Cummins’ initial heavy-duty emissions strategy for 2010 was to rely solely on exhaust gas recirculation (EGR). Based on data on new aftertreatment materials, however, the engine maker said last month that it would add selective catalytic reduction (SCR) in a bid to improve fuel economy.
By Avery Vise and Jack Roberts
Diesel engine manufacturers had been gearing up for a fight over 2010 engine emissions technology for North America. On one side were proprietary engine makers Detroit Diesel, Volvo, Mack and newcomer Paccar, which planned to use selective catalytic reduction (SCR) – an exhaust aftertreatment that uses a urea-based liquid to neutralize oxides of nitrogen.
On the other side were big bore engine newcomer Navistar, with its proprietary MaxxForce engine, and Cummins – the largest on-highway heavy-duty engine supplier in North America. Cummins and Navistar would rely on high-pressure fuel injection systems and enhancements to exhaust gas recirculation (EGR) technology, avoiding the need for aftertreatment hardware or the purchase of diesel emissions fluid (DEF).
The only wild-card question was answered in June when Caterpillar announced that it would forego a 2010 heavy-duty on-highway engine and instead focus its resources on off-highway engines in North America, on- and off-highway engines elsewhere in the world and a planned venture to market a Cat-branded severe service truck built by Navistar. (See “Cat’s out of the bag,” CCJ, July 2008.) Cat’s decision, coupled with Freightliner’s announced plans to add Cummins in heavy-duty trucks, means Cummins is the lone non-captive heavy-duty engine supplier to on-highway truck owners. And everyone other than Mack and International would offer both SCR and EGR-only solutions.
So everything was settled – until Aug. 13. That was the day that Cummins changed the dynamics substantially by abruptly announcing that it now would add SCR to its engine offering. Any lingering doubts regarding SCR apparently vanished in an instant. As of now, Navistar – probably the most vocal manufacturer pushing a non-SCR approach – stands alone in pursuing an EGR-only emissions solution for 2010.
Fuel for thought
SCR supporters have been touting fuel economy benefits of their approach. By using an aftertreatment to transform NOx in exhaust into nitrogen and water vapor, the engine itself can be allowed to run more efficiently, they noted. Of course, purchasing and managing DEF as well as maintaining the aftertreatment device itself were factors to consider. But as the price of diesel fuel neared $5 a gallon and remains in the $4 range, the fuel economy improvements began to look more attractive.
In its announcement, Cummins conceded that SCR allowed for fuel economy improvements. Cummins Emission Solutions, a provider of SCR systems, will supply integrated exhaust aftertreatment systems for Cummins heavy-duty and midrange engines. (Cummins already had planned to use SCR in medium-duty trucks.)
Cummins said it changed its mind based on data establishing the superiority of new copper zeolite emissions technology compared to conventional iron zeolite technology commonly used in SCR particulate filters. Zeolites are, in essence, materials that act as molecular filtration systems. Copper zeolite technology emerged about two years ago as engineers sought more efficient exhaust gas filtration systems and became available for automotive applications late last year.
Copper zeolite-based SCR systems will offer improved heat rejection, lighter weight and improved fuel economy over EGR-only engines and SCR systems based on iron zeolite, Cummins says.
“Cummins’ decision to move rapidly to integrate this technology into our engine platforms – including midrange and heavy-duty offerings – highlights our agility and capability to respond to market demands and our commitment to meet customer demands,” said Ed Pence, vice president and general manager of Cummins’ heavy-duty engine business.
Navistar stays the course
Navistar still plans an EGR-only solution for its MaxxForce big bore engines, says Stephen Gilligan, assistant general manager for the Heavy Vehicle Center. “We can get to a non-SCR solution.” Moreover, Navistar’s own testing to date has shown that the fuel economy benefit of SCR over Navistar’s EGR solution amounts to only about 1 to 2 percent – a level that could be offset by the cost and management of urea, the additional cost of SCR components, and through other fuel-saving options – not the 6 percent to 7 percent others are touting on their own engines, he says. Navistar is continuing to work with Cummins to ensure “we offer an EGR solution on all International trucks,” Gilligan says.
For all other truck makers, though, it’s SCR all the way – at least until the next surprise announcement.
Focus turns to urea supply
Stakeholder workshop addresses key issues
Executives of major companies involved in making selective catalytic reduction (SCR) technology work – truck and engine makers, truck stops and diesel exhaust fluid (DEF) makers – last month met in a daylong workshop aimed at ensuring that there will be a supply of urea-based DEF once heavy-duty trucks relying on the technology roll out in 2010. The workshop was held by the North American SCR Stakeholder Group in conjunction with the U.S. Department of Energy’s Diesel Engine-Efficiency and Emissions Research (DEER) Conference. The participants identified the needs and next steps toward building a tailored distribution network for supplying DEF.
More than 500,000 heavy-duty trucks in Europe use SCR to neutralize oxides of nitrogen (NOx). Small quantities of DEF injected into the exhaust stream convert NOx into nitrogen – the air’s most abundant element – and water.
For Class 8 over-the-road trucks, estimates are that truck operators will need to refill DEF tanks every other fuel fill – basically every 2,000 to 4,000 miles, depending on load weights and applications. Creating the distribution network for urea is a major goal of the North American SCR Stakeholder Group, which includes the U.S. Department of Energy, the U.S. Environmental Protection Agency, automotive and heavy-duty engine and truck manufacturers and trade associations, fuel retailers and truck stop trade associations, chemical and oil companies, and DEF producers, distributors and dispensing equipment manufacturers.
At the August workshop, discussion centered on topics specific to Class 8 truck needs, including:
Standardization of equipment, packaging, storage, handling, placement, size and labeling;
Regulations to addressing information needs;
The scale, flexibility and time horizons needed to ramp up DEF availability; and
The awareness campaign needed for the public, industry sectors, fleets, owner-operators and drivers.
More than 60 representatives from various companies across the industry sectors participated in the infrastructure workshop.