对置活塞二冲程缸内直喷汽油机混合气形成的数值研究

针对对置活塞二冲程汽油机缸径小、冲程长的特点,利用三维CFD软件AVL-Fire对缸内喷雾方向进行优化,实现全负荷工况下(6 000r/min)的缸内混合气均匀混合;并且基于优选的喷雾方向,研究部分负荷工况下(2 000r/min)二次喷射策略(不同喷油时刻和喷油比例)对缸内混合气分层分布的影响。结果显示,增大排气侧3束喷雾的中心线与气缸中心面夹角β会导致燃油蒸发率降低,而增大进气侧3束喷雾的中心线与气缸中心面夹角α有利于提高缸内混合气的均匀度;在部分负荷时,当第一次喷油时刻为内止点前140°曲轴转角,第二次喷射时刻为内止点前60°曲轴转角,第二次喷油量为总喷油量的33%时,缸内形成理想的混合气分层分布。

Numerical Simulation on Mixture Formation of Opposed-piston Two-stroke GDI Engine

For the characteristics of small bore and long stroke for opposed-piston two-stroke engine ,the spray direction was optimized with CFD AVL Fire software and the homogenous mixture formed in full load at 6 000 r/min .The effects of second injection strategy with different injection timing and injection ratio on mixture stratification in part load at 2 000 r/min were studied based on optimized spray direction .The results show that the increase of angle between the central line of three fuel sprays in exhaust side and the central plane of cylinder can reduce fuel evaporation and the increase of angle in intake side can improve uniformity index of mixture .The first injection at 140°CA BTDC and the second injection at 60°CA BTDC with 33%total fuel injection quantity finally lead to ideal in-cylinder mixture stratified distribution in part load .