Strained Diffusion Flames Research Articles

Reduced chemical reaction mechanisms for simulating sodium emissions by solid-fuel combustion

Starting from a reference and comprehensive chemical mechanism for alkali metal emissions (Glarborg and Marshall, 2005), combined with an hydrocarbon oxidation described with a skeleton mechanism (Kazakov and Frenklach, 1994), reduced and optimized chemical kinetics are derived. The objective is to provide a set of chemical schemes useful for three-dimensional (3D) numerical simulations of alkali metal emissions by pulverized solid-fuel combustion systems. An automated procedure relying on one-dimensional (1D) premixed flames is applied to obtain a combined reduced mechanism, whose performance is then evaluated in one-dimensional strained diffusion flames, micro-mixing based canonical problems and three-dimensional carrier-phase direct numerical simulation (DNS) of coal combustion. Predictions of the reduced mechanism on major sodium species, i.e., Na, NaOH, NaCl and Na2SO4 agree well with that of the detail reference scheme under all the considered conditions. A parametric study with 14 two-dimensional (2D) DNS cases is then performed to better understand the reactive flow properties and estimate the prediction capabilities of the reduced mechanism for various Na/Cl/S ratio in the volatiles. After pursuing the chemistry reduction, a global sodium mechanism with only 9 species and 8 reaction-steps is also discussed. The systematic comparison between the 3D DNS results obtained with the reference chemical scheme against those with the reduced ones confirm the validity of the reduction strategy. A reduction of up to 84% in computational cost is reached with the optimized global scheme, thus allowing for addressing real pulverized-coal combustion systems.

The barely implicit correction algorithm for low-Mach-Number flows II: Application to reactive flows

In this paper, the Barely Implicit Correction (BIC) algorithm is applied to the simulation of low-Mach-number, reactive flows. The BIC algorithm is a solution procedure consisting of an explicit predictor step to solve the convective portion of the Navier-Stokes equations and an implicit corrector step which removes the acoustic limit on the integration time step. We show how to include reaction processes into the BIC integration procedure. The algorithm is then applied to four test problems with successively increased difficulty. First, a series of one-dimensional flames are computed, showing that BIC can reproduce the correct flame properties. Second, simulations of two-dimensional counter-flow diffusion flames show that the integration procedure can compute the structure of a strained diffusion flame. Third, triple flames are computed and the results show that BIC can compute complex and multi-dimensional heat release structures. Finally, simulations of a three-dimensional, unsteady fire whirl show that the algorithm can compute complex heat release structures in a turbulent vortex flow field. These results indicate that the algorithm is robust, stable for flows with combustion, and can be used to study a wide variety of reactive flows.

Simulations of a turbulent line fire with a steady flamelet combustion model coupled with models for non-local and local gas radiation effects

The general objective of this study is to develop accurate combustion and radiation models for large eddy simulations (LES) of well-controlled laboratory-scale turbulent fires. The combustion model features a library of flamelet solutions corresponding to steady, laminar, strained diffusion flames. The radiation model features a classical description of non-local radiation phenomena through the Radiative Transfer Equation (RTE). Different treatments of coupled combustion and radiation effects at flamelet scale are considered: a treatment in which local radiation phenomena are neglected inside the flamelet solver; and a treatment in which these phenomena are included inside the flamelet solver and also subgrid-scale turbulence-radiation interactions are included in the RTE solver. This modeling framework is incorporated into the LES solver FireFOAM, developed by FM Global. It is evaluated in simulations of a buoyancy-driven, methane-air, turbulent diffusion flame experimentally characterized by measurements of local temperatures and global flame emissive power. Comparisons between simulated and measured temperatures show significant discrepancies that may be explained by overestimated values of the width of the presumed probability density function representing subgrid-scale variations of mixture fraction. Similar comparisons for the global radiative loss fraction show good agreement provided that local radiation phenomena and turbulence-radiation interactions are included in the model.

Automatic reduction and optimisation of chemistry for turbulent combustion modelling: Impact of the canonical problem

In a preliminary part, reduced chemical schemes from the literature on methane/air turbulent combustion are tested in one-dimensional premixed flames at various equivalence ratios. As discussed by Peters (1985), for the very same number of chemical species transported with the flow, a scheme introducing essential intermediate species through analytical relations derived from quasi-steady state and equilibrium assumptions, provides much better predictions than the global schemes limited to the transported species. Along these lines, a fully automated reduction procedure is discussed. The calibration of reduced chemistry usually relies on canonical problems, also computed with reference detailed chemical schemes. To cover at once a given range of chemical compositions, equivalence ratios and temperatures, the chemical properties of stochastic particles, submitted to micro-mixing and chemical reactions, are combined with the computation of deterministic one-dimensional composition-space trajectories, issued from an arbitrary number of inlet conditions. Along these trajectories, well-established methods to reduce the numbers of species and reactions are applied, cast in a fully automated manner. The rates of the resulting reduced scheme are then optimised, following a genetic algorithm, to match the detailed chemistry response. The discussed strategy is applied to methane/vitiated-air combustion. The accuracy of the resulting reduced scheme is evaluated in the simulation of freely propagating one-dimensional premixed flames, at various equivalence ratios, and also in strained diffusion flames in a one-dimensional counter-flowing jet configuration, up to the quenching point. The accurate reproduction of the flame speed response versus equivalence ratio requires adding premixed flames as target in the optimisation loop. Once the flame speed is captured, the quenching scalar dissipation rate of the diffusion flames is also well reproduced, as anticipated by Peters in a relation between the flame speed and the quenching scalar dissipation rate (Peters, 1991, 2000). Finally, the optimisation of the chemical rates is demonstrated under specific operating conditions, featuring four inlets with a large variety of flow compositions.

Combustion characteristics of C4 iso-alkane oligomers: Experimental characterization of iso-dodecane as a jet fuel surrogate component

Global combustion characteristics of iso-dodecane (2,2,4,6,6-pentamethylheptane, iC12) are measured and compared to those of iso-octane (2,2,4-trimethylpentane, iC8), iso-cetane (2,2,4,4,6,8,8-heptamethylnonane, iC16) and a 50/50 molar blend of iC8/iC16. The fuels are experimentally characterized by measuring combustion property targets (derived cetane number and smoke point/threshold sooting index), reflected shock ignition delay times at 20 and 40 atm, and extinction limits of strained laminar diffusion flames at 1 atm. The derived cetane number (DCN) and threshold sooting index (TSI) of iC12 are measured to be 16.8 (±1) and 15.4 (±0.5), respectively. In addition to average molecular weight (MW) and overall hydrogen-to-carbon ratio (H/C ratio), the combustion property targets for iC12 are very nearly molar averages of those for iC8 and iC16. Values agree very well with the measured combustion property indicators for the 50/50 blend of iC8/iC16. Further analysis of fuel chemical functional group distributions also finds that the abundances of methylene and methyl groups in iC12 and the 50/50 blend of iC8/iC16 are identical, further supporting that the global combustion characteristics of iC12 can be emulated by the molar averaged mixture of iC8 and iC16. Measurements of reflected shock ignition delays show that the ignition delay times of iC12 are in close agreement with those of the 50/50 molar mixture of iC8/iC16 over a broad range of temperature conditions. It is also found that the ignition delays of the three neat iso-alkanes exhibit quantitatively identical behaviors for both high and low temperature regimes, an observation that can guide the construction of combustion kinetic models for iC12. Measurements of strained diffusion flame extinction and their interpretation by the transport-weighted enthalpy (TWE) metric also support that the high temperature chemical kinetic potentials of the three iso-alkanes are essentially identical. Moreover, it is shown that molecular diffusivity (inherent in molecular weight) is the major parameter that differentiates flame extinction behaviors amongst the three iso-alkanes. In summary, this experimental study further supports the utility and characteristics of combustion property target formulation concepts for producing mixtures that emulate the pre-vaporized global combustion properties of a specific target fuel. The work also points to a strong correlation of the combustion property target data for these iso-alkanes with methylene and methyl functional group distributions for each fuel.

Assessing LES models based on tabulated chemistry for the simulation of Diesel spray combustion

In the context of large-eddy simulation (LES) of Diesel engine combustion, two LES combustion models are proposed. Their ability to predict autoignition delays and heat release of an autoigniting liquid α-methylnaphthalene/n-decane jet injected into a constant-volume chamber under Diesel-like conditions is assessed. These models retain the tabulation of a complex chemistry scheme using autoigniting homogeneous reactors (HR) at constant pressure. This allows accounting for the chemical complexity of heavy hydrocarbon fuels over the wide range of conditions representative for Diesel engines, at comparatively low CPU time overhead. The tabulated homogeneous reactor (THR) approach assumes the local structure of the reaction zone to be that of an HR, while the approximated diffusion flame (ADF) approach is based on autoigniting strained diffusion flames. Two variants of each approach are considered, either neglecting sub-grid-scale mixture fraction variance (THR and ADF models), or accounting for it via a presumed β-PDF (THR-pdf and ADF–PCM models). LES results indicate that the ADF model assuming diffusion flame structures tends to predict faster propagation of the combustion toward less reactive mixture fractions then the THR model. Moreover, neglecting the mixture fraction fluctuations strongly overestimates initial experimental heat release rates after autoignition. Comparison between models shows that this assumption yields higher reaction rates and temperature levels close to the stoichiometric mixture fraction zones. Predictions in terms of autoignition are remarkably close with all models, and exhibit very few variations from one realization to the other. Variations in global heat release rate become more apparent for different realizations at later instants, in relation to the interaction of large flow scales with combustion.

Multidimensional flamelet-generated manifolds for partially premixed combustion

Flamelet-generated manifolds have been restricted so far to premixed or diffusion flame archetypes, even though the resulting tables have been applied to nonpremixed and partially premixed flame simulations. By using a projection of the full set of mass conservation species balance equations into a restricted subset of the composition space, unsteady multidimensional flamelet governing equations are derived from first principles, under given hypotheses. During the projection, as in usual one-dimensional flamelets, the tangential strain rate of scalar isosurfaces is expressed in the form of the scalar dissipation rates of the control parameters of the multidimensional flamelet-generated manifold (MFM), which is tested in its five-dimensional form for partially premixed combustion, with two composition space directions and three scalar dissipation rates. It is shown that strain-rate-induced effects can hardly be fully neglected in chemistry tabulation of partially premixed combustion, because of fluxes across iso-equivalence-ratio and iso-progress-of-reaction surfaces. This is illustrated by comparing the 5D flamelet-generated manifold with one-dimensional premixed flame and unsteady strained diffusion flame composition space trajectories. The formal links between the asymptotic behavior of MFM and stratified flame, weakly varying partially premixed front, triple-flame, premixed and nonpremixed edge flames are also evidenced.

On the sublimit solution branches of the stripe patterns formed in counterflow diffusion flames by diffusional–thermal instability

The nonlinear dynamics of striped diffusion flames, formed in a two-dimensional counterflow by diffusional–thermal instability with Lewis numbers sufficiently less than unity, is investigated numerically by examining various two-dimensional flame-structure solutions bifurcating from the one-dimensional steady solution. The Lewis numbers for fuel and oxidizer are identically set to be 0.3, and an overall single-step Arrhenius-type chemical reaction with a Zel'dovich number of 7 is employed as the chemistry model. Particular attention is focused on the flame-stripe solution branches in the sub-extinction regime and on the hysteresis encountered during the transition between different solution branches. In the numerical simulations, a nonlinear solution with eight stripes is first realized from the one-dimensional solution at a Damköhler number slightly greater than the extinction Damköhler number. The eight-stripe solution survives Damköhler numbers much smaller than the extinction Damköhler number until successive bifurcations, leading to the doubling of the pattern wavelength, occur at the subsequent forward-transition conditions. At the first forward-transition Damköhler number occurs the transition to a four-stripe solution, which in turn transits to a two-stripe solution at the second forward-transition Damköhler number, a value somewhat smaller than the first. However, further transition from a two-stripe solution to a one-stripe solution is not always possible even if a one-stripe solution can be accessed independently for particular initial conditions. The Damköhler-number ranges and shapes for the two-stripe and one-stripe solutions are found to be virtually identical, implying that each stripe could be an independent structure if the distance between stripes is sufficiently large. By increasing the Damköhler number, backward transitions can be observed. In comparison with the forward-transition Damköhler numbers, the corresponding backward-transition Damköhler numbers are always much greater, thereby indicating significant hysteresis between the stripe patterns of strained diffusion flames.

대향류 확산화염에서 확산-전도 불안정의 비선형 거동에 대한 수치해석

Nonlinear dynamics of striped diffusion flames, by the diffusional-thermal instability with Lewis numbers sufficiently less than unity, is numerically investigated by examining various two-dimensional flame-structure solutions. The Lewis numbers for fuel and oxidizer are assumed to be identical and an overall single-step Arrhenius-type chemical reaction rate is employed in the model. Particular attention is focused on identifying the flame-stripe solution branches corresponding to each distinct stripe pattern and hysteresis encountered during the transition. At a Damkohler number slightly greater than the extinction Damkohler number, eight-stripe solution first emerges from one dimensional solution. The eight-stripe solution survives Damkohler numbers much smaller than the extinction Damkohler number until the transition to four-stripe solution occurs at the first forward transition Damkohler number. At the second forward transition Damkohler number, somewhat smaller than the first transition Damkohler number, the transition to two-stripe solution occurs. However, any further transition from two-stripe solution to one-stripe solution is not always possible even if one-stripe solution can be independently accessed for particular initial conditions. The Damkohler number ranges for two-stripe and one-stripe solutions are found to be virtually identical because each stripe is an independent structure if distance between stripes is sufficiently large. By increasing the Damkohler number. the backward transition can be observed. In comparison with the forward transition Damkohler numbers, the corresponding backward transition Damkohler numbers are always much greater, thereby indicating significant hysteresis between the stripe patterns of strained diffusion flames.

Structural Studies of Locally Strained Diffusion Flames. 4th Report. Analysis on Characteristics of Positively and Negatively Stretched Flames.

Numerical analysis is made on the H2/N2-air nonpremixed laminar counterflow diffusion flames with positive or negative stretch rate induced by locally sucking flow from fuel and air side. Adjusting the suction velocity forms typical three flames of flat shape and concave or convex curvature. Numerical computations taking into account detail chemical kinetics and multi-conponent diffusion makes it clear the effects of negative stretch rate on the flame structure and characteristics. In addition, the effects of preferential diffusion In relation to the flame curvature under the negative stretch are discussed. The results show that (1) Temperature increases with decreasing the stretch rate, and the tendency is the same even in the negative stretch rate. (2) H. concentration due to the preferential diffusion and excess enthalpy due to nonunity Lewis number effect becomes relatively significant with decreasing the stretch rate. This is one of the reasons of (1). (3) Temperature increasing due to the negative stretch rate depends on the flame curvature. (4) The maximum flame temperature cannot be rationlized by local stretch rate, and changes widely depending on the preferential diffusion in relation to flame curvature.

On PAH formation in strained counterflow diffusion flames

The structural response of methane/air and methane-nitrogen/air counterflow diffusion flames to strain was investigated by measurements and computations. The numerical predictions were found to be in reasonably good agreement with the experiments. Different reaction pathways leading to PAH formation are examined computationally to obtain a deeper understanding of the process of soot precursor formation in strained diffusion flames. Both experimental and computational results indicate that the concentration of C 2H 2 and C 3H 3, as well as that of the PAH, leading candidates for soot precursor formation, diminish with increasing strain rates. The decrease of the PAH is caused by a depletion of the benzene precursors. In looking to find control parameters for strained reactive flows, it is suggested to image strain rates based on the CH 2O, respectively CHO, to C 2H 2 ratio.

Nonlinear dynamic characteristics of flame stripes formed in strained diffusion flames by diffusional—thermal instability

The nonlinear dynamics of striped diffusion flames, formed in the two-dimensional counterflow field by the diffusional-thermal instability with Lewis numbers sufficiently less than unity, is investigated numerically by examining the nonlinear two-dimensional transient flame-structure solutions bifurcating from the one-dimensional steady solution by various initial perturbations. The Lewis numbers for the fuel and oxidizer are assumed to be identical and an overall single-step Arrhenius-type chemical reaction rate is employed as the chemistry model. Attention is focused on two nonlinear phenomena, namely the development of the two-dimensional flame-stripe structure and the extension of the flammability limit beyond the static extinction condition of a one-dimensional flame. A time-dependent solution, carried out for a Damköhler number slightly above the static extinction Damköhler number, exhibited the developmental procedure of flame stripes with the most unstable wavelength from a long-wave initial perturbation with a small amplitude. In contrast to the chaotic cellular premixed-flame structures predicted from numerical integration of the Kuramoto-Sivashinsky equation, the stripe structure in diffusion flames is found to be stationary, consequently leading to the conclusion that the nonlinear term in the corresponding nonlinear bifurcation equation would be a simple cubic term. Two-dimensional flame-stripe solutions are also found to be able to survive Damköhler numbers significantly below the static extinction Damköhler number of the one-dimensional flame structure. Extension of the flammability is found to be greatest if the imposed initial perturbation possesses the wavenumber of the fastest growing mode.

Direct numerical simulation of heat release and NOx formation in turbulent nonpremixed flames

Attempts to use complex chemistry and transport in direct numerical simulations (DNS) of premixed combustion (even for kinetically simple systems, such as H2/air and CH4/air) often result in excessive needs of memory and CPU time. This paper presents a methodology (integrated combustion chemistry [ICC]) capable of integrating complex chemistry effects into DNS while maintaining computational efficiency. The methodology includes the use of a limited number of species and reactions with parameters which are derived to match a number of flame properties. It is illustrated through a four-step reaction mechanism appropriate for a stoichiometric methane/air flame, and which compares favorably with predictions of the detailed gri 2.11 mechanism. The proposed scheme includes one reaction for the methane oxidation, one for the thermal, one for the Fenimore, and one for the nonpremixed reburn chemical NOx routes. The kinetic parameters for the hydrocarbon oxidation were determined by matching the gri 2.11 predictions for laminar burning velocity and adiabatic flame temperature, main reactants concentrations, and extinction strain rates for both premixed (steady) and nonpremixed (steady and unsteady) strained laminar flames. The chemical parameters for the three steps corresponding to NOx chemistry were determined by matching the NOx profiles obtained for strained diffusion flames with gri 2.11. Finally, this four-step mechanism was used in DNS of two- and three-dimensional turbulent nonpremixed combustion to assess the validity of flamelet approaches. While the flamelet approaches were found to perform well for heat release, their extension to NOx formation appears to be not as successful because of the existence of compressed zones where products accumulate and increase the NOx production.

Structure and acoustic-pressure response of hydrogen–oxygen diffusion flames at high pressure

The flame structures and extinction characteristics of undiluted hydrogen–oxygen strained diffusion flames at high pressures with detailed and reduced chemistry are numerically studied with an intention of application to acoustic instabilities of rocket engines. The numerical results of extinction strain rate for undiluted hydrogen–oxygen flames are found to be qualitatively different from those for hydrogen–air flames in that extinction strain rate for undiluted hydrogen–oxygen flames increases linearly with pressure up to 100 atm whereas extinction strain rate for hydrogen–air flames saturates around 50 atm. Comparison of the characteristic flow time with the characteristic chemical time shows that extinction strain rate varies linearly with pressure for flames controlled by two-body chain-branching reactions that are found to be dominant up to 100 atm. The four-, three-, and two-step reduced mechanisms are also tested to exhibit that the linearity of the extinction strain rate with pressure is preserved. Based on these results, the asymptotic methods, previously used in low-pressure hydrogen–air flames, can be extended to predict the asymptotic structure of hydrogen–oxygen flames at high pressures. On the other hand, the fall-off effect and real-gas effect are found to be minimal on extinction characteristics. Since the characteristic flow time is estimated to be several orders of magnitude shorter than the characteristic acoustic time in rocket engines, acoustic responses are satisfactorily reproduced from the quasisteady flame structures. Finally, the sensitivity analysis identifies the reaction step, H + O 2 + M → HO 2 + M as a favorable reaction path to stabilize acoustic oscillations by depressing the reaction rate.

Structual Studies of Locally Strained Diffusion Flames. 1st Report. Observation of Temperature Characteristics and Flame Extinction.

Experimental studies are made of H2/N2-air laminar counterflow diffusion flames strained by impinging micro fuel or air jet from fuel or air side. Direct observation and two-dimensional temperature measurements by laser Rayleigh scattering method reveal the following phenomena. (1) The flame strained by the micro fuel jet from the fuel side is easily quenched locally, but the flame strained from the air side hardly extinguishes and the flame temperature tends to increase. (2) The flame is extinguished by higher strain rate even in the case of impinging micro air jet. (3) Relighting is observed at the place far from the initial flat flame. Phenomenological discussions with respect to preferential diffusion and flame curvature effects are included.

Structural Studies on Locally Strained Diffusion Flames. 3rd Report. Analysis on Local Flame Extinction and Reignition Phenomena of Unsteady Strained Flames.

Experimental and numerical studies are made of transient H2/N2-air counterflow diffusion flames unsteadily strained by an impinging micro jet. Two-dimensional temperature measurements by the laser Rayleigh scattering method and numerical computations taking into account detailed chemical kinetics reduce the following results. (1) Transient local flame extinction is observed where the micro jet impinges. The transient flame can survive instantaneously in spite of the quite high stretch rate where the steady flame cannot exist. (2) Reignition is observed after the local extinction induced by an impinging micro air jet. The predicted behaviors of the local transient extinction and reignition are well confirmed by the experiment. (3) The reignition is hardly observed after the extinction by the micro fuel jet impingement. (4) These characteristic phenomena of (2) or (3) are dominated by the concentration or dilution of H2 due to the preferential diffusion with the concave or convex flame curvature, respectively. (5) The maximum flame temperature cannot be rationalized by the stretch rate but changes widely depending on the unsteadiness and the flame curvature in relation to preferential diffusion.

Acoustic response of droplet flames to pressure oscillations

The acoustic pressure response of spherical H 2 /liquid oxygen droplet flames is studied by the premixed-flame regime of activation-energy asymptotics to examine acoustic Instability mechanisms in liquid-propellant rocket engines. Depending on the diameters of the droplets, the combustion condition is classified as near-equilibrium or near-extinction, and the acoustic pressure response for each condition is determined for a wide range of the acoustic frequency. Compared with the results previously obtained for strained diffusion flames, the reaction sheet of the droplet flame is found to exhibit a behavior similar to that of strained diffusion flames, in that the reaction sheet moves toward the oxidizer boundary, at which the mass flux of the oxidizer is greater, to balance the high reactivity during the period of high acoustic pressure. Oscillations of the reaction sheet also give rise to an additional attenuation mechanism, associated with reduction of the reaction-surface area, thereby resulting in a much smaller response of the heat-release rate for droplet flames than that for strained diffusion flames.

Unsteady counterflowing strained diffusion flames: diffusion-limited frequency response

A detailed numerical study has been conducted on the effect of unsteadiness on the dynamics of counterflowing strained diffusion methane/oxygen/nitrogen flames. The modelling included the solution of the unsteady conservation equations of mass, momentum, energy, and species along the stagnation streamline in an opposed jet using detailed descriptions of chemistry and transport. The unsteadiness was introduced by independently imposing sinusoidal variations of the reactant velocity, concentration and temperature at the exits of the nozzles. The results demonstrate that the flame's response is quasi-steady at low frequencies, while at higher frequencies the amplitudes of the induced oscillations are reduced and phase shifted with respect to the imposed signal. At still higher frequencies, the flame no longer responds to the oscillations in the external field. A rigorous physical explanation of the frequency response was provided from first principles by identifying that oscillations imposed at the nozzle exits result in reactant concentration and temperature oscillations at the outer edge of the preflame diffusive zones. The diffusion attenuates the oscillations in this zone in a manner analogous to the velocity attenuation in Stokes’ second problem. The validity of the analogy was confirmed by examining flames over a wide range of frequencies and initial conditions. The current analysis also provided a criterion for the cutoff frequency separating the quasi-steady and transient regimes – information which can be useful in the establishment of laminar flamelet libraries.

On strained flames with hypergolic reactants: The H2/NO/F2 system in high-speed, supersonic and subsonic mixing-layer combustion

We report on a numerical investigation on the dynamics and structure of strained, non-premixed and premixed, H_2/NO/F_2 flames. This is an important, hypergolic reacting system that has been used in high- power chemical-laser systems and, presently, relied upon in experimental studies of high-speed, supersonic and subsonic, turbulent shear-layer mixing and combustion. The study included a detailed description of the chemical kinetics and molecular transport for the H_2 /NO/F_2 system and was conducted for a wide range of reactant concentrations and inert diluents, with flow/chemical parameters chosen to correspond to specific chemically reacting, supersonic mixing-layer experiments. Both non-premixed and premixed flames were studied using opposed-jet flow configurations. The results confirmed the experimental conclusion that, even at low reactant concentrations, the H_2/NO/F_2 system can sustain high Damkohler number chemical activity at high strain rates with room-temperature free streams. A comparison between the results of the present numerical simulations and the experimental chemically reacting mixing-layer studies, however, indicates that the predominant fraction of product formation in high-speed, turbulent, mixing layers must take place in a mode in which the reactants are in premixed, rather than in non-premixed, strained diffusion flames.

95/06369 Soot formation in strained diffusion flames with gaseous additives

95/06369 Soot formation in strained diffusion flames with gaseous additives