Researches On Double-Layers Diffluent Combustion System Of DI Diesel Engine

The combustion process and emission characteristics in DI diesel engine mainly depend on the quality of the air-fuel mixture. The matching between the combustion chamber structure and the fuel spray is the main factor that affects the mixture formation in the combustion chamber. Effective utilization of the ubiquitous diesel spray impingement could improve the spatial distribution and the atomization of the spray, also promote a rapid mixing and combustion of the air and fuel. In this dissertation, based on the principle of spray-impingement and space-atomization, a new Double-Layers Diffluent Combustion System was proposed. A series of CFD simulation and experimental research were carried out on this system. The following research work has been done in this paper:(1) According to the principle of spray-impingement and fuel space-atomization, the Double-Layers Diffluent Combustion System was developed. The spray-oriented stairs which divide the combustion chamber into upper and lower layers is set inside the combustion chamber. In this combustion system, the upper layer’s diameter is larger than the lower layer’s, that result in a smaller clearance volume. The fuel injected from the multi-hole injector impact on the oriented stairs and then expand into two parts along the oriented-surface. That can avoid the stagnant fuel around impingement location and accelerate the formation of the air-fuel mixture.(2) Numerical simulation about the mixture formation, the process of air flow and the combustion processes in the Double-Layers Diffluent Combustion System and the original ω combustion system was carried out with AVL FIRE v2008. The result shows that the new combustion system can effectively promote the formation of homogeneous mixture. The utilization rate of air and the quality of the mixture in the cylinder were improved through the simultaneous combustion of the both layers.(3) The influence of injection pressure, injection advance angle, nozzle holes and the protrusion height on the performance of the Double-Layers Diffluent Combustion System were tested on a single cylinder135diesel engine.(4) The performance of the Double-Layers Diffluent Combustion System was compared with the original combustion system. The result shows that with a8X0.16X150o nozzle and protrusion height is1.4mm, while the rail pressure is11OMPa and injection time is9o CA BTDC, both fuel consumption and soot emissions of the new combustion system are lower than the original combustion system, but NOx emissions are higher. Under the100%load, fuel consumption and soot emission dropped by7.7g/(kW-h) and0.11BSU respectively, NOx emissions increased by120ppm in the new combustion system.