中文摘要：

使用二维直接数值模拟方法研究HCCI发动机条件下浓度和温度不均匀性对庚烷点火过程的影响。计算中考虑了详细的组分输运过程、活塞运动带来的气体压缩效应以及简化的庚烷化学动力学机理。二维直接数值模拟展示了燃料的负温度系数（NTC）特性对点火过程的影响,结果表明浓度分层增加使得第二阶段点火延迟时间缩短;温度分层增加,点火延迟时间增加,与具有单一阶段点火特性的燃料相反。之后使用相同DNS程序计算了一维算例,发现初始温度在NTC以内,并且温度与浓度不相关时,浓度分层对点火过程起主导作用,浓度高温度较低的区域先着火;初始温度在NTC以外,并且温度与浓度负相关时,存在一个最容易着火的区域：浓度和温度都较高的地方先点火。

英文摘要：

Two-dimensional direct numerical simulation（2-D DNS） is used to study the effect of charge and temperature stratifications on n-heptane/air auto-ignition in HCCI engine related conditions.Detailed species transport,compression/expansion effects due to piston motion as well as a skeletal n-heptane chemical kinetic,mechanism are considered.The results show the influence of NTC characteristic of fuel in 2-D space and find that increasing charge stratification will decrease the second-stage ignition delay time;higher thermal inhomogeneity can retard the on-set of main heat release rate,which contradicts to single-stage ignition fuel.In the second part,1-D DNS is employed using the same code.It is found that when the initial mean temperature is within NTC region and uncorrelated temperature-equivalence ratio（T — 0） distribution is considered,the charge stratification plays an important on first ignition which is the position of high φ and low T;while the initial temperature is outside of NTC region and with a negative（T — φ） correlation,there is a most reactive mixture in both high T and φ position.