Oil Circulation Ratio in CO2 Climate Control Systems

This paper presents the effect of the oil circulation ratio on the system performance of a CO₂ climate control system and the effect of an oil separator on the oil circulation behavior using a new oil circulation ratio measurement method. In this study, the oil circulation ratio of a CO₂/PAG mixture at various system conditions was measured. When the oil circulation ratio increases from 0.5 wt.% to 7 wt.%, the coefficient of performance decreases by 8% and 11% for idling and driving conditions, respectively. Without the oil separator, the oil circulation ratio increases more than 10 wt.%; with the oil separator, it was maintained at below detection level and 1.1 wt.% for idling and driving conditions, respectively.