Modeling knock in a GDI engine using LES incorporated with the G-equation and chemical kinetics

The knocking phenomenon in a GDI (gasoline direct injection) engine was modeled and investigated using KIVA-3V code with LES (large eddy simulation) combined with the level set G-equation for modeling flame propagation and chemical kinetics for modeling knock. A turbulent flame correlation of the level-set G-equation model for LES (large eddy simulation) is developed. A k-equation SGS model was applied in the KIVA-3V code to calculate the turbulent flow field. In the LES framework, a turbulent intensity closure method based on ADM (approximate de-convection method) was proposed to form a new turbulent flame correlation in the level set G-equation combustion model. The early flame kernel growth progress was predicted with the DPIK (Discrete Particle Ignition Kernel) ignition model. The turbulent flame propagation was described by the level set G-equation combustion model. A 47-species, 142-reactions PRF mechanism, including low C-number species and hydrogen oxidation was used to predict auto-ignition process of the end gas in front of the flame front and the post-oxidation process in burned zone. The model describes end gas auto-ignition and the spatial distribution of intermediate combustion radicals during spark ignition engine combustion. The simulation results agree with the experimental data in term of pressure trace. The model captured the turbulent flame propagation, flame wrinkles and end gas auto-ignition during SI engine combustion. The pressure distribution of the simulation result indicates that the local pressure in the combustion chamber is extremely uneven during the knocking process.