二冲程自由活塞发动机扫气与排放仿真研究

Simulation study on scavenging and emission of two stroke free piston engine

利用CONVERGE软件建立二冲程自由活塞发动机的三维计算流体动力学(computational fluid dynamics,CFD)仿真模型,研究扫气压力、点火时刻对缸内扫气、燃烧和CO_(2)、NO_(x)、CO废气排放的影响。仿真研究结果表明:随着扫气压力增大,缸内扫气效果变好,更多新鲜气体进入缸内,CO_(2)和NO_(x)的生成和排放增加,CO减少;点火时刻影响缸内燃烧,随着点火时刻推迟,缸压峰值和缸内平均温度降低,CO的生成及排放增加,NO_(x)的生成及排放减少。自由活塞发动机试验过程时,应当综合选取工况条件,使得燃烧、扫气、排放等达到综合最优效果。

A CFD simulation model of a two-stroke free piston engine is established by CONVERGE software.The effects of scavenging pressure,ignition time on in-cylinder scavenging,combustion and exhaust emissions(CO_(2),NO_(x),CO)are studied.The results show that with the increase of scavenging pressure,the scavenging effect in the cylinder becomes better,more fresh gas enters the cylinder,the emission of CO_(2)and NO_(x)increase,and CO decreases.The ignition time affects the combustion in the cylinder,with the delay of ignition time,the peak cylinder pressure and the average temperature in the cylinder decrease,the emission of CO increases,and NO_(x)decreases.In the process of free piston engine test,the operating conditions should be comprehensively selected to achieve the comprehensive optimal effect of combustion,scavenging,emissions,etc.