EPA warms up to SCR solution

EPA has reconsidered its stance against selective catalytic reduction (SCR) as a viable technology for on-highway diesel engines to meet stringent 2010 emissions standards

EPA has reconsidered its stance against selective catalytic reduction (SCR) as a viable technology for on-highway diesel engines to meet stringent 2010 emissions standards, and sent a letter to manufacturers outlining its intent to certify SCR engines.

The letter outlines criteria SCR-equipped vehicles must meet to attain EPA certification. Much of the document addresses loopholes that end users could potentially exploit to operate vehicles while circumventing the emissions-related benefits. Specifically, the guidelines seek to ensure that SCR end users maintain the system’s supply of reducing agent—typically urea—a consumable component of the emissions reduction technology.

EPA had previously resisted the certification of SCR-equipped vehicles because the system relies heavily on the end user filling “a second tank” of urea regularly. Just as fuel is consumed to keep an engine running, urea is consumed to produce the emissions benefits of SCR. Additionally, EPA was concerned about developing a sufficient national infrastructure to provide end users a convenient supply of urea or ammonia.

Allen Schaeffer, director of the Diesel Technology Forum, an advocacy group supporting diesel engine manufacturers, said these guidelines signal that EPA is warming up to SCR technology.

“They’ve come to the recognition as we come closer to zero emissions, the conventional regulatory certification requirements in the past…may not work in the future,” Schaeffer told FleetOwner.

A low-tank warning light, combined with “last-resort persuasive measures to induce users to replenish [the urea supply]” will be necessary for SCR-equipped vehicles to gain certification. Although EPA declined to require specific measures, it did note some no-start engine options or activation of a “limp home” mode if the SCR tank is too low.

EPA said it is “imperative” that SCR-equipped vehicles are able to detect that it is, in fact, urea or ammonia, that’s in the tank and not other fluids such as water. Possible mechanisms to ensure this are NOx sensors or urea sensors. EPA said the same control measures used in a low-tank scenario would be appropriate when a non-urea fluid fills the tank.

To ensure end users have a convenient supply of urea, EPA wants it to be available at dealerships and truckstops, with a “back-up plan” for users unable to access either.

“Some of the engine manufacturers already have outstanding repair and service networks,” Schaeffer said. “I think there’s a good feeling there’s already a decent infrastructure for supplying urea.”

EPA now requires regular emission-related maintenance to begin no sooner than 100,000 miles of use—far longer than what manufacturers say is possible due to urea consumption. EPA has indicated that it will approve of shorter maintenance intervals.

“The guidance suggested there’ll be a need for rulemakings,” Schaeffer said. “I think now the ball is in court of manufacturers to bring their requests for waivers [on the 100,000 mi. interval rule] to EPA.”

To read the letter, go to www.epa.gov/otaq/cert/dearmfr/cisd0707.pdf

To comment on this article, write to Terrence Nguyen at [email protected]

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