The asymptotic structure of counterflow diffusion flames for large activation energies

Liñán, A.

doi:10.1016/0094-5765(74)90066-6

Cited by 770 publications

(180 citation statements)

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“…They play a significant role in flame attachment, lift-off, ignition and reignition processes of non-premixed systems. Many theoretical and experimental studies have been devoted to the structure and propagation of triple flames from various viewpoints [1][2][3][4][5][6][7][8]. However, fewer studies on NO X formation in triple flames have been reported.…”

Section: Introductionmentioning

confidence: 99%

A numerical investigation on NOX formation in counterflow n-heptane triple flames

Guo

Smallwood

2007

International Journal of Thermal Sciences

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/npsi/ctrl?action=rtdoc&an=6597458&lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=6597458&lang=frAccess and use of this website and the material on it are subject to the Terms and Conditions set forth at http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. For the publisher's version, please access the DOI link below./ Pour consulter la version de l'éditeur, utilisez le lien DOI ci-dessous.http://dx.doi.org/10.1016/j.ijthermalsci. 2006.11.002 International Journal of Thermal Sciences, 46, September, pp. 936-943, 2007 A numerical investigation on NOx formation in counterflow n-heptane triple flames Guo, Hongsheng; Smallwood, Gregory J. AbstractThe formation of NO X in counterflow n-heptane/air triple flames was investigated by numerical simulation. Detailed chemistry and complex thermal and transport properties were employed. The results indicate that a triple flame produces more NO and NO 2 than the corresponding premixed flames due to not only the appearance of the diffusion flame but also the interaction between different flame branches. The relative contributions of different routes to NO formation in the premixed flame branches change with the variation of the equivalence ratio, but the thermal mechanism always dominates in the diffusion flame branch. The interaction between flame branches is enhanced with the decrease of the distance between them. Both heat and radical exchange between flame branches contribute to the interaction. A new feature that does not exist in methane/air triple flame was observed in n-heptane/air triple flames, i.e. when the rich mixture equivalence ratio is higher, there are two peaks of CH concentration on the rich side of the diffusion flame branch, which leads to that some NO is formed beside the diffusion flame branch by the prompt route. Crown

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Section: Introductionmentioning

confidence: 99%

A numerical investigation on NOX formation in counterflow n-heptane triple flames

Guo

Smallwood

2007

International Journal of Thermal Sciences

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“…The solution for the innermost scale follows the large activation energy asymptotic method (Liñán 1974;Fachini 1996;Fachini, Liñán & Williams 1999;Fachini 2005). Finally, typical results are presented and discussed in view of the model.…”

Section: Length Scales and Thermal Non-equilibriummentioning

confidence: 99%

“…The parameter m represents the ratio of the thermal flux downstream from the flame to the total heat release. Liñán (1974) proposed an approximate expression for a curve fit of the numerical solution of the problem in the reaction region, relating these two parameters by…”

Section: Outer Zone: Problem Of the Order Of Unitymentioning

confidence: 99%

Theoretical analysis of ultra-lean premixed flames in porous inert media

2010

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The structure of stationary adiabatic premixed flames within porous inert media under intense interphase heat transfer is investigated using the asymptotic expansion method. For the pore sizes of interest for combustion in porous inert media, this condition is reached for extremely lean mixtures where lower flame velocities are found. The flame structure is analysed in three distinct regions. In the outer region (the solid-phase diffusion length scale), both phases are in local thermal equilibrium and the problem formulation is reduced to the one-equation model for the energy conservation. In the first inner region (the gas-phase diffusion length scale), there is local thermal non-equilibrium and two equations for the energy conservation are required. In this region, the gas-phase temperature at the flame is limited by the interphase heat transfer. In the second inner region (the reaction length scale), the chemical reaction occurs in a very thin zone where the highest gas-phase temperature is found. The results showed that superadiabatic effects are reduced for leaner mixtures, smaller pore sizes and smaller fuel Lewis numbers. The results also show that there is a minimum superadiabatic temperature for the flame propagation to be possible, which corresponds to the lean flammability limit for the premixed combustion in porous inert media. A parameter that universalizes the leading-order flame properties is identified and discussed.

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“…For oxidizer-stream temperatures above T c , the ignited branch bifurcates from the frozen solution at a finite valué of the strain rate. The occurrence of ignition as a bifurcation as opposed to a smooth turning point as in conventional one-step asymptotic analyses [12] is a consequence of the autocatalytic character of the kinetic mechanism em-"An exception is a recent study by activation-energy asymptotics (S. R. Lee and C. K. Law, Combust. Sci.…”

Section: Introductionmentioning

confidence: 99%

A bifurcation analysis of high-temperature ignition of H2−O2 diffusion flames

Sánchez

Liñán

Williams

1994

Symposium (International) on Combustion

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The form of the ignition branch for steady, counterflow, hydrogen-oxygen diffusion flames, with dilution permitted in both streams, is investigated for two-step reduced chemistry by methods of bifurcation theory. Attention is restricted to fuel-stream temperatures less than or equal to the oxidizer-stream temperature T x and to T" larger than or of the order of the crossover temperature T c at which the rates of production and consumption of H atoms are equal. Two types of solutions are identified, a frozen solution that always exists in this kinetic approximation because all rates are proportional to the concentration of the intermedíate H atom, and an ignited solution, represented by a branch of the curve giving the máximum H concentration in terms of a Damkohler number constructed from the strain rate and the rate of the branching step H + O s -• OH + O. For T" > T" the latter bifurcates from the frozen solution if the Damkohler number is increased to a critical valué. For T" larger than a valué T s > T c , the effeets of chemical heat reléase are small, and ignition is always gradual in the sense that the limiting ignited-branch slope is positive (supercritical bifurcation) and there is no S curve. For T" in the range T c < T" < T" the heat reléase associated with the radical-consumption step causes the limiting ignition-branch slope to become negative (subcritical bifurcation), producing abrupt ignition which leads to an S curve. For valúes of T x below crossover, the ignited branch appears as a C-shaped curve unconnected to the frozen solution. The method of analysis introduced here offers a first step toward analytical description of nonpremixed H 2 -0 2 autoignition.

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The asymptotic structure of counterflow diffusion flames for large activation energies

Cited by 770 publications

References 18 publications

A numerical investigation on NOX formation in counterflow n-heptane triple flames

A numerical investigation on NOX formation in counterflow n-heptane triple flames

Theoretical analysis of ultra-lean premixed flames in porous inert media

A bifurcation analysis of high-temperature ignition of H2−O2 diffusion flames

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