Thermoelectric Generation For Automobile Exhaust Heat Recovery

With the rapid economic development, the number of cars in China increased with a rate of 11 million per year. However, at present, for the gasoline vehicles, only about 25 percent of the fuel combustion can be utilized for vehicle operation, whereas more than 30 percent is discharged to the environment in the form of waste heat of exhaust gas. Thus, if this part energy can be recycled and reused, it would be very important to improve the vehicle efficiency as well as reduce the environment pollution. Thermoelectric generation is a solid-state energy converter which can convert the heat to the electricity directly, and it has some advantages of stable, no noise, long life and so on. So it presents good potential applications in the automotive exhaust heat recovery.Aiming at the factors, Thomson effect and additional thermal resistance which caused by the ceramic plate, the metal interconnects and thermal contact resistance, that influence on the performance of thermoelectric module, in this paper, by the means of the numeric simulation, the performance of thermoelectric module which considering and not considering the Thomson effect and additional thermal resistance were compared. The results show that, when the working current of thermoelectric module is big, considering the Thomson effect and additional thermal resistance, the output power, the thermoelectric conversion efficiency and the exergy efficiency decrease significantly. As the increment of the hot side temperature of thermoelectric module, the output power difference between considering and not considering the Thomson effect and additional thermal resistance improve, the thermoelectric conversion efficiency difference increase first and then decrease while the exergy efficiency difference decrease.In addition, one of the main methods to improve the performance of thermoelectric generator is strengthening the heat exchange in the hot side. Aiming at the problem that the pressure drop of the exhaust gas increased when strengthen the heat exchange in the hot side, by the means of numeric simulation, this paper incorporating net output power, which result by the total output power minus the pumping power that is used to maintain the pressure drop of exhaust do not increase, as the main comparative parameter, investigated the performance of thermoelectric generator when the exhaust heat exchanger using two types of heat transfer enhancement, the rectangular offset-strip fins and the metal foams, under the same exhaust heat exchanger exterior dimensions. The results show that, there are optimal values of the fin transverse spacing and the fin thickness maximize the net power output. When using the metal foam for exhaust heat transfer enhancement, for the same metal foam material, the lower the porosity and the smaller the pore density, the bigger the net output power. Although the metal foam can offer advantages over the rectangular offset-strip fin in terms of the total power output and the thermoelectric conversion efficiency, the net power output of the metal foams even become negative which result in the big pressure drop when the exhaust flow through the exhaust heat exchanger. Therefore, as a follow-on work, this paper designed a new thermoelectric generator which combines thermoelectric generation with catalytic conversion, expect to avoid too large pressure drop when the exhaust flow through the entire exhaust system.