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Carmakers Scrambling to Convert Heat Energy into More MPG

By KBB.com Editors on August 13, 2008 4:33 PM
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It’s not quite as impressive as being able to spin straw into gold, but automakers the world over are intensifying their efforts to transform otherwise wasted heat energy -- primarily from a vehicle’s exhaust -- into an efficiency-boosting electrical equivalent using a process known as thermoelectric generation. At the moment, the highest profile work is being done by GM and BMW, both of whom are slated to start a new phase of practical testing on current production vehicles during 2009.

The concept of thermoelectric generation has been around for decades, and saw its first practical applications during the 1960s when it was used by NASA in its space program. More recently, the Department of Energy (DOE) challenged automakers to apply the same fundamental principles to passenger vehicles, with the goal of improving fuel economy by 10 percent in the near term. GM claims meeting that objective could translate into an annual savings of over 100 million gallons of gasoline in the U.S. on its vehicles alone. In the longer run, the DOE hopes to see overall economy gains approach 20 percent late in the next decade and 35 percent by 2030-2035, at which time conventional internal combustion engines would likely be rendered obsolete by newer forms of power modules.

Basically, this heat-to-electricity conversion (The Peltier-Seebeck effect for you physics buffs) is accomplished by placing a series of thermoelectric generators (TEGs) in close proximity to a car’s primary heat sources: namely its exhaust system, catalytic converter and radiator. These solid-state TEG devices are made from two dissimilar metallic elements that generate a small amount of current when a temperature differential is created between them. Since internal combustion engines typically convert only 25-30 percent of their primary fuel’s intrinsic energy into actual propulsive force, there’s plenty of free “source material” to be recovered here. Electricity generated in this manner can be used to reduce parasitic drain created by the alternator -- itself a notoriously inefficient and power-robbing device -- and thereby help improve the engine’s fuel economy. The total bonus output created during typical freeway running could run 700-800 watts or more, and the most optimistic proponents of this technology believe that it may someday replace the alternator altogether.

All of the energy recovery systems currently being evaluated still need several more years of real-world development to optimize their efficiency and durability -- and trim their still-too-high production costs. However, the potential payback clearly makes it a goal worth pursuing. The DOE contends that fully utilizing the thermoelectric generation process would be the functional equivalent of improving a vehicle’s overall operating efficiency to nearly 50 percent. It also would help offset the increasingly severe demands created by today’s ever broadening array of power-swilling on-board electronics, from vehicle dynamics/collision avoidance systems to steer-by-wire and electronic braking to high-wattage audio packages and navigation devices. TEG power could even be used to speed up recharging times for the battery pack in a hybrid.

GM will begin testing its latest TEG package on a 2009 Suburban during the next 12 months while the BMW Group, currently working with thermoelectric specialist BSST and scientists at Ohio State University, plans to evaluate its setup on a new 5 Series during that same period. BSST was selected along with GM to be part of the DOE’s initial TEG development program for passenger vehicles, which began in 2004. A subsidiary of thermoelectric leader Amerigon Incorporated, BSST also has commercial links to Visteon, the key component supplier to Ford Motor Company.

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