Corrected 3/13/2011. Navistar International is looking at some "exciting technologies" to reduce oxides of nitrogen in the exhaust of its later diesels, but aftertreatment using urea -- at least in liquid form -- will not be one of them.

Navistar's engines must get down to the absolute levels demanded by the federal Environmental Protection Agency in its 2010 emissions standard. "Point 2" - the required 0.2 gram per horsepower-hour for oxides of nitrogen, or NOx - is Navistar's goal after a period when its current diesels emit slightly more than that, said Jim Hebe, senior vice president for North American sales operations, in a press conference during the Work Truck Show in Indianapolis.

For now, Navistar and one other builder are using credits earned in the past by producing cleaner-than-necessary engines sooner than required. Navistar engineers are looking at methods not at hand when they decided to go with Advanced Exhaust Gas Recirculation. A-EGR cuts NOx emissions within the cylinders instead of using liquid urea aftertreatment, as all competitors are.

"We always said we would stay with in-cylinder [NOx reduction] unless we found something better," Hebe said at the press conference. A-EGR bought Navistar time to consider other methods, and "fortunately, there are some exciting technologies out there that we never had before -- one of them ours."

One of those technologies could be a solid form of urea injection being developed by Amminex, a Danish company Navistar invested in last year. Solid urea would not require operators to replenish the liquid urea supply - called diesel exhaust fluid - which they must do with selective catalytic reduction, the method chosen for 2010 by most other truck-diesel makers here and abroad. Hebe and other Navistar executives have been vociferous in their criticism of SCR.

I wonder what solid urea injection would cost. Would fuel economy be better, as competitors now claim for their SCR engines? How much would a dealer charge to change out the canister containing the urea-impregnated salt? Might it be more costly and inconvenient than just pouring some diesel exhaust fluid into a tank?

Such questions are premature until Navistar announces what it will do to get to point 2 after its EPA credits run out, and they're still considering the possibilities. Any form of exhaust aftertreatment chosen by Navistar would apply only to its heavy-duty engines. Medium-duty engines will still be dealt with in-cylinder.

Editor's Note: This article was corrected 3/13/2011, replacing a previous version that indicated Navistar might consider liquid urea injection. After checking with other reporters at the event, we realized our reporter misinterpreted Mr. Hebe's remarks. We regret the error.