Exergy analysis of a combined engine-organic Rankine cycle configuration

Abstract This article presents an exergy analysis of a combined engine-organic Rankine cycle configuration (E-ORC) using the exergy topological method. A detailed roadmap of exergy flow is presented using an exergy destruction chart to clearly depict the exergy accounting associated with each thermodynamic process. The analysis indicates that an ORC combined with an engine not only improves the engine thermal efficiency but also increases the exergy efficiency. Different organic fluids are evaluated in this article. Depending on the organic fluid employed, the thermal and exergy efficiencies could be increased by approximately 10 per cent. Parameters such as the thermodynamic influence coefficient and degree of thermodynamic perfection are identified as useful design metrics to assist exergy-based design of devices. This article also examines the effect of the pinch-point temperature difference (PPTD) on the E-ORC performance. Results show that the lower the PPTD the higher the thermal and exergy efficiencies.