WASHINGTON -- After getting the EPA to admit that the 2010 emissions rules for SCR engines need some tightening, Navistar is now calling on the agency to force a recall of those engines currently in the market and introduce a new guidance that requires SCR engines to shut down immediately when out of diesel exhaust fluid (DEF).

In a 41-page comment letter to the U.S. Environmental Protection Agency filed on August 20, Navistar – the only engine maker not using SCR for 2010 engines – stated it is "encouraged" that the EPA and the California Air Resources Board (CARB) acknowledged some of the company's concerns about rival SCR engines' ability to meet 2010 NOx-reduction standards, but, says Navistar, the agencies should go further to correct the previous guidance, "which illegally affords preferential environmental breaks to one technology to make it more marketable to customers."

Although EPA’s and CARB’s post-2010 proposals "are a step in the right direction," they "must still be scrapped," Navistar commented.

A new rule should require SCR engines to employ sensors that "immediately" recognize the difference between proper DEF and the wrong fluid or an empty DEF tank, the company urges.

As rivals often point out, while Navistar criticizes
SCR systems' ability to comply with the 2010
standards, it does not yet have an engine that
meets the EPA's 2010 NOx limit.

In the meantime, EPA and CARB must "require the recall of all SCR engines that are programmed to run … without DEF, with the wrong fluid, with slush or frozen DEF, or with the system disconnected." And, Navistar adds, nonconformance penalties should be imposed on SCR-equipped engines that operate for extended periods without DEF aftertreatment.

The letter is a follow-up to a presentation the Chicago-based truck maker made last month at a public workshop it won by dropping its lawsuits against the EPA and CARB.

At the meeting, in which competitors Daimler Trucks, Volvo and Cummins begrudgingly observed, Navistar demanded that regulators fix "loopholes" which allow trucks to continue operating in a derated mode if DEF runs out or is substituted with another liquid.

In a video demonstration, Navistar showed that some trucks can operate without DEF for extended periods and freely driven up to 11,000 miles with water in place of DEF, thereby "illegally" relaxing -- Navistar claims -- the agency's own 0.20g NOx standard.

SCR competitors counter that the demonstration is misleading since, in actuality, sensors would identify the NOx limits being breached and the system would initiate a derating "inducement," which would eventually shut the truck down at the next fuel fill-up interval.

(One engineer suggested to us that Navistar appears to have repeatedly topped up the fuel tank to defeat subsequent derate inducements. "Do you know of anyone that will carry extra diesel fuel around to defeat an SCR system?" he says. "That’s just plain stupid.")

Regardless, it's the "inducement" allowance that's the problem, Navistar emphasized in its letter to EPA.

Not only is it not uniform among all engine makers – permitting some model trucks to operate longer under a minimal derate – but it currently only "discourages" rather than prevents the operation of commercial trucks without proper levels of DEF present, says Navistar.

"If EPA and CARB do not require the recall of SCR vehicles … and deem them to be lawfully certified, (the agencies) will illegally relax the 0.20g NOx standard preferentially for SCR-equipped engines."

In the event that the EPA and CARB maintain the "inducement" process within the rule, Navistar demands that the agencies test each SCR suppliers' inducement mechanism, across the U.S. and in different climates and duty cycles, before certification is granted.

-- For more on how the simmering engine feud between Navistar and SCR engine suppliers has boiled over, see the Sept. print issue of Today's Trucking