Improving the applicability of CO2 transcritical cycles to finite cold sources: A mixture solution considering properties and vehicle integration

CO2 has emerged as a promising working fluid for waste heat recovery due to its favorable thermodynamic properties and environmental friendliness. However, its practical application in transcritical cycles is constrained by its limited condensation capacity. Blending CO2 with refrigerants has been proposed to enhance its thermophysical properties, thereby improving system compatibility and adaptability to various cold sources. This study systematically investigates the safe operating range and optimal composition of CO2-based mixtures, focusing on the effects on physical properties, thermodynamic performance, and system dimensions. Results show that CO2/R32 with 30 %–70 % CO2 satisfies the condensation and flame retardancy requirements of vehicular waste heat recovery. In extreme conditions, CO2/R32 mixtures improve heat utilization, efficiency, and power output through enhanced energy matching, albeit at the cost of increased heat exchangers and turbine sizes. For combined cooling and power cycles, the optimal mixture of CO2/R32 = 0.4/0.6 delivers 10.11 kW power output and 10.8 kW cooling capacity in cogeneration mode. When considering fan power consumption for condensation, the optimal engineering composition is CO2/R32 = 0.3/0.7, boosting vehicular power output to 183.86 kW, representing a 4.47 % improvement. This study offers theoretical insights to balance mixture performance and engineering constraints in waste heat recovery.