Fuel injection is a system for squirting fuel into gasoline and diesel engines. When used on gasoline engines, it replaces the carburetor, a device that mixes air and fuel.
Most gasoline engines for cars use multi-port fuel injection. In this system, a pump forces fuel under pressure to a nozzle called a fuel injector located at each of the engine’s cylinders. The injectors then spray the fuel into intake ports (chambers) near each cylinder. There the fuel partially mixes with air before a valve opens to admit the mixture into the cylinder. Some newer cars use direct fuel injection, in which fuel is sprayed directly into the cylinder.
Some older gasoline engines use a system called single point or throttle body fuel injection. This system has only one or two fuel injection nozzles. Each nozzle delivers fuel to several cylinders.
Fuel injection overcomes disadvantages of carburetors. In a carburetor, fuel is drawn into the engine at one location. Poor distribution of the fuel-air mixture can prevent some of the fuel from burning, resulting in lower fuel economy and higher exhaust emissions. The engine also may flood or ice up during the winter, or develop vapor lock during the summer (see Vapor lock ).
Fuel injection includes electronic or mechanical controls to measure the amount of air being drawn into the engine. These controls adjust the amount of time that each injector valve opens to spray fuel, maintaining the proper ratio of fuel to air. The nozzles help break the fuel into a fine spray so that it mixes well with the air and therefore burns almost completely. Precise control of the fuel-air mixture also helps control exhaust emissions and enables cold engines to start quickly and run smoothly.
All diesel engines use fuel injection. In most of these engines, the nozzles spray the fuel directly into the cylinder after the piston has compressed the air to high pressures. A diesel pump compresses the fuel to a much higher pressure than for gasoline fuel injection. In some cases, a single pump is located centrally on the engine. In other cases, each of the engine’s cylinders has a pump.
