A combustion engine is a type of engine that converts fuel into mechanical energy through a process called combustion. In this process, fuel, such as gasoline or diesel, is mixed with air and ignited, creating a controlled explosion. This explosion pushes pistons within cylinders, which then turn the crankshaft to produce motion. There are two main types of combustion engines: internal combustion engines and external combustion engines. Internal combustion engines, commonly found in cars, burn fuel inside the engine itself, while external combustion engines, like steam engines, burn fuel outside the engine to produce steam that drives the pistons.