Engine Knock Prediction and Evaluation based on Detonation Theory using a quasi-dimensional Stochastic Reactor Model

Paper #:
  • 2017-01-0538

Published:
  • 2017-03-28
Abstract:
Engine knock limits the efficiency of spark ignited engines. It is therefore an important phenomenon that needs consideration in gasoline engine development. Beside the engine design and operating mode, the fuel quality has a major impact on engine knock. The fuel quality and composition differs worldwide due to different national regulations and therefore needs to be considered in engine simulations. In these simulations one of the key issues is to predict and evaluate the transition of harmless deflagration induced by auto-ignition in the unburnt zone to undesirable knocking combustion. Hence, it is important to classify the severity of the auto-ignition event. In our method, the auto-ignition and emissions are calculated based on a new reaction scheme for mixtures of iso-octane, n-heptane, toluene and ethanol. In combination with a correlation based mixture formulation tool, gasoline surrogates can be formulated with close agreement to the physical and chemical properties of the commercial gasoline. The engine simulations are carried out with a quasi-dimensional stochastic reactor model used for example in Pasternak et al. [SAE Technical Paper 2015-01-1243]. A post-processing strategy is used to evaluate the character and the severity of the auto-ignition event based on the detonation theory by Bradley et al. [SAE Technical Paper 2002-01-2868]. Bates et al. [Combustion and Flame 2016] successfully applied the theory to LES CFD simulations. In our work this approach is transferred to the stochastic engine model which allows to study cycle-to-cycle variations. Sensitivities to different octane numbers and ignition timing are shown.
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