Simulation Research On Generation And Propagation Of Pressure Fluctuation For High Pressure Common Rail System Of Diesel Engine

With the development of the diesel engine,the emission requirements are higher.As one of the important parts of the diesel engine,the high-pressure common rail system meets the requirements of high-pressure injection,flexible injection characteristics and injection pressure control.However,because of the pulsation of the high-pressure oil pump and the intermittent injection of the injector,when the high-pressure common rail system works,the pressure fluctuation will occur.Which will effect the stability and stability of fuel injection,so it is of great significance to study the generation and propagation of pressure fluctuation in high pressure common rail system.In current paper,5V high-pressure common rail system is adopted as the research object,and the pressure fluctuation characteristics in the working process of high-pressure common rail system are simulated.The main work is as follows:Firstly,the high-pressure common rail system has been simplified reasonably.Combined with the corresponding mathematical and physical models,the one-dimensional simulation model of the high-pressure common rail system is established,and the accuracy of the model is verified.Based on the one-dimensional simulation model,the influences of injection frequency,injection quantity,injection pressure,injection duration,common rail pipe structure and high-pressure pipe structure parameters(diameter and length)on the pressure fluctuation characteristics under different conditions were studied.Secondly,there is a volume cavity in the high-pressure oil pump,which can restrain the pressure fluctuation in the process of oil supply.Therefore,the three-dimensional simulation model of the volume cavity is established.UDF program has been written to control the working time and working order of each plunger and determine the pressure boundary.The fuel flow and pressure wave propagation in the volume cavity are studied.It is concluded that the pressure fluctuation is not a constant energy transfer,but a conversion of kinetic energy and pressure energy of fuel flow.Finally,the three-dimensional simulation model of the volume cavity of the injector is established.The boundary condition of three-dimensional simulation is provided by one-dimensional hydraulic simulation through the combination of one-dimensional and three-dimensional simulation.Combined with the pressure fluctuation curve of one-dimensional simulation calculation results,the pressure distribution nephogram,velocity distribution nephogram and velocity vector graph of the volume cavity in the single injectionprocess are studied to analyze the control valve.The process of fuel flow and pressure wave propagation in the volume chamber before and after opening.The influence of the structural parameters of the valve on the pressure fluctuation is studied.It is found that the pressure fluctuation can be reduced by reducing the diameter of the orifice,increasing the orifice diameter and reducing the piston mass.