| One of the main factors to determine the performance of the direct injection diesel engine is the fuel spray and the formation quality of the gas mixture in the cylinder.In this paper,the formation and distribution of the mixture in a direct injection diesel engine are studied based on the double-layers diffluent combustion system,and three kinds of improved diesel engine double layered combustion chambers were designed.Those combustion chamber structure makes full use of the impingement spray theory and the principle of fuel atomization in space,under optimization matching with the fuel injection pressure,nozzle protrusion height and injection timing,realize double-layers diffluent in the combustion chamber.And make the gas mixture in the combustion chamber space distributed more uniform,thereby improving combustion process and emission performance of diesel engine,and also the engine performance.The main research work is as follows:(1)The design principle and calculation method of the main parameters in the structure design of direct injection diesel engine double-layers diffluent combustion system are analyzed in detail.Based on the impingement spray theory and the principle of fuel atomization in space,put forward the new double-layers diffluent combustion chamber structure in three sizes,through collision stage in the combustion chamber of direct injection diesel engine,the fuel spray is divided into two layers.By using the stripping function of the cambered surface and the guide surface to avoid the formation of oil accumulation in the near wall collision point,so that fuel and gas can be mixed more quickly;(2)Use 3D CFD software AVL FIRE v2008 making numerical simulation for working process of diesel engine of the three new double-layers diffluent combustion chamber project.Analysis the formation,flow and distribution of the mixture in the cylinder under this structure of combustion chamber.The results show that the new combustion chamber structure can effectively improve the quality of the gas mixture formation,and improve the utilization ratio of the air in the cylinder and the combustion quality of the gas mixture;(3)Compared the effects of the structure of the new double-layers diffluent combustion chamber matching with different spray cone angle,nozzle protrusion height,number of nozzle hole on the quality of the gas mixture in the cylinder.In the double-layers diffluent combustion chamber,the distribution of the gas mixture of 8×0.16×145°nozzle is better than that of the 6×0.18×145° nozzle.8×0.16×145° nozzle with 1.8mm nozzle protrusion height is better then that with 1.0mm and 1.4mm nozzle protrusion height on performance as a whole.A lower nozzle protrusion height can make the increase of diffusion range,so the air utilization rate in combustion chamber is increased,improves the quality of the mixed gas,and the soot emission decreases;(4)The injection strategies of three combustion chamber schemes and diffent injection timing were compared and analyzed.The results show,when the fuel injection advance angle is 11°CA,the engine performance of the diesel engine is the best. |
