Research On Organization Forms Of Combustible Mixture For Gasoline Direct Injection Engine

With the rapid increase of the world’s vehicle possession, people take more andmore attention to the crisis of energy and environment. In order to keep thedevelopment of auto industry, many automobile manufacturers devote themselves todevelop vehicle power system which is more energy-efficient and environment friendly.At present, vast majority passenger vehicles’ power systems are gasoline engines, butthe fuel economy of gasoline engine is worse than diesel engine, so reducing gasolineengine’s fuel consumption becomes the most important issue for automobilemanufactures. It’s the most important goal for us to develop better vehicle engineswhich not only have many advantages of gasoline engine such as low noise, less PMemission, better low-temperature startup performance and power, but also own somesuperiority of diesel engine such as high-power, better fuel combustion etc. Thetechnology of GDI has become main development direction of vehicle gasoline engine.The key technology of GDI is how to organize combustible mixture. Because of thedifficulty of mixture measurement in the cylinder, it is a very important method tosimulation mixture formation process by means of CFD. The combustible mixtureformation processes of GDI engine were simulated from four aspects in this thesis.The influence of tumble intake passage on combustible mixture formation processwas studied. The mixture formation process only depending on tumble intake passagewas studied. Tumble intake passage is coming from common intake passage, the anglebetween intake port and the axis of cylinder is bigger. The piston is flat-roofed. Thegeometrical model of intake passage and chamber was built by means of Pro/E. Thesimulation mesh was generated by using FIRE software, which is a kind of professionalCFD software of engine simulation, the Solver Steering File was set, and the mixtureformation process was simulated. The results show that the tumble intake passage isable to produce better tumble flow, and this flow is very important for organizingcombustible mixture of GDI engine.The influence of fuel injection advanced angles and operating condition tocombustible mixture formation process were simulated. The results show that theoptimal fuel injection advanced angle of the GDI engine is46°, and its effective range is36°~56°. The tumble intake passage used in this research is able to organizecombustible mixture well at different engine operating conditions.The influence of chamber structure (piston roof shape) on combustible mixtureformation process was simulated. The simulation results show that the crater-bulgeroofed piston is easier to form combustible mixture than flat roofed piston, and it can organize richer mixture around spark plug. From spark plug to remote position of thecombustion chamber, the mixture concentration reduces gradually, so the GDI enginegets stratified combustion and the fuel economy can be improved.Finally, the combustible mixture formation at different operating conditions werecalculated. Simulation results show that the combustible mixture is able to be organizedwell at not only lower speed and load but the operating conditions of higher speed andload. At all operating conditions, the ignition timing can be controlled within8°~30°BTDC. GDI engine can get higher power output at this little advanced ignition angle.