Fuel injection is a system for mixing fuel with air in an internal combustion engine. It has become the primary system used in automotive engines, having almost completely replaced carburetors in the late 1980s.
A fuel injection system is designed and calibrated specifically for the type(s) of fuel it will handle: gasoline (petrol), Autogas (LPG, also known as propane), ethanol, methanol, methane (natural gas), hydrogen or diesel. The majority of fuel injection systems are for gasoline or diesel applications. With the advent of electronic fuel injection (EFI), the diesel and gasoline hardware has become similar. EFI's programmable firmware has permitted common hardware to be used with multiple different fuels. For gasoline engines, carburetors were the predominant method to meter fuel before the widespread use of fuel injection. However, a wide variety of injection systems have existed since the earliest usage of the internal combustion engine.
The primary functional difference between carburetors and fuel injection is that fuel injection atomizes the fuel by forcibly pumping it through a small nozzle under high pressure, while a carburetor relies on low pressure created by intake air rushing through it to add the fuel to the airstream.
The fuel injector is only a nozzle and a valve: the power to inject the fuel comes from farther back in the fuel supply, from a pump or a pressure container.
Typical EFI components
Animated cut through diagram of a typical fuel injector.
Injectors Fuel Pump Fuel Pressure Regulator ECM - Engine Control Module; includes a digital computer and circuitry to communicate with sensors and control outputs. Wiring Harness Various Sensors (Some of the sensors required are listed here.)
Crank/Cam Position: Hall effect sensor Airflow: MAF sensor, sometimes this is inferred with a MAP sensor Exhaust Gas Oxygen: Oxygen sensor, EGO sensor, UEGO sensor