Multidimensional Numerical Simulation Of Flame Propogation And Knocking Combustion In Boosted GDI Engine

The fuel economy of gasoline direct injection(GDI) engine is usually improved due to high compression ratio(CR) and turbo-charging techniques. However, in high load operation conditions, high CR and intake pressure would lead to knocking phenomenon in boosted GDI engines. This thesis is focused on boosted GDI engine, applying large eddy simulation(LES) coupling with flamelet combustion model and chemical mechanics to the numerical analysis of knocking combustion and its mechanism.In RANS framework, a generalized renormalization group(G-RNG) turbulence model was applied to simulate non-reacting flows in an optical single-cylinder engine. Turbulent flow in this 4-valve engine was simulated with the standard k ?? and a generalized RNG turbulence model using the KIVA-3V code. Experimental data were used as the boundary and initial conditions for the calculation setup, the simulation results were compared to the measured data. Good agreement was found between the experiment results and simulation results with the G-RNG turbulence model.The LES one equation kinetic energy sub-grid model was applied in the open source code KIVA-CHEMKIN, and was validated by a backward-facing step flow case. The spray sub-model was modified under LES method, and was validated by a spray case in a constant volume bomb. The intake process and fuel-air mixing procedure of a GDI engine was calculated by both RANS and LES method. With the analysis of the effection of turbulent fluctuations on velocity field, the distributions of turbulent viscosity and kinetic energy, the LES method could capture more details of instant turbulent flow and make more reasonable predictions of mixing process in the GDI engine.The Discrete Particle Ignition Kernel(DPIK) model and G-equation combustion model were modified under LES method and validated by a turbulent combustion case in a SI engine with simple geometry. A one equation kinetic energy sub-grid model was adopted to calculate the flow field. The early flame kernel growth progress was predicted with the DPIK ignition model. The turbulent flame propagation was described by the level set G-equation combustion model. A 47-species, 142-reaction PRF mechanism was used to predict the auto-ignition process of the end gas in front of the flame front and post-oxidation process in the burned zone. Knocking combustion in the GDI engine under highly boosted conditions was simulated. The knock intensity was evaluated by monitoring pressure oscillations at different measurement points. The effection of spark timing and equivalence ratio on knocking combustion was studied based on the numerical analysis.