A three-dimensional computational fluid dynamics(CFD) simulation model of two-stroke hydraulic free-piston engine(HFPE) was built by the CONVERGE. The effects of specific time-area value

compression ratio of scavenge case

piston top angle

and piston rod diameter on scavenging process were studied based on the unique structure of the HFPE. The results show that the scavenging efficiency is mainly affected by the specific scavenging time-area value when there is no backflow of exhaust gas

and the improvement of the later is beneficial to the former. The capture ratio is mainly affected by the specific time-area value of exhaust

and the reduction in the later can increase the former. Increasing the scavenge case compression ratio from 1.2 to 2.1 can promote the scavenging efficiency by 9.8%. The appropriate increase of the piston top angle is beneficial to the improvement of the scavenging efficiency and capture ratio. Decreasing the diameter of the piston rod diameter can increase the scavenging efficiency

but it will reduce the capture ratio.