Paul Richards is editor of Commercial Carrier Journal. E-mail firstname.lastname@example.org or call (610) 993-9430.
Before his recent retirement from the American Trucking Associations, then-Vice President of Engineering Larry Strawhorn warned members that although the industry is currently preoccupied with ’02 engines, it should look up, “because 2007 is coming like a freight train.”
The changes dictated by the Environmental Protection Agency for 2007, with full implementation by 2010, are staggering. While ’02 emissions regs cut oxides of nitrogen (NOx) emissions in half (from 4 g/hp-hr to 2), particulate matter (PM) emissions were allowed to stay at .1 g/hp-hr, where they had been since 1994. But when 2007 regs come thundering through, they will require a tenfold reduction in both NOx and PM – to .2 g/hp-hr and .01 g/hp-hr, respectively. And since traditional methods of lowering NOx tend to raise PM, and vice versa, some extreme technology will be needed.
While most engine makers aren’t saying much yet, it looks like, in addition to EGR or Caterpillar’s Advanced Combustion Emissions Reduction Technology (ACERT), trucks will need PM traps and NOx adsorbers to meet the new standards. A NOx adsorber collects the offending pollutant on the outside of its internal element (as opposed to an absorber), then “the system goes through a rich cycle to convert it [to less harmful substances],” explains Patrick Charbonneau, vice president and chief technical officer, International Engine Group, International Truck & Engine Corp.
Particulate traps, which resemble mufflers, extract approximately 90 percent of exhaust soot via a ceramic or metallic filter that’s continuously or periodically purged and regenerated.
Regeneration involves incinerating the soot, using the equivalent of an internal toaster or a fuel-fired burner (active), or by relying solely on exhaust heat (passive). “We’re working with active regeneration,” reveals Charbonneau.
One maintenance issue is that non-combustible ash may accumulate within a trap and require periodic removal, but “it remains to be seen how often that’ll be necessary,” says Charbonneau.
While traps will involve additional cost and complexity, it’s probable that they will prove viable. According to Amy Davis, Cummins’ director, communications, strategy and industry relations, the company is, indeed, “considering cooled EGR enhancements, and NOx and particulate aftertreatment for our 2007 solution.”
An alternative to NOx adsorbers and, in some cases, traps, is selective catalytic reduction (SCR). More likely to be used in Europe than in the United States, SCR uses ammonia provided by introducing a urea/water mixture from a vehicle-mounted tank into the exhaust, upstream of a catalyst.
SCR systems reportedly can reduce NOx by 70 to 90 percent, while allowing for an engine calibration with 15 percent better fuel economy and good levels of power and torque. However, there are concerns, such as additional tanks, frequent replenishing of urea, and the urea/water mixture freezing.
Another part of the equation for ’07 is that more expensive, ultra-low-sulfur fuel – 15 parts per million (ppm), down from the current 500 ppm – will be needed, since even relatively small amounts of sulfur add PM to exhaust emissions and will poison aftertreatment devices.
As these technologies are being developed, it’s agreed that ’07 emissions levels are attainable, but there will be higher purchase prices, more weight, more onboard space required, possible additives and increased maintenance.
“We can see people coming to us and asking, ‘Do you have any more ’02 engines left?'” jokes Steve Ginter, marketing vocational product manager for Mack Trucks. “Seriously, we know we can meet the numbers, and we’re close to settling on a group of technologies that we think will do the job, while keeping customers happy.”
“The standards can be met,” agrees International’s Charbonneau. “And in the process, fuel systems will evolve, and there will be further improvements in boost control and combustion.
“Everyone’s involved,” he concludes. “This is an industrywide challenge, and it’s moving in a positive direction.”