necessary to ensure it continues to prevent the particulates from entering the atmosphere. If and when soot and ash builds up in a DPF, it restricts system flow and creates significant back pressure. A number of unwanted problems can result from neglecting DPF maintenance, including: • Plugged DPF. • Low vehicle power. • Engine derate. • Cracked DPF. • Melted filters. • Engine damage. DPF BUILDUP AND REGENERATION CYCLES “Each time one of the regenerations occurs and clears out the accumulated soot, the DPF can once again ‘breathe,’ but a small amount of material is left behind that does not burn off, ” says Drew Taylor, owner/vice president of global sales, FSX Equipment, a provider of filter cleaning systems and services for cleaning DPFs and industrial filter cartridges (www.fsxinc.com). According to Taylor, soot builds up due to diesel fuel. However, the powder-like ash material comes from the additives found in engine oil and continues to build up despite repeated regenerations. After a little more than 33,000 miles, nearly half the material trapped in a DPF is ash, he says. At the U.S. Environmental Protection Agency’s mandated service interval of 150,000 miles, ash makes up approximately 80 percent of the accumulated material in a DPF (compared to 20 percent for soot). “If only 20 percent of the material can burn off by way of the onboard active regeneration system, then what about the 80 percent that cannot burn off?” asks Taylor. “The DPF must be removed from the exhaust line and mechanically cleaned to remove the remaining 80 percent ash content.” When the soot-ash ratio reaches such a level, back pressure becomes more of an issue and regenerations are repeated. After time, those regenerations only serve to transform the ash into a “hardened, immovable block that destroys the DPF,” he says. Paying attention to the frequency of a vehicle’s regeneration cycles is the most effective way to determine whether or not there has been significant ash buildup in its DPF. If they are ignored, the end result could be an irreversibly-damaged DPF that is cracked, glazed or melted. “Sensors detect high-pressure differential caused by ash deposits in the DPF and an active regeneration is initiated,” says Taylor. “However, trying to burn ash is like trying to burn rock. It’s not going to happen.” Heavy Duty | key 4 considerations when dealing with DPF ash buildup 1. Get the diesel particulate filter (DPF) off the truck, get it cleaned with proper cleaning tools and conduct an inspection process appropriately. 2. Ensure a careful visual inspection is performed and flow and gauge pin testing is conducted. This certifies that a complete cleaning has been done. Some DPFs require more time in cleaning than others, and the cleaning process must be visible to the operator in order to determine when it is complete. 3. Never allow for the DPF to be “baked” in a kiln at a high temperature without first putting it through a thorough pneumatic airknife cleaning that strips as much soot and ash out of the DPF before proceeding to “bake” it. If this isn’t done, the onboard fuel could ignite and heat to near or above the melting point of the DPF substrate, causing permanent damage. 4. Insist on a dated data sheet that summarizes the before and after cleaning condition of the DPF. Tracking and recording the condition of the DPF is critical to managing future cleanings. If a small, hardened ash island has appeared in the DPF, maintenance intervals must be shortened and ash should be removed sooner (before it hardens and can no longer be cleaned). Information provided by FSX Equipment Soot and ash build up in a diesel particulate filter with time. After awhile, a DPF must be removed from the exhaust line and mechanically cleaned, as repeated regenerations will not be enough to address the ash buildup. Photo courtesy of FSX Equipment IF REGENERATIONS ARE IGNORED, the end result could be an irreversibly-damaged DPF. According to Daimler’s Lewallen and Allemang, the primary reason for an unsuccessful DPF regeneration is failure to attain the desired exhaust gas temperature in the diesel oxidation catalyst (DOC) and DPF to burn the collected soot. Continued page 19 VehicleServicePros.com ❚ APRIL 2016 ❚ FLEET MAINTENANCE 17
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