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Truck’s engine taps own heat for power

A 195-year-old discovery is the basis for a new system that will save vehicles hundreds of litres of fuel and reduce their carbon emissions by as much as 2 to 3 tonnes per year.

Working with automotive manufacturer Scania, researchers from KTH Royal Institute of Technology have been testing semi trucks equipped with a system that converts exhaust heat into power — with a thermoelectric generator (TEG). The voltage produced by the system can power the truck and reduce the strain on the engine, explains researcher Arash Risseh.

The TEG system operates on the principle of the thermoelectric effect, by which differences in temperature are converted into voltage — a phenomenon discovered in 1821 by German physicist Thomas Johann Seebeck, and often referred to as the “Seebeck effect”. (Watch video)

“Most fuel energy is not used to drive a truck forward,” Risseh says. “A great portion of this unused energy — some 30 percent — disappears in the form of heat through the exhaust pipes.”

How much energy are we talking about? For a truck that generates 440kW, that lost energy would total about 132kW. “That’s enough to power a typical passenger vehicle.”

Capturing this excess energy takes a load off the truck’s generator, and in turn, the engine, Risseh says. That means better fuel efficiency and lower emissions.

The Seebeck effect requires a temperature differential — cool on one end of the circuit and hot on the other, which means a truck must rely on a coolant in order to stimulate the voltage. Cooling the circuit is easier with natural alternatives, such as seawater for a ship’s engines. Ships also make good candidates for TEG because their buoyancy offsets the constraints of weight and volume that road vehicles face, he says.

TEG is also regarded as a potential energy saver in data centres that are located in cold climates. Near the Arctic circle in northern Sweden, a data centre that uses 1 Terawatt hour per year could potentially recover 1 Gigawatt per year — a savings of some EUR 100,000, he says.

The research project, which is funded by the Swedish Energy Agency, also includes partners Eberspächer, TitanX and Swerea IVF.

David Callahan

David Callahan
David Callahan is editor for international news and media at KTH Royal Institute of Technology.

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