The most prevalent internal combustion engine design is the four-stroke engine, which is used in a variety of vehicles including cars, trucks, and some motorcycles that utilize gasoline as their fuel (many motorbikes use a two stroke engine). Every two piston cycles in a four-stroke engine result in one power stroke (or four piston strokes).
- During the intake stroke, the piston descends to the bottom, increasing the chamber's volume and allowing a fuel-air mixture to enter.
- During the compression stroke, the intake valve is shut, and the piston climbs to the top of the chamber. In turn, the fuel-air mixture is compressed. A spark plug ignites the compressed gasoline at the conclusion of this stroke, supplying it with the activation energy needed to start combustion.
- Power stroke: As the fuel burns out, the heat from the burning hydrocarbons raises the pressure, which causes the gas to push against the piston and provide the power.
- Exhaust stroke: The exhaust valve opens as the piston descends. The piston pushes out the last of the exhaust gas as it ascends.
Depending on the model and layout of the vehicle, these gasoline engines' thermal efficiency will change. In contrast, gasoline engines typically convert 20% of the fuel's chemical energy into mechanical energy, of which only 15% is used to move the wheels (the rest is lost to friction and other mechanical elements). A higher compression ratio is one way engines' thermodynamic efficiency can be enhanced. The ratio represents the difference between the engine chamber's minimum and maximum volume. A greater fuel-air mixture will be allowed to enter with a higher ratio, creating a higher pressure that raises the chamber's temperature and improves thermal efficiency.
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