The combustion chamber of the two-stroke engine was modified to a direct-injection combustion chamber by using 3-D entity modeling software UG

then 3-D CFD software Fluent was used to simulate and analyze the in-cylinder fluid structure. The results show that

when the height of combustion chamber is reduced to 24mm from 32mm

and the distance from the top of piston to the bottom of cylinder head is reduced to 3mm from 7mm

the roll back flow structure in the process of compression disappears

and the scavenging efficiency increases from 87% to 91%. The simulation results provide a good basis for further structure optimization of combustion chamber.