浓度分层下正庚烷自点火过程的直接数值模拟

Direct Numerical Simulation of n-Heptane Autoignition Process with Charge Stratification

针对实际内燃机内存在浓度分层的情况,采用直接数值模拟,研究了浓度分层对正庚烷在空气中的自点火过程的影响.结果表明:在压力2.4MPa,初始温度860K(位于负温度系数区域)下,随着浓度分层的增加,整体着火时间提前,但是第1阶段点火延迟时间几乎没有变化.第2阶段着火位置的混合物分数随着浓度分层的增加而变大,说明两阶段着火不存在统一的最易着火的混合分数.通过budget分析,揭示低温反应和高温反应阶段存在不同的火焰传播模式.

Considering the existence of charge stratification in real engines,direct numerical simulation is used to study the effect of charge stratification on the n-heptane/air autoignition process.Results show that under the initial pressure of 2.4MPa and initial temperature of 860 K(within the negative temperature coefficient regime),the overall ignition delay time decreases with the increasing charge stratification;however,the first-stage ignition delay time barely changes.The mixture fraction in the second-stage ignition area increases with the increasing charge stratification,indicating that there is no uniform most reactive mixture fraction for the two-stage ignition process. Through budget analysis,different flame propagation modes are revealed to exist in the low- and hightemperature reaction stages.