Purdue University researchers are developing technology that will turn the heat from vehicle exhaust into electricity. Collaborating with GM, the researchers are developing thermoelectric generators (TEGs) that will take that heat and use it to run vehicle electrical systems and reduce fuel use.
One of the challenges that the Perdue reasearchers face is finding materials that can withstand the heat of exhaust gases. According to Xianfan Xu, a Purdue professor of mechanical engineering and electrical and computer engineering, the gases inside a catalytic converter reach 700 to 1,500 degrees. Those temperatures are too high for current thermoelectric materials.
The research team is working towards developing thermoelectric materials that can be embedded in chips at various points in the exhaust system. Those chips need to be able to harvest energy from the extremely hot portions like the catalytic converter on out. By transforming the heat into electricity, it will cut down on the load of the engine and ultimately fuel consumption.
Thermoelectric technology means that electricity is generated when there is a difference in temperature.
“The material is hot on the side facing the exhaust gases and cool on the other side, and this difference must be maintained to continually generate a current,” said Xu, who has been collaborating with GM in thermoelectric research for about a decade.
In order to maintain that constant heat difference Xu and the rest of the team are working on improving the efficiency and reliability of the chips and the materials used. Part of that involves incorporating a variety of different materials so that some will expand more under certain conditions and “extract the most heat possible.”
Currently skutterudite, a mineral made of cobalt, arsenide, nickel or iron is being used as a base material. Rare-earth elements like lanthanum, cesium, 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.
In order to keep the thermoelectric material affordable, cheaper elements or combinations of rare-earth metals needed. That is why “mischmetal” alloys are used. Mischmetal is actually “an alloy of rare earth elements in various naturally-occurring proportions.”
The first prototype that will be developed is expected to reduce fuel use by five percent. With further research and development of systems able to withstand high temperatures, the second prototype is expected to reduce fuel consumption by ten percent.
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 un-thought of ways.
Top Photo: Purdue University photo/Mark Simons