Ultra High Pressure Tribometer for Testing CO2 Refrigerant at Realistic Compressor Conditions and the Role of CO2 in the Tribological Behaviour of Compressor Surfaces

In recent years, the environmental necessity to replace HFC refrigerants with natural refrigerants like carbon dioxide (CO2) in refrigeration and air-conditioning applications has led to the development of an Ultra High Pressure Tribometer (UHPT) specifically customized for testing in CO2 environment at pressures comparable to those found in compressors up to 13.8 MPa (2000 psi). It was found that at three different pressures of CO2 refrigerant under unlubricated conditions the experimental results were similar. However, under boundarylubricated conditions, the highest pressure had a slightly more positive effect on friction than in the case of the lower pressures. Furthermore, the role of oxygen and in particular CO2 in the tribological performance of compressor surfaces was examined. It was found that the presence of oxygen is beneficial and that the use of CO2 promotes a different wear mechanism than in the case of pure O2 while it is superior to other environments.