TLC For DPFs
Those diesel particulate filters on new trucks will need be to cleaned sometime. Still a big question is, when?
Tom Berg, Senior Equipment Editor
Diesel particulate filters are part of the package on most diesel-powered trucks starting this month, and they'll require special maintenance to keep working. How often? No one knows. While builders have tested the 2007-spec diesels more than any other previous products, none has run enough miles to give a definitive answer.
As you've probably heard, most '07 diesels will exhale through an exhaust system equipped with an oxygen catalyst and the DPF. The catalyst will chemically change certain pollutants into non-harmful substances, leaving water and carbon dioxide (CO2is not toxic, even if it is a greenhouse gas blamed for global warming). The DPF will trap particulates, or soot, which will periodically burn off. But ash from motor oil will collect in the DPF and have to be removed through special cleaning.
Exhaust heat from high-load highway operations will be enough to burn off soot in a process called passive regeneration. In stop-and-go operations, extra heat will be needed for what's called active regeneration. This comes from injecting small amounts of fuel into the exhaust stream, or from a temporarily rich mixture in the cylinders. When the fuel hits the oxygen catalyst, a reaction causes high heat, which then passes into the DPF and burns off the accumulated particulates. Caterpillar diesels won't use an O<->2 catalyst, so fuel is injected and ignited, and the resulting heat then enters the DPF.
However, ash particles are not burned off in regeneration, so eventually they must be blown out on special machines that most dealers will have. Only time and experience will show users exactly how long their trucks can go before coming in for this service. Builders' tests thus far indicate that the DPF cleaning intervals will range from about a year to two or three years, depending on the kind of truck and type of duty it sees.
Over-the-road tractors will go the longest, probably 200,000 to 300,000 miles; local trucks might go less than 100,000 miles. Trash trucks are the most difficult type to deal with because they spend a lot of time idling. Mack says it will install a "burner" type of DPF on its MR and LE trash trucks. The units, made by ArvinMeritor, inject fuel directly into the device to burn away soot. Most other Macks will get regular DPFs made by Cummins Emission Solutions.
EPA Minimums
The U.S. Environmental Protection Agency, which wrote the new exhaust limits that make DPFs and other expensive equipment necessary, has established minimum periods that the devices must work before cleaning. One minimum is 150,000 for heavy-duty trucks; another is 80,000 miles for special applications, where filters might be too small to go the full 150,000. The latter might be on vehicles where regular DPFs are too large to fit in available space behind or under the cab. Examples are beverage, utility, dump and snow-plow trucks, whose bodies, extra axles and other equipment take up room that DPFs might otherwise go in.
Some fleet managers who've read the EPA's rules inferred that DPFs must be cleaned at those mileage levels. Not so. Those mileages are minimums that manufacturers have to meet, and they are free to install filters that go well beyond that. Most will. Owners have no direct legal requirement to clean the filters, but EPA notes that engines will lose power and eventually shut down if the the DPFs are not serviced.
Cleaning ash out of the DPFs will be a new service procedure. In most cases, cleaning will be done by removing the DPF element from the truck – an easy job, partly because parts will be made of stainless steel to resist corrosion, manufacturers say – and placing it on a special machine. (Because Caterpillar engines don't use an O<->2 catalyst, its DPF will come with connections that will allow attaching hoses to clean it right on the chassis.)
The console-like machine will blow compressed air at normal shop pressure (about 90 psi) through the filter in pulses. This will take about half an hour, during which the technician can perform other service work on the truck. Removal and reinstallation of the DPF will together consume another half hour and maybe less.
Detroit Diesel (which also markets and supports Mercedes Benz MBE diesels) will recommend filter cleaning with deionized water. This will be done on larger, more complex machines at Detroit's remanufacturing centers. In that case, an exchange program will use cleaned filters with dirty filters turned in for core value. Detroit will also allow the air-cleaning method, but says it doesn't work as well as the fluid.
Most builders will offer clean DPFs on an exchange basis, but dealers will be encouraged to obtain the simpler and less costly air machines.
Not Needed Soon
Most dealers and fleet shops will not be faced with special servicing of '07 diesels for a while. Unless there are bugs that crop up early on, a typical heavy road tractor delivered early this year should not need cleaning of its DPF until sometime in '08. (It will be earlier for those involved in ongoing test programs for '07 diesels – which builders claim are longer and more rigorous than for any previous models.)
Even so, engine and truck builders say they've begun training dealer technicians on the new systems. Cat, for example, is trying to eliminate the "fear factor" inherent with new and unknown equipment by producing educational sessions on the Internet and CDs, and in its closed-circuit TV broadcasts. All builders have begun printing special literature and training materials, and are preparing to put special tools in dealers' hands.
They say they've also tried to minimize the number of tools needed by dealers. The air cleaning machine, for example, is a generic design usable for all DPFs. One model is built by tool maker SPX, a name familiar to dealer shop people. It runs on 110-volt power and standard shop air, sits on rollers so it can be moved among service bays, and costs several thousand dollars (though one estimate had it closer to $10,000).
Most smaller fleets rely on dealers to service the high-tech items already on trucks, and will for '07-spec equipment, too. Is your dealer getting ready to do this? Now might not be too soon to ask.
Maintenance continued...
