04 Jul Exhaust Thermoelectric Generator for Military Vehicle Application
Continuously updated development of green energy techniques is a good alternative to resolve global energy crisis and environmental protection. Owing to several advantages such as having little vibration, being highly reliable and durable, and having no moving parts, there have been considerable emphases on the development of thermoelectric modules (TEMs) for a variety of photovoltaic, automotive, military and aerospace applications over the past years. With the rapid development of economy and society, automobiles have become a necessity. For the internal combustion engine used in traditional automobiles, only about 25% of its fuel energy is converted to mechanical energy, whereas approximately 40% of the fuel energy is wasted through exhaust gas, 30% is dissipated in the engine coolant, apart from friction and parasitic losses. Thus, recovery of exhaust heat energy via thermoelectric technology for use in the military vehicle system is important and can significantly enhance both fuel economy and system performance. To achieve this goal, use of thermoelectric generators (TEGs) based on single, low, and intermediate temperature TEMs has been a novel research focus.
Since the first automobile exhaust thermoelectric generator (AETEG) emerged in 1963, in the open literature, many research groups have made great efforts to install the TEMs in automobile exhaust pipes to study the potential use of TEG systems in exhaust gas heat recovery. Review of the literature shows that the development of various TEGs for vehicles application based on experimental setup is in progress. However, only a few works focus on the road test performance based on real vehicle after 2010. According to the research achievements, the maximum power of most of the TEGs is almost below 400 W, which cannot meet the electrical requirements (usually above 600 W) for automotive applications such as turn signals, stop lamps, electric windows, air conditioners, seat heaters, etc. To enhance the maximum power and improve the AETEG, several studies have shown that well-designed inner topology of heat exchanger contributes to the efficient heat transfer and large temperature difference, and the optimized design of heat sink (cold side) and geometry of TEMs is also significant. Different types of heat exchanger have been constructed, the heat uniformity and the overall output power have been improved after optimization since 2010, the lack of comprehensive performance evaluation regarding thermoelectric efficiency, generation capacity, temperature distribution, inner resistance, backpressure of AETEG and their significant influence factors in both test bench and real prototype vehicle need to be further evaluated.
Automotive waste heat recovery based on TEMs presents a promising research focus worldwide but enhancing AETEG performance and heat recovery efficiency without degrading the fuel economy, heat balance, and emission behaviour of engine remains a significant challenge. The compound Bi2Te3 is the most common commercially available material used in TEMs to date. Despite the high ZT value of about 1.1 offered by this material, it has a very restrictive operational temperature range (usually from 20 °C to 300 °C) and relative large thermal resistance. Also, it is not technically possible to greatly enhance the TEMs performance only by increasing the ZT value of the Bi2Te3 material at present. Furthermore, the intermediate-temperature TEMs are still in progress and are not commercially available so far.
To further enhance output power and maximize system efficiency of AETEGs, there are four effective ways: raising the hot side temperature and its uniformity as much as possible by optimizing the exhaust manifold structure and heat exchanger inner topology until the military vehicle speed approaches the highway speed limitation; lowering the cold side temperature by precooling its inlet coolant; reducing the heat loss by covering the exposed area with thermal insulation materials; and increasing the number of TEMs. Moreover, the unwished increased backpressure caused by heat exchangers should be restricted even if the maximum power of AETEG is increased, for it will deteriorate the fuel economy and emission performance of an engine. Future work focusing on the optimization measures above is in progress and the relevant results will be reported in the next few years.
This is an excerpt of the journal article: Performance Investigation of an Exhaust Thermoelectric Generator for Military SUV Application by Quan, Rui; Liu, Guangyin; Wang, Chengji; Zhou, Wei; Huang, Liang; Deng, Yadong. Published: January 22. 2018 in Coatings 2018, 8(1), 45; DOI: https://doi.org/10.3390/coatings8010045 under a Creative Commons Attribution License (CC BY 4.0).