Researchers at Purdue University and General Motors (GM) are creating a system that harvests heat from an engine’s exhaust so as to generate electricity. This new thermoelectric generator research, aims to yield as much as a 10% reduction in fuel consumption by converting waste heat into electricity. A prototype of the thermoelectric system is due to be developed next year. Once completed, its characteristics will be assessed by installing it in an exhaust system behind the catalytic converter, where it will harvest heat from exhaust gases at 700oC.
Thermoelectric generators, based on the Seebeck effect, create electricity directly from a temperature difference. This is very similar to the Peltier-effect, which does the exact opposite; creating a temperature difference when a voltage is applied. The limiting factor of the thermoelectric effect in car exhaust systems until now has been the extreme temperatures, which can reach from 700 to 1500 degrees Celsius. Those temperatures are too high for current thermoelectric materials.
Part of the solution ( according to the researchers ), involves incorporating a variety of different materials so that some will expand more under certain conditions and “extract the most heat possible.” The prototype ( which is a small metal chip ), will basically hook up to the exhaust system and tap into heat coming from the gases. Currently the researchers are using skutterudite, a mineral made of cobalt, arsenide, nickel or iron as a base material in the chip. Rare-earth elements like lanthanum, caesium, neodymium and erbium, are being mixed with it inside a furnace. The object is to reduce the heat conducting properties of skutterudite so that the transfer of heat from the hot side to the cold side occurs slowly enough to maintain a steady current.
The first prototype that will be developed is expected to reduce fuel use by 5%. With further research and development of systems able to withstand high temperatures, the second prototype is expected to reduce fuel consumption by 10%. Besides improving fuel economy, this technology could also be used for a new type of solar-cell and harvesting waste heat to power homes and businesses. Once the technology reaches commercial use, harvesting waste heat will be used in a variety of unprecedented ways.