Analysis Of Thermal Load On Piston Of High Power Diesel Engine

In recent years,the development trend of internal combustion engine towards high speed and high compression ratio.As one of the most severe working environment parts in the internal combustion engine,the piston is directly affected by the high temperature gas,which caused the high thermal and mechanical load.Therefore,higher structural strength and more effective cooling methods is needed.In this paper,the piston of a diesel engine was taken as the research object,and the thermal load was studied by using 3-D finite element method.The paper had carried out from the following aspects.(1)A test bench was set up to measure piston temperature by using the hardness plug.The temperature of the piston top was obtained from the test.The analysis of cylinder piston temperature difference was based on six cylinders of the engine.The temperature distribution of the piston top was also concluded which could verify the simulation result of the piston temperature field.(2)A multi-field coupling method was used to calculate piston temperature field.The calculation and analysis was focused on determining the boundary conditions of the piston top and cooling gallery.To determining the piston top boundary conditions,one-dimensional and three-dimensional computational models were established,from which the temperature and heat transfer coefficient were got.To determining the cooling gallery boundary conditions,a transient calculation was carried out based on an inner oscillating-oil-cooling channel finite element model.(3)The FEA model was established to calculate piston temperature field.Empirical formulas and multi-field coupling method were used to determining the boundary conditions.The analysis was based on the different results of the piston temperature field by two methods.Three dimensional calculation of combustion chamber was abstracted and mapped to the piston top as its heat transfer boundary conditions.The conclusion was summed up by the mapping result,and the rule of the piston temperature field was analysed based on it.A certain amount of grid nodes of(4)the piston top were collected,and the temperature and heat transfer coefficient were got from them.Least squares was used to fit curve and formula based on the mapping results.In order to verify the correctness of the formula,a simulation was carried out on other piston.(5)A FEA model was established to calculate piston stress field.The piston pin and connecting rod were considered in the calculation.gas pressure,inertia force,bolt pre-tightening force and so on were included in the stress boundary conditions.According to the results of piston stress and deformation,optimizing the piston structure and verifying the rationality.