Finite Element Analysis Of High Power Diesel Engine Piston Under Thermal Mechanical Load Coupling

As the power density of marine engines continues to increase,the combustion heat and mechanical load in the cylinders of diesel engines will greatly increase.As one of the most important components of the combustion chamber,pistons work in harsh environments with higher temperatures and explosion pressures,resulting in diesel High mechanical and thermal loads.Its reliability has become a key link to improve the performance of diesel engines.Aiming at the reliability problem of a real product piston,this paper focuses on the analysis of the stress and strain characteristics of the piston under high mechanical load and thermal load.Based on the use of CFD software to obtain its three-dimensional heat transfer boundary,the finite element analysis method is used to complete the piston Stress and strain calculation,complete the reliability analysis of the piston according to the calculation results.The specific research content and research results are as follows:The three-dimensional CFD software was used to simulate the combustion process in the diesel engine cylinder and the oscillating cooling process in the cooling cavity of the piston,respectively.The value changes with the crank angle.Through post-processing,specific values of the three-dimensional heat transfer parameters of the two heat exchange regions are obtained,which provides boundary conditions for subsequent finite element analysis.Based on the three-dimensional model of the piston and the finite element software,the meshing is completed.The definitions of the contact relationship,boundary conditions and load application of each component are respectively established to establish the piston temperature field model,mechanical load model,thermal load model and thermalmechanical coupling model.It solves the finite element results,and uses Fe-safe to complete the fatigue safety analysis of the piston based on the thermal-mechanical coupling calculation results.Through the analysis of the calculation results,it can be seen that the highest temperature of the piston temperature field is 614.6K,which appears in the head,the temperature of the remaining parts is about 400K,and the temperature of the first ring groove is lower than the safe temperature of 490K.According to the stress-strain cloud diagram of the piston,the overall stress-strain of the piston is gradually decreasing from top to bottom,but it is in a safe state.The maximum stress is 539.2MPa and the maximum strain is 0.409 mm,which all occur in the thermo-mechanical coupling working condition,and the generating part is the piston head.Through the analysis of stress and strain in various working conditions,it can be seen that burst pressure and temperature load are the main causes of stress and strain of the piston.Through the analysis of stress and strain in various working conditions,it can be seen that burst pressure and temperature load are the main causes of stress and strain of the piston.In addition,the fatigue safety analysis of the piston shows that the overall safety factor(FOS intensity factor)of the piston is greater than the safety value of 1,but the position safety factor between the surface of the piston head and the two sides of the inner cavity and the outer cavity is at least 1.18,which is close to the critical value.It is found that it is caused by the combined effect of heat-machine load and the thin structure of the two places.It can be optimized by thickening the two places on the basis of ensuring the cooling effect of the cooling cavity.