Harnessing automobile energy

Researchers at Ohio State University have invented a new material that may make cars even more efficient by converting heat wasted through engine exhaust into electricity.

The material is claimed to have twice the efficiency of anything currently on the market.

The same technology could work in power generators and heat pumps, said Joseph Heremans, one of the developers of the new material.

The efficiency of thermoelectric materials is based on how much heat they can convert into electricity at a given temperature.

Previously, the most efficient material used commercially in thermoelectric power generators was an alloy called sodium-doped lead telluride, which had a rating of 0.71. The new material, thallium-doped lead telluride, has a rating of 1.5 - more than twice that of the previous leader.

What is more important to Heremans is that the new material is most effective between 450 and 950 degrees Fahrenheit - a typical temperature range for power systems such as automobile engines.

Only about 25 per cent of the energy produced by a typical gasoline engine is used to move a car or power its accessories, and nearly 60 per cent is lost through waste heat - much of which escapes in engine exhaust.

A thermoelectric device could capture some of that waste heat. It would also make a practical addition to an automobile, because it has no moving parts to wear out or break down.

Heremans designed the new material with Vladimir Jovovic in the Department of Mechanical Engineering at Ohio State.

Researchers at Osaka University then created samples of the material for testing, while their colleagues at the California Institute of Technology tested it at high temperatures. For their part, Heremans and Jovovic tested it at low temperatures.

The team found that near 450 degrees Fahrenheit, the material converted heat to electricity with an efficiency rating of about 0.75 - close to that of sodium-doped telluride. But as the temperature rose, so did the efficiency of the new material. It peaked at 950 degrees Fahrenheit, with a rating of 1.5.

Heremans' team is continuing to work on this patent-pending technology.