Cermet Filter Reduces Pm, No, Hc, Co Nearly 100% In Tests

Diesel Fuel News, Oct 15, 2001 by Jack Peckham

Portsmouth, Va. -- A novel intermetallic/ceramic-powder "cermet" filter can achieve near-100% reduction of the four key diesel criteria emissions -- without requiring any separate reductant -- according to laboratory results at Idaho National Engineering & Environmental Laboratory (INEEL), one of the U.S. Department of Energy national laboratories.

The key requirement for the near-total destruction of nitrogen oxides (NOx), particulate matter (PM), hydrocarbon (HC) and carbon monoxide (CO) is periodic boosting or continuous heating of filter temperature to around 800[degrees]C. This could be achieved partly via close coupling to exhaust manifold, along with engine/combustion controls.

Alternatively, the filter system could tap supplemental electric heat, perhaps provided by alternator power or through new turbo compounding devices that are seen likely to debut in commercial diesel markets soon.

Total estimated fuel/energy penalty over a typical duty cycle hasn't yet been determined, as R&D is still in the early stages. But INEEL believes that based on tests to date, energy penalty isn't likely to be a show-stopper.

The net-shaped cermet filter is formed via a single-step combustion synthesis process, and could easily be configured for typical diesel exhaust pipes, INEEL researcher Peter Kong reported at DOE's Diesel Engine Emissions Reduction workshop here. Making such a filter only requires "very low cost materials," he said.

The filter material has a suitably high melting temperature ([greater than]1,500[degrees]C), high heat capacity, high particulate filtration efficiency, self cleaning capability, compatibility for electrode incorporation (for direct electric heating), and the sort of thermal shock resistance required for a commercial diesel application, he said.

Remarkably, the cermet material can (when activated by engine exhaust) generate its own NOx reductants: ammonia and light hydrocarbons, as well as partial oxidation products from carbon particulate matter.

It's possible to develop a closed-loop system employing a NOx sensor that could modulate ammonia output and light hydrocarbon gases through an exhaust slipstream cermet filter cartridge unit -- upstream of the main cermet filter -- in order to avoid possible ammonia slip, Kong explained to us in an interview.

A close-coupled cermet filter would require only about 8-10 amps of power for continuous heating during regeneration cycles, he said.

Due to the cermet filter's composition, INEEL believes the fuel/lubes-borne sulfur poisoning problem typical of today's commercial NOx traps shouldn't present a problem, although this contention would require thorough testing in subsequent R&D.

In research so far, INEEL also has found what looks like a practical single-step process to bum-in heating elements that would carry electric power for supplemental heating. These elements however also would need thorough testing to ensure stability and compliance with U.S. EPA's 435,000 miles minimum durability requirements for 2007 heavy-duty highway diesel emissions limits.

INEEL is about to file a patent application on the Cermet filter, and meantime is searching for an industrial partner for commercial development.

Idaho National Engineering and Environmental Laboratory

CERMET DESTRUCTION OF NITRIC OXIDE TEST

Test condition: 5% NO  1.67% [C.sub.2][H.sub.4]   93.33%
He % NO conversion to [N.sub.2] under reducing atmosphere


Temperature [degrees]C  Sample 1  Sample 2  Sample 3

         300              0          0         0
         400              0         2.5        0
         475              0         2.6        2
         550              0         4.7        2
         623              3.8       13.3       2
         696              11.3      43.1       3
         797              38.7      98.3       7
         904                        100