Simulation Research On The Working Process Of An Opposed-piston Two-stroke GDI Engine

With advantages such as high efficiency, high power density and excellent balance, opposed-piston two-stroke(OP2S) gasoline direct injection(GDI) engine caused the dramatic attention among the researchers. OP2 S GDI engine is a new type of reciprocating piston internal combustion engine that has different working process with the conventional gasoline engine. However, few researchers paid attention to the working process. In this paper, the working process of OP2 S GDI engine was investigated with the method of numerical simulation.According to the structural characteristics and working principle of OP2 S GDI engine, the CFD model of OP2 S engine was established, and the working process is studied based on the model. The main research contents are as follows:Organizations of air motion in cylinder of OP2 S GDI engine were investigated, and the influence of the tangential angle of intake port and the structure of intake cavity on the working process was analyzed. Results showed that the swirl airflow increased by the increasing of the tangential angle of intake port. Swirl level can improve the turbulence in cylinder and the distribution of spray, but strong swirl will cause collisions between oil and cylinder. 10° tangential angle will obtain reasonable airflow and mixture formation. Tumble airflow was organized by asymmetric structure of intake cavity, which will contribute to turbulence and mixture formation. Although tumble airflow is bad for scavenging process, the influence is little loss on engine performance.The influence of parameters of injection, including direction of injection, injection timing, injection pressure and injection strategy, on mixture formation was analyzed. Results showed that the direction of injection has great effect on the distribution of mixture. Fuel evaporation rate decreased by the increasing of the exhaust intersection angle ? and uniformity index increased by the increasing of the intake intersection angle ?. Based on no fuel short circuit happened, mixture formation improved with injection timing forward. With the consideration of the coupling between the distribution of spray and the collision, reasonable mixture was formed with injection pressure is 13 MPa. Two-stage injection strategy had great effect on the distribution of mixture at some working condition. Fuel quantities of the second injection influences the distribution of mixture and second injection timing influences the uniformity index of mixture. The reasonable stratified mixture distribution is formed with second injection time at 270°CA and second injection account for a five of total fuel quantities.The influence of the number of spark plug and the mode of mixture on combustion characteristic was investigated. Results showed that the increasing of the number of spark plug was beneficial to combustion process in cylinder, but too many spark plugs caused the flame interference. In the condition of lean mixture, stratified mixture distribution accelerated combustion process, shorten 30% time of flame developing period and shorten 15% time of rapid burning period compared with homogeneous mixture.The research of this paper provides deep information about the working process in cylinder of opposed-piston two-stroke GDI engine, which is helpful to optimization of the engine.