直喷式柴油机燃烧过程及碳烟生成的初步计算

PRELIMINARY COMPUTATION OF DI DIESEL ENGINE COMBUSTION PROCESS AND SOOT FORMATION

依据已简化的包含多环芳烃生成的正庚烷气相详细化学反应机理,基于专业流体解析软件FLUENT6.3对直喷式柴油机压缩、膨胀冲程内的自燃和燃烧过程进行了动态模拟,得到了缸内平均温度、主要反应物以及中间产物多环芳烃生成量随转角变化的特性曲线。在数值上,计算得到以苯环质量为主的多环芳烃总生成量水平比试验测量结果约高出1～2个量级,但是在随转角变化的特性上,计算与试验测量曲线定性趋势一致。针对特定转角时刻主要火焰结构参数的截面分布,分析研究了柴油机缸内化学反应特性与流体流动相互作用下的空间分布特征。通过耦合详细碳烟粒子动力学模型,对碳烟表象尺寸进行了初步模拟。

Utilizing a simplified gas-phase reaction mechanism of n-heptane oxidation including polycyclic aromatic hydrocarbons （PAHs） formation, based on professional CFD solver FLUENT6.3, dynamic modeling of the auto-ignition and combustion process in direct injection diesel engine compression and expansion stroke was implemented. Evolution trend of in-cylinder reactive flow mean temperature, major reactants as well as PAHs intermediates molar fraction production have been displayed. The calculated overall PAHs production magnitude, overwhelmed by benzene, is about 1～2 order higher than tested results. Nevertheless, the calculated PAHs production curve consists with tested results in qualitative trend. Analysis of the primary flame ingredients＇ sectional distribution has illustrated the spatial morphology of interacted reaction chemistry and fluid flow dynamics inside the diesel cylinder. By integrated with a comprehensive soot particles kinetic model, preliminary computation of soot presentational size feature was modeled.