Revving up the race for better fuel efficiency

Image: sporty red sedan
Coming soon: a sporty red sedan. Oh yeah, and it gets 100 miles per gallon. As part of the $10 million Progressive Automotive X Prize, sponsored by the X Prize Foundation, college teams across the country are working toward an ultra-fuel efficient auto, like this concept of a plug-in hybrid electric vehicle from Cornell University’s 100+ MPG team.Courtesy of Cornell 100+ MPG

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.

Bringing fuel droplets down to size
Researchers at Temple University have taken several big steps toward the mass production goal with six months of road tests suggesting that another device, an inexpensive electrically charged tube that attaches to the fuel line, can likewise increase fuel efficiency.

The technology is based on reducing the fuel’s viscosity, allowing smaller droplets to be injected into the engine. Because of evaporation, combustion in an internal combustion engine must be completed quickly. Small fuel droplets offer an advantage because they burn more completely.

Automotive engineers have been actively exploring how to use very high pressure to reduce the droplet size, but the method would require an expensive engine redesign.

An electrical tube developed by physics professor Rongjia Tao and his collaborators, however, could be easily and inexpensively attached to the fuel line of an older car’s existing engine, near the fuel injector.

Within diesel and many other fuels, bigger molecules are held in suspension and possess a higher viscosity than the base liquid. Viscosity means more friction, the sworn enemy of energy. But when polarized in an electric field, those molecules clump together and get even bigger. Friction increases with the cumulative surface area of the suspended particles.

So, if engineers can reduce that surface area by getting many of the particles to aggregate, they can reduce the viscosity and increase the combustion efficiency.

The researchers first tested the device in Milan, Italy, in a diesel engine built by Italian manufacturer Cornaglia Iveco. As documented in the new study, published in the Nov. 19 issue of Energy & Fuels, the add-on yielded a 5 percent improvement in mileage.

Everyone was “very delighted,” Tao said — everyone except him. He was convinced he could do better when he realized that diesel fuel stays in the system less than one second.

After changing the design to allow fuel to linger longer, the team installed the device in a Mercedes-Benz and measured the equivalent of a 20 percent improvement in power output.

Building a fuel-efficient car from scratch
Political battles over increasing fuel efficiency standards are nothing new. And neither are attempts to build an ultra fuel-efficient car.

All of Detroit’s Big Three automakers created a concept car capable of at least 72 miles per gallon in the 1990s before the U.S. government-led Partnership for a New Generation of Vehicles was scrapped in 2001 over cost concerns. The partnership spent $1.5 billion to help U.S. manufacturers develop and produce an affordable family sedan rated at up to 80 miles per gallon,

But the urgency of coming up with less-polluting cars has ramped up interest not only in new technology aimed at reducing emissions, but also in competitions aimed at integrating that technology into a seamless and affordable whole.

Entrants in the $10 million Progressive Automotive X Prize, for example, are hoping to tap a range of innovations to create showroom-worthy cars capable of maintaining 100 miles per gallon over a variety of courses simulating real-life driving patterns.

“Basically it’s a race — the fastest car wins,” said Trey Riddle, a graduate student in Cornell University’s Department of Mechanical and Aerospace Engineering and leader of the university’s X Prize team. To become an official contender, however, each car must average an equivalent of 100 miles per gallon over the course.

Another entrant, Germany’s Loremo, already boasts an eye-popping fuel efficiency of 130 to 150 miles per gallon using concepts like minimal drag (thanks in part to a unique wing door-entry system) and a highly efficient 2-cylinder turbodiesel engine. The Loremo, short for “low-resistance mobile,” is slated for a 2009 release in Europe (with a base price of about $22,000), with a North American rollout possible by 2010.

None of Detroit’s Big Three automakers have joined the competition. Nevertheless, some industry observers believe the Chevrolet Volt, a plug-in hybrid featuring a 375-pound lithium ion battery, could reach 100 miles per gallon when it arrives in late 2010.

The Cornell 100+ MPG team, one of only two university entrants among more than 60 contenders in the X Prize competition’s mainstream auto class, is designing a plug-in hybrid electric car from scratch.

So far, a modified 1991 Geo Metro has allowed them to get their “hands dirty” and try out several new features, Riddle said.

The first qualifying race, slated for September 2009, will include an alternative class where nearly anything goes, and the mainstream class, which requires a car that seats four people, contains 10 cubic feet of storage and can accelerate to 60 miles per hour in 12 seconds. “They’re marketed more as a normal car that someone might want to buy,” Riddle said.

Which, after all, is the whole point.