External combustion engines are machines that generate power by burning fuel outside the engine itself. In these engines, the heat produced from combustion is used to heat a working fluid, such as water or air, which then expands and moves to create mechanical energy. This type of engine is commonly found in applications like steam engines and some types of power plants. Unlike internal combustion engines, where fuel is burned inside the engine's cylinders, external combustion engines can use a variety of fuels, including coal, wood, or natural gas. This flexibility allows for different designs and efficiencies, making them suitable for various industrial applications and even some vehicles.