稀燃条件下废气再循环对缸内直喷汽油机 微粒排放粒径分布的影响
Effects of EGR on the Particle Emission Size Distribution in Lean Burn Condition for Gasoline Direct Injection Engine

在一台壁面/空气导向组合式喷雾的汽油缸内直喷(GDI)发动机上进行废气再循环(EGR)实验,以研究稀燃条件下EGR对GDI发动机均质和分层模式下微粒排放粒径分布及燃烧的影响。实验结果表明:EGR的引入会抑制缸内燃烧,使缸压和瞬时放热率峰值降低、燃烧相位推迟、碳氢化合物排放增多;在均质和分层模式下随着EGR率升高,核态粒子数量浓度均呈先降后增的趋势,即存在最优EGR率使核态粒子数量浓度最低,均质模式下最优EGR率为8％,降幅为未加入EGR时的50％左右,而分层模式最优EGR率为5％,降幅只有20％左右;在分层模式下,积聚态粒子数量浓度随EGR率不断升高而持续降低;均质模式相较分层模式产生的积聚态粒子较少、核态粒子较多,2 000 r/min相较1 500 r/min产生的积聚态粒子较多、核态粒子较少。该结果可为直喷汽油机稀薄燃烧的微粒排放控制提供参考。
The effects of exhaust gas recirculation (EGR) on the combustion and particle emissions of a gasoline direct injection (GDI) engine in homogeneous or stratified combustion mode under lean burn condition were investigated by an EGR experiment on a GDI engine with a combination of wall？？guiding spray and air？？guiding spray. The results show that the adoption of EGR suppresses the cylinder combustion, reduces the peak values of cylinder pressure and instantaneous heat release rate, delays the combustion phase and increases the emission of hydrocarbon. In the homogeneous and stratified mode, the nucleation particle number concentration firstly decreases and then increases with the increasing EGR rate, so there exists an optimum EGR rate to lead to a least number concentration of nucleation mode particles. The optimum rate of 8％ results in a 50％ reduction of concentration in the homogeneous mode while the rate of 5％ results in a 20％ reduction of concentration in the stratified mode. The number concentration of accumulation mode particle decreased with the increase of EGR rate in the stratified mode. The number concentration of accumulation mode gets less and the number concentration of nucleation mode gets more in the homogeneous mode compared with the stratified mode. The number concentration in accumulation mode gets more and the number concentration in nucleation mode less at the speed of 2 000 r/min compared with the speed of 1 500 r/min