Design Feasibility of a Free Piston Internal Combustion Engine/Hydraulic Pump

A direct acting free piston internal combustion engine/hydrostatic pump is analyzed. This device would take the place of a conventional engine-driven hydrostatic pump, and would be expected to offer significant advantages in cost, weight, and efficiency. The free piston configuration eliminates the need for a crankshaft-connecting rod system, and the comparable mechanism of the pump that converts rotary to reciprocating motion. Analysis of the design was done by computer simulation using a thermodynamic model of the combustion cylinder in combination with the system dynamics. A parametric study was performed to determine operating characteristics with a wide variety of mechanical parameters, and as a guide to developing a preliminary design. The results show that good performance is possible with reasonable mechanical dimensions and other parameters. Several different design configurations are presented.