| As the shortage of oil resources in the world and the improvement of people’s environmental protection consciousness, the nations all over the world make use of more and more resources in order to improve the efficiency of the engines, reduce emissions of pollutants and meet increasingly stringent emission regulations. Engine fuel injection components are as the execution parts of fuel injection of which importance is self-evident. In recent years, many scientific research units and universities pay attention to the research of improve the nozzle structure and parameters. With the emergence of new spray hole processing technology, the variability and complexity appear especially in the electrical discharge machining, laser punching technology and jet orifice cross-section shape. The performance under certain conditions of these nozzles is more superior to the one of ordinary nozzle so it is necessary to analysis and study on it to improve the range application of the variable cross-section spray holes.At first, the writer presents the definitions of two common variable cross-section spray holes in this paper, such as taper variable cross-section orifice and swell-shrink deformation section orifice. On the basis of D6114diesel engine, the writer designs the three-dimensional flow field models of cone, inverted cone, hyperbola and ellipse cross-section of jet fuel nozzles by adopting the three-dimension drawing software Pro-e. Before using CFD, the writer meshes and sets boundary conditions on four kinds of variable cross-section nozzle flow field models by pretreatment software Gambit. And on the basis of the hole model and a mixed two-phase flow model, the writer also does a modeling analysis on physical parameters, such as the fuel injection components pressure field, velocity vector and holes distribution using computational fluid analysis software Fluent6.3and using Euler-Euler algorithm solver. In addition, the writer compared and analyzed on the flow rate quality of different types of nozzle, too. Finally, the writer concludes the rules that the different types of variable cross-section orifices influence on the performance of fuel flow and hole.Secondly, by previous researches, it is known that the excessive rounded corners at the entrance of the orifice have an important influence on the formation of the fuel flow performance and hole inside the nozzle. However, it is necessary to research on it due to its small geometry size and difficult machining. The research indicates that excessive rounded corners at the entrance of the average diameter nozzle increase within a certain range, which can make the hole intensity and the scope of area increase. However, if exceeding a certain value, hole intensity will obviously decreases. Taper variable cross-section nozzle is more sensitive for entrance to the excessive rounded corners. Therefore, when the excessive rounded corners increase, conical variable cross-section nozzle hole intensity decreases and mass flow rate at the nozzle exit increases, however, the taper variable cross-section nozzle is opposite to it. Conversely, swell-shrink deformation section orifices is less sensitive to the change of the nozzle entrance excessive rounded corners and have almost no changes on fuel hole in the nozzle and the flow velocity, especially hyperbolic variable cross-section orifice.In this dissertation, the writer does a qualitative analysis on the changes of oil flow properties caused by geometry change of two types of common variable cross-section orifices and points out the advantages and disadvantages of the nozzles, which provide the basis for improving diesel engine nozzle structure and parameter optimization and provide certain theoretical guidance on the related areas researches. |
PDF Full Text Request