Fuel injection

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Fuel injection is a collective term for all mixture formation systems in internal combustion engines that do not have a carburettor . In the specialist literature, various types and systems of fuel injection are described, some of which differ considerably from one another, the most important differentiating criterion being the position of the injection nozzle. In simplified terms, a distinction is made between direct injection with internal mixture formation and indirect injection with internal or external mixture formation , although there are also detailed differences between injection systems of individual engine types depending on their functional principles ( diesel , gasoline, etc.). Furthermore, a distinction can also be made between the type of regulation, which can be purely mechanical or electronic (or computer-controlled). This article therefore only gives an overview of the individual systems without explaining them in detail.

There are also other colloquial terms that are not all-encompassing and, above all, are intended to express a differentiation from the carburetor without being described in the specialist literature, such as (electronic) gasoline injection , which usually means types of direct gasoline injection and manifold injection, injection , Injection system or injector .

Direct injection

As a direct injection method for internal mixture formation in which the designated fuel directly into the combustion chamber is injected:

There are also special procedures:

  • FM method (hybrid method derived from the M method)

Indirect injection

With internal mixture formation

In the case of indirect injection with internal mixture formation, the fuel is injected into the secondary combustion chamber of a combustion chamber which is divided into main and secondary combustion chambers. Injection takes place at an early stage during the beginning of the compression, which means that only a relatively low injection pressure has to be overcome, while the fine atomization and evaporation of the fuel are achieved primarily through swirling and heating during the continued compression. Diesel engines with indirect injection are also known as chamber diesel engines . Indirect injection processes include:

With external mixture formation

With indirect injection with external mixture formation , the fuel is injected into the intake pipe of the engine and a finished fuel-air mixture is drawn in by the piston. This process, which is mainly used in gasoline and rotary engines , is known as manifold injection and can be divided into two subtypes:

  • Central injection
  • Multipoint injection


  • Richard van Basshuysen, Fred Schäfer (Ed.): Handbuch Internal Combustion Engine , 8th Edition, Springer, Wiesbaden, 2017, ISBN 978-3-658-10901-1 , Chapter 12, pp. 641-656; Chapter 15, pp. 751-756
  • Alfred Böge (Ed.): Vieweg Handbook Mechanical Engineering Basics and Applications of Mechanical Engineering Technology, 18th edition, Springer, 2007, ISBN 978-3-8348-0110-4 , p. L 86-101 (1002-1017)
  • Dr.-lng. Kurt Lohner, Dr.-Ing. Herbert Müller (authors): Mixture formation and combustion in gasoline engines , in Hans List (ed.): The combustion machine, Volume 6, Springer, Vienna, 1967, ISBN 978-3-7091-8180-5 , pp. 60-64