Performance analysis of a dual-loop bottoming organic Rankine cycle (ORC) for waste heat recovery of a heavy-duty diesel engine, Part I: Thermodynamic analysis

Abstract

In this paper, which is the part 1 of this study, the energy and exergy characteristics of a dual-loop organic Rankine cycle (ORC) combining with a heavy-duty diesel engine were investigated. The proposed cycle is driven by the waste heat of the exhaust gases, intake air, and the coolant. Central composite design (CCD), which is a standard response surface methodology (RSM) technique, was applied to design of experiments (DoE) and to investigate the influence of both the engine and cyclic parameters such as the engine speed, the start of injection (SOI), the higher pressure of the high-temperature loop, and the higher pressure of the low-temperature loop. Adequacy of the developed RSM models has been evaluated by the ANOVA tables. The results revealed an increase in whether the engine or cycle parameters led to an enhance in the produced power of the system. As a comparison, the variation in engine variables has more impact on the produced power. On the opposite side, a change in the engine speed and SOI have a minor effect on the thermal efficiency of the system. The maximum produced power of the dual-loop ORC system was identified as 310 kW, which was resulted at the engine speed of 1800 RPM, and 0.0 degrees of CA bTDC for SOI; while the higher pressures of the HT and LT loops were in 2400 and 2100 kPa, respectively. This obtained power is 31% of the engine brake power. The maximum values for the thermal and exergy efficiencies were observed as 9.5% and 43%, respectively. Also, the exergy analysis demonstrated that the highest exergy destruction rate of the system is determined to be 500 kW.