Laminar propagation of lean premixed flames ignited in stratified mixture

Balusamy, Saravanan; Cessou, Armelle; Lecordier, Bertrand

doi:10.1016/j.combustflame.2013.08.023

Cited by 33 publications

(14 citation statements)

References 30 publications

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“…Furthermore, the increase in flame speed was more prominent when the flame approached the flammability limits and encountered higher equivalence ratio gradients. In a recent experimental study by Balusamy et al [11], a propane/air flame was ignited in a rich mixture and propagated into a lean mixture in a constant volume chamber. The flame propagation in the lean mixture was found back-supported by ignition in richer conditions, as the flame benefited from the rich composition of the burnt gas compared to that of lean homogeneous flames.…”

Section: Introductionmentioning

confidence: 99%

“…Flame stretch and curvature undermine the accuracy of measured flame speeds. For example, in [11], due to the initial mixture preparation and ignition setup, an oval contour of flame front was developed instead of an ideal sphere. Consequently, tracking flame front propagation and extrapolation of the unstretched laminar flame speed are problematic.…”

Section: Introductionmentioning

confidence: 99%

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Laminar flame speeds of stratified methane, propane, and n-heptane flames

Shi

Chen

2017

Combustion and Flame

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A numerical study on stratified flames of three hydrocarbon fuels, i.e., methane, propane and n-heptane, is conducted using a unsteady, compressible and reacting flow solver ASURF-Parallel. For each fuel, both fuel consumption speeds and flame front propagation speeds of a rich-to-lean stratified flame are compared to those of their corresponding homogeneous flames. For fuel consumption speeds, the methane/air stratified flame is overall faster than those of homogeneous flames due to chemical activities enhanced by key radicals and species from rich burnt gas mixtures. In contrast, stratified flames of both propane/air and n-heptane/air mixtures have lower fuel consumption speeds compared to their homogeneous flames on the rich side, due to reduced level of key radicals consumed by intermediate hydrocarbon species from rich burnt gases. For flame front propagation speeds, stratified flames of all three fuels are found faster than their corresponding homogeneous flames, due to consistently enhanced total heat release rate. Stronger enhancement of laminar flame speeds of stratified mixtures is observed in methane/air mixtures, compared to propane and n-heptane. Burnt gas of rich methane/air mixtures consists of relatively more molecular hydrogen, which assists fuel consumption and heat release at flame front. Moreover, molecular hydrogen has a stronger impact on laminar flame speeds of methane/air mixtures thus an even stronger enhancement on laminar flame speeds of methane/air stratified mixtures is observed. H/C ratio along with local equivalence ratio at flame front are proposed to provide a unique identification of the exact mixture composition of stratified flames.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Laminar flame speeds of stratified methane, propane, and n-heptane flames

Shi

Chen

2017

Combustion and Flame

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“…There have been extensive theoretical, experimental and numerical research on stratified flames propagating along mixture stratification layer: Effects of stratification on flammability limit [11,12,13], flame propagation speed [14,15], flame structure [16,17,18] and etc. have been investigated, with regard to different fuel components including hydrogen [13], methane [14,15] and iso-octane [16]. As to the effect of stratification on laminar flame speeds, two mechanisms have been proposed to explain the behavior of stratified flames.…”

Section: Introductionmentioning

confidence: 99%

Numerical study of laminar flame speed of fuel-stratified hydrogen/air flames

Shi

Chen

2016

Combustion and Flame

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Numerical studies on hydrogen/air stratified flames in 1-D planar coordinate are performed using a time-accurate and space-adaptive numerical solver A-SURF. A step change in equivalence ratio is initialized as fuel stratification. Flame characterizations including fuel consumption speed and flame front propagation speed are compared between stratified flames and corresponding homogeneous flames. Two transport models, with equal diffusivity and mixture-average diffusivity assumptions respectively, are considered. With equal diffusivity assumption and stratification thickness larger than flame thickness, local fuel consumption speeds of stratified and homogeneous flames are identical, indicating that neither thermal effect nor chemical effect is present in stratified flames. When stratification thickness is reduced to the order of flame thickness, the difference between local fuel consumption speeds of stratified and homogeneous flames is caused by chemical effect due to different level of H radical in burnt gas. The same mechanism also leads to the difference between local fuel consumption speeds with mixture-average diffusivity assumption. In addition, preferential diffusion of H radical further increases the difference. The difference between flame front propagation speeds of stratified and homogeneous flames is mainly caused by additional heat release in the burnt gas with equal diffusivity assumption, while the difference with mixture-average diffusivity assumption is mainly caused by local chemical effect. Hydrodynamic effect due to fluid continuity on flame front propagation speeds is observed in both transport models. Additionally, with increasing stratification thickness, both local chemical and hydrodynamic effect are reduced. No significant lean flammability extension of hydrogen/air mixture is introduced by fuel stratification.

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“…A number of previous analyses concentrated on flame propagation in stratified mixtures based on experimental (Anselmo-Filho et al, 2009;Balusamy et al, 2014;Grune et al, 2013;Kang and Kyritsis, 2005;Mulla and Chakravarthy, 2014;Renou et al, 2004;Samson, 2002;Sweeney et al, 2013;Zhou et al, 1998Zhou et al, , 2013 and direct numerical simulations (DNS) (Cruz et al, 2000;Haworth et al, 2000;Hélie and Trouvé, 1998;Jiménez et al, 2002;Malkeson and Chakraborty, 2010;Patel and Chakraborty, 2014;Pera et al, 2013;Swaminathan et al, 2007) data. These studies demonstrated that the flame propagation statistics are strongly affected by the local gradient of equivalence ratio.…”

Section: Introductionmentioning

confidence: 99%

Effects of Mixture Distribution on Localized Forced Ignition of Stratified Mixtures: A Direct Numerical Simulation Study

Patel

Chakraborty

2016

Combustion Science and Technology

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The influences of initial mixture distribution on localized forced ignition of globally stoichiometric stratified mixtures have been analyzed using three-dimensional compressible direct numerical simulations. The globally stoichiometric mixtures (i.e., hϕi ¼ 1:0) for different root-meansquare (rms) values of equivalence ratio (i.e., ϕ 0 = 0.2, 0.4, and 0.6) and the Taylor micro-scale lϕ of equivalence ratio ϕ variation (i.e., lϕ=l f ¼ 2.1, 5.5, and 8.3 with l f being the Zel'dovich flame thickness of stoichiometric mixture) have been analyzed for different initial rms values of turbulent velocity u 0 . The equivalence ratio variation is initialized following both Gaussian and bi-modal distributions for a given set of values of ϕ 0 and lϕ=l f in order to analyze the effects of mixture distribution. The localized forced ignition is accounted for by considering a source term in the energy conservation equation that deposits energy for a stipulated time interval. It has been demonstrated that the initial equivalence ratio distribution has significant effects on the extent of burning of stratified mixtures following successful localized forced ignition. It has been found that an increase in u 0 =S b ϕ¼1 ð Þ (ϕ 0 ) has adverse effects on the burned gas mass, whereas the effects of lϕ=l f on the extent of burning are nonmonotonic and dependent on ϕ 0 for initial bi-modal mixture distribution. The initial Gaussian mixture distribution exhibits an increase in burned gas mass with decreasing lϕ=l f , but these cases are more prone to flame extinction for high values of u 0 than the corresponding bi-modal distribution cases. Detailed physical explanations have been provided for the observed mixture distribution, ϕ 0 , u 0 , and lϕ=l f dependences on the extent of burning following localized forced ignition of stratified mixtures. ARTICLE HISTORY

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Laminar propagation of lean premixed flames ignited in stratified mixture

Cited by 33 publications

References 30 publications

Laminar flame speeds of stratified methane, propane, and n-heptane flames

Laminar flame speeds of stratified methane, propane, and n-heptane flames

Numerical study of laminar flame speed of fuel-stratified hydrogen/air flames

Effects of Mixture Distribution on Localized Forced Ignition of Stratified Mixtures: A Direct Numerical Simulation Study

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