a b s t r a c tOrganic Rankine Cycle (ORC) could be used to recover low-grade waste heat. When a vehicle is running, the engine exhaust gas states have a wide range of variance. Defining the operational conditions of the ORC that achieve the maximum utilization of waste heat is important. In this paper the performance of different working fluids operating in specific regions was analyzed using a thermodynamic model built in Matlab together with REFPROP. Nine different pure organic working fluids were selected according to their physical and chemical properties. The results were compared in the regions when net power outputs were fixed at 10 kW. Safety levels and environmental impacts were also evaluated. The outcomes indicate that R11, R141b, R113 and R123 manifest slightly higher thermodynamic performances than the others; however, R245fa and R245ca are the most environment-friendly working fluids for engine waste heat-recovery applications. The optimal control principle of ORC under the transient process is discussed based on the analytical results.

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a b s t r a c tAn organic Rankine cycle (ORC) can be used to harness the wasted heat from an internal combustion engine. In this paper, the characteristics of a novel system combining a gasoline engine with a dual loop ORC which recovers the waste heat from both the exhaust and coolant systems is analyzed. A high temperature loop recovers the exhaust heat while a low temperature loop recovers both the residual high temperature loop heat and the coolant heat. The performance map of a gasoline engine is measured on an engine test bench and the heat quantities wasted by the exhaust and coolant systems are calculated and compared within the engine's entire operating region. Based on this data, the working parameters of a dual loop ORC are defined, and the performance of a combined engine-ORC system is evaluated across this entire region. The results show that the net power of the low temperature loop is higher than that of the high temperature loop, and the relative output power improves by from 14 to 16% in the peak effective thermal efficiency region to 50% in the small load region, and the absolute effective thermal efficiency increases by 3e6% throughout the engine's operating region.

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