| As the highest thermal efficiency of power machinery, diesel engines will maintain the essential position of the driving force in the field of transportation for a long time in the future. But due to the rising cost of fossil fuels and hazardous emissions, its developments have been limited and challenged. In diesel engines, fuel injection, the shape of spray and quality of atomization strongly affect the combustion and the performance of engine. Therefore, the research for fuel spray mechanism attracted more attention of domestic and foreign researchers. But due to complexity of spray, a lot of mechanism has not been fully revealed so far, such as the effect of injector geometry. The test and numerical simulation of cavitation flow in the nozzle hole and the spray flow field have been analyzed and summarized fully and systematically. Combining methods of scaled high-speed photography about the cavitation turbulence in the transparent nozzle, accurate test of injector geometry by synchrotron radiation X-ray, PDPA and PIV test of spray flow and three dimensional CFD numerical simulation to carry out researches about the effect of injector geometry on the performance of the cavitation flow and spray. The main conclusions are as flows:(1) There is no direct link between the occurrence of cavitation flow and the Reynold number, but the cavitation number. With the reduction of the nozzle diameter, the hole primary critical pressure increases, it is difficult to occur cavitation in small-caliber or prototype nozzle. The tip orifice aspect ratio and inclination and needle lift pressure chamber will affect the performance of the cavitation flow. The physical characteristics of the fuel has an important influence on the cavitation flow in the nozzle hole, biodiesel appears much harder than diesel to occur cavitation. So to obtain good spray quality, biodiesel needs higher injection pressure.(2) Based on the theory of Multiphase flow and bubble dynamics, three-dimensional numerical model of the cavitation flow in the nozzle hole was builded, and combined with the date of visualization test in scaling transparent nozzle holes to simulate the cavitation flow accurately. In this study, the effects of nozzle geometry on the internal nozzle flow were investigated by numerical simulation. And found that the sharp edge of the inlet has superior spray performance than fillet one. Improvement of fuel injection pressure can greatly improve performance of the spray and the nozzle flow.(3) Synchrotron radiation X-ray technology can access accurate three-dimensional geometry non-destructively. Experiments found that the circumferential direction of each nozzle hole has substantially uniform distribution, import and export interfacial area is basically the same, and contraction or expansion does not appear on the spray hole interface and mismachining tolerance is small, but not equal to the length of each nozzle hole and there is a big difference between the upper and lower corner radius. Based on the PDPA technology of spray high-speed photography study found that spray cone angle "hump" of soybean oil methyl ester/0#diesel hybrid fuel has change phenomenon. The axial velocity is a key factor affecting the spray performance and also the determinants of the radial velocity, higher axial velocity leads to higher radial velocity and bigger spray cone angle. Based on PIV technology, it is found that the enhancement of the injection pressure contributes to the momentum exchange between oil droplets and the surrounding environment.This paper puts forward a ELSA (Euler-Lagrangian Spray and Atomization) spray simulation methods, Euler method is used in the orifice outlet near-field fuel dense area, and the far-field spray uses Lagrangian method, and coupling the cavitation flow in nozzle hole to get a more accurate simulation results. |
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