PERFORMANCE ANALYSIS OF ORC SYSTEM WITH IHE USING THE ZEOTROPIC MIXTURE AND THE PURE WORKING FLUID FOR VEHICLE CNG ENGINE

asme-orc2015 Tracking Number 37

The thermal efficiency of most compressed natural gas (CNG) engines is about 30%, large amount fuel energy is rejected from CNG engines to the surroundings as waste heat, with a significant fraction through the exhaust [1]. Therefore, recovering the exhaust waste heat from CNG engines so as to improve thermal efficiency and save fuel has become a hot focus of recent research work. The organic Rankine cycle (ORC) is an effective method to recover waste heat from exhaust waste heat of internal combustion engines (ICE)[2]. For the working fluids of ORC system, the match of organic working fluids with heat source and systems significantly affects system performance. In this paper we analyze the exhaust characteristics from a six-cylinder CNG engine over its whole operating range by engine experiments, and a set of ORC system with internal heat exchanger (IHE) is designed to recover exhaust waste heat from the CNG engine. The organic working fluids under investigation are the pure working fluid R245fa and the zeotropic mixture R416A. Subsequently, the influence of the two different working fluids on performance parameters such as net power output, thermal efficiency, exergy efficiency and output energy density of working fluid are analyzed. The results show that R416A performs better. Finally, a combined CNG engine and ORC system with IHE is defined to evaluate the performance improvement. Results show that, Compared with the CNG engine, the thermal efficiency of the combined system can be increased by a maximum 7%.