Automotive Thermoelectric Generators

Automotive Thermoelectric Generators (ATEG) are devices utilizes the Seebeck effect to recover lost heat in an internal combustion engine powered vehicle. A typical ATEG consists of four main elements: A hot-side heat exchanger, a cold-side heat exchanger, thermoelectric materials, and compression assembly system. ATEGs can be classified according to their hot-side heat exchanger [ [http://eprints.utm.my/4162/ M. Saqr, Khalid and Musa, Md. Nor (2007) "State of the art of thermoelectric generators for waste heat recovery applications". Jurnal Teknos-2k, 7 (2). pp. 1-10. ISSN 1411 - 4151] ] to exhaust-based ATEGs and coolant-based ATEGs. The first type converts the heat lost in the IC engine exhaust, while the second type converts the heat lost in the engine coolant, into electricity.

Operation principles

In ATEGs, thermoelectric materials are packed between the hot-side and the cold-side heat exchangers. The temperature difference between the two surfaces of the thermoelectric module generates electricity. The compression assembly system aims to decrease the thermal contact resistance between the thermoelectric module and the heat exchanger surfaces. In exhaust-based ATEGs, the cold side heat exchanger uses engine coolant as the cooling fluid, while in coolant-based ATEGs, the cold-side heat exchanger uses ambient air as the cooling fluid.

Efficiency

The efficiency of an ATEG is governed by the thermoelectric conversion efficiency of the materials and the thermal efficiency of the two heat exchangers. The ATEG efficiency can be expressed [ [http://ieeexplore.ieee.org/iel4/5970/15978/00740419.pdf?isnumber=15978&arnumber=740419 Ikoma, K., M.Munekiyo, K.Furuya, M.Kobayashi, T.Izumi, and K.Shinohara (1998). Thermoelectric Module and Generator for Gasoline Engine Vehicle. Proc. 17th International Conference on Thermoelectrics. Nagoya, Japan: IEEE pp. 464-467.] ] as:

ζ_OV = ζ_CONV х ζ_HX х ρ

Where:

ζ_OV : The overall efficiency of the ATEG

ζ_CONV : Conversion efficiency of thermoelectric materials

ζ_HX: Efficiency of the heat exchangers

ρ : The ration between the heat passed through thermoelectric materials to that passed from the hot side to the cold side

History

Although the Seebeck effect was discovered in 1821, the use of thermoelectric power generators has been restricted mainly to military and space applications until the second half of the twentieth century. This restriction was caused by the low conversion efficiency of thermoelectric materials at that time.

In 1963, the first ATEG was built and reported by Neild et al [ A. B. Neild, Jr., SAE-645A (1963). ] . In 1988, Birkholz et al published the results of their work in collaboration with Porsche. These results described an exhaust-based ATEG which integrating Fe based thermoelectric materials between a carbon steel hot-side heat exchanger and an aluminium cold-side heat exchanger. This ATEG could produce multiple tens of watts out of a Porsche 944 exhaust system [Birkholz, U., et al. "Conversion of Waste Exhaust Heat in Automobile using FeSi2 Thermoelements". Proc. 7th International Conference on Thermoelectric Energy Conversion. 1988, Arlington, USA, pp. 124-128.] .

In the early 1990s, [http://hi-z.com Hi-Z Inc] designed an ATEG which can produce 1 kW from a diesel truck exhaust system. The company in the following years introduced other designs for diesel trucks as well as military vehicles [http://www.hi-z.com/websit30.htm] .

In the late 1990s, Nissan Motors published the results of its ATEG which utilizes SiGe thermoelectric materials. Nissan ATEG produced 35.6 W in testing conditions similar to running conditions of a 3.0 L gasoline engine in hill-climb mode at 60.0 km/h.

Clarkson university in collaboration with [http://www.hi-z.com Hi-Z] has designed an ATEG for a GM Sierra pick-up truck. The program was funded by the American DOE and NYSERDA. The published literature of this ATEG explained its ability to produce 255 W at a vehicle speed of 112 mph. [Thacher E. F., Helenbrook B. T., Karri M. A., and Richter Clayton J. "Testing an automobile thermoelectric exhaust based thermoelectric generator in a light truck" Proceedings of the I MECH E Part D Journal of Automobile Engineering, Volume 221, Number 1, 2007, pp. 95-107(13)] [ [http://www.eere.energy.gov/vehiclesandfuels/pdfs/deer_2004/session4/2004_deer_kushch.pdf Kushch A., Karri M. A., Helenbrook B. T. and Richter Clayton J., "The Effects of an Exhaust Thermoelectric Generator of a GM Sierra Pickup Truck." Proceedings of Diesel Engine Emission Reduction (DEER) conference, 2004, Coronado, California, USA] ] . In the year 2006, scientists in BSST and BMW of North America have announced their intention to launch the first commercial ATEG in 2013 [ [http://www1.eere.energy.gov/vehiclesandfuels/pdfs/deer_2006/session6/2006_deer_fairbanks.pdf LaGrandeur J., Crane D., Eder A., "Vehicle Fuel Economy Improvement through Thermoelectric Waste Heat Recovery", DEER Conference, 2005, Chicago, IL, USA] ]

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