A G-equation Combustion Model Incorporating Detailed Chemical Kinetics for PFI/DI SI Engine Simulations

A G-equation-based combustion model incorporating detailed chemical kinetics has been developed and implemented in KIVA-3V for Spark-Ignition (SI) engine simulations for better predictions of flame propa- gation and pollutant formation. A progress variable concept is introduced into the turbulent flame speed correlation to account for the laminar to turbulent evolution of the spark kernel flame. The flame front in the spark kernel stage is tracked using the Discrete Particle Ignition Kernel (DPIK) model. In the G-equation model, it is assumed that after the flame front has passed, the mixture within the mean flame brush tends to local equilibrium. The subgrid-scale burnt/unburnt volumes of the flame-containing cells are tracked for the primary heat release calculation. An iso-octane kinetic mechanism coupled with a reduced NOX mechanism is used to describe the chemical processes in the post-flame region and the potential heat release from the end gas. The integrated model was used to simulate the combustion pro- cess in a Ford four-valve single-cylinder SI engine, which is equipped with both Port-Fuel-Injection (PFI) and Direct-Injection (DI) fuel systems. For both PFI and DI operational modes, good agreement with experimental in-cylinder pressure, heat release rates and engine-out NOX was obtained for different spark timings and internal residual levels.