Enough time seen before critical NOx/PM system tech decision; fuel economy the real 2010 challenge

Diesel Fuel News, March 18, 2002 by Jack Peckham

Detroit -- While time is running out for diesel emissions control developers to make a technology choice for U.S. EPA highway heavy-duty 2007-2010 emissions limits, there's still a strong chance that an optimal solution will emerge on time, according to a leading diesel emissions technology analyst.

The battle mostly boils down to a choice between the nitrogen oxides (NOx) trap combined with a particulate matter (PM) filter, versus urea-selective catalytic reduction (SCR) probably combined with a PM filter. U.S. EPA clearly favors the combined PM/NOx trap, medium-duty truck maker International does too, and so do the truckers who will be the major end-users of the technology.

But unlike the NOx trap, urea-SCR is rather more proven for heavy-duty diesels, so SCR wouldn't have much difficulty at least to meet the 2007 average NOx limits of 1.1 grams/brake horsepower-hour, if not the final 0.2 g/bhp-hrNOx limits in 2010.

Meantime, the ultra-low-sulfur diesel (ULSD) fuel required to make any of these technologies work will probably emerge on time, even though refiners are battling EPA over the ULSD mandates in U.S. Appeals Court (see Diesel Fuel News 3/4/2002, p1).

A court decision is likely this summer, probably removing a key uncertainty that might otherwise stall refiner investment for timely engineering/construction of ULSD production units. Meantime, U.S. EPA is likely to reaffirm its 2006/7 highway diesel rules and deadlines following what should be a routine Federal Advisory Committee Act (FACA) technology review this summer.

On a related front, the agency promises to publish a proposed rule on non-road diesel by year-end, possibly removing a critical uncertainty for refiners trying to plan reactor sizes and investments for total ULSD production over the next 10 to 15 years.

* Pessimism Unwarranted Even though the SCR-versus NOx/PM trap decision has yet to be made, much of today's pessimism and skepticism about meeting future U.S. clean-diesel limits isn't warranted, as Tim Johnson, Corning Inc.'s manager of emerging technologies & regulations, told Diesel Fuel News in an interview here.

For the third straight year, Johnson kicked-off the Society of Automotive Engineers World Congress diesel emissions control sessions here (see SAE 2002-01-0285), while also helping to organize related sessions.

Johnson's annual "Diesel Emissions Control In Review" SAE papers summarize scientific/engineering highlights from scores of technical papers from diesel researchers around the globe. This annual emissions-control tour-de-force culminates his 15-years (and counting) career at Corning, the company that invented the ceramic honeycomb substrate used on hundreds of millions of vehicle exhaust catalysts worldwide.

Besides taking a leading role on diesel panels at SAE, Johnson is an active member of U.S. EPA's mobile source tech review subcommittee (MSTRS), probably the premier advisory body to EPA officials charged with developing ultra-clean diesel regulations hitting both highway and non-road sectors this decade.

He's also chair of the Manufacturers of Emission Control Association (MECA) diesel committee, and probably attends more diesel emissions conferences in various parts of the world than many or most of his colleagues.

So, Johnson has a perspective on diesel emissions control R&D trends that probably few can match. This probably makes predicting the future a little easier, assuming that past is precedent.

"If I had said two years ago that engine out emissions would touch the corner of Euro-4 limits for 2005, I would have been laughed out of this conference," Johnson said.

Yet only last month at a heavy-duty vehicles conference, technology developer Ricardo revealed that recent R&D shows this is quite possible, thanks to evolutionary breakthroughs on engine controls for NOx/PM tradeoffs, Johnson points out. This follows similar conclusions reached at other major engineering centers, he said.

"So when you see predictions for 2007 [EPA target limits], understand that engine-out is getting 10% better year-on-year," and this will greatly aid future exhaust aftertreatment.

As a result, "I believe that 80% efficiency for exhaust emission control will be required for NOx limits for 2010. That's my bet -- they can hit the 2010 target, but the question will become: At what fuel penalty?"

Meantime, "no one could say to me today with a straight face that you can't get 85% efficiency from a PM filter in 2007, or that SCR can't get 50% NOx reduction in 2007. These are in the bag, with lean NOx traps coming up very fast."

One possible scenario: Engine makers could let the PM filter take over the bulk of the engine-out emissions clean-up job, allowing a shift of NOx/PM curve strategies for higher engine-out PM and low NOx, but at some fuel penalty. "For 2010, the biggest challenge is fuel economy, not the PM/NOx limits. So, the big motivator for technology development is for fuel economy," he says.

Another factor: Engine makers are likely to boost R&D spending to try to defend fuel economy while minimizing engine-out emissions, then let whatever evolves as the lowest-cost aftertreatment system handle whatever's left.