Investigation On The Thermal Effect Characteristic Of High-Pressure Common-Rail Fuel Injector In The Working Process

With the development of strict emission regulations,various countries continue to develop new technologies to achieve lower fuel consumption and lower harmful emissions of diesel engines.The high-pressure common rail fuel system is widely used in modern diesel engines,because it can achieve flexible injection timing,injection regulation,and injection volume without depending on operating conditions.As the key part of high-pressure common rail fuel system,many scholars have done a lot of theoretical and experimental researches on the common rail fuel injector,such as the cavitation flow in the injection hole,the influence of injector injection stability,and injector performance optimization.However,these researches content is under the assumption of common rail injector isothermal conditions.In fact,the large pressure differential will lead to the temperature rise in injector nozzle and control valve,the temperature rise will strongly affect the fuel internal high-pressure flow characteristics,and the high-speed solenoid valve control accuracy on the injection characteristics.Therefore,research for the thermal effects on the common rail injector and its fuel injection volume could provide engineering application reference and theoretical significance.In this paper,the thermal effects of Bosch common rail injector in real working condition is studied on the fuel pump test bench,and the influence of thermal effect on the dynamic response of high-speed solenoid valve and fuel injection characteristics of common rail injector are analyzed by testing and simulation.The experimental research in this paper is based on the fuel pump test table,focusing on the effect of injection pressure and injection pulse width on the heat effect of injector,without considering the effect of fuel combustion in cylinder on the heat effect of injector.The Bosch common rail injector is modified to measure the fuel temperature in the oil collecting chamber at the nozzle head and the control valve.The surface temperature of injector is measured by infrared thermal imager and thermocouple sensor.The effect of injection pressure and pulse width on the temperature rise of the common rail injector was studied on the fuel pump test bench.The experimental data of the temperature rise of the injector nozzle and the control valve as a function of working time,and the steady-state temperature rise under different operating conditions can be obtained.At the same time,the inaccuracy of infrared thermal imager measuring injector surface temperature is pointed out.A temperature-dependent study on magnetization of soft magnetic material for high-speed solenoid valve was carried out in a temperature range of 23-140℃.Experimental data of hysteresis loop and B-H magnetization curves at different temperatures are obtained.In the aspect of studying the temperature dependence of coil copper wire resistance,the experiment of copper wire resistance for solenoid valve at different temperature was carried out,and the resistivity coefficient was corrected.The dynamic response characteristics of high-speed solenoid valves at different temperatures are studied by 3D electromagnetic simulation.Experimental study on dynamic response of high-speed solenoid valve in common rail injector was carried out on high-speed solenoid valve test bench.For the solenoid valve with large electromagnetic force,the correct simulation of armature is important,and the dynamic response model of high speed solenoid valve with current feedback drive circuit considering armature impact is established based on one-dimensional and three-dimensional coupling method.A calculation model of common rail injector with considering adiabatic condition and a calculation model with considering heat transfer are established by AMESim software.By comparing with the experimental data of temperature rise in this paper,it is found that the mathematical model of adiabatic common rail injector cannot correctly predict the temperature rise in the working process of injector.The simulation results are in good agreement with the experimental data in the steady-state temperature rise and temperature rise versus working time curves of the common rail injector model,with considering heat transfer effect.Finally,based on the theoretical model,the influence law and mechanism of temperature rise on the circulating fuel injection are analyzed.