An engine is a mechanism that converts other forms of energy into kinetic energy. The main form of automotive engines is the internal combustion engine, which uses cylinders and pistons as the conversion mechanism.
According to the type of fuel, they can be classified as gasoline engines, diesel engines, and engines that use hydrogen, natural gas, or liquefied petroleum gas as fuel, with combustion forms similar to those of gasoline engines.
The engine displacement is the total working volume of all cylinders and is generally expressed in liters (L) (for example, a displacement of 1998 ml is usually considered as 2.0 L).
The working volume of a cylinder refers to the volume of gas swept by the piston from the top dead center to the bottom dead center, also known as the single-cylinder displacement, which depends on the cylinder diameter and piston stroke.
According to the cylinder arrangement, they can be classified as L-type (in-line), V-type, W-type, H-type (opposed engine), and R-type (rotary engine). According to the number of cylinders, they can be classified as 3-cylinder, 4-cylinder, 6-cylinder, 8-cylinder, 10-cylinder, 12-cylinder, etc. According to the intake form, they can be classified as naturally aspirated, turbocharged, supercharged, mechanical + turbocharged, twin-turbocharged, triple-turbocharged, quad-turbocharged, and twin-supercharged, etc.