| Compared to conventional port fuel injection gasoline, direct injection gasoline can precisely control fuel inject quantity leading to the fuel consumption decrease 35%. Direct injection gasoline injects the fuel into cylinder directly. Fuel vapors by absorbing heat through air rather than cylinder wall, which can improve volumetric efficiency and decrease knocking. But, GDI engine has short fuel air mixing time result in improper mixing condition. To achieve required in_cylinder air fuel mixture is a key technology. The mixing process is influenced by injector’s characteristic, injection position, injection angle, in_cylinder tumble flow, chamber geometry and injection strategy. The air fuel mixing process and control in the model of homogenous stoichiometric mixture combustion of GDI engine base on Star-CD software and get some conclusions as follows.First, the break up model, which is used in the simulation is calibrated based on experimental data. The testing condition of injection experiment including background pressure, temperature and injection parameters are determined. Then, geometry model and mesh model of high pressure container are set up. Finally, the break_up model’s parameters are determined by penetration and spray images from text. The calibration result shows that the simulation results matches experimental data and the parameter of the break_up model can be used in the following in_cylinder spray simulation.Secondly, in_cylinder flow and spray simulation model is set up with Star-CD software. The influence of injector’s fix location, fix angle, injection star time and chamber geometry on in_cylinder air fuel mixing process are analyzed. The following conclusions are obtained.1) The injector’s location at intake side is better than that at exhaust side and middle of in/exhaust valves. It can format stable flammable mixture near spark plug at ignition time only when the injector is located in the middle side and intake side. The mixture homogeneity in the middle side is worst while the mixture homogeneity in the intake side and exhaust side are much better. Vertical stratified mixture can be obtained when the injector’s location is at exhaust side while radial stratified mixture can be formed when the injector’s location is at middle side. But neither of the stratified mixture are required.2) Scheme 2 is the best among the three injector fixing angle schemes. Scheme 2 can form stable flammable mixture near spark plug at ignition time. In scheme 3 fuel vapors fast leading to partial fuel mixture as the injector’s fixing angle is too large. In scheme 1 has much more impingement at cylinder wall and piston head.3) Mixture homogeneity become worse at ignition time with delay of injection start time and impingement in cylinder wall increase. The proper injection star time should be at early stage of intake stroke which can increase mixing time.4) Bowl piston crown can guide the air flow and it can speed up fuel evaporation, which can get uniform fuel mixture distribution at TDC compare with plate piston crown. |
