Knock Limited Spark Advance Prediction of a Direct-Injection Spark-Ignition Engine Using a Livengood-Wu Integral Transport Equation Based Knock Model

Knocking combustion limits the application of high compression ratios in gasoline engines and therefore obstructs the improvement of thermal efficiency. Predicting knock and knock limited spark advance (KLSA) can guide engine upfront design and optimization before the prototype is built. This study employed three-dimensional computational fluid dynamics (CFD) simulations coupled with an accurate and computation-efficient knock model to predict the KLSA of a turbocharged direct-injection spark-ignition engine. The knock model predicted the end-gas auto-ignition based on a Livengood-Wu (L-W) integral transport equation instead of directly using detailed chemical mechanisms, which was able to achieve a fast computation time. To keep the predictability, ignition delay data was calculated using zero-dimensional chemistry simulation and tabulated a priori, which was then used for CFD simulation on the fly. The results showed that the CFD model was able to well reproduce engine combustion processes and predict KLSA under different operating conditions. It showed that the errors between predicted and measured KLSA were within 2° crank angles. In addition, the model successfully predicted the increasing knocking tendency when the intake temperature increased, which further verified the accuracy of the knock model.