Chemical Structures of Low-Pressure Premixed Methylcyclohexane Flames as Benchmarks for the Development of a Predictive Combustion Chemistry Model

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• 作者：Scott A. Skeen ; Bin Yang ; Ahren W. Jasper ; William J. Pitz ; Nils Hansen
• 刊名：Energy & Fuels
• 出版年：2011
• 出版时间：December 15, 2011
• 年：2011
• 卷：25
• 期：12
• 页码：5611-5625
• 全文大小：1443K
• 年卷期：v.25,no.12(December 15, 2011)
• ISSN：1520-5029

文摘

The chemical compositions of three low-pressure premixed flames of methylcyclohexane (MCH) are investigated with the emphasis on the chemistry of MCH decomposition and the formation of aromatic species, including benzene and toluene. The flames are stabilized on a flat-flame (McKenna type) burner at equivalence ratios of 蠁 = 1.0, 1.75, and 1.9 and at low pressures between 15 Torr (= 20 mbar) and 30 Torr (= 40 mbar). The complex chemistry of MCH consumption is illustrated in the experimental identification of several C₇H₁₂, C₇H₁₀, C₆H₁₂, and C₆H₁₀ isomers sampled from the flames as a function of distance from the burner. Three initiation steps for MCH consumption are discussed: ring-opening to heptenes and methyl-hexenes (isomerization), methyl radical loss yielding the cyclohexyl radical (dissociation), and H abstraction from MCH. Mole fraction profiles as a function of distance from the burner for the C₇ species supplemented by theoretical calculations are presented, indicating that flame structures resulting in steeper temperature gradients and/or greater peak temperatures can lead to a relative increase in MCH consumption through the dissociation and isomerization channels. Trends observed among the stable C₆ species as well as 1,3-pentadiene and isoprene also support this conclusion. Relatively large amounts of toluene and benzene are observed in the experiments, illustrating the importance of sequential H-abstraction steps from MCH to toluene and from cyclohexyl to benzene. Modeled results using the detailed chemical model of Pitz et al. (Proc. Combust. Inst.2007, 31, 267鈥?75) are also provided to illustrate the use of these data as a benchmark for the improvement or future development of a MCH mechanism.