Researchers: Heat From Exhaust Could Be Harnessed For Improved MPG

December 29, 2010
Porsche 911 Sport Exhaust

Porsche 911 Sport Exhaust

If you've ever crept along in gridlock and noticed the floor of your car getting a little warm, or 'seen' all the heat energy escaping from a hot exhaust pipe on a cold day, you know that exhaust systems send a lot of heat right out the tailpipe—heat that could potentially be put to use.

What if you could recapture that energy and turn it back into electricity that could be used by vehicle accessories?

As automakers look for incremental improvements in fuel economy, that's one of the potential uses of an advanced thermoelectric material that's being researched by physicists and engineers at the University of Michigan. They've studied the material that could potentially be wrapped around a vehicle's exhaust system and would produce energy that could supplement the vehicle's electrical system—therefore allowing higher mpg.

Such a system could make the most difference in low-speed stop-and-go driving, where exhaust pipes typically heat up and the mechanical load from vehicle alternators has a greater impact on fuel economy; supplemental power from these materials in the exhaust system, along with the newer smart-alternator systems already used in some vehicles, could together significantly ease that load.

The research was funded through a grant from the university's Center for Solar and Thermal Energy Conversion, which is funded by the U.S. Department of Energy, has found that recent advances in the materials—including mechanically strong skutterudites combined with barium, can improve the efficiency of existing thermoelectrics by 15 to 20 percent, making them practical for some automotive applications.

As MotorAuthority has reported, GM and Purdue University have been working on a project that aims to cut fuel use by five percent with its first prototype, and BMW is working on a similar system. Both use materials that are more common than those being developed at Michigan.

Because these newly developed materials are expensive, automakers would initially be looking at hot spots where the greatest temperature differentials exist—such as between the engine and catalytic converter—although they could be used in a number of other spots to cumulatively recover more energy.

While electric cars such as the Nissan Leaf have shown that internal combustion engines are no longer necessary for some uses, gasoline- and diesel-burners will be common for decades. With as much as 70 percent of the energy in a gasoline vehicle is lost to waste heat, there's a lot of progress yet to be made.

[University of Michigan]

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