压缩比和EGR对自由活塞发动机HCCI爆震燃烧的影响

基于AVL FIRE仿真平台建立了液压自由活塞发动机气缸的三维仿真模型，使用大涡模拟（large eddy simulation, LES）耦合甲醇的详细化学反应动力学机理研究了压缩比和废气再循环（exhaust gas recirculation, EGR）率对均质压燃（homogeneous charge compression ignition, HCCI）爆震燃烧过程的影响。结果表明:甲醇的HCCI燃烧需要一定的进气加热；随着压缩比的提高，最小进气温度逐渐降低，缸内的最高燃烧温度、最大爆发压力和爆震强度均明显增加；在高压缩比工况下引入EGR时可以降低爆震强度，但EGR率较小时效果并不明显，因此需要较大的EGR 率来抑制爆震；最后，对压力振荡曲线的频谱特性进行了分析，发现爆震燃烧时压力振荡的峰值频率位于10～15 kHz区间内。

Influence of compression ratio and EGR on knock combustion in a HCCI free piston engine

A three-dimensional simulation model on cylinder of hydraulic free piston engine was established based on AVL FIRE simulation platform. The influence of compression ratio and exhaust gas recirculation (EGR) rate on homogeneous charge compression ignition (HCCI) knock combustion process was studied by using large eddy simulation (LES) coupled with detailed chemical reaction kinetics mechanism of methanol. The results showed that the HCCI combustion of methanol needs certain intake heating. With the increase of compression ratio, the minimum intake temperature decreases, while the maximum combustion temperature, the maximum explosion pressure and the knock intensity in the cylinder increase significantly. Under the condition of high compression ratio, the introduction of EGR can decrease the knock intensity, but the effect is not obvious with a low EGR rate, so the bigger EGR rate is necessary to suppress the knock. Finally, the spectrum characteristics of pressure oscillation curve were analyzed, and the result showed that the peak frequency of pressure oscillation in knock combustion locates in the range from 10 to 15 kHz.