Performance evaluation of R744-hydrocarbon blends in a two-stage refrigeration cycle for transport applications

The increasing environmental concerns and regulations are forcing the HVAC&R sector to shift towards low-GWP refrigerants. Hence, research is actively exploring sustainable alternatives to traditional HFC-based systems. This study provides a numerical drop-in analysis of CO2 (R744) - hydrocarbon blends in a two-stage vapor compression cycle designed for a mid-sized refrigerated truck. By simulating blends of R744 with small amounts (up to 10 %) of R290, R600a, R1270, and RE170 under various ambient conditions, this research identifies the options that could match or enhance the performance with respect to pure R744. Seasonal simulations, accounting for typical thermal loads in two Italian cities, i.e., Milan and Palermo, reveal that R744 blends with R290 and R1270 achieve comparable or improved seasonal COP (SCOP), especially in colder climates where the system performance benefits from temperature glide. The optimal blend, 92 % R744 and 8 % R290, provides SCOP increases of 2.96 % in Milan and 2.13 % in Palermo, while blends with R600a or RE170 show reduced efficiency. These findings suggest the R744 - R290 and R744 - R1270 blends as a promising low-GWP option for refrigerated transport.