Injection systems

injection engine

In engines that use fuel injection systems, there are various classifications that respond to several fundamental factors of its design and operation.

In order to classify each injection, we must take into account the number of injectors in the system, your location, the shape and synchronization of injections, and system that drives each one of them.

Injection systems according to the number of injectors

In the first place, according to the first classification, it is then that the systems of multipoint or single point injection.

  • Regarding the systems single point, as its name seems to indicate, we only find one injector, which occupies a role similar to that played by carburettors on old engines.
  • A system multipoint, on the other hand, uses one injector for each cylinder of the engine, then the number of injectors directly proportional to the number of cylinders.

injectors of an engine

Injection systems according to location

As we mentioned at the beginning, there are classification criteria according to the injector location, and therefore the place where the mixture of fuel and air occurs. Something independent of the number of injectors used (classification that we developed in the previous point).

In this classification, we must mention two types of locations, under the name of direct or indirect.

  • In the direct injection, the injectors deliver the fuel directly into the combustion chamber. This is a system used for many years in diesel engines (for example, UIS and UPS) and which has spread widely in gasoline engines, since its appearance in production gasoline engines with the Mitsubishi GDI. This is because the old problems that caused the high temperatures, who They crashed the system too often..
  • La indirect injection, on the other hand, has the injectors in the intake manifold or if necessary in a swirl chamber. That is where it mixes with the air so that it reaches the combustion chambers well distributed, once the doors are opened intake valves.

If you want to know more about these two injection systems, we recommend that you visit the article about their fundamental differences. Both have a number of advantages and disadvantages that make them suitable for different engine types.

electric fuel pump
Related article:
Fuel pump: operation, prices, breakdowns and checks

Engines that combine direct and indirect injection

As each system works better than the other in certain circumstances, there are brands that try to bring out the good in both worlds. There are models, such as the Ford Mustang GT or the Audis with the 2.5 TFSI engine, that use a dual injection system direct and indirect.

They use the direct injection al starting and under heavy acceleration, because it is a system that facilitates ignition and reduces the risk of self-detonation when a lot of fuel is injected into the combustion chambers. Instead, when driving at peak throttle or light acceleration, choose the indirect injection because less polluting gases are emitted, as the fuel mixes better with the air.

Continuous and intermittent injection systems

This differentiation can still be made, although the most widespread for fuel saving reasons is the intermittent one.

  • continuous injection: the injection is uninterrupted, although the amount of fuel required at any time can be varied. It was used in indirect injection engines, since this system is not compatible with direct injection.
  • intermittent injection: the Engine Control Unit (ECU) It is capable of controlling the fuel supply given by the injectors. This way you can cut off the injection completely and make them work only when required.

Injector systems according to their timing

Finally, we have to develop the classification according to injector timing. In systems of intermittent injection, fuel injection can be coordinated in different ways: simultaneous, sequential and semi-sequential. Each one with a different operation.

  • Simultaneous injection: fuel is injected at the same time in all the injectors, which start or stop their unison operation if the central unit requires it.
  • in the injection sequential, the injection is synchronized with the opening of the intake valve, although each injector act at different times.
  • in the injection semi-sequential, the injectors eject the fuel in pairs.

1965 Chevrolet Corvette Sting Ray HP Fuel Injection Engine

Mechanical or electronic injection system

Again here there is a differentiation of injection systems although one of them has been completely imposed.

  • mechanical injection: It is an obsolete system that was used in the first decades of injection use. In the 40s, the electronics of today's cars did not exist, so the injection was activated by a mechanical distributor that distributed the fuel to each injector. The amount of fuel was determined by the flow meter.
  • Electronic injection: The introduction of electronics in the 60s allowed for more precise and efficient control of the injection system. A good example is the engine that you can see in the image immediately above: that of the 1965 Chevrolet Corvette Sting Ray Fuel Injection. Over the years it has been perfected, until achieving the current results. Today, the ECU receives information from multiple engine sensors and decides much more accurately when to supply fuel and how much.

For example, the injection system electronics allows you to control the degrees of ignition advance, thanks to the fact that it receives information on temperature, pressure, air quality, engine speed, etc. It also makes it possible to avoid harmful effects on the engine, such as self-ignition, detonation and crank knock, or even apply a injection cut in case of accident.


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      Jose said

    I want you to explain to me what lifters are and when they should be repaired or changed. Because the engine of my car has a loud sound and this is due to the lifter. This was told to me at an auto mechanic shop.

      walter meadow said

    hello good evening I have a Japanese mitsubishi pajero 3.5 gdi exceed 1999 and I have a problem because it makes a noise sometimes not always when I turn it on a quite loud noise that after a moment stops and not a single noise is as if it were a bearing or something like that I don't know well and the other thing is I can't locate the gasoline filters where are they located??? how many does it take??? since I understand that some gdi have up to 3 please help and where can I find spare parts for this model since in Chile it is quite difficult to locate

      Valeria Arias-Cordova said

    Good night, I have a Mitsubishi car, it gave way with GDI, I used 97 gasoline, I had no problems until the tap made 90 gasoline, the amount of 10 soles, from there my problem began, the car would not start, it would start until it started and it began to fail me. the check turns on and only the starter does not turn on what would be the reason can you help me I would appreciate it

      Agustina said

    They ate the first part of injector systems according to the injection timing it seems to me

      Alberto Andres Gutierrez Gonzalez said

    Hello, I am a student of automotive mechanics, this information helped me to complement my knowledge, I just have an evaluation related to gasoline and diesel injection systems, very grateful for these pages that share information on these contents,
    Thank you.

      Miguel Angel Carpio Espinoza said

    good explanation, thanks.