Simulation Research Of Pressure Fluctuation In The Process Of Fuel Supply And Injection For Common Rail System Of Diesel Engine

Under the background of the country s vigorous promotion of the development of efficient and clean energy vehicles,society is increasingly demanding emission standards for traditional engines.At present,electronic control diesel engines are still being used on high-powered vehicles on a large scale and in order to meet emission targets,it is necessary to optimize the process of fuel injection,atomization and combustion performance.The high-pressure common rail system has become a core component of the diesel engine because it can realize flexible control of fuel injection quantity,fuel injection frequency and fuel injection law,while the pressure fluctuation generated by the common rail system during the working process has a great impact on the consistency and stability in the process of injection,which will affect the combustion process in the cylinder.Therefore,the precise rail pressure control technology is one of the core tasks of diesel engine research.In this paper,the 5V high pressure common rail system is taken as the research object,and the generation and propagation processes of pressure fluctuation during oil supply and injection process are comprehensively studied,which provides a theoretical basis for the research of pressure fluctuation suppression technology.The work and achievements are mainly reflected in the following aspects:Firstly,the working process of high-pressure fuel supply pump,common rail pipe and injector is rationally simplified and the mathematical model of the above three major structures is elaborated.According to the structure and working process of the pump-rail-injector,the 1-D simulation model of the oil supply pump,injection and whole 5V high-pressure common rail system was built and the calculation results of 1-D model and experimental data of high pressure common rail test platform were carried out under the same conditions.Finally,the accuracy of the model is verified by comparing the experimental data with the simulated data.Secondly,the average pressure fluctuation,peak pressure and fluctuation period are taken as the characteristic parameters of the pressure fluctuation in the high pressure common rail system.The target rail pressure,fuel supply pump structural parameters(cam structure,phase and oil valve ball valve quality)and injector structural parameters(inlet,outlet hole diameter,needle lift,orifice diameter and control chamber volume)and injector operating parameters(injection pulse width,injection interval and injection sequence)have a great influence on pressure fluctuations and the law of their influence on pressure fluctuations are studied comprehensively.In addition,based on the schematic diagram of structure of the research object,the 3-D flow field simulation model of pressure fluctuation of high pressure common rail system is established.Combined with the boundary conditions of the model provided by the 1-D calculation results and the injection sequence of the physical research object,the UDF control program is programmed to realize the control of fuel injection process.In the process of circulating work,the fuel flow and fluctuation superposition in the process of injection and oil supply are studied.Finally,it is concluded that the mutual conversion of kinetic energy and wave energy is the main reason of pressure fluctuation.Finally,a 3-D simulation model of the flow field of the injector control chamber is established and the 1D-3D co-simulation technology is used to study the pressure fluctuation characteristics of the control chamber during the injection process of the injector and its influence on the fuel injection performance.In the development of fuel pressure and velocity distribution,it is concluded that the control room is one of the sources of fluctuation during the injection process.The generated pressure fluctuation induces cavitation in the position of the oil hole,reducing the effective flow area of the control chamber outlet.The circulation characteristics have a negative impact on injection performance.At last,the effects of different structures on cavitation is studied,and the results show that the design of the rounded corner can effectively reduce the degree of cavitation.