Correlation Analysis On Piston Design Parameters And Thermal Damage

With the improvement of diesel engine, the thermal load of engine is increasing. Excessive thermal load will produce the phenomena of piston top crack, burn, pit, collapse, piston ring glued and so on, reducing the reliability and durability of diesel engine seriously. So improving the working environment and reducing the excessive thermal load of diesel piston is very important to improve the engine performance.First, comparing the different simulating models of grid, collision and turbulence through the transient simulation of combustion and oil-inject shaking cooling of one type engine to find the right combination of different models, then comparing the numerical simulation results with the test results. After the models calibrated, applying them to the other three calculations of thermal boundary. Secondly, calculating and analyzing the temperature and thermal stress field of four kinds of piston. Last, modifying the design parameters of piston, including the height of piston top land, the distance between oil cavity and piston top and material properties, analyzing the effects of different design parameters on piston thermal load and giving the thermal load changes with the design parameters of piston.The piston temperature field shows that temperature distribution of piston is not uniform. The maximum temperature occurs near the chamber rim, the lowest temperature takes place in the bottom of the piston. In addition, the first groove temperature is very high. For the temperature field changes with the design parameters of piston:(1) With the increasement of the height of top land, the temperature of the piston top and the first ring increased.(2) With the increasement of chamber rim radius, the temperature of chamber rim increased.(3) Without oil cavity, the temperature of piston top and first groove increased.(4) With the distance between oil cavity and piston top close, the temperature of piston top and first groove decreased.(5) With the increasement of the surface area of oil cavity, the temperature of piston top and first groove decreased. (6)With the increasement of coefficient of thermal conductivity, the temperature of piston top and first groove decreased.The thermal stress field analysis shows that the thermal stress distribution is not uniform. Because the maximum temperature gradient occurs between oil cavity and second groove, the maximum thermal stress takes place in second groove. Besides, the thermal stress in chamber rim and the top of inner cavity is very high, other places’ thermal stress is not very high. For the thermal stress field changes with the design parameters of piston:(1) With the increasement of the height of top land, the maximum thermal stress changes little, but the thermal stress of the chamber rim decreased. (2) With the increasement of chamber rim radius, the thermal stress of the chamber rim decreased. (3) Without oil cavity, the maximum thermal stress of piston and the thermal stress of chamber rim decreased.(4) With the distance between cavity and second groove close, maximum thermal stress increased. With the distance between oil cavity and piston top close, thermal stress of chamber rim increased.(5) With the decreasement of the surface area of oil cavity, the maximum thermal stress and the thermal stress of chamber rim decreased. (6) With the increasement of coefficient of thermal conductivity, thermal stress of piston decreased. (7) With the increasement of the coefficient of linear expansion, thermal stress of piston increased.