Featured Article: DPF maintenance

John Baxter | April 01, 2010

While the diesel particulate filter itself requires little maintenance, proper attention to related systems will help avoid problems.

 

dpf
The compact Volvo and Mack DPF fits comfortably behind the step on the passenger side door.

The U.S. Environmental Protection Agency’s 2007 emissions standards required a reduction in both diesel particulate and nitrogen oxides. The new particulate standard was so low that, even with advanced injection and air handling systems, a particulate filter was needed to bring exhaust soot levels down to required levels.

The porous ceramic filter under normal, over-the-road driving conditions burns off the soot it collects and does not require frequent maintenance. However, it still has to be cleaned periodically because some ash ends up in the filter.

“The regeneration of soot in the DPF does not form ash buildup or any residue in the DPF,” says Zack Ellison, director of customer technical support at Cummins. “Ash collected in the DPF is primarily caused by sulfated ash (TBN) in the oil.” Ash, which results from burning of a small amount of lube oil, does not burn, even at temperatures that burn off soot, and must be cleaned up.

While certain specific DPF-related maintenance tasks are required, both the vehicle’s maintenance and its operation have a significant effect on DPF performance. Therefore, running a 2007 or later model truck will keep you on your toes. The payback could be lower costs since your equipment will last longer, run better and fetch a higher resale value.

While the filter burns off soot as fast as it collects under normal highway driving conditions, soot will accumulate during idling or while crawling through traffic. In response, you have to actuate a fuel dosing system to clean the DPF, a process called active regeneration. Warning lamps on the dash will indicate the need for active regeneration or ash cleaning. Which lamp turns on depends on how fast backpressure is building up in the DPF, as soot accumulates much faster than ash.

You need to allow the DPF to go into active regeneration mode whenever practical. Prevent regeneration, however, when the vehicle is entering a shop or an enclosed environment where a super-hot DPF would not be safe.

regeneration
TIn the Cummins particulate filter the diesel oxidation catalyst is at left and the ceramic filter at the center.

DPF regeneration helps ensure exhaust backpressure does not rise to the point where fuel economy is reduced. So, “if needed, induce an active regeneration when prompted by the warning lamp,” says Mike Kalkoske, quality services manager for Kenworth.

Another concern is recognition of turbo failure. “The DPF does such an efficient job of exhaust-out particulate removal that the previous symptom of a turbo failure – lots of exhaust smoke – no longer shows up,” says Mack’s David McKenna, director of powertrain sales and marketing. “At the very first symptom of a turbocharger failure, which is an almost instant loss of power with turbine/compressor wheel noise, the engine must be shut down.”

The consequences of not doing this can be dire. McKenna says, “If the failure is contained within the first few moments, then DPF damage will be somewhat mitigated. Small amounts of engine lube oil can be force-regenerated off.” But if operation continues more than a few minutes, the accumulation in the DPF will be so great that it will require “replacement of both the DPF catalyst and the actual filter as well,” he says.

On-board diagnostics may help prevent some of the potential problems that might cause secondary DPF damage, but “there are still failure modes that OBD does not catch that would cause it to be damaged,” says Amanda Phillips, manager for product planning for Detroit Diesel. “A turbo losing its oil or an engine leaking coolant are two examples.”

Drivers need to be aware of unusual sounds, power loss, a loss of coolant from the radiator (especially when accompanied by a rising temperature indication) or high oil consumption. Any of these require immediate attention.

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