Alkanes as working fluids for high-temperature exhaust heat recovery of diesel engine using organic Rankine cycle

• Published in: Applied energy Vol. 119; pp. 204 - 217
• Main Authors: Shu, Gequn, Li, Xiaoning, Tian, Hua, Liang, Xingyu, Wei, Haiqiao, Wang, Xu
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 15.04.2014; Elsevier
• Subjects: Alkanes; Applied sciences; cyclohexanes; diesel engines; Energy; energy use and consumption; Energy. Thermal use of fuels; Engines and turbines; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; exergy; fuels; heat recovery; High-temperature exhaust gas; mass flow; Organic Rankine cycle (ORC); steam; temperature; Waste heat recovery (WHR); wastes; Working fluids; Working fluids; Alkanes; High-temperature exhaust gas; Organic Rankine cycle (ORC); Waste heat recovery (WHR); Waste recovery; Diesel engine; High temperature; Working fluid; Heat recovery; Exhaust; Alkane; Rankine cycle; Exhaust gas; Waste heat
• DOI: 10.1016/j.apenergy.2013.12.056
• ISSN: 0306-2619

•Less complex fluids are preferred due to their excellent performances.•The cyclic Alkanes are considered as the most promising candidate.•Maximum improvement of 10% in BSFC is obtained by DE-ORC combined systems.•Alkane-based ORCs may be more attractive than steam cycle for exhaust heat recovery. Study on recovering waste heat of engine exhaust gas using organic Rankine cycle (ORC) has continuously increased in recent years. However, it is difficult to find out appropriate working fluids to match with exhaust gas waste heat due to high temperature. In this work, several tentative attempts and explorations are made in selecting Alkanes as working fluid owing to their excellent thermo-physical and environmental characteristics. Parameters optimization of the combined system of diesel engine with bottoming ORC (DE-ORC) is performed on Alkane-based working fluids with six indicators, including thermal efficiency (η), exergy destruction factor (EDF), turbine size parameter (SP), total exergy destruction rate (IORC), turbine volume flow ratio (VFR) and net power output per unit mass flow rate of exhaust (Pnet). Afterwards, the impact of molecular complexity on the indicators of VFR and SP is analyzed. Furthermore, the energy distribution of engine exhaust gases and the improvement of fuel economy, after integrating the bottoming ORC with diesel engine, are also discussed. Finally, the performance comparison between Cyclohexane-based ORCandsteam cycle with relative pressure is carriedout. The results show that optimized working fluids are not always constant subject to different indicators and operation parameters. However, cyclic Alkanes, Cyclohexane and Cyclopentane are considered as the most suitable working fluids when taking into account of all comprehensive indicators. The maximum improvement of 10% in brake specific fuel consumption (BSFC) is obtained for DE-ORC combined systems with Cyclohexane used as working fluid. In addition, although steamhasmoreadvantagesin thermal efficiency in the current conditions, from a technical and economic point of view, Alkane-based ORCs may be more attractive than conventional steam cycles, specifically for DE waste gas heat recovery.