Thermal Stability Research of Vehicle Exhaust Waste-Heat Recovery System with Intermediate Medium 2016-01-0228

Vehicle exhaust waste-heat recovery with thermoelectric power generators can improve energy efficiency, as well as vehicle fuel economy. In the conventional structure, the hot-end of thermoelectric module is directly connected with the outer wall of the exhaust pipe, while the cold-end is connected with the water pipe’s outer wall of the vehicle engine cooling cycle. However, the variety of vehicle engine operating conditions leads to the instability of the hot-end temperature, which will reduce the generating efficiency of the thermoelectric modules and also shorten its service life. This research is on the basis of constructing a heat transfer oil circulation, and to study the action principles and implementation methods of it. In this circulation, the heat transfer oil, as the intermediate medium, absorbs the exhaust waste heat and transfers the heat to the hot-end of the thermoelectric module steadily, which stabilizes the hot-end temperature under various vehicle engine operating conditions. The final purpose of this circulation is to improve the power generation efficiency of the thermoelectric module and prolong its service life. Firstly, the temperature and flow characteristics of the vehicle exhaust under a specific engine working condition are studied. Secondly, the dynamic model of the oil-gas heat exchanger as well as the dynamic heat transfer model of the thermoelectric evaporation module is established. Then the effect law of the waste-heat recovery system with intermediate medium on the hot-end temperature stability under the driving conditions of city road and rural road are focused in this research. Finally, with the comparison of the conventional engine waste heat recovery system, the multiple-performance analysis and evaluation of the whole system are carried out. The result shows that the heat transfer oil circulation can lower the temperature gradient of thermoelectric modules’ hot-end greatly, and stabilize the power generation status of this system though the structure of this waste heat recovery system needs additional oil pump, tubes and other components, which will increase the cost and energy consumption of the whole system,. What’s more, the power generation efficiency of thermoelectric module is improved by 10%-15%, with its working life being prolonged as well.