How Do Electric Fuel Injectors Work?

Electronic fuel injection has been the most popular method of delivering fuel into automobile engines since the early 1980s. Before then, carburetors metered fuel, atomized it and delivered it into the intake manifold, for the purpose of combustion. Electronic fuel injection, which has several configurations and applications, eliminates inefficient fuel burning by using numerous sensors that tell the computer just how much fuel is needed, for how long and during what conditions. At the heart of the fuel-injection system is the injector itself, which contains a number of components that allow it to function precisely.

Fuel Injector Construction

Fuel injectors are about the size of a small spark plug. They have an electrical connector at their top, which receives signals from the vehicle computer. The interior of the injector contains a electromagnetic solenoid coil, an armature, a sealing device, such as disc, pintle or check ball, filter, a valve seat and needle valve, a spray orifice and a return spring. All the components act in sequence to provide the opening and closing of the valve, which allows fuel to pass through it and enter the intake port of the engine in a precise and timed amount.

Fuel Injector Location

Fuel injectors are attached at one end to a fuel rail, which consists of a system of small fuel lines that lead to individual cylinders, or to a throttle body that has one or two injectors. The other end of the injector is positioned directly above the intake port of the engine in very close proximity to the intake valve, or attached to the throttle body above the intake manifold. All injectors are located downstream of the fuel pump, and as close as possible to the intake combustion chamber. Direct fuel injectors, as in the case of diesel engines, are ported directly into the combustion chamber.

Fuel Injector Electronic Signal

The engine computer receives data from various engine sensors that monitor rpm, load weight and air pressure. At the precise time of engine rotation when the intake valve is about to open, an electronic signal from the computer is sent to the injector, which is actually a ground. The ground completes a circuit that energizes the solenoid coil inside the injector. The solenoid coil pulls a disc, check ball or pintle off of its seat. Fuel enters the injector through the open seat, under pressure from the fuel pump. The computer has already determined the amount and duration of fuel to send to the injector

Injector Fuel Delivery

Once the fuel has entered the injector body it travels rapidly to the injector tip, which has a small spray orifice. The pressure behind the fuel forces it through the very tiny openings in the spray orifice, which causes it to atomize or mist into very fine droplets. The atomized fuel passes through the intake valve and into the combustion chamber, where the spark plug ignites the mixtures and causes combustion. Simultaneously the computer disconnects the ground circuit, demagnetizing the solenoid coil, which forces a spring to close the pintle, disc or ball against its seat. The entire sequence of injection is called the duty cycle, and it can last from 1.5 to 6 milliseconds.

Injector Variations

Injectors come in different sizes, depending on the engine cubic inches, horsepower and type. The number of injectors and injection types can also vary. For instance, throttle body injection may use one or two injectors to deliver fuel to all the cylinders at the same time. Multiport injection uses individual injector nozzles for each cylinder. Sequential fuel injection sends a signal to each nozzle, triggering them independently. Diesel engines use injectors for each cylinder, but they port directly into the combustion chamber, without the use of intake valves.