Abstract: The air exchange air heat engine is essentially a single piston heat engine. An expansion body (transposition piston) is rigidly connected with the piston in the cylinder. When the piston moves in the cylinder, the expansion body also moves together. At the same time, the air guide hole opened timely is set between the cylinder and the outside. The function of the expansion body is that its occupation forces the working medium air in the cylinder to change between the high and low temperature heat sources. When the air working medium begins to be compressed after passing through the high-temperature heat source, the air guide hole is opened, and the high-temperature air working medium in the cylinder is partially discharged out of the cylinder to reduce the resistance to the movement of the piston; When the air working medium begins to expand after passing through the low-temperature heat source, the air guide hole is opened, and the external air enters the cylinder through the small hole to increase the thrust to the piston. When the piston moves in the cylinder, the air guide hole is opened twice every cycle. The comprehensive effect is that the air working medium does positive work to the piston, which is shown as the state parameters of the air working medium on the PV diagram, and a positive cycle of the heat engine is completed.

Key words: heat engine, air working medium, positive cycle of heat engine, PV diagram, multiparty process