Experimental investigations on a cascaded steam-/organic-Rankine-cycle (RC/ORC) system for waste heat recovery (WHR) from diesel engine

•A novel cascaded RC/ORC system was constructed for WHR of a heavy-duty diesel engine.•The RC/ORC system was experimentally investigated under engine operating conditions.•Good system stability and satisfying thermal states of working fluids were observed.•The power increment can reach up to 5.6% by equipping the novel cascaded RC/ORC system. A novel cascaded RC/ORC system that comprises a steam Rankine cycle as the high-temperature loop (H-RC) and an organic Rankine cycle as the low-temperature loop (L-ORC) was constructed and experimentally investigated to recover waste heat from exhaust gas of a heavy-duty diesel engine (DE). By monitoring key parameters of the RC/ORC system against time, good system stability and satisfying thermal states of working fluids were observed. Impacts that the engine operations have on this proposed waste-heat-recovery (WHR) system were studied, indicating that waste heat recovered from the gas increases gradually and greatly as the engine load increases, yet decreases slightly as the speed grows. At full loads at speeds lower than 2050rpm, up to 101.5kW of waste heat can be abstracted from the gas source, showing a promising heat transfer potential. Besides, observations of key exergy states as well as estimations and comparisons of potential output power were carried out stepwise. Results indicated that up to 12.7kW of output power could be obtained by the novel RC/ORC system under practical estimations. Comparing to the basic diesel engine, the power increment reaches up to 5.6% by equipping the cascaded RC/ORC system.