Analysis Of Cavitation Of A Needle Valve Injector And Structural Optimization

The fuel injector is one of the key components in the engine.The development of fuel injectors has promoted the development of diesel engines.Especially in the past 70 years,the performance of various diesel engines has been rapidly improved.The diesel fuel injector analyzed this time is a high-power low-speed heavy-duty marine diesel fuel injector.Although various indicators of marine diesel have been continuously improved,so far,there are still many problems in the diesel engine that need to be resolved,such as high noise,A high degree of poor performance,serious emission pollution,atomization quality and other problems.Among them,the combustion process of fuel is directly related to the quality of diesel engine spray(atomization cone angle,particle size,penetration distance).Good spray quality can effectively improve fuel economy and fuel utilization,thereby reducing pollutant emissions.At present,a large number of studies have proved that the phenomenon of cavitation inside the fuel injection hole plays a key role in fuel spray,thereby affecting the atomization characteristics.Therefore,it is very important to study the cavitation phenomenon inside the fuel injection hole and optimize the structure of the fuel injector to reduce the volume fraction of the gas phase,reduce the mechanical wear,and avoid the leakage of the fuel injector due to cavitation cavitation.In this paper,the numerical simulation method and the corresponding turbulence model are used to analyze the flow characteristics of the injector under different needle valve lifts.The RNG model-was determined based on the structural characteristicsof the fuel injector to simulate the internal speed and pressure distribution of the diesel fuel injector.Through analysis,it is found that the maximum fuel pressure inside the injector is mainly located in the pressure chamber.The pressure drops sharply at the corner of the inlet of the injection hole.An ultra-low pressure area appears at the corner of the fillet and the pressure near the inner wall of the lower edge of the injection hole reaches the lowest The value shows a clear negative pressure zone.No matter how the lift of the needle valve changes,there is an area with a large fuel velocity at the corner of the lower edge of the injection hole inlet,and this phenomenon is more obvious as the lift of the needle valve increases.Secondly,a cavitation model was used to study the cavitation phenomenon in the injector.It was found that when the cross section of the fuel flow path suddenly decreases and the fuel flow direction changes suddenly,a part of low pressure area will appear at theentrance of the fuel injection hole.As the lift of the needle valve increases,the gas volume fraction at the corner of the injection hole will increase slightly and the thickness of the gas phase region will not change significantly.When the inlet needle valve lift reaches 0.4mm,the injection hole The volume fraction of the gas phase no longer increases,and the cavitation area remains basically stable.When the outlet pressure of the injection hole is smaller,that is,the pressure difference between the inlet and outlet of the injector is larger,the flow rate of the fuel in the injection hole is faster,and the pressure is lower,so it is easier to reach the fuel saturation at the ambient temperature at that time Vapor pressure makes it easier to form cavitation.Based on the aforementioned research,in view of the cavitation problem of the injector,this paper carried out structural analysis and optimization through orthogonal test design,and found that the gas volume fraction is the smallest and the mass flow is the largest when the nozzle diameter is 0.6mm and the inclination angle is 66 °.Therefore,the occurrence of cavitation of the injector is effectively suppressed.Finally,in order to verify whether the thermal stress experienced by the optimized injector meets the limit of the material can bear.In this paper,the maximum thermal stress suffered by the injector is calculated at the corner of the inlet of the injection hole,the value is 412 Mpa,and the fatigue limit of the injector material is 848 Mpa and the lower limit of the fatigue limit is766 Mpa,which meets Requirements,no fatigue damage will occur.