Tribological performance of lubricating oils with iron tribopairs under elevated temperature and pressure in carbon dioxide refrigerant

Abstract

Recent interest in carbon dioxide-based refrigeration has increased. Despite the positive environmental impacts, carbon dioxide makes a complex refrigerant due to elevated pressures and temperatures inside the compressor and the reactivity of CO2 with the lubricant. Tribological experiments were performed using synthetic oils paired with ductile iron tribo-pairs under high pressure CO2. The three lubricants investigated were PAG (Polyalkylene Glycol) and two POE (Polyolester) oils of different viscosities. Elevated temperatures resulted in higher unstable COF for POE and quicker corrosion and degradation of the tribolayer on the surface. In the case of POE, corrosion is significant in causing unstable COF performance at higher temperatures as the ester groups in POE result in more reactivity with the iron surface.