How Exhaust Heat Recovery and Recirculation Works

Electricity from Exhaust
Thermoelectric devices would help boost a hybrid car's range by filling in for the batteries that run its electric motor.
Thermoelectric devices would help boost a hybrid car's range by filling in for the batteries that run its electric motor.
Bryan Mitchell/Getty Images News

Thermoelectric materials, as the name implies, can produce heat from electricity. These materials were discovered in 1821 by the German physicist Thomas Seebeck. They've generally been too expensive and inefficient to be of any use to automotive engineers, but this has started to change: The U.S. Department of Energy has expressed interest in funding the development of a practical thermoelectric system that could be used in cars.

There are many sources of wasted heat in cars, including the radiator and the engine, but the biggest source is probably the exhaust. Given that most cars already recirculate exhaust in an EGR loop and that this technology will be even more important in the future, this provides an ideal opportunity to trap this otherwise wasted heat and use thermoelectric devices to convert it into electricity. This electricity could be used to power the car's electrical systems, recharge the batteries, and perhaps most importantly, run the electric motor in hybrid and plug-in battery electric vehicles. This would be a nearly perfect confluence of several technologies, and would have the side effect of helping to reduce nitrous oxide emissions by further cooling the exhaust before it's mixed with fuel.

Any type of car could benefit from this thermoelectric boost, but once again, it would be most useful when applied to hybrid vehicles. It would extend their range by supplementing the batteries that run the electric motor and reduce the amount of time required to recharge those batteries.

The development of fuel-efficient and low pollution technologies like exhaust recirculation and thermoelectric power will make the cars of the future -- which will have little or no use for fossil fuels -- possible. It's important that we develop these technologies now, before fossil fuels run out and pollution does significant damage to the Earth's atmosphere and climate.

Related HowStuffWorks Articles


  • Green Car Congress. "Thermoelectrics Gaining More Attention and Development Focus." July 22, 2005. (April 14, 2009)
  • Heremans, Joseph. " Material may help autos turn heat into electricity." Eureka Alert. July 24, 2008. (April 15, 2009)
  • Thaindian News. "Recycling Exhaust Heat May Power Green Cars." February 26, 2008. (April 14, 2009)

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