Studies On Performance Characteristics And Structure Optimization Method Of Engine Exhaust-based Thermoelectric Generator System

70% of the energy of automobile engine emits into the surrounding environment as heat,which is often wasted.The potential of engine waste heat recovery is enormous,which may significantly reduce the fuel consumption,improve the total efficiency and reduce harmful substances in emissions.Thermoelectric generator(TEG)is a kind of old and new environmental protection technology,which utilizes the characteristic of thermoelectric materials directly by converting the waste heat into electrical energy,with small size,light weight,long working life,no noise,no need to maintain and so on.TEG therefore has broad application potential in vehicle engine.Through the experimental study on TEG,working principle of TEG is investigated.Based on the experimental data,a simple one-dimensional model and three-dimensional numerical model are established.Through simulation,the deep working mechanism is explored.The internal heat transfer process of thermoelectric generator and the characteristics of the material are studied.In the case of the low efficiency of thermoelectric conversion for single thermoelectric material,based on the experimental study and simple numerical simulation,this paper proposes the integrated design method of the segmented TEG unit based on the length ratio.In addition,the influence of the structure of the exhaust channel and cooling channel on the performance of exhuast TEG(TEG)system is studied by establishing the numerical simulation model of a six cylinder turbocharged diesel engine with ETEG system.The coupled numerical simulation of the exhaust passage,cooling passage and ETEG system is carried out.The structure design of the exhaust channel and the cooling channel is studied,with optimal design of cooling channel structure to two kinds of cooling methods,air cooling and water cooling.The main contents of this paper are as follows.(1)Through setting up the experimental system of the basic performance of TEG,the influences of cooling mode,heat sink temperature,heat source temperature,load resistance,current and other factors on the performance of TEG are studied.Experimental data for the further model validation are also provided.(2)A one-dimensional model is developed,which has the characteristics of simple structure,good flexibility,small calculation amount and high calculation efficiency.Based on the different conservation equations and boundary conditions,a 3D TEG model is created,and the simulation is carried out.And the experimental results are verified to understand the geometric structure,exhaust characteristics and different boundary conditions,different models and other factors on the performance of TEG.(3)At present,the main problem of TEG is the low conversion efficiency,which limits the wide application of thermoelectric generator.There is a huge temperature difference between the hot and cold side of the waste heat recovery of the engine.Almost no material will be effective in such a large temperature range.The TEG design of the segmented design is an effective way to solve this problem.In this paper,the optimal temperature range of two kinds of thermoelectric materials is determined by the power factor and efficiency factor.In view of the different design requirements and working conditions,the integrated design method of TEG unit is proposed.The method can be used as an effective tool for the rapid and accurate design of different thermoelectric materials.(4)The temperature distribution of the exhaust channel determines the hot end temperature of ETEG system,and the temperature difference between the hot and cold ends directly determines the performance of TEG.In this paper,the influences of the geometrical structure parameters of the exhaust channel,such as the size of the exhaust channel,the number of exhaust channel,the number of bafflers,the angle of baffles are studied to investigate the heat distribution,the thermoelectric conversion and the the performance of ETEG system.Based on the results of numerical calculation and analysis,the optimal design of the exhaust channel of ETEG system is proposed in detail.(5)The temperature distribution of the cooling channel determines the cold end temperature of ETEG system,and the cold end temperature directly determines the temperature difference between the cold and hot ends,and then affects the performance of TEG.In this paper,the cooling effect of air cooling and cooling liquid cooling is studied,and the influences of different cooling methods on the ETEG system,such as flow arrangement,inlet flow rate,the number of bafflers,the installation position of the bafflers,and the installation angle of the baffler,are studied.Based on the results of numerical calculation and analysis,the optimization design of cooling channel of ETEG system is proposed in detail.