Thermal-mechanical Coupling Analysis And Application Of Diesel Piston

In this paper,a combination piston of a certain type of high-strength diesel engine is taken as the research object.The strength evaluation technology research based on the analysis method of transient thermo-mechanical coupling analysis is carried out.The research contents including theoretical model and finite element analysis model of piston thermo-mechanical analysis,optimization of piston temperature field and transient thermo-mechanical coupling stress analysis method,and analysis of the influence of piston structure parameters on coupling stress are completed.The main work of the paper is as follows:1.Established a finite element calculation model for the transient thermal-mechanical coupling analysis of the piston,and took the single cylinder diesel piston as a specific research object,analyzed the influence of the finite element mesh size on the calculation accuracy,and combined with the experimental data,the inverse method was used to optimize the calculation boundary conditions of the thermo-mechanical coupling.The introduction of contact thermal resistance corrected the temperature calculation error of the piston head and skirt.Through comparison and verification of experimental data,the calculation error of the established finite element model is less than 10%.2.Using the established finite element model to deeply analyze the change law of the transient temperature and heat flux density of the piston,and found that there is a critical layer of temperature fluctuations on the gas side of the piston temperature field,and then delved into the relationship between the heat transfer coefficient and the critical temperature layer.The influence of the heat transfer coefficient of the piston top surface,the cooling cavity,and the ring zone on the temperature critical layer is analyzed.The results show that the top layer heat transfer coefficient has the greatest effect on the critical layer,followed by the cooling cavity,and the ring zone is the smallest.It provides analysis ideas for piston structure optimization and strength evaluation.3.Established a thermo-mechanical coupling calculation model including thermal stress,mechanical stress and reciprocating inertia force,optimized the constrained loading method in the coupling calculation of the piston,and performed a transient analysis on the distribution of thermal stress,mechanical stress and coupled stress in the piston.The calculation results show that the maximum coupling stress appears at the bottom of the connecting bolt,and the maximum coupling deformation reaches about 0.95 mm,which reflects the stress state of the piston in the real working environment and provides a theoretical basis for the fatigue life analysis and reliability design of the piston.4.Using the established transient thermo-mechanical coupling calculation model,the correlation analysis calculation of the piston structure parameters and the coupling stress distribution law was carried out.The influence of parameters such as the shape and thickness of the piston top surface,the height of the first ring bank,the height of the fire bank,and the area of the cooling cavity on the temperature field,coupled stress distribution,and deformation are analyzed in detail.The rationality of the analysis method is verified by taking single cylinder diesel engine piston as an example.The thermo-mechanical coupling model of the diesel piston established in this paper can calculate the changes of the temperature field,stress field and heat flow density of the diesel piston in detail.The proposed thermo-mechanical coupling analysis method has certain guiding significance for the optimization design of the piston structure and the thermal load analysis and evaluation.