Award-winning invention could expand diesel filters

Diesel Fuel News, Feb 17, 2003 by Jack Peckham

Many diesel fleets around the world run older, "high-emitter" engines that aren't suited for retrofits with catalyzed diesel particulate filters (DPFs), or they may have nothing but high-sulfur fuel and thus can't use catalyzed filters.

Still other fleets might have relatively newer, cleaner engines and even low-sulfur fuel, but the economic incentives might not be big enough to cover the costs of installing today's DPF systems. More: The cost of replacing an old engine with a new "clean" engine might be cost-prohibitive for some fleets.

Still other fleets might consider installing a relatively cheap, uncatalyzed DPF, then use an off-board regeneration system (such as electric heating). But this might require a high-voltage line, or a special oven, or might seem a bit too complicated or complex for some fleets.

But a new, simple invention -- selected by United Kingdom's National Endowment for Science, Technology & the Arts (NESTA) for a competitive R&D award -- could help many such fleets take a huge bite out of diesel PM emissions, at an estimated one-quarter the cost of catalyzed DPFs.

The so-called Diesel Emission Reduction Technology (DERT) employs ordinary cloth fibers such as cotton, linen or jute, in a series of five to seven corrugated "cassettes" stuffed inside a steel sleeve that would be attached to the end of the exhaust tailpipe.

Rather than oxidizing soot as with typical DPFs, this system merely collects the soot for periodic disposal at a central recycling site. The filters could be easily removed, washed and re-used several times, with the water/soot waste product perhaps mixed with boiler fuel for burning, or with asphalt for road-paving.

As compared to the rather complex ash-removal/servicing intervals for conventional catalyzed DPFs, these "DERT" cassettes could be easily removed and swapped-out with fresh filters on a weekly or monthly basis, depending upon engine PM emission rate and vehicle mileage.

Tests on an engine dynamometer show that the cloth-based DPF does a good job of PM capture (65% with just one cassette, higher with multiple cassettes) and can withstand the relatively low end-of-pipe exhaust temperatures. A remaining engineering challenge is to develop a sealing material that's more resistant to oxidation than the cotton fiber, explains DERT inventor Julian Hasinski of UK-based Aerotech Engineering.

The company has paid for patent extension to the U.S "and the patent is centered on the maintenance of a useable temperature range," Hasinski told us.

The device has an estimated installation cost of 500 pounds-sterling (about U.S. $820) and the filter itself has a manufacturing cost of about (U.S.)$8-13.

Relatively newer vehicles with low engine-out PM emission probably would require changing the leading filter cassette monthly, whereas older, "dirtier" engines could require lead-filter swap-out weekly, Hasinski estimates. Washed filters are expected to be recycled about 10 times. So, filter replacement cost might be as little as $l00-$150/year -- or perhaps double that when including a retail mark-up. At the high-end (more frequent cassette replacements), annual maintenance cost might be around $600/year.

While all DPFs have an impact on backpressure to the engine, the key is to avoid excessive backpressure.

The DERT device is designed as an "expansion chamber" to avoid such backpressure, and daily or weekly filter inspections would check soot-build-up impact on backpressure.

The U.K. already offers tax breaks for clean-diesel retrofit technologies including DPFs, so the DERT system cost would be more than offset after one year, Hasinski says.

Fleets in other parts of the world -- where clean-diesel retrofit tax breaks might not exist -- could find the DERT technology a far cheaper alternative than, for example, government-mandated conversions to "clean" technologies such as compressed natural gas (CNG) or LP Gas. It's also a lot cheaper than the capital cost of catalyzed DPFs -- especially important to fleet operators in "developing countries" where money is especially hard to come by.

Aerotech now hopes to take the DERT device to field trials with a diesel taxi, to prove durability, efficiency and serviceability. City-vehicle fleets -- both light and heavy-duty -- are the logical target markets initially, because of the government tax incentives, he says.

Concurrently, Aerotech is starting to initiate talks with potential licensees, and "I'm quite open to investment suggestions," Hasinski told us.