Study On Transient Stress And Shape Tolerance Of Piston-Cylinder Liner Considering Air Intake Cooling

As increase of the thermal and mechanical loads of internal combustion engines,stricter requirements are imposed on the strength and stiffness of pistons and cylinder liners.The piston and the cylinder liner contact with the high-temperature gas and are affected by the cooling medium such as the intake air and the cooling water.They are also subjected to the alternating mechanical loads.The working conditions are bad,and the problems such as insufficient strength,severe deformation and poor fitting are prone to occur.Research on the transient stress and shape tolerance of piston-cylinder under thermal-mechanical load is of great significance for improving the reliability of diesel engine.At present,there are several problems in the simulation analysis of the pistoncylinder liner.First,the temperature of the piston top surface and the inner wall of the cylinder liner is high and fluctuating drastically.The heat transfer boundary of the piston top surface calculated by the empirical formula is not accurate.Second,the displacement constraints in the thermal stress calculation leads to stress concentration.Third,the geometrical tolerance dynamic measurements of cylinder liner is not easy to achieve.Combustion simulation,finite element analysis and simplex algorithm are combined in this paper to study the transient stress and deformation of piston-cylinder liner under the effect of intake air cooling.The strength and geometrical tolerance are analyzed and the simulation method of calculating the geometrical tolerance of cylindrical components by means of simulation.The heat transfer boundary condition of the piston top surface is obtained by combustion simulation and the piston-cylinder-body finite element model is established.The transient temperature distribution of the piston-cylinder liner is studied by combining the empirical formula and the moving boundary loading method.The temperature measurement experiment is carried out to verify the temperature simulation results.The simulation method of piston temperature field considering the intake air cooling effect reflect the top surface temperature’s fluctuations in time and unevenness in space more accurately.The nonlinear contact pairs are established,and the mechanical load is calculated by the dynamics of the crank-link mechanism.The simulation results of the temperature field is combined to study the transient thermal stress,mechanical stress and thermal machine coupling stress of the piston and the cylinder liner,and the strength analysis is performed according to the fourth strength theory.Setting the nonlinear contacts improves the artificial thermal stress concentration caused by the displacement constraints.The thermal stress on the intake side of the piston is 11.9% higher than then exhaust side.The dangerous points of thermo-mechanical stress locate on the main and secondary thrust surfaces of the piston,the upper part of the pin hole and the head of the cylinder liner.The mechanical load has a greater influence on the thermomechanical coupling s stress of the piston heat engine than the heat load.The finite element method,the simplex algorithm and the least square method are combined and the parameters such as out-of-roundness and concentricity are used to evaluate the deformation of the cylinder liner.The effect of each load on the deformation of the piston-cylinder liner is studied.The out-of-roundness of the cylinder liner is mainly affected by the side thrust and the concentricity is mainly affected by the burst pressure.The lateral thrust easily causes the piston profile change unevenly.The calculation results of the profile line provide reference for the calculation of frictional power consumption and the lubricant pressure of the piston skirt,and the optimization of the skirt profile.