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A numerical study of thermal and chemical effects in interactions of n-heptane flames with a single surface

机译：正庚烷火焰与单表面相互作用中热化学效应的数值研究

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摘要

The thermal and chemical effects of a one-dimensional, premixed flame quenching against a single surface are studied numerically. Fuels considered include n-heptane and molar-based mixtures of 95/5 and 70/30 percent n-heptane and hydrogen, respectively. A reduced gas-phase kinetic mechanism for n-heptane is employed. Wall boundary conditions investigated include both an adiabatic and an isothermal wall with temperatures ranging from 298 to 1200 K. The effects of equivalence ratio variations between 0.7 and 3 are investigated. The computations with n-heptane and n-heptane/hydrogen mixtures show that for wall temperatures greater than 400 K heat release rates have a higher value for the wall-interacting flame than for the freely propagating flame. It is also seen that the peak wall heat flux increases with increasing wall temperatures up to 1000 K. Chemical pathway analysis reveals the importance of radical recombination reactions at the surface to the heat release profiles of this study. The effect of H, O, and OH radical recombination near the inert wall is observed to lower the heat release spike on a 750 K isothermal boundary. The concentrations of intermediate hydrocarbons in the near-wall region are studied and related to unburned hydrocarbon formation in an engine cylinder. It is shown that a simple one-step global reaction rate expression for n-heptane fuel conversion cannot reproduce the flame-wall trends observed with the reduced n-heptane mechanism.
机译：数值研究了一维预混合火焰淬火对单个表面的热和化学效应。所考虑的燃料分别包括正庚烷和95/5和70/30％正庚烷和氢的摩尔基混合物。使用还原的正庚烷气相动力学机理。研究的壁边界条件包括绝热壁和等温壁，温度范围从298到1200K。研究了当量比变化在0.7和3之间的影响。用正庚烷和正庚烷/氢混合物进行的计算表明，对于壁温大于400 K的壁，与壁上自由传播的火焰相比，与壁相互作用的火焰的放热率更高。还可以看到，最高壁热通量会随着壁温的升高而增加，最高可达1000K。化学途径分析表明，表面的自由基重组反应对本研究的放热曲线非常重要。观察到惰性壁附近的H，O和OH自由基重组的效果降低了750 K等温边界上的放热峰值。研究了近壁区域中中间碳氢化合物的浓度，并与发动机气缸中未燃烧的碳氢化合物形成有关。结果表明，对于正庚烷燃料转化而言，简单的一步全局反应速率表达式无法重现正庚烷机理减少时观察到的火焰壁趋势。

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