| Large amount petroleum resources are consumed by vehicle engine which has caused serious environmental pollution. How to improve the fuel economy has become a hot focus of recent research work. Based on the energy balance of vehicle engine, a considerable proportion of the fuel combustion energy is released into the air in the form of waste heat in exhaust gas and coolant. Therefore, recovering the waste heat from internal combustion engine is an effective method for the improvement of thermal efficiency, reducing pollutant emission, and saving fuel. In this paper, organic Rankine cycle(ORC) system was used to recover the waste heat from engine exhaust by producing useful work that can be converted to mechanical energy. According to theoretical calculation, numerical simulation and experimental research, the operating characteristics of ORC system with different configurations under engine various operating conditions were studied. In addition, the effects of refrigerant mixture and running parameters on operating performances of vehicle engine-ORC combined system(combined system) were investigated, and then the operating performance variation of engine equipped with ORC system were analyzed. The application condition and the operating performance of ORC system based on single screw expander were discussed. Subsequently, the particle swarm optimization method was adopted for multi-objective and multi-parameter optimization of the combined system. Finally, the test bench of combined system was improved, and the preliminary experiment was conducted.Based on the theoretical calculation, the operating performances of vehicle engine-simple ORC combined system and vehicle engine-ORC with IHE combined system under various operating conditions were analyzed, respectively. Subsequently, the operating performances of simple ORC system, ORC system with IHE and dual loop ORC system under a certain operating condition of vehicle engine were studied by using Aspen Plus software. The results showed that, for a selected vehicle engine with rated power of 280 k W, the net power output of simple ORC system, ORC system with IHE and dual loop ORC system can reach up to 30.76 k W, 36.90 k W and 43.70 k W, respectively. Although the dual loop ORC system has maximum net power output, its thermal efficiency is some lower and configuration is more complicated. So, the ORC system with IHE is more suitable for vehicle engine. Furthermore, the simple ORC system was designed for experimental research due to the installation space in our lab.Based on the theoretical calculation, the operating performances of the ORC system with pure working fluid, azeotropic mixture and zeotropic mixture were studied. Effects of zeotropic mixture on the operating performances of vehicle engine-simple ORC combined system and vehicle engine-ORC with IHE combined system were emphatically studied. The results showed that, for a selected vehicle engine with rated power of 280 k W, the operating performances of combined system with zeotropic mixture R416 A are optimal. The maximum net power output, thermal efficiency, exergy efficiency and waste heat recovery efficiency can reach up to 34.38 k W, 12.63%, 38.23% and 11.74% respectively.Based on simple ORC system and ORC system with IHE, the particle swarm optimization method was adopted for multi-objective and multi-parameter optimization of the combined system. The net power output and exergy efficiency of ORC system were used as the objective function, the evaporating pressure, degree of superheat and expansion ratio under various operating conditions were optimized. The results showed that, the optimal running parameters are different with the engine operating conditions and the ORC system configurations.According to the experimental research, the working performance of a selected single screw expander was analyzed. Based on the working performances of the engine and the single screw expander under various operating conditions, the operating performances of vehicle engine-ORC combined system were studied, and then the application condition of the ORC system was investigated. The results showed that, the waste heat energy between 100 k W and 750 k W can be recovered by using the ORC system with above mentioned single screw expander. For a selected vehicle engine with rated power of 280 k W, the maximum power output of vehicle engine-ORC combined system is 310.6k W. Compared with the engine itself, the maximum power output can be increased by 10.92%.Numerical simulation work was carried out. The vehicle engine was modeled by using GT-Power software, and then the operating performances of engine were analyzed. Meanwhile, the simulation model of evaporator was built by using Fluent software to study the flow and heat transfer processes of engine exhaust in the evaporator. Effects of back pressure caused by evaporator on the operating performances of engine were analyzed. The results showed that, by employing the ORC system, the evaporator has some influence on the operating performance of vehicle engine.The test bench for vehicle engine-ORC combined system was established. Then, the cooling system, pump and evaporator of ORC system were improved, and the preliminary experiments were carried out. The experimental results showed that, condensing temperature and pressure, evaporating temperature and mass flow rate of ORC system can be improved obviously. |
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