Study On Failure Factors Of Needle Valve Injector

Owing to overcoming the shortcomings of diesel engine constantly,such as poor high-speed performance,high noise,serious emission pollution and inconvenience in maintenance,its application scope is expanding.As an important part of diesel engine,fuel injector has a compact structure compared with other parts of diesel engine,and its working environment is in the state of high temperature,high pressure and high gas.The performance of diesel engine depends on whether the injector works normally.Based on the design and development project of diesel injector of a certain enterprise,this paper analyses the problems in the work of diesel engine injector,and puts forward a systematic research method.The main work is as follows:? Nonlinear explicit dynamic impact response analysis of a needle valve injectorBased on the elastic mechanics and finite element theory,Hypermesh is used to pretreat the dynamic model of injector pin-valve seat impact response.Then,the pretreatment model is imported into Abaqus for dynamic analysis,and the corresponding pre-and post-treatment program is developed to analyze the steady-state process of impact response.At the same time,the corresponding steady-state evaluation index of impact response is established to provide a basis for wear analysis of needle valve-seat.? The needle valve injector thermal stress analysisFirstly,the Design module in the Ansys Workbench software platform is used to extract the internal flow channel of the injector and the 3d fluid dynamics model of the injector fuel is established.Using the turbulence model and energy model in fluent module for fluid dynamics analysis,and obtaining the fuel pressure change and temperature field during fuel injection of injector.In the Ansys Workbench software platform,the sequential coupling method is adopted to analyze the fluid-solid coupling of the injector,and the fluid-thermal-solid coupling finite element analysis model of the valve seat,pressure chamber and nozzle of the injector is established.Using the CFD analysis results of fuel inside the injector mentioned above,the temperature distribution data of the injector is coupled to the finite element structure model by means of boundary node mapping.The distribution of temperature field during fuel injection is obtained.Finally,the fuel pressure distribution data calculated by the aforementioned fluid and all the temperature field analysis data of the injector are coupled to the finite element structure model,and the thermal stress and thermal deformation of the injector are finally calculated,thus establishing the method of heat transfer boundary conditions of the injector.? Cavitation analysis of needle valve injector under normal working pressureFirstly,the Design module in the Ansys Workbench software platform is used to extract the internal flow passage of the injector and the 3d fluid dynamics model of fuel injector is established.Then,the fluent module is used to analyze the transient fluid dynamics by using turbulence model,two-phase flow model and cavitation model.According to the initial conditions and parameters,the distribution of fuel gas and liquid phase,pressure and flow velocity in the injector under different pressures and different elevations are obtained.The results show that the higher fuel inlet pressure and needle valve lift,the more cavitation in the injector.The cavitation inside the injector become more serious when the back pressure are reduced and saturated vapor are increased.In this article,the impact of needle valve movement on the valve seat of injector is carried out by means of display dynamics analysis method and the secondary development of pre-and post-processing program.And the two-phase flow model and cavitation model are used to analyze the cavitation of fuel inside the injector.The sequential coupling method is used to simulate the flow-heat-solid multidisciplinary coupling model of the injector.The possible problems in the key parts of the injector are systematically analyzed,so as to provide relevant reference for the structural optimization design of the injector.