| High-efficiency and low-emission diesel engines all use high-pressure common rail fuel injection systems.Fuel pressure stability in the fuel rail is prerequisite that insures the consistency of multi-cylinder injection and the stability of single-cylinder fuel injection systems.Therefore,the high-pressure common rail system emphesises great importance on the fuel pressure fluctuation characteristics of the high-pressure fuel rail.The causes,propagation process and laws of pressure fluctuations in the fuel rail are studied in detail.At present,many researches are mainly focused on the pressure fluctuations in the high-pressure fuel pipe between the injector and the fuel rail,but there is very little research on the pressure fluctuation process and rules in the fuel rail itself.This paper focuses on the characteristics of high-pressure fuel pressure fluctuations in the fuel rail.Using the method of simulation calculation and analysis,the reasons for the formation of pressure fluctuations in the fuel rail,the fluctuation rules and the influence of geometric parameters on the fluctuations were studied.First of all,based on the working principle of the high-pressure common rail system and the principle of hydraulic process,this paper analyzes the pressure fluctuations in the high-pressure common rail hydraulic system theoretically,and determines the source of the pressure fluctuations in the fuel rail.Secondly,in order to better analyze the factors that affect the pressure fluctuation process in the fuel rail,a complete simulation calculation model of the high-pressure common rail fuel injection system is established,and the accuracy of the simulation calculation model is verified by comparison with the test results.Finally,using the built high-pressure common rail system simulation model,the effects of the high-pressure fuel supply pump speed,injection pressure,injection interval,fuel rail and high-pressure fuel pipe geometric parameters on the pressure fluctuation process in the fuel rail are studied.The main conclusions obtained in the thesis are as follows: both the fuel supply of the high-pressure fuel pump and the fuel injector will cause pressure fluctuations in the fuel rail,and the pressure waves caused by the two are separated from each other.The pressure fluctuation in the fuel rail is much smaller than the pressure fluctuation at the nozzle end of the injector.The total pressure fluctuation caused by the fuel injection in the rail is related to the injection pressure and the injection pulse width: the higher the injection pressure,the greater the pressure fluctuation and the injection pulse width.The pressure trend in the fuel rail is the same after the change;the frequency of pressure fluctuations in the rail has little effect at different injection pressures and injection intervals,and the injection pressure has no effect on the pressure fluctuation frequency,but it will affect the amplitude corresponding to the pressure fluctuation frequency.At different injection intervals,If the oil pump frequency is unchanged,the fuel injection frequency will change.The speed of the high-pressure fuel supply pump has no effect on the pressure drop of the pressure wave,but it will affect the frequency change of the pressure fluctuation in the fuel rail.The diameter and length of the fuel rail will affect its pressure fluctuations.The larger the diameter and the longer the length of the fuel rail,the frequency of pressure fluctuations in the rail will not change but the corresponding amplitude will become smaller.Therefore,in order to reduce pressure fluctuations in the fuel rail,its diameter or length can be changed.The oil pipe is divided into the high-pressure oil pipe at the oil pump end and the high-pressure oil pipe at the injector end.The two have the same influence on pressure fluctuations.The larger the diameter and the length,the more obvious the change of the pressure fluctuation at the rail end. |
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