| Organic Rankine Cycle (ORC) is an effective approach to recover low grade wasteheat and has been widely used in many fields. In the field of vehicle engine, the wasteheat in the engine exhaust could be recovered when the vehicle engine is combinedwith a set of ORC system. In this study, the performance of ORC system wasanalyzed using different working fluids and cycle configurations in order to find outthe optimal working fluid and cycle configuration. Then, the ORC system usingoptimal working fluid and cycle configuration was examined under various operatingconditions of the vehicle engine. Finally, a test bench was built up and somepreliminary experiments were conducted. The main contents are as follows:1. The type of working fluid has a very significant impact on the performance ofORC system. On the basis of meeting requirements of the environmental performance,five pure organic fluids, R245fa, isopentane, R123, R236ea and butane, were selectedas alternative working fluids for ORC system. The variation of the parameters of ORCsystem such as thermal efficiency, exergy efficiency, mass flow rate of working fluidand evaporating pressure with the change of condensing temperature and expansionratio was studied. According to the performance of each pure organic fluid, R245faand isopentane were chosen as working fluid components to make up zeotropicmixtures in the mass fraction of0.9:0.1,0.7:0.3,0.5:0.5,0.3:0.7and0.1:0.9. Usingthese zeotropic mixtures, the impact of the changes in mass fraction of working fluidcomponent on the performance of ORC system was studied. Finally, considering theenvironmental performance and thermal properties of the working fluid, the zeotropicmixture of R245fa and isopentane in a0.44:0.56mass fraction was the optimalworking fluid for ORC system.2. According to the first and second law of thermodynamics, calculating models forthree different cycle configurations (basic ORC, regenerative ORC and reheat ORC)were established. The zeotropic mixture of R245fa and isopentane in a0.44:0.56massfraction (marked as isopentane/R245fa) was selected as working fluid. The influenceof intermediate pressure on the performance of regenerative ORC system and reheatORC system was analyzed. By comparing the thermodynamic parameters, thermalefficiency, exergy efficiency, exergy destruction rate, of three type ORC systemsunder different evaporating pressures and superheating degrees, the regenerative ORCis considered as the optimal organic Rankine cycle configuration. 3. A regenerative ORC (RORC) system was designed aiming at recovering theexhaust heat of a diesel engine, and the influence of the intermediate pressure onperformance parameters such as net power output, thermal efficiency and mass flowrate of the working fluid was analyzed. The organic working fluids underinvestigation were R245fa and the zeotropic mixture isopentane/R245fa. Based oncalculating results, the intermediate pressure was set to1.15MPa for the regenerativeORC system when using isopentane/R245fa as the working fluid, and1.2MPa whenusing R245fa as the working fluid. A performance analysis of the RORC system usingthe two different working fluids was then conducted under various operatingconditions of the diesel engine.4. The appropriate components for vehicle diesel engine and the correspondingmeasurement and control system were selected, as well as for the ORC system and thecorresponding data acquisition system. Then a test bench of ORC system for vehiclediesel engine was built up. With this test bench,15operating points of the dieselengine were selected to examine the performance of the ORC system. Results showedthat the expansion ratio of the expander in ORC system is between1.5and2, and themaximum power output is only0.28kW, which is far below the theoretical value. |
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