Finite Element Analysis Of Composite Piston For Medium-speed Diesel Engine

Piston is one of the most important components with complicated structure in diesel engine.It withstands the high thermal and mechanical loads.3D finite element analysis (FEA) is effective for piston’s developing and evaluating and the key of FEA is to determine the piston’s thermal boundary conditions accurately.In this paper the thermal boundary conditions for steel-aluminium composite piston of mid-speed diesel engine are discussed and the emphasis is put on the researches to determine those of gas-side of combustion chamber and cooling-side of cooling gallery. The main achievements are arranged as followed:(1) Woschni formula(1990) is determined to be used for heat-transfer calculation of gas-side of combustion chamber,based on the researches to different calculate methods; (2) A formula is given to calculate the radial mean heat-transfer coefficient of the gas-side of combustion chamber,which is developed based on Seal-Taylor formula;(3) The Bush formula and the Bush revised formula are determined to use for calculating heat-transfer coefficient of diffirent surface areas of cooling-side of shaker cooling gallery.At the same time the principles to distribute heat-transfer coefficient are given;Using the achievements above,the steady thermal analysis of PA6 piston has been accomplished with 1/4 multi-bodies analysis model by means of ANSYS software in this paper. The results of analysis meet the measured data accurately. During the analysis,the contact thermal resistance has been considered and appling the radial mean heat-transfer coefficient to piston crown with“function loader”in ANSYS has been realized.Then the steady thermal analysis of another steel- aluminium composite piston is accomplished and those achievements above are proved.PA6 piston is chosen for thermal-mechanical coupling analysis with 1/4 multi-bodies analysis model.In the analysis,the special attention has been paid to the match design of junction plane between piston crown and skirt.The result of analysis shows that the thermal deformation and stress meet the fact accurately and the piston’design is good.The research indicates that: The way to ascertain thermal boundary conditions has higher analysis efficiency and the result of thermal-mechanical coupling FEA by using multi-bodies model may promise enough analytical accuracy. The achievements given in this paper have great practical value and can be applied to steel-aluminium composite pistons of mid-speed diesel engine.