Researchers Study DEF Alternatives

CINCINNATI — Researchers are developing emissions control systems that could someday replace the selective catalytic reduction setups now found on diesel-powered medium-duty trucks.

Their work is driven, in part, by concerns that diesel exhaust fluid, the urea-based solution used by all SCR systems, presents problems that alternative technologies could overcome.

“DEF is extremely peculiar. It is a harsh and aggressive liquid,” said Richard Petti, the chief operating officer of Wema System, a Norwegian firm that makes components for SCR systems. Petti and others discussed the engineering challenges of working with DEF and potential alternatives during a conference on diesel emissions and DEF hosted here in October by market analysis firm Integer Research Ltd., London.

DEF is mainly distilled water — more than 65% — and dissolved urea, a nitrogen-carbon-hydrogen-oxygen compound making up 32.5%. It is a necessary ingredient for reducing nitrogen oxide emissions in a truck’s SCR system. And that system has become the uncontested method of emissions compliance for North American medium-and heavy-duty trucks.

DEF is injected into diesel exhaust, enabling it to interact with a catalytic converter that removes NOx.

However, the liquid can freeze into a dome on a cold winter day, or the water can evaporate in the heat, Petti said. Therefore, sensors made by Wema are designed to heat the crystallized dome back into a liquid, and the company’s engineers have had to develop algorithms to compensate for temperature differences.

Petti said the Wema sensors are designed to last 15 years on a truck, even when submerged in liquid urea, and that sealing a system so DEF cannot invade it is very difficult.

Tenneco Automotive makes components for SCR systems for a variety of engine types, from cars to stationary power generators, but is also looking to develop alternative technologies, said company vice president Ben Patel.

“Liquid urea for SCR is here to stay. It is the proven, incumbent technology,” Patel said before launching into his descriptions of the alternatives.

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© 2013, Transport Topics Publishing Group. All rights reserved.

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