Abstract: The processes of intake, mixture formation and combustion of opposed-piston two-stroke (OP2S) gasoline direct injection engine are simulated by AVL-Fire code. The effects of three scavenging system configurations, viz., flat piston-uniform scavenging chamber, flat piston-non-uniform scavenging chamber and pit piston non-uniform scavenging chamber, on the in-cylinder fluid flow and scavenging process are comparatively analyzed. Test verification is also carried out. The effects of flat piston- non-uniform scavenging chamber and pit piston-non-uniform scavenging chamber on the mixture formation and combustion process are comparatively analyzed. Results show that the uniform scavenging chamber can organize swirl and increase scavenging efficiency, and the non-uniform scavenging chamber can organize tumble and increase turbulent kinetic energy. Pit top surface of piston with non-uniform scavenging chamber is favorable to organize tumble and maintain the in-cylinder turbulence intensity. It helps to form the combustible mixture around spark plug at ignition. Compared with flat piston- non-uniform scavenging chamber, the turbulent kinetic energy of pit piston-non-uniform scavenging chamber is increased by 150 percent and its fuel evaporation is increased by 10 percent at ignition, which is favorable to form more uniform mixture and accelerate combustion process.

Key words: power machinery eugineering, opposed-piston, two-stroke, in-cylinder flow, tumble, mixing