Journal articles: 'Flammes de diffusion'

1

Wang, H. Y., S. Rouvreau, P. Cordeiro, G. Legros, and P. Joulain. "Simulation numérique directe de flammes de diffusion laminaires en microgravité." Mécanique & Industries 5, no. 5 (September 2004): 607–12. http://dx.doi.org/10.1051/meca:2004063.

Full text

APA, Harvard, Vancouver, ISO, and other styles

2

Robin, Vincent, Arnaud Mura, Michel Champion, and Pierre Plion. "Modélisation de la combustion turbulente des mélanges hétérogènes en richesse : Des flammes de prémélange aux flammes de diffusion." Comptes Rendus Mécanique 337, no. 8 (August 2009): 596–602. http://dx.doi.org/10.1016/j.crme.2009.07.003.

Full text

APA, Harvard, Vancouver, ISO, and other styles

3

Laurent, Frédérique, Marc Massot, and Vitaly Volpert. "Propagation de flammes gazeuses dans la limite d'une diffusion massique nulle." Comptes Rendus Mathematique 335, no. 4 (January 2002): 405–10. http://dx.doi.org/10.1016/s1631-073x(02)02487-1.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Ban, H., S. Venkatesh, and K. Saito. "Convection-Diffusion Controlled Laminar Micro Flames." Journal of Heat Transfer 116, no. 4 (November 1, 1994): 954–59. http://dx.doi.org/10.1115/1.2911471.

Full text

Abstract:

Small laminar diffusion flames (flame height ≃2–3 mm) established by a fuel jet issuing into a quiescent medium are investigated. It was found that for these flames buoyancy effects disappeared as the flame size decreased (Fr≫1), and diffusive transport of the fuel was comparable to the convective transport of the fuel. The effect of buoyancy on these flames was studied by examining the flame shape for horizontally oriented burners. A phenomenological model was developed (based on experimentally determined flame shapes) to compare diffusion and convection transport effects. Finally, the flame shapes were theoretically determined by solving the conservation equations using similarity methods. It was seen that when the axial diffusion (in momentum and species equations) terms are included in the conservation equations, the calculated flame shape is in better agreement (as compared to without the axial diffusion term) with the experimentally measured flame shape.

APA, Harvard, Vancouver, ISO, and other styles

5

Kim, J. S., F. A. Williams, and P. D. Ronney. "Diffusional-thermal instability of diffusion flames." Journal of Fluid Mechanics 327 (November 25, 1996): 273–301. http://dx.doi.org/10.1017/s0022112096008543.

Full text

Abstract:

The diffusional–thermal instability, which gives rise to striped quenching patterns that have been observed for diffusion flames, is analysed by studying the model of a one-dimensional convective diffusion flame in the diffusion-flame regime of activation-energy asymptotics. Attention is focused principally on near-extinction conditions with Lewis numbers less than unity, in which the reactants with high diffusivity diffuse into the strong segments of the reaction sheet, so that the regions between the strong segments become deficient in reactant and subject to the local quenching that leads to the striped patterns. This analysis differs from other flame stability analyses in that the complete description of the dispersion relation is obtained from a composite expansion of the results of an analysis with the conventional convective-diffusive scaling and one with reaction-zone scaling. The results predict that striped patterns will occur, for flames sufficiently close to quasi-steady extinction, with a finite wavenumber that in convective–diffusive scaling is proportional to the cube root of the Zel'dovich number. The convective–diffusive response contributes to the stabilization of long-wavelength disturbances by through positive excess enthalpies by which the flame becomes more resistant to instability, while the reaction-zone response provides stabilization of short-wavelength disturbances by transverse diffusion, within the reactive inner layer, which relaxes the perturbed scalar fields towards their unperturbed states. As quasi-steady extinction is approached, marginal stability arises first at an intermediate range between these two scalings. Parametric results for this bifurcation point are obtained through numerical solutions of the associated generalized eigenvalue problems. Comparisons with measured pattern dimensions for different sets of reactants and diluents reveal excellent qualitative agreement.

APA, Harvard, Vancouver, ISO, and other styles

6

Yao, Jiajie, Jiahao Liu, and Jian Wang. "Experimental Study of Coflow Propane—Air Laminar Diffusion Flames at Subatmospheric Pressures." Applied Sciences 11, no. 13 (June 27, 2021): 5979. http://dx.doi.org/10.3390/app11135979.

Full text

Abstract:

The effect of pressure on the flame’s physical structure and soot formation of the coflow propane—air laminar diffusion flames was studied experimentally at subatmospheric pressures from 30 to 101 kPa. Flames with a constant fuel mass flow rate combined with two different coflow air mass flow rates were investigated at different pressures. The spatially resolved relative soot volume fraction was measured using the laser-induced incandescence (LII) method. The height of the visible flame decreased moderately as the pressure (p) reduced from 101 to 30 kPa. The maximum flame diameter increased proportionally to pn , where the exponent changed from −0.4 to −0.52 as the air-to-fuel velocity ratio decreased from 1.0 to 0.5. Strong pressure dependence of the maximum relative soot volume fraction and the normalized maximum soot mass flow were observed and could be described by a power law relationship. However, a nonmonotonic dependence of soot formation on the air-to-fuel velocity ratio was observed at all the considered pressures.

APA, Harvard, Vancouver, ISO, and other styles

7

Baker, John, Mark E. Calvert, and David W. Murphy. "Structure and Dynamics of Laminar Jet Micro-Slot Diffusion Flames." Journal of Heat Transfer 124, no. 4 (July 16, 2002): 783–90. http://dx.doi.org/10.1115/1.1482083.

Full text

Abstract:

Results of an experimental investigation into the behavior of laminar jet diffusion flames, produced using micro-slot burner ports, are presented. Under certain conditions, the cross-sectional shape of micro-slot flames is qualitatively similar to the cross-sectional shape of circular burner port flames produced in an environment where molecular diffusion is the primary transport mechanism. An order of magnitude analysis reveals that, over the range of experimental conditions examined, the behavior of the experimentally observed micro-slot flames is not necessarily diffusion-controlled. A comparison of the experimental data with an accepted theoretical model shows that current theoretical models do not accurately predict the experimentally observed flame heights. A theoretical expression for purely diffusion-controlled micro-slot flame height is developed and compared with experimental micro-slot flame data. The region where this theoretical expression is valid is identified through an examination of the diffusion to buoyancy parameter. A qualitative discussion of micro-slot flame structure is also presented.

APA, Harvard, Vancouver, ISO, and other styles

8

Xie, Yu, Zhilong Wei, Teng Zhou, Haishen Zhen, Zihao Liu, and Zuohuang Huang. "Combustion Characteristics of Small Laminar Flames in an Upward Decreasing Magnetic Field." Energies 14, no. 7 (April 2, 2021): 1969. http://dx.doi.org/10.3390/en14071969.

Full text

Abstract:

The combustion characteristics of laminar biogas premixed and diffusion flames in the presence of upward decreasing magnetic fields have been investigated in this study. The mechanism of magnet–flame interaction in the literature, in which magnetic fields change the behaviors of laminar flames due to the paramagnetic and diamagnetic properties of the constituent gases, is examined and the results are as follows. The magnetic field has no noticeable effect on premixed flames due to low oxygen concentration of the mixed gas at the injection and the relatively high flow momentum. However, due to the diffusion nature of diffusion flames and paramagnetic property of oxygen in ambient air, oxygen distributions are subjected to the gradient of magnetic flux, thus shortening the height of diffusion flames. Results also show that the flame volume is more strongly varied than flame height. Altered oxygen distributions result in improved combustion and higher flame temperature. In the case of current magnet–flame interaction, the magnetic driving force is combined with gravitational force, and a modified gravity g* as well as gravity modification factor G are derived to characterize the paramagnetism theory of oxygen.

APA, Harvard, Vancouver, ISO, and other styles

9

McNesby, K. L., R. G. Daniel, J. M. Widder, and A. W. Miziolek. "Spectroscopic Investigation of Atmospheric-Pressure Counterflow Diffusion Flames Inhibited by Halons." Applied Spectroscopy 50, no. 1 (January 1996): 126–30. http://dx.doi.org/10.1366/0003702963906762.

Full text

Abstract:

Infrared spectra of atmospheric-pressure counterflow diffusion flames inhibited by halons (a contraction of halogenated hydrocarbons) and a few of their potential replacements are measured with the use of Fourier transform spectroscopy. Results are compared to spectra of similar flame systems examined at low pressure. It is shown that, for atmospheric-pressure counterflow diffusion methane/air flames inhibited by CF3Br, CF2H2, and CF4, the two major fluorine-containing combustion products are HF and CF2O. A correlation is shown between flame inhibition efficiency and CF2O formation for atmospheric-pressure counterflow diffusion flames inhibited by these halons. For low-pressure premixed flames inhibited by CF3Br, HF appears to be the only fluorine-containing combustion product, even at relative dopant levels 15 times higher than those capable of extinguishing atmospheric-pressure counterflow diffusion flames. The results of these experiments illustrate the need for flame inhibitant testing over a wide spectrum of flame conditions, while providing further evidence that, for atmospheric-pressure inhibition of real fires by halons, CF2O may be a good indicator of inhibitor efficiency when that inhibition is at least partly accomplished by chemical scavenging of reactive combustion intermediates.

APA, Harvard, Vancouver, ISO, and other styles

10

Li, X. "On the Scaling of the Visible Lengths of Jet Diffusion Flames." Journal of Energy Resources Technology 118, no. 2 (June 1, 1996): 128–33. http://dx.doi.org/10.1115/1.2792703.

Full text

Abstract:

Length of jet diffusion flames is of direct importance in many industrial processes and is analyzed by applying scaling method directly to the governing partial differential equations. It is shown that for jet-momentum-dominated diffusion flames, when the buoyancy effects are neglected, the flame length normalized by the burner exit diameter increases linearly with the Reynolds number at the burner exit in the laminar burning regime and decreases in inverse proportion to the Reynolds number in the transitional regime. For turbulent diffusion flames, the normalized flame lengths are independent of the burner exit flow conditions. It is further found that for vertical upward flames, the buoyancy effect increases the flame length in the laminar and transitional regime and reduces the length in the turbulent regime; while for vertical downward flames, the buoyancy effect decreases the flame length in the laminar and transitional regime and increases the length in the turbulent regime, provided that jet momentum is dominated, and there is no flame spreading out and then burning upward like a downward-facing pool fire. Hence, for turbulent flames the flame lengths depend on the Froude number, Fr, and increase (or decrease) slightly as Fr increases for upward (or downward) flames. By comparison, it is found that the foregoing theoretical results are in good agreement with the experimental observations reported in literature.

APA, Harvard, Vancouver, ISO, and other styles

11

KIM, J. S. "Diffusional-Thermal Instability of Diffusion Flames in the Premixed-Flame Regime." Combustion Science and Technology 118, no. 1-3 (September 1996): 27–48. http://dx.doi.org/10.1080/00102209608951970.

Full text

APA, Harvard, Vancouver, ISO, and other styles

12

GHOSAL, SANDIP, and LUC VERVISCH. "Theoretical and numerical study of a symmetrical triple flame using the parabolic flame path approximation." Journal of Fluid Mechanics 415 (July 25, 2000): 227–60. http://dx.doi.org/10.1017/s0022112000008685.

Full text

Abstract:

In non-premixed turbulent combustion the reactive zone is localized at the stoichiometric surfaces of the mixture and may be locally approximated by a diffusion flame. Experiments and numerical simulations reveal a characteristic structure at the edge of such a two-dimensional diffusion flame. This ‘triple flame’ or ‘edge flame’ consists of a curved flame front followed by a trailing edge that constitutes the body of the diffusion flame. Triple flames are also observed at the edge of a lifted laminar diffusion flame near the exit of burners. The speed of propagation of the triple flame determines such important properties as the rate of increase of the flame surface in non-premixed combustion and the lift-off distance in lifted flames at burners. This paper presents an approximate theory of triple flames based on an approximation of the flame shape by a parabolic profile, for large activation energy and low but finite heat release. The parabolic flame path approximation is a heuristic approximation motivated by physical considerations and is independent of the large activation energy and low heat release assumptions which are incorporated through asymptotic expansions. Therefore, what is presented here is not a truly asymptotic theory of triple flames, but an asymptotic solution of a model problem in which the flame shape is assumed parabolic. Only the symmetrical flame is considered and Lewis numbers are taken to be unity. The principal results are analytical formulas for the speed and curvature of triple flames as a function of the upstream mixture fraction gradient in the limit of infinitesimal heat release as well as small but finite heat release. For given chemistry, the solution provides a complete description of the triple flame in terms of the upstream mixture fraction gradient. The theory is validated by comparison with numerical simulation of the primitive equations.

APA, Harvard, Vancouver, ISO, and other styles

13

Zhang, Ting, Qinghua Guo, Xudong Song, Zhijie Zhou, and Guangsuo Yu. "The Chemiluminescence and Structure Properties of Normal/Inverse Diffusion Flames." Journal of Spectroscopy 2013 (2013): 1–7. http://dx.doi.org/10.1155/2013/304717.

Full text

Abstract:

The flame emission spectrometry was applied to detect the distribution of excited radicals in two types CH4/O2 coflow jet diffusion flames (normal and inverse diffusion flames). Combining the image analysis along with the spectrometry, the chemiluminescence and structure characteristics of these diffusion flames were investigated. The results show that the inverse diffusion flame (IDF) with relatively high inlet oxygen velocity is composed of two regions: a bright base and a tower on top of the base, which is quite different from the normal diffusion flame (NDF). The flame is divided into two regions along the flame axis based on maximum OH* position (Region I: initial reaction zone; Region II: further oxidation zone). The degree of the further oxidization taking place in Region II is obvious in accordance with OH* distribution, which is the main difference in reaction zone between fuel-rich condition and fuel-lean condition for NDFs. For IDFs, the change of OH* distribution with increasing equivalence O/C ratio ([O/C]e) in Region II is not conspicuous. More OH* and CH* are generated in IDFs, due to the inner high-speed O2 flow promoting the mixing of fuel and oxygen to a certain extent.

APA, Harvard, Vancouver, ISO, and other styles

14

Han, Yongtaek, Kihyung Lee, Wonnam Lee, Jaewoo Chung, and Chunbum Lee. "Quantitative Measurements of Soot Particles in Laminar Diffusion Flame Using a LII/LIS Technique(Measurement PM in Flames)." Proceedings of the International symposium on diagnostics and modeling of combustion in internal combustion engines 2004.6 (2004): 377–85. http://dx.doi.org/10.1299/jmsesdm.2004.6.377.

Full text

APA, Harvard, Vancouver, ISO, and other styles

15

Shimada, T., T. Akiyama, S. Fukushima, K. Mitsui, M. Jinno, K. Kitagawa, N. Arai, and Ashwani K. Gupta. "Time-Resolved Temperature Profiling of Flames With Highly Preheated/Low Oxygen Concentration Air in an Industrial Size Furnace." Journal of Engineering for Gas Turbines and Power 127, no. 3 (June 1, 2004): 464–71. http://dx.doi.org/10.1115/1.1914801.

Full text

Abstract:

A high-speed video camera was combined with a newly developed optical system to measure time resolved two-dimensional (2D) temperature distribution in flames. This diagnostics has been applied to measure the temperature distribution in an industrial size regenerative test furnace facility using highly preheated combustion air and heavy fuel oil. The 2D distributions of continuum emission from soot particles in these flames have been simultaneously measured at two discrete wave bands at 125 frames/sec. This allowed us to determine the temperature from each image on the basis of two-color 2D thermometry, in which the ratio of the 2D emission intensity distribution at various spatial position in the flame was converted into the respective 2D temperature distribution with much higher spatial resolution as compared to that obtainable with thermocouples. This diagnostic method was applied to both premixed and diffusion flames with highly preheated low oxygen concentration combustion air using heavy fuel oil. The results show that higher temperature regions exist continuously in the premixed flame as compared to the diffusion flame. This provided clear indication of higher NO emission from the premixed flame as compared to diffusion flames during the combustion of heavy fuel oil under high-temperature air combustion conditions. This observation is contrary to that obtained with normal temperature combustion air wherein diffusion flames result in higher NOx emission levels.

APA, Harvard, Vancouver, ISO, and other styles

16

Camacho, Jorge R., and Ahsan R. Choudhuri. "Shapes of Elliptic Methane Laminar Jet Diffusion Flames." Journal of Engineering for Gas Turbines and Power 128, no. 1 (October 21, 2004): 1–7. http://dx.doi.org/10.1115/1.2032449.

Full text

Abstract:

Buoyant and nonbuoyant shapes of methane flames issued from a 2:1 aspect ratio elliptic tube burner were measured. Nonbuoyant conditions were obtained in the KC-135 microgravity research aircraft operated by NASA’s Johnson Space Center. A mathematical model based on the extended Burke-Schumann flame theory is developed to predict the flame length of an elliptic burner. The model utilizes Roper’s theoretical method for circular burners and extends the analysis for elliptic burners. The predicted flame length using the theoretical model agrees well with experimental measurements. In general for the elliptic burner the nonbuoyant flames are longer than the buoyant flames. However, measured lengths of both buoyant and nonbuoyant flame lengths change proportionally with the volumetric fuel flow rate and support the L vs Q correlation. The maximum flame width measured at buoyant and nonbuoyant conditions also show a proportional relation with the volumetric fuel flow rate. Normalized buoyant and nonbuoyant flame lengths of the elliptic burner correlate (L∕d∝Re) with the jet exit Reynolds number and exhibit a higher slope compared to a circular burner. Normalized flame width data show a power correlation (w∕d=cFrn) with the jet exit Froude number.

APA, Harvard, Vancouver, ISO, and other styles

17

Tewarson, A., and M. M. Khan. "Extinguishment of Diffusion Flames of Polymeric Materials by Halon 1301." Journal of Fire Sciences 11, no. 5 (September 1993): 407–20. http://dx.doi.org/10.1177/073490419301100503.

Full text

Abstract:

Halon 1301 flame extinction results are discussed for the com bustion of polymethylmethacrylate (PMMA), eight composite materials, and carbon in the gas phase. Two types of combustion and flame extinction experi ments were performed: (1) in the Factory Mutual Research Corporation (FMRC) flammability apparatus (50 kW scale) for PMMA and composite materials, and (2) in the FMRC electrical arc apparatus for carbon in the gas phase. For char forming composite materials, mass transfer from the surface was low, turbulent diffusion flames were not generated, and flame extinction oc curred between 3 to 4.5% of Halon 1301, close to the value reported for the lam inar diffusion flames of polymers. For non-charring PMMA, mass transfer from the surface was high, flames were turbulent, and flame extinction was found at about 6% of Halon 1301, contrary to the accepted value of about 4% for the lam inar diffusion flames of polymers. With Halon 1301 the conditions for flame in stability and extinction for combustion efficiency less than about 0.40, with sig nificant increase in the amounts of products of incomplete combustion (such as CO and hydrocarbon), were in agreement with flame instability and extinction found for fuel-rich conditions inside well-ventilated laminar and turbulent diffusion flames, in ceiling layers of combustion products, in enclosure fires, in ventilation-controlled buoyant diffusion flames of polymers, and for flame ex tinction of heptane flames by water. Experiments in the FMRC electrical arc apparatus showed that in the gas phase combustion of carbon vapors generated in high energy arc, chemical heat release rate and combustion efficiency decreased with increase in Halon 1301. At about 7.5% of Halon 1301, conditions were close to flame extinction and at 9.0%, oxidative pyrolysis of carbon was indicated. Concentrations of Br- and F- ions, generated from the decomposition of Halon 1301, were also measured. Concentration of Br- ions was higher than the concentration of F- ions, al though there are three F atoms and only one Br atom in Halon 1301. There was brown deposit on the walls of the apparatus with extensive corrosion of rubber gaskets, electrical fan, and other components. The techniques discussed in this article appear to be attractive for the assess ment of flame extinguishability and corrosive characteristics of fire suppres sants to replace ozone layer depleting Halons.

APA, Harvard, Vancouver, ISO, and other styles

18

Ju, Yiguang, Kaoru Maruta, and Takashi Niioka. "Combustion Limits." Applied Mechanics Reviews 54, no. 3 (May 1, 2001): 257–77. http://dx.doi.org/10.1115/1.3097297.

Full text

Abstract:

Combustion limits and related flame behaviors are reviewed, especially with regard to fundamental problems. As for premixed flames, after a brief historical overview of research on the flammability limit, recent trends of research on planar propagating flames, curved propagating flames, flame balls, and stretched premixed flames are discussed, and then all types of flames are summarized. Finally, instability and dynamics near limits is discussed. With regard to combustion limits of counterflow diffusion flames and droplet flames, their instability is demonstrated, then an explanation of lifted flames and edge flames is presented. Suggestions for future work are also discussed in the concluding remarks. There are 166 references cited in this review article.

APA, Harvard, Vancouver, ISO, and other styles

19

Veynante, D., A. Trouvé, K. N. C. Bray, and T. Mantel. "Gradient and counter-gradient scalar transport in turbulent premixed flames." Journal of Fluid Mechanics 332 (February 1997): 263–93. http://dx.doi.org/10.1017/s0022112096004065.

Full text

Abstract:

In premixed turbulent combustion, the modelling of the turbulent flux of the mean reaction progress variable remains somewhat controversial. Classical gradient transport assumptions based on the eddy viscosity concept are often used while both experimental data and theoretical analysis have pointed out the existence of countergradient turbulent diffusion. Direct numerical simulation (DNS) is used in this paper to provide basic information on the turbulent flux of and study the occurrence of counter-gradient transport. The numerical configuration corresponds to twoor three-dimensional premixed flames in isotropic turbulent flow. The simulations correspond to various flame and flow conditions that are representative of flamelet combustion. They reveal that different flames will feature different turbulent transport properties and that these differences can be related to basic dynamical differences in the flame-flow interactions: counter-gradient diffusion occurs when the flow field near the flame is dominated by thermal dilatation due to chemical reaction, whereas gradient diffusion occurs when the flow field near the flame is dominated by the turbulent motions. The DNS-based analysis leads to a simple expression to describe the turbulent flux of , which in turn leads to a simple criterion to delineate between the gradient and counter-gradient turbulent diffusion regimes. This criterion suggests that the occurrence of one regime or the other is determined primarily by the ratio of turbulence intensity divided by the laminar flame speed, and by the flame heat release factor, τ ≡ (Tb — Tu)/Tu, where Tu and Tb are respectively the temperature within unburnt and burnt gas. Consistent with the Bray-Moss-Libby theory, counter-gradient (gradient) diffusion is promoted by low (high) values and high (low) values of τ. DNS also shows that these results are not restricted to the turbulent transport of . Similar results are found for the turbulent transport of flame surface density, Σ. The turbulent fluxes of and Σ are strongly correlated in the simulated flames and counter-gradient (gradient) diffusion of always coincides with counter-gradient (gradient) diffusion of Σ.

APA, Harvard, Vancouver, ISO, and other styles

20

Vance, Faizan Habib, Yuriy Shoshin, Philip de Goey, and Jeroen van Oijen. "Flame Stabilization and Blow-Off of Ultra-Lean H2-Air Premixed Flames." Energies 14, no. 7 (April 2, 2021): 1977. http://dx.doi.org/10.3390/en14071977.

Full text

Abstract:

The manner in which an ultra-lean hydrogen flame stabilizes and blows off is crucial for the understanding and design of safe and efficient combustion devices. In this study, we use experiments and numerical simulations for pure H2-air flames stabilized behind a cylindrical bluff body to reveal the underlying physics that make such flames stable and eventually blow-off. Results from CFD simulations are used to investigate the role of stretch and preferential diffusion after a qualitative validation with experiments. It is found that the flame displacement speed of flames stabilized beyond the lean flammability limit of a flat stretchless flame (ϕ=0.3) can be scaled with a relevant tubular flame displacement speed. This result is crucial as no scaling reference is available for such flames. We also confirm our previous hypothesis regarding lean limit blow-off for flames with a neck formation that such flames are quenched due to excessive local stretching. After extinction at the flame neck, flames with closed flame fronts are found to be stabilized inside a recirculation zone.

APA, Harvard, Vancouver, ISO, and other styles

21

Shih, Hsin Yi, and Jou Rong Hsu. "Computed Extinction Limits and Flame Structures of Opposed-Jet Syngas Diffusion Flames." Applied Mechanics and Materials 110-116 (October 2011): 4899–906. http://dx.doi.org/10.4028/www.scientific.net/amm.110-116.4899.

Full text

Abstract:

This paper reports a numerical study on the extinction limits and flame structures of opposed-jet syngas diffusion flames. A narrowband radiation model is coupled to the OPPDIF program, which uses detailed chemical kinetics and thermal and transport properties to enable the study of 1-D counterflow syngas diffusion flames over the entire range of flammable strain rates with flame radiation. The effects of syngas composition, strain rate, ambient pressure, and dilution gases on the flame structures and extinction limits of H2/CO synthetic mixture flames were examined. Results indicate the flame structures and flame extinction are impacted by the composition of syngas mixture significantly. From hydrogen-lean syngas to hydrogen-rich syngas fuels, flame temperature increases with increasing hydrogen content and ambient pressure, but the flame thickness is decreased with ambient pressure and strain rates. Besides, the dilution effects from CO2, N2, and H2O, which may be present in the syngas mixtures, were studied. The flame is thinner and flame temperature is lower when CO2 is the diluents instead of N2. The combustible range of strain rates is extended with increasing hydrogen percentage and ambient pressure, but it is decreased the most with CO2 as the dilution gas due to the dilution effects. Complete flammability limits using strain rates, maximum flame temperature as coordinates can provide a fundamental understanding of syngas combustion and applications.

APA, Harvard, Vancouver, ISO, and other styles

22

Xia, Xi, and Peng Zhang. "A vortex-dynamical scaling theory for flickering buoyant diffusion flames." Journal of Fluid Mechanics 855 (September 24, 2018): 1156–69. http://dx.doi.org/10.1017/jfm.2018.707.

Full text

Abstract:

The flickering of buoyant diffusion flames is associated with the periodic shedding of toroidal vortices that are formed under gravity-induced shearing at the flame surface. Numerous experimental investigations have confirmed the scaling,$f\propto D^{-1/2}$, where$f$is the flickering frequency and$D$is the diameter of the fuel inlet. However, the connection between the toroidal vortex dynamics and the scaling has not been clearly understood. By incorporating the finding of Gharibet al.(J. Fluid Mech., vol. 360, 1998, pp. 121–140) that the detachment of a continuously growing vortex ring is inevitable and can be dictated by a universal constant that is essentially a non-dimensional circulation of the vortex, we theoretically established the connection between the periodicity of the toroidal vortices and the flickering of a buoyant diffusion flame with small Froude number. The scaling theory for flickering frequency was validated by the existing experimental data of pool flames and jet diffusion flames.

APA, Harvard, Vancouver, ISO, and other styles

23

BABA, YUYA, and RYOICHI KUROSE. "Analysis and flamelet modelling for spray combustion." Journal of Fluid Mechanics 612 (October 10, 2008): 45–79. http://dx.doi.org/10.1017/s0022112008002620.

Full text

Abstract:

The validity of a steady-flamelet model and a flamelet/progress-variable approach for gaseous and spray combustion is investigated by a two-dimensional direct numerical simulation (DNS) of gaseous and spray jet flames, and the combustion characteristics are analysed. A modified flamelet/progress-variable approach, in which total enthalpy rather than product mass fraction is chosen as a progress variable, is also examined. DNS with an Arrhenius formation, in which the chemical reaction is directly solved in the physical flow field, is performed as a reference to validate the combustion models. The results show that the diffusion flame is dominant in the gaseous diffusion jet flame, whereas diffusion and premixed flames coexist in the spray jet flame. The characteristics of the spray flame change from premixed–diffusion coexistent to diffusion-dominant downstream. Comparisons among the results from DNS with various combustion models show the modified flamelet/progress-variable approach to be superior to the other combustion models, particularly for the spray flame. Where the behaviour of the gaseous total enthalpy is strongly affected by the energy transfer (i.e. heat transfer and mass transfer) from the dispersed droplet, and this effect can be accounted for only by solving the conservation equation of the total enthalpy. However, even the DNS with the modified flamelet/progress-variable approach tends to underestimate the gaseous temperature in the central region of the spray jet flame. To increase the prediction accuracy, a combustion model for the partially premixed flame for the spray flame is necessary.

APA, Harvard, Vancouver, ISO, and other styles

24

Saito, K., F. A. Williams, and A. S. Gordon. "Structure of Laminar Coflow Methane–Air Diffusion Flames." Journal of Heat Transfer 108, no. 3 (August 1, 1986): 640–48. http://dx.doi.org/10.1115/1.3246984.

Full text

Abstract:

Measured temperature and composition profiles are reported for a number of flames. Implications concerning flame structure are deduced, with emphasis on soot formation and on correlations involving conserved scalars.

APA, Harvard, Vancouver, ISO, and other styles

25

Li, S. C., N. Ilincic, and F. A. Williams. "Reduction of NOx Formation by Water Sprays in Strained Two-Stage Flames." Journal of Engineering for Gas Turbines and Power 119, no. 4 (October 1, 1997): 836–43. http://dx.doi.org/10.1115/1.2817062.

Full text

Abstract:

Staged combustion can be employed to reduce the formation of CO and NOx, stabilize the flame, decrease the flame temperature, and create better working conditions in gas turbine combustors. To help understand influences of partial premixing and addition of water on NOx formation, we study two-stage flames in a counterflow spray burner. This paper reports experimental and theoretical results concerning two-stage combustion in which one feed stream is composed of a fuel-rich mixture of methane and air and the other is air. Water sprays are added to the air stream. This two-phase laminar counterflow configuration exhibits a green premixed flame, a blue diffusion flame, and a vaporization plane. All three are flat and parallel. The separation distances between them decrease with increasing equivalence ratio and strain rate. Flow visualization is provided through illumination by an argon ion laser sheet, velocity fields and spray structure are measured by a phase-doppler particle analyzer, concentration fields of major stable species are measured by gas chromatography of samples withdrawn from the flame, and temperature fields are measured by a thermocouple. Numerical integrations that employ a recent chemical-kinetic data base are performed to model the flame structure and NOx formation. Comparisons of experimental results with numerical predictions are made to test agreement. This work provides information on hydrocarbon combustion in both premixed flames and diffusion flames, indicates how NOx is formed in fuel-rich flames, and suggests how the pollutants can be reduced.

APA, Harvard, Vancouver, ISO, and other styles

26

Leu, Jai Houng, and Ay Su. "Structure of Combustion Enhancement on Impinging Diffusion Flame." Applied Mechanics and Materials 152-154 (January 2012): 872–76. http://dx.doi.org/10.4028/www.scientific.net/amm.152-154.872.

Full text

Abstract:

For the purpose to clear obverse the impingement and entrainment of the impinging diffusion flame, numbers of the tests are executed under various sets of momentum ratios in this paper. The oxidizer-fuel impinging flames shorten the fully development length. The peak temperature distributions are also greater than that of pure methane impinging flame. Furthermore, its flame width in YZ plane is thicker than that of the pure impinging flame. This effect is more obvious under lean combustion condition. Also, nitrogen gas in the mixture can increase the mixing rate.

APA, Harvard, Vancouver, ISO, and other styles

27

Ravikrishna, RV, and AB Sahu. "Advances in understanding combustion phenomena using non-premixed and partially premixed counterflow flames: A review." International Journal of Spray and Combustion Dynamics 10, no. 1 (November 14, 2017): 38–71. http://dx.doi.org/10.1177/1756827717738168.

Full text

Abstract:

Counterflow flames provide an ideal platform for understanding the flame structure and as a model to study the effect of physical and chemical perturbations on the flame structure. This article reviews the advances made in the understanding of combustion dynamics and chemistry through experimental and numerical studies in counterflow non-premixed and partially premixed flames. Key contributions on fundamental aspects such as extinction, ignition and effect of perturbations on the stability of diffusion flames are first summarized and analysed. The review then focuses on the progress made in the understanding of the effect of inert particles and flame suppressants on the flame characteristics. A review of detailed studies on edge flames facilitates further understanding of local quenching and re-ignition phenomena in highly turbulent flames. The influence of radiation model and unsteady flow-conditions on the flame kinetics and dynamics along with work on NOx kinetics has been discussed. The review also outlines that specific experiments need to be carried out over a wide range of conditions for further understanding and validation of numerical models.

APA, Harvard, Vancouver, ISO, and other styles

28

Kalman, Joseph, Nick G. Glumac, and Herman Krier. "Experimental Study of Constant Volume Sulfur Dust Explosions." Journal of Combustion 2015 (2015): 1–11. http://dx.doi.org/10.1155/2015/817259.

Full text

Abstract:

Dust flames have been studied for decades because of their importance in industrial safety and accident prevention. Recently, dust flames have become a promising candidate to counter biological warfare. Sulfur in particular is one of the elements that is of interest, but sulfur dust flames are not well understood. Flame temperature and flame speed were measured for sulfur flames with particle concentrations of 280 and 560 g/m3and oxygen concentration between 10% and 42% by volume. The flame temperature increased with oxygen concentration from approximately 900 K for the 10% oxygen cases to temperatures exceeding 2000 K under oxygen enriched conditions. The temperature was also observed to increase slightly with particle concentration. The flame speed was observed to increase from approximately 10 cm/s with 10% oxygen to 57 and 81 cm/s with 42% oxygen for the 280 and 560 g/m3cases, respectively. A scaling analysis determined that flames burning in 21% and 42% oxygen are diffusion limited. Finally, it was determined that pressure-time data may likely be used to measure flame speed in constant volume dust explosions.

APA, Harvard, Vancouver, ISO, and other styles

29

Ga, Bui Van, Le Van Tuy, Huynh Ba Vang, Le Van Lu, and Nguyen Ngoc Linh. "Experimental study of radiation heat transfer coefficient of diffusion flames." Vietnam Journal of Mechanics 29, no. 2 (July 31, 2007): 98–104. http://dx.doi.org/10.15625/0866-7136/29/2/5595.

Full text

Abstract:

Basing on analysis of flame pictures given by visioscope by two-color method, the paper presents evolution of radiation heat transfer coefficient $\varepsilon_s$ of soot in diffusion flames in air, in furnace and in combustion chamber of Diesel engine. $\varepsilon_s$ reaches respectively its maximal value of 0.15; 0.30 and 0.45 in regions of maximal soot fraction of the three above flames.

APA, Harvard, Vancouver, ISO, and other styles

30

Bhadraiah, K., and V. Raghavan. "A numerical study of the effect of radial confinement on the characteristics of laminar co-flow methane–oxygen diffusion flames." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 225, no. 5 (April 28, 2011): 1213–28. http://dx.doi.org/10.1177/2041298310393446.

Full text

Abstract:

A numerical investigation of the characteristics of laminar co-flow methane–oxygen diffusion flames has been carried out. The temperature and nitric oxide (NO) distributions in unconfined and partly confined flames are studied in detail. Radial confinements of different diameters and with a length of 150 times the fuel jet diameter have been considered to allow atmospheric nitrogen entry only from the top. A numerical model with a 43-step chemical kinetics mechanism and an optically thin radiation sub-model is employed to carry out simulations. The numerical model has been validated using the experimental data available in the literature. The effect of oxygen flowrate on temperature distributions is studied thoroughly. Confined flame extents are compared with the corresponding unconfined flame extents with the help of OH contours. The effect of confinement diameter on temperature and NO distributions is analysed in detail. At low oxygen flowrates, the extents of confined flames are higher than those of an unconfined flame. At a higher oxygen flowrate, the extent of unconfined flame becomes higher. The confined flames are in general hotter than the unconfined flames. However, at the highest oxygen flowrate and for an intermediate confinement diameter, the flame has the lowest maximum temperature. The amount of NO produced in confined flames is higher than the unconfined flames, due to air entrainment from the top of the confining tube, which increases the residence time for nitrogen transport and its oxidation. At the highest oxygen flowrate considered, numerical predictions show that for a given confinement length, there is an optimum confinement diameter which results in a minimum net production of NO among all the flames.

APA, Harvard, Vancouver, ISO, and other styles

31

Takahashi, F., M. Mizomoto, and S. Ikai. "Structure of the Stabilizing Region of a Laminar Jet Diffusion Flame." Journal of Heat Transfer 110, no. 1 (February 1, 1988): 182–89. http://dx.doi.org/10.1115/1.3250450.

Full text

Abstract:

Velocity, temperature, and composition of major species were measured in the base region of a two-dimensional, laminar methane jet diffusion flame in unconfined still air under a low-velocity jetting condition. The velocity data showed acceleration near the flame zone caused primarily by thermal expansion and buoyancy. The heat flux vectors showed substantial heat flow from the flame base to both downstream and the burner wall. The premixed zone was formed in the dark space by convective penetration of oxygen and back-diffusion of methane. The molar flux vectors of methane and oxygen at the base pointed to the opposite directions, typical of diffusion flames.

APA, Harvard, Vancouver, ISO, and other styles

32

Sarlak, R., M. Shams, and R. Ebrahimi. "Numerical simulation of soot formation in a turbulent diffusion flame: comparison among three soot formation models." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 226, no. 5 (October 3, 2011): 1290–301. http://dx.doi.org/10.1177/0954406211421997.

Full text

Abstract:

Combustion and soot formation in a turbulent diffusion flame are simulated. Chemistry of combustion is treated with a detailed reaction mechanism that employs 49 species and 277 reactions. Turbulence is taken into account via the corrected k–ε model. Radiation heat transfer from flame is modelled by the P-1 model. An empirical model proposed by Khan and Greeves and two semi-empirical models proposed by Tesner and Lindstedt are used to simulate the soot formation in the flame. Khan and Greeves model showed to underpredict the maximum soot volume fraction. Nevertheless, the main shortcoming of Khan and Greeves model which undermines the applicability of this model to prediction of soot formation in turbulent diffusion flames is the inability to locate the highly sooting regions of the flame properly. Tesner model underpredicts the soot formation significantly, although the predicted shapes of the soot profiles are in accordance with the experimental measurements. Lindstedt model performs well in predicting both the maximum soot formation and the soot profile shapes in the chamber. Therefore, Lindstedt model can be considered as the most suitable model for the prediction of soot formation in turbulent diffusion flames.

APA, Harvard, Vancouver, ISO, and other styles

33

Marley, Stephen K., Eric J. Welle, and Kevin M. Lyons. "Combustion Structures in Lifted Ethanol Spray Flames." Journal of Engineering for Gas Turbines and Power 126, no. 2 (April 1, 2004): 254–57. http://dx.doi.org/10.1115/1.1688768.

Full text

Abstract:

The development of a double flame structure in lifted ethanol spray flames is visualized using OH planar laser-induced fluorescence (PLIF). While the OH images indicate a single reaction zone exists without co-flow, the addition of low-speed co-flow facilitates the formation of a double flame structure that consists of two diverging flame fronts originating at the leading edge of the reaction zone. The outer reaction zone burns steadily in a diffusion mode, and the strained inner flame structure is characterized by both diffusion and partially premixed combustion exhibiting local extinction and re-ignition events.

APA, Harvard, Vancouver, ISO, and other styles

34

Mohan, S., and M. Matalon. "Diffusion flames and diffusion flame-streets in three dimensional micro-channels." Combustion and Flame 177 (March 2017): 155–70. http://dx.doi.org/10.1016/j.combustflame.2016.12.004.

Full text

APA, Harvard, Vancouver, ISO, and other styles

35

Robert, Etienne, and Peter A. Monkewitz. "Thermal-diffusive instabilities in unstretched, planar diffusion flames." Combustion and Flame 159, no. 3 (March 2012): 1228–38. http://dx.doi.org/10.1016/j.combustflame.2011.10.020.

Full text

APA, Harvard, Vancouver, ISO, and other styles

36

JUNG, Byong-koog, Toshiaki YANO, Shuichi TORII, and Hiroaki MOCHIZUKI. "Flame Reignition Phenomenon of Hydrogen Jet Diffusion Flames." Transactions of the Japan Society of Mechanical Engineers Series B 67, no. 661 (2001): 2347–52. http://dx.doi.org/10.1299/kikaib.67.2347.

Full text

APA, Harvard, Vancouver, ISO, and other styles

37

GORDON, A. S., S. C. LI, and FA WILLIAMS. "Visible Flame Heights of Laminar Coflow Diffusion Flames." Combustion Science and Technology 141, no. 1-6 (June 1999): 1–18. http://dx.doi.org/10.1080/00102209908924179.

Full text

APA, Harvard, Vancouver, ISO, and other styles

38

MIKOFSKI, M., T. WILLIAMS, C. SHADDIX, and L. BLEVINS. "Flame height measurement of laminar inverse diffusion flames." Combustion and Flame 146, no. 1-2 (July 2006): 63–72. http://dx.doi.org/10.1016/j.combustflame.2006.04.006.

Full text

APA, Harvard, Vancouver, ISO, and other styles

39

Abam, D. P. S. "Methane Combustion in Laminar Diffusion Flames." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power Engineering 203, no. 1 (February 1989): 65–72. http://dx.doi.org/10.1243/pime_proc_1989_203_008_02.

Full text

Abstract:

This paper is concerned with methane combustion in laminar diffusion flames. Data on methane concentration distributions in different diffusion flame geometries are correlated against a conserved scalar called mixture fraction. The correlation is used to determine a global methane combustion rate applicable in the rich to stoichiometric regions of laminar diffusion flames. The global rate is consistent with methane disappearance through the forward kinetic step: CH4 + H → CH3 + H2 with [H] equilibrated according to [Formula: see text] on the rich side. This equilibration results from the three-body reaction [Formula: see text] which is equilibrated in the region 1.1 ≤ φ ≤ 2.74, 1300 K ≤ T ≤ 2000 K. These results indicate that initial radical attack on the fuel molecule provides the rate-controlling step for methane combustion.

APA, Harvard, Vancouver, ISO, and other styles

40

Lee, S., and J. Kim. "Nonlinear dynamic characteristics of flame stripes formed in strained diffusion flames by diffusional—thermal instability." Combustion Theory and Modelling 4, no. 1 (March 2000): 29–46. http://dx.doi.org/10.1088/1364-7830/4/1/302.

Full text

APA, Harvard, Vancouver, ISO, and other styles

41

Getty, J. D., S. G. Westre, D. Z. Bezabeh, G. A. Barrall, M. J. Burmeister, and P. B. Kelly. "Detection of Benzene and Trichloroethylene in Sooting Flames." Applied Spectroscopy 46, no. 4 (April 1992): 620–25. http://dx.doi.org/10.1366/0003702924124907.

Full text

Abstract:

The utility of resonance Raman spectroscopy as an analytical method is studied for application to multicomponent sooting flames. Far-ultraviolet resonance Raman spectra of benzene and trichloroethylene in methane diffusion flames have been obtained. The feasibility of flame temperature determination has been demonstrated for the benzene/methane flame. Resonance enhancement provides the sensitivity and selectivity required to detect low concentrations of aromatics and chlorinated hydrocarbons, in contrast to conventional spontaneous Raman spectroscopy, which suffers from low sensitivity and interference from laser-induced fluorescence of polycyclic aromatic hydrocarbons (PAHs).

APA, Harvard, Vancouver, ISO, and other styles

42

Katragadda, Mohit, and Nilanjan Chakraborty. "A PrioriDirect Numerical Simulation Modelling of the Curvature Term of the Flame Surface Density Transport Equation for Nonunity Lewis Number Flames in the Context of Large Eddy Simulations." International Journal of Chemical Engineering 2012 (2012): 1–14. http://dx.doi.org/10.1155/2012/103727.

Full text

Abstract:

A Direct Numerical Simulation (DNS) database of freely propagating statistically planar turbulent premixed flames with Lewis numbersLeranging from 0.34 to 1.2 has been used to analyse the statistical behaviours of the curvature term of the generalised Flame surface Density (FSD) transport equation, in the context of the Large Eddy Simulation (LES). Lewis number is shown to have significant influences on the statistical behaviours of the resolved and sub-grid parts of the FSD curvature term. It has been found that the existing models for the sub-grid curvature termCsgdo not capture the qualitative behaviour of this term extracted from the DNS database for flames withLe<<1. The existing models ofCsgonly predict negative values, whereas the sub-grid curvature term is shown to assume positive values within the flame brush for theLe=0.34and 0.6 flames. Here the sub-grid curvature terms arising from combined reaction and normal diffusion and tangential diffusion components of displacement speed are individually modelled, and the new model of the sub-grid curvature term has been found to captureCsgextracted from DNS data satisfactorily for all the different Lewis number flames considered here for a wide range of filter widths.

APA, Harvard, Vancouver, ISO, and other styles

43

Gollahalli, S. R. "Effects of Flame Lift-Off on the Differences Between the Diffusion Flames From Circular and Elliptic Burners." Journal of Energy Resources Technology 120, no. 2 (June 1, 1998): 161–66. http://dx.doi.org/10.1115/1.2795028.

Full text

Abstract:

An experimental study conducted to determine the effects of lifting the flame base off the burner rim on the differences between the flame characteristics of diffusion flames from circular and elliptic burners is presented. The in-flame profiles of temperature, concentrations of fuel and combustion product species, and the mean and fluctuating components of axial velocity are presented. This study has shown that the effects of burner geometry in turbulent lifted flames are considerable only in the near-burner region. In the midflame and far-burner regions, the effects traceable to burner geometry are much weaker, contrary to those observed in the attached flame configuration. The observations are attributed to the turbulence and additional air entrainment into the jet prior to the flame base accompanying the lift-off process, which mitigate the effects of burner geometry.

APA, Harvard, Vancouver, ISO, and other styles

44

Ratna Kishore, V., M. R. Ravi, and Anjan Ray. "Effect of Hydrogen Content and Dilution on Laminar Burning Velocity and Stability Characteristics of Producer Gas-Air Mixtures." International Journal of Reacting Systems 2008 (2008): 1–8. http://dx.doi.org/10.1155/2008/310740.

Full text

Abstract:

Producer gas is one of the promising alternative fuels with typical constituents of H2, CO, CH4, N2, and CO2. The laminar burning velocity of producer gas was computed for a wide range of operating conditions. Flame stability due to preferential diffusional effects was also investigated. Computations were carried out for spherical outwardly propagating flames and planar flames. Different reaction mechanisms were assessed for the prediction of laminar burning velocities of CH4, H2, H2-CO, and CO-CH4and results showed that the Warnatz reaction mechanism with C1 chemistry was the smallest among the tested mechanisms with reasonably accurate predictions for all fuels at 1 bar, 300 K. To study the effect of variation in the producer gas composition, each of the fuel constituents in ternary CH4-H2-CO mixtures was varied between 0 to 48%, while keeping diluents fixed at 10% CO2and 42% N2by volume. Peak burning velocity shifted fromϕ=1.6to 1.1 as the combined volumetric percentage of hydrogen and CO varied from 48% to 0%. Unstable flames due to preferential diffusion effects were observed for lean mixtures of fuel with high hydrogen content. The present results indicate that H2has a strong influence on the combustion of producer gas.

APA, Harvard, Vancouver, ISO, and other styles

45

Caetano, N. R., T. Z. Stapasolla, F. B. Peng, P. S. Schneider, F. M. Pereira, and H. A. Vielmo. "Diffusion Flame Stability of Low Calorific Fuels." Defect and Diffusion Forum 362 (April 2015): 29–37. http://dx.doi.org/10.4028/www.scientific.net/ddf.362.29.

Full text

Abstract:

Mechanisms related to diffusion flame stabilization have been the subject of several studies within the last decades due the industrial and scientific interests. Information on flame stability is of fundamental importance in energy efficiency and safety regarding industrial applications. Thus, an experimental study was performed in order to examine the flame characteristics and regions of stability limits. In this study, a representative burner of industrial applications was employed, which allows the stabilization of several combustion regimes. The lift-off and blow-out flame regimes were investigated for different proportions of carbon dioxide in natural gas. In this way, an analysis of the calorific fuel influence on the flame stability was performed based on the measurements and a comparison with classical literature models was done. The fuel dilution by adding carbon dioxide was found to decrease the soot production, leading to lower flame heights and also, lower lift-off and blow-out limits. Results obtained from this study encourage future works which consider flames in large scale, in order to equate to industrial applications.

APA, Harvard, Vancouver, ISO, and other styles

46

See, Yee Chee, and Matthias Ihme. "Effects of finite-rate chemistry and detailed transport on the instability of jet diffusion flames." Journal of Fluid Mechanics 745 (March 25, 2014): 647–81. http://dx.doi.org/10.1017/jfm.2014.95.

Full text

Abstract:

AbstractLocal linear stability analysis has been shown to provide valuable information about the response of jet diffusion flames to flow-field perturbations. However, this analysis commonly relies on several modelling assumptions about the mean flow prescription, the thermo-viscous-diffusive transport properties, and the complexity and representation of the chemical reaction mechanisms. In this work, the effects of these modelling assumptions on the stability behaviour of a jet diffusion flame are systematically investigated. A flamelet formulation is combined with linear stability theory to fully account for the effects of complex transport properties and the detailed reaction chemistry on the perturbation dynamics. The model is applied to a methane–air jet diffusion flame that was experimentally investigated by Füriet al.(Proc. Combust. Inst., vol. 29, 2002, pp. 1653–1661). Detailed simulations are performed to obtain mean flow quantities, about which the stability analysis is performed. Simulation results show that the growth rate of the inviscid instability mode is insensitive to the representation of the transport properties at low frequencies, and exhibits a stronger dependence on the mean flow representation. The effects of the complexity of the reaction chemistry on the stability behaviour are investigated in the context of an adiabatic jet flame configuration. Comparisons with a detailed chemical-kinetics model show that the use of a one-step chemistry representation in combination with a simplified viscous-diffusive transport model can affect the mean flow representation and heat release location, thereby modifying the instability behaviour. This is attributed to the shift in the flame structure predicted by the one-step chemistry model, and is further exacerbated by the representation of the transport properties. A pinch-point analysis is performed to investigate the stability behaviour; it is shown that the shear-layer instability is convectively unstable, while the outer buoyancy-driven instability mode transitions from absolutely to convectively unstable in the nozzle near field, and this transition point is dependent on the Froude number.

APA, Harvard, Vancouver, ISO, and other styles

47

Hancock, R. D., F. R. Schauer, R. P. Lucht, V. R. Katta, and K. Y. Hsu. "Thermal diffusion effects and vortex-flame interactions in hydrogen jet diffusion flames." Symposium (International) on Combustion 26, no. 1 (January 1996): 1087–93. http://dx.doi.org/10.1016/s0082-0784(96)80323-7.

Full text

APA, Harvard, Vancouver, ISO, and other styles

48

Krupa, R. J., T. F. Culbreth, B. W. Smith, and J. D. Winefordner. "A Flashback-Resistant Burner for Combustion Diagnostics and Analytical Spectrometry." Applied Spectroscopy 40, no. 6 (August 1986): 729–33. http://dx.doi.org/10.1366/0003702864508232.

Full text

Abstract:

A general utility burner for the production of laminar, homogenous diffusion flames, which is immune to flashbacks, is presented. Because the fuel and oxidant mix on the surface of the burner rather than within the spray chamber, the flames cannot flashback. A wide variety of gas mixtures has been investigated, including oxygen, nitrous oxide, and nitric oxide as the oxidants. Any combination of fuel and oxidant can be safely burned to produced a stable, laminar, and audibly quiet flame. Flame temperatures can be varied over a wide range either by changing the fuel-oxidant ratio or by diluting the flame gases with an inert gas. In this manner, the optimum flame temperature and composition can be achieved. These burners are of general use in analytical emission, fluorescence, and photoacoustic spectrometry, as well as combustion diagnostics.

APA, Harvard, Vancouver, ISO, and other styles

49

Wang, H. Y., J. K. Bechtold, and C. K. Law. "Forced oscillation in diffusion flames near diffusive–thermal resonance." International Journal of Heat and Mass Transfer 51, no. 3-4 (February 2008): 630–39. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2007.04.042.

Full text

APA, Harvard, Vancouver, ISO, and other styles

50

Mokrin, Sergey, R. V. Fursenko, and S. S. Minaev. "Thermal-Diffusive Stability of Counterflow Premixed Flames at Low Lewis Numbers." Advanced Materials Research 1040 (September 2014): 608–13. http://dx.doi.org/10.4028/www.scientific.net/amr.1040.608.

Full text

Abstract:

Dynamics of radiative, near-limit, stretched premixed flames is investigated analytically and numerically. Investigation of counterflow premixed flames stability is important for the development of new combustion technologies such as those associated with low-NOx emission, lean burn and material synthesis. Emphasis is paid on the linear stability of multiple flame regimes. The present analysis, for the first time, gives out a dispersion equation describing growth rate of small spatial perturbations of the flame front. The stability diagram is obtained and the region of instability is distinguished.

APA, Harvard, Vancouver, ISO, and other styles

Journal articles on the topic 'Flammes de diffusion'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles