Performance assessment and comparative study on novel carbon dioxide based power cycles for the cascade engine waste heat recovery

Abstract

• Two novel CO 2 based power cycles for waste heat recovery are proposed. • Thermodynamic and exergoeconomic models are established for these systems. • Comparative studies and optimizations for these thermal systems are performed. • The novel systems show the better overall performance in exhaust heat extraction. Exploiting waste heat from engine could greatly alleviate current severe energy and environmental situation. Carbon dioxide (CO 2 ) based power cycle is considered as a type of competitive and promising energy utilization system for engine waste heat recovery (WHR) due to its high efficiency, compact design and environmentally friendly property. However, a large space is left for CO 2 -based power cycle to improve the thermodynamic and economic performance. To more efficiently and thoroughly utilizing engine waste heat, two novel CO 2 -based power cycles are proposed. Mathematical models are developed based on the software MATLAB to conduct quantitative thermodynamic and exergoeconomic analysis, parametric analysis, system optimization, and exergy analysis on the proposed systems and two traditional systems. The results show that the first proposed system can enhance net power output by 57.95% and 4.31% and meanwhile reduce total product unit cost by 14.96% and 20.74%, respectively, compared with two traditional systems. As well, the improvement of 61.61% and 6.73% for net power output and 4.11% and 10.62% for total product unit cost can be achieved by the second proposed system. Exergy analysis indicates that the cooler and low-temperature waste heat exchanger have the first and second highest exergy destructions for two proposed systems.