甲醇发动机缸内EGR分层的研究

摘要

针对一台具有螺旋进气道的点火式甲醇发动机 ,采用进气道加装EGR管的方式实现了EGR和新鲜充量的分开引入.应用CFD仿真软件Fire模拟了不同EGR通入时间、不同燃烧室凹坑形状等对EGR分层的影响.结果显示 ,加装EGR管能够实现EGR的分层 ,EGR的通入时长和燃烧室凹坑形状都对EGR的分层产生影响.当燃烧室凹坑形状为浅圆柱型、新鲜充量的通入压力为100 kPa、EGR通入压力为160 kPa时 ,在300°BTDC(压缩上止点前)停止通入 ,能够形成火花塞周围EGR浓度低、越远离燃烧室顶部EGR浓度越高的EGR分层结构.同时 ,在保证EGR率和燃油消耗量相同条件下 ,通过改变点火提前角 ,分析分层EGR和均质EGR对甲醇发动机缸内燃烧的影响.分层EGR能有效地提高缸压峰值、缩短燃烧滞燃期、提前燃烧始点 ,有利于发动机缸内燃烧的改善.%Separate introduction of the recycling exhaust and fresh charge of a spark ignition methanol engine was realized by installing an EGR tube in the helical intake port .The effects of different EGR access times and different combustion chamber pit shapes on EGR stratification were simulated with the CFD FIRE software .The results show that the addition of EGR tube can realize the EGR stratification and the EGR access time and the combustion chamber pit shape have significant effect on EGR stratification .The stratification of low EGR concentration around the spark plug and higher EGR concentration far from com-bustion chamber top is formed when the combustion chamber pit shows shallow cylinder shape ,the pressures of fresh charge and EGR are 100 kPa and 160 kPa respectively and the recirculation finished at 300° BTDC .The influence of stratified EGR and homogeneous EGR on in-cylinder combustion of methanol engine is analyzed based on the same EGR ratio and fuel consump-tion .The stratified EGR can improve the peak cylinder pressure ,shorten the combustion delay period and advance the combus-tion starting point effectively and is useful to improve the in-cylinder combustion of methanol engine .