Ignition delay

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Ignition delay in the diesel engine, specified for a cetane number of ~ 56

As ignition delay is the time of commencement of injection in the cylinder of an engine until the actual start of combustion of the air-fuel mixture.

Ignition delay is known as a speed-limiting feature, especially in diesel engines , since combustion does not start immediately with injection. The maximum speed is characterized for four-stroke diesel engines to about 5500 min -1 limited.

The ignition delay has two temporal components:

  • The physical ignition delay describes the time that passes when the fuel mixes with the air.
  • The chemical ignition delay is characterized by heating of the fuel and chemical pre-reactions up to spontaneous ignition.

The ignition delay depends on various factors:

  • the ignitability of the fuel, which is described by the cetane number ,
  • the temperature in the combustion chamber,
  • the pressure in the combustion chamber and
  • the type of mixture formation, which can be influenced, for example, by the nozzle (distribution of the droplet size in the fuel jet) or the air flow (e.g. umbrella valves in the inlet, tangential flow channels, shape of the piston crown).

In diesel engines, the lowest possible ignition delay is desired, also so that the amount of fuel present in the combustion chamber at the time of ignition is not too large, which would result in rough engine running (so-called nailing). In gasoline engines, the fuel should be as unwilling as possible to ignite in order to avoid knocking combustion.

See also


  • Richard van Basshuysen , Fred Schäfer: Handbook internal combustion engine. Basics, components, systems, perspectives. 3rd completely revised and expanded edition. Friedrich Vieweg & Sohn Verlag / GWV Fachverlage GmbH, Wiesbaden 2005, ISBN 3-528-23933-6 .
  • Friedrich Sass : History of German internal combustion engine construction from 1860 to 1918 , Springer, Berlin / Heidelberg 1962, ISBN 978-3-662-11843-6 , pp. 407-408