Steady-state Thermal Analysis Of Functional Gradient Materials As Thermal Barrier Coating Of Engine Piston

Based on the design principle of low injection engine, the piston with functional gradient thermal barrier coating can increase the temperature at piston top, and has a good heat insulation effect. This kind of piston is made from Si-Al alloy, functional gradient transition layers and ceramic heat insulation layer. The ceramic layer has a good heat insulation effect, the functional gradient transition coatings with a graded composition are designed to reduce thermal stress resulted from the mismatch of thermal expansion performances between ceramics and substrate Si-Al alloy, and the Si-Al alloy can endure the deformation from the high pressure burning gas.In this thesis, ZrO₂ ceramic and Si-Al alloy piston were firstly chosen to investigate. A 3-D model for the functionally gradient materials piston was established with Pro/E software. It gained one cycle pressure of the burning-gas through the experiment of pressure-corner diagrams. Based on the experiential formula, the instantaneous pressure and temperature were calculated and then the instantaneous exchange coefficient was obtained. Thus, the average exchange coefficient can be thought as the third boundary conditions in the finite element analysis of piston. Using ANSYS software the piston with functional gradient materials was analyzed. Before analyzed the model, the continuous gradient layers with index distribution were divided into six layers using dispersion method. During the dispersion process, it selected different gradient distribution index. It was then analyzed the temperature and the thermal stress of functional gradient cylinder with different distribution index (simplified as the head of piston), pure ceramic cylinder and Si-Al alloy cylinder. Finally, it was also analyzed that the temperature field and the thermal stress field of the functional gradient piston with different distribution index, pure ceramic piston and Si-Al alloy piston. The results indicated that using gradient transition layers could obviously change the temperature distribution of the piston and relax the stress at the interface between the gradient layer and the Al-Si alloy piston. By analyzing the temperature and thermal stress of both cylinder and piston with different gradient indexes, it can be gained the optimal gradient index p=0.6, which is based on the insulation effect and thermal stress between the gradient layer and Si-Al alloy.