Parametric analysis of a dual-loop ORC system for waste heat recovery of a diesel engine

The maximum potential of a dual-loop organic Rankine cycle (ORC) applied to a light-duty diesel engine is analyzed over the engine's operational range by developing a mathematical model based on physical processes and boundary conditions specified according to measured data from an engine test. We further evaluate the effects of three working parameters - expander isentropic efficiency, evaporation pressure of the high-temperature loop, and condensation temperature of the low-temperature loop - on the performance of the dual-loop ORC system. The results show that using the proposed dual-loop ORC system improves the net power output of a diesel automotive engine by 19-22% in the peak thermal-efficiency region under allowable working conditions of the engine, and by 53-72% in the high-speed and low-load regions. Over the engine's entire operational range, the effective thermal efficiency increases by a maximum of 8%. Moreover, the expander isentropic efficiency and the condensation temperature of the low-temperature loop are two critical parameters that affect combined system performance.