Analysis Of Oscillation Cooling And Thermal-fluid-solid Coupling Fatigue Characteristics Of Diesel Engine Piston

In recent years,the strengthening degree of diesel engine has been continuously improved,followed by the continuous increase of cylinder pressure and cylinder temperature,and the thermal load.The strength and safety of parts are facing a huge test,especially the core part of diesel engine — — piston,whose top surface is directly in contact with high-temperature and high-pressure fuel gas,which is particularly easy to cause damage.Its reliability is directly related to the reliable and stable operation of the whole machine.Taking the piston of a high power density diesel engine as the research object,this paper numerically simulates and analyzes the two-phase flow and heat transfer characteristics in the piston oil cavity,studies the influence of different influencing factors on the two-phase flow and heat transfer characteristics,and then further studies the influence of various factors on the piston cooling and structural strength based on the thermal-fluid-solid coupling method.The main work of this paper is as follows:Firstly,the CFD simulation model of piston oil cavity oscillation is built by using AVL FIRE software.FIRE uses the Euler-Euler method to calculate the multiphase flow,and selects the Multi-fluid model which has the more high accuracy to calculate the multiphase flow in the piston oil cavity.According to the calculation results,the variation law of two-phase flow state in the oil cavity and the spatial variation law of convective heat transfer coefficient on the wall of the oil cavity in a cycle are analyzed in detail,which lays a foundation for subsequent research.Finally,based on the established numerical simulation model of piston oil cavity,this paper further studies the effects of different influencing factors on two-phase flow and heat transfer characteristics in piston oil cavity.On the basis of not changing the piston structure,five factors are selected for numerical simulation calculation: injection speed,diesel engine speed,oil cavity space inclination angle,fuel injection nozzle size and injection temperature.The effects of various factors on the two-phase flow and heat transfer characteristics in the oil cavity are studied,and the boundary conditions are provided for the subsequent study of piston fatigue characteristics.Further more,this paper uses AVL FIRE software to build a three-dimensional combustion model coupled with inlet and exhaust,which is verified by the experimental data,and maps the calculated near wall fluid temperature and convective heat transfer coefficient to the upper surface of the piston.The finite element model of the piston is built by using ABAQUS software,and the temperature field and stress field of the piston are calculated and analyzed.The piston temperature distribution,the piston thermal stress,mechanical stress and thermal mechanical coupling stress distribution were obtained.Four factors that have great influence on the heat transfer of the oil cavity are selected,and the CFD calculation results of each factor are mapped to the surface of the oil cavity to analyze and study the influence law of each factor on the temperature field and stress field of the piston.