What is the function of the injectors in a car?

What is the function of the injectors in a car?
An injector is an element of the fuel injection system whose function is to introduce a certain amount of fuel into the combustion chamber in a powdered form, distributing it as homogeneously as possible within the air contained in the chamber. The beginning and end of the injection must be well defined, not allowing subsequent leaks of fuel.

Location and physical description   

The injectors are located in the cylinder head ( cylinder head) being composed of two parts of high precision: body and needle, which have recesses that allow greater heat transfer with the fuel. They are made of high quality steel and have undergone a very fine adjustment. These parts cannot be replaced separately. It is necessary to keep the nozzle at a lower temperature than the decomposition of the fuel, and thus prevent carbon from forming in the holes. The nozzle is often provided with a jacket that allows cooling water to be carried to the head and effectively cool that area.

The cooling system in the injectors is independent, so that in case of fuel leakage in one of them the other systems are not affected. Water is driven by an independent pump and its return to the tank is open to allow control. The inlet and outlet pipes of each injector are provided with valves that allow the injector to be disassembled without the need to discharge water from the circuit.

The strikes in pumps and between the needle and the body of the injectors is three microns and they have a two micron filter, which serves so that particles detached from the inner walls of the high pressure tube enter the injector.

In naval engines, where the common rail cannot be applied due to its high electronic complexity, the conventional mechanical system is still used for injectors.


The injector is governed by the fuel pressure. The pressure generated by the injection pump (which can be single or double zipper) acts on the conical part of the needle and lifts it from the seat when the force applied from below is greater than the antagonistic force exerted from above by the spring, the fuel is injected into the combustion chamber through the holes of the injector (if it is a closed type injector). Once the stroke is finished, the pressure spring pushes the valve againof the injector against its seat. The injector opening pressure is determined by the initial (adjustable) tension of the pressure spring inside the injector holder. The stroke of the valve is limited by the existing front surface at the junction of the valve stem and the pressure pin.

Once the quantity driven by the injection pump has been injected, the spring pushes the needle back against its seat, thus being prepared for an upcoming new stroke. Its operation can be mechanical, which is just explained, or electronic (common-rail) 56296.

Types of Injectors

  • OPEN INJECTORS: They are generally used where fine spraying is not obtained with the injector but by other methods such as engines provided with turbulence pre-chambers or combustion pre-chambers. The nozzle of these injectors has a needle with a spray pin at its special shaping end, by various measures and the shape of the spikes can vary the injection jet. In addition, the spike keeps the hole free of deposits.

There are also them with a throttle effect, these allow a previous injection when opening the valve first, it leaves free a narrow circular gap, which allows only a little fuel to pass, as it continues to open, it increases the passage section and towards the end of the The needle completely injects the main cone-shaped amount. In this way, the fuel intake is done gradually and consequently the combustion is smoother.

  • CLOSED INJECTOR: Also called "Hole Injector", they are used in direct injection engines. The nozzle and the needle form a valve, which is strongly pressed on the seat by the action of a spring, and is separated therefrom by the action of the fuel. These injectors can be of one or several holes, in which case the angle of separation of said holes is always the same.

If it has a single hole, it can be located in the center or on the side of the end. It should be noted that the length and diameter of the holes influence the penetration power of the calorific and functional dart.

Color Code

The injectors can also be classified by the mass flow that can be emitted, this flow is measured in Pounds per Hour Lb / h. Many manufacturers to help differentiate the injector according to its flow use color coding for example:
  • White = 14 Lb / h
  • Yellow = 19 Lb / h
  • Gray = 24 Lb / h
  • Red = 30 Lb / h
  • Black = 36 Lb / h

The color depends on the manufacturer since there is no standardization an example the Manufacturer of Bosch injectors has the following code:
  • Gray = 14 lb. (5.0L Ford Truck)
  • Yellow / Orange = 19 lb.
  • Light Blue = 24 lb.
  • Red = 30 lb.
  • Brown = 35 lb. (4-cyl. SVO Turbo) (Low Impedance)
  • Dark Blue = 36 lb.
  • Lime Green = 42 lb.