Fatigue And Wear Life Prediction And Structural Optimization Of Marine Exhaust Valve Based On TMC Model

The valve-valve seat is one of the important frictional parts of diesel engine air distribution mechanism,and the fatigue and wear problem of the valve is one of the important factors affecting the economy,power and reliability of diesel engine.In recent years,with the increasing performance and power of marine diesel engines,the working environment of marine exhaust valves has become more severe,which leads to the increasingly severe fatigue and wear problems of exhaust valves.Therefore,in order to reveal the failure mechanism of a marine diesel engine exhaust valve and effectively improve its reliability,this thesis carries out the work on the fatigue and wear life prediction of the exhaust valve based on the thermo-mechanical coupling（TMC）model of a marine diesel engine exhaust valve;meanwhile,based on the response surface method and NSGA2optimization algorithm,the structure of the exhaust valve is optimized and the fatigue and wear life of the exhaust valve is improved.The main research contents are as follows:（1）The exhaust valve was divided into seven regions,and the thermal load of the exhaust valve was calculated based on the diesel engine simulation platform constructed by AVL-Boost,the flow characteristic equation,and the equivalent thermal resistance method;the mechanical load of the exhaust valve was calculated based on the multi-mass model theory using the dynamics model of the air distribution mechanism.（2）Based on the load state of the exhaust valve,the TMC model of the exhaust valve was built using Ansys Workbench,and the temperature field,stress field and contact pressure results of the exhaust valve were calculated.The results show that the high temperature region of the exhaust valve is concentrated in the center of the valve face and the center of the neck;the high stress region is concentrated at the cone,and the maximum thermo-mechanical coupling stress at the moment of deflagration;the maximum contact pressure at the contact surface is generated at the moment of deflagration,and the contact pressure is not uniformly distributed on the contact surface.To verify the accuracy of the model was conducted for the overall hardness method of temperature measurement test,the contact force test results were introduced.The maximum error between the test and simulation are within 10%,and the test and simulation results are in good agreement.（3）Based on the TMC model of the exhaust valve,the fatigue life and wear life of the exhaust valve were predicted using the nominal stress method and the Archard wear model,respectively.The prediction results show that the fatigue hazard point of the exhaust valve is concentrated in the location of the bottom of the exhaust valve neck,and the fatigue life of the exhaust valve is 1.86×10¹⁰cycles;the hardest hit area of wear occurs in the edge area of the contact between the exhaust valve and the exhaust valve seat,and by fitting the relationship between the maximum wear depth and the number of wear cycles,the wear life of the exhaust valve is calculated to be 9.9×10⁹cycles.（4）The relationships between the structural parameters such as valve cone angleα,neck transition cone angleβ,neck transition radius R_n and exhaust valve fatigue life and wear life were investigated,and the structure was optimized based on the response surface method and NSGA2 algorithm with the fatigue life and wear life of the exhaust valve as the target value.The results show that the best optimization results are obtained forα=23.64°,β=23.44°and R_n=32.45mm.The fatigue life of the exhaust valve after optimization is2.03×10¹⁰cycles and the wear life is 1.69×10¹⁰cycles,which are 9.14%and 54.54%higher than before optimization.