3M(TM) Diesel Particulate Filter Systems
23 February 1998
3M(TM) Diesel Particulate Filter Systems Make the Grade In International Trials, Offer Simple, Cost-Effective Solutions
ST. PAUL, Minn., Feb. 23 -- Anyone who has ever driven behind
an older model diesel-powered truck or bus is aware that these vehicles can
create a serious cloud of noxious smoke. While diesels produced within the
past decade or so are 90 percent cleaner than previous designs, the problem of
how to cost-effectively upgrade aging diesels has remained a challenge,
particularly in economically depressed areas around the world.
3M is currently addressing diesel particulate filtration with a new line
of self-cleaning 3M(TM) Diesel Particulate Filters. According to Rich Daykin,
market development manager for 3M's Diesel Filtration Project in St. Paul, the
filter technology is proving extremely effective in tests conducted in Europe
and the U.S. "Systems containing our particulate filter cartridges are
already certified by the Romanian government for use on city buses. Field
trials have proven the 3M filters can reduce smoke levels by more than
70 percent on some of the world's oldest and smokiest diesel buses," Daykin
said. Working in conjunction with an inexpensive fuel-borne catalyst, the
filters have performed well for over 110,000 miles so far. Field testing of
3M diesel filters has also been launched on buses in Turkey, Korea and Costa
Rica.
In the United States 3M diesel filter evaluations have been performed for
over a year on a heavy-duty highway diesel tractor. This test, presenting a
duty cycle which is significantly different than the bus trials, uses 3M
filter cartridges in a specially designed canister which replaces the standard
muffler. Results to date show dramatic reduction of diesel smoke and
consistent filter performance over time.
3M's particulate filter cartridges use the company's unique Nextel(TM)
Ceramic Fibers. Made from alumina, silica and boria, the metal oxide strands
are expanded to expose individual fiber filaments. The resulting structure
traps particles throughout its cross section, so the effect of particle
loading on exhaust back pressure is reduced significantly. Ceramic fiber is
especially well suited for particulate filtering because it can withstand very
high temperature and resists thermal and mechanical shock.
The basic 3M particulate filter cartridge consists of Nextel yarn wound
around a perforated metal support tube in a diamond pattern that maximizes the
capture of particles as small as 0.1 micron (0.000004 inches). Several
cartridges are generally mounted inside a single canister so that exhaust
gases are forced to pass through the walls of the filter media. Cartridges of
varying diameters also may be arranged concentrically and separated by annular
rings that block the space between each support tube on alternate ends.
Durability is perhaps the primary measure of success for a diesel
particulate filter. Many configurations can trap soot particles. But without
a way to burn off the accumulation periodically, particulate filters would
soon clog and cause unwanted exhaust system back pressure. The trick is to
raise exhaust gas temperatures enough to incinerate the soot but not so high
that oil ash in the exhaust melts onto the filter media. The operating window
is roughly between 400 degrees C and 900 degrees C (750 degrees F and 1,650
degrees F).
Current regulations concerning diesel particulates vary around the world,
but the trend is unmistakable. "Allowable emissions for soot and smoke are
going to go down in the next few years," predicts Daykin. When they do, he
says, 3M will be ready with a particulate filtering system that has proven
itself effective, especially in bringing older diesel vehicles into compliance
simply and effectively.
SOURCE 3M Automotive