Thermal design of automobile exhaust based thermoelectric generators: Objectives and challenges

Abstract

The potential for thermoelectric power generation (via waste heat recovery onboard automobiles) to displace alternators and/or provide additional charging to a vehicle battery pack has increased with recent advances in thermoelectric material processing. In gasoline fueled vehicles (GFVs), about 40% of fuel energy is wasted in exhaust heat, while a smaller amount of energy (30%) is ejected through the engine coolant. Therefore, exhaust-based thermoelectric generators (ETEG) have been a focus for GFV applications since the late 1980s. The conversion efficiency of modern thermoelectric materials has increased more than three-fold in the last two decades; however, disputes as to the thermal design of ETEG systems has kept their overall efficiency at limited and insufficient values. There are many challenges in the thermal design of ETEG systems, such as increasing the efficiency of the heat exchangers (hot box and cold plate), maintaining a sufficient temperature difference across the thermoelectric modules during different operating conditions, and reducing thermal losses through the system as a whole. This paper focuses on a review of the main aspects of thermal design of ETEG systems through various investigations performed over the past twenty years. This paper is organized as follows: first, the construction of a typical ETEG is described. The heat balance and efficiency of ETEG are then discussed. Then, the third section of this paper emphasizes the main objectives and challenges for designing efficient ETEG systems. Finally, a review of ETEG research activities over the last twenty years is presented to focus on methods used by the research community to address such challenges.

Feasibility of Thermoelectrics for Waste Heat Recovery in Conventional Vehicles

“…In most vehicle applications currently being explored, the TE device employs heat exchangers to carry heat from the exhaust system to the hot side of the device (and isolate the device from peak exhaust system temperatures) as well as to remove heat from the cold side of the device [8,11]. The cold side commonly uses ethylene glycol as a working fluid, either shared with the engine cooling loop or using its own dedicated radiator.…”

Energy Management of Automobile Exhaust Thermoelectric Hybrid Power Based on Maximum Power Point Tracking and Fuzzy Logic Control

“…Furthermore, according to the heat balance descriptions of AETEG [7] and the presentation of a recent case study [8], supposing the exhaust gas energy at the outlet of heat exchanger account for 45% of the total exhaust heat, while another 45% is represented in the heat lost from the leg-sides of the TEMs by convection and radiation, the heat lost by conduction in the TEMs due to thermal contact resistance, and the effective heat transferred through TEMs together, the corresponding maximum waste heat recovery efficiency of AETEG during UDDS is shown in Figure.8. The maximum waste heat recovery efficiency of AETEG relatively decreases as the speeds of engine increase, it is 1.3% based on 64 Be2Ti3 TEMs with the maximum generation efficiency being 5%, which illustrates that much more exhaust heat is lost with form of non-used zones of heat exchanger by radiation and convection, leg-sides of the TEMs by convection and radiation, gaps between the TEMs as the output power and speeds of engine increase.…”

Performance Evaluation of Waste Heat Recovery Systems Based on Semiconductor Thermoelectric Generators for Hypersonic Vehicles

“…The results presented the status of the system architecture, modeling and key technologies and provided a performance prediction. Saqr et al [22] described the construction of a typical exhaust-based thermoelectric generator, and discussed the heat balance and efficiency of exhaust-based thermoelectric generators. The main objectives and challenges for designing efficient exhaust-based thermoelectric generator systems were also emphasized.…”