Energetic performance and driving range investigation of the CO₂ indirect system with ejector used in vehicle thermal management

Natural refrigerant CO₂ is a promising alternative to R134a for electric vehicle thermal management system (TMS), with environmental friendliness and superior heating capability. Although ejectors can enhance the cooling efficiency of CO₂ TMS by reducing throttling losses, their application in indirect systems remains insufficiently validated. This study assesses the passive adaptability of a fixed-geometry ejector in both direct and indirect systems by examining the performance discrepancies and thermodynamic mechanisms across the full operating conditions. The results demonstrate that the indirect system effectively mitigates the impact of external temperature fluctuations on the primary refrigerant cycle through its secondary heat exchange process, expanding the ejector's applicable temperature range to −15 °C–45 °C, superior to the direct system's range of −5 °C–45 °C. Seasonal performance analysis further reveals that the indirect system achieves annual performance factor improvements of 1.85 %–7.08 % across all regions, while the direct system only shows improvements of 4.57 %–6.76 % in non-cold regions, with a 1.17 % performance degradation observed in Harbin, representative of severe cold climates. The driving range results indicate that the application of the ejector in the direct and indirect systems achieves maximum driving range improvements of 19.5 km and 21.0 km, respectively, while reducing the energy consumption of the TMS by 1.2 kWh and 1.45 kWh per 100 km.