The Stirling Engine is an External Combustion Engine (the heat source is outside the engine) and can use any available source of adequate heat or cold. It is a classic illustration of converting heat energy into mechanical work using a thermodynamic cycle similar to the well-known Carnot cycle. In this case, however, the engine needs two pistons, a small power piston and a larger "displacement piston" that also stores heat energy. This Sterling engine is powered by a built-in alcohol lamp. This powers the steam engine which acts as the motor for the 'car'. A very good visual demonstration of the conversion of heat to mechanical energy. All Sterling engines are tested before shipping.