Performance Study On Free Piston Linear Generator In ORC Waste Heat Recovery System For Vehicle Internal Combustion Engine

From the point of energy balance,the thermal efficiency of internal combustion engine is very low(about 20%-45%),and most of the thermal energy is taken away by the exhaust system et al.Therefore,improving the total energy conversion efficiency and reducing the fuel consumption by effectively utilizing the exhaust waste heat energy of ICEs are crucial.For the ORC waste heat recovery system used for internal combustion engine,there is no suitable expansion machine can be used as the best choice.This article puts forward a novel free piston linear generator(FPLG),and according to experimental research,theoretical analysis,and numerical simulation,the performance of FPLG is studied.First,based on FPLG test rig using CAM valve mechanism and solenoid valve mechanism,the the influences of different factors on FPLG performance are studied.Then,based on the test data,the performance prediction and optimization model of FPLG is established and the sensitivity of the factors influencing the FPLG using orthogonal experimental design is studied.The FPLG simulisation model is established,and the performance has been performed from operation parameters,model parameters and linear generator matching.ORC-FPLG combined system has been established,which is achieving the coplling of ORC waste heat recovery system with dynamic model of the vehicle,vehicle engine and FPLG model,and modular combination based on FPLG has been proposed.Based on FPLG test rig using CAM valve mechanism,the key factors influencing the FPLG performance have been exploered and the influencing mechanism has been revealed.Piston assembly displacement and velocity decreases with increasing the operation frequency,wheraes increase with the intake pressure.When the load resistance insresases,piston assembly displacement,velocity and actual stroke show gradualy increasing trend.In addition,there exist an optimal load resistance which achieving the maximum peak power output.The energy conversion efficiency first increase and then decrease with the intake pressure and load resistance.When operation frequency is 1.5 Hz,intake pressure 0.26 MPa and load resistance is 40?,the maximum energy conversion efficiency is 73.33%.Moreover,the reasonable design and matching of valve-train and high inlet pressure are bebefit to improving cycle-to-cycle variation and stability of the FPLG.FPLG test rig using solenoid valve mechanism has been established,and the control strategies based displacement and time have been proposed.On the basis of stable operation,the operation characteristics and output characteristics with different control strategies have been investigated.When FPLG operates with displacement control strategy,the actual stroke increases with theoretical stroke,load resistance and advanced exhaust time.And the operation frequency shows an increasing trend with increasing the intake pressure and load resistance,whereas decreases with the intake/exhaust time and advanced exhaust time.However,the operation frequency is only related with the intake/exhaust time and advanced exhaust time.The average power output shows a decreasing trend with coefficient of equilibrium oscillation.The smaller the coefficient of equilibrium oscillation is,the higher the average power output is.Prediction and optimization model based on machine learning has been established.Then,combined with the artificial neural network and genetic algorithm,the key parameters of FPLG is optimized.The experiment condition has been optimized using orthogonal experimental design(OED).The model optimized with Particle Swarm Optimization(PSO)has smaller error and higher prediction accuracy.The optimized results using OED is almost in accordance with that using machine learning,which indicates the accuracy of the perdection and optimization model.The maximum peak voltage output,average power output,operation frequency and energy conversion efficiency are 51.2 V,27.57 W,4.51 Hz and 21%,respectively.The corresponding optimal schemes are A₅B₅C₄D₄,A₅C₁B₄D₂,A₅C₁B₅D₂and A₅D₁B₁C₁?The intake pressure has significant influence on the various indicators.The FPLG simulation model is built by using GT-Suite and MATLAB/simulink softwares.Then,based on the simulation model,the effect of operation parameters and model parameters on the FPLG performance has been investageted.The relative errors are within±10%,indicating the high evidence of simulation model.The piston assembly displacement,velocity,voltage output and power output show increasing trend with the intake pressure and intake temperature.The displacement,mass flow rate,the pressure difference and power output decrease with the operation frequency.And there exists an optimal friction coefficient which achieving the maximum displacement,mass flow rate,the pressure difference and power output.The piston assembly velocity increases with increasing the flux linkage,but the electromagnetic force and the power output increase gradually.Based the FPLG model,the ORC-FPLG combined system simulation model has been established.The influences of operation parameters are studied.From the perspective of multi module combination,the operation characteristic of ORC-FPLG combined system under serial mode and series mode.The net power output increases when the operation frequency,exhaust temperature,exhaust flow rate and coolant flow rate increase,whereas it decreases with internal/external resistance and condensation temperature.The thermal efficiency and waste heat recovery efficiency increase with the operation frequency and coolant flow rate increasing,there exists an optimal pipe diameter which achieving the maximum thermal efficiency and waste heat recovery efficiency.When operation frequency is 18 Hz,the maximum net power outputand waste heat recovery efficiency is 2.51 k W and 1.36%,respectively.Furthermore,when the ORC-FPLG system is coupled to the vechicle,the power output and thermal efficiency of engine-ORC-FPLG has great improvement.When operates with parallel mode,the power output and thermal efficiency show first increasing and then decreasing trend with increasing the module number,namely there exists an optimal module number which achieving the maximum net power output and thermal efficiency.When operates with series mode,the power output and thermal efficiency increase gradually with the module number.The more the module number is,the higher the net power output and thermal efficiency are.When operation frequency is 16 Hz,module number is 4,the maximum net power output and waste heat recovery efficiency can be reached 11.92 kW and 7.73%.