We wanted to share some key elements in a recent article in Fleet Maintenance Magazine. The article was written by Emily Markham and discussed diesel particulate filters (DPFs) and the choice to clean or replace them. The article was fairly lengthy, so we will try and distill the main points in the article below.
In 2007, diesel particulate filters (DPFs) were introduced to on-road heavy duty diesel engines as a way to trap diesel particulate matter for engine manufacturers to meet the U.S. Environmental Protection Agency’s (EPA) emissions standards These standards were put in place not only for environmental protection but to protect the public from breathing in pollutants released from diesel exhaust. According to the EPA, the particulate matter and NOx emissions found in diesel exhaust can pose serious public health problems. Exposure to the pollutants can cause lung damage and aggravate existing respiratory illnesses such as asthma. DPFs help keep the environment and people safe from these pollutants.
The DPF is a ceramic filter with thousands of micro pores, which are designed to capture the PM and ash from the engine in order to release a less harmful exhaust from the vehicle. To ensure this process continues to function properly, fleets must implement a maintenance schedule for cleaning and maintaining the DPF. If not handled with the appropriate care, not only can the DPF begin to release harmful particulates into the vehicle’s exhaust, but it may cause damage to the rest of the aftertreatment system and the engine itself.
How Do DPFs Work?
In order to understand how to maintain a DPF, it is important to first know how the DPF works. As the DPF collects particulate matter and ash from the engine, that matter is filling the DPF, creating a backpressure within the filter.
“[Once the] backpressure reaches a certain threshold, a regeneration to oxidation is performed,” explains Ryan Koukal, chief operating officer for Clean Diesel Specialists. “Oxidation occurs when the particulate matter is broken down into gases and non-combustible material. The non-combusti- ble material, along with ash from oil consumption, cannot be removed from the filter, requiring the filter to be cleaned periodically.”
Clean Diesel Specialists services DPFs and diesel oxidation catalysts (DOCs) to help reduce diesel fuel’s carbon footprint on the environment. Regenerations within the DPF are necessary to “clean-out” as much of the engine particulates as possible. If regeneration does not occur period- ically it could create problems with the engine. Three types of regenerations can occur: passive, active, and forced.
Passive regeneration occurs during normal vehi- cle operation. “When the DPF hits a specific temperature [around 1,112 degrees F], it goes into a regenera- tion cycle,” says Cory Just, director of dealer field service for Navistar, a manufacturer of commer- cial trucks, buses, and engines. “It converts the soot [particulate matter] into ash which is a much smaller particle of waste from the engine, and it’s trapped within the DPF.” According to Koukal, this form of regeneration typically occurs in vehicles with a high duty cycle, such as long-haul trucks.
If the aftertreatment system does not reach 1,112 degrees F, the engine control module (ECM) on the vehicle will activate an active regeneration cycle, Just explains. “The turbo will change the pitch of the vanes to increase the load on the engine creating high- er exhaust temperatures,” Koukal says. “Once the temperatures reach a specific range, the system will inject atomized diesel fuel into the exhaust by either injecting fuel on the exhaust stroke of a cylinder or using a ‘seventh’ injector mounted in the exhaust after the turbo. That fuel reacts with the precious metals in the DOC to create heat. That heat then oxidizes the particulate matter in the DPF.”
A forced regeneration is similar to an active regen- eration but calls for driver intervention. The same actions will take place as with the active regen- eration, but instead of the ECM activating the regeneration, the driver initiates it. “If [there is] prolonged use of the vehicle where it does not reach that [1,112 degrees F] and active regeneration is not able to occur, the driver is alert- ed with various warnings, [such as] warning lights on the dash,” Just says. Failing to activate the regeneration or not waiting for it to complete could lead to the vehi- cle derating, Koukal warns.
Maintaining a DPF
Proper maintenance for a DPF involves two parts: a preventive maintenance schedule and an effective cleaning method.
Preventive maintenance for the DPF is more than just caring for the DPF, it means taking the time to maintain the aftertreatment system as a whole. “Perform visual inspections at regular [preven- tive maintenance] scheduled service inter- vals looking for exhaust leaks [and] fluid leaks upstream, [as well as] perform required mainte- nance on the aftertreatment hydrocarbon injec- tor,” says John Moore, product marketing manager — powertrain for Volvo Trucks North America, a global truck manufacturer.
When it comes to cleaning a DPF, fleets have a vari- ety of options available for cleaning methods, such as pulse cleaning, thermal cleaning, and liquid cleaning. Each fleet or DPF cleaning specialist will have their own method for cleaning. Currently, no standard exists specifying what a “clean” DPF is, which leaves room for misinformation to spread on “proper” cleaning for DPFs.
In order to help combat any misinformation, TMC has passed a new RP, RP 374, for Cleaning Diesel Particulate Filters and Diesel Oxidation Catalysts. Bruce Balfour, vice president of Clean Diesel Specialists, and Wayne Juchno, executive director for the National Automotive Radiator Service Association, were the co-chairs for the RP on the TMC S.3 Engine Study Group. They want- ed to set a standard on DPF and DOC cleaning to educate fleets and technicians on the proper way to clean and test the filters. “There [are] a lot of myths and bad information on how to clean filters such as steam cleaning or pressure washing the filters,” Balfour says. “Yes, it will clean the filter, but it’s also going to wash off the coatings and damage the substrate as most steam cleaners or pressure washers operate between 1,200 to 4,000 psi.”
- Clean Diesel Specialists takes a bit of a different approach when cleaning DPFs. Koukal provides a step-by-step explanation of how they go from inspection to final testing of their DPFs.
The substrate, temperature/pressure ports, and gasket mounting surfaces are checked to ensure there is no damage or corrosion.
- The flow of the filter is checked.
- The filter is weighed.
- Then, the filter is blasted with air and water until no particulate matter is seen.
- The filter is then baked and goes through a post-bake air blast.
- The filter is inspected for proper flow and cell depth/health.
- If the filter fails any of these tests, the process is repeated.
“In our experience, the way to ensure the filter is as clean as possible is to put the filter through a thermal regeneration to oxidation by baking in a kiln,” Koukal says. “This ensures as much of the particulate has been processed as possible. We also firmly believe in using a manual cleaning system over automated. By having a technician physically clean the filter, they can focus on problem areas that an automated process cannot. While filter flow specs can be a good reference tool for filter cleanli- ness it cannot be the deciding factor. Pin rod testing and light testing, along with weight and flow, can ensure a filter’s health much more consistently [than filter flow specs by themselves].”
When to Replace a DPF
With proper care and maintenance, the DPF should last the life of the truck, but this is not always the case. When cleaning the DPF there are signs technicians can look for indicating the DPF is no longer fit for service as well as tests that can be run on the filter. When replacing a DPF, fleets have three options available: OEM, aftermarket, and remanufactured.
An OEM or original equipment manufacturer DPF comes from the original truck manufacturer. “The nice thing about [OEM DPFs is] we know we’re providing our customers a component that is certified to original manufacturing, meaning it meets EPA/CARB [California Air Resource Board] certifications that are required for that engine emissions model year,” Navistar’s Just says. Though OEM DPFs meet the efficiency standards set, Anderson advises they tend to be rather costly and may not always be available for purchase.
An aftermarket filter can come from a number of suppliers who have replicated the filter, says Daimler’s Gedert. Aftermarket filters are typically less expensive than OEM filters, and there are more options to choose from, but aftermarket DPFs are banned in California as most do not follow the same efficiency standards required in OEM DPFs. Additionally, DPF perfor- mance may be hindered.
Remanufactured DPFs are reused substrates, Just says, that were in another vehicle, but have been cleaned and certified and should provide the same level of life expec- tancy as an OEM DPF. Just cautions, however, that if the remanufactured DPF was not remanufactured for OEM purposes it may not be meeting the EPA/CARB specifications. Remanufactured DPFs are the least costly of all the DPF replacement options, but they are also banned in California. Fleets should take any non-OEM remanufactured DPFs into careful consideration before buying them.
“There is no history to where this filter came from or how it was treated by its previous owner,” Koukal says. “If the previous owner mistreated the aftertreatment system by ignor- ing regenerations or prolonging cleaning intervals or if there was a catastrophic failure that occurred, the DPF’s life could be compromised. Also, the process used to remanufacture a filter has shown to provide quetionable results. The term ‘remanufacture’ itself is a misnomer as there are no parts replaced as there are with [other] remanufactured products.”
Though replacing a DPF is something fleets hope to prevent through careful maintenance and cleaning, it cannot always be avoided. When it comes to choosing a replacement DPF, be sure to keep in mind any recommendations from the engine’s OEM, budget, driving routes, and the reputation of the company you are buying the replacement DPF from.
You can read the article titled Diesel Particulate Filters: Clean or Replace? by clicking HERE
The helpful Enviromotive staff would be happy to discuss any of the aspects on this article. We not only sell the cleaning equipment used in the cleaning of diesel particulate filters, we also offer replacement DPFs and DPF gaskets, clamps and bungs. We are truly your one stop shop for all things related to diesel particulate filters.
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