June 10th, 2008 · No Comments

By John DeFore

As anyone can tell you who has touched the hood or tailpipe of a car after a long drive, much of the energy produced by a tank of gas goes not to forward motion but to producing heat. A typical car’s engine is said to waste around two thirds of its energy generating heat, in fact, making it a frustratingly inefficient use of limited resources.

One of the groups working to combat this inefficiency, Germany’s Fraunhofer Institute for Physical Measurement Techniques, part of a group that bills itself as “the largest organization for applied research in Europe,” thinks it is near the point of building prototypes of a device that could reduce gas consumption by between five and seven percent.

Fraunhofer’s thermoelectric generators, or TEGs, would integrate with exhaust systems to capture heat from exhaust fumes and produce electricity from it. (About half of a car’s wasted energy results in heated exhaust fumes; the other half heats the engine block itself.) This energy would be re-routed to the electrical system, where a growing number of devices like on board navigational systems need it. “The long-term objective,” says an announcement from the researchers, “is to make the alternator [which produces electricity from the engine's movement using a fan belt] superfluous.”

The TEG would work because of a “temperature gradient”; it would produce more electricity when exhaust was hotter in comparison to the air around it. As one of the researchers, Dr. Harald Böttner, points out, “the temperatures in the exhaust pipe can reach 700 degrees Celsius or more. The temperature difference between the exhaust pipe and a pipe carrying engine cooling fluid can thus be several hundred degrees Celsius.” Using semiconductors, the TEG will harness the flow of heat between exhaust and coolant to generate current.

Now, if only someone would repeal the laws of thermodynamics, Fraunhofer’s next project could be a refrigerator that uses the inside/outside temperature differential to make its own electricity.

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