A Numerical Simulation Study Of The Effects On The Mixture Formation By The Intakeport Geometry In GDI Engine

The gasoline direct injection(GDI) engine has an advantage on fuel economy compared to the port fuel injection(PFI) gasoline engine. By combining with turbo-charge, VVT, EGR and other advance engine technologies, GDI has wider applied. It is considered to be the main technology for future gasoline engine. In this paper, to study the effects on the mixture formation by the intake port structure parameters of GDI engine, the simulation for steady flow test with different intake ports and the operations of GDI engine was carried out. This study can provide guidance for optimization design of the intake port of the GDI engine.First, the grid independent verification for numerical simulation based on the three-dimensional model of a GDI engine was conducted in this paper, and the grid size for subsequent calculations was set to be 0.25mm-2mm. The simulations for the spray test and GDI engine work process at high-speed Wide-Open throttle(WOT) operating condition were carried out. The accuracy of the computing models such as spray model and combustion model were verified by comparing the numerical results of with the experimental data.Then, this paper created four different structures were created by changing the throat and the inlet area and the steady flow test simulation were carried out. In order to verify the reliability of the numerical simulation, the the steady flow test for Case1 was carried out. Comparing the flow coefficient of Case1 obtained by simulation and the experimental data, the maximum relative error is 4.70%, the simulation results and experimental results are in good agreement. The analysis of the flow field in intake port and cylinder show that the flow coefficient increases with the increase of the area of the throat and inlet, and reducing the area of the throat and inlet can improve tumble ratio.At last, the transient CFD simulation of the four GDI engine models with different intake port structure at high-speed WOT conditions conducted. The analysis showed that the amount of air intake for the three GDI engines were almost the same under pressurized conditions. It can be concluded that the intake flow coefficient has little influence on the amount of air intake for a Turbocharged gasoline engine. Reducing the area of throat can increase the tumble ratio in cylinder, and the tumble ratio also can be increased by reducing the inlet area, but this increase is not obvious at high-speed WOT conditions. The larger tumble ratio and the stronger turbulent kinetic energy intensity of the in-cylinder flow is beneficial to form a homogeneous mixture, but the combustion and emission are not the best, because the tumble ratio and turbulent kinetic energy intensity influence the uniformity of the mixture directly. It can’t determine the concentration distribution of the air-fuel mixture at ignition time which influences the combustion and emission performance.