Optimization of CO₂ Transcritical Power Cycle (CTPC) for engine waste heat recovery based on split concept

CO₂ Transcritical Power Cycle with a preheater and regenerator has emerged as a promising technology to recover engine waste heat. Jacket water, engine exhaust gas and CO₂ exhaust after expansion have been considered the main recovery sources in terms of external and internal utilization objectives. During the three consecutive heating processes, however, the issue of temperature interference may reduce the exhaust gas utilization and thermal efficiency. Therefore, this research proposes a split concept for the objective of investigating temperature interference. Three corresponding split systems are studied. This article develops comprehensive mathematical models to compare the performances and a detailed analysis of each advantage is carried out. The results showed that temperature interference could be solved to achieve maximum utilization of the exhaust gas and increase the thermal efficiency. In addition, the net power could be improved from 14.7 kW to 19.0 kW after optimization. Among the studied systems, the low-temperature split system showed an increment of 90.0% in cycle efficiency, and the medium-temperature split system was found 4.9% improvement in heat recovery efficiency. The high-temperature split system displayed superior characteristics to the others in both the cycle and heat recovery efficiency, which were improved by 18.3% and 10.4%.