Alkanes based two-stage expansion with interheating Organic Rankine cycle for multi-waste heat recovery of truck diesel engine

The environment issue combined with the rising of crude oil price has attracted more attention in waste heat recovery of diesel engine. The Organic Rankine cycle (ORC) offers a good solution to utilize multi-grade waste heats of diesel engine. Conventional multi-source ORC systems are too complex for vehicle application. This paper proposed a two-stage expansion with interheating organic Rankine cycle (ORC) system using alkanes as working fluids, in order to recover multi-waste heats (exhaust gas, EGR gas and engine coolant) with simple system configuration and solve the problem of overlarge expansion ratio of alkanes. Thermodynamic models based on first and second thermodynamic law are established. A correlation was proposed to estimate the optimum intermediate pressure to achieve maximum net power output. System performance comparison among alkanes shows that cyclic alkanes are superior to linear alkanes regarding net power output, thermal efficiency and exergy losses although they are weaker in recovering heat from engine coolant. Compared with the conventional preheating-regenerative ORC system, the proposed system can recover waste heat of exhaust gas (100%) and EGR gas (71.8%) more efficiently and generate 6.7% more output power, and it is more compact in terms of heat exchangers size, pump volumes and turbine structure.