Energy and exergy analyses for organic Rankine cycle driven by cooling water of passenger car engine using sixteen working fluids

Abstract

In this study, energy and exergy analyses of an organic Rankine cycle (ORC) for waste heat recovery from a passenger car engine cooling water are performed numerically. Sixteen different organic working fluids were selected according to their high-performance indicators recommended in the literature, their physical and chemical properties, and their environmental impact. Appropriate matching conditions between the low-temperature Rankine cycle with the engine cooling system and the properties of the working fluid were established. Thermodynamic models based on the first and second thermodynamic laws are developed. The ORC's cycle thermal efficiency, exergy destruction, and second law efficiency are assessed to choose the most suitable working fluid. The analyses investigate how the thermo-physical characteristics of the working fluid affect the performance metrics.Results show that ORC operating with R245fa and R123 as working fluids have the highest thermal efficiencies (7.76% and 7.49 % respectively), and low exergy destructions (1.538 kW and 1.586 kW respectively) in addition to moderately low mass flow rate necessity. The passenger car engine with ORC operated by R245fa as a working fluid shows an average value of 9.7 % fuel saving over the studied engine speeds and loads range.