Thermodynamic, economic, environmental analysis and multi-objective optimization of a novel combined cooling and power system for cascade utilization of engine waste heat

Combined system based on supercritical CO₂ Brayton cycle exhibits great potential to recover waste heat from engine. However, the effective utilization of waste heat from jacket water along with that from engine exhaust still remains a challenge, owing to the heat load mismatching of different heat sources. In this paper, a novel combined cooling and power (CCP) system, comprised of a topping supercritical CO₂ Brayton cycle and a bottoming transcritical CCP cycle using CO₂-based mixture, is proposed to realize the heat recovery of both engine exhaust and jacket water. Detailed parametric analysis is conducted to study the effect of seven key parameters on system performance from thermodynamic, economic and environmental viewpoints. Thereafter, a multi-objective optimization is performed to explore the performance improvement potential. The results show that the increasing turbine Ⅰ inlet pressure and the decreasing compressor inlet temperature are conductive to all performances. Through multi-objective optimization, the optimal thermal efficiency, cost rate per unit of exergy output and environment impact per unit of exergy output are 38.42%, 0.0529$/kWh and 0.0762mPts/kWh, respectively. Under optimal conditions, the maximum net power output of the system could achieve 384.64 kW, accounting for 13.14% of the engine output, with a cooling capacity output of 268.35 kW.