Numerical Study On Tribological Characteristics Of Wedge Triangle Micro-texture On Cylinder-liner Surface

The cylinder-piston friction pair is one of the most important friction pairs in an internalcombustion engine.The energy loss of friction caused by the cylinder-piston pair account for44% of the friction loss of the entire internal combustion engine.The friction between cylinder-piston friction pair has a serious effect on the reliability and service life of the internal combustion engine.Surface texture technology become one of the most effective methods of anti-friction and lubrication due to enhance hydrodynamic pressure effect and storage oil and crumbs,and has attracted wide attention from scholars around the world.In this paper,a new type of wedge triangle micro-texture is designed based on the hydrodynamic lubrication theory for the cylinder-piston friction pair,in order to improve the friction and lubrication characteristics between the cylinder-piston pair.The cavitation flow field of lubricating oil for the wedge triangle micro-texture is numerically studied by the computational fluid dynamics(CFD)method.The physical quantities of flow field such as pressure,vapor volume fraction(VVF)and velocity are obtained.The details of the cavitation flow field are analyzed.The bearing capacity and friction force of the lubricating oil film on the piston moving wall are calculated.Furthermore,the anti-friction and lubrication mechanism of the wedge triangle micro-texture are revealed.In addition,the effects of configuration parameters of the wedge triangle micro-texture such as the depth,the angle between the two sides of triangle and the area occupancy fraction on the cavitation characteristics and the anti-friction characteristics are studied.The optimal size is given for the wedge triangle micro-texture.Finally,compared with the experimental results of friction and wear,the numerically simulated results are verified in this paper.The cavitation characteristics of the flow field for wedge triangle micro-texture are numerically studied by applying the three-phase mixture model of with Singhal full cavitation model.The numerical results show that the oil pressure drops rapidly in the texture divergence zone as the lubricating oil enters the micro-texture inlet.The minimum pressure can be reduced to the threshold value of cavitation and cavitation could occur in the entrance of the divergence zone of the micro-texture.Because the space inside the micro-texture becomes narrower along flow direction,the fluid dynamic pressure effect is enhanced.The flow pressure reaches the peak value near the outlet of the micro-texture,being about 1.1 MPa.Due to the existence of micro-texture,the high pressure and low pressure are formed on the piston moving wall by both of the cavitation effect and dynamic pressure effect.The sliding speed and direction of piston have effects on the anti-friction and lubrication of micro-texture.As the piston speed increases,the cavitation zone is enlarged,and cavitation inside the micro-texture becomes more serious.The friction coefficient of the micro-texture increases and then decreases with the piston speed.Different sliding direction of piston changes the locations of flow-in and flow-out of the micro-texture.It results in a significant change in the cavitation characteristics of flow field and pressure distribution on the moving wall.The bearing capacity of oil film decreases as sliding direction of piston β is increased.The wedge micro-texture exhibits the excellent anti-friction lubrication effect as β=0°.Effects of the micro-texture configuration parameters,such as the depth,the angle between the two sides of triangle and the area occupancy,on anti-friction and lubrication performance explored.Furthermore,the optimal micro-texture parameters are obtained.The vortex range inside the texture is enlarged as the depth of micro-texture is increased.The increase of pressure around the outlet of micro-texture is suppressed by the vortex.The friction coefficient decreases then increases with the depth of micro-texture.There is an optimal texture depth considering the anti-friction and lubrication effect.The friction coefficient decreases then increases,and then slightly decreases with angle.As angle increases,the high and low pressure zones on the moving wall are enlarged,and vortex inside the micro-texture is enhanced.The friction coefficient decreases and then slightly increases with the area occupancy of texture.The synergistic effect between the micro-textures becomes more significant as the area occupancy of texture is relatively great,which leads to a decrease in the high pressure around the convergence zone.Finally,the optimal micro-texture parameters of the depth of 15μm,the angle of 60°,and the area occupancy of 15.4%.The wedge triangle micro-textures with different area occupancy fraction were prepared by 3D printer technology.Moreover,the morphology of micro-textured surface was observed.The friction and wear experiments were performed.The experimental results show that the wedge triangle micro-textures could be prepared well by 3D printer technology.The micro-texture with the area occupancy fraction of 15.4% has the best lubrication and anti-friction performance.The friction coefficient is the smallest and the slight wear occurs around the tip of the wedge micro-texture for the area occupancy fraction of 15.4%.The numerically simulated results are consistent with the friction experimental results,which verifies the accuracy and reliability of the numerical simulation of the lubricating oil cavitation flow field with the wedge triangle micro-texture in this paper.