Parametric and working fluid analysis of a dual-loop organic Rankine cycle (DORC) used in engine waste heat recovery

A novel dual-loop organic Rankine cycle (DORC) is proposed in this study, which consists a high-temperature (HT) loop and a low-temperature (LT) loop to recover the waste heat of the exhaust, engine coolant and residual heat of the HT loop. Net output power, utilization rate of engine coolant, DORC thermal efficiency and exergy efficiency are chosen as the objective functions. R124, R134a, R245fa, R600, R600a and R1234yf are chosen as the candidate working fluids of the LT loop. Based on engine data and pre-set model parameters, energy and exergy analysis are conducted. Results show that maximum net output power, utilization rate of the engine coolant and exergy efficiency are obtained with R1234yf at Tevp,HT = 570 K and Tevp,LT = 343 K and corresponding values are 36.77 kW, 96.8% and 55.05%. The top two ηth are obtained with R600 and R245fa at Tevp,HT = 570 K and Tevp,LT = 365 K and corresponding values are 20.07% and 20.06%. Furthermore, based on the R1234yf-based system operating at Tevp,HT = 570 K and Tevp,LT = 343 K, the maximum irreversibility occurs in turbine and exergy efficiency of evaporator E3,LT is worst, which are the optimization objectives for the improvement of system exergy performance. In addition, based on Pnet, ηth and ηe, for all working fluids, system performs better at high operating load. R1234yf is found to be a better working fluid for high operating load. R124 possesses the worst performance under all operating loads.