Study On Marine Diesel Piston Failure Analysis And Its Structural Optimization

Piston,as the "heart" of the engine,is one of the most important components of the engine.Its continuous and efficient and stable operation plays a vital role in the operation of the whole diesel engine.There is one kind of marine diesel engines which has widely used in China for about 40 years.With the requirements of high coefficient of strengthening,low oil consumption and the applicability of heavy fuel,a company improved and designed a new type.In order to meet the need of high detonation pressure,its piston was optimized and improved,and the original one-piece piston was changed to a composite one with steel crown and iron casting skrit.However,with the enhancement of the strengthening coefficient and the decrease of oil consumption,the failure rate of the piston has been obviously improved,and a number of accidents in connection with the cracking of the piston top have occurred.This topic is based on this background,and this paper focuses on the following aspects:(1)Aiming at the cracking of failed piston of a marine medium speed diesel engine,the macroscopic appearance,microstructure and dimension inspection,chemical analysis,metallographic examination and mechanics were analyzed.Combined with the theory of fatigue analysis,the cause of piston cracking was analyzed..(2)Based on current domestic and foreign research on finite element analysis of piston,selected for the study of the piston boundary conditions;the establishment of 3D model of the piston assembly,simulation calculation of the temperature field of the piston and the stress field distribution using Abaqus finite element technology,through the calculation of variation of temperature at the maximum cracking source,and the comprehensive stress cracking is largest,and verified the correctness of failure analysis.(3)The optimum design of the piston structure was researched.Two design are adopted respectively: one is to improve the structure of the cooling chamber,increase the cooling and reduce the temperature of the failure part,thereby reducing the thermal stress;the other is to increase the thermal barrier coating,and reduce the temperature of the whole piston top surface by using the thermal insulation property of the coating material.(4)Using Abaqus analysis software,the two optimization schemes are simulated by the optimized boundary conditions,and compared with the calculation results before improvement.Combined with the engineering application of process feasibility and economy,the optimal plan is determined.The research shows that through the optimization of piston structure,the maximum thermal stress of piston will be significantly reduced and the hidden danger of piston top cracking will be eliminated.The research results will provide technical support for developing high-performance diesel engines in China.