Initial Pre-ignition: Identification of the mechanism for initial pre-ignition by a combination of experimental investigations and simulation of drop ignition

Thorsten Schweizer, Heiko Kubach, Norbert Zöbinger, Thomas Lauer, Markus Eder, Peter Grabner, Robert Schießl, Chien Chia Liu

Research output: Chapter in Book/Report/Conference proceedingChapter

Abstract

In the framework of this research project, the fundamental mechanism of the initial pre-ignition in highly charged gasoline engines was investigated at low engine speeds. In order to get insight into the characteristics of this stochastically occurring, irregular phenomenon, testbed experiments in combination with numerical simulations were conducted. Besides the thermo-dynamic characterization of the LSPI frequency (LSPI: Low-speed pre-ignition) under varying engine conditions, processes inside the combustion chamber are optically recorded. Addition-ally, the influence of the liquid fuel on the pre-ignition mechanism is investigated by modifying the engine configuration to CNG operation. Furthermore, the possibility of oil droplet induced ignitions was investigated by supplying lubricating oil to the engine manifold.
In order to investigate the LSPI phenomenon numerically, the thermodynamic conditions inside the combustion chamber are calculated using a 3D-CFD engine model. On top of this, a de-tailed 11-component fuel surrogate approach was used to investigate the wetting of the com-bustion chamber walls by the fuel spray. Based on this data, comprehensive numerical studies on oil-droplet-induced ignitions and hot-particle-induced ignitions are carried out.
The performed investigations showed that all initial pre-ignitions are induced by light-emitting surface deposits or flying objects. The areas of deposit formation and detachment events could be correlated with regions of intensive fuel wall wetting. Further on, there was no experimental or simulative evidence of oil-droplet-induced pre-ignitions. In the case of inert particles, numer-ical studies showed that they were not able to surpass the necessary minimum surface tem-perature to initiate a pre-ignition within two consecutive cycles.
Based on the results obtained, a fundamental formation mechanism could be synthesized, which suggests that accumulations of oil and fuel in the combustion chamber are processed through multiple combustion processes in such a way that highly reactive deposits can arise. These can be heated up in such a way that they can trigger premature ignition of the mixture directly at the wall or in the gas phase.
The objective of the research project was achieved.
Translated title of the contributionInitiale Vorentflammung: Identifikation des Mechanismus zur initialen Vorentflammung mittels Kombination von experimentellen Untersuchungen und Simulation der Tropfenzündung
Original languageEnglish
Title of host publicationFVV Final Report
Subtitle of host publicationCombustion Noise Otto Engine II
Place of PublicationFrankfurt
PublisherForschungsvereinigung Verbrennungskraftmaschinen e.V.
Chapter7
Number of pages126
VolumeR597 (2021)
Publication statusPublished - 2021

Fields of Expertise

  • Mobility & Production

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