Study On Influencing Factors Of Spray Characteristics Of Diesel Engine And Formation Of Mixture

Along with the updating emission regulations and serious energy shortage, hing power density, low fuel consumption, clean emission has gradually become the mainstream development trend of modern internal combustion engine. Depend on its special performance advantages, diesel engine is applied in more and more field. Diesel engine is mainly about diffusion combustion. The mixing process of diesel and air is the key point that has effect on combustion quality, and the quality of mixture directly has effect on the engine performance of power, economic and emission. For this reason, for a high-speed DI diesel engine, with the combining methods of testing and numerical simulation, spray characteristic, mixing process, and mixture quality of diesel engine were studied, and the factors that affect mixture forming were analyzed and studied.Firstly, the three-dimension model of the flow space of this diesel engine injector was established, and the dynamic simulation computational model which could simulate the motion law of injector needle was established, and cavitating flow of nozzle hole was computed. During the needle rising, keeping, and descent process, the variation of cavitating area and flow were analyzed, and the detailed flow information of hole exit plane was transferred to spray simulation model as boundary conditions. The result indicate that: during the needle rising process, the cavitating flow developed rapidly and cavitating area expend gradually; during the needle keeping process, cavitating flow of hole was basically steady, but cavitating flow of hole exit plane keep on developing, and completed cavitating area has emerged and tend to steady; during needle descent, the whole cavitating area of hole was steady, but completed cavitating area expended gradually, and the completed cavitating area run through the hole before needle closed.Secondly, with spray high-speed photography testing bench, spray characteristics of this engine injector were studied. Though tow groups of photography experiments, the effect of spray pressure and environment backpressure on spray characteristics were studied. The results show that: when environment backpressure was fixed, spray penetration and cross-sectional positively varied with spray pressure; when spray pressure was fixed, spray penetration and cross-sectional negatively varied with environment backpressure; spray cone angle was influenced by spray pressure and environment backpressure, but also by spray duration.Then, the dynamic simulation model for diesel engine circulation process, including compress, spray, combustion and expansion, was built by CFD software. This simulation model was verified by cylinder pressure data that got by testing, and the result showed that the total error was lower than 5%. Four sections were chosen, and the mixture forming process of diesel engine was analyzed, and the uniformity and mixing rate of mixture were evaluated. The result indicates:in section 2, which section that axis of the nozzle hole would pass through, uniformity was the worst but mixing rate was the best; in section 4, which section that was the farthest from nozzle hole axis, uniformity was the best but mixing rate was the lowest.In addition, the influences of cylinder initial swirl ration, initial pressure, spray pressure, nozzle hole diameter and combustion bowl shape on mixture forming process were respectively studied. The influence laws of these parameters on mixture uniformity and mixing rate were analyzed. The results show that:cylinder initial swirl ration, initial pressure, spray pressure, nozzle hole diameter and combustion bowl shape have an effect on mixture forming process, uniformity and mixing rate to a certain extent, and these research results would contribute to optimization and improvement of mixing process of diesel engine.