The simulation experiment of the single combustion process of a hydraulic free piston engine(HFPE) under different initial pressures in the cylinder was conducted on a rapid compression-expansion test machine

and the super-charging simulation study was carried out by using OpenFoam and CONVERGE three-dimensional computational fluid dynamics(CFD) simulation platform. Results show that under the same compression ratio

as the initial pressure in the cylinder increases

the cycle time of the engine and the residence time of the piston near top dead center are shortened

thereby increasing the compression ratio of knock limit and antiknock ability. Appropriately increasing the initial pressure is beneficial to improve the indicated efficiency. When the initial pressure in the cylinder is increased to 0.15 MPa

the engine indicated efficiency is increased from 0.30 to 0.31

but when the initial pressure reaches 0.20 MPa

the indicated efficiency drops to 0.30. In the simulation study of the problem

it is found that the multi-spark ignition scheme can achieve a higher indicated efficiency without knocking even at an initial pressure of 0.80 MPa.