| For the past few years,the hazy weather in most areas of China has seriously affected people's health and travel safety.As the major emitter of the air pollutants,the energy saving and emission reduction of the traditional vehicle internal combustion(IC)engine has more work to do.Based on the waste heat characteristics of the IC engine,the thermodynamic,heat transfer,economic and optimization models of simple organic Rankine cycle(ORC)and dual loop ORC are established to obtain the coordinated variation law of key operating parameters.An artificial neural network(ANN)model is developed for the purpose of predicting and optimizing the performance of the ORC waste heat recovery system.Compared with the traditional thermodynamic modeling method,the prediction accuracy has significantly improved.Aiming at solving the technical bottleneck of kilo watt class expander,a novel non internal combustion free piston expander-linear generator(FPE-LG)is proposed and optimized.According to the waste heat characteristics of the IC engine,the thermodynamic,heat transfer and optimization models of simple ORC and dual loop ORC are established,respectively.The effects of key operating parameters on the thermodynamic and heat transfer performances are investigated.Aiming at improving the thermodynamic and heat transfer performances,the key operating parameters of the ORC system are optimized using genetic algorithm.For the simple ORC,the optimal evaporation pressure,whose value is in the range of 1MPa to 2.97 MPa,increases with the increase of engine speed and load.The optimal condensation temperature is almost kept at 298.15 K.Under most operating conditions of the diesel engine,the optimal superheat degree is in the range of 0K to 1K.For the dual loop ORC,the optimal evaporation pressure of the high temperature(HT)cycle is above 2.2MPa.The optimal superheat degree of the HT cycle is mainly affected by the operating conditions of the IC engine.The optimal condensation temperature of the HT cycle,whose value is nearly kept around 350.15 K,has almost no change with the operating conditions.The optimal evaporation temperature of the low temperature(LT)cycle is in the range of 339 K to 343 K,and increases with decreasing the engine torque.The optimal condensation temperature of the LT cycle is almost kept at 298.15 K.The optimal exhaust temperature at the outlet of the evaporator is 423.15 K at most operating conditions.The thermodynamic,heat transfer,economic and optimization models of simple ORC and dual loop ORC are established.The effects of key operating parameters and working fluids on the thermoeconomic performance of these two kinds of ORC configurations are investigated under various operating conditions of the IC engine.The Pareto optimal solutions of thermodynamic and economic performances for these two kinds of ORC configurations are obtained using genetic algorithm,and then the corresponding optimal operating parameters are determined.The thermodynamic performance of the ORC is improved at the expense of economic performance.A higher evaporation pressure is beneficial to improving the thermodynamic and economic performances of the ORC.The superheat degree has almost no effect on the thermoeconomic performances while the thermoeconomic performances worsen with increasing the condensation temperature and exhaust temperature at the outlet of evaporator.For two subsystems of the dual loop ORC,a higher evaporation pressure and a lower condensation temperature exhibit a positive effect on the thermodynamic performances,while the effects of variation in superheat degree and exhaust temperature at the outlet of evaporator on the thermoeconomic performances are not obvious.According to the dynamic operation characteristic of a test bench of combined diesel engine and ORC waste heat recovery system,an artificial neural network(ANN)prediction model is established for parameters influence analysis of the ORC.Combined with the ANN model and genetic algorithm,the key parameters of the ORC is optimized for maximizing the expander power output and manimizing the exhaust outlet temperature of the diesel engine.The proposed ANN model performs high prediction accuracy,which can be used to predict and optimize the combined diesel engine and ORC waste heat recovery system.The absolute value of relative error for both training data and test data is lower than 5%.The expander power output can reach up to 7.68 kW based on the optimization results of the ANN model.The optimization results are preferred to have a large pressure difference between the inlet and outlet of the expander,rather than a higher superheat degree at the inlet of the expander.Similar to the optimization results of the thermodynamic model,a lower condenser outlet temperature is beneficial to decrease the back pressure of the expander and increase the power output.In addition,the expander power output increases with increasing the working fluid flow rate under the condition of enough heat transfer.Based on the novel FPE-LG prototype,the effects of intake pressure,operation frequency and external load resistance on the motion charactetistics of the FPE-LG is investigated using compressed air as driven working fluid.The displacement and velocity of the free piston assembly increase with increasing the intake pressure.The peak voltage and power output show same variation tendency.The displacement and velocity of the free piston assembly decrease with increasing the operation frequency.The peal voltage and power output increase at first,then decrease with the increase of operation frequency.The external load resistance has almost no effect on the displacement of the free piston assembly,while the velocity of the free piston assembly shows a slight increase with increasing the external load resistance.In addition,an ANN model is also established to predict and optimize the performance of the FPE-LG.Based on the optimization results,the maximum power output of the FPE-LG can reach up to 100.47 W. |
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