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 it to contract. One of the key features of a Stirling engine is its efficiency, as it can operate on a variety of heat sources. These engines are often used in applications like solar power generation and submarine propulsion, where quiet operation and reliability are essential.