Computational Fluid Dynamics (CFD) Modelling of Mixture Formation in Gasoline Direct Injection (GDI) Engine

Abstract

Automotive engine faces stringent regulations on emission with improved fuel consumption. As such, the Gasoline Direct Injection (GDI) engines which have the potential to meet these requirements are being improved on especially the mixture formation to the burning of the mixture. In GDI, late injection compared with early injection scheme generates charge stratification which contributes to the optimised fuel consumption and combustion. As a result, this strategy in GDI engines is considered to be promising with increasing research focus. This paper aims at evaluating the computational fluids dynamics (CFD) modelling of two-phase transient injection process in generic GDI engines with the late injection to study the features of fuel atomisation process, injection velocity and its influence on turbulence. The commercial CFD code Star CCM+ was used to perform this simulation due to its advanced polyhedral mesh technology and the user-friendly interface. Transient liquid and gas flow inside the combustion chamber was simulated using the Eulerian multiphase segregated flow model with k-epsilon turbulence. The contour plots show that during the injection period turbulence for each phase was independent of the spray shape predicted to be asymmetric under non-vaporisation conditions. In addition, increasing injection velocity of liquid fuel causes stronger turbulence for the liquid phase. The results also show that the variation of turbulence for gas-phase is mainly centred in the region of the inlet during the injection process and non-homogenous turbulent characteristics were observed for the late injection with the volume fraction of the liquid phase also seen to be asymmetric.