A Stirling engine is a type of heat engine that converts thermal energy into mechanical work. It operates by cyclically compressing and expanding a gas, which moves a piston. The engine uses an external heat source, such as burning fuel or solar energy, to heat the gas, while a cooler area allows the gas to cool down, creating a pressure difference that drives the piston. One of the key features of a Stirling engine is its efficiency, as it can operate on any heat source. It is often used in applications like solar power generation and submarine propulsion, where quiet operation and reliability are essential.