二冲程发动机机械增压与曲轴箱增压进排气性能对比研究

Comparison of Intake and Exhaust Gas Behavior between Supercharging and Crankcase Charging of Two-stroke Engine

分析曲轴箱增压和机械增压两种不同增压方式对二冲程发动机进排气过程中压力波动、进排气流速和流量变化过程等的影响,从而揭示不同增压方式下二冲程发动机进排气行为变化规律。研究表明,不同增压方式下,二冲程发动机进气过程存在非常明显的差别,而排气过程差异较小。使用机械增压替代曲轴箱增压,可增加压缩冲程缸内湍流强度,加速喷雾混合。在相同充气效率前提下,机械增压可提高扫气利用效率,增加内部EGR率,提升混合气温度,促进蒸发,同时增加混合气比热容,提高热效率。

The influences of supercharging and crankcase charging on the pressure fluctuation ,flow velocity and mass flow rate of intake and exhaust gas were analyzed in order to find out the intake and exhaust behaviors under different charging sys-tems .The results show that the intake processes of two-stroke engine are significantly different ,but the exhaust processes are almost the same under different charging systems .The supercharging replacing crankcase charging can increase the in-cylinder turbulent flow and accelerate the mixing of fuel and air .At the same charge efficiency ,the supercharging can improve the scav-enging efficiency ,increase the internal EGR rate ,and improve the temperature of mixture and evaporation .In addition ,the su-percharging can increase the specific heat capacity of mixture and hence improve the thermal efficiency .