Abstract: This gas pressure generating engine has a totally unconnected piston running between a combustion chamber and a rebounding volume. The piston uncovers the outlet port after moving a short distance from the combustion chamber and utilizes the rest of the piston's long stroke to draw in new air; and after turning around at the stroke's end to pump to the outlet a large part of the drawn-in air. The remainder of the drawn-in air is further compressed for combustion. The stroke of the piston is restricted only by the energy it receives from the combustion chamber. The rebounding volume's pressure is adjustable to adjust the pressure-volume ratio of the outlet gas. A tuned valve in the outlet and a tuned blowdown tube maximize gas momentum scavenging of the combustion chamber to improve the efficiency and extend the operating range.

Abstract: A free-piston engine in which combustion gas is conducted around a piston for a short time during the expansion stroke. The resulting lowered pressure enables intaking in the final part of this stroke. Pressure from the gas conducted around the piston serves as the piston rebounding force and as the engine output.