Abstract
A novel approach to realizing and enhancing a transcritical carbon dioxide (CO2) power cycle can be achieved by simultaneously utilizing waste heat from an internal combustion engine at two different temperature levels. This paper introduces a combined power system integrating a transcritical CO2 power cycle and an ejector refrigeration cycle (tCO2-ERC) via internal condensation for engine waster heat recovery, where the ERC driven by jacket water provides cooling energy for the condensation of CO2 in the tCO2 subsystem driven by exhaust gas. Comprehensive analyses, including energy, exergy, and economic aspects, are conducted through parameter analysis and system optimization to explore the mechanisms underlying the performance improvement of the combined power system. The results of refrigerant screening demonstrate that implementing R717 in the ERC of the tCO2-ERC system yields better overall thermoeconomic performance. Exergy analysis demonstrates that the exergy losses from the exhaust and jacket water to the environment in the tCO2-ERC system are reduced to 17.62% and 30.27% of the total exergy input, respectively, which represents a reduction of 7.32%pt (percentage point) and 12.51%pt compared to the standalone reference CO2 power system. Multi-objective optimization results indicate that the optimized net power output and levelized cost of electricity of the tCO2-ERC system are 388.79 kW and 0.09023 $/(kW·h), respectively, which are 13.01% higher and 6.91% lower than those of the reference CO2 power cycle system. Furthermore, the net power output of the tCO2-ERC system exceeds that of the reference CO2 power system by 5.44% to 14.34% when the ambient temperature ranges from 10 ℃ to 30 °C. Additionally, the tCO2 subsystem consistently operates in a transcritical mode within an ambient temperature range of 10–30 °C, thereby expanding its application range.
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