Characteristics and Lubricity of Refrigeration Oil for R290

The switch from HFC refrigerants with a high global warming potential (GWP) to low GWP refrigerants is currently in progress all over the world, and HFO and HCFO refrigerants are being increasingly used. Natural refrigerants, propane (R290) and carbon dioxide (R744), have also been attracting attention. R290 refrigeration systems are now commercially installed for showcases, water heaters, dehumidifiers, etc., and the scope of application will likely continue to expand to relatively small refrigeration equipment. Mineral and synthetic oils have been used as the refrigeration oil for R290, and polyol ester (POE) and polyalkylene glycol (PAG) have been widely used as the synthetic oil. Although various types of oils are used depending on the equipment, POE has high volume resistivity and is said to have a low risk of electrical leakage. POE has also been reported to be less explosive and safer than PAG in a previous experiment simulating an accident during the pump-down of an air conditioner. In this paper, we introduce our developed POE oil suitable for R290. It has an optimal flash point, pour point, volume resistivity, and the chemical structure of POE so that it is compatible with R290. In addition, we determined that the anti-wear performance of the novel POE oil is an improvement over that of conventional POE oils and mineral oils. The surface analysis of the test specimen revealed that the additive system designed for the POE effectively improved the lubricity.