Revving up the race for better fuel efficiency

Bryn Nelson Columnist

One car of the not-so-distant future is powered in part by a battery weighing more than two fully grown men. Another lacks side doors in the interest of reducing drag. And dozens of teams from around the world — both amateur and professional — are racing to build sleek, ultra-fuel efficient cars powered by alternative energy and attractive to cash-conscious consumers.

But what about the cars we already own?

Amid the push toward plug-in electric hybrids, hydrogen fuel cells and biodiesel-friendly roadsters, new research suggests that impressive increases in fuel economy could be obtained by integrating innovative devices into the nation’s fleet of gas-guzzling vehicles.

In one recent study, scientists discovered a thermoelectric material that increases fuel efficiency by 10 percent or more. In another, engineers found that a simple electrically charged tube attached to the fuel injector could boost mileage by up to 20 percent.

Although neither device is quite ready for rush hour, both exemplify how a number of small changes could really start to add up.

The search for fuel efficiency heats up
Normally, thermoelectric devices have a cold side and hot side and exploit the temperature difference between the two. A small fraction of the heat is converted into electricity when electrons move from the hot end to cold end, producing positive and negative electrodes and an electrical voltage, while the vast majority of the heat dissipates.

Mercouri G. Kanatzidis, a professor of chemistry at Northwestern University in Evanston, Ill., and colleagues had been trying to find more efficient materials when they observed a strange phenomenon with a common semiconductor, lead telluride.

When the team added tiny inclusions of the metals lead and antimony and turned up the heat, the material’s conductivity doubled, freeing up the movement of the electrons, hence upping the efficiency of converting heat into electricity.

“Normally, when you add nano-inclusions into semi-conductors you tend to mess them up and things get worse,” he said. “In this case, things got better.”

The only problem is that the researchers don’t really understand why. “Nobody has seen anything like this before and we’re still struggling to come up with a primitive model for this,” said Kanatzidis, who published the results Oct. 27 in the German chemistry journal Angewandte Chemie International Edition.

Kanatzidis believes his team can already demonstrate a doubling of typical thermoelectric efficiency, and a quadrupling may yet be achievable, with financial backing from the U.S. Office of Naval Research.

Once fully deciphered, the phenomenon could give rise to better thermoelectric devices in automobiles and trucks. Collaborators at Michigan State University, in fact, are attaching such devices to the exhaust pipes of trucks, where temperatures approaching 400 to 600 degrees Celsius (750 to 1,100 degrees Fahrenheit) could be tapped for energy.

“It’s a place where there is a lot of wasted heat,” said Kanatzidis. “Can we do something to minimize that? Because it’s an easy type of energy to have. We know where it is.”

Currently, about 75 percent of the energy from every gallon of gas sails right out the tailpipe, with only 25 percent actually propelling the car forward. That means even a 5 percent increase in energy harvesting could be significant. Converting some of the tailpipe heat into electricity that is directed back into the engine to increase the torque would yield greater mileage.

Kanatzidis doesn’t see the device as more expensive than most other car add-ons, but concedes that far more testing would be needed before anyone dreams of making it a standard feature.

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