Simulation Reseach Of Pressure Fluctuation And Structural Optimization Of High Pressure Pipeline In Common Rail System

With the development of electronic control technology, the electronic control diesel engine is widely used in many engineering fields, such as automobile, machinery and so on. The emergence of energy crisis and environmental pollution make people pay more and more attention to the efficiency and emissions of diesel engine. Precise control of fuel injection process is an important means to improve fuel economy and emission performance of the engine. High pressure common rail system becomes the focus of research at home and abroad because of its implementation of precise control of the number of injection, injection pressure, fuel injection quantity and injection rate. However, pressure fluctuation in high pressure pipeline is unavoidable due to the continuous fuel injection and supply of the engine, which adversely affects the precise control of the injection process. Advanced rail pressure control technology is an important way to maintain the stability of the pressure in the common rail. At the same time, it is also an effective way to improve the pressure fluctuation characteristics of the high pressure pipeline by reasonably matching and designing of the structure of the high pressure pipeline. In this paper, the pressure fluctuation characteristics of high pressure pipeline are studied, and the structure of the high pressure pipeline is optimized.The composition and working principle of high pressure common rail system are described, and mathematical model of the main parts is built. A one-dimensional hydraulic simulation model of high pressure common rail system is established by using the AMESIM software. The model is validated by comparing the simulation results with the experimental data.The influence of structural parameters on the pressure fluctuation characteristics of the high pressure pipeline is studied by using the one-dimensional hydraulic simulation model of the high pressure common rail system. Effects of high pressure pipeline structure on pressure fluctuation are studied by changing the length and diameter of fuel supply pipe and fuel injection pipe as well as the length, diameter, volume and aspect ratio of common rail. Volume and aspect ratio of fuel supply pipe, fuel injection pipe and common rail are changed to study the variation of the time for pressure building in common rail.A three-dimensional model of high pressure pipeline flow field is built.The meshes are all built in hexahedron by cutting the model into blocks. Simulation of the three-dimensional flow field of high pressure pipeline is carried out by using FLUENT software. Pressure contours, velocity contour, vector of the fuel in high pressure pipeline and the one-dimensional hydrodynamic simulation results are analysed to study the generation and propagation process of the pressure wave and fuel flow in the high pressure pipeline.Pressure fluctuation curves of common rail under different working conditions and high pressure pipeline structures are studied by means of spectrum analysis. The influence of operation and structure parameters of high pressure common rail system on pressure fluctuation frequency, amplitude in common rail are researched.Finally, on the basis of previous research, one-dimensional hydraulic simulation experiments of different lengths and diameters of fuel supply pipe, common rail and fuel injection pipe are carried out by orthogonal design with the aim to enhance the comprehensive performance index of high pressure common rail system.Two high pressure pipeline structures are obtained within the volume limit. With the high pressure pipeline capacity limit of 60ml, the comprehensive performance index of high pressure common rail system is better compared with that of the original structures when fuel supply pipe lenth is 300mm and diameter is 4mm, common rail length is 450mm and diameter is 12mm, fuel injection pipe length is 300mm and diameter is 4mm. With the high pressure pipeline capacity limit of 100ml, the common rail system performs better when fuel supply pipe lenth is 300mm and diameter is 4mm, common rail length is 750mm and diameter is 12mm, fuel injection pipe length is 300mm and diameter is 3.5mm.