A new, highly efficient material that converts heat into electricity may one day help cars get the most out of a gallon of gas, U.S. researchers said on Thursday.
Only about 25 percent of the energy produced by a typical gasoline engine is used to move the vehicle or run accessories like the radio or windshield wipers, they said. Much of the rest escapes through the exhaust pipe.
Researchers at Ohio State University in Columbus and Caltech in Pasadena, California, think they can recycle some of that lost energy with a new thermoelectric material that is twice as effective as current materials.
"The material does all the work. It produces electrical power just like conventional heat engines — steam engines, gas or diesel engines — that are coupled to electrical generators, but it uses electrons as the working fluids instead of water or gases, and makes electricity directly," Joseph Heremans, who led the project, said in a statement.
Jeff Snyder of Caltech, who worked on the project, said a thermoelectric device that converts heat from exhaust into electricity could improve a car's fuel efficiency by 10 percent.
Snyder, who previously developed such devices for NASA's Jet Propulsion Laboratory, said the idea of using thermoelectrics had been around for a long time, but the economics did not make sense when oil cost $20 a barrel.
"Now that energy costs have gone up by a factor of five, these alternative ideas that have been around for awhile are a lot more viable," Snyder said in a telephone interview.
He believes it would be possible to make the systems within the next five to 10 years.
Whether it catches on, Snyder said, will depend on the cost of the system and the energy market. If made on a large scale, Snyder said it might be possible to develop the systems for $10 a unit or less.
Currently, the most efficient material used commercially in thermoelectric power generators is an alloy called sodium-doped lead telluride, which has a rating of 0.71. By adding a bit of thallium to the lead telluride, the researchers doubled the efficiency rating to 1.5.
Tests of the material found it might be ideally suited for use in engines. They found that at near 450 degrees Fahrenheit (230 degrees Celsius), the material converted heat to electricity at about the same efficiency rating as currently available materials.
At higher temperatures, it became more efficient, hitting its peak efficiency rating of 1.5 at 950 degrees F (500 degrees Celsius).
Between 450 degrees and 950 degrees Fahrenheit is about the typical range for power systems, such as car engines, Heremans said.
The researchers have applied for a patent and are refining the material. The hope is to combine this finding with other recent discoveries that may produce further improvements in efficiency.
Snyder said a thermoelectric device using the material would need to be encased because thallium is highly toxic, but such devices could be recycled. He said it might be possible to find another, nontoxic thermoelectric system that shows the same kind of efficiency.