PISTON-RING LUBRICATION PROBLEMS FOR REFRIGERATION COMPRESSORS CONSIDERING COMBINED EFFECTS OF SUPPLY OIL QUANTITY AND SURFACE-ROUGHNESS

Reciprocating-type compressors are widely used for refrigeration syste ms, and an understanding of piston-ring lubrication in the compressor is vital for designers in reducing the energy losses due to friction b ecause a substantial portion of friction in the compressors is attribu table to the piston-ring assembly. This study aimed at developing a on e-dimensional analysis for lubrication between the piston-ring and cyl inder of refrigeration compressors considering the combined effects of supply oil quantity and surface roughness on piston-ring face and cyl inder wall. In the theoretical model, the piston-ring is treated as a one-dimensional dynamically loaded bearing with combined sliding and s queezing motion, The one-dimensional modified Reynolds equation based on the average flow model by Patir and Cheng is used as a governing eq uation. In the analysis of the modified Reynolds equation, two-types o f inlet boundary conditions, flooded condition and starvation conditio n, are applied at the lending edge according to the supply oil quantit y: and the Reynolds boundary condition is applied at the trailing edge , A numerical procedure is then developed to estimate the cyclic varia tion of minimum film thickness, inlet and outlet positions of lubricat ion film and friction force, and the combined effects of supply oil qu antity and surface roughness height are examined for a typical refrige ration compressor, It is clarified from the numerical results that the supply oil quantity and surface roughness affect significantly the fr iction force of the piston-ring for refrigeration compressors.