Knock Model Covering Thermodynamic and Chemical Influences on the Two-Stage Auto-Ignition of Gasoline Fuels



SAE WCX Digital Summit
Authors Abstract
Engine knock is limiting the efficiency of spark ignition engines and consequently further reduction of CO2 emissions. Thus, an combustion process simulation needs a well working knock model to take this phenomenon into account. As knocking events result from auto-ignitions, the basis of a knock model is the accurate modeling of the latter. For this, the introduced 0D/1D knock model calculates the Livengood-Wu integral to estimate the state of the pre-reactions of the unburnt mixture and considers the two-stage auto-ignition of gasoline fuels, which occurs at specific boundary conditions. The model presented in this publication is validated against measurement data of a single cylinder engine. For this purpose, more than 12 000 knocking working cycles are investigated, covering extensively varied operating conditions for a wide-ranging validation. This enables to analyze the influence of different gasoline fuels, varying compression ratios, turbulence levels, injection strategies, EGR, wall temperatures as well as engine loads and speeds on the prediction of the auto-ignition onset. To specify the auto-ignition onsets of so many measured working cycles an automated and yet reliable method, analyzing the bandpass filtered indicated cylinder pressure, is used. The input of the knock model is gained via pressure trace analysis of the corresponding measurement data. The predicted auto-ignition onset is then compared to the one of the respective measured working cycles. It is shown that the introduced 0D/1D knock model can accurately predict the auto-ignition onset for all of the investigated knocking working cycles at extensively varied operating conditions with a standard deviation below 2 °CA.
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Hess, M., Grill, M., Bargende, M., and Kulzer, A., "Knock Model Covering Thermodynamic and Chemical Influences on the Two-Stage Auto-Ignition of Gasoline Fuels," SAE Technical Paper 2021-01-0381, 2021,
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Apr 6, 2021
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Technical Paper