Study on the thermal stability and performance evaluation of CO2/HFO-1234ze(E) mixtures in transcritical power cycles: Insights from CVHD simulation and thermodynamic analysis

CO2-based mixtures exhibit favorable thermophysical properties for transcritical power cycles (TPC), but high-temperature thermal decomposition poses safety concerns. This study investigates the decomposition mechanisms of CO2/HFO-1234ze(E) mixtures using CVHD-accelerated ReaxFF molecular dynamics, density functional theory (DFT), first-order reaction kinetics modeling, and thermodynamic performance evaluation. Results show that decomposition is predominantly temperature-driven, with CO2 enhancing thermal stability by diluting reactive species and scavenging radicals, while pressure plays a secondary role. For CO2/HFO-1234ze(E) mixtures with molar ratios of 30/70, 50/50, and 70/30, decomposition onset temperatures range from 483.15 K to 683.15 K, corresponding to activation energies of 129.32–190.79 kJ/mol. The maximum allowable operating temperatures at 5 % decomposition are 474.46 K, 549.23 K, and 669.53 K, respectively. Reaction pathway analysis identifies HF formation as the dominant fluorine release mechanism, with CO2 acting as both a stabilizer and radical inhibitor. Under 300 °C and 400 °C waste heat conditions, CO2-based mixtures increase net power output by 20–30 % and thermal efficiency by 6 %–8 % compared to pure HFO-1234ze(E), with higher CO2 content further enhancing high-temperature adaptability. This work provides theoretical guidance for the safe and efficient application of CO2-based mixtures in transcritical power cycle systems.