DPF failures stem from false assumption
With a little more time to spend on the R&D side and work out the physics, the various OEMs may have been able to offer earlier clues for more effective and less disastrous approach to cleaning and maintaining a Diesel Particulate Filter (DPF).
The 2007 EPA emissions apparently went into effect before many engine and DPF manufacturers were fully prepared, leaving them to go to market with the best – and maybe the only solution – they had at that time. As it stands today with the earliest DPFs coming out of warranty after five years, it has become very clear the traditional filtration cleaning methods do not apply to the new technology.
Drew Taylor, president, FSX Inc, Granite Falls, WA, a tier-one provider of industrial filtration cleaning, says prior to 2004 this industry had never encountered a DPF filter, and assumed falsely that pulse technology, the only available cleaning method at the time, would work fine.
Taylor and his team were doing work for Boeing when they got the first call for help from King Country Metro, Seattle, WA.
“The agency prematurely invested millions in its own filter cleaning equipment not meant for the job,” says Taylor. “In fact, we started with pulse technology ourselves. Once we realized its failings, we spent the better part of a year on our own learning curve to know how to correctly clean a ceramic DPF.”
Taylor and his crew actually resorted to cleaning by hand, which was good for only a few filters at a time until the task grew physically and mentally exhausting.
“We determined then and there to develop a better way,” he says. “We began by looking for the reasons traditional pulse technology could not do the job.”
According to Taylor, the pulse method assumes the 6,000 individual cells within a DPF load equally. Not the case, as FSX discovered trying to shotgun blast the soot out of the cells all at once.
The FSX solution involves a bi-directional air knife that Taylor says attacks the filter as if it is 6,000 separate little garbage cans, as opposed to the one big target a pulse system sees. Over time, that merely serves to exacerbate the situation.
“We learned the cell loads are lighter at the center and heavier toward the edges,” says Taylor. “The pulsed air simply takes the least path of resistance, with all the energy going directly to the center cells in the filter, clearing an easy path and barely addressing the heavier clogged cells filled with ash— and not soot.”
Which brings up the next point: ash is different than soot.
The DPF may oxidize and remove the soot by the thousands of pounds; the ash left behind is the residue from engine lubricants, fuel additives and engine wear collecting in mostly the outer cells.
“Ash is like a cancerous growth,” says Taylor. “It occupies the space made available by soot and it does not burn off. It just sits there and devours the more frequent doses of fuel.”
As the re-generation sensors detect the restrictions and go after the problem, the system doses the engine with another shot of diesel fuel to kick up the furnace and incinerate the heavier soot deposits.
“Not so with ash,” says Taylor. “The damage is irreparable, as the weakened ceramic core ultimately cracks under the intense heat and pressure.”
FSX sees the respective industries beginning to view the DPF as a more fragile piece of equipment than first realized.
Read more of the technical details of the FSX bi-directional air knife in the digital-only April edition of BUSRide Maintenance, as well as the clients who are catching on to the new system and saving millions of dollars from going up in smoke.