Fuel injection is a technology used in internal combustion engines to mix the fuel with air prior to combustion.

As in a traditional carburetor, fuel is converted to a fine spray and mixed with air. However, fuel injection forces the fuel through nozzles under pressure, rather than using the force of the air rushing through.

The major advantage of the system is that the amount of fuel being mixed with air can be more precisely controlled, and the mixture can be more evenly spread throughout the air coming into the engine. In combination with an electronic computer which monitors engine conditions, fuel injection can increase fuel efficiency and reduce pollution.

Fuel injection has been used in diesel engines since the mid 1920s, almost from their introduction (due to the higher temperature required for diesel to evaporate). It was adapted for use in petrol-powered aircraft during World War II and was first used in a car in 1955 with the introduction of the Mercedes 300SL.

Fuel injection became widespread with the introduction of electronically controlled fuel injection systems in the 1980s and the gradual tightening of emissions and fuel economy laws. Meeting modern emissions standards whilst retaining acceptable performance would be very difficult without it. In addition, the development of microprocessor technology made it possible to control the amount of fuel injected precisely.

Many modern diesel engines use direct injection, in which the injection nozzle is located inside the combustion chamber. Several manufacturers are experimenting with its use in gasoline engines, where it is expected to further increase efficiency and reduce pollution.