What are the three types of heat engines?

The detailed classification of heat engines is based on the working fluid used in the thermodynamic cycle:

Gas cycles. In these cycles, the working fluid is always a gas. Otto cycles and the diesel cycle (cars used) are also typical examples of gas-only cycles. Modern gas turbine and air jet engines are also based on a gas-only cycle, following the Brighton cycle.

Liquid cycles. Liquid-only cycles are quite exotic. In these cycles, the working fluid is always liquid.

Cycles with phase changes. Steam engines are typical examples of external phase change motors.