Numerical simulation on in-cylinder gas motion of hydraulic free piston diesel engine

Based on the development of the single-piston hydraulic free piston diesel engine prototype, numerical simulation on in-cylinder gas motion was studied. The study results showed that the in-cylinder gas motion was influenced by the piston motion. Compared with the traditional internal combustion engine, the in-cylinder gas motion characteristics of hydraulic free piston engine are as follows: in early compression stroke, the average velocity of in-cylinder gas is smaller due to the smaller piston velocity; in late compression stroke, the piston movement velocity increases near the TDC, in-cylinder gas accelerated radial flow out from the combustion chamber, the average radial velocity increases, the squish enhancement; in early expansion stroke, the higher piston movement velocity lead to the average radial velocity substantial increases and the inverse squish significantly enhanced in this period. The piston instantaneous velocity influenced the squish and inverse squeeze nearby TDC, with the piston velocity increasing at the same piston position, the average radial velocity increasing, squish and reverse squish enhancement.