Hydraulic free piston internal combustion engine. Theoretical investigation of the opposed piston type.

Depending on the previously reported experimental results of the free piston internal combustion engine of opposed piston type, a mathematical model, which describes the behavior of a free piston, is derived and numerically calculated in this paper. In the first part of this paper, the design method to determine the cross-sectional areas of the hydraulic piston and piston rod is discussed. In the latter part of this paper, control methods of the gas compression ratio and the free piston position at the end of the cycle are discussed. Even if the friction loss changes during the operation of the free piston engine, it is possible to maintain a fixed value of the compression ratio by changing the hydraulic pressure at the high-pressure side. The free piston position at the end of the cycle can be controlled by the hydraulic pressure at the low-pressure side. Its controllable range, however, is relatively narrow.