快速压缩机缸内温度不均匀性及其对自燃的影响

Temperature Non-Uniformity and Its Effects on Auto-Ignition in a Rapid Compression Machine

快速压缩机中活塞运动产生涡流会导致缸内温度分布不均匀,并对自燃时刻产生显著影响.针对这一问题,对不同活塞缝隙下缸内温度不均匀性及其对自燃时刻的影响进行了研究.首先,建立了Fluent网格模型并耦合氢气详细化学反应机理,研究了无缝隙活塞缸内温度场及自燃过程;然后,对不同活塞缝隙结构进行缸内温度场的数值模拟,确定最佳活塞缝隙结构;最后,对比了基于CHEMKIN、Livengood-Wu积分以及Fluent 3种方法获得的自燃时刻.结果表明:无缝隙活塞缸内未受涡流影响区域先发生自燃,并引发明显火焰传播.体积为原燃烧室体积9.5%,左右的活塞缝隙能很好抑制涡流产生.Livengood-Wu积分在预测快速压缩机缸内气体,尤其是缸内受涡流影响区域气体的自燃时刻时具有较高的准确性.

The roll-up vortex initiated by the piston motion may lead to temperature non-uniformity,which has asignificant impact on auto-ignition in a rapid compression machine(RCM).In order to restrain the disturbance of rollupvortex,effects of piston head crevice on temperature field and auto-ignition were investigated.First,the temperaturefield and auto-ignition progress in an RCM with the flat piston were simulated using Fluent CFD model with adetailed chemical kinetic mechanism for hydrogen.Then,an optimal piston head crevice was designed by comparingthe final temperature fields of varying piston configurations using non-reaction Fluent model.Finally,in order tostudy the influences of temperature non-uniformity on auto-ignition time,CHEMKIN reactors,Livengood-Wu integraland Fluent were applied respectively to calculate the auto-ignition times.The results show that the vortex causedby the motion of the flat piston leads to the auto-ignition of core gas which is free of the disturbance of the vortex,followed by obvious flame propagation process.A crevice volume occupying about9.5%of the original chamber volumeis sufficient to suppress the disturbance of the vortex.Livengood-Wu integral,a relatively low computationalcostmethod,has high accuracy in predicting auto-ignition times in an RCM,especially for the gases affected byvortex.