The internal combustion engine is a kind of power machine. It is a heat engine that burns fuel inside the machine and directly converts the heat energy it emits into power.
In a broad sense, internal combustion engines include not only reciprocating piston internal combustion engines, rotary piston engines, and free piston engines, but also jet engines of rotary vane type, but the internal combustion engine generally refers to piston internal combustion engines.
The reciprocating piston type internal combustion engine is the most common. A piston type internal combustion engine mixes fuel and air and burns it in its cylinder. The heat released makes the cylinder produce high-temperature and high-pressure gas. Gas expansion pushes the piston to perform work, and then the mechanical work is output through the crank connecting rod mechanism or other mechanisms to drive the driven machinery to work.
The common ones are diesel engines and gasoline engines, which convert internal energy into mechanical energy and change internal energy through work.