The problem became real for Nicholson earlier this year when he had his first "thermal event breakdowns."
"Some trucks have had failures," he says, "and it's been a progressive failure, meaning that it had some injectors or turbo take a dump, and it doses that DPF with either fuel or oil, so when that happens, that's not the normal process of soot and ash that the DPF is supposed to be handling. It now has oil or fuel in it. We've had some where they have done so many regenerations and have gotten to the point where they are restricted because they're at that 250,000 mile range, and we've had to pull them off and get them cleaned.
"That needs to be factored in," Nicholson stresses. "It's not just the fuel economy, although that's a big deal, your're also damaging the DPF."
"A Sophisticated Garbage Can"
After some early missteps, Nicholson has found what seems to be a winning strategy. He has persuaded his Kenworth dealer in Olathe, MHC, to purchase DPF cleaning units from Granite Falls, WA-based FSX, Inc. a process that has recently begun.
In late June, FSX co-owner Drew Taylor spent some time at MHC, where he trained technicians from both the dealer and the trucking company on the proper use of the new DPF cleaning machine, and he offers a description of the cleaning process that is both simple and complicated:
"A diesel particulate filter--also referred to as catalyzed regenerating technology--is the heart and soul of clean diesel technology," says Taylor. "What you have here is a very sophisticated garbage can, that's about the only way I can put it. It performs a very, very vital function, and it does it very, very well. It strips and burns off most of the hydrocarbon that is found in diesel emissions, and it does a very good job of protecting you and I, the truck drivers and the community at large from this very damaging, very toxic carcinogen. But there are some wrinkles that are starting to appear, that pose a threat to the bottom lines and the balance sheets of those that rely on this equipment--the fleets--that need to be addressed."
As Taylor describes it, the DPF operates in 'out of sight, out of mind' mode, and so drivers and fleet managers don't think about the build-up of ash inside the filter until the dash indicator comes on. The DPF can inventory a great deal of ash, but in time the ash reacts with the crystalline substrate of the filter, a ceramic wall that consists of billions of small pores between 11 and 15 microns in size.
"As long as these pores remain open the DPF breathes well," Taylor explains. "The hydrocarbon enters the DPF, and impinges itself on the substrate, and because it's such a high temperature--about 750 degrees Fahrenheit--it burns off there and leaves more or less harmless gasses to pass through to the other side. As long as that process goes on, everything's fine. But there are residues from the engine oil that do not pass through, and do not burn off, that continually, at a linear rate, build up. This is the ash."
Ash contains potassium and the calcium. "Those are the real bugaboos," says Taylor, because, between them, they cause the pores in the DPF to glaze over with a glass-like substance and clog up.
"So, it's very important to get the ash out, sooner than later," Taylor goes on. "You don't want to just sit there and let it build up, or you place your whole DPF pool at risk. The fleet owner needs that like he needs two heads. He's suddenly presented with a gigantic cost that he did not anticipate as he starts to see these DPFs go down right and left.
"There's a false sense of security out there, because people think they're getting their filters cleaned by the various processes that are out there, but, unfortunately, the processes that first came on the scene leave a lot of ash behind, and this process of 'sintering' goes on unabated," he explains.