigations have been conducted via experimental, analytical and computational approaches, with strong coupling between the individual components.

  15. The distribution of excess charges in the diffusion flame of hydrocarbons

    NASA Astrophysics Data System (ADS)

    Reshetnikov, S. M.; Zyryanov, I. A.; Pozolotin, A. P.; Budin, A. G.

    2016-01-01

    The paper discusses the experimental investigation results of the potentials distribution (probing) and the excess charges in diffusion flames of propane and polymers - PMMA (polymethyl methacrylate) and divinyl rubber. The study of the excess charges distribution was made by analysis of flame deformation in the presence of an external lateral electrostatic field. The existence and the accumulation of excess charges in the flame are generally explained on the basis of consideration of the interaction processes of condensed phase particles and charges (electrons) generated during combustion in the presence of a dusty plasma. However, this mechanism does not give the opportunity to consider the sign and magnitude of the excess charges distribution in the flame, depending on the products composition and the value of the oxidant excess. It is unclear how oppositely charged immiscible streams of flame are formed and coexist.

  16. Effects of Structure and Hydrodynamics on the Sooting Behavior of Spherical Microgravity Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Sunderland, P. B.; Axelbaum, R. L.; Urban, D. L.

    1999-01-01

    Recent experimental, numerical and analytical work has shown that the stoichiometric mixture fraction (Z(sub st)) can have a profound effect on soot formation in diffusion flames. These findings were obtained at constant flame temperature (T(sub ad)), employing the approach described in Du and Axelbaum (1995, 1996). For example, a fuel mixture containing 1 mole of ethylene and 11.28 moles of nitrogen burning in pure oxygen ((Z(sub st)) = 0.78) has the same adiabatic flame temperature (2370 K) as that of pure ethylene burning in air ((Z(sub st)) = 0.064). An important finding of these works was that at sufficiently high (Z(sub st)), flames remain blue as strain rate approaches zero in counterflow flames, or as flame height and residence time approach infinity in coflowing flames. Lin and Faeth (1996a) coined the term permanently blue to describe such flames. Two theories have been proposed to explain the appearance of permanently-blue flames at high (Z(sub st)). They are based on (1) hydrodynamics and (2) flame structure. Previous experimental studies in normal gravity are not definitive as to which, if either, mechanism is dominant because both hydrodynamics and structure suppress soot formation at high (Z(sub st)) in coflowing and counterflowing diffusion flames. In counterflow flames with (Z(sub st)) < 0.5 streamlines at the flame sheet are directed toward the fuel. Newly formed soot is convected into richer regions, favoring soot growth over oxidation. For (Z(sub st)) > 0.5, convection at the flame is toward the oxidizer, thus enhancing soot oxidization. Thus, in counterflow flames, hydrodynamics causes soot to be convected towards the oxidizer at high (Z(sub st)) which suppresses soot formation. Axelbaum and co-workers maintain that while the direction of convection can impact soot growth and oxidation, these processes alone cannot cause permanently-blue flames. Soot growth and oxidation are dependent on the existence of soot particles and the presence of soot

  17. Triple flames and flame stabilization

    NASA Technical Reports Server (NTRS)

    Broadwell, James E.

    1994-01-01

    It is now well established that when turbulent jet flames are lifted, combustion begins, i.e., the flame is stabilized, at an axial station where the fuel and air are partially premixed. One might expect, therefore, that the beginning of the combustion zone would be a triple flame. Such flames have been described; however, other experiments provide data that are difficult to reconcile with the presence of triple flames. In particular, laser images of CH and OH, marking combustion zones, do not exhibit shapes typical of triple flames, and, more significantly, the lifted flame appears to have a propagation speed that is an order of magnitude higher than the laminar flame speed. The speed of triple flames studied thus far exceeds the laminar value by a factor less than two. The objective of the present task is the resolution of the apparent conflict between the experiments and the triple flame characteristics, and the clarification of the mechanisms controlling flame stability. Being investigated are the resolution achieved in the experiments, the flow field in the neighborhood of the stabilization point, propagation speeds of triple flames, laboratory flame unsteadiness, and the importance of flame ignition limits in the calculation of triple flames that resemble lifted flames.

  18. Experimental investigation of the morphology and stability of diffusion and edge flames in an opposed jet burner

    SciTech Connect

    Ciani, A.; Kreutner, W.; Hubschmid, W.; Frouzakis, C.E.; Boulouchos, K.

    2007-08-15

    The stability of methane/air and hydrogen/air flames in an axisymmetric counterflow burner was investigated experimentally for different burner geometries, degrees of fuel dilution, and combinations of flow velocities. Both planar diffusion flames and edge flames were observed, and the transitions between these flame types were studied. The experimental results confirmed previously published numerical predictions on diluted hydrogen/air flames: the existence of two distinct stable flame types; the possibility of switching between the two flame types by perturbing the flames, e.g., by suitably changing a flow velocity; and the strong hysteresis for the transition from one flame type to the other. Flame stability diagrams were compiled which delineate the range of fuel and air flow velocities for which the planar diffusion flame and the toroidal edge flame are stable. The lower boundary curve for the edge flame stability exhibits a characteristic minimum at a well-defined value of the fuel velocity. For fuel velocities lower than this value, the transition between the edge and the diffusion structure is reversible, and the flames exhibit bistable behavior. For higher fuel velocities, the decrease of air velocity leads to the extinction of the edge flame. An investigation of both the cold and the reactive flow field identified bistable behavior for the flow field as well. Except for very low flow rates, the stagnation plane stabilizes in two positions, close to either of the two nozzles. Detailed numerical simulations of hydrogen flames capture the essentials of this behavior. The observed flame extinction results from the interaction of the flame dynamics with the dynamics of the flow field. (author)

  19. Modeling Study of Hydrogen/Oxygen and n-alkane/Oxygen Counterflow Diffusion Flames

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-wei; Cai, Guo-biao; Yang, Vigor

    2011-04-01

    A comprehensive analysis of hydrogen/oxygen and hydrocarbon/oxygen counterflow diffusion flames has been conducted using corresponding detailed reaction mechanisms. The hydrocarbon fuels contain n-alkanes from CH4 to C16H34. The basic diffusion flame structures are demonstrated, analyzed, and compared. The effects of pressure, and strain rate on the flame behavior and energy-release rate for each fuel are examined systematically. The detailed chemical kinetic reaction mechanisms from Lawrence Livermore National Laboratory (LLNL) are employed, and the largest one of them contains 2115 species and 8157 reversible reactions. The results indicate for all of the fuels the flame thickness and heat release rate correlate well with the square root of the pressure multiplied by the strain rate. Under the condition of any strain rate and pressure, H2 has thicker flame than hydrocarbons, while the hydrocarbons have the similar temperature and main products distributions and almost have the same flame thickness and heat release rate. The result indicates that the fuels composed with these hydrocarbons will still have the same flame properties as any pure n-alkane fuel.

  20. OH radical imaging in a DI diesel engine and the structure of the early diffusion flame

    SciTech Connect

    Dec, J.E.; Coy, E.B.

    1996-03-01

    Laser-sheet imaging studies have considerably advanced our understanding of diesel combustion; however, the location and nature of the flame zones within the combusting fuel jet have been largely unstudied. To address this issue, planar laser-induced fluorescence (PLIF) imaging of the OH radical has been applied to the reacting fuel jet of a direct-injection diesel engine of the ``heavy-duty`` size class, modified for optical access. An Nd:YAG-based laser system was used to pump the overlapping Q{sub 1}9 and Q{sub 2}8 lines of the (1,0) band of the A{yields}X transition at 284.01 nm, while the fluorescent emission from both the (0,O) and (1, I) bands (308 to 320 nm) was imaged with an intensified video camera. This scheme allowed rejection of elastically scattered laser light, PAH fluorescence, and laser-induced incandescence. OH PLIF is shown to be an excellent diagnostic for diesel diffusion flames. The signal is strong, and it is confined to a narrow region about the flame front because the threebody recombination reactions that reduce high flame-front OH concentrations to equilibrium levels occur rapidly at diesel pressures. No signal was evident in the fuel-rich premixed flame regions where calculations and burner experiments indicate that OH concentrations will be below detectable limits. Temporal sequences of OH PLIF images are presented showing the onset and development of the early diffusion flame up to the time that soot obscures the images. These images show that the diffusion flame develops around the periphery of the-downstream portion of the reacting fuel jet about half way through the premixed burn spike. Although affected by turbulence, the diffusion flame remains at the jet periphery for the rest of the imaged sequence.

  1. Measurements of soot production and thermal radiation from confined turbulent jet diffusion flames of methane

    SciTech Connect

    Brookes, S.J.; Moss, J.B.

    1999-01-01

    Turbulent methane/air jet diffusion flames at atmospheric and elevated pressure have been studied experimentally to provide data for coupled thermal radiation and soot production model development and validation. Although methane is only lightly sooting at atmospheric pressure, at elevated pressure the soot yield increases greatly. This allows the creation of a highly radiating flame, of moderate optical depth, within a laboratory scale rig. Spatially resolved flame properties needed for model validation have been measured at 1 and 3 atm. These measurements include detailed maps of mean mixture fraction, mean temperature, mean soot volume fraction, and mean and instantaneous spectrally resolved, path integrated radiation intensity.

  2. Timewise morphology of turbulent diffusion flame by means of image processing

    SciTech Connect

    Torii, Shuichi; Yano, Toshiaki; Tsuchino, Fumihiro

    1999-07-01

    An experimental study is performed to investigate the dynamic behavior of jet diffusion flames from a vertical circular nozzle. A real-time image processing on slow-motion video recording using the high-speed video camera is employed to clarify the flame morphology. Emphasis is placed on the timewise variation of the flame length, H, the peripheral distance of the flame, L, and the projected area of the flame contour, S, based on the RGB values of the flame. Here, RGB implies the three primary colors, i.e., red, green and blue, respectively. Propane is used as fuel and a burner tube of 2.40 mm inside diameter is employed here. It is found from the study that (1) a real-time color image processing with the aid of a slow-motion video recording discriminates the flame shape and discloses the flame behavior with time, (2) H, L and S vary periodically with time, and (3) the time-averaged value of L{sup 2}/S and its turbulence intensity, which is defined here, are intensified with an increase in the Reynolds number.

  3. Unsteady Diffusion Flames: Ignition, Travel, and Burnout (SUBCORE Project: Simplified Unsteady Burning of Contained Reactants)

    NASA Technical Reports Server (NTRS)

    Fendell, Francis; Rungaldier, Harald

    1999-01-01

    An experimental apparatus for the examination of a planar, virtually strain-rate-free diffusion flame in microgravity has been designed and fabricated. Such a diffusion flame is characterized by relatively large spatial scale and high symmetry (to facilitate probing), and by relatively long fluid-residence time (to facilitate investigation of rates associated with sooting phenomena). Within the squat rectangular apparatus, with impervious, noncatalytic isothermal walls of stainless steel, a thin metallic splitter plate subdivides the contents into half-volumes. One half-volume initially contains fuel vapor diluted with an inert gas, and the other, oxidizer diluted with another inert gas-so that the two domains have equal pressure, density, and temperature. As the separator is removed, by translation in its own plane, through a tightly fitting slit in one side wall, a line ignitor in the opposite side wall initiates a triple-flame propagation across the narrow layer of combustible mixture formed near midheight in the chamber. The planar diffusion flame so emplaced is quickly disrupted in earth gravity. In microgravity, the planar flame persists, and travels ultimately into the half-volume containing the stoichiometrically deficient reactant; the flame eventually becomes extinguished owing to reactant depletion and heat loss to the walls.

  4. Dilution effects analysis of opposed-jet H2/CO syngas diffusion flames

    NASA Astrophysics Data System (ADS)

    Shih, Hsin-Yi; Hsu, Jou-Rong

    2013-06-01

    This paper reported the analysis of dilution effects on the opposed-jet H2/CO syngas diffusion flames. A computational model, OPPDIF coupled with narrowband radiation calculation, was used to study one-dimensional counterflow syngas diffusion flames with fuel side dilution from CO2, H2O and N2. To distinguish the contributing effects from inert, thermal/diffusion, chemical, and radiation effects, five artificial and chemically inert species XH2, XCO, XCO2, XH2O and XN2 with the same physical properties as their counterparts were assumed. By comparing the realistic and hypothetical flames, the individual dilution effects on the syngas flames were revealed. Results show, for equal-molar syngas (H2/CO = 1) at strain rate of 10 s-1, the maximum flame temperature decreases the most by CO2 dilution, followed by H2O and N2. The inert effect, which reduces the chemical reaction rates by behaving as the inert part of mixtures, drops flame temperature the most. The thermal/diffusion effect of N2 and the chemical effect of H2O actually contribute the increase of flame temperature. However, the chemical effect of CO2 and the radiation effect always decreases flame temperature. For flame extinction by adding diluents, CO2 dilution favours flame extinction from all contributing effects, while thermal/diffusion effects of H2O and N2 extend the flammability. Therefore, extinction dilution percentage is the least for CO2. The dilution effects on chemical kinetics are also examined. Due to the inert effect, the reaction rate of R84 (OH+H2 = H+H2O) is decreasing greatly with increasing dilution percentage while R99 (CO+OH→CO2+H) is less affected. When the diluents participate chemically, reaction R99 is promoted and R84 is inhibited with H2O addition, but the trend reverses with CO2 dilution. Besides, the main chain-branching reaction of R38 (H+O2→O+OH) is enhanced by the chemical effect of H2O dilution, but suppressed by CO2 dilution. Relatively, the influences of thermal/diffusion

  5. Combined diffusion and strain MRI reveals structure and function of human myocardial laminar sheets in vivo.

    PubMed

    Dou, Jiangang; Tseng, Wen-Yih I; Reese, Timothy G; Wedeen, Van J

    2003-07-01

    The mechanism of ventricular thickening in normal humans was investigated using in vivo MRI. The hypothesis that myocardial laminar sheets contribute to ventricular thickening predominantly via sheet shear and sheet extension, as previously found invasively in canine studies at particular ventricular sites, was tested. In normal human subjects, registered images of myocardial sheet architecture and strain at the mid-left ventricle (mid-LV) at mid-systole were acquired with diffusion and strain MRI. Sheet function was analyzed by computing myocardial strain in the local fiber-sheet coordinates. In general, myocardial sheets contribute to ventricular thickening through all three cross-fiber strain components: sheet shear, sheet extension, and sheet-normal thickening (previously undocumented). Each of these components demonstrated substantial spatial heterogeneity, with sheet shear and sheet extension usually predominant in the anterior free wall, and sheet-normal thickening predominant near the right ventricular (RV) insertions. However, considerable intersubject variability was also found. In all cases, the contributions to thickening of fiber strains were small. Sheet function in normal humans was found to be heterogeneous and variable, contrasting with the uniform and symmetric ventricular patterns of fiber shortening and wall thickening. The study demonstrates that noninvasive NMR imaging is a promising tool for investigations of myocardial sheet architecture and function, and is particularly suited to the evident complexity of this field of study.

  6. Chemical kinetic modeling of a methane opposed flow diffusion flame and comparison to experiments

    SciTech Connect

    Marinov, N.M., Pitz, W.J.; Westbrook, C.K.; Vincitore, A.M.; Senka, S.M.; Lutz, A.E.

    1998-01-01

    The chemical structure of an opposed flow, methane diffusion flame is studied using a chemical kinetic model and the results are compared to experimental measurements. The chemical kinetic paths leading to aromatics and polycyclic aromatics hydrocarbons (PAHs) in the diffusion flame are identified. These paths all involve resonantly stabilized radicals which include propargyl, allyl, cyclopentadienyl, and benzyl radicals. The modeling results show reasonable agreement with the experimental measurements for the large hydrocarbon aliphatic compounds, aromatics, and PAHs. the benzene was predicted to be formed primarily by the reaction sequence of Allyl plus Propargyl equals Fulvene plus H plus H followed by fulvene isomerization to benzene. Naphthalene was modeled using the reaction of benzyl with propargyl, while the combination of cyclopentadienyl radicals were shown to be a minor contributor in the diffusion flame. The agreement between the model and experiment for the four-ring PAHs was poor.

  7. Prediction of the blowout of jet diffusion flames in a coflowing stream of air

    SciTech Connect

    Karbasi, M.; Wierzba, I.

    1995-12-31

    The blowout limits of a lifted diffusion flame in a coflowing stream of air are estimated using a simple model for extinction, for a range of fuels, jet diameters and co-flowing stream velocities. The proposed model uses a parameter which relates to the ratio of a time associated with the mixing processes in a turbulent jet to a characteristic chemical time. The Kolmogorov microscale of time is used as time scale in this model. It is shown that turbulent diffusion flames are quenched by excessive turbulence for a critical value of this parameter. The predicted blowout velocity of diffusion flames obtained using this model is in good agreement with the available experimental data.

  8. An Experimental and Theoretical Study of Radiative Extinction of Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Atreya, Arvind

    1995-01-01

    The objective of this research was to experimentally and theoretically investigate the radiation-induced extinction of gaseous diffusion flames in microgravity. The microgravity conditions were required because radiation-induced extinction is generally not possible in 1-g but is highly likely in microgravity. In 1-g, the flame-generated particulates (e.g. soot) and gaseous combustion products that are responsible for flame radiation, are swept away from the high temperature reaction zone by the buoyancy-induced flow and a steady state is developed. In microgravity, however, the absence of buoyancy-induced flow which transports the fuel and the oxidizer to the combustion zone and removes the hot combustion products from it enhances the flame radiation due to: (1) transient build-up of the combustion products in the flame zone which increases the gas radiation, and (2) longer residence time makes conditions appropriate for substantial amounts of soot to form which is usually responsible for most of the radiative heat loss. Numerical calculations conducted during the course of this work show that even non-radiative flames continue to become "weaker" (diminished burning rate per unit flame area) due to reduced rates of convective and diffusive transport. Thus, it was anticipated that radiative heat loss may eventually extinguish the already "weak" microgravity diffusion flame. While this hypothesis appears convincing and our numerical calculations support it, experiments for a long enough microgravity time could not be conducted during the course of this research to provide an experimental proof. Space shuttle experiments on candle flames show that in an infinite ambient atmosphere, the hemispherical candle flame in microgravity will burn indefinitely. It was hoped that radiative extinction can be experimentally shown by the aerodynamically stabilized gaseous diffusion flames where the fuel supply rate was externally controlled. While substantial progress toward this

  9. Computation of low Fronde number turbulent diffusion flames

    NASA Astrophysics Data System (ADS)

    Garreton, D.; Mechitoua, N.; Viollet, P. L.

    This study is related to the development of a model for the computation of pool fires of liquefied natural gas -sponsered by GAZ de FRANCE and SOCIETE NATIONALE d'EXPLORATION d'AQUITAINE-PRODUCTION. -As a first step, low Froude number flames which are similar to pool fires, are simulated.

  10. A MODEL OF TURBULENT DIFFUSION FLAMES AND NITRIC OXIDE GENERATION

    EPA Science Inventory

    The report describes a new view of mixing and chemical reactions in turbulent fuel jets discharging into air. Review of available fundamental data from jet flames leads to the idea that mixing begins with a large scale, inviscid intertwining of entrained air and fuel throughout t...

  11. Near-Limit Flamelet Phenomena in Buoyant Low Stretch Diffusion Flames Beneath a Solid Fuel

    NASA Technical Reports Server (NTRS)

    Olson, S. L.; Tien, J. S.

    2000-01-01

    A unique near-limit low stretch multidimensional stable flamelet phenomena has been observed for the first time which extends the material flammability limit beyond the one-dimensional low stretch flammability limit to lower burning rates and higher relative heat losses than is possible with uniform flame coverage. During low stretch experiments burning the underside of very large radii (greater than or = 75 cm stretch rate less than or = 3/s) cylindrical cast PMMA samples, multidimensional flamelets were observed, in contrast with a one-dimensional flame that was found to blanket the surface for smaller radii samples ( higher stretch rate). Flamelets were observed by decreasing the stretch rate or by increasing the conductive heat loss from the flame. Flamelets are defined as flames that cover only part of the burning sample at any given time, but persist for many minutes. Flamelet phenomena is viewed as the flame's method of enhancing oxygen flow to the flame, through oxygen transport into the edges of the flamelet. Flamelets form as heat losses (surface radiation and solid-phase conduction) become large relative to the weakened heat release of the low stretch flame. While heat loss rates remain fairly constant, the limiting factor in the heat release of the flame is hypothesized to be the oxygen transport to the flame in this low stretch (low convective) environment. Flamelet extinction is frequently caused by encroachment of an adjacent flamelet. Large-scale whole-body flamelet oscillations at 1.2 - 1.95 Hz are noted prior to extinction of a flamelet. This oscillation is believed to be due a repeated process of excess fuel leakage through the dark channels between the flamelets, fuel premixing with slow incoming oxidizer, and subsequent rapid flame spread and retreat of the flamelet through the premixed layer. The oscillation frequency is driven by gas-phase diffusive time scales.

  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. CONTROL OF POLLUTANT EMISSIONS IN NATURAL GAS DIFFUSION FLAMES BY USING CASCADE BURNERS

    SciTech Connect

    Dr. Ala Qubbaj

    2001-12-30

    The goal of this exploratory research project is to control the pollutant emissions of diffusion flames by modifying the air infusion rate into the flame. The modification was achieved by installing a cascade of venturis around the burning gas jet. The basic idea behind this technique is controlling the stoichiometry of the flame through changing the flow dynamics and rates of mixing in the combustion zone with a set of venturis surrounding the flame. A natural gas jet diffusion flame at burner-exit Reynolds number of 5100 was examined with a set of venturis of specific sizes and spacing arrangement. The thermal and composition fields of the baseline and venturi-cascaded flames were numerically simulated using CFD-ACE+, an advanced computational environment software package. The instantaneous chemistry model was used as the reaction model. The concentration of NO was determined through CFD-POST, a post processing utility program for CFD-ACE+. The numerical results showed that, in the near-burner, midflame and far-burner regions, the venturi-cascaded flame had lower temperature by an average of 13%, 19% and 17%, respectively, and lower CO{sub 2} concentration by 35%, 37% and 32%, respectively, than the baseline flame. An opposite trend was noticed for O{sub 2} concentration; the cascaded flame has higher O{sub 2} concentration by 7%, 26% and 44%, in average values, in the near-burner, mid-flame and far-burner regions, respectively, than in the baseline case. The results also showed that, in the near-burner, mid-flame, and far-burner regions, the venturi-cascaded flame has lower NO concentrations by 89%, 70% and 70%, in average values, respectively, compared to the baseline case. The numerical results substantiate that venturi-cascading is a feasible method for controlling the pollutant emissions of a burning gas jet. In addition, the numerical results were useful to understand the thermo-chemical processes involved. The results showed that the prompt-NO mechanism

  14. Predictions of soot and thermal radiation properties in confined turbulent jet diffusion flames

    SciTech Connect

    Brookes, S.J.; Moss, J.B.

    1999-03-01

    Computational modeling of well-documented jet diffusion flames, burning methane at atmospheric and elevated pressure, is presented. The main emphasis of the work is on the intimate coupling between the soot production of rate and the flame radiative heat loss. This coupling is found to be vital for flame soot prediction. A number of methods for closing soot production source terms in the turbulent flow are presented and assessed. In particular it is shown that the degree of correlation assumed between soot particles and their oxidizing species exerts a large influence on both the growth of the soot and its subsequent burnout. Finally, predictions of the mean radiative emission spectra from these flames are presented.

  15. Influence of a Simple Heat Loss Profile on a Pure Diffusion Flame

    NASA Technical Reports Server (NTRS)

    Ray, Anjan; Wichman, Indrek S.

    1996-01-01

    The presence of soot on the fuel side of a diffusion flame results in significant radiative heat losses. The influence of a fuel side heat loss zone on a pure diffusion flame established between a fuel and an oxidizer wall is investigated by assuming a hypothetical sech(sup 2) heat loss profile. The intensity and width of the loss zone are parametrically varied. The loss zone is placed at different distances from the Burke-Schumann flame location. The migration of the temperature and reactivity peaks are examined for a variety of situations. For certain cases the reaction zone breaks through the loss zone and relocates itself on the fuel side of the loss zone. In all cases the temperature and reactivity peaks move toward the fuel side with increased heat losses. The flame structure reveals that the primary balance for the energy equation is between the reaction term and the diffusion term. Extinction plots are generated for a variety of situations. The heat transfer from the flame to the walls and the radiative fraction is also investigated, and an analytical correlation formula, derived in a previous study, is shown to produce excellent predictions of our numerical results when an O(l) numerical multiplicative constant is employed.

  16. Synthesis of Fullerenes in Low Pressure Benzene/Oxygen Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Hebgen, Peter; Howard, Jack B.

    1999-01-01

    The interest in fullerenes is strongly increasing since their discovery by Kroto et al. in 1985 as products of the evaporation of carbon into inert gas at low pressure. Due to their all carbon closed-shell structure, fullerenes have many exceptional physical and chemical properties and a large potential for applications such as superconductors, sensors, catalysts, optical and electronic devices, polymers, high energy fuels, and biological and medical materials. This list is still growing, because the research on fullerenes is still at an early stage. Fullerenes can be formed not only in a system containing only carbon and an inert gas, but also in premixed hydrocarbon flames under reduced pressure and fuel rich conditions. The highest yields of fullerenes in flames are obtained under conditions of substantial soot formation. There is a need for more information on the yields of fullerenes under different conditions in order to understand the mechanisms of their formation and to enable the design of practical combustion systems for large-scale fullerene production. Little work has been reported on the formation of fullerenes in diffusion flames. In order to explore the yields of fullerenes and the effect of low pressure in diffusion flames, therefore we constructed and used a low pressure diffusion flame burner in this study.

  17. Experimental Observations on a Low Strain Counter-Flow Diffusion Flame: Flow and Bouyancy Effects

    NASA Technical Reports Server (NTRS)

    Sutula, J. A.; Torero, J. L.; Ezekoye, O. A.

    1999-01-01

    Diffusion flames are of great interest in fire safety and many industrial processes. The counter-flow configuration provides a constant strain flow, and therefore is ideal to study the structure of diffusion flames. Most studies have concentrated on the high velocity, high strain limit, since buoyantly induced instabilities will disintegrate the planar flame as the velocity decreases. Only recently, experimental studies in microgravity conditions have begun to explore the low strain regimes. Numerical work has shown the coupling between gas phase reaction rates, soot reaction rates, and radiation. For these programs, size, geometry and experimental conditions have been chosen to keep the flame unaffected by the physical boundaries. When the physical boundaries can not be considered infinitely far from the reaction zone discrepancies arise. A computational study that includes boundary effects and accounts for the deviations occurring when the major potential flow assumptions are relaxed was presented by Borlik et al. This development properly incorporates all heat loss terms and shows the possibility of extinction in the low strain regime. A major constraint of studying the low strain regime is buoyancy. Buoyant instabilities have been shown to have a significant effect on the nature of reactants and heat transport, and can introduce instabilities on the flow that result in phenomena such as flickering or fingering. The counter-flow configuration has been shown to provide a flame with no symmetry disrupting instabilities for inlet velocities greater than 50 mm/s. As the velocity approaches this limit, the characteristic length of the experiment has to be reduced to a few millimetres so as to keep the Rayleigh number (Ra(sub L) = (Beta)(g(sub 0))(L(exp 3) del T)/(alpha(v))) below 2000. In this work, a rectangular counter-flow burner was used to study a two-dimensional counter-flow diffusion flame. Flow visualisation and Particle Image Velocimetry served to describe

  18. Formation of soot and nitrogen oxides in unsteady counterflow diffusion flames

    SciTech Connect

    Cuoci, A.; Frassoldati, A.; Faravelli, T.; Ranzi, E.

    2009-10-15

    The formation of pollutant species in turbulent diffusion flames is strongly affected by turbulence/chemistry interactions. Unsteady counterflow diffusion flames can be conveniently used to address the unsteady effects of hydrodynamics on the pollutant chemistry, because they exhibit a larger range of combustion conditions than those observed in steady flames. In this paper, unsteady effects on the formation of soot (and its main precursors) and nitrogen oxides (NO{sub x}) are investigated by imposing harmonic oscillations on the strain rate of several counterflow diffusion flames fed with propane. Numerical results confirm that the dynamic response of each species is strongly affected by the strain rate oscillations and the characteristic time governing its chemistry. At low frequencies of imposed oscillations the soot and NO{sub x} profiles show strong deviations from the steady-state profile. At large frequencies a decoupling between the concentration and the velocity field is evident. In particular, the formation of soot and NO{sub x} is found less sensitive to velocity fluctuations for flames with large initial strain rate. The significant increase of soot and NO{sub x} concentrations in unsteady conditions appears to be a function of both forcing frequency and flame global strain rate. Moreover, the cut-off frequency, defined as the minimum frequency above which the strain rate oscillations have negligible effects on the formation of each species, was found to be strongly dependent on the chemical characteristic time and the flame global strain rate, but only marginally affected by the amplitude of imposed oscillations. (author)

  19. Design and Fabrication of a Hele-Shaw Apparatus for Observing Instabilities of Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Wichman, I. S.; Oravecz-Simpkins, L.; Olson, S.

    2001-01-01

    Examinations of flame fronts spreading over solid fuels in an opposed flow of oxidizer have shown that the flame front fragments into smaller (cellular) flames. These 'flamelets' will oscillate, recombine, or extinguish, indicating that they are in the near extinction limit regime (i.e., to one side of the quenching branch of the flammability map). Onset of unstable cellular flamelet formation for flame spread over thin fuels occurs when a heat-sink substrate is placed a small distance from the underside of the fuel. This heat-sink substrate (or backing) displaces the quenching branch of the flammability map in a direction that causes the instabilities to occur at higher air velocities. Similar near-limit behavior has been observed in other works using different fuels, thus suggesting that these dynamic mechanisms are fuel-independent and therefore fundamental attributes of flames in this near-limit flame spread regime. The objective of this project is to determine the contributions of the hydrodynamic and thermodiffusive mechanisms to the observed formation of flame instabilities. From this, a model of diffusion flame instabilities shall be generated. Previously, experiments were conducted in NASA drop towers, thereby limiting observation time to O(1-5 sec). The NASA tests exhibited flamelet survival for the entire drop time, suggesting that flamelets (i.e., small cellular flames) might exist, if permitted, for longer time periods. By necessity, experiments were limited to thermally thin cellulose fuels (approximately 0.001 in thick): instabilities could form by virtue of faster spread rates over thin fuels. Unstable behavior was unlikely in the short drop time for thicker fuels. In the International Space Station (ISS), microgravity time is unlimited, so both thin and thick fuels can be tested.

  20. FLame

    1995-03-03

    FLAME is data processing software explicitly written to support the ACAP software of DSP Technologies, Inc., of Fremont, CA. ACAP acquires and processes in-cylinder pressure data for reciprocating engines. However, it also has the capability to acquire data for two Sandia-developed technologies, ionization-probe instrumented head gaskets and fiber-optic instrumented spark plugs. FLAME post processes measurements of flame arrival from data files aquired with ACAP. Flame arrival time is determined from analog ionization-probe or visible-emission signals.more » The resulting data files are integrated with the standard ACAP files, providing a common data base for engine development.« less

  1. An experimental and numerical study of gas jet diffusion flames enveloped by a cascade of venturis

    NASA Astrophysics Data System (ADS)

    Qubbaj, Ala Rafat

    1999-06-01

    A new technique to control carbon monoxide, nitric oxide, and soot emissions of a propane diffusion flame by modifying the air infusion rate into the flame was developed. In this study, the effectiveness of the ``venturi-cascading'' technique was experimentally as well numerically investigated. Propane jet diffusion flames at three burner-exit Reynolds numbers ( 3600, 5100 and 6500) corresponding to burner-rim-attached, undergoing transition from attached to lifted, and fully-lifted configurations were examined with several sets of venturis of different sizes and spacing arrangements. Temperature, and the concentrations of carbon dioxide, oxygen, carbon monoxide and nitric oxide in the exhaust products were measured before and after the modification, and optimal conditions to minimize pollutant emissions were obtained. The optimal value of venturi throat/burner-exit diameter ratio (D/d) was 32 +/- 3, which corresponded to an approximate clearance of 5 +/- 2 mm between the venturi throat and the burning jet width at the mid-flame height. The venturi-cascading technique at its optimal conditions resulted in a decrease of 87% and 33% in CO and NO emission indices along with a 24% decrease in soot emission from a propane jet flame, compared to the baseline condition (same flame without venturis). The reduction of NO without increasing CO was the main attraction of this technique. The temperature and composition measurements, at the optimal conditions, showed that, in the near-burner region, the venturi-cascaded flame had lower temperature and CO2 concentration by an average of 5% and 7%, respectively, than the baseline flame. However, in the mid-flame and far-burner regions, it has higher temperature by 13% and 12%, and higher CO2 concentration by 16% and 13%, in average values, respectively. Laser Induced Fluorescence (LIF) measurements, in the near-burner region of the venturi-cascaded flame, indicated an average decrease of 18%, 24% and 12% in OH, CH and CN radical

  2. The Impact of Buoyancy and Flame Structure on Soot, Radiation and NOx Emissions from a Turbulent Diffusion Flame

    NASA Technical Reports Server (NTRS)

    Kennedy, I. M.; Kollman, W.; VanderWal, R. L.

    1999-01-01

    It is hypothesized that the spatial structure of a turbulent diffusion flame plays an important role in determining the emissions of radiative energy, soot and NO, from a combustor. This structure, manifested in the two point statistics, is influenced by buoyancy. Radiation, soot and NOx emissions are the cumulative result of processes that occur throughout a flame. For example, radiation fluxes along a line of sight can be found from summing up the contributions from sources in individual pockets of hot soot that emit, and from sinks in cold soot that absorb. Soot and NOx are both the results of slow chemistry and are not equilibrium products. The time that is available for production and burnout is crucial in determining the eventual emissions of these pollutants. Turbulence models generally rely on a single point closure of the appropriate time averaged equations. Hence, spatial information is lost and needs to be modeled using solution variables such as turbulence kinetic energy and dissipation rate, often with the assumption of isotropy. However, buoyancy can affect the physical structure of turbulent flames and can change the spatial extent of soot bearing regions. Theoretical comparisons with models are best done in the limit of infinite Froude number because the inclusion of buoyancy in flow models introduces significant uncertainties. Hence, LII measurements of soot, measurements of radiation fluxes from soot, Particle Imaging Velocimetry (PIV) of the flow field and measurements of post flame NOX will be carried out on the NASA Lewis 2.2 sec drop tower and eventually on the parabolic flight aircraft. The drop rig will be a modified version of a unit that has been successfully used at Lewis in the past.

  3. POLYCYCLIC AROMATIC HYDROCARBON FORMATION IN OPPOSED FLOW DIFFUSION FLAMES OF ETHANE. (R825412)

    EPA Science Inventory

    Abstract

    The effect of fuel-side carbon density on the levels of polycyclic aromatic hydrocarbon (PAH) formation in atmospheric pressure, opposed flow, ethane diffusion flames has been studied using heated micro-probe sampling and gas chromatography/mass spectrometry (...

  4. The carrier gas pressure effect in a laminar flow diffusion chamber, homogeneous nucleation of n-butanol in helium.

    PubMed

    Hyvärinen, Antti-Pekka; Brus, David; Zdímal, Vladimír; Smolík, Jiri; Kulmala, Markku; Viisanen, Yrjö; Lihavainen, Heikki

    2006-06-14

    Homogeneous nucleation rate isotherms of n-butanol+helium were measured in a laminar flow diffusion chamber at total pressures ranging from 50 to 210 kPa to investigate the effect of carrier gas pressure on nucleation. Nucleation temperatures ranged from 265 to 280 K and the measured nucleation rates were between 10(2) and 10(6) cm(-3) s(-1). The measured nucleation rates decreased as a function of increasing pressure. The pressure effect was strongest at pressures below 100 kPa. This negative carrier gas effect was also temperature dependent. At nucleation temperature of 280 K and at the same saturation ratio, the maximum deviation between nucleation rates measured at 50 and 210 kPa was about three orders of magnitude. At nucleation temperature of 265 K, the effect was negligible. Qualitatively the results resemble those measured in a thermal diffusion cloud chamber. Also the slopes of the isothermal nucleation rates as a function of saturation ratio were different as a function of total pressure, 50 kPa isotherms yielded the steepest slopes, and 210 kPa isotherms the shallowest slopes. Several sources of inaccuracies were considered in the interpretation of the results: uncertainties in the transport properties, nonideal behavior of the vapor-carrier gas mixture, and shortcomings of the used mathematical model. Operation characteristics of the laminar flow diffusion chamber at both under-and over-pressure were determined to verify a correct and stable operation of the device. We conclude that a negative carrier gas pressure effect is seen in the laminar flow diffusion chamber and it cannot be totally explained with the aforementioned reasons.

  5. The carrier gas pressure effect in a laminar flow diffusion chamber, homogeneous nucleation of n-butanol in helium.

    PubMed

    Hyvärinen, Antti-Pekka; Brus, David; Zdímal, Vladimír; Smolík, Jiri; Kulmala, Markku; Viisanen, Yrjö; Lihavainen, Heikki

    2006-06-14

    Homogeneous nucleation rate isotherms of n-butanol+helium were measured in a laminar flow diffusion chamber at total pressures ranging from 50 to 210 kPa to investigate the effect of carrier gas pressure on nucleation. Nucleation temperatures ranged from 265 to 280 K and the measured nucleation rates were between 10(2) and 10(6) cm(-3) s(-1). The measured nucleation rates decreased as a function of increasing pressure. The pressure effect was strongest at pressures below 100 kPa. This negative carrier gas effect was also temperature dependent. At nucleation temperature of 280 K and at the same saturation ratio, the maximum deviation between nucleation rates measured at 50 and 210 kPa was about three orders of magnitude. At nucleation temperature of 265 K, the effect was negligible. Qualitatively the results resemble those measured in a thermal diffusion cloud chamber. Also the slopes of the isothermal nucleation rates as a function of saturation ratio were different as a function of total pressure, 50 kPa isotherms yielded the steepest slopes, and 210 kPa isotherms the shallowest slopes. Several sources of inaccuracies were considered in the interpretation of the results: uncertainties in the transport properties, nonideal behavior of the vapor-carrier gas mixture, and shortcomings of the used mathematical model. Operation characteristics of the laminar flow diffusion chamber at both under-and over-pressure were determined to verify a correct and stable operation of the device. We conclude that a negative carrier gas pressure effect is seen in the laminar flow diffusion chamber and it cannot be totally explained with the aforementioned reasons. PMID:16784271

  6. The effects of ferrocene concentration on soot in an ethylene laminar diffusion flame

    EPA Science Inventory

    Metal fuel-borne catalysts are of interest in the combustion and environmental communities due principally to their ability to reduce carbon particulate mass emissions. However, a negative aspect to their use is the potential emission of the metals themselves. Post-combustion, th...

  7. Real Time Quantitative 3-D Imaging of Diffusion Flame Species

    NASA Technical Reports Server (NTRS)

    Kane, Daniel J.; Silver, Joel A.

    1997-01-01

    A low-gravity environment, in space or ground-based facilities such as drop towers, provides a unique setting for study of combustion mechanisms. Understanding the physical phenomena controlling the ignition and spread of flames in microgravity has importance for space safety as well as better characterization of dynamical and chemical combustion processes which are normally masked by buoyancy and other gravity-related effects. Even the use of so-called 'limiting cases' or the construction of 1-D or 2-D models and experiments fail to make the analysis of combustion simultaneously simple and accurate. Ideally, to bridge the gap between chemistry and fluid mechanics in microgravity combustion, species concentrations and temperature profiles are needed throughout the flame. However, restrictions associated with performing measurements in reduced gravity, especially size and weight considerations, have generally limited microgravity combustion studies to the capture of flame emissions on film or video laser Schlieren imaging and (intrusive) temperature measurements using thermocouples. Given the development of detailed theoretical models, more sophisticated studies are needed to provide the kind of quantitative data necessary to characterize the properties of microgravity combustion processes as well as provide accurate feedback to improve the predictive capabilities of the computational models. While there have been a myriad of fluid mechanical visualization studies in microgravity combustion, little experimental work has been completed to obtain reactant and product concentrations within a microgravity flame. This is largely due to the fact that traditional sampling methods (quenching microprobes using GC and/or mass spec analysis) are too heavy, slow, and cumbersome for microgravity experiments. Non-intrusive optical spectroscopic techniques have - up until now - also required excessively bulky, power hungry equipment. However, with the advent of near-IR diode

  8. Laser-Induced Fluorescence Measurements and Modeling of Nitric Oxide in Counterflow Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Ravikrishna, Rayavarapu V.

    2000-01-01

    The feasibility of making quantitative nonintrusive NO concentration ([NO]) measurements in nonpremixed flames has been assessed by obtaining laser-induced fluorescence (LIF) measurements of [NO] in counterflow diffusion flames at atmospheric and higher pressures. Comparisons at atmospheric pressure between laser-saturated fluorescence (LSF) and linear LIF measurements in four diluted ethane-air counterflow diffusion flames with strain rates from 5 to 48/s yielded excellent agreement from fuel-lean to moderately fuel-rich conditions, thus indicating the utility of a model-based quenching correction technique, which was then extended to higher pressures. Quantitative LIF measurements of [NO] in three diluted methane-air counterflow diffusion flames with strain rates from 5 to 35/s were compared with OPPDIF model predictions using the GRI (version 2.11) chemical kinetic mechanism. The comparisons revealed that the GRI mechanism underpredicts prompt-NO by 30-50% at atmospheric pressure. Based on these measurements, a modified reaction rate coefficient for the prompt-NO initiation reaction was proposed which causes the predictions to match experimental data. Temperature measurements using thin filament pyrometry (TFP) in conjunction with a new calibration method utilizing a near-adiabatic H2-air Hencken burner gave very good comparisons with model predictions in these counterflow diffusion flames. Quantitative LIF measurements of [NO] were also obtained in four methane-air counterflow partially-premixed flames with fuel-side equivalence ratios (phi(sub B)) of 1.45, 1.6, 1.8 and 2.0. The measurements were in excellent agreement with model predictions when accounting for radiative heat loss. Spatial separation between regions dominated by the prompt and thermal NO mechanisms was observed in the phi(sub B) = 1.45 flame. The modified rate coefficient proposed earlier for the prompt-NO initiation reaction improved agreement between code predictions and measurements in the

  9. Experimental Assessment and Enhancement of Planar Laser-Induced Fluorescence Measurements of Nitric Oxide in an Inverse Diffusion Flame

    NASA Technical Reports Server (NTRS)

    Partridge, William P.; Laurendeau, Normand M.

    1997-01-01

    We have experimentally assessed the quantitative nature of planar laser-induced fluorescence (PLIF) measurements of NO concentration in a unique atmospheric pressure, laminar, axial inverse diffusion flame (IDF). The PLIF measurements were assessed relative to a two-dimensional array of separate laser saturated fluorescence (LSF) measurements. We demonstrated and evaluated several experimentally-based procedures for enhancing the quantitative nature of PLIF concentration images. Because these experimentally-based PLIF correction schemes require only the ability to make PLIF and LSF measurements, they produce a more broadly applicable PLIF diagnostic compared to numerically-based correction schemes. We experimentally assessed the influence of interferences on both narrow-band and broad-band fluorescence measurements at atmospheric and high pressures. Optimum excitation and detection schemes were determined for the LSF and PLIF measurements. Single-input and multiple-input, experimentally-based PLIF enhancement procedures were developed for application in test environments with both negligible and significant quench-dependent error gradients. Each experimentally-based procedure provides an enhancement of approximately 50% in the quantitative nature of the PLIF measurements, and results in concentration images nominally as quantitative as LSF point measurements. These correction procedures can be applied to other species, including radicals, for which no experimental data are available from which to implement numerically-based PLIF enhancement procedures.

  10. Opposed jet diffusion flames of nitrogen-diluted hydrogen vs air - Axial LDA and CARS surveys; fuel/air rates at extinction

    SciTech Connect

    Pellett, G.L.; Northam, G.B.; Wilson, L.G.; Jarrett, O. Jr.; Antcliff, R.R.

    1989-01-01

    An experimental study of H-air counterflow diffusion flames (CFDFs) is reported. Coaxial tubular opposed jet burners were used to form dish-shaped CFDFs centered by opposing laminar jets of H2/N2 and air in an argon bath at 1 atm. Jet velocities for extinction and flame restoration limits are shown versus input H2 concentration. LDA velocity data and CARS temperature and absolute N2, O2 density data give detailed flame structure on the air side of the stagnation point. The results show that air jet velocity is a more fundamental and appropriate measure of H2-air CFDF extinction than input H2 mass flux or fuel jet velocity. It is proposed that the observed constancy of air jet velocity for fuel mixtures containing 80 to 100 percent H2 measure a maximum, kinetically controlled rate at which the CFDF can consume oxygen in air. Fuel velocity mainly measures the input jet momentum required to center an H2/N2 versus air CFDF. 42 refs.

  11. Effects of soot absorption coefficient-Planck function correlation on radiative heat transfer in oxygen-enriched propane turbulent diffusion flame

    NASA Astrophysics Data System (ADS)

    Consalvi, J. L.; Nmira, F.

    2016-03-01

    The main objective of this article is to quantify the influence of the soot absorption coefficient-Planck function correlation on radiative loss and flame structure in an oxygen-enhanced propane turbulent diffusion flame. Calculations were run with and without accounting for this correlation by using a standard k-ε model and the steady laminar flamelet model (SLF) coupled to a joint Probability Density Function (PDF) of mixture fraction, enthalpy defect, scalar dissipation rate, and soot quantities. The PDF transport equation is solved by using a Stochastic Eulerian Field (SEF) method. The modeling of soot production is carried out by using a flamelet-based semi-empirical acetylene/benzene soot model. Radiative heat transfer is modeled by using a wide band correlated-k model and turbulent radiation interactions (TRI) are accounted for by using the Optically-Thin Fluctuation Approximation (OTFA). Predicted soot volume fraction, radiant wall heat flux distribution and radiant fraction are in good agreement with the available experimental data. Model results show that soot absorption coefficient and Planck function are negatively correlated in the region of intense soot emission. Neglecting this correlation is found to increase significantly the radiative loss leading to a substantial impact on flame structure in terms of mean and rms values of temperature. In addition mean and rms values of soot volume fraction are found to be less sensitive to the correlation than temperature since soot formation occurs mainly in a region where its influence is low.

  12. Opposed jet diffusion flames of nitrogen-diluted hydrogen vs air - Axial LDA and CARS surveys; fuel/air rates at extinction

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Northam, G. B.; Wilson, L. G.; Jarrett, Olin, Jr.; Antcliff, R. R.

    1989-01-01

    An experimental study of H-air counterflow diffusion flames (CFDFs) is reported. Coaxial tubular opposed jet burners were used to form dish-shaped CFDFs centered by opposing laminar jets of H2/N2 and air in an argon bath at 1 atm. Jet velocities for extinction and flame restoration limits are shown versus input H2 concentration. LDA velocity data and CARS temperature and absolute N2, O2 density data give detailed flame structure on the air side of the stagnation point. The results show that air jet velocity is a more fundamental and appropriate measure of H2-air CFDF extinction than input H2 mass flux or fuel jet velocity. It is proposed that the observed constancy of air jet velocity for fuel mixtures containing 80 to 100 percent H2 measure a maximum, kinetically controlled rate at which the CFDF can consume oxygen in air. Fuel velocity mainly measures the input jet momentum required to center an H2/N2 versus air CFDF.

  13. 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.

  14. Pressure dependence of NO formation in laminar fuel-rich premixed CH{sub 4}/air flames

    SciTech Connect

    van Essen, V.M.; Sepman, A.V.; Mokhov, A.V.; Levinsky, H.B.

    2008-05-15

    Effects of pressure on NO formation in CH{sub 4}/air flames at a fixed equivalence ratio of 1.3 are investigated. The axial profiles of temperature, OH, CH, and NO mole fractions are measured using laser-induced fluorescence and compared with one-dimensional flame calculations. The measured and calculated temperature, CH, and NO profiles in free flames are observed to vary upon increasing the pressure from 40 to 75 Torr, following a scaling law derived for a chemical mechanism containing only second-order reactions. At pressures 300-760 Torr, the measurements and calculations in burner-stabilized flames show increasing flame temperature and NO mole fractions when the mass flux is increased linearly with pressure, while the CH profiles remain unchanged. The observed deviation from the scaling law in the temperature profiles arises from the increasing contribution of three-body reactions to the flame front propagation velocity, leading to a decrease in the degree of burner stabilization. The deviation from the pressure scaling law for the NO mole fractions is due to the temperature dependence of the rate coefficient for the reaction between CH and N{sub 2} and the fact that the temperature profiles themselves do not scale. In contrast, the surprisingly good scaling of the CH mole fractions with pressure indicates the dominant role of two-body reactions participating in the chain of chemical reactions leading to CH formation. The calculations using GRI-Mech 3.0 substantially overpredict (up to 50%) the measured nitric oxide concentrations for all pressures studied. The observed differences in the NO mole fraction may be addressed by improving the CH prediction. (author)

  15. Heat and mass transfer in flames

    NASA Technical Reports Server (NTRS)

    Faeth, G. M.

    1986-01-01

    Heat- and mass-transfer processes in turbulent diffusion flames are discussed, considering turbulent mixing and the structure of single-phase flames, drop processes in spray flames, and nonluminous and luminous flame radiation. Interactions between turbulence and other phenomena are emphasized, concentrating on past work of the author and his associates. The conserved-scalar formalism, along with the laminar-flamelet approximation, is shown to provide reasonable estimates of the structure of gas flames, with modest levels of empiricism. Extending this approach to spray flames has highlighted the importance of drop/turbulence interactions; e.g., turbulent dispersion of drops, modification of turbulence by drops, etc. Stochastic methods being developed to treat these phenomena are yielding encouraging results.

  16. The interaction of high-speed turbulence with flames: Turbulent flame speed

    SciTech Connect

    Poludnenko, A.Y.; Oran, E.S.

    2011-02-15

    Direct numerical simulations of the interaction of a premixed flame with driven, subsonic, homogeneous, isotropic, Kolmogorov-type turbulence in an unconfined system are used to study the mechanisms determining the turbulent flame speed, S{sub T}, in the thin reaction zone regime. High intensity turbulence is considered with the r.m.s. velocity 35 times the laminar flame speed, S{sub L}, resulting in the Damkoehler number Da=0.05. The simulations were performed with Athena-RFX, a massively parallel, fully compressible, high-order, dimensionally unsplit, reactive-flow code. A simplified reaction-diffusion model, based on the one-step Arrhenius kinetics, represents a stoichiometric H{sub 2}-air mixture under the assumption of the Lewis number Le=1. Global properties and the internal structure of the flame were analyzed in an earlier paper, which showed that this system represents turbulent combustion in the thin reaction zone regime. This paper demonstrates that: (1) The flame brush has a complex internal structure, in which the isosurfaces of higher fuel mass fractions are folded on progressively smaller scales. (2) Global properties of the turbulent flame are best represented by the structure of the region of peak reaction rate, which defines the flame surface. (3) In the thin reaction zone regime, S{sub T} is predominantly determined by the increase of the flame surface area, A{sub T}, caused by turbulence. (4) The observed increase of S{sub T} relative to S{sub L} exceeds the corresponding increase of A{sub T} relative to the surface area of the planar laminar flame, on average, by {approx}14%, varying from only a few percent to as high as {approx}30%. (5) This exaggerated response is the result of tight flame packing by turbulence, which causes frequent flame collisions and formation of regions of high flame curvature >or similar 1/{delta}{sub L}, or ''cusps,'' where {delta}{sub L} is the thermal width of the laminar flame. (6) The local flame speed in the cusps

  17. Diffusive-thermal oscillations of rich premixed hydrogen-air flames in a microflow reactor

    NASA Astrophysics Data System (ADS)

    Miroshnichenko, Taisia; Gubernov, Vladimir; Maruta, Kaoru; Minaev, Sergei

    2016-03-01

    In this paper the dynamics of rich hydrogen-air flames in a microflow reactor with controlled temperature of the walls is investigated numerically using the thermal-diffusion model with two-step kinetics in one spatial dimension. It is found that as the parameters of the system are varied the sequence of bifurcation occurs leading to the formation of complex spatio-temporal patterns. These include pulsating, chaotic, mixed-mode and FREI (Flames with Repetitive Extinction and Ignition) oscillations. The critical parameter values for the existence of different dynamical regimes are found in terms of equivalence ratio and flow velocity.

  18. An experimental and theoretical study of radiative extinction of diffusion flames

    NASA Technical Reports Server (NTRS)

    Wichman, Indrek S.; Atreya, A.

    1994-01-01

    Our work was primarily theoretical and numerical. We investigated the simplified modeling of heat losses in diffusion flames, then we 'ramped up' the level of complexity in each successive study until the final chapter discussed the general problem of soot/flame interaction. With regard to the specific objective of studying radiative extinction, we conclude that in the steady case a self-extinguishing zero-g flame is unlikely to occur. The soot volume fractions are too small. On the other hand, our work does provide rational means for assessing the mixture of chemical energy release and radiative heat release. It also provides clues for suitable 'tailoring' this balance. Thus heat fluxes to surrounding surfaces can be substantially increased by exploiting and modifying its sooting capability.

  19. Enhanced soot formation in flickering CH{sub 4}/air diffusion flames

    SciTech Connect

    Shaddix, C.R.; Harrington, J.E.; Smyth, K.C.

    1994-12-31

    Optical methods are used to examine soot production in a co-flowing, axisymmetric CH{sub 4}/air diffusion flame in which the fuel flow rate is acoustically forced to create a time-varying flowfield. For a particular forcing condition in which tip clipping occurs (0.75 V loudspeaker excitation), elastic scattering of vertically polarized light from the soot particles increases by nearly an order of magnitude with respect to that observed for a steady flame with the same mean fuel flow rate. Peak soot volume fractions, as measured by time-resolved laser extinction/tomography at 632.8 and 454.5 run and calibrated laser-induced incandescence (LII), show a factor of 4-5 enhancement in this flickering flame. A Mie analysis suggests that most of the enhanced soot production results from the formation of larger particles in the time-varying flowfield.

  20. Large Eddy Simulation Of Gravitational Effects In Transitional And Turbulent Gas-Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Jaberi, Farhad A.; Givi, Peyman

    2003-01-01

    The influence of gravity on the spatial and the compositional structures of transitional and turbulent hydrocarbon diffusion flames are studies via large eddy simulation (LES) and direct numerical simulation (DNS) of round and planar jets. The subgrid-scale (SGS) closures in LES are based on the filtered mass density function (FMDF) methodology. The FMDF represents the joint probability density function (PDF) of the SGS scalars, and is obtained by solving its transport equation. The fundamental advantage of LES/FMDF is that it accounts for the effects of chemical reaction and buoyancy exactly. The methodology is employed for capturing some of the fundamental influences of gravity in equilibrium flames via realistic chemical kinetic schemes. Some preliminary investigation of the gravity effects in non-equilibrium flames is also conducted, but with idealized chemical kinetics models.

  1. Mapping of soot particles in a weakly sooting diffusion flame by aerosol techniques

    SciTech Connect

    Hepp, H.; Siegmann, K.

    1998-10-01

    The evolution of detailed particle size distributions has been measured along the centerline of an axisymmetric diffusion flame of CH{sub 4} + Ar burning in air at 1 atm. Soot particles with mean diameters of 3--18 nm were observed. Changes in the size distribution exhibited zones where either nucleation, coagulation, or destruction of soot particles dominated. These highly sensitive measurements were made by microprobe sampling with an immediate dilution of 1:400, to quench the aerosol, and by subsequent application of aerosol measurement techniques. In parallel, the yield of photoemitted electrons from size-selected particles was determined. The yield shows a characteristic dependence on location in the flame, indicating changes of the particle`s surface. Multiphoton, time-of-flight mass spectrometry was used to investigate the correlation between polycyclic aromatic hydrocarbons in the flame and enhanced photoemission yield from the soot particles.

  2. Laser Raman Diagnostics in Subsonic and Supersonic Turbulent Jet Diffusion Flames.

    NASA Astrophysics Data System (ADS)

    Cheng, Tsarng-Sheng

    1991-02-01

    UV spontaneous vibrational Raman scattering combined with laser-induced predissociative fluorescence (LIPF) is developed for temperature and multi-species concentration measurements. For the first time, simultaneous measurements of temperature, major species (H_2, O_2, N_2, H_2O), and minor species (OH) concentrations are made with a "single" narrowband KrF excimer laser in subsonic and supersonic lifted turbulent hydrogen-air diffusion flames. The UV Raman system is calibrated with a flat -flame diffusion burner operated at several known equivalence ratios from fuel-lean to fuel-rich. Temperature measurements made by the ratio of Stokes/anti-Stokes signal and by the ideal gas law are compared. Single-shot uncertainties for temperature and concentration measurements are analyzed with photon statistics. Calibration constants and bandwidth factors are used in the data reduction program to arrive at temperature and species concentration measurements. UV Raman measurements in the subsonic lifted turbulent diffusion flame indicate that fuel and oxidizer are in rich, premixed, and unignited conditions in the center core of the lifted flame base. The unignited mixtures are due to rapid turbulent mixing that affects chemical reaction. Combustion occurs in an intermittent annular turbulent flame brush with strong finite-rate chemistry effects. The OH radical exists in sub-equilibrium and super-equilibrium concentrations. Major species and temperature are found with non-equilibrium values. Further downstream the super-equilibrium OH radicals decay toward equilibrium through slow three-body recombination reactions. In the supersonic lifted flame, a little reaction occurs upstream of the flame base, due to shock wave interactions and mixing with hot vitiated air. The strong turbulent mixing and total enthalpy fluctuations lead to temperature, major, and minor species concentrations with non-equilibrium values. Combustion occurs farther downstream of the lifted region. Slow

  3. Sooting Limits Of Diffusion Flames With Oxygen-Enriched Air And Diluted Fuel

    NASA Technical Reports Server (NTRS)

    Sunderland, P. B.; Urban, D. L.; Stocker, D. P.; Chao, B. H.; Axelbaum, R. L.

    2003-01-01

    Oxygen-enhanced combustion permits certain benefits and flexibility that are not otherwise available in the design of practical combustors, as discussed by Baukal. The cost of pure and enriched oxygen has declined to the point that oxygen-enhanced combustion is preferable to combustion in air for many applications. Carbon sequestration is greatly facilitated by oxygen enrichment because nitrogen can be eliminated from the product stream. For example, when natural gas (or natural gas diluted with CO2) is burned in pure oxygen, the only significant products are water and CO2. Oxygen-enhanced combustion also has important implications for soot formation, as explored in this work. We propose that soot inception in nonpremixed flames requires a region where C/O ratio, temperature, and residence time are above certain critical values. Soot does not form at low temperatures, with the threshold in nonpremixed flames ranging from about 1250-1650 K, a temperature referred to here as the critical temperature for soot inception, Tc. Soot inception also can be suppressed when residence time is short (equivalently, when the strain rate in counterflow flames is high). Soot induction times of 0.8-15 ms were reported by Tesner and Shurupov for acetylene/nitrogen mixtures at 1473 K. Burner stabilized spherical microgravity flames are employed in this work for two main reasons. First, this configuration offers unrestricted control over convection direction. Second, in steady state these flames are strain-free and thus can yield intrinsic sooting limits in diffusion flames, similar to the way past work in premixed flames has provided intrinsic values of C/O ratio associated with soot inception limits.

  4. Reduction of soot emissions by iron pentacarbonyl in isooctane diffusion flames

    SciTech Connect

    Kim, K.B.; Masiello, K.A.; Hahn, D.W.

    2008-07-15

    Light-scattering measurements, in situ laser-induced fluorescence, and thermophoretic sampling with transmission electron microscopy (TEM) analysis, were performed in laboratory isooctane diffusion flames seeded with 4000 ppm iron pentacarbonyl. These measurements allowed the determination of the evolution of the size, number density, and volume fraction of soot particles through the flame. Comparison to unseeded flame data provided a detailed assessment of the effects of iron addition on soot particle inception, growth, and oxidation processes. Iron was found to produce a minor soot-enhancing effect at early residence times, while subsequent soot particle growth was largely unaffected. It is concluded that primarily elemental iron is incorporated within the soot particles during particle inception and growth. However, iron addition was found to enhance the rate of soot oxidation during the soot burnout regime, yielding a two-thirds reduction in overall soot emissions. In situ spectroscopic measurements probed the transient nature of elemental iron throughout the flame, revealing significant loss of elemental iron, presumably to iron oxides, with increasing flame residence, suggesting catalysis of soot oxidation via iron oxide species. (author)

  5. Absorption and scattering of laser radiation by the diffusion flame of aviation kerosene

    SciTech Connect

    Gvozdev, S V; Glova, A F; Dubrovskii, V Yu; Durmanov, S T; Krasyukov, A G; Lysikov, A Yu; Smirnov, G V; Solomakhin, V B

    2012-04-30

    The absorption coefficient of the radiation of a repetitively pulsed Nd : YAG laser with an average output power up to 6 W and of a cw ytterbium optical fibre laser with an output power up to 3 kW was measured in the diffusion flame of aviation kerosene burning on a free surface in the atmospheric air. The absorption coefficient as a function of flame length, radiation power, and radiation intensity, which was varied in the {approx}10{sup 3} - 5 Multiplication-Sign 10{sup 4} W cm{sup -2} range, was obtained for two distances (1 and 2 cm) between the laser beam axis and the surface. The coefficient of radiation absorption by kerosene flame was compared with that in ethanol and kerosene - ethanol mixture flames. The radiation power scattered by a small segment of the kerosene flame irradiated by Nd : YAG laser radiation was measured as a function of longitudinal and azimuthal coordinates. An estimate was made of the total scattered radiation power.

  6. Analysis of opposed jet hydrogen-air counter flow diffusion flame

    NASA Technical Reports Server (NTRS)

    Ho, Y. H.; Isaac, K. M.

    1989-01-01

    A computational simulation of the opposed-jet diffusion flame is performed to study its structure and extinction limits. The present analysis concentrates on the nitrogen-diluted hydrogen-air diffusion flame, which provides the basic information for many vehicle designs such as the aerospace plane for which hydrogen is a candidate as the fuel. The computer program uses the time-marching technique to solve the energy and species equations coupled with the momentum equation solved by the collocation method. The procedure is implemented in two stages. In the first stage, a one-step forward overal chemical reaction is chosen with the gas phase chemical reaction rate determined by comparison with experimental data. In the second stage, a complete chemical reaction mechanism is introduced with detailed thermodynamic and transport property calculations. Comparison between experimental extinction data and theoretical predictions is discussed. The effects of thermal diffusion as well as Lewis number and Prandtl number variations on the diffusion flame are also presented.

  7. A comparative study of TiO2 nanoparticles synthesized in premixed and diffusion flames

    NASA Astrophysics Data System (ADS)

    Ma, Hsiao-Kang; Yang, Hsiung-An

    2010-12-01

    Previous studies have been shown that synthesis of titania (TiO2) crystalline phase purity could be effectively controlled by the oxygen concentration through titanium tetra-isopropoxide (TTIP) via premixed flame from a Bunsen burner. In this study, a modified Hencken burner was used to synthesize smaller TiO2 nanoparticles via short diffusion flames. The frequency of collisions among particles would decrease and reduce TiO2 nanoparticle size in a short diffusion flame height. The crystalline structure of the synthesized nanoparticles was characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), Barrett-Joyner-Halenda (BJH) and Brunauer-Emmett-Teller (BET) measurements. The characteristic properties of TiO2 nanoparticles synthesized from a modified Hencken burner were compared with the results from a Bunsen burner and commercial TiO2 (Degussa P25). The results showed that the average particle size of 6.63 nm from BET method was produced by a modified Hencken burner which was smaller than the TiO2 in a Bunsen burner and commercial TiO2. Moreover, the rutile content of TiO2 nanoparticles increased as the particle collecting height increased. Also, the size of TiO2 nanoparticles was highly dependent on the TTIP loading and the collecting height in the flame.

  8. Appearance, temperature, and NO{sub x} emission of two inverse diffusion flames with different port design

    SciTech Connect

    Sze, L.K.; Cheung, C.S.; Leung, C.W.

    2006-01-01

    Experiments were carried out to investigate the appearance, temperature distribution, and NO{sub x} emission index of two inverse diffusion flames, one with circumferentially arranged ports (CAPs) and the other with co-axial (CoA) jets, both burning LPG with 70% butane and 30% propane. Flame appearances were investigated first with a fixed fueling rate at different airflow rates equivalent to air jet Reynolds numbers (Re) of 1000 to 4500; and then at a fixed airflow rate with different fueling rates equivalent to overall equivalence ratios (F) of 1.0 to 2.0. The CAP flame is found to consist of two zones: a lower entrainment zone and an upper mixing and combustion zone. The CoA flame in most cases is similar to a diffusion flame. The two-zone structure can be observed only at Re larger than 2500. The temperature distributions of the flames are similar at overall equivalence ratios of 1.0 and 1.2 for Re=2500, except that the corresponding CoA flame is longer. The flame temperature is higher in the CAP flame than the CoA flame at higher overall equivalence ratios. A measurement of centerline oxygen concentrations shows that the oxygen concentration reaches a minimum value at a flame height of 50 mm in the CAP flame but decreases more gradually in the CoA flame. It can be concluded that there is more intense air-fuel mixing in a CAP flame than the CoA flame. Investigation of the emission index of NO{sub x} (EINO{sub x}) for both flames at Re=2500 and overall equivalence ratios of 1.0 to 6.0 reveals that the EINO{sub x} curve of each flame is bell-shaped, with a maximum value of 3.2 g/kg at F=1.2 for the CAP flame and 3 g/kg at F=2.2 for the CoA flame.

  9. Extinguishment of a Methane Air Diffusion Flame by Using Blast Wave

    NASA Astrophysics Data System (ADS)

    Torikai, H.; Saito, S.; Ito, A.

    After the occurrence of a large-scale disaster such as the Great East Japan Earthquake, multiple simultaneous fires, consisting of diffusion flames, often break out. At the same time, infrastructure, such as water utilization for firefighting, roads and etc., is destroyed violently by the disaster impact. Therefore, it is difficult to use conventional firefighting techniques against the post-disaster fires. To mitigate and minimize the damages, the development of a new firefighting method which can extinguish each fire promptly is needed.

  10. Series of Laminar Soot Processes Experiment

    NASA Technical Reports Server (NTRS)

    2003-01-01

    Study of the downlink data from the Laminar Soot Processes (LSP) experiment quickly resulted in discovery of a new mechanism of flame extinction caused by radiation of soot. Scientists found that the flames emit soot sooner than expected. These findings have direct impact on spacecraft fire safety, as well as the theories predicting the formation of soot -- which is a major factor as a pollutant and in the spread of unwanted fires. This sequence was taken July 15, 1997, MET:14/10:34 (approximate) and shows the ignition and extinction of this flame. LSP investigated fundamental questions regarding soot, a solid byproduct of the combustion of hydrocarbon fuels. The experiment was performed using a laminar jet diffusion flame, which is created by simply flowing fuel -- like ethylene or propane -- through a nozzle and igniting it, much like a butane cigarette lighter. The LSP principal investigator was Gerard Faeth, University of Michigan, Arn Arbor. The experiment was part of the space research investigations conducted during the Microgravity Science Laboratory-1R mission (STS-94, July 1-17 1997). LSP results led to a reflight for extended investigations on the STS-107 research mission in January 2003. Advanced combustion experiments will be a part of investigations planned for the International Space Station. (189KB JPEG, 1350 x 1517 pixels; downlinked video, higher quality not available) The MPG from which this composite was made is available at http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0300183.html.

  11. The combustion of pure and composite propellants - The expansion and application of laminar flame theory to heterogeneous solid propellants.

    NASA Technical Reports Server (NTRS)

    Hertzberg, M.

    1971-01-01

    Development of a combustion theory based on the laminarized solutions to the energy and flow conservation equations, which is more realistic in recognizing the nature of the heating-rate problem and in obtaining a practical solution to estimating its magnitude. A new experimental approach is used for studying the combustion behavior of pure monopropellants and composite propellants which uses a laser beam to supply additional heat feedback to a burning surface. New experimental data are presented for the laser-induced combustion rate and ignition delay of pure ammonium perchlorate. The pure monopropellant theory is generalized to include such nonadiabatic effects, and the new experimental data are in good agreement with the nonadiabatic theory.-

  12. Weakly Bound Free Radicals in Combustion: "Prompt" Dissociation of Formyl Radicals and Its Effect on Laminar Flame Speeds.

    PubMed

    Labbe, Nicole J; Sivaramakrishnan, Raghu; Goldsmith, C Franklin; Georgievskii, Yuri; Miller, James A; Klippenstein, Stephen J

    2016-01-01

    Weakly bound free radicals have low-dissociation thresholds such that at high temperatures, time scales for dissociation and collisional relaxation become comparable, leading to significant dissociation during the vibrational-rotational relaxation process. Here we characterize this "prompt" dissociation of formyl (HCO), an important combustion radical, using direct dynamics calculations for OH + CH2O and H + CH2O (key HCO-forming reactions). For all other HCO-forming reactions, presumption of a thermal incipient HCO distribution was used to derive prompt dissociation fractions. Inclusion of these theoretically derived HCO prompt dissociation fractions into combustion kinetics models provides an additional source for H-atoms that feeds chain-branching reactions. Simulations using these updated combustion models are therefore shown to enhance flame propagation in 1,3,5-trioxane and acetylene. The present results suggest that HCO prompt dissociation should be included when simulating flames of hydrocarbons and oxygenated molecules and that prompt dissociations of other weakly bound radicals may also impact combustion simulations.

  13. Testing of a Hydrogen Diffusion Flame Array Injector at Gas Turbine Conditions

    SciTech Connect

    Weiland, Nathan T.; Sidwell, Todd G.; Strakey, Peter A.

    2013-07-03

    High-hydrogen gas turbines enable integration of carbon sequestration into coal-gasifying power plants, though NO{sub x} emissions are often high. This work explores nitrogen dilution of hydrogen diffusion flames to reduce thermal NO{sub x} emissions and avoid problems with premixing hydrogen at gas turbine pressures and temperatures. The burner design includes an array of high-velocity coaxial fuel and air injectors, which balances stability and ignition performance, combustor pressure drop, and flame residence time. Testing of this array injector at representative gas turbine conditions (16 atm and 1750 K firing temperature) yields 4.4 ppmv NO{sub x} at 15% O{sub 2} equivalent. NO{sub x} emissions are proportional to flame residence times, though these deviate from expected scaling due to active combustor cooling and merged flame behavior. The results demonstrate that nitrogen dilution in combination with high velocities can provide low NO{sub x} hydrogen combustion at gas turbine conditions, with significant potential for further NO{sub x} reductions via suggested design changes.

  14. Molecular Characterization of Organic Content of Soot along the Centerline of a Coflow Diffusion Flame

    SciTech Connect

    Cain, Jeremy P.; Laskin, Alexander; Kholghy, Mohammad Reza; Thomson, Murray; Wang, Hai

    2014-10-29

    High-resolution mass spectrometry coupled with nanospray desorption electrospray ionization was used to probe chemical constituents of young soot particles sampled along the centerline of a coflow diffusion flame of a three-component Jet-A1 surrogate. In lower positions where particles are transparent to light extinction (n= 632.8 nm), peri-condensed polycyclic aromatic hydrocarbons (PAHs) are found to be the major components of the particle material. These particles become enriched with aliphatic components as they grow in mass and size. Before carbonization occurs, the constituent species in young soot particles are aliphatic and aromatic compounds 200-600 amu in mass, some of which are oxygenated. Particles dominated by PAHs or mixtures of PAHs and aliphatics can both exhibit liquid-like appearance observed by electron microscopy and be transparent to visible light. The variations in chemical composition observed here indicate that the molecular processes of soot formation in coflow diffusion flames may be more complex than previously thought. For example, the mass growth and enrichment of aliphatic components in an initially, mostly aromatic structure region of the flame that is absent of H atoms or other free radicals indicates that there must exist at least another mechanism of soot mass growth in addition to the hydrogen-abstraction-carbon addition mechanism currently considered in fundamental models of soot formation.

  15. Large Eddy Simulation of Gravitational Effects on Transitional and Turbulent Gas-Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Givi, Peyman; Jaberi, Farhad A.

    2001-01-01

    The basic objective of this work is to assess the influence of gravity on "the compositional and the spatial structures" of transitional and turbulent diffusion flames via large eddy simulation (LES), and direct numerical simulation (DNS). The DNS is conducted for appraisal of the various closures employed in LES, and to study the effect of buoyancy on the small scale flow features. The LES is based on our "filtered mass density function"' (FMDF) model. The novelty of the methodology is that it allows for reliable simulations with inclusion of "realistic physics." It also allows for detailed analysis of the unsteady large scale flow evolution and compositional flame structure which is not usually possible via Reynolds averaged simulations.

  16. Chemical Kinetic Modeling of Dimethyl Carbonate in an Opposed-Flow Diffusion Flame

    SciTech Connect

    Glaude, P A; Pitz, W J; Thomson, M J

    2003-12-08

    Dimethyl carbonate (DMC) has been of interest as an oxygenate additive to diesel fuel because of its high oxygen content. In this study, a chemical kinetic mechanism for DMC was developed for the first time and used to understand its combustion under conditions in an opposed flow diffusion flame. Computed results were compared to experimental results from an opposed flow diffusion flame. It was found that the decomposition rate DMC {yields} H{sub 3}COC(=O)O. + CH{sub 3} in the flame was much slower than originally thought because resonance stabilization in the H{sub 3}COC(=O)O. radical was less than expected. Also, a new molecular elimination path for DMC is proposed and its rate calculated by quantum chemical methods. In the simulations of DMC in the flame, it was determined that much of the oxygen in dimethyl carbonate goes directly to CO{sub 2}. This characteristic indicates that DMC would not be an effective oxygenate additive for reducing soot emissions from diesel engines. In an ideal oxygenate additive for diesel fuel, each oxygen atom stays bonded to one carbon atom in the products thereby preventing the formation of carbon-carbon bonds that can lead to soot. When CO2 is formed directly, two oxygen atoms are bonded to one carbon atom thereby wasting one oxygen atom in the oxygenate additive. To determine how much CO{sub 2} is formed directly, the branching ratio of the key reaction, CH{sub 3}OC.=O going to the products CH{sub 3} + CO{sub 2} or CH{sub 3}O + CO was determined by ab initio methods. The A-factors of the rate constant of this reaction were found to be about 20 times higher than previous factors estimates. The new reaction rate constants obtained can be used as reaction rate rules for all oxygenates that contain the ester moiety including biodiesel.

  17. Experimental investigation on butane diffusion flames under the influence of magnetic field by using digital speckle pattern interferometry.

    PubMed

    Kumar, Manoj; Agarwal, Shilpi; Kumar, Varun; Khan, Gufran S; Shakher, Chandra

    2015-03-20

    In this paper, the effect of magnetic fields on the temperature and temperature profile of a diffusion flame obtained from a butane torch burner are investigated experimentally by using digital speckle pattern interferometry (DSPI). Experiments were conducted on a diffusion flame generated by a butane torch burner in the absence of a magnetic field and in the presence of uniform and nonuniform magnetic fields. A single DSPI fringe pattern was used to extract phase by using a Riesz transform and monogenic signal. Temperature inside the flame was determined experimentally both in the absence and in the presence of magnetic fields. Experimental results reveal that the maximum temperature of the flame is increased under the influence of an upward-decreasing magnetic gradient and decreased under an upward-increasing magnetic gradient while a negligible effect on temperature in a uniform magnetic field was observed. PMID:25968534

  18. OPPDIF: A Fortran program for computing opposed-flow diffusion flames

    SciTech Connect

    Lutz, A.E.; Kee, R.J.; Grcar, J.F.; Rupley, F.M.

    1997-05-01

    OPPDIF is a Fortran program that computes the diffusion flame between two opposing nozzles. A similarity transformation reduces the two-dimensional axisymmetric flow field to a one-dimensional problem. Assuming that the radial component of velocity is linear in radius, the dependent variables become functions of the axial direction only. OPPDIF solves for the temperature, species mass fractions, axial and radial velocity components, and radial pressure gradient, which is an eigenvalue in the problem. The TWOPNT software solves the two-point boundary value problem for the steady-state form of the discretized equations. The CHEMKIN package evaluates chemical reaction rates and thermodynamic and transport properties.

  19. Quantification of the uncertainties in the prediction of extinction of hydrogen-air diffusion flames

    NASA Astrophysics Data System (ADS)

    Kseib, Nicolas; Urzay, Javier; Iaccarino, Gianluca

    2011-11-01

    The study of the physical processes that lead to extinction of flames in gaseous hydrogen-air non-premixed combustion is of paramount importance for the reliable design of power plants and advanced propulsion systems in automobiles and hypersonic aircrafts. However, there remain several uncertainties in the experimental quantification of reaction rates of elementary steps in most of hydrogen-air mechanisms, which can produce hazards in hydrogen manipulation and engine malfunction. In this study, the effects of aleatory uncertainties in the chemical reaction-rate constants induced in hydrogen-air counterflow diffusion-flame extinction processes are addressed, with a probabilistic representation of the uncertain parameters sampled with a Markov-Chain Monte Carlo algorithm. Measurements of the reaction-rate constants and their associated uncertainty factors, reported earlier for the Stanford hydrogen-air detailed chemical mechanism, are used to study the propagation of uncertainties in the calculation of scalar dissipation rates at extinction. Non-intrusive methods are used to analyze the variablities, with the probability density function of the scalar dissipation rate being sampled around regions involving flame extinction and global sensitivity indices being computed by Monte Carlo sampling.

  20. Bifurcations and structure of surface interacting methane-air diffusion flames

    SciTech Connect

    Gummalla, M.; Vlachos, D.G.; Delichatsios, M.A.

    2000-02-01

    Methane-air diffusion flames near surfaces are modeled using numerical bifurcation theory. Ignition, extinction, and stability boundaries are studied as functions of fuel flow rate and oxidizer strain rate, using three reaction mechanisms of varying complexity (a one-step reaction, a C{sub 1} reaction mechanism, and the Gas Research Institute [GRI 1.2] mechanism). It is found that as the fuel flow rate increases, the ignition temperature increases, whereas the extinction temperature decreases. For sufficiently high fuel flow rates and low oxidizer strain rates, the flame separates from the surface, and extinction cannot be caused by thermal quenching. In the absence of surface heat low, two distinct extinction branches are found, namely, a blowoff or stretch limit branch at high fuel flow rates and a thermal quenching limit branch at low fuel flow rates. The complexity of the reaction mechanism affects primarily the blowoff branch at high fuel flow rates but not the thermal quenching branch due to the O{sub 2} leaking through the reaction zone at low strain rates. Surface radiation alters the bifurcation behavior, beyond an absolute stability curve. The theoretically predicted flame structure and stability limits compare well with experimental results. Implications for modeling of extinction of complex condensed fuels are also discussed.

  1. Extinguishment of a Diffusion Flame Over a PMMA Cylinder by Depressurization in Reduced-Gravity

    NASA Technical Reports Server (NTRS)

    Goldmeer, Jeffrey Scott

    1996-01-01

    Extinction of a diffusion flame burning over horizontal PMMA (Polymethyl methacrylate) cylinders in low-gravity was examined experimentally and via numerical simulations. Low-gravity conditions were obtained using the NASA Lewis Research Center's reduced-gravity aircraft. The effects of velocity and pressure on the visible flame were examined. The flammability of the burning solid was examined as a function of pressure and the solid-phase centerline temperature. As the solid temperature increased, the extinction pressure decreased, and with a centerline temperature of 525 K, the flame was sustained to 0.1 atmospheres before extinguishing. The numerical simulation iteratively coupled a two-dimensional quasi-steady, gas-phase model with a transient solid-phase model which included conductive heat transfer and surface regression. This model employed an energy balance at the gas/solid interface that included the energy conducted by the gas-phase to the gas/solid interface, Arrhenius pyrolysis kinetics, surface radiation, and the energy conducted into the solid. The ratio of the solid and gas-phase conductive fluxes Phi was a boundary condition for the gas-phase model at the solid-surface. Initial simulations modeled conditions similar to the low-gravity experiments and predicted low-pressure extinction limits consistent with the experimental limits. Other simulations examined the effects of velocity, depressurization rate and Phi on extinction.

  2. Anomalous diffusion of fluid momentum and Darcy-like law for laminar flow in media with fractal porosity

    NASA Astrophysics Data System (ADS)

    Balankin, Alexander S.; Valdivia, Juan-Carlos; Marquez, Jesús; Susarrey, Orlando; Solorio-Avila, Marco A.

    2016-08-01

    In this Letter, we report experimental and theoretical studies of Newtonian fluid flow through permeable media with fractal porosity. Darcy flow experiments were performed on samples with a deterministic pre-fractal pore network. We found that the seepage velocity is linearly proportional to the pressure drop, but the apparent absolute permeability increases with the increase of sample length in the flow direction L. We claim that a violation of the Hagen-Poiseuille law is due to an anomalous diffusion of the fluid momentum. In this regard we argue that the momentum diffusion is governed by the flow metric induced by the fractal topology of the pore network. The Darcy-like equation for laminar flow in a fractal pore network is derived. This equation reveals that the apparent absolute permeability is independent of L, only if the number of effective spatial degrees of freedom in the pore-network ν is equal to the network fractal (self-similarity) dimension D, e.g. it is in the case of fractal tree-like networks. Otherwise, the apparent absolute permeability either decreases with L, if ν < D, e.g. in media with self-avoiding fractal channels, or increases with L, if ν > D, as this is in the case of the inverse Menger sponge.

  3. Extinction and Scattering Properties of Soot Emitted from Buoyant Turbulent Diffusion Flames. Appendix D

    NASA Technical Reports Server (NTRS)

    Krishnan, S. S.; Lin, K.-C.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2001-01-01

    Extinction and scattering properties at wavelengths of 250-5200 nm were studied for soot emitted from buoyant turbulent diffusion flames in the long residence time regime where soot properties are independent of position in the overfire region and characteristic flame residence times. Flames burning in still air and fueled with gas (acetylene, ethylene, propane, and propylene) and liquid (benzene, toluene, cyclohexane, and n-heptane) hydrocarbon fuels were considered Measured scattering patterns and ratios of total scattering/absorption cross sections were in good agreement with predictions based on the Rayleigh-Debye-Gans (RDG) scattering approximation in the visible. Measured depolarization ratios were roughly correlated by primary particle size parameter, suggesting potential for completing RDG methodology needed to make soot scattering predictions as well as providing a nonintrusive way to measure primary soot particle diameters. Measurements of dimensionless extinction coefficients were in good agreement with earlier measurements for similar soot populations and were independent of fuel type and wavelength except for reduced values as the near ultraviolet was approached. The ratios of the scattering/absorption refractive index functions were independent of fuel type within experimental uncertainties and were in good agreement with earlier measurements. The refractive index function for absorption was similarly independent of fuel type but was larger than earlier reflectometry measurements in the infrared. Ratios of total scattering/absorption cross sections were relatively large in the visible and near infrared, with maximum values as large as 0.9 and with values as large as 0.2 at 2000 nm, suggesting greater potential for scattering from soot particles to affect flame radiation properties than previously thought.

  4. Extinction and Scattering Properties of Soot Emitted from Buoyant Turbulent Diffusion Flames. Appendix F

    NASA Technical Reports Server (NTRS)

    Krishnan, S. S.; Lin, K.-C.; Faeth, G. M.; Yuan, Z.-G. (Technical Monitor); Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2001-01-01

    Extinction and scattering properties at wavelengths of 250-5200 nm were studied for soot emitted from buoyant turbulent diffusion flames in the long residence time regime where soot properties are independent of position in the overfire region and characteristic flame residence times. Flames burning in still air and fueled with gas (acetylene, ethylene, propane, and propylene) and liquid (benzene, toluene, cyclohexane, and n-heptane) hydrocarbon fuels were considered. Measured scattering patterns and ratios of total scattering/absorption cross sections were in good agreement with predictions based on the Rayleigh-Debye-Gans (RDG) scattering approximation in the visible. Measured depolarization ratios were roughly correlated by primary particle size parameter, suggesting potential for completing RDG methodology needed to make soot scattering predictions as well as providing a nonintrusive way to measure primary soot particle diameters. Measurements of dimensionless extinction coefficients were in good agreement with earlier measurements for similar soot populations and were independent of fuel type and wavelength except for reduced values as the near ultraviolet was approached. The ratios of the scattering/absorption refractive index functions were independent of fuel type within experimental uncertainties and were in good agreement with earlier measurements. The refractive index junction for absorption was similarly independent of fuel type but was larger than earlier reflectometry measurements in the infrared. Ratios of total scattering/absorption cross sections were relatively large in the visible and near infrared, with maximum values as large as 0.9 and with values as large as 0.2 at 2000 nm, suggesting greater potential for scattering from soot particles to affect flame radiation properties than previously thought.

  5. Laser Raman diagnostics in subsonic and supersonic turbulent jet diffusion flames

    NASA Technical Reports Server (NTRS)

    Cheng, T. S.; Wehrmeyer, J. A.; Pitz, R. W.

    1991-01-01

    Ultraviolet (UV) spontaneous vibrational Raman scattering combined with laser-induced predissociative fluorescence (LIPF) is developed for temperature and multi-species concentration measurements. Simultaneous measurements of temperature, major species (H2, O2, N2, H2O), and minor species (OH) concentrations are made with a 'single' narrow band KrF excimer laser in subsonic and supersonic lifted turbulent hydrogen-air diffusion flames. The UV Raman system is calibrated with a flat-flame diffusion burner operated at several known equivalence ratios from fuel-lean to fuel-rich. Temperature measurements made by the ratio of Stokes/anti-Stokes signal and by the ideal gas law are compared. The single shot measurement precision for concentration and temperature measurement is 5 to 10 pct. Calibration constants and bandwidth factors are determined from the flat burner measurements and used in a data reduction program to arrive at temperature and species concentration measurements. These simultaneous measurements of temperature and multi-species concentrations allow a better understanding of the complex turbulence-chemistry interactions and provide information for the input and validation of CFD models.

  6. Solving turbulent diffusion flame in cylindrical frame applying an improved advective kinetics scheme

    NASA Astrophysics Data System (ADS)

    Darbandi, Masoud; Ghafourizadeh, Majid

    2015-12-01

    In this work, we derive a few new advective flux approximation expressions, apply them in a hybrid finite-volume-element (FVE) formulation, and solve the turbulent reacting flow governing equations in the cylindrical frame. To derive these advective-kinetic-based expressions, we benefit from the advantages of a physical influence scheme (PIS) basically, extend it to the cylindrical frame suitably, and approximate the required advective flux terms at the cell faces more accurately. The present numerical scheme not only respects the physics of flow correctly but also resolves the pressure-velocity coupling problem automatically. We also suggest a bi-implicit algorithm to solve the set of coupled turbulent reacting flow governing equations, in which the turbulence and chemistry governing equations are solved simultaneously. To evaluate the accuracy of new derived FVE-PIS expressions, we compare the current solutions with other available numerical solutions and experimental data. The comparisons show that the new derived expressions provide some more advantages over the past numerical approaches in solving turbulent diffusion flame in the cylindrical frame. Indeed, the current method and formulations can be used to solve and analyze the turbulent diffusion flames in the cylindrical coordinates very reliably.

  7. Numerical investigation of high pressure and high Reynolds diffusion flame using Large Eddy Simulation

    NASA Astrophysics Data System (ADS)

    Nichkoohi, Ali Lohrasbi; Tousi, Abolghasem Mesgarpour

    2014-10-01

    Today, with nonstop improvement in computational power, Large-Eddy Simulation (LES) is a high demanding research tool for predicting engineering flows. Such flows on high pressure condition like diesel engines is extensively employed in ground and marine transportation, oblige the designer to control and predict toxic pollutants, while maintaining or improving their high thermal efficiency. This becomes one of the main challenging issues in decades. In the present work, numerical investigation of diffusion flame dynamics is performed in the near-field of high-Reynolds jet flow on high pressure condition encountered in diesel engine applications. This work discusses the implementation of Partially Stirred Reactor (PaSR) combustion model by the approaches of large eddy simulation (LES). The simulation results show that LES, in comparison with Reynolds-Averaged Navier-Stokes (RANS) simulation predicts and captures transient phenomena very well. These phenomena such as unsteadiness and curvature are inherent in the near-field of high Reynolds diffusion flame. The outcomes of this research are compared and validated by other researchers' results. Detailed comparisons of the statistics show good agreement with the corresponding experiments.

  8. Laser Raman diagnostics in subsonic and supersonic turbulent jet diffusion flames. Final Report

    SciTech Connect

    Cheng, T.S.; Wehrmeyer, J.A.; Pitz, R.W.

    1991-01-01

    Ultraviolet (UV) spontaneous vibrational Raman scattering combined with laser-induced predissociative fluorescence (LIPF) is developed for temperature and multi-species concentration measurements. Simultaneous measurements of temperature, major species (H{sub 2}, O{sub 2}, N{sub 2}, H{sub 2}O), and minor species (OH) concentrations are made with a 'single' narrow band KrF excimer laser in subsonic and supersonic lifted turbulent hydrogen-air diffusion flames. The UV Raman system is calibrated with a flat-flame diffusion burner operated at several known equivalence ratios from fuel-lean to fuel-rich. Temperature measurements made by the ratio of Stokes/anti-Stokes signal and by the ideal gas law are compared. Single-shot uncertainties for temperature and concentration measurements are analyzed with photon statistics. Calibration constants and bandwidth factors are used in the data reduction program to arrive at temperature and species concentration measurements. The results of these measurements are presented, and these simultaneous measurements of temperature and multi-species concentrations allow a better understanding of the complex turbulence-chemistry interactions and provide information for the input and validation of CFD models.

  9. Mechanisms and enhancement of flame stabilization. Annual report, January 15, 1992--January 14, 1993

    SciTech Connect

    Law, C.K.

    1993-02-01

    During the reporting period, useful contributions have been made in understanding the structure of laminar premixed and diffusion flames, with emphasis on the influence of aerodynamics and chemical kinetics. These contributions include (1) derivation of the missing closure condition for the activation energy asymptotic analysis of premixed flames, (2) identification of a dual extinction mode for radiation-affected flames, (3) formulation of a unified theory of fundamental flammability limits, and (4) demonstration that flame stabilization can be achieved in the absence of heat loss. These investigations have been conducted via experimental, analytical and computational approaches, with strong coupling between the individual components.

  10. Calcium oxalate precipitation by diffusion using laminar microfluidics: toward a biomimetic model of pathological microcalcifications.

    PubMed

    Laffite, G; Leroy, C; Bonhomme, C; Bonhomme-Coury, L; Letavernier, E; Daudon, M; Frochot, V; Haymann, J P; Rouzière, S; Lucas, I T; Bazin, D; Babonneau, F; Abou-Hassan, A

    2016-04-01

    The effect of mixing calcium and oxalate precursors by diffusion at miscible liquid interfaces on calcium oxalate crystalline phases, and in physiological conditions (concentrations and flow rates), is studied using a microfluidic channel. This channel has similar dimensions as the collection duct in human kidneys and serves as a biomimetic model in order to understand the formation of pathological microcalcifications. PMID:26974287

  11. Physical and chemical comparison of soot in hydrocarbon and biodiesel fuel diffusion flames: A study of model and commercial fuels

    SciTech Connect

    Matti Maricq, M.

    2011-01-15

    Data are presented to compare soot formation in both surrogate and practical fatty acid methyl ester biodiesel and petroleum fuel diffusion flames. The approach here uses differential mobility analysis to follow the size distributions and electrical charge of soot particles as they evolve in the flame, and laser ablation particle mass spectrometry to elucidate their composition. Qualitatively, these soot properties exhibit a remarkably similar development along the flames. The size distributions begin as a single mode of precursor nanoparticles, evolve through a bimodal phase marking the onset of aggregate formation, and end in a self preserving mode of fractal-like particles. Both biodiesel and hydrocarbon fuels yield a common soot composition dominated by C{sub x}H{sub y}{sup +} ions, stabilomer PAHs, and fullerenes in the positive ion mass spectrum, and C{sub x}{sup -} and C{sub 2x}H{sup -} in the negative ion spectrum. These ion intensities initially grow with height in the diffusion flames, but then decline during later stages, consistent with soot carbonization. There are important quantitative differences between fuels. The surrogate biodiesel fuel methyl butanoate substantially reduces soot levels, but soot formation and evolution in this flame are delayed relative to both soy and petroleum fuels. In contrast, soots from soy and hexadecane flames exhibit nearly quantitative agreement in their size distribution and composition profiles with height, suggesting similar soot precursor chemistry. (author)

  12. Raman measurement of mixing and finite-rate chemistry in a supersonic hydrogen-air diffusion flame

    SciTech Connect

    Cheng, T.S.; Wehrmeyer, J.A.; Pitz, R.W. . Dept. of Mechanical Engineering); Jarrett, O. Jr.; Northam, G.B. . Langley Research Center)

    1994-10-01

    Ultraviolet (UV) spontaneous vibrational Raman scattering and laser-induced predissociative fluorescence (LIPF) from a KrF excimer laser are combined to simultaneously measure temperature, major species concentrations (H[sub 2], O[sub 2], N[sub 2], H[sub 2]O), and OH radical concentration in a supersonic lifted co-flowing hydrogen-air diffusion flame. The axisymmetric flame is formed when a sonic jet of hydrogen mixes with a Mach 2 annular jet of vitiated air. Mean and rms profiles of temperature, species concentrations, and mixture fraction are obtained throughout the supersonic flame. Simultaneous measurements of the chemical species and temperature are compared with frozen chemistry and equilibrium chemistry limits to assess the local state of the mixing and chemistry. Upstream of the lifted flame base, a very small amount of reaction occurs form mixing with hot vitiated air. Downstream of the lifted flame base, strong turbulent mixing leads to sub equilibrium values of temperature and OH concentration. Due to the interaction of velocity and temperature in supersonic compressible flames, the fluctuations of temperature and species concentrations are found to be higher than subsonic flames. Farther downstream, slow three-body recombination reactions result in super equilibrium OH concentrations that depress temperatures below their equilibrium values.

  13. Ex Vivo 3D Diffusion Tensor Imaging and Quantification of Cardiac Laminar Structure

    PubMed Central

    Helm, Patrick A.; Tseng, Hsiang-Jer; Younes, Laurent; McVeigh, Elliot R.; Winslow, Raimond L.

    2007-01-01

    A three-dimensional (3D) diffusion-weighted imaging (DWI) method for measuring cardiac fiber structure at high spatial resolution is presented. The method was applied to the ex vivo reconstruction of the fiber architecture of seven canine hearts. A novel hypothesis-testing method was developed and used to show that distinct populations of secondary and tertiary eigenvalues may be distinguished at reasonable confidence levels (P ≤ 0.01) within the canine ventricle. Fiber inclination and sheet angles are reported as a function of transmural depth through the anterior, lateral, and posterior left ventricle (LV) free wall. Within anisotropic regions, two consistent and dominant orientations were identified, supporting published results from histological studies and providing strong evidence that the tertiary eigenvector of the diffusion tensor (DT) defines the sheet normal. PMID:16149057

  14. Ex vivo 3D diffusion tensor imaging and quantification of cardiac laminar structure.

    PubMed

    Helm, Patrick A; Tseng, Hsiang-Jer; Younes, Laurent; McVeigh, Elliot R; Winslow, Raimond L

    2005-10-01

    A three-dimensional (3D) diffusion-weighted imaging (DWI) method for measuring cardiac fiber structure at high spatial resolution is presented. The method was applied to the ex vivo reconstruction of the fiber architecture of seven canine hearts. A novel hypothesis-testing method was developed and used to show that distinct populations of secondary and tertiary eigenvalues may be distinguished at reasonable confidence levels (P < or = 0.01) within the canine ventricle. Fiber inclination and sheet angles are reported as a function of transmural depth through the anterior, lateral, and posterior left ventricle (LV) free wall. Within anisotropic regions, two consistent and dominant orientations were identified, supporting published results from histological studies and providing strong evidence that the tertiary eigenvector of the diffusion tensor (DT) defines the sheet normal.

  15. Kinetic effects of toluene blending on the extinction limit of n-decane diffusion flames

    SciTech Connect

    Won, Sang Hee; Sun, Wenting; Ju, Yiguang

    2010-03-15

    The impact of toluene addition in n-decane on OH concentrations, maximum heat release rates, and extinction limits were studied experimentally and computationally by using counterflow diffusion flames with laser induced fluorescence imaging. Sensitivity analyses of kinetic path ways and species transport on flame extinction were also conducted. The results showed that the extinction strain rate of n-decane/toluene/nitrogen flames decreased significantly with an increase of toluene addition and depended linearly on the maximum OH concentration. It was revealed that the maximum OH concentration, which depends on the fuel H/C ratio, can be used as an index of the radical pool and chemical heat release rate, since it plays a significant role on the heat production via the reaction with other species, such as CO, H{sub 2}, and HCO. Experimental results further demonstrated that toluene addition in n-decane dramatically reduced the peak OH concentration via H abstraction reactions and accelerated flame extinction via kinetic coupling between toluene and n-decane mechanisms. Comparisons between experiments and simulations revealed that the current toluene mechanism significantly over-predicts the radical destruction rate, leading to under-prediction of extinction limits and OH concentrations, especially caused by the uncertainty of the H abstraction reaction from toluene, which rate coefficient has a difference by a factor of 5 in the tested toluene models. In addition, sensitivity analysis of diffusive transport showed that in addition to n-decane and toluene, the transport of OH and H also considerably affects the extinction limit. A reduced linear correlation between the extinction limits of n-decane/toluene blended fuels and the H/C ratio as well as the mean fuel molecular weight was obtained. The results suggest that an explicit prediction of the extinction limits of aromatic and alkane blended fuels can be established by using H/C ratio (or radical index) and the

  16. Opposed jet burner studies of silane-methane, silane-hydrogen, and hydrogen diffusion flames with air

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Guerra, Rosemary; Wilson, L. G.; Northam, G. B.

    1986-01-01

    An atmospheric pressure tubular opposed jet burner technique was used to characterize certain diffusion-flame transitions and associated burning rates for N2-diluted mixtures of highly-reactive fuels. The paper presents: (1) details of the technique, with emphasis on features permitting the study of flames involving pyrophoric gases and particle-forming combustion reactions; (2) discoveries on the properties of these flames which correspond to physically and chemically distinct stages of silane and hydrogen combustion; and (3) unburnt gas velocity data obtained from flames based on SiH4-CH4-N2, SiH4-H2-N2, and H2-N2 fuel mixtures, and plotted as functions of combustible-fuel mole fraction and fuel/oxygen molar input flow ratios. In addition, these burning velocity results are analyzed and interpreted.

  17. Opposed jet burner studies of silane-methane, silane-hydrogen and hydrogen diffusion flames with air

    NASA Technical Reports Server (NTRS)

    Pellett, G. L.; Guerra, Rosemary; Wilson, L. G.; Northam, G. B.

    1986-01-01

    An atmospheric pressure tubular opposed jet burner technique was used to characterize certain diffusion-flame transitions and associated burning rates for N2-diluted mixtures of highly-reactive fuels. Presented are: (1) details of the technique, with emphasis on features permitting the study of flames involving pyrophoric gases and particle-forming combustion reactions: (2) discoveries on the properties of these flames which correspond to physically and chemically distinct stages of silane and hydrogen combustion; and (3) unburnt gas velocity data obtained from flames based on SiH4-CH4-N2, SiH4-H2-N2, and H2-N2 fuel mixtures, and plotted as functions of combustible-fuel mole fraction and fuel/oxygen molar input flow ratios. In addition, these burning velocity results are analyzed and interpreted.

  18. Homogenous nucleation rates of n-propanol measured in the Laminar Flow Diffusion Chamber at different total pressures.

    PubMed

    Görke, Hanna; Neitola, Kimmo; Hyvärinen, Antti-Pekka; Lihavainen, Heikki; Wölk, Judith; Strey, Reinhard; Brus, David

    2014-05-01

    Nucleation rates of n-propanol were investigated in the Laminar Flow Diffusion Chamber. Nucleation temperatures between 270 and 300 K and rates between 10(0) and 10(6) cm(-3) s(-1) were achieved. Since earlier measurements of n-butanol and n‑pentanol suggest a dependence of nucleation rates on carrier gas pressure, similar conditions were adjusted for these measurements. The obtained data fit well to results available from literature. A small positive pressure effect was found which strengthen the assumption that this effect is attributed to the carbon chain length of the n-alcohol [D. Brus, A. P. Hyvärinen, J. Wedekind, Y. Viisanen, M. Kulmala, V. Ždímal, J. Smolík, and H. Lihavainen, J. Chem. Phys. 128, 134312 (2008)] and might be less intensive for substances in the homologous series with higher equilibrium vapor pressure. A comparison with the theoretical approach by Wedekind et al. [Phys. Rev. Lett. 101, 12 (2008)] shows that the effect goes in the same direction but that the intensity is much stronger in experiments than in theory. PMID:24811635

  19. Laminar Soot Processes

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Image of soot (smoke) plume made for the Laminar Soot Processes (LSP) experiment during the Microgravity Sciences Lab-1 mission in 1997. LSP-2 will fly in the STS-107 Research 1 mission in 2002. The principal investigator is Dr. Gerard Faeth of the University of Michigan. LSP uses a small jet burner, similar to a classroom butane lighter, that produces flames up to 60 mm (2.3 in) long. Measurements include color TV cameras and a temperature sensor, and laser images whose darkness indicates the quantity of soot produced in the flame. Glenn Research in Cleveland, OH, manages the project.

  20. Laminar Soot Processes

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Interior of the Equipment Module for the Laminar Soot Processes (LSP-2) experiment that fly in the STS-107 Research 1 mission in 2002 (LSP-1 flew on Microgravity Sciences Lab-1 mission in 1997). The principal investigator is Dr. Gerard Faeth of the University of Michigan. LSP uses a small jet burner (yellow ellipse), similar to a classroom butane lighter, that produces flames up to 60 mm (2.3 in) long. Measurements include color TV cameras and a radiometer or heat sensor (blue circle), and laser images whose darkness indicates the quantity of soot produced in the flame. Glenn Research in Cleveland, OH, manages the project.

  1. Laminar Soot Processes

    NASA Technical Reports Server (NTRS)

    2001-01-01

    The Laminar Soot Processes (LSP) experiment under way during the Microgravity Sciences Lab-1 mission in 1997. LSP-2 will fly in the STS-107 Research 1 mission in 2001. The principal investigator is Dr. Gerard Faeth of the University of Michigan. LSP uses a small jet burner, similar to a classroom butane lighter, that produces flames up to 60 mm (2.3 in) long. Measurements include color TV cameras and a temperature sensor, and laser images whose darkness indicates the quantity of soot produced in the flame. Glenn Research in Cleveland, OH, manages the project.

  2. Consideration of Turbulence Effects in One-Dimensional Laminar Flamelet Equations

    NASA Astrophysics Data System (ADS)

    Chan, Wai Lee; Ihme, Matthias

    2014-11-01

    The laminar flamelet formulation has been used as a fundamental building block for the construction of turbulent combustion closures. By assuming that turbulence only leads to a deformation and straining of the local flame structure, the turbulence/chemistry interaction is then considered through a presumed shape probability density function (PDF) approach. However, the consistency of this approach remains unclear in the context of large-eddy simulations (LES), and the objective of this study is to examine the representation of turbulent scalar fluxes and turbulence/chemistry coupling on the flame structure. To this end, a detailed numerical simulation of a turbulent counterflow diffusion flame is performed, and the simulation results are used to analyze the limitations of the classic laminar flamelet formulation and explore a possible alternative approach. Financial support through the Air Force Office of Scientific Research under Award No. FA9550-11-1-0031 is gratefully acknowledged.

  3. Radial diffusion and penetration of gas molecules and aerosol particles through laminar flow reactors, denuders, and sampling tubes.

    PubMed

    Knopf, Daniel A; Pöschl, Ulrich; Shiraiwa, Manabu

    2015-04-01

    Flow reactors, denuders, and sampling tubes are essential tools for many applications in analytical and physical chemistry and engineering. We derive a new method for determining radial diffusion effects and the penetration or transmission of gas molecules and aerosol particles through cylindrical tubes under laminar flow conditions using explicit analytical equations. In contrast to the traditional Brown method [Brown, R. L. J. Res. Natl. Bur. Stand. (U. S.) 1978, 83, 1-8] and CKD method (Cooney, D. O.; Kim, S. S.; Davis, E. J. Chem. Eng. Sci. 1974, 29, 1731-1738), the new approximation developed in this study (known as the KPS method) does not require interpolation or numerical techniques. The KPS method agrees well with the CKD method under all experimental conditions and also with the Brown method at low Sherwood numbers. At high Sherwood numbers corresponding to high uptake on the wall, flow entry effects become relevant and are considered in the KPS and CKD methods but not in the Brown method. The practical applicability of the KPS method is demonstrated by analysis of measurement data from experimental studies of rapid OH, intermediate NO3, and slow O3 uptake on various organic substrates. The KPS method also allows determination of the penetration of aerosol particles through a tube, using a single equation to cover both the limiting cases of high and low deposition described by Gormley and Kennedy (Proc. R. Ir. Acad., Sect. A. 1949, 52A, 163-169). We demonstrate that the treatment of gas and particle diffusion converges in the KPS method, thus facilitating prediction of diffusional loss and penetration of gases and particles, analysis of chemical kinetics data, and design of fluid reactors, denuders, and sampling lines. PMID:25744622

  4. Vortex-scalar element calculations of a diffusion flame stabilized on a plane mixing layer

    NASA Technical Reports Server (NTRS)

    Ghoniem, Ahmed F.; Givi, Peyman

    1987-01-01

    The vortex-scalar element method, a scheme which utilizes vortex elements to discretize the region of high vorticity and scalar elements to represent species or temperature fields, is utilized in the numerical simulations of a two-dimensional reacting mixing layer. Computations are performed for a diffusion flame at high Reynolds and Peclet numbers without resorting to turbulence models. In the nonreacting flow, the mean and fluctuation profiles of a conserved scalar show good agreement with experimental measurements. Results for the reacting flow indicate that for temperature independent kinetics, the chemical reaction begins immediately downstream of the splitter plate where mixing starts. Results for the reacting flow with Arrhenius kinetics show an ignition delay, which depends on reactant temperature, before significant chemical reaction occurs. Harmonic forcing changes the structure of the layer, and concomitantly the rates of mixing and reaction, in accordance with experimental results. Strong stretch within the braids in the nonequilibrium kinetics case causes local flame quenching due to the temperature drop associated with the large convective fluxes.

  5. Diffusion Flame Synthesis of Hydroxyapatite Nanoparticles using Urea Assisted Precursor Solution

    NASA Astrophysics Data System (ADS)

    Widiyastuti; Setiawan, Adhi; Setyawan, Heru; Kusdianto; Nurtono, Tantular; Nia, Suci Madha; Winardi, Sugeng

    2011-12-01

    Hydroxyapatite (HA) or (Ca10(PO4)6(OH)2 has been widely used in orthopedics and dental applications for human bone implant and teeth filler due to their biocompatibility and osteoconductive properties. Fine to nanoparticles of HA with appropriate stoichiometry and purity are preferred because they enhance densification and bioactive properties. Here, we reported the synthesis of hydroxyapatite particles in a diffusion flame reactor. LPG mainly consisting of butane and propane was used as fuel and compressed air was used as oxidizer and carrier gas. The effects of urea adding into precursor on morphology and crystallinity of the generated particles were investigated. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to observe particles morphology and crystallinity, respectively. Purity of the generated particles was analyzed quantitatively from XRD pattern using Rietveld method. Spherical shape of particles morphology was obtained for particles synthesized without urea added into precursor. Increasing fuel flow rate and urea concentration led to further disintegration of the generated particles. Nano sized particles were generated using fuel flow rate of 1 L/min and 30 w% concentration of urea added into precursor. However, increasing urea concentration led to the increase of tricalcium phosphate as a further reaction of hydroxyapatite for flame generated by using LPG as fuel of 1 L/min.

  6. Measuring and mapping cardiac fiber and laminar architecture using diffusion tensor MR imaging.

    PubMed

    Helm, Patrick; Beg, Mirza Faisal; Miller, Michael I; Winslow, Raimond L

    2005-06-01

    The ventricular myocardium is known to exhibit a complex spatial organization, with fiber orientation varying as a function of transmural location. It is now well established that diffusion tensor magnetic resonance imaging (DTMRI) may be used to measure this fiber orientation at high spatial resolution. Cardiac fibers are also known to be organized in sheets with surface orientation varying throughout the ventricles. This article reviews results on use of DTMRI for measuring ventricular fiber orientation, as well as presents new results providing strong evidence that the tertiary eigenvector of the diffusion tensor is aligned locally with the cardiac sheet surface normal. Considered together, these data indicate that DTMRI may be used to reconstruct both ventricular fiber and sheet organization. This article also presents the large deformation diffeomorphic metric mapping (LDDMM) algorithm and shows that this algorithm may be used to bring ensembles of imaged and reconstructed hearts into correspondence (e.g., registration) so that variability of ventricular geometry, fiber, and sheet orientation may be quantified. Ventricular geometry and fiber structure is known to be remodeled in a range of disease processes; however, descriptions of this remodeling have remained subjective and qualitative. We anticipate that use of DTMRI for reconstruction of ventricular anatomy coupled with application of the LDDMM method for image volume registration will enable the detection and quantification of changes in cardiac anatomy that are characteristic of specific disease processes in the heart. Finally, we show that epicardial electrical mapping and DTMRI imaging may be performed in the same hearts. The anatomic data may then be used to simulate electrical conduction in a computational model of the very same heart that was mapped electrically. This facilitates direct comparison and testing of model versus experimental results and opens the door to quantitative measurement

  7. A second-order closure analysis of turbulent diffusion flames. [combustion physics

    NASA Technical Reports Server (NTRS)

    Varma, A. K.; Fishburne, E. S.; Beddini, R. A.

    1977-01-01

    A complete second-order closure computer program for the investigation of compressible, turbulent, reacting shear layers was developed. The equations for the means and the second order correlations were derived from the time-averaged Navier-Stokes equations and contain third order and higher order correlations, which have to be modeled in terms of the lower-order correlations to close the system of equations. In addition to fluid mechanical turbulence models and parameters used in previous studies of a variety of incompressible and compressible shear flows, a number of additional scalar correlations were modeled for chemically reacting flows, and a typical eddy model developed for the joint probability density function for all the scalars. The program which is capable of handling multi-species, multistep chemical reactions, was used to calculate nonreacting and reacting flows in a hydrogen-air diffusion flame.

  8. CONTROL OF POLLUTANT EMISSIONS IN NATURAL GAS DIFFUSION FLAMES BY USING CASCADE BURNERS

    SciTech Connect

    Ala Qubbaj

    2001-03-30

    The advanced CFDRC software package was installed on a SUN-SPARC dual processor workstation (UTPA funded). The literature pertinent to the project was collected. The physical model was set and all parameters and variables were identified. Based on the physical model, the geometric modeling and grid generation processes were performed using the CFD-GEOM (Interactive Geometric Modeling and Grid Generation software). A total number of 11160 cells (248 x 45) were generated. The venturis in the cascade were modeled as two-dimensional axisymmetric convergent nozzles around the jet. With the cascade being added to the jet, the geometric complexity of the problem increased; which required multi-domain structured grid systems to be connected and matched on the boundaries. The natural gas/propane jet diffusion flame is being numerically analyzed. The numerical computations are being conducted using the CFDRC-ACE+ (advanced computational environment) software package. The results are expected soon.

  9. A direct approach to generalised multiple mapping conditioning for selected turbulent diffusion flame cases

    NASA Astrophysics Data System (ADS)

    Sundaram, Brruntha; Klimenko, Alexander Yuri; Cleary, Matthew John; Ge, Yipeng

    2016-07-01

    This work presents a direct and transparent interpretation of two concepts for modelling turbulent combustion: generalised Multiple Mapping Conditioning (MMC) and sparse-Lagrangian Large Eddy Simulation (LES). The MMC approach is presented as a hybrid between the Probability Density Function (PDF) method and approaches based on conditioning (e.g. Conditional Moment Closure, flamelet, etc.). The sparse-Lagrangian approach, which allows for a dramatic reduction of computational cost, is viewed as an alternative interpretation of the Filtered Density Function (FDF) methods. This work presents simulations of several turbulent diffusion flame cases and discusses the universality of the localness parameter between these cases and the universality of sparse-Lagrangian FDF methods with MMC.

  10. Estimation of Laminar Burning Velocities by Direct Digital Photography

    ERIC Educational Resources Information Center

    Uske, J.; Barat, R.

    2004-01-01

    The Bunsen burner flame, which is the most common flame in the laboratory, can be easily studied for its dynamics because of modern, economical digital technology available to student laboratories. Direct digital photography of Bunsen flames is used to obtain laminar burning velocities of selected gaseous hydrocarbon/air flames.

  11. Sooting Limits Of Microgravity Spherical Diffusion Flames. [conducted in the NASA Glenn 2.2-second drop tower

    NASA Technical Reports Server (NTRS)

    Sunderland, P. B.; Urban, D. L.; Stocker, D. P.; Chao, B.-H.; Axelbaum, Richard L.; Salzman, Jack (Technical Monitor)

    2001-01-01

    Limiting conditions for soot-particle inception were studied in microgravity spherical diffusion flames burning ethylene at atmospheric pressure. Nitrogen was supplied in the fuel and/or oxidizer to obtain the broadest range of stoichiometric mixture fraction. Both normal flames (oxygen in ambience) and inverted flames (fuel in ambience) were considered. Microgravity was obtained in the NASA Glenn 2.2-second drop tower. The flames were observed with a color video camera and sooting conditions were defined as conditions for which yellow emission was present throughout the duration of the drop. Sooting limit results were successfully correlated in terms of adiabatic flame temperature and stoichiometric mixture fraction. Soot free conditions were favored by increased stoichiometric mixture fractions. No statistically significant effect of convection direction on sooting limits was observed. The relationship between adiabatic flame temperature and stoichiometric mixture fraction at the sooting limits was found to be in qualitative agreement with a simple theory based on the assumption that soot inception can occur only where temperature and local C/O ratio exceed threshold values (circa 1250 K and 1, respectively).

  12. INVESTIGATION OF THE PATHWAYS TO PCDDS/FS FROM AN ETHYLENE DIFFUSION FLAME: FORMATION FROM FLAME SOOT AND AROMATICS

    EPA Science Inventory

    Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, PCDDs/Fs, occur in the combustion of a wide variety of fuels, and is related to poor combustion conditions. This study looks at the importance of flame soot, including associated adsorbed and condensed aeromati...

  13. Temperature measurement of axi- symmetric butane diffusion flame under the influence of upward decreasing gradient magnetic field using digital holographic interferometry

    NASA Astrophysics Data System (ADS)

    Kumar, Varun; Kumar, Manoj; Shakher, Chandra

    2015-08-01

    In this paper, digital holographic interferometry (DHI) is implemented to investigate the effect of upward decreasing gradient magnetic field on the temperature and temperature profile of diffusion flame created by butane torch burner. In the experiment double exposure digital holographic interferometry is used to calculate the temperature distribution inside the flame. First a digital hologram is recorded in the absence of flame and second hologram is recorded in the presence of flame. Phases in two different states of air (i.e. in absence of flame and presence of flame) are reconstructed individually by numerical method. The phase difference map is obtained by subtracting the reconstructed phase of air in presence and absence of flame. Refractive index inside the flame is obtained from the axi-symmetric phase difference data using the Abel inversion integral. Temperature distribution inside the flame is calculated from the refractive index data using Lorentz - Lorentz equation. Experiment is conducted on a diffusion flame created by butane torch burner in the absence of magnetic field and in presence of upward decreasing gradient magnetic field. Experimental investigations reveal that the maximum temperature inside the flame increases under the influence of upward decreasing magnetic field.

  14. RANS predictions of turbulent diffusion flames: comparison of a reactor and a flamelet combustion model to the well stirred approach

    NASA Astrophysics Data System (ADS)

    Kösters, Anne; Karlsson, Anders; Oevermann, Michael; D'Errico, Gianluca; Lucchini, Tommaso

    2015-01-01

    The flame stabilisation process in turbulent non-premixed flames is not fully understood and several models have been developed to describe the turbulence-chemistry interaction. This work compares the performance of the multiple Representative Interactive Flamelet (mRIF) model, the Volume Reactor Fraction Model (VRFM), and the Well-Stirred reactor (WS) model in describing such flames. The predicted ignition delay and flame lift-off length of n-heptane sprays are compared to experimental results published within the Engine Combustion Network (ECN). All of the models predict the trend of ignition delay reasonably well. At a low gas pressure (42 bar) the ignition delay is overpredicted compared to the experimental data, but the difference between the models is not significant. However, the predicted lift-off lengths differ. At high pressure (87 bar) the difference between the models is small. All models slightly underpredict the lift-off length compared to the experimental data. At low gas pressure (42 bar) the mRIF model gives the best results. The VRFM and WS models predict excessively short lift-off lengths, but the VRFM model gives better results than the WS model. The flame structures of the models are also compared. The WS model and the VRFM model yield a well defined flame stabilisation point whereas the mRIF model does not. The flame of the mRIF model is more diffuse and the model is not able to predict flame propagation. All models were able to predict the experimental trends in lift-off and ignition delay, but certain differences between them are demonstrated.

  15. Suppression Characteristics of Cup-Burner Flames in Low Gravity

    NASA Technical Reports Server (NTRS)

    Takahashi, Fumiaki; Linteris, Gregory T.; Katta, Viswanath R.

    2004-01-01

    The structure and suppression of laminar methane-air co-flow diffusion flames formed on a cup burner have been studied experimentally and numerically using physically acting fire-extinguishing agents (CO2, N2, He, and Ar) in normal earth (lg) and zero gravity (0g). The computation uses a direct numerical simulation with detailed chemistry and radiative heat-loss models. An initial observation of the flame without agent was also made at the NASA Glenn 2.2-Second Drop Tower. An agent was introduced into a low-speed coflowing oxidizing stream by gradually replacing the air until extinguishment occurred under a fixed minimal fuel velocity. The suppression of cup-burner flames, which resemble real fires, occurred via a blowoff process (in which the flame base drifted downstream) rather than the global extinction phenomenon typical of counterflow diffusion flames. The computation revealed that the peak reactivity spot (the reaction kernel) formed in the flame base was responsible for attachment and blowoff phenomena of the trailing diffusion flame. The thermal and transport properties of the agents affected the flame extinguishment limits.

  16. Human protein kinase inhibitor screening by capillary electrophoresis using transverse diffusion of laminar flow profiles for reactant mixing.

    PubMed

    Nehmé, Hala; Nehmé, Reine; Lafite, Pierre; Routier, Sylvain; Morin, Philippe

    2013-11-01

    A capillary electrophoresis (CE)-based enzyme assay method has been developed to screen protein kinase inhibitors. Four human kinases GSK3β, DYRK1A, CDK5/p25 and CDK1/cyclin B were chosen to test this novel method. These enzymes have been identified as very promising targets to develop treatments against cancer and neurodegenerative diseases. The efficiency of drugs against these relevant biological targets has never been carried out by CE. For this proposal, the capillary was used as a nanoreactor in which four reactants (the enzyme, its two substrates and its potential inhibitor) were successively injected, mixed by using transverse diffusion of laminar flow profiles and incubated. The adenosine 5'-diphosphate (ADP) formed during the enzymatic reaction was detected by UV and quantified. The efficiency of the developed CE method was validated by determining the IC50 values of a wide variety of inhibitors covering a large domain of affinity toward kinases and containing representative and chemically divergent skeletons. Excellent agreement was found between the results obtained by CE and those reported in the literature when using conventional radiometric enzyme assays. Moreover, CE was successfully used to determine the inhibitory effect of several potential inhibitors that was not yet assessed by conventional methods and is crucial for structure activity relation studies. This novel CE method is simple, rapid, very economic (few tens of nanoliters per IC50) and eco-friendly since no radioactivity was required. It could be extended to high-throughput screening of kinase inhibitors, which is of great interest for biomedical and pharmaceutical research fields. PMID:24075461

  17. Turbulence-Flame Interactions in Type Ia Supernovae

    SciTech Connect

    Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 50A-1148, Berkeley, CA 94720; Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064; Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794; Aspden, Andrew J; Aspden, Andrew J.; Bell, John B.; Day, Marc S.; Woosley, Stan E.; Zingale, Mike

    2008-05-27

    The large range of time and length scales involved in type Ia supernovae (SN Ia) requires the use of flame models. As a prelude to exploring various options for flame models, we consider, in this paper, high-resolution three-dimensional simulations of the small-scale dynamics of nuclear flames in the supernova environment in which the details of the flame structure are fully resolved. The range of densities examined, 1 to 8 x 107 g cm-3, spans the transition from the laminar flamelet regime to the distributed burning regime where small scale turbulence disrupts the flame. The use of a low Mach number algorithm facilitates the accurate resolution of the thermal structure of the flame and the inviscid turbulent kinetic energy cascade, while implicitly incorporating kinetic energy dissipation at the grid-scale cutoff. For an assumed background of isotropic Kolmogorov turbulence with an energy characteristic of SN Ia, we find a transition density between 1 and 3 x 107 g cm-3 where the nature of the burning changes ualitatively. By 1 x 107 g cm-3, energy diffusion by conduction and radiation is exceeded, on the flame scale, by turbulent advection. As a result, the effective Lewis Number approaches unity. That is, the flame resembles a laminar flame, but is turbulently broadened with an effective diffusion coefficient, D_T \\sim u' l, where u' is the turbulent intensity and l is the integral scale. For the larger integral scales characteristic of a real supernova, the flame structure is predicted to become complex and unsteady. Implications for a possible transition to detonation are discussed.

  18. Analysis of the structure and mechanisms of extinction of a counterflow methanol-air diffusion flame

    SciTech Connect

    Seshadri, K.; Trevino, C.; Smooke, M.D.

    1989-05-01

    Numerical calculations were performed to determine the structure and to clarify the extinction mechanisms of diffusion flames stabilized between counterflowing streams of methanol and air. The calculations were performed at a value of the thermodynamic pressure equal to 1 atmosphere, with different values for the rate of strain and with two different chemical kinetic mechanisms, mechanism a and mechanism b. Mechanism a and mechanism b have the same set of elementary reactions, but the rate constants for these elementary reactions were obtained from