Pre-ignition

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The pre-ignition is a combustion anomaly in gasoline engine , mostly highly charged combustion processes. It differs from knocking in that the mixture begins to burn before the end of the compression stroke and ignition. Particularly in the context of the downsizing of gasoline engines , the phenomenon is gaining in importance pre-ignition. In order to achieve better consumption and pollutant values, for example, the cubic capacity is reduced and the cubic capacity increased at the same time. Pre-ignition is a limiting factor for further optimization. Not all influencing factors and causes for the phenomenon have yet been clarified. However, these include: pressure and temperature conditions, hot spots on the cylinder walls, residual gas, temperature fluctuations in the working gas, the detachment of lubricant droplets from the cylinder wall and a critically high compression temperature, particles and certain properties of the fuels.

Pre-ignition is characterized by a particularly rapid pressure increase in the combustion chamber that occurs before the actually intended time . Since the ignition occurs during the compression stroke, this particularly high pressure occurs. The maximum permissible engine pressure is often exceeded. The resulting high mechanical stress on the engine block and cylinder head then leads to the sudden failure of these components. Even a few pre-ignition can seriously damage an internal combustion engine.

While most of the influencing factors primarily pose a problem for the further development of gasoline engines, deposits and particles can trigger pre-ignition in current engines too. Both causes can hardly be avoided in gasoline engines with direct injection. The reasons are, among other things, different driving profiles, which cannot all be covered in the design, as well as the properties of the fuels and engine oils. The result can be sooty combustion and oil entry in the cylinder. Oil and soot particles can accumulate on the walls and components and come off as particles during the work process. As free-moving particles, they absorb the temperature in the cylinder and cannot dissipate it via walls or components. Above a certain size, the particles no longer extinguish in time and can then lead to a pre-ignition of the fuel-air mixture in the following cycle. Developers around the world see the solution as a comprehensive approach that takes the further development and optimization of engine design, oil and fuel composition into account. Several manufacturers offer additives and special cleaning agents for the combustion chamber for the current generation of engines .

Individual evidence

  1. ↑ KIT - Research - Research Projects - Preignition
  2. ↑ Willand, Jürgen; Daniel, Marc; Montefrancesco, Emanuela; Geringer, Bernhard; Hofmann, Peter; Kieberger, Markus: Limits of downsizing in gasoline engines through pre-ignition . In: Motorentechnische Zeitschrift . No. 5 , 2009, p. 423-429 .
  3. ↑ Kadunic, Samir: Influence of the charge air temperature on the Otto engine. A potential for increasing the efficiency and performance of supercharged engines . Springer Vieweg, Berlin 2014, p. 23 .
  4. ^ Graf, Philipp: Investigation of irregular combustion phenomena in supercharged gasoline engines with direct injection, dissertation at the Faculty of Mechanical Engineering at the University of Karlsruhe . Karlsruhe 2015, p. 87-98 ( kit.edu ).
  5. ↑ Dedl, Jörg; Geringer, Bernhard; Budak, Oguz; Pischinger, Stefan: Key fuel figures for the description of pre-ignition in gasoline engines . In: Motorentechnische Zeitschrift . No. 5 , 2018, p. 76-81 .
  6. ↑ Chabot, Bob: Resolving Low-Speed ​​Pre-Ignition. Motor.com, January 2017, accessed January 10, 2019 .
  7. ↑ Trautermann, Lena: LSPI - the downsizing debacle. Autobild.de, March 8, 2020, accessed August 26, 2020 .
  8. ↑ Clean gas injectors efficiently without removing them. In: Auto Motor Accessories. Schlütersche Verlagsgesellschaft mbH, September 2, 2019, accessed on August 26, 2020 .