Modeling Knock in Spark-Ignition Engines Using a G-equation Combustion Model Incorporating Detailed Chemical Kinetics

In this paper, knock in a Ford single cylinder direct-injection spark-ignition (DISI) engine was modeled and investigated using the KIVA-3V code with a G-equation combustion model coupled with detailed chemical kinetics. The deflagrative turbulent flame propagation was described by the G-equation combustion model. A 22-species, 42-reaction iso-octane (iC₈H₁₈) mechanism was adopted to model the auto-ignition process of the gasoline/air/residual-gas mixture ahead of the flame front. The iso-octane mechanism was originally validated by ignition delay tests in a rapid compression machine. In this study, the mechanism was tested by comparing the simulated ignition delay time in a constant volume mesh with the values measured in a shock tube under different initial temperature, pressure and equivalence ratio conditions, and acceptable agreements were obtained. The mechanism was further validated by modeling a gasoline homogeneous charge compression ignition (HCCI) engine at both low and high engine speeds. The G-equation combustion model was validated on the Ford DISI engine with spark advance and intake manifold pressure sweeps. Based on the model validation, knocking combustion under boost and globally stoichiometric operating conditions was simulated. Finally, knock mitigation strategies using cooled EGR and/or “two-stage mixing” were assessed based on the numerical analysis.