Study on the asymmetry characteristics of piston motion of the hydraulic free piston engine

Based on the hydraulic free piston engine fundamental theory, the analytical model of the system was built. The asymmetry of the piston motion and the influencing factors were investigated by simulation and prototype tests. The results indicate that the piston motion around top dead center of the single piston hydraulic free piston engine appears asymmetry. The energy transfer characteristics and the forces on the piston around top dead center determined that the asymmetry characteristic is inherent. The piston motion around top dead center is mainly determined by the cylinder gas pressure. The faster the compression procession is, the faster the expansion process is. The responses of the distributing valves affect the piston motion around top dead center little. The operation position of the load pressure mainly affects the end of the expansion process.