Tribological studies on scuffing due to the influence of carbon dioxide used as a refrigerant in compressors

Because hydrofluorocarbon (HFC) refrigerants in air-conditioning systems are known to have a negative effect on the environment, carbon dioxide (CO2) is a candidate as a replacement refrigerant. Research work related to CO2 as a refrigerant has been focused primarily on its thermodynamicperformance, whereas work in the area of tribology related to carbon dioxide is absent. In this study, the effects Of CO2 used as a refrigerant on the tribological behavior of surfaces in contact in such systems were investigated. Controlled experiments were performed at constant loads in environments of CO2 and the conventional HFC refrigerant, R134a, as well as under conditions of step-increasing loads in the presence of refrigerant (CO2 or R134a) and polyalkylene glycol lubricant. The experiments were performed on a high-pressure tribometer that is particularly suited for tribological testing of compressor contact interfaces. The tribological behavior of contacting surfaces in a CO2 environment was nearly identical to that in an R134a environment when tested under the same operating conditions.