Gaseous actuating medium is hermetically sealed in the engine's loop. The actuating medium gets the heat from the cyclinders walls, expands and pushes the piston, thus performing the effective power. Then the actuating medium passes to a cold cylinder where the heat is rejected outside, the medium cools down and compresses, whereupon it is displaced back to the hot cylinder by the displacer piston. The cycle repeats.
Engine that operate on the defined principle are known as Stirling engine.
utilization of industrial heat,
co-generation plants (heat and electricity generation),
anaerobic power generating systems for underwater vehicles,
solar energy conversion.
Benefits in comparison with internal-combustion engines