| Gasoline direct-injection(GDI) engine is a promising alternative to cope with the more stringent emission legislation and the energy crisis. A GDI engine has the potential for significant improvement in fuel economy while maintaining higher output over port injection engine. The characteristics of mixture preparation in a GDI engine can be divided into two different regimes in terms of the load condition. In a full-load condition, fuel is injected in the intake stroke to form a nearly homogeneous mixture in the chamber. The combustion characteristics in this case are similar to that of a port-injection engine. In a part-load condition, fuel injection occurs in the later stage of the compression stroke to form ignitable stratified charge around the sparkplug, the air-fuel ratio is up to 30-40. The in-cylinder vaporization of the liquid fuel reduce the temperature and increases the density of the intake charge. This reduction in temperature also enhances the anti-knock performance of the engine and in turn allows GDI combution at higher compression ratio. In a word, GDI has become an important means to improve the economlcal performance and decrease the emission level for the coming gasoline engines.These advantages are dependent on a correct mixture preparation,distribution and ignition timing inside the cylinder. This means that both a proper atomizer and a thorough understanding of the processes involved in spray formation, vaporization and fuel distribution are needed. And the spray characteristics also affects the fuel distribution,the ignition process and the combustion process. The computational results reveal that spray wall impingement is important and the fuel distribution is controlled by the spray momentum and the combustion chamber shape. Under certain conditions, the mixing is characterized by the existence of many lean regions in the cylinder and the burning speed is very low; hence the combustion can be poor in these cases. In other word, we should study that a correct mixture preparation affects combustion stability for a wall-guided GDI engine.High pressure swirl atomizers are so far the most common design proposed to fulfil the requirements of GDI engine. The spray characteristics of high pressure swirl atomozers was studied in a constant volume chamber to validate the spray model and the effects of different parameters on the mixture concentration distribution in the combustion chamber was studied to evaluate the performance of a GDI engine with AVL FIRE. And the injection timing,injector orientation,tumble ratio and ignition timing significantly influences the fuel stratification pattern, which results in different combustion characteristics was studied . The main work includes: 1,Validate the spray model against the experiment data in a constant volume chamber and study the effects of injection pressure, in-cylinder pressure and SMD on the spray characteristics with AVL FIRE.2,Pouring of sillicagel for the chamber in cylinder head and the top of piston of GDI engine in order to get the 3D surface cloud data .Deal with the 3D surface cloud data with Gemagic, export the surface model in STL format,mesh generation and calculation with AVL FIRE.3,Simulation study the effects of injection timing and ignition timing on the stratified mixture combustion process in the wall-guided GDI engine combustion chamber.The conclusions are drawn via the simulation:1. As the advance of injection timing, the maximum of rate of mean pressure and mean temperature was increased, NOx emission was increased,but Soot and CO emission was reduced.2. As the advance of injection timing, the maximum of rate of heat release was increased and then decreased; It occur before the top dead center, and the advace angle was increased and then decreased too; When the injection timing was 40°CA BTDC, the advace angle was 2.4°before the the top dead center and was not at the range of 5-10°CA BTDC.3. The injection timing 50°CA BTDC was later injection, so the time of mixture formation became shorter in the spray,ignition and combustion process, hence the stratified mixture had the existence of many too concentrated regions (equivalence ratio>1.5),which caused higher Soot emission. But the injection timing 70°CA BTDC was earlier injection,so there was sufficient the time of mixture formation, hence the stratified mixture had the existence of many equivalence ratio equal to 1 regions, which caused higher NOx emission.4. As the delay of ignition timing, the maximum of rate of mean pressure was reduced, and power was reduced; the maximum of rate of heat release and temperature was increased and then decreased,but CO emission was reduced.5. The maximum of rate of heat release occured before or after the top dead center, as the advance of ignition timing, the advace angle was increased; When the ignition timing was 18°CA BTDC, its maximum of rate of heat release was the maximum in the four cases, and the advace angle was 6.8°before the the top dead center and was at the range of 5-10°CA BTDC. But ohers were not at the range of 5-10°CA BTDC.6. The ignition timing 23°CA BTDC was earlier ignition, so the time of mixture formation became shorter in the spray,ignition and combustion process, hence the stratified mixture had the existence of many too concentrated regions (equivalence ratio>1.5),which caused higher Soot emission. But the ignition timing 8°CA BTDC and 13°CA BTDC was later ignition, so there was sufficient the time of mixture formation, hence the stratified mixture had the existence of many equivalence ratio equal to 1 regions, which caused higher NOx emission.
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