Parametric and Exergetic Analysis of Diesel Engine Bottoming with a Dual-loop Organic Rankine Cycle System

摘要

As the temperature diversities of various engine waste heat(exhaust and coolant)and large temperature gradient during recovering exhaust waste heat,a dual-loop ORC system,which contains the hot temperature cycle(HTC)loop and the low temperature cycle(LTC)loop,is proposed to recover the waste heat of the exhaust and the engine coolant and the residual waste heat of the HTC loop.In this paper,the detailed calculated subcritical cycle models based on the energy and exergy balance have been established.Keeping the water as the HTC's working fluid,the suitable 5 working fluids for the LTC loop have been recommended and analyzed on the various loads(75％,90％and100％)condition of one popular commercial diesel engine.The cycle parameters,including the thermal efficiency(ηth),the net power output(Pnet),the exergy efficiency(ηe)and the total thermal efficiency of DE-ORC combined systems(ηcc)have also been analyzed and optimized.The results show that the dual-loop ORC system can improve the global thermal efficiency at each engine load.Comparing to the considered working fluids,water-R123 system express a better performance.At 100％operating load,the maximum values of the net output power and the system efficiency of water-R123 system are 23.69kW,18.9％and improve engine efficiency from 41.8％to 45.8％.It is also found that the HTC loop has the bigger contribution to the system performance than LTC loop and its condenser and preheater have the top two irreversibilities.