Finite Element Analysis For A Medium Speed Diesel Engine's Composite Piston

To meet market requirements, a medium speed engine was intensified with 10% higher power compared with the original engine. Since the thermal load and mechanical load of major moving components of the intensified engine are higher than before, users concern much about the safety of them. Therefore, this thesis made finite element analysis on one of the key components, piston assembly, to calculate temperature field and stress field, and evaluate the safety situation. The analysis results provide one of the references for the improvement of engine design.The piston is composed of steel head and aluminum skirt, which are secured by eight bolts. In order to save calculation time, the contact pair was simplified as no clearance existing. The author utilized Pro/E to create CAD model of the composite piston, HyperMesh to generate mesh, and ANSYS to make finite element analysis.The thesis has finished the following main work:(1) Definition of thermal boundary. With the aid of 1-D engine simulation software and empirical equation, the heat exchange coefficient of different heat exchange surface were determined.(2) Static thermal analysis of piston. The temperature and heat exchange coefficient were applied on FEA model as third boundary condition and the temperature field was calculated. Based on the temperature distribution, thermal stress and thermal deformation were analyzed.(3) Coupled analysis of thermal and mechanical loads. Maximum cylinder pressure was applied on piston head as the mechanical load boundary to make strength analysis. Then indirect coupling method was used to analyze coupled stress field.(4) Transient analysis of piston. A quarter of piston head was used to analyze the thermal shock during engine start period. The thesis used direct coupling method to analyze the variation tendency of temperature and stress field during five hundred working cycles. Based on the calculation results, the safety factors of key positions of the piston were obtained, and safety check was made.Through the above work, the safety evaluation reference of the composite piston was obtained, which provide the basis of further improvement of piston design for the intensified engine.