Predictive Simulation of PFI Engine Combustion and Emission

This paper reports a methodology to estimate combustion pattern and emission by predictive simple simulation with good accuracy on various conditions of PFI engine. 3D-CFD cord VECTIS has been applied for this simulation, its settings and methods are as follows. RANS equation with liner k-epsilon model has been used as the turbulence model. Turbulent burning velocity equation contains not only turbulent velocity term but also laminar burning velocity term. For ignition model, we use a predictive model called DPIK. We iterate cycle calculation until wallfilm behavior is stabilized to get the reasonable mixture formation. We have applied this methodology to 125cc engine of motorcycle. As a result, we have obtained heat release curve and pressure curve with good accuracy on various operating conditions such as engine speed, engine load, air fuel ratio, wall temperature, and spray direction. CO and NOx calculated simultaneously have also been acceptable. CO formation is based on chemical equilibrium, and NOx formation is based on the extended Zeldovich mechanism. Using these results obtained by this methodology, optimal air-fuel distribution that affects heat release pattern and emission formation is suggested.