Experimental And Modeling Studies Of Thermoelectric Generator For Enigne Exhuast Heat Recovery

Recovering waste heat from engine exhaust provides an attractive opportunity to improve engine power output and reduce fuel consumption and emissions. Thermoelectric generator(TEG) represents a promising technology that can utilize such waste heat. The main advantages of TEG include direct conversion from thermal to electrical energy, high reliability, low maintenance cost, and no moving part that can cause noise and vibration.Experimental and modeling studies are carried out to investigate the TEG operating characteristics for engine exhaust heat recovery. This study begins at the investigation of single thermoelectric(TE) units and then multi-element modules. After that, a transient TEG model coupled with a vehicle model are developed and validated by experimental results. The TEG performance under different dynamic vehicle operating conditions is analyzed. The work can be summarized as follows:(1) Two three-dimensional numerical models are developed for TEGs based on different formulations and boundary conditions, but with similar abilities for heat and electricity transfer analysis and performance prediction. Based on the models developed, the thermal and electrical conversion processes are studied, and the TE leg shape is optimized to increase the power output. The temperature and electrical distributions of TE leg under various operating conditions are also revealed.(2) The effects of cooling methods, hot and cold source temperatures, clamping force, compound mode and load resistance on the multi-element TEG performance are investigated experimentally. The emphasis is the TEG transient behavior, the overshoot phenomenon is observed during the TEG start-up processes, and this phenomenon is caused by the different rate of temperature variation between hot and cold sides of TEG. The experimental results provide proper validation of the numerical TEG models.(3) A transient model of TEG based on engine exhaust waste heat recovery is developed. The start-up modes include constant current, constant voltage, constant power and maximum power modes, and the differences among these modes are analyzed. The heat flow during a start-up process caused by thermoelectric effects including Peltier effect, Joule heat and Thomson heat is investigated in details. In addition, the effect of vehicle speed and ambient temperature on TEG performance is investigated.(4) This transient TEG model is coupled with a vehicle model, and the TEG system behavior is investigated for constant and dynamic driving conditions, such as constant speed, acceleration and deceleration, step-changed conditions. The performance also is compared among three typical driving cycles: Japanese 10-15 cycle, New European Driving Cycle(NEDC) and Urban Driving Dynamometer Schedule(UDDS) cycles. The effect of TEG on the increment of power output during the different driving conditions is estimated as well.(5) The exhaust heat recovery on engine with TEG is conducted experimentally. The heat source is the exhaust gas out of a 1.5 L gasoline engine, and the cold source is constant temperature water tank. The steady-state performance and transient behavior of TEG modules under different engine conditions are investigated. The experimental results provide the validation of the numerical model of TEG based on engine exhaust heat recovery.