Supercritical CO₂-cycle configurations for internal combustion engine waste-heat recovery: A comparative techno-economic investigation

Supercritical-CO₂(S-CO₂) cycle systems have appeared as an attractive option for waste-heat recovery from internal combustion engines (ICEs) thanks to the advantages offered by CO₂as a working fluid, which is nontoxic and non-flammable, and does not suffer decomposition at high temperatures. Since the high density of CO₂in the supercritical region enables compact component design, various S-CO₂cycle system configurations have been presented involving different layouts and combinations of heat exchangers with which to enhance heat recovery from both engine exhaust gases and jacket water streams. Despite the thermodynamic performance improvement offered by more complex configurations, the additional heat exchangers bring extra costs and therefore key thermo-economic decisions need to be considered carefully during the design and development of such systems. This paper seeks to conduct both thermodynamic and economic (cost) assessments of a variety of S-CO₂cycle system configurations in ICE waste-heat recovery applications, with results indicating that in some cases a significant thermodynamic performance improvement can compensate the extra costs associated with a more complex system structure. The comparison results across a range of ICEs can also be a valuable guide for the early-stage S-CO₂cycle system design in ICE waste-heat recovery and other similar applications.