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首页> 外文会议>IUTAM Symposium on Turbulent Mixing and Combustion, Jun 3-6, 2001, Kingston, Ontario, Canada >A MODEL DESCRIPTION OF THE EFFECTS OF VARIABLE FUEL-AIR MIXTURE COMPOSITION ON TURBULENT FLAME PROPAGATION
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A MODEL DESCRIPTION OF THE EFFECTS OF VARIABLE FUEL-AIR MIXTURE COMPOSITION ON TURBULENT FLAME PROPAGATION

机译：可变燃料-空气混合物对湍流火焰传播影响的模型描述

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摘要

Stratified direct-injection spark-ignition engines feature a fuel-air mixing field characterized by large spatio-temporal variations of the mean mixture composition, Z(x_i,t), as well as regions with significant statistical fluctuations around Z. Modifications to the Coherent Flame Model (CFM) are proposed in the present study to account for the effects of variable mixture strength on the primary premixed flame, as well as for the downstream formation of a secondary non-premixed reaction zone. Compared to previous work, the domain of validity of the present modifications is extended to the case of combustion with occurences of premixed flame extinction. The modeling strategy is based on previous results from direct numerical simulations as well as a theoretical analysis of a simplified problem due to Kolrnogorov, Petrovskii and Piskunov (KPP). The KPP problem corresponds to a one-dimensional, turbulent flame propagating steadily into frozen turbulence and frozen fuel-air distribution, and provides a convenient framework to test the modified CFM model. In this simplified but somewhat generic configuration, the following trends are predicted: for small variations in mixture strength, i.e. in the absence of premixed flame extinction, partial fuel-air premixing has a net negative (positive) impact on the turbulent flame speed, s_T, for mixtures close to stoichiometry (close to the flammability limits); for large variations in mixture strength, i.e. in the presence of premixed flame extinction, partial fuel-air premixing has a net negative impact on s_T and results in increased levels of secondary burning.
机译：分层直喷式火花点火发动机的特点是燃料-空气混合场，其特征是平均混合气成分Z（x_i，t）的时空变化大，以及Z周围统计波动显着的区域。在本研究中提出了火焰模型（CFM），以说明可变的混合强度对一次预混火焰的影响以及第二次非预混反应区的下游形成。与先前的工作相比，本修改的有效性范围扩展到发生预混火焰熄灭的燃烧情况。该建模策略基于直接数值模拟的先前结果以及对由于Kolrnogorov，Petrovskii和Piskunov（KPP）导致的简化问题的理论分析。 KPP问题对应于一维湍流火焰，其稳定地传播到冻结湍流和冻结的燃料-空气分布中，并为测试改进的CFM模型提供了方便的框架。在这种简化但有些通用的配置中，可以预测以下趋势：对于混合物强度的微小变化，即在没有预混火焰熄灭的情况下，部分燃料-空气预混会对湍流火焰速度s_T产生负面（正）影响，用于接近化学计量的混合物（接近易燃性限值）；对于混合物强度的大变化，即在存在预混火焰熄灭的情况下，部分燃料-空气预混会对s_T产生净负面影响，并导致二次燃烧水平提高。

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