Experimentelle und numerische Untersuchungen zur oberflächeninduzierten Vorentflammung im Ottomotor

Aachen (2019) [Dissertation / PhD Thesis]

Page(s): 1 Online-Ressource (II, 136 Seiten) : Illustrationen, Diagramme

Abstract

This work investigates the phenomenon of surface-induced pre-ignition with regard to the influence of different hydrocarbon-air mixtures. The selection of the investigated fuels includes blends of market fuel conforming to standards with individual hydrocarbons, as typically found in gasoline fuels, but also biofuels for potential future applications in gasoline engines. With this selection and further fuels (37 in total) both experimental and numerical investigations were carried out. In the experimental part, a single-cylinder research engine was equipped with a glow plug, whose feedback controlled temperature was used to set up a reproducible hot spot in the combustion chamber to initiate surface-induced pre-ignition. Based on these experiments, it can be deduced that the addition of isohexane, n-hexene, n-heptane or cyclohexane reduces the pre-ignition resistance of a fuel. The mixture quantities of these hydrocarbons are chosen between 15 and 21 %-vol. within the fuel blends. The influence of n-heptane in particular is already reflected in a reduced critical glow plug temperature at smaller proportions of 3 to 5 %-vol. above which a frequency of pre-ignition cycles of 2 % can be observed. Although an admixture of toluene and ETBE does not lead to an increase or decrease in the pre-ignition resistance of the base fuel in the blends investigated, it does cause the pre-ignition resistance of the fuel mixture to be maintained even with a significant increase in the proportion of n-heptane. Methanol and ethanol behave almost neutrally with regard to the pre-ignition resistance of the fuel mixture at low admixture proportions. In each case, methanol with a proportion of 7 %-vol. and ethanol with 10 %-vol. were added. The pre-ignition resistance of the blended fuel only decreases with higher proportion of these alcohols added. Furthermore, the following dependence between the reaction kinetics and the surface-induced pre-ignition tendency of the biofuels present was demonstrated with the aid of numerical investigations: none of the biofuels shows NTC behaviour. For such a case, a significant chemical heat release only occurs immediately in the course of self-ignition. This, in turn, is almost exponentially dependent on the temperature, which is why surface-induced pre-ignition with the underlying biofuels only occurs at high temperatures, where the ignition delay time of the gas drops to values on the engine time scale of a few milliseconds. Due to this fact, the critical glow plug temperature of the biofuels under consideration correlates with gas temperatures in the high temperature range of the reaction kinetics. The critical glow plug temperature at 5 % pre-ignition frequency and the gas temperature at an ignition delay time of 0.1 ms correlate in a linear regression with a coefficient of determination R$^{2}$ of approx. 96 %.

Authors

Authors

Budak, Oguz

Advisors

Pischinger, Stefan
Heufer, Karl Alexander

Identifier

  • REPORT NUMBER: RWTH-2019-03609

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