Numerical Simulation Study On Diesel Exhaust Heat Recovery Based On Thermoelectric Power Generation

In order to avoid excessive waste of energy,it is very important to recovery low grade energy,which including industrial waste heat and automobile exhaust waste heat.TEG(Thermoelectric power generation)is a simple and non-pollution technology for recycling waste heat,which can be used to convert waste heat directly into electric energy.In this paper,the thermoelectric properties and influence factors of TEG are studied and analyzed by using finite element analysis method.The influence of the series and parallel connection modes of the TEG model on the output performance of the TEG model is explored.The diesel engine exhaust heat recovery system is optimized and the multi physical field coupling analysis of diesel engine exhaust heat recovery system is carried out.The specific contents are as follows:(1)The effects of the pairs of P/N junction,temperature,semiconductor height and material properties on TEG models were studied.The control variable method is used to change an influence factor and study its influence on the open circuit voltage,short circuit current,output power and efficiency of the TEG model.The output performance of TEG models increase with the increase of the pairs of P/N junction and the temperature difference.With the increase of the height of semiconductor,the output power decreases and the conversion efficiency increases.Output performance of TEG models enhance with the increase of Seebeck coefficient and the decrease of resistivity and thermal conductivity of the semiconductor.And thermal conductivity has great influence on efficiency.(2)The characteristics of series and parallel connection of different TEG models are studied,and the influence of different connection modes on output performance of TEG model is analyzed.Three kinds of TEG models are connected in series and parallel,and the characteristics of series and parallel connection from the same TEG model and different TEG models are studied.A larger voltage can be obtained by a series connection mode,and a larger current can be obtained by a parallel connection mode.The maximum output power and efficiency of the two same TEG models connected in series are equal to that of this two same TEG models connected in parallel,and the maximum output power is twice as much single model.The maximum output power and efficiency of different TEG models connected in series are larger than that of connected in parallel.(3)The multi field coupling simulation analysis of diesel engine exhaust heat recovery is carried out.The output performance of TTEGS(Three TEG models connected in series)at different locations on HEMs(Heat exchanger model)is analyzed.The influence of different structural HEM and engine conditions on waste heat recovery system is compared and analyzed.The TTEGS has different output performance at different positions,mainly because the temperature of the hot side at different positions is inconsistent.Through the analysis of the internal flow and surface temperature,it is easy to find that HEM-2 has better heat transfer effect than HEM-1,and the temperature distribution on heat exchanger surface which coupled with TTEGS is more uniform.With the increase of engine load,the maximum output power and efficiency of TTEGS at each location are significantly increased.When the power of the diesel engine is 56.1 kW,the overall theoretical recovery power of the exhaust heat recovery system of diesel engine is up to 6.5 % compared with the actual output power of the diesel engine.