Abstract
A new combustion model has been introduced for the prediction of turbulent propagating combustion in SI engines. The model assumes that the flamelets consist of a turbulent dissipation part and a laminar part and is called Hybrid Fractal Flame Model (HFFM). A CFD code integrated the model and separately a pure laminar flamelet model, which was tested for comparison. Computational results were compared with measured pressures and heat release rates for several different engine speeds. It is shown that the HFFM agrees well with the measurements for 1000, 1500 and 1800 rpm, while the pure laminar flamelet model overestimates at lower engine speed and underestimates at higher engine speed. The analysis of the computed results indicates that the turbulent dissipation heat release rate contributes more to the total heat release rate as engine speed increases; from around 27% at 1000 rpm to 52% at 1800 rpm.
