废气再循环对直喷汽油机燃烧及排放影响的仿真

Simulation of EGR on combustion and emission of gasoline direct-injection engine

应用计算流体力学(CFD)软件对一台带有废气再循环(Exhaust gas recirculation,EGR)系统的均质缸内直喷(Gasoline direct-injection,GDI)汽油机进气冲程至作功冲程排气门开启时段进行了三维仿真,研究了不同EGR率和过量空气系数λ对缸内状态及排放特性的影响,探讨了温度场、火焰面密度、NO浓度场、CO浓度场、微粒浓度场等参数的变化趋势。结果表明:EGR率为10%时,能在对燃烧过程影响不大的情况下有效降低排放质量;同时,在缸压稍有下降的情况下,λ=1.1时能有效降低排放质量;λ=1.0时能保持较高的缸压和中等的排放水平。

In this paper,three-dimensional（3D）simulation was carried out for the process from intake stroke to exhaust valve opening of a Gasoline Direct-Injection（GDI）engine combined with Exhaust Gas Recirculation（EGR）system using Computational Fluid Dynamics（CFD）software.The effects of different EGR rates and excess air factor,λ,on combustion and emission performances were analyzed.The temperature field,flame surface density,NO concentration field,CO concentration field and soot concentration field were also investigated.Simulation results show that the EGR has little influence on the combustion but it can effectively reduce the emission when the EGR rate is 10%.In addition,while the cylinder pressure descends slightly,the emission can be obviously reduced whenλ=1.1;while asλ=1.0,the engine has higher cylinder pressure and moderate emission.