Engine Knock Prediction and Evaluation Based on Detonation Theory Using a Quasi-Dimensional Stochastic Reactor Model 2017-01-0538

Engine knock is an important phenomenon that needs consideration in the development of gasoline fueled engines. In our days, this development is supported by the use of numerical simulation tools to further understand and subsequently predict in-cylinder processes. In this work, a model tool chain based on detailed chemical and physical models is proposed to predict the auto-ignition behavior of fuels with different octane ratings and to evaluate the transition from harmless auto-ignitive deflagration to knocking combustion. 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 (Ethanol consisting Toluene Reference Fuel, ETRF). The reaction scheme is validated for a wide range of mixtures and every desired mixture of the four fuel components can be applied in the engine simulation. The engine simulations are carried out with a quasi-dimensional stochastic reactor model that allows studying cycle-to-cycle variations. A novel post-processing strategy based on the detonation theory by Bradley et al. (2012) is developed to evaluate the character and the severity of the auto-ignition event for stochastic engine models. This theory has been successfully applied to three-dimensional computational fluid dynamics simulations before by other groups (Bates et al. 2016, Robert et al. 2015). For the discussed approach, the theory is in this paper transferred to a quasi-dimensional stochastic internal combustion engine model. We suggest to use the variance of the auto-ignition severity to characterize the harmfulness of knocking operating conditions. By using the suggested tool chain, the knock limit can be predicted close to experimental findings. Fuel properties such as octane ratings can be studied. The transition from harmless deflagration to knocking combustion can be pictured, further investigated and the severity of the auto-ignition event evaluated.