Feasibility Study on Two Novel Lubricants for a Carbon Dioxide Reciprocating Compressor

In recent years, increasing research efforts have been made on modeling and testing positive displacement compressors with low global warming potential (GWP) working fluids and their systems. The ongoing HFC phase-down is forcing the HVAC &R industry to investigate low-GWP refrigerant alternatives as well as natural refrigerants (e.g., water, hydrocarbons, \(\text {CO}_{2}\) ). The transition to low-GWP and natural refrigerants requires research efforts on cycle configurations and components including compressors. More specifically, most of the existing positive displacement compressors employed in HVAC &R systems rely on lubricant oils to ensure correct operation and performance. To better understand the potential research directions in lubricant oils, a reciprocating compressor with \(\text {CO}_{2}\) as refrigerant was selected as the case study to investigate alternative lubricant oil formulations. In this study, a baseline POE reference and two alternative lubricant oils were evaluated on a transcritical \(\text {CO}_{2}\) reciprocating compressor with respect to performance enhancement and potential issues and challenges. A hot gas bypass test stand was used to carry out the experimental studies. A total of 66 steady-state data points were collected, and control tests were performed after each alternative oil formulation to ensure correct operation of the compressor. The alternative lubricant oils showcased comparable performance data to the baseline lubricant oil under a wide range of operating conditions without sign of decomposition and wear.