Purdue mechanical engineering doctoral student Yaguo Wang works with a high-speed laser at the Birck Nanotechnology Center to study thermoelectric generators.
Photo by Mark Simons and courtesy of Purdue University

Researchers are testing thermoelectric generators as a part of a system that harvests heat from an engine's exhaust to generate electricity, reducing a car's fuel consumption.

A Purdue University team is collaborating with General Motors, which is developing a prototype using thermoelectric generators (TEGs), says Xianfan Xu, a Purdue professor of mechanical engineering and electrical and computer engineering. TEGs generate an electric current to charge batteries and power a car's electrical systems, reducing the engine's workload and improving fuel economy.

The prototype, to be installed in the exhaust system behind the catalytic converter, will harvest heat from gases that are nearly 1,300°F (~700°C), Xu says. Current thermoelectric technology cannot withstand the temperatures inside catalytic converters, where gases are about 1,830°F (~1,000°C), says Xu. However, researchers also are working on new thermoelectrics capable of withstanding such high temperatures, a step that would enable greater fuel savings. The thermoelectric material is contained in chips a few inches square that will be tailored for their specific location within the system.

"They are optimized to work best at different temperatures, which decrease as gas flows along the system," Xu says.

Because thermoelectric materials generate electricity when there is a temperature difference, a critical research goal is to develop materials that are poor heat conductors.

"You don't want heat to transfer rapidly from the hot side to the cool side of the chip," says Xu, who has been collaborating with GM in thermoelectric research for about a decade. "You want to maintain the temperature difference to continuously generate current."

The researchers at the West LaFayette, Ind.-based university are tackling problems associated with the need to improve efficiency and reliability, to integrate a complex mix of materials that might expand differently when heated, and to extract as much heat as possible from the exhaust gases.

The project began January 1. The first prototype aims to reduce fuel consumption by 5 percent, and future systems capable of working at higher temperatures could make possible a 10 percent reduction, says Xu, whose work is based at the Birck Nanotechnology Center in Purdue's Discovery Park.

The research team, led by Xu, involves Purdue faculty members Timothy Fisher, a professor of mechanical engineering; Stephen Heister, a professor of aeronautics and astronautics; Timothy Sands, the Basil S. Turner Professor of Engineering, a professor of materials engineering and electrical and computer engineering, and executive vice president for academic affairs and provost; and Yue Wu, an assistant professor of chemical engineering. The effort is funded with a $1.4 million, three-year grant from the National Science Foundation and the U.S. Department of Energy.