缸内滚流对废气再循环汽油机性能影响的计算研究

摘要

For a 1 .8 L gasoline engine ,the influences of in-cylinder tumble on EGR engine combustion and emission were re-searched by the CFD Fire software and the optimization and match of ignition timing and tumble ratio and the performance com-parison of different initial tumble positions were further analyzed .The calculated results show that high tumble ratio can im-prove combustion and compensate the loss caused by EGR from the perspective of combustion .Compared with the combustion without tumble ,the combustion with 2 .5 tumble ratio can shorten 90% fuel combustion duration of 5% ,15% and 25% EGR ratio by 31% ,31 .7% and 34 .8% respectively .The enhanced tumble motion can reduce HC emission of EGR gasoline engine , but increase NOx emission .The maximum mean indicated pressures of different tumble ratios correspond to different ignition angles and the value of low tumble ratio at 5% EGR ratio is higher than that of high tumble ratio .The different initial tumble positions can not continue for a long time and the tumble centre will move to the centre of combustion chamber soon ,which has little influence on combustion performance .%以某款1．8 L汽油机为研究对象，利用CFD模拟软件FIRE研究了缸内滚流对引入EGR后发动机燃烧和排放特性的影响，并进一步分析了点火正时与滚流比的优化匹配和不同气流初始旋转位置的性能对比。计算结果表明：从燃烧的角度，高滚流比气流运动可以促进燃烧，弥补废气带来的燃烧损失，滚流比为2．5时相比无滚流工况可以将5％，15％，25％ EGR率下90％燃油燃烧期分别缩短31．0％，31．7％和34．8％；加强缸内滚流可以降低废气再循环汽油机的HC排放，但同时也会增加NO x 排放；不同滚流比下的最大平均指示压力对应不同的点火角，并且在5％ EGR率工况低滚流运动反而平均指示压力值更高；不同初始滚流旋转位置并不能保持很长的曲轴转角，旋转中心会很快向燃烧室中心转移，对燃烧特性影响不大。