二冲程自由活塞发动机扫气与排放仿真研究

张宇¹，肖进^1*，张宸²

1.上海交通大学动力机械与工程教育部重点实验室,上海  200240；

2.上海交通大学智慧能源创新学院,上海  200240

摘要：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CO₂、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，CO₂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。

关键词：自由活塞发动机；二冲程；扫气；换气；燃烧；排放；三维CFD仿真

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

ZHANG Yu¹，XIAO Jin^1*，ZHANG Chen²

1. Key laboratory for Power Machinery and Engineering of the Ministry of Education，Shanghai Jiao Tong University, Shanghai 200240, China；

2. College of smart energy, Shanghai Jiao Tong University, Shanghai 200240, China

Abstract：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 (CO₂, 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 CO₂ 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.

Keywords:free piston engine; two stroke; scavenging;ventilation; combustion;emission;3D CFD simulation