Clearing the air: Filtering diesel

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Photo 1. The DPF selected was the 180-lb, DPX Catalytic Soot Filter, designed by Engelhard and built by Fleetguard.

Illustration 1. A DPF forces exhaust gas through semiporous material, where soot is trapped.

Photo 2. As the DPF-retrofitted vehicle operates, a catalyst and exhaust heat burn the particulates into a fine ash.

Photos 3 & 4. To ensure engine protection, de-rate devices – both in-dash and add-on – were used to alert drivers and reduce power output when backpressure exceeded a predetermined threshold.

Photos 3 & 4. To ensure engine protection, de-rate devices – both in-dash and add-on – were used to alert drivers and reduce power output when backpressure exceeded a predetermined threshold.

Photo 5. DPF internal substrate laden with ash before cleaning.

Photo 6. Cleaning starts with donning latex gloves and respirators, and loosening clamps and brackets.

Photo 7. The 100-lb filter section is removed, and air is forced, backward and forward, through it. The ash is collected in a bag and stored in 55-gallon drums for proper disposal.

Editor’s note: This is the first in a series of articles on what to expect from 2007 engines in terms of maintenance, component durability, fuel economy and overall cost. In future installments, we will hear from engine manufacturers, truck manufacturers, particulate filter manufacturers and, where possible, end users.

Two and a half years ago, Unified Western Grocers (UWG) of Commerce, Calif., took a drive into the future. The fleet volunteered to retrofit many of its vehicles with diesel particulate filters (DPFs) – much like the ones that will be standard on all new, heavy-duty trucks in the United States in 2007. The DPFs will be necessary to meet ultra-stringent limits on particulate-matter (PM) emissions that will take effect that year.

The fleet received a grant from the California Air Resources Board (CARB) as part of the board’s Diesel Risk Reduction Plan, which seeks to reduce diesel emissions from new and existing vehicles. It then trained all concerned personnel in DPF operation and maintenance, and retrofitted 138 of its heavy-duty, on-road trucks in the fall of 2002. The trucks have been in service since.

UWG is a retailer-owned, wholesale grocery cooperative that supplies independent retailers in nine western states and several countries in the South Pacific. It operates nine distribution and manufacturing facilities throughout California and Oregon – three distribution and two manufacturing facilities in the Los Angeles area, and distribution facilities in Fresno, Stockton and Hayward, Calif., and in Portland, Ore.

Why did the fleet take on such a project? Well, certainly, pre- ’07 experience will prove valuable once DPFs are required. But perhaps more importantly, “We wanted to be proactive,” says Patrick Guillermety, UWG’s environmental health & safety specialist. “We’re a co-op. We want our members and community to know that we care about them and the environment.”

The equipment
Vehicles chosen for retrofit were powered by post-’95, but pre-’02, Detroit Diesel Series 60 and Cummins ISM engines. That means, of course, that the engines did not incorporate exhaust gas recirculation technology, so performance with 2007 engines could vary. The DPF selected was the 180-lb, DPX Catalytic Soot Filter, designed by Engelhard and built by Fleetguard (see Photo 1, above). The DPX was verified by CARB to reduce total PM by at least 85 percent, at a cost of $6,500 to $10,000 per unit.

A DPF works by forcing exhaust gas to flow through semiporous material, where soot is trapped (see Illustration 1, above). As the vehicle operates, a catalyst and exhaust heat burn the particulates into a fine ash (see Photo 2, right).

It should be noted, however, that in ’07, in applications where exhaust heat is not sufficient to burn off PM, additional fuel may be introduced into the DPF to raise the temperature.

The remaining ash accumulates in the DPF, and can cause exhaust backpressure to increase gradually. Since that can reduce power and fuel economy, and eventually damage an engine – and because the grant required it – backpressure had to be monitored by means of sensors in the retrofit vehicles. And to ensure engine protection, de-rate devices – both in-dash and add-on – were used to alert drivers and reduce power output when backpressure exceeded a predetermined threshold (see Photos 3 & 4, on page 72).

However, “We incorporated a time delay,” says Guillermety, “so a driver can be warned and safely get out of any situation he may be in before the de-rate occurs.”

To prevent damage to the DPF, ultra-low-sulfur fuel (15 parts per million) must be used. Fortunately, it’s available in California, but for longer runs, UWG had some trucks fitted with an extra 110-gallon fuel tank to avoid having to refuel with standard diesel on the road.

The maintenance
Eventually, the ash in a DPF must be cleaned out to keep backpressure low. Photo 5 (below) shows the internal substrate laden with ash before cleaning. UWG chose a 60,000-mile interval for the cleaning procedure, but “We inspect sensors, monitors, brackets and clamps at 30,000 miles,” says Guillermety. UWG selected 60,000 miles as the interval to coincide with other maintenance schedules, but required minimum intervals should be much longer. And some manufacturers predict that DPFs could run as long as 400,000 miles without cleaning.

Cleaning involves donning latex gloves and respirators, loosening clamps and brackets (see Photo 6, page 74), removing the 100-lb filter section (see Photo 7, page 74), and forcing air, backward and forward, through it. “We had a cleaning machine custom-built by Dinex, a European company, for that purpose,” Guillermety reports. Once DPFs are used widely, dealers and independent shops can be expected to offer DPF cleaning services.

Unfortunately, CCJ can’t publish pictures of the $20,000 machine since it’s patent-pending, but it consists of an enclosed cabinet, with hepa filters, a strong vacuum at one end, and a provision for 125-psi air pressure at the other. The unit cleans in one direction, then flips the DPF and cleans in the other. In UWG’s case, there’s also a hand wand for sucking up any residual ash.

A shaker causes the ash to fall into an enclosed bucket lined with a bag. The bucket is removed, and the bag is tied off and stored in a 55-gallon drum for disposal. “In California, the ash is removed from the filters and handled as California regulated waste, mainly because of materials found in today’s engine oils,” says Guillermety. That, of course, could change once DPF-friendly, PC-10 oils become available. For now, “The waste ash is sent out for incineration.”

Removal of the filter section reportedly takes about 20 minutes, and the entire cleaning operation, including reinstallation, takes about an hour and a half. But there are other maintenance and operating concerns. For one, DPF mounting bracket and clamp breakage has been a problem because of vibration, the unit’s weight and less-than-ideal mounting. “In some cases, we’ve added supports and brackets – it’s a safety issue,” says Guillermety. But such spare parts can be difficult, if not impossible, to come by, and sometimes have to be custom-made.

Another unexpected issue causing engine de-rate was radio-frequency interference from CB radio operation. The fix was to ensure that CBs and antennas all were grounded.

The payoff
“I’ve got to say the filters work beautifully,” says Guillermety. “There’s virtually no particulate emission.” He’s even found rust inside trucks’ exhaust pipes – something that doesn’t happen when they’re lined with diesel soot. The project has removed 4.8 tons of particulate matter from the air.

But is it worth the effort and expense? “I like what we’re doing,” answers Guillermety. “I even tried the ‘white-glove’ test on the exhaust. It came away clean. I feel like we’re doing something good for future generations.”

St. Louis gets first EPA grant in vocational retrofit program

Chris Amos, commissioner of equipment services for the City of St. Louis, thinks the diesel engines in his refuse trucks are ideal candidates for retrofitting exhaust-emissions-reducing technology. “They hardly ever get up to speed; they usually go 20 feet and have to stop; they have high idle at compaction; and they’re operating in residential areas,” he says. “They’re right up there with transit buses as far as polluters go.”

That reasoning may be behind a recent $124,952 U.S. Environmental Protection Agency (EPA) grant that will allow the city to retrofit 44 of its more than 90 refuse trucks. The EPA doled out $1.6 million in grants in February to 18 municipality emission projects – ranging from construction vehicles in Denver to fire engines in Baltimore. Many of the grants are focusing on the two emission solutions St. Louis will use: diesel oxidation catalysts and crankcase filters.

The retrofits won’t affect the engine as much as ancillary systems, like exhaust. Amos says his department will replace mufflers on the waste-hauling trucks with new ones that incorporate catalytic converters. He expects the diesel oxidation catalyst to turn up to 90 percent of unburned hydrocarbons and carbon monoxide and as much as 50 percent of particulate matter (PM) into H20 and C02.

The crankcase emissions control system will collect oil vapor and PM, using a filter system comprising a housing, pressure regulator, pressure relief valve and an oil check valve. According to the grant, such a system virtually could eliminate those substances, which account for 10 to 25 percent of total diesel engine emissions. But, unlike the catalytic converter, the unit will need periodic filter replacement.

The catalytic converters and crankcase system will cost about $1,700 per truck and take about four man-hours to install, Amos estimates.

The grants are part of EPA’s Clean Diesel Campaign, which combines regulatory and voluntary efforts to reduce diesel engine emissions through retrofits, cleaner fuels, reduced idling and other pollution-cutting measures. For more information on the retrofit program, visit this site.

The City of St. Louis had considered importing lower-sulfur diesel as part of the grant, Amos says, but was unable to justify the expense. When that fuel becomes more available, he expects emissions from the trucks, which run 40 hours a week in residential areas, will fall further.
-Sean Kelley