An internal combustion engine converts the thermal energy of the burning air-fuel mixture into mechanical energy. A four-stroke gasoline engine is a type of combustion engine widely used in automobiles. It consists of an intake valve, an exhaust valve, a spark plug, and a piston connected to a crankshaft. It involves four strokes to execute one complete combustion cycle. During the intake stroke, the descending piston draws the air-fuel mixture through the open intake valve. In the compression stroke, the intake valve is closed. The rising piston compresses the mixture adiabatically. In the power stroke, the spark plug ignites the gas. The heated gas expands almost adiabatically to its maximum volume. Work is done on the piston by pushing it down. Finally, the exhaust valve opens, and the piston moves up, expelling the burned gas from the cylinder and preparing the cylinder for the next intake stroke. The combustion engine's efficiency is expressed using a compression ratio. It is the ratio of the maximum to minimum volume. For automobile engines, it ranges from 8 to 10.