In an internal combustion engine, the fuel injection system is that which delivers fuel or a fuel-air mixture to the cylinders by means of pressure from a pump. It was originally used in diesel engines because of diesel fuel's greater viscosity and the need to overcome the high pressure of the compressed air in the cylinders. A diesel fuel injector sprays an intermittent, timed, metered quantity of fuel into a cylinder, distributing the fuel throughout the air within. Fuel injection is also now used in gasoline engines in place of a carburetor. In gasoline engines the fuel is first mixed with air, and the resulting mixture is delivered to the cylinder. Computers are used in modern fuel injection systems to regulate the process. The positive effects of fuel injection are that there is more efficient fuel combustion, better fuel economy and engine performance and reduced polluting exhaust emissions.

Carburetor

This is a device in a gasoline engine. It vaporizes the gas and mixes it with a regulated amount of air that aids in efficient combustion in the engine cylinders. Land vehicles, boats, and light aircraft have a float carburetor, in which a float regulates the fuel level in a reservoir from which the fuel is continuously sucked into the intake manifold at a restriction called a venturi. The carburetor has been replaced by the fuel injection system in many modern vehicles.