Optimization of hybridization strategy for improving the efficiency of thermoelectric generator to recover automobile exhaust waste heat

Abstract

This paper investigates the existing efficiency formulations of a thermoelectric generator (TEG) and compares them with overall efficiency formulation (η overall). As TEG efficiency is the key factor in TEG performance, η overall formulation is validated and compared to the maximum efficiency (η max) formulation with consideration of temperature independent figure of merit (ZT). We have found that the (η max - η overall) is minimum (1.5%) at low temperature difference (100 K) and it increases (up to 12.67%) when temperature difference increases (up to 800 K). η overall is close to η max at low temperature difference but when temperature difference increases, η overall shows the overestimation of the efficiency results. Compatibility factor is the crucial factor for effective hybridization and segmentation of thermoelectric materials. Thermoelectric materials of Half-heusler alloys of Hf0.75Zr0.25Ni0.9Pd0.1Sn0.975Sb0.025 and FeV1.2−xTixSb (x = 0.4) are considered for the p-n couple and TEG module design. The exhaust thermoelectric generator (ETEG) system consisting of 56 TEG modules is proposed to recover the automobile exhaust waste heat. Output power of 51.52 W is obtained from the ETEG system at a temperature difference of 458 K. At a temperature difference of 800 K (when cold end temperature is fixed at 315 K and hot end temperature vary up to 1115 K), the ETEG system can achieve 75.8 W of power. This ETEG system also provides an additional advantage in the life increment of the muffler due to a reduction in peak temperature. The overall efficiency of the proposed ETEG system is found to be 7.81%.