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Showing papers on "Diffusion flame published in 1988"


Journal ArticleDOI
01 Jan 1988
TL;DR: In this article, it is shown that the inner structure of the flamelets is one-dimensional and time dependent, and a new coordinate transformation using the mixture fraction Z as independent variable leads to a universal description.
Abstract: The laminar flamelet concept covers a regime in turbulent combustion where chemistry (as compared to transport processes) is fast such that it occurs in asymptotically thin layers—called flamelets—embedded within the turbulent flow field. This situation occurs in most practical combustion systems including reciprocating engines and gas turbine combustors. The inner structure of the flamelets is one-dimensional and time dependent. This is shown by an asymptotic expansion for the Damkohler number of the rate determining reaction which is assumed to be large. Other non-dimensional chemical parameters such as the nondimensional activation energy or Zeldovich number may also be large and may be related to the Damkohler number by a distinguished asymptoiic limit. Examples of the flamelet structure are presented using onestep model kinetics or a reduced four-step quasi-global mechanism for methane flames. For non-premixed combustion a formal coordinate transformation using the mixture fraction Z as independent variable leads to a universal description. The instantaneous scalar dissipation rate χ of the conserved scalar Z is identified to represent the diffusion time scale that is compared with the chemical time scale in the definition of the Damkohler number. Flame stretch increases the scalar dissipation rate in a turbulent flow field. If it exceeds a critical value χ q the diffusion flamelet will extinguish. Considering the probability density distribution of χ , it is shown how local extinction reduces the number of burnable flamelets and thereby the mean reaction rate. Furthermore, local extinction events may interrupt the connection to burnable flamelets which are not yet reached by an ignition source and will therefore not be ignited. This phenomenon, described by percolation theory, is used to derive criteria for the stability of lifted flames. It is shown how values of ∋ q obtained from laminar experiments scale with turbulent residence times to describe lift-off of turbulent jet diffusion flames. For non-premixed combustion it is concluded that the outer mixing field—by imposing the scalar dissipation rate—dominates the flamelet behaviour because the flamelet is attached to the surface of stoichiometric mixture. The flamelet response may be two-fold: burning or non-burning quasi-stationary states. This is the reason why classical turbulence models readily can be used in the flamelet regime of non-premixed combustion. The extent to which burnable yet non-burning flamelets and unsteady transition events contribute to the overall statistics in turbulent non-premixed flames needs still to be explored further. For premixed combustion the interaction between flamelets and the outer flow is much stronger because the flame front can propagate normal to itself. The chemical time scale and the thermal diffusivity determine the flame thickness and the flame velocity. The flamelet concept is valid if the flame thickness is smaller than the smallest length scale in the turbulent flow, the Kolmogorov scale. Also, if the turbulence intensity v′ is larger than the laminar flame velocity, there is a local interaction between the flame front and the turbulent flow which corrugates the front. A new length scale L G =v F 3 /∈ , the Gibson scale, is introduced which describes the smaller size of the burnt gas pockets of the front. Here v F is the laminar flame velocity and ∈ the dissipation of turbulent kinetic energy in the oncoming flow. Eddies smaller than L G cannot corrugate the flame front due to their smaller circumferential velocity while larger eddies up to the macro length scale will only convect the front within the flow field. Flame stretch effects are the most efficient at the smallest scale L G . If stretch combined with differential diffusion of temperature and the deficient reactant, represented by a Lewis number different from unity, is imposed on the flamelet, its inner structure will respond leading to a change in flame velocity and in some cases to extinction. Transient effects of this response are much more important than for diffusion flamelets. A new mechanism of premixed flamelet extinction, based on the diffusion of radicals out of the reaction zone, is described by Rogg. Recent progress in the Bray-Moss-Libby formulation and the pdf-transport equation approach by Pope are presented. Finally, different approaches to predict the turbulent flame velocity including an argument based on the fractal dimension of the flame front are discussed.

1,268 citations


Journal ArticleDOI
TL;DR: In this paper, global reaction schemes for the combustion of alkane hydrocarbons up to butane in mixtures with air in premixed and diffusion flames have been derived using analysis of flame structures.

914 citations


Journal ArticleDOI
01 Jan 1988
TL;DR: In this paper, a theoretical and experimental study of the structure of a counterflow diffusion flame burning diluted methane in diluted air is reported. But the results are compared using both the physical coordinate and the mixture fraction as the independent variable.
Abstract: Results of a theoretical and experimental study of the structure of a counterflow diffusion flame burning diluted methane in diluted air are reported. Concentration profiles of the stable species were measured using gas sampling techniques with quartz microprobes. The samples were analyzed with a gas chromatograph. Temperature profiles were measured using coated thermocouples. Numerical calculations of the structure of the flame were performed with an adaptive nonlinear boundary value method at conditions identical to those used in the experiment. The results are compared using both the physical coordinate and the mixture fraction as the independent variable. Excellent agreement is obtained for concentration profiles of CH4, O2, N2, CO2 and H2O and for the peak value of the temperature. The complete temperature profile and the H2 and CO profiles are not in as good agreement and the differences are attributed to the neglect of C2 chemistry in the numerical calculations.

234 citations


Journal ArticleDOI
TL;DR: In this paper, the asymptotic structure of a counterflow methane-air diffusion flame is analyzed using a three-step chemical kinetic mechanism, which was deduced in a systematic way through steady state and partial equilibrium assumptions from a detailed chemical kinetic model for oxidation of methane.

208 citations


Journal ArticleDOI
01 Jan 1988
TL;DR: In this article, the symmetrical counterflow flame configuration and LDV mapping of the velocity profile were used to determine the flame speeds as a function of the equivalence ratio and stretch, as well as the stretch rates and associated flame speeds at the state of extinction.
Abstract: By using the symmetrical counterflow flame configuration and LDV mapping of the velocity profile, we have accurately determined for methane/air and propane/air mixtures their flame speeds as a function of the equivalence ratio and stretch, as well as the stretch rates and the associated flame speeds at the state of extinction. These data are expected to be quantitatively useful for the modeling of more complex flame and combustor phenomena. Results further show that for these mixtures the flame speed mostly increases linearly with increasing stretch, that the flame speed is finite at the state of extinction, and that the extinction limits for nearly adiabatic, stretchless, and planar flames appear to correspond to the flammability limits of the respective mixtures. Implications of the present results on the concept of flammability limits are also discussed.

205 citations


Journal ArticleDOI
01 Jan 1988
TL;DR: In this paper, it was shown that the instability of the annular flow is responsible for the flickering of large diffusion flames, and the authors have confirmed this phenomenon and proposed a theoretical explanation.
Abstract: Large diffusion flames are known to flicker at a frequency (∼12Hz) that is remarkably insensitive to flow rate, burner size, or gas composition. We have confirmed this phenomenon and propose a theoretical explanation. We note that, in addition to the forced convection associated with a tube-burner diffusion flame, there is strong natural convection generated by the hot gases. This bouyancy-induced flow surrounds the forced component and depends only on the thermomechanical properties of the hot and cold gas, together with g , the gravitational acceleration. We argue that it is the instability (of modified Kelvin-Helmholtz type) of this annular flow that is responsible for the flickering. A paradigm for this flow is defined by the infinite candle , an ideal plane diffusion flame in which the flow field is induced solely by buoyancy. The infinite candle admits a similarity solution. An inviscid, parallel flow stability analysis of this flow-field yields a frequency for which the spatial growth of the disturbance is a maximum. This is within a factor of 2 of the observed frequency.

137 citations


Journal ArticleDOI
TL;DR: In this article, the authors model the agglomeration growth process in a diffusion flame via thermophoretic sampling and show that the spherules have a relatively low density of the structure with much open space.
Abstract: Dobbins and Megaridis have observed soot agglomerates in a diffusion flame via thermophoretic sampling. The agglomerates are made up of spherules with a typical diameter of about 30 nm. A characteristic of the agglomerate is the relatively low density of the structure with much open space. This study is concerned with modeling the agglomeration growth process.

110 citations


Journal ArticleDOI
TL;DR: In this article, a laminar flamelet model is applied to turbulent, recirculating premixed combustion in a jet-stirred conical reactor, and the complete statistical description of the thermochemistry is obtained from a one point probability density function (pdf) and detailed chemical kinetic lamin-ar flame structure.

92 citations


Journal ArticleDOI
TL;DR: In this paper, the structure of a strained premixed laminar propane-air flame is examined and a flame is formed in the neighborhood of the stagnation point produced by the counterflow of fresh mixture and hot combustion products.
Abstract: —The structure of a strained premixed laminar propane-air flame is examined. The flame is formed in the neighborhood of the stagnation point produced by the counterflow of fresh mixture and hot combustion products. The governing conservation equations are solved numerically by employing adaptive continuation techniques. The model includes detailed transport and complex kinetics using a reaction scheme due to Warnatz. Flame structures, ignition regimes and extinction regimes are exhibited. The results are in excellent qualitative agreement with the asymptotic theory of Libby and Williams and can be used to develop a flame let description of turbulent premixed propane-air combustion.

84 citations


Journal ArticleDOI
TL;DR: In this paper, an experimental and theoretical study of the structure and radiation properties of luminous, round, turbulent acetylene/air diffusion flames was described, and measurements were made of mean and fluctuating velocities, mean concentrations, laser extinction (514 and 632.8 nm), spectral radiation intensities (1200-5500 nm), and radiative heat fluxes.
Abstract: An experimental and theoretical study of the structure and radiation properties of luminous, round, turbulent acetylene/air diffusion flames is described. Measurements were made of mean and fluctuating velocities, mean concentrations, laser extinction (514 and 632.8 nm), spectral radiation intensities (1200--5500 nm), and radiative heat fluxes. The measurements were used to evaluate structure predictions based on the laminar flamelet concept, and radiation predictions based on a narrow-band model both ignoring and considering turbulence/radiation interactions. State relationships needed for the laminar flamelet concept were found from auxiliary measurements in laminar flames. Predictions were encouraging;however, quantitative accuracy was inferior to earlier findings for luminous flames. This is attributed to the large radiative heat loss fractions of acetylene/air flames (approaching 60 percent of the heat release rate);coupled structure and radiation analysis should be considered for improved results. The findings suggest significant turbulence/radiation interactions (increasing spectral intensities 40--100 percent from estimates based on mean properties);and that soot volume fractions may approximate universal fractions of mixture fraction in turbulent acetylene/air diffusion flames.

84 citations


Journal ArticleDOI
TL;DR: The detailed structure of laminar opposed-flow diffusion flames with a fuel composition of 40% CO, 30% H2, and 30% N2 and an oxidizer composition of 79% N 2 and 21% O2 was calculated over a wide range of stretch conditions (α = 0.1-5000s-1) using 32 elcmenlal chemical reactions and realistic transport properties as mentioned in this paper.
Abstract: The detailed structure of laminar opposed-flow diffusion flames with a fuel composition of 40% CO, 30% H2, and 30% N2 and an oxidizer composition of 79% N2 and 21% O2 has been calculated over a wide range of stretch conditions (α = 0.1-5000s-1) using 32 elcmenlal chemical reactions and realistic transport properties. Previously, when compared to experimental measurements at χ = 70, 180, and 330s-', this model was found to predict peak flame temperatures within 150K. widths of temperature profiles to 20%, and positions of temperature maxima to 0.1 cm. The present paper presents calculations over a wider range of stretch (χ = 0.1-5000s-1) and quantifies the effect of stretch on fundamental flame processes such as preferential diffusion. overlap of fuel and air. superequilibrium radical formation. deviations from partial equilibrium, and extinction. Preferential diffusion of H2 leads to superadiabatic temperatures in the α = 0.1 s-1 flame. Pronounced nonequilibrium effects occur even in the α = 0.1 ...

Journal ArticleDOI
TL;DR: In this article, the propagation of starch-dust air flames has been investigated in a tube (3m long; square cross section 0.2m × 0.4m).
Abstract: Propagation of starch-dust air flames has been investigated in a tube (3 m long; square cross section 0.2 m × 0.2 m). Laminar, cellular and slightly turbulent propagation regimes have been observed. Several analogies with premixed gaseous flames have been displayed. Conduction heat transfer through the flame appears to be predominant for preheating the mixture. The burning of the mixture occurs in the gas phase after complete pyrolysis of particles. The laminar burning velocity is found equal to 0.27 m/s, the quenching distance 7 mm, the flame thickness 3-4 mm and the lean flammability limit 70g/m3. Some questions, such as the actual role of flame radiation, are not yet completely elucidated.

Journal ArticleDOI
TL;DR: In this paper, the effects of fuel dilution and flame temperalure variation on soot formation have been investigated experimentally for counterflow dilTusion flames, and it was shown that dilution contributes to a reduction in the soot volume fraction and dilution accounts for a substantial amount of this reduction.
Abstract: —The isolated effects of fuel dilution and flame temperalure variation on soot formation have been investigated experimentally for counterflow dilTusion flames. The methodology of isolation through temperature adjustment involves changing the concentration of the fuel by diluting it with nitrogen, and then incrcasing the maximum temperature of the diluted flame back to that of the undiluted Rame by replacing a portion of the nitrogen in the oxidizer flow with an equal portion of argon. Soot quantities are determilied by using light-scattering and extinction techniques, flame temperatures by thermocouple measurements, and velocities by LDV mapping. Results on ethylene show that both temperature and dilution contribute to a reduction in the soot volume fraction and dilution accounts for a substantial amount of this reduction. I t is further found that the soot formation rate and specific surface area are linearly dependent on the initial fuel concentration, while the specific surtace growth rate is...

Journal ArticleDOI
TL;DR: In this paper, an asymptotic analysis of the laminar mixing of the simultaneous chemical reaction between parallel supersonic streams of two reacting species is presented, which is based on a one-step irreversible Arrhenius reaction and on large activation energy asymPTotics.
Abstract: The purpose of this paper is to present an asymptotic analysis of the laminar mixing of the simultaneous chemical reaction between parallel supersonic streams of two reacting species. The study is based on a one-step irreversible Arrhenius reaction and on large activation energy asymptotics. Essentially it extends the work of Linan and Crespo to include the effect of free shear and Mach number on the ignition regime, the deflagration regime and the diffusion flame regime. It is found that the effective parameter is the product of the characteristic Mach number and a shear parameter.

Journal ArticleDOI
01 Jan 1988
TL;DR: In this article, the Fourier Transform Infrared Infrared (FT-IR) spectrometer has been extended to include measurements on particles, as well as gases and soot particles.
Abstract: An infrared emission/transmission (E/T) technique, (a method previously used as an in-situ diagnostic for gases and soot particles using dispersive infrared) has been implemented with a Fourier Transform Infrared Infrared (FT-IR) spectrometer and extended to include measurements on particles, as well as gases (CO2, H2O, ethylene, methane, butane, and acetylene) and soot particles. The method can measure both the concentration and temperature of each of the phases. This paper presents the applications of FT-IR E/T spectroscopy to gases and soot particles in reacting flows. Several examples are presented including a coannular laminar ethylene diffusion flame. The results for soot particle temperature and concentration in this flame are in good agreement with measurements reported by other investigators.

Journal ArticleDOI
TL;DR: In this article, the effect of addition of a variety of gases to the silane combustion which proceeds through the following two gross reactions, SiH4 + O2 → SiO2(s) + 2H2

Journal ArticleDOI
TL;DR: In this paper, the authors quantified how the flame temperature increases as swirl is systematically increased; it also quantifies how flame temperature decreases as fuel jet momentum is increased, showing that at high swirl limit, the temperature levels and profile shapes in the non-premixed flame become similar to those of the premixed swirl flame studied by Gouldin.
Abstract: The addition of swirl to a non-premixed flame is known to increase the fuel-air mixing rate, which can cause local premixing and thereby increase flame temperature. The present paper quantifies how the flame temperature increases as swirl is systematically increased; it also quantifies how the flame temperature decreases as fuel jet momentum is increased. Of particular interest are two limits which have not been studied previously in much detail. At the high swirl limit, the temperature levels and profile shapes in the non-premixed flame become similar to those of the premixed swirl flame studied by Gouldin. Thus the rapid internal mixing makes the non-premixed flame behave like a premixed flame. A second limit of interest is the transition from a cooler "jet-like" flame to a hotter "strongly recirculating" flame; the temperature change during this transition is reported and the critical level of swirl and fuel jet momentum required to cause such a transition is quantified. Temperatures were meas...

Journal ArticleDOI
TL;DR: In this paper, the Marble problem of a viscous core vortex interacting with a non-premixed flame is treated, and the analysis is numerical, detailed calculations of the flame structure are performed.
Abstract: Abstract-Combustion in vortex flow fields is of interest in fundamental studies and also because it occurs in many practical situations. Some important analytical contributions to this topic are due to Marble and his students. The Marble problem of a viscous core vortex interacting with a non-premixed flame is treated in the present paper. The analysis is numerical, Detailed calculations of the flame structure are performed.Results obtained confirm intuitive aspects of Marble's analysis. The growth of the core of products is examined. Similarity laws for the radius of this core and for the global reaction rateare verified. Influences of equivalence ratio and Reynolds number are illustrated and discussed.

Journal ArticleDOI
TL;DR: In this paper, the influence of the combustion process on the turbulence structure of combustible jet flows is investigated, and results of numerical prediction methods for such flows embodying various turbulence and combustion models can be compared, with a view to improving our understanding of relevant transport processes and on guiding modelling and prediction efforts of such flows.

Journal ArticleDOI
TL;DR: In this article, some recent measurements of turbulence intensity, turbulerlce length scale and flame structure in valved and ported engines operated at practical conditions are reviewed and the following conclusions are reached: TDC turbulence intensity is homogeneoys and isotropic to within f 30 percent, except near walls, and the turbulent flame in premixed-charges is made up of laminar flames that are wrinkled by the turbulent eddies.
Abstract: Some recent measurements of turbulence intensity, turbulerlce length scale and flame structure in valved and ported engines operated at practical conditions are reviewed and the following conclusions are reached. In an engine, what is turbulence and what is bulk flow is relative to the process that is influenced by the flow; characteristic length and time scales can be used to make the distinction. In the absence of strong squish and/or swirl, TDC turbulence intensity is homogeneoys and isotropic to within f 30 percent, except near walls, and the turbulent flame in premixed-charges is made up of laminar flames that are wrinkled by the turbulent eddies. In many practical conditions, the small-scale tubulent eddies are also likely to interact with the structure of the laminar flame. The interactionwould be stronger for lean flames. Turbulence influences the laminar flame from the very begirining to the very end of combustion. Current zero- and multi-dimensional models of premixed-charge engine comb...

Journal ArticleDOI
TL;DR: In this article, a numerical analysis of the initiation and evolution of a combustion reaction generated by fuel vapor absorption of radiation over an evaporating combustible surface in an oxidizer stagnation point flow is conducted.
Abstract: A numerical analysis is conducted of the initiation and evolution of a combustion reaction generated by fuel vapor absorption of radiation over an evaporating combustible surface in an oxidizer stagnation point flow. The combustible is initially evaporating due to an externally applied irradiance, and is assumed to be in equilibrium vaporization. The transient, stagnation point, gas conservation equations, including one-step Arrhenius type kinetics and fuel vapor absorption of radiation, are solved numerically for the case of PMMA as combustible evaporating in air. Detailed calculations are presented, for a specific case of irradiance and flow velocity, of the evolution of the velocity field, and temperature and species concentration distributions during the ignition of the mixture, and subsequent establishment of a diffusion flame over the combustible surface. Ignition is characterized by thermal run-away of the gas and it is considered to have occurred if, after discontinuing the external irrad...

Journal ArticleDOI
01 Jan 1988
TL;DR: In this article, a theoretical analysis for the propagation and extinguishment of coal dust flames and of dust and gas flames containing inhibitor powders is presented based on the established mechanisms for homogeneous flame propagation and the well known concept of a constant limit flame temperature for a given class of homogeneous fuels.
Abstract: A theoretical analysis is presented for the propagation and extinguishment of coal dust flames and of dust and gas flames containing inhibitor powders. The analysis is based on the established mechanisms for homogeneous flame propagation and the well known concept of a constant limit flame temperature for a given class of homogeneous fuels. The analysis is expanded to phase-heterogeneous systems such as coal dust by means of a volatility model. The analysis includes the singly heterogeneous system of a solid fuel dust in air; the singly heterogeneous solid inhibitor dust in a homogeneous fuel-air flame: and the doubly heterogeneous system consisting of a solid fuel and inhibitor dust mixture in air. The data for measured explosion pressures, flammability limits, and extinguishant requirements for heterogeneous systems are shown to be consistent with the established mechanisms and processes for homogeneous flame propagation provided that one adds an additional process: the heating and devolatilization of the solid fuel or inhibitor. The limitations on the rates of devolatilization of the solid particles become rate controlling at high burning velocities, at high dust loadings, and for large particle sizes. Devolatization rates are controlled by the intrinsic devolatilization rate constant for the solid fuel or inhibitor and the effective heating flux of the approaching flame front. The effective vield of volatiles is a function of those factors, the decomposition chemistry, and the time available for devolatilization. The fraction of the total volatiles that can be generated in the time available is the β-factor, and it determines the effective yield of fuel or inhibitor that participates in the flame propagation process. The data for explosion pressure, Flammability limits, and extinguishant requirements are readily understood in terms of those β-factors.

Journal ArticleDOI
TL;DR: In this article, a turbulent combustion model for a CO/H2/N2-air turbulent jet diffusion flame has been developed by combining a velocity-composition joint pdf turbulence closure, a Monte Carlo solution algorithm, and a two-scalar stretched laminar f1amelet chemistry approach.
Abstract: —A turbulent combustion model for a CO/H2/N2-air turbulent jet diffusion flame has been developed by combining a velocity-composition joint pdf turbulence closure, a Monte Carlo solution algorithm, and a two-scalar stretched laminar f1amelet chemistry approach In the flamelet model, it is assumed that the structure of the turbulent diffusion flame is locally that of a laminar diffusion flame at the same instantaneous value of the mixture fraction (ξ) and scalar dissipation (X) A library of stretched laminar flamelets (density, temperature, and species concentrations vs, ξ and X) is generated for a laminar opposed-flow configuration including 15 chemical species, 32 reactions, and differential diffusion A modeled transport equation for the joint probability density function of the velocities, ξ, and X is then solved numerically by a Monte Carlo method Calculated profiles of mean mixture fraction, temperature, and species concentrations are compared both with experimental data and with earlier

Journal ArticleDOI
01 Jan 1988
TL;DR: In this article, the evolution of large-scale structures in a two-dimensional temporally developing mixing layer was examined by examining the local quenching of a diffusion flame, and the primary important parameter to be considered for flame extinction is the local instantaneous scalar dissipation rate, conditioned at the scalar stoichiometric value (Xst).
Abstract: Nonequilibrium effects leading to the local quenching of a diffusion flame were investigated by examining the evolution of large-scale structures in a two-dimensional temporally developing mixing layer. Pseudospectral calculations of a temperature-dependent, nonpremixed, constant-density, reacting shear layer indicate that the primary important parameter to be considered for flame extinction is the local instantaneous scalar dissipation rate, conditioned at the scalar stoichiometric value (Xst). At locations where this value is increased beyond a critical value (Xq), the local temperature decreases and the instantaneous reaction rate drops to zero. This is consistent with the results of perturbation methods employing large activation energy asymptotics for the study of flame extinction in nonpremixed flames.

Journal ArticleDOI
TL;DR: In this article, the role of metallic fuel additives in relation to soot suppression in a well defined laboratory-scale diffusion flame was clarified, where the additives were in the form of aqueous solutions of salts of the preceding metals.
Abstract: Experiments were performed to clarify the role of metallic fuel additives in relation to soot suppression in a well defined laboratory-scale diffusion flame. Principal emphasis was given to three alkaline-earth metals; namely, Ba, Sr and Ca. The experiments included Cu, Sn, Li, Na and K as well. but only to the extent that the latter contributed to understanding the details of alkaline-earth behavior. The additives were in the form of aqueous solutions of salts of the preceding metals. The solutions were aspirated into the oxidant flow of a nearly two-dimensional laminar C:H/air flame emanating from a symmetric Wolfhard-Parker burner. Soot size, number density and volume fraction were determined from Mie scattering. Metal species concentrations were determined semiempirically by combining H-measurements with known equilibrium constants for the metal/radical reactions occurring in the flame. The flame temperature was measured via sodium line reversal. The alkaline-earth metals were observed to alt...

Journal ArticleDOI
TL;DR: In this article, the authors used global reaction schemes involving only major species and found that the critical parameter determining name extinction is the maximum reaction zone temperature, which is found to be in acceptable agreement with measurements.
Abstract: —Counterflow diffusion flames burning undiluted and diluted methane-air and propane-air mixtures have been computed using global reaction schemes involving only major species. Agreement for the undiluted methane-air and propane-air flames has been found to be excellent and realistic variations of species profiles with increasing rates of strain are obtained. Computations of diluted methane-air flames at different rates of strain confirm the experimental findings that the critical parameter determining name extinction is the maximum reaction zone temperature, which is found to be in acceptable agreement with measurements. The critical fuel concentration at the limit of low strain for the case of fuel diluted with nitrogen is also in acceptable agreement with measurements. Effects of varying degrees of approximation of transport properties is also investigated, including the common approximation of unity Lewis numbers. Implications of the results as regards to the inclusion of direct kinetic effect...

Journal ArticleDOI
01 Jan 1988
TL;DR: In this article, a non-unity Lewis number interpretation of stretched flame phenomena was presented, and it was shown that deviations of the flame temperature from the adiabatic flame temperature can occur only in the simultaneous presence of stretch and preferential diffusion.
Abstract: Flame temperature distributions over axisymmetric and two-dimensional Bunsen flames have been experimentally measured for methane, ethylene, and propane mixtures with air, and interpreted on the basis of preferential diffusion and aerodynamic stretching induced by flame curvature. Results substantite the validity of the non-unity Lewis number interpretation of stretched flame phenomena, verify the theoretical prediction that deviations of the flame temperature from the adiabatic flame temperature can occur only in the simultaneous presence of stretch and preferential diffusion, and demonstrate that such a deviation can be correlated by a nondimensional stretch factor for extensive experimental data obtained with various concentrations, flow velocities, and nozzle diameters. Identification of such a correlation strongly suggests the possibility of synthesizing the diverse experimental data on stretched flames in accordance with the generalized expression derived theoretically.

BookDOI
01 Jan 1988
TL;DR: In this paper, a nonlinear elliptic problem describing the propagation of a curved mixture of flames is described, and an algorithm for allocating and temperature, and its consequences for the chemistry of H2-O2-combustion is presented.
Abstract: Reminiscences on the Life and Work of G.S.S. Ludford.- I : Invited Lectures.- A Nonlinear Elliptic Problem Describing the Propagation of a Curved Premixed Flame.- Mathematical Modeling in the Age of Computing : Is it redundant ?.- Combustion and Compressibility in Gases.- Cool Flame Propagation.- Modeling the Chemistry in Flames.- Computer Simulation of 2D/3D Reacting Flows in Complicately Shaped Regions for Engineering.- Radiative Transfer in Unsteady, Weakly Curved, Particle-Laden Flames.- Numerical Simulation of Coherent Structures in Free Shear Flows.- Diffusion Flame Attachment and flame front propagation along mixing layers.- Some Remarks on Turbulent Combustion from the Attractor Point of View.- Grid Requirements Due to the Inner Structure of Premixed Hydrocarbon Flames.- Nonlinear Studies of Low-Frequency Combustion Instabilities.- Nonlinear Effects of Blow Up and Localization Processes in Burning Problems.- Remarks on the Stability Analysis of Reactive Flows.- Experiments with Premixed Flames.- Solution of Two-Dimensional Axisymmetric Laminar Diffusion Flames by Adaptive Boundary Value Methods.- Shock Induced Thermal Explosion.- Influences of Detailed Chemistry on Asymptotic Approximations for Flame Structure.- II : Shorter Papers.- Numerical Study of Particle-Laden Jets: A Lagrangian Approach.- Mathematical Modelisation of Enclosed Combustion at Constant or Variable Pressure by Vibe Law.- Experimental and Numerical Study of a Heated Turbulent Round Jet.- Interet des Methodes de Calculs en Combustion dans le Developpement des Foyers de Turboreacteurs.- Characterizing Self-Similar Blow-Up.- Some Finite-Element Investigations of Stiff Combustion Problems : Mesh Adaption and Implicit Time-Stepping.- Modeling of Turbulent Diffusion Flames with Detailed Chemistry.- Kinetic Modelling of Light Hydrocarbons Combustion.- Application de Methodes Variationnelles a une Combustion Turbulente Premelangee, Homogene et Stationnaire.- A Minimal Model for Turbulent Flame Fronts.- A Theoretical Study of Air-Solid Two-Phase Flows.- Dynamic Transition of a Self-Igniting Region.- Numerical Model for Turbulent Reactive Flows with Swirl.- Experimental Analysis on the Stability of an Oblique Flame Front.- Vector Computers and Complex Chemistry Combustion.- Numerical Model for Propellant Grain Burning Surface Recession.- Global Existence of Solutions for a Problem in Dynamics of Thermal Explosions.- Elements Finis Autoadaptatifs a Multimaillages pour le Calcul de Vitesses de Flamme.- Flammes minces et interfaces.- Second Order Remeshing Method in 2D Lagrangian Fluid Dynamics.- On Numerical Analysis of Two-Dimensional, Axisymmetric, Laminar Jet Diffusion Flames.- An Algorithm for Allocation and Temperature, and its Consequences for the Chemistry of H2-O2 Combustion.- Existence and Stability in a Plane Premixed Flame Problem.- Computation of Turbulent Diffusion and Premixed Flames with Radiation.


Journal ArticleDOI
TL;DR: In this article, measurements of luminous flame extensions under steady burning conditions are presented for a range of energy supply rates up to 400 kW and burner-to-ceiling heights up to 2·3 m.