Numerical and Experimental Analysis of Automotive Exhaust Gas Thermoelectric Generator

Abstract

This present study focuses on the utilization of waste heat from internal combustion engines through the use of automotive exhaust gas thermoelectric generators (AETEGs). The ine ciency of internal combustion engines, where approximately 70% of the heat produced is wasted, presents an opportunity to increase the e ciency of automobiles by converting this waste heat into useful electricity. TEGs, which are solid-state devices that directly convert heat to electricity, have the potential to harness the heat energy from automotive exhaust gases. However, these devices are currently less explored and have lower e ciency, typically below 10%. Despite their lower e ciency, even the extraction of a small amount of energy from waste heat can have a signi cant impact. The objective is to evaluate the properties and performance of a commercially avail- able thermoelectric generator module and analyze the e ciency of AETEGs. The present work involves designing and fabricating heat exchangers to analyze AETEGs. Theoreti- cal, numerical, and machine learning approaches are employed for analysis, and experi- mental methods validate results. The current study delves into the concepts of equivalent and e ective material prop- erties, considering contact resistance and heat loss during experimentation. Equivalent material properties are in uenced by temperature, making their theoretical and numerical modeling intricate. On the other hand, e ective material properties remain una ected by temperature, making them more suitable for theoretical and numerical modeling. The experimental analysis results of power output are compared with those obtained from theoretical and numerical modeling using e ective material properties; they are compa- rable with a maximum deviation of 13% and 12% , respectively. As a result, chapter 4 and 5 adopts the use of e ective material properties. Skuttrudite (CoSb3) is a promising thermoelectric material for AETEGs; in the present work, it produced low voltage output due to electric contact resistance and a metal-semiconductor junction. Hence AETEG analysis is conducted on the commercially used bismuth telluride (Bi2T e3) Modules. A commercially available TEG module (TEM-12706) is simulated, and its perfor- mance under di erent conditions is studied. For commercial TEG 12706, the hot side temperature is maintained at 700 C, and the cold side temperature is maintained at 300 C. The peak power produced is 168 milliwatts at a load resistance of 2.4Ω. The analysis includes the e ects of load resistance, source and sink temperatures, and leg length. The present study also explores the impact of TEG shape on internal resistance and e ciency, suggesting that square-shaped TEGs are more suitable for low load resistance, while cir- cular cross-sections are better for high load resistance due to load and internal resistance tuning. Di erent shapes of uni-couple thermoelectric generators are examined, revealing the advantages of trapezoid cross-sections in terms of increased e ciency. The variation in sink temperature is found to have a greater e ect on performance compared to source temperature. The concept of segmented legs is applied to increase power output. The study highlights the role of heat exchangers in power production from AETEGs. Heat exchangers are designed and fabricated, with one experiment involving blowing hot air from a hot air gun on one side and circulating cold water on the other side of the heat exchanger. The results demonstrate a peak power of approximately 59 watts when 24 TEGs are connected in series with an 81 Ω load resistance. The analysis considers the e ects of hot side temperature, load resistance, cold side temperature, and mass ow rate. Theoretical and numerical simulation results are compared with experimental results, showing close agreement with minor deviations attributed to heat losses and assumptions regarding e ective material properties. Furthermore, a heat exchanger is designed, fabricated, and mounted on the exhaust of a single-cylinder diesel engine to evaluate the performance of AETEG, the e ect of temperature, the ow rate of hot exhaust gases, cold uid, and the number of TEGs on the performance of AETEG are studied for exhaust gas mass ow of 12gm/s. The power of 10 TEG in series at matched load resistance is 35 watts. The matched load resistance is 24Ω. In summary, this present work contributes to the understanding and improvement of AETEGs, providing insights into their properties, performance, and potential for in- creasing the e ciency of AETEGs. The ndings emphasize the importance of material properties, heat exchanger design, and AETEG system tuning for maximizing power generation from waste heat. Moreover, the present study validates e ective material properties for thermoelectric generator simulations, enabling more accurate modeling and analysis. The optimization of the thermoelectric generator shape and the emphasis on the role of heat exchangers contribute to improved performance and power production from AETEGs.