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

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• 作者：Xian Shi ; ^{xshi@berkeley.edu} ; ^{shixian0039@gmail.com} ; Jyh-Yuan Chen ; Yulin Chen
• 关键词：Stratified flame ; Laminar flame speed ; Chemical effect ; Preferential diffusion
• 刊名：Combustion and Flame
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：176
• 期：Complete
• 页码：38-47
• 全文大小：1813 K
• 卷排序：176

文摘

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.