Fleets Give Mixed Reviews Of DPF Performance
By Frederick Kiel, Staff Reporter
This story appears in the November/December 2010 issue of Equipment & Maintenance Update, a supplement to the Nov. 8 print edition of Transport Topics. Click here to subscribe today.
Some fleet maintenance managers say they have seen higher-than-expected failure rates from diesel particulate filters that cracked or melted before the first scheduled maintenance cleaning or replacement. Concern about this problem is supported by an executive of the manufacturer of DPF cleaning machines that are used by original equipment makers.
Other fleets, however, are having little trouble with the filters, which is creating a split in the industry over the components’ durability.
Failures that occur out of warranty can get expensive because DPF replacement prices can range from $1,500 to more than $2,000.
“We run both Volvo and Cummins engines and have had failures with DPFs of both, but much more serious ones with Cummins,” Stephen Sabo, maintenance manager of Norrenberns Truck Service, a less-than-truckload carrier based in Nashville, Ill., told Equipment & Maintenance Update.
Sabo also is immediate past chairman of American Trucking Associations’ Technology & Maintenance Council.
“What we’ve seen on the Volvo DPF is that we can get over 400,000 miles of service with it on LTL service, even though the lower part of the exterior of it sometimes breaks off,” Sabo said. “It has nothing to do with the filter inside, though fixing it is still pretty expensive.
“What’s happening with Cummins DPFs is that they’re running too hot,” Sabo explained. “I think there is some kind of seventh injector failure that is pumping too much fuel into the filter, overheating it and breaking it up. Some have been under warranty when this happened and some have not.”
Jim Nichoalds, service manager at Diamond Companies Inc.’s branch in Little Rock, Ark., an International truck dealership based in Memphis, Tenn., said that his technicians have had to deal with DPF failures, mostly from engines manufactured by Cummins Inc. and Caterpillar Inc.
“The main problem we’ve encountered in DPFs is when there is an [exhaust gas recirculation] cooler failure, and the DPF filter gets washed with cooler fluid,” Nichoalds told E&MU. “If that happens, it has to be replaced entirely or baked.”
He said that “with Cummins, you typically don’t have any DPF problems, unless you have an EGR cooler failure.”
He added that his branch serviced the DPFs of several large private fleets based in Arkansas, which operated engines from all manufacturers.
“The cells of the filter can be damaged, even melted, if they get washed during a ‘regen,’ ” Nichoalds said. “If you have an EGR failure while burning soot into ash, that can also damage the DPF.”
“Regen” has become the colloquial, most commonly used term for “regeneration,” the process by which a DPF undergoes an automatic self-cleaning. Regenerations occur until a service maintenance level is reached, usually every 200,000 to 300,000 miles.
Nichoalds said that proper maintenance could prevent DPF failures.
“Since it’s so expensive [to replace a DPF], maintenance is important,” especially for large fleets that typically keep trucks for about three years, Nichoalds said. “With proper maintenance, the original DPF can last as long as the owner has its trucks,” he added.
Some fleets have seen few, if any, DPF problems. David Murdock, director of service operations at TEC Equipment Inc. — a Mack and Volvo dealer with eight locations, based in Portland, Ore.— said that maintenance on DPFs has not been a problem.
“For a Class 8 highway truck, the DPF warranty is for 250,000 miles,” Murdock said. “We’ve had only isolated problems with the so-called seventh injector failing and spraying hot diesel into the DPF, which can ruin it. We don’t often see filters that need cleaning.”
In fact, he’s seen DPFs in tractors with 400,000 to 500,000 miles on them that have never needed cleaning.
“That’s because they’ve been running long distances at full temperature,” Murdock said. “Although DPF cleaning is recommended at 250,000 or 300,000 miles, it isn’t always necessary. When you’re a manufacturer, you have to put a broad brush recommendation, because the consumer wants to know what limits he has to live with.”
UPS Inc., which ranks No. 1 on the Transport Topics 100 list of the largest for-hire carriers in the United States and Canada, has few DPF issues, and does not clean its own DPFs.
“At this time, we have very limited issues with the DPF system,” UPS spokeswoman Elizabeth Rasberry told E&MU.” The few exceptions that we have experienced have been covered under the manufacturer’s warranty. The overall regeneration system has been working satisfactorily. We do not have any [DPF] cleaning machines. We outsource this procedure through an exchange program.”
She added, however, that the company will “continually review this as a maintenance item to determine the cost feasibility.”
Rasberry said that UPS is currently is in the process of removing some components prematurely for analysis for future DPF service intervals.
The U.S. Environmental Protection Agency mandated that by Jan. 1, 2007, all new heavy-duty diesel-powered vehicles had to reduce their emissions of diesel particulates — the 50-cent word for soot — by 90%. To comply, manufacturers began installing DPFs on trucks starting with the 2007 model year. Most DPFs are oblong-shaped and encased in metal containers 18 inches to 2 feet or more in height.
DPFs work by collecting particulate matter from the exhaust gas. Soot is trapped within DPFs as exhaust gas flows into open channels and through the filter wall. By the time emissions leave the DPF, the soot has been left behind, mostly turned into ash, inside the DPF.
OEMs developed new technology not only to trap the much lower levels of soot but also to clean the DPFs of what remained automatically, to keep the trucks on the road.
They developed what came to be called “active” and “passive” regeneration of the DPF.
Passive regeneration occurs automatically when exhaust gases become hot enough when the truck is in operation, usually with sustained highway driving or heavy loads that make the engines work hard. They burn off the accumulated soot and ash. It is a continual process that the driver does not notice.
Active regeneration means that fuel is injected into the exhaust automatically, when soot builds up inside the filter to a designated level. The driver does not initiate the process.
Specialized machines have been developed to clean DPFs, ranging from blasting high-powered air through the filter, to baking the ceramic core of the DPF filter to rid it of built-up soot, ash and other clogging materials.
Navistar Inc. maker of International Trucks and MaxxForce engines, and Paccar Inc., parent company of Kenworth Truck Co. and Peterbilt Motors, as well as builder of its first heavy-duty engine, the Paccar MX, put on the market earlier this year, use machines from FSX Equipment Inc., Granite Falls, Wash., to clean DPFs.
Jeff Sass, general marketing manager of Paccar Parts, a division of Paccar Inc., said it recommends customers take DPFs to cleaners built by FSX.
Most Kenworth and Peterbilt trucks currently use engines from Cummins and Caterpillar, though Caterpillar withdrew from the heavy-duty engine market after the 2009 production year.
“The FSX machine is the machine we found to provide the best results for cleaning our DPFs,” Navistar spokesman Roy Wiley told E&MU. “Other cleaning systems have limitations and do not clean in a manner to provide the best results for our customer.”
Wiley added that Navistar’s parts division has launched a program to market the machine to dealers because, “we need our dealers to purchase this machine.”
Like other DPF cleaning systems, FSX’s includes separate machinery for using high-pressure air to clean out the filters, for checking how effective each stage of the cleaning process has gone to restoring the DPF, and a separate component to “bake” the filter, the core of which is made from a composite ceramic material.
“We clean many of the DPFs, and we started to track any problems rather carefully right from the beginning,” Drew Taylor, FSX national sales manager, told E&MU.
“At FSX, we like to think of the DPF as a sophisticated garbage can consisting of 6,000 tiny garbage cans. And like your garbage can at home, the DPF is intended for reuse over and over again,” he said.
“For this to happen,” Taylor added, “ the collected garbage must be dumped from time to time. In the case of a DPF, it is collected ash that needs to be dumped on a regular basis. Ash that is ignored creates the conditions that cause a variety of DPF problems — such as premature cracking, breaching, glazing and melting.
“Too frequent onboard thermal regenerations are triggered by back pressure caused by growing ash deposits that add unnecessary thermal stress to the DPF. Throw in the occasional EGR or turbo failure that dumps additional flammable fluid onto the DPF and you have a recipe for in-service failure as well as a ruined DPF.
“All 6,000 cells of a DPF must be addressed and thoroughly cleaned . . . to maximize DPF life. At FSX, we recommend proactive servicing of the DPF at or before 150,000 miles,” he said.
Taylor said that a problem FSX has seen is that if a failure occurs inside the engine, it can overload the DPF with soot and other combustible materials.
“Soot and fluids can build up in the filter if problems with the engine overload it with fuel,” he said.
“If a turbo goes out, it releases a lot of fluid such as engine oil and ethylene glycol, which is antifreeze, into the DPF,” Taylor explained. “Or, if you have a leaky [exhaust gas recirculation] system, that would add some fuel into the DPF, and that is a pretty combustible mix.”
He said that a driver could get the engine or turbo problem fixed and return to the road, not thinking about the DPF.
“But if you continue driving and get a normal ‘regen,’ it will turn into what we call a thermal spike that will melt the filter,” Taylor said. “We see that it can happen any time.”
He said the DPF must be taken off and cleaned after any engine event that could possibly deposit inflammable materials into the filter.
Taylor said that FSX experience coincided with projections of OEMs that over-the-road longhaul trucks needed less DPF maintenance than other applications. This is because they run at high speed for sustained periods, giving the active regeneration process plenty of heat to burn off the soot.
“Even over-the-road trucks still get a steady ash buildup,” he added. That is the intended way the DPF technology works, to burn soot and other impurities down to ash before they reach the atmosphere.
“A filter can be presented with problems much sooner than some maintenance schedules, and one reason for that is ash buildup,” Taylor said.
He added that the high-pressure air of FSX and other systems was the only way to clean a DPF.
“Ash doesn’t respond to baking, because it’s composed of about 20 different materials that can’t burn,” he explained.
He explained that the DPF was designed to be “a trap, and it works as designed, trapping anything that comes from upstream and converting them to ash.”
Taylor said that even low-ash lubricants will leave an ash deposit behind when burned.
“The DPF also traps minute pieces of metal from normal engine wear, and also collects waste from engine additives, and all of it is collected in a very predictable way,” he explained.
“It collects on the walls of the cell. It changes the cell very slightly and builds up on the walls of the cell, but when you have an active ‘regen,’ that means the heat runs up against the cooler part covered with ash, and it can cause cracking, and that starts a downward spiral for the DPF,” Taylor added.
He said that this cracking can occur “easily within 150,000 miles.” That is far below the recommended maintenance mileage of all OEMs, which start at 200,000 miles for over-the-road applications.
“The crystalline ceramic substrate of the DPF is brittle and cracking results from repeated thermal events brought on by onboard regeneration when intense heat clashes with cooler ash deposits. The cracks constitute irreversible damage that lead to greater damage requiring replacement of the DPF,” Taylor said.
He said that if the filter is split, even if only by a very small amount, “one slab will slide over another, and you can get a massive breach eventually. It starts when there is direct contact with an adjoining cell.”
Taylor said that the FSX system examines the DPF with high technology. One of the devices is a boroscope, or a fiber optic camera, which FSX combines with sonic imaging equipment.
“We have detected these cracks a lot quicker, within 100,000 miles of use,” he said. “When you send a truck in for regular maintenance, we suggest that you at least put it through a stage one pneumatic cleaning to be on the safe side.”
