Cdt, Psa/Rhodia Data Show Epa Misunderstood Pm Trap/Additive Combo Effectiveness

Diesel Fuel News, Jan 22, 2001 by Jack Peckham

U.S. EPA's "response to comments" document explaining its now-final diesel emissions control rule (see related story, above) mistakenly under-rates the particulate matter (PM) reduction efficiency of PM filters using metallic additives for soot regeneration.

In fact, the PM filters virtually eliminate the solid portion of PM, just like the PM trapping efficiency of other systems using catalyzed filters for NO to [NO.sub.2] oxidation for soot reduction. Some "volatile" PM (fuel/lube-borne sulfate and some hydrocarbon) can slip by PM traps but this small amount becomes even smaller with ultra-low sulfur fuel (see Diesel Fuel News 3/20/2000, p6).

PSA/Peugeot Citroen reported in an SAE paper last year (SAE 2000-01-0473) that its filter/additive combo, using the cerium additive system developed by Rhodia, achieves nearly 100% reduction of solid PM (both mass and number), with the result that post-filter PM emissions are virtually indistinguishable from ambient air PM (see Diesel Fuel News 3/20/2000, PS).

That SAE paper shows PSA achieved a 65% engine-out reduction in PM mass with its new common-rail-equipped engine, plus a further reduction with the PM filter, to near-zero solid PM emission. These results were further confirmed in tests at Germany's ADAC Motorwelt automobile club supervised by Germany's UBA (equivalent to U.S. EPA), in an article reported in Der Spiegal last year.

(Note: Quotation that follows is a German-to-English translation of the ADAC findings, courtesy of Rhodia).

"In standardized tests, the Peugeot emitted only 0.000239 grams of soot per kilometer, far less than 1% of the mass of PM emitted by a (non-filter-equippped) Mercedes. The number of ultra-fine PM (under 300 nanometers), which is also a concern for public health, was itself 6,000 times lower than those emitted by the Mercedes," the ADAC report found.

However, in EPA's new diesel rule "response to comments document," EPA mistakenly says that the PSA system only captures 60% of PM -- just the engine-out PM level. Then EPA compounds its error by unfavorably comparing this 60% result to the much higher (over 90%) PM trapping efficiency of catalyzed PM traps such as Johnson-Matthey's "CRT."

Similarly, EPA seems to have misunderstood the PM soot regeneration balance point test results of Clean Diesel Technology (CDT) platinum/cerium bimetallic additive used for PM trap regeneration, as explained in CDT's two most recent SAE papers (SAE 1999-01-0113 and 2000-01-1934).

These data show a PM trap balance point (where soot accumulation roughly equals soot oxidation) of 300[degrees]C rather than the 450[degrees]C temperature cited by EPA.

"Our data show balance point temperatures of 300[degrees]C using either uncatalyzed or lightly precatalyzed filters on a 350 ppm sulfur fuel, which we expect to be in the 280[degrees]C range on 15 ppm sulfur fuel," CDT's chief operating officer Jim Valentine explains.

The SAE papers include data from engine dyno tests as well as a four-week field evaluation (in cooperation with Cummins) on a 5.9 liter engine on a pickup truck.

* Over 200 Vehicles Tested

"We also reported on over 200 vehicles in Europe and Asia using the fuel-borne catalyst (FBC)/filter system and noted tests that showed that the FBC dropped the balance point for catalyzed filters by 50-70[degrees]C below what the catalyzed filter alone achieved," CDT's Valentine told us.

Similarly, CDT reported 96% PM reduction results from Southwest Research Institute tests on a modern heavy-duty diesel engine with EGR for NOx control (see Diesel Fuel News 1/10/2000, pl), even with ordinary, 368 ppm sulfur diesel fuel. This system actually out-performed the PM reduction of catalyzed PM traps.

"CDT believes that its lower use of precious metals, at 5-8 grams of platinum per year, per heavy-duty vehicle, will provide significant cost advantages versus highly catalyzed systems using as much as 45-90 grams of platinum on the filter surface or on upstream NO oxidation catalysts," he said.

"We'll be presenting a paper at SAE World Congress in March, 2001, with data showing the ability to achieve 0.01 grams/brake horsepower-hour PM [the EPA 2007 heavy-duty diesel limit] with both lightly catalyzed and uncatalyzed filters using 50 ppm sulfur CARB diesel and the FBC. We believe that performance should be marginally better when we get 15-20 pm sulfur fuel."

Thus, a platinum additive-assisted PM filter could (for about 5-1/2 to 9 years) use less total lifetime platinum than a pre-catalyzed (45 grams) PM filter -- assuming a pre-catalyzed filter would last that long, CDT contends. Given high annual mileage accumulation by many highway diesel vehicles, 9 years could well exceed the EPA-mandated 435,000 miles "useful life" requirement for PM/NOx catalysts/filters. Still, it's conceivable that PM traps could last far longer than 435,000 miles, with proper periodic cleaning/maintenance.

"We still believe that the FBC approach used with a lightly catalyzed filter will allow for lower cost and easy replacement of filter cartridges for under $1,000 on a three- or four-year maintenance interval, if required," Valentine said.