| Based on the energy balance of engine,about one third of the fuel combustion energy is released into the air in the form of waste heat in exhaust gas.This not only wastes a large amount of petroleum resources,but also causes serious environmental pollution.Therefore,recovering the waste heat from internal combustion engine is an effective method for reducing pollutant emission and saving fuel.In order to achieve the purpose of improving thermal efficiency of internal combustion engine,organic Rankine cycle(ORC)is used to recover the waste heat in exhaust gas.According to theoretical calculation,numerical simulation and experimental research,the performance of exhaust waste heat recovery system for stationary engine under engine various operating conditions were studied.In addition,the integrated simulation model of vehicle engine-ORC combined system(combined system)was built,and then the running mode and control strategy of combined system were analyzed.Subsequently,the operating performances of combined system were optimized based on genetic algorithm.Finally,the test rig of key components in ORC system was built,and the preliminary experiments were conducted.According to the exhaust waste heat characteristics of stationary engine,the operating performances of stationary engine-ORC with internal heat exchanger(IHE)combined system and stationary engine-ORC combined system were analyzed,respectively.The results showed that,when evaporation pressure is 3MPa,the thermal efficiency of stationary engine-ORC with IHE combined system is higher than that of stationary engine by 5.0%.When evaporation pressure is 2.9MPa,the thermal efficiency of stationary engine-ORC combined system is higher than that of stationary engine by 5.0%.In addition,the component amount of ORC system is less than other structural schemes.Therefore,the ORC system has a larger advantage in the vehicle engine waste heat recovery.This lays the foundation of theoretical calculation and numerical simulation for vehicle engine waste heat recovery system.The simulation models of vehicle engine and ORC system were built by using GT-Suite software.The Effects of evaporation pressure,condensation pressure,pressure loss,pinch point temperature difference and working fluid mass flow rate on the performance of ORC system were analyzed.The results showed that,the effect of pressure loss in condenser on the power output of expander is larger than that of in evaporator.With the increase of evaporation pressure and working fluid mass flow rate,the maximum variation of pinch point temperature difference is 24.8K.According to the analysis results,the integrated simulation model of combined system was built.For the integrated simulation model of combined system,a discriminant method of running mode for combined system was proposed.Subsequently,the running mode was determined according to the analysis results of design of experiment(DOE).In the operating conditions of combined system,the variation tendency of optimum operating parameters was obtained by using model-based virtual calibration method.The results showed that,the optimal pump speed is about 1000r/min under the low load region of engine.When the engine speed is higher than 1800r/min,the optimal pump speed increses with engine load.While the optimum expander speed is 1500r/min under various operating conditions of engine.In addition,the dual open-loop control and single close-loop control model was set up by using GT-Suite and Matlab/simulink software.Based on the integrated simulation model of combined system,the operating parameters of combinded system were optimized by using genetic algorithm.The power output of combined system was used as the objective function.The injection timing,pump speed and expander speed under various operating conditions were optimized.The results showed that,the optimal running parameters vary with the vehicle engine operating conditions.At the engine rated condition,the themal efficiency of combined system is higher than that of vehicle engine by 3.89%,brake specific fuel consumption(BSFC)of combined system decreases by 10.09g/(kW·h).For the key components of ORC system,the air test rig of the FPE-LG integrated system and test rig of multistage centrifugal pump were built,respectively.Subsequently,the preliminary experiments were conducted.This research is helpful to improve the test rig and validate the simulation model of vehicle engine-ORC combined system. |
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