| 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 is 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. Because of the in-cylinder vaporization of the liquid fuel, which reduces 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.These advantages are dependent on a correct mixture preparation and distribution 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.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.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 , tumble ratio and injection angle on the mixture concentration distribution in the combustion chamber. The conclusions are drawn via the simulation:1. As the increase of in-cylinder pressure ,spray tip penetration was shorted,the spray angle was reduced and SMD was increased2. As the increase of injection pressure,the spray tip penetration was increased,the spray angle was increased too,but not as obvious as spray tip penentration,the SMD was reduced.3. The SMD greatly influences on spray characteristics,the the spray tip penetration and spray angle of the shorter SMD is shorter。Airflow in the center of the spray is completely different between two cases.4. For a given reverse tumble ratio, injection timing should be selected carefully for evaporation and mixing. Too early and too late injection are not favorable for both ignition and combustion.5. The in-cylinder reverse tumble and the scalloped piston shape are the key features of GDI stratified combustion engine. An optimum tumble ratio is necessary. Low tumble ratio is insufficient to transport t he fuel to the spark plug and high tumble ratio causes over-rich mixture near the spark plug at the timing of ignition.6. The injector orientation greatly influences on the equivalence ratio distribution. Relative early impingement of the spray on the piston surface is favorable to get ignitable stratified mixture near the spark plug.
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