Another Diesel Dilemma
Engine makers are split on technologies to meet next emissions hurdle. But it's a no-brainer: one has a payback, the other just cost, cost, cost.
Steve Sturgess
Senior Editor
The truck manufacturing industry faces some hard questions as it heads toward the next emissions hurdle, timed for 2007 and phasing in through 2010.
In presentations at a Diesel Engines Emissions Summit at the Technology and Maintenance Council's summer meeting, truck engine manufacturers were split on the technologies to meet the upcoming emissions targets.
Freightliner president Rainer Schmuckle and Volvo president and Mack chairman Michel Gigou both resoundingly championed selective catalytic reduction (SCR), a technology also promoted by Detroit Diesel/DaimlerChrysler power systems' Tim Tindall, who is the companies' lead on emissions technologies.
Steve Charlton, head of Cummins' advanced engineering, along with International's technology chief Pat Charbonneau and Caterpillar's truck engine director John Campbell all said that other technologies, all involving NOx absorbers, would be preferable to the use of SCR.
It's not purely coincidental that the manufacturers with strong ties to Europe favor SCR - the use of urea injection into the exhaust to remove NOx, leaving nitrogen and water. That is the preferred technology to reach European emissions regulations set to hit between now and 2008.
Cummins and International are likely to use heavy exhaust gas recirculation (HEGR) along with improvements in combustion from fuel system, air handling and combustion chamber design to improve the engine-out emissions. These can then be cleaned by more aggressive exhaust aftertreatment involving catalytic reduction over noble metals.
The new emissions regulations will be a tough target, all agreed, as particulates (PM) and NOx both are reduced by 90% — even over the tough levels set for '04.
For the audience of truck maintainers and specifiers, it was mostly bad news. They were told that most technologies involving NOx absorbers would bring significant losses in fuel economy, increased maintenance and add many thousands of dollars to both the initial cost of engines and to re-engineer truck chassis to accommodate them.
Fuel handling will also need to move to another level to avoid contamination of the low-sulfur diesel - a major issue as a $5,000+ converter can be wiped out by one tankful of the wrong fuel.
On the other hand, SCR technology is already proven. It's in use today on transit buses in Europe. By 2007 more than a million SCR-powered vehicles a year will be in production, significantly lowering their unit costs.
And SCR technology brings a fuel economy boost. It can actually pay for itself by taking fuel use back to 1999 levels.
What may not be ready for 2007, though - and is a potential stumbling block - is the infrastructure to replenish the on-board SCR reagent, urea.
But Volvo Powertrain vice president of engine engineering Tony Greszler said that the need to have urea available at every fueling station might not be an issue. Urea is used in such low concentrations - roughly 4% of the fuel usage - that it would be very easy to accommodate 20 gallons of urea solution for upwards of 3,000 miles in a separate tank on a truck.
Also detracting from the SCR case is EPA's concern that engines would be able to run with the urea tank dry, thus defeating the emissions benefits. Most panelists agreed this isn't an issue given today's electronic controls.
Urea's other big attraction is that it is not so sensitive to fuel quality. And SCR works so well it allows an engine to be optimized for performance rather than emissions, thus improving fuel economy. And SCR installation is much less complex than that of the low NOx absorber favored by EPA.
Cummins' Charlton was most vociferous in his concerns about SCR technology. He pointed out that the Europeans have to deal with a less stringent NOx level, and that fuel is far more expensive there. Technologies that save fuel have more chance, and the cost of the urea is about a quarter of the diesel fuel it replaces. In the United States the costs would be a wash.
But for some of us there, it seems a no-brainer: One set of technologies has a payback — albeit slower here than in Europe — the other is all cost, cost, cost. Which one would you back for 2007?
