Simulation Study Of Characteristics Of Shock Waves Induced By High Fuel Injection Pressure

With the increasingly stringent engine emission regulations,researchers from all over the world have invested in researches to reduce engine emissions.High-pressure common rail systems,pre-spraying,and low-temperature combustion technologies are increasingly applied to actual diesel engines.These techniques greatly increase the speed of fuel injection while reducing the speed of sound in the fuel injection environment,which causes the fuel injection speed to exceed the sound speed.When the speed of injection reaches to supersonic,the phenomenon of shock wave will occur.The generation of shock waves has a huge impact on the ambient gas around the spray,causing the state of environmental gas to change drastically and affect the development of fuel spray.It will hinder researchers from predicting the development of the fuel spray and then affect the precise control of diesel injection.At present,the research on high-pressure fuel injection induced shock wave is mainly based on experimental methods,but the experimental method can only obtain the macro information of shock wave and spray,which is not conducive to analyzing the relationship between spray and shock wave.Therefore,the three-dimensional simulation software of computational fluid dynamics is used to simulate the high-pressure fuel injection and its induced shock waves in this paper,and explore induced shock waves characteristics and their effects on fuel spray.In this paper,the Euler-Eulerian method is used to simulate the fuel injection process and induced shock phenomenon under different environmental pressures and different injection pressures.The simulation results show that when the induced shock wave is oblique shock wave which attaches the spray,the shock wave can continuously obtain energy from the spray.The temperature,density and pressure in the area of shock wave will be improved,and the effect become more obvious with the increase of injection pressure,especially under the condition of ultra-high pressure injection.When the injection pressure reaches to 320 MPa,the maximum temperature can be increased by nearly 16%.The higher temperature can promote the evaporation and atomization of the spray.Under the same condition of injection pressure,the induced shock will separate from the spray with the increase of ambient pressure,and the oblique shock wave will become bow shock wave.Then the energy of shock wave gradually decreases with the development of shock wave under the condition of high ambient pressure.And the higher the ambient pressure is,the faster the energy reduces.The high-pressure fuel injection also lead to the generation of compression waves and expansion waves,which are generated in the "disturbed" position of the interface between ambient and spray.When the spray develops at supersonic velocity,these positions will cause a strong disturbance to the ambient gas,resulting in the generation of compression waves and expansion waves.The effects of shock waves and associated waves on ambient gas flow are obvious.Under atmospheric pressure,the ambient gas which is in the front shock wave will flow at a direction that is approximately perpendicular to the shock wave surface.There is a large expansion wave behind the leading shock wave.The gas in the expansion wave will flow toward the spray until the location of the first compression wave.The compression wave is similar to the front shock wave,where the gas meets the return gas in the expansion wave.After the gas flow to the surface of spray,the eddy currents will generated and promotes the mixture of fuel and ambient gases.The region where the associated expansion wave and compression wave are alternately generated will also produce a similar eddy current structure,but the scale is smaller.At higher ambient pressure conditions,ambient gas flow is similar to that at the condition of atmospheric pressure before the shock wave is separated from the spray.After the separation,the leading shock wave continues to propagate,and the ambient gas continues to flow.When the shock wave touch the wall,the reflection of wave will occur,and will have a superposition effect with the original waves.When the reflected shock wave or the reflected compression wave meets another compression wave,the effect of compression on the gas will enhance,and density of gas will increase.When the reflected expansion wave meets another expansion wave,the gas effect of expansion will enhance,and the density will reduce.when the compression wave and the expansion wave are superimposed on each other,the effects of compression and expansion will interfere with each other.