Lightweight Design Of Marine Diesel Engine Piston Structure Based On Thermal-mechanical Coupling Strength Analysis

With the continuous improvement of diesel engine economy,the lightweight of parts has become one of the important ways to achieve.Piston is the core moving part of diesel engine.The lightweight design of piston can effectively reduce the weight of diesel engine and improve the economy of diesel engine.With the continuous improvement of diesel engine power,the piston thermal load and mechanical load are aggravated,and the piston failure problem is becoming increasingly prominent.Therefore,on the premise of satisfying piston strength,piston lightweight design has obvious scientific research value.In this paper,the fluid structure coupling method is used to analyze the temperature field,thermal mechanical coupling stress field and deformation of diesel engine piston.Aiming at the piston of a certain type of marine high-power medium speed diesel engine,the structural strength analysis and lightweight design are carried out.Firstly,the structural strength of the piston prototype is analyzed,and the results show that the maximum temperature of the piston is located in the area of the piston top pyramid.The maximum stress of the piston is located in the edge area of the top edge of the piston and the thin wall area of the oscillating outer cavity,and the minimum safety factor of the piston is 1.75.The results show that the stress in some areas of the piston is very small and the safety factor is high,so the lightweight design of the piston can be carried out.In this paper,the lightweight design mainly includes two ways: one is to optimize the support arm of the piston skirt,the side push shoulder and the lower part of the skirt,and reduce the wall thickness of the three areas.After optimization,the weight of the piston is reduced by 12%,the stress increase in the weight reduction area is less than 30 MPa,the maximum stress of the piston does not change,and the minimum safety factor of the optimization area is 2.4,which meets the design requirements;The second way is to optimize the structure of the piston top oscillating cavity,increase the height of the oscillating outer cavity and increase the angle of the oil pipe on the inner cavity.The results show that after optimization,the piston weight is reduced by 1.2%,the top temperature of the top oscillation chamber is reduced by 36 K,and the temperature of the central area of the fire surface is reduced by 22 K.The results show that the fatigue life meets the design safety factor requirements.Finally,this paper explores the influence of piston top wall thickness on piston temperature and strength.The results show that with the increase of piston crown wall thickness,the maximum temperature of piston crown increases,the maximum coupling stress decreases and the coupling deformation increases;The variation of piston top wall thickness has a great influence on the thermal stress and mechanical stress in the center area of piston top,has a great influence on the thermal stress in the pit area of piston top,and has a little influence on the mechanical stress.Reducing the wall thickness of the center area of the piston crown can effectively reduce the temperature of the piston crown,and increasing the wall thickness can effectively improve the strength of the center area and the concave area of the piston crown.