Editor’s note: Information cited in an earlier version of this article indicated that aftermarket DPFs were banned in the state of California. An update has been made to reflect the restrictions in place for replacement parts.
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. Prior to 2007, the emissions standards were set at limits of 2g/bhp-hr (grams per brake horsepower hour) for NOx emissions and 0.1g/bhp-hr for particulate matter (PM) emissions. Beginning with 2007 model year vehicles, a new limit of 0.01g/bhp-hr for PM emissions went into full effect, while the new limit of 0.2g/bhp-hr for NOx emissions was phased in between 2007 and 2010. Currently, these limits remain the emissions standard requirements for diesel engines.
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.
Additionally, fleets should be aware that the DPF could reach a point where cleaning is no longer enough, meaning the DPF is failing and must be replaced. When it comes to replacing a DPF, fleets have three options: buy brand new from the original equipment manufacturer (OEM), buy aftermarket, or buy remanufactured. Each option has its benefits and drawbacks, which will be discussed later in the article.
For fleets to keep their DPFs functional, it is crucial they understand proper maintenance, cleaning methods, and replacement options, when necessary.
How do DPFs work?
In order to understand how to maintain a DPF, fleets first need to know how the DPF works.
As the DPF collects the 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-combustible 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 catalyst (DOC) 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 periodically it could create problems with the engine. There are three types of regenerations that can occur: passive, active, and forced.
Passive regeneration
Passive regeneration occurs during normal vehicle operation.
“When the DPF hits a specific temperature [around 1,112 degrees F], it goes into a regeneration cycle,” says Cory Just, director of dealer field service for Navistar, a manufacturer of commercial 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.”
There is no outside influence prompting the passive regeneration cycle to begin. In fact, other than a possible dash light appearing during the process, the driver will have no knowledge of the regeneration occurring at all.
According to Koukal, this form of regeneration typically occurs in vehicles with a high duty cycle, such as long-haul trucks.
Active regeneration
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 higher exhaust temperatures,” Koukal says. “Once the temps 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 ‘7th' 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.”
Whether an active regeneration takes place depends on the driving cycles of the vehicle, Just says. This means active regeneration could happen as often as once a week, or even daily. It is also possible that active regeneration could never take place throughout the life of the vehicle.
Typically though, this kind of regeneration happens on vehicles with lower duty cycles as well as those with the capability for longer drive cycles, such as trucks with local routes, Koukal notes.
Forced regeneration
A forced regeneration is similar to an active regeneration but calls for driver intervention. The same actions will take place as with the active regeneration, 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 alerted with various warnings, [such as] warning lights on the dash,” Just says.
It is then recommended that the driver pulls over and activates a regeneration cycle and waits for the cycle to complete.
Failing to activate the regeneration or not waiting for it to complete could lead to the vehicle derating, Koukal warns. Designed to prevent damage to the engine and aftertreatment system, the ECM will limit vehicle speed or power to initiate a derate. If the driver gets back on the road while the truck is derating, this may cause problems with the engine and a technician may have to step in to force another regeneration.
Maintaining a DPF
Proper maintenance for a DPF involves two parts: a preventive maintenance schedule and an effective cleaning method.
Preventive maintenance
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 [preventive maintenance] scheduled service intervals looking for exhaust leaks [and] fluid leaks upstream, [as well as] perform required maintenance on the aftertreatment hydrocarbon injector,” says John Moore, product marketing manager — powertrain for Volvo Trucks North America, a global truck manufacturer.
Additionally, Moore notes, be sure not to ignore regeneration requests.
“System performance is compromised when regenerations are continuously interrupted,” he says.
For more guidance on DPF maintenance, the Technology & Maintenance Council (TMC) offers their Recommended Practice (RP) 355, Maintenance and Inspection Guidelines for OEM-installed Exhaust Particulate Filters for Diesel-Powered Vehicles. TMC RP 355 covers information on DPF function, performance, diagnostics, maintenance, and cleaning. TMC advises, however, that this RP should not replace the engine’s OEM recommendations for maintenance and cleaning.
Overall, proper care and maintenance of all aftertreatment system components as well as following OEM guidelines will help ensure a properly functioning DPF.
Cleaning methods
When it comes to cleaning a DPF, fleets have a variety of options available for cleaning methods, such as pulse cleaning, thermal cleaning, liquid cleaning, etc. 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 wanted 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.”
TMC RP 374 offers information on methods for cleaning, testing, and documenting maintenance on OEM and aftermarket DPFs and DOCs. Though again, this RP is not meant to replace OEM recommendations for cleaning. Practices such as knowing when to clean the DPF can vary.
“It really depends on the application,” says Jeremy Anderson, national sales manager for FSX Equipment, a provider of filter cleaning systems and services for cleaning DPFs and industrial filter cartridges. “It varies widely depending on the engine and the duty cycle and … sometimes on the operator and how they drive the vehicle. Every fleet is going to have their own sweet spot, so to speak, when it comes to maintaining [the DPF] properly.”
For on-highway vehicles, the DPF should be pulled off for its first cleaning after 150,000 to 200,000 miles, and then every 100,000 miles after that for preventive maintenance cleaning, Anderson notes. Though for severe duty applications, like sweepers or garbage trucks, those DPFs can require cleaning every 50,000 to 75,000 miles, he says.
Even with cleanings every 100,000 miles or so, fleets should watch for increased frequency of regenerations. This is a sign the DPF needs cleaning, or possible replacement.
“What happens is when the ash builds up, the regenerations start happening more frequently … [and] when you regenerate more frequently, two things are happening,” Anderson says. “One, you're using more fuel, which costs the fleet money. And two, it’s hardening the ash plug, which makes it more difficult to clean out over many, many thousands of miles.”
To remove that ash buildup, Anderson says, “Our philosophy has been to clean [the DPF] using dry air with an air scanning approach – it's often referred to as air knife technology. It's bidirectional air scanning of the filter.”
This method cleans both ends of the DPF, and according to Anderson, is “the most effective and only OEM-approved cleaning system on the market.”
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 cleanliness 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].”
Aside from FSX Equipment and Clean Diesel Specialists’ cleaning methods, there is also pulse cleaning. This cleaning method may not get the DPF fully clean, Anderson notes, as the air tends to take the path of least resistance, especially when using an automated system. Once a path is created with the first air pulse, the remaining pulses will likely follow that same path leaving particulate matter behind.
Liquid or wet cleaning is another approach. This method uses water to flush the DPF out, which Anderson explains could actually make it harder to clean. The water mixes with the ash and other particulate matter creating a sludge, which can plug the micro pores and is more difficult to remove.
Ultimately, fleets opting to clean DPFs, whether in-house or through an outside DPF cleaning provider, must decide which process gives them the best results. That may include solely a wet cleaning or pulse cleaning method, or some combination of methods.
Cleaning equipment considerations
Cleaning DPFs in-house requires consideration of the method of cleaning the fleet will be using as well as protective gear for the technicians cleaning the DPFs and proper disposal methods for the ash and particulate matter.
Cost and maintenance of the cleaning equipment are two major factors to keep in mind when deciding whether to clean in-house. Navistar’s Just points out the equipment could also call for an increase in electrical capacity or a need to upgrade the shop’s air compressor system to get the volume necessary for pneumatic cleaning equipment.
As for personal protective equipment needed for the technicians doing the cleaning, gloves and dust masks are recommended. Once the filter goes into the machine for cleaning, Anderson says, it is safe, as the ash and PM are being vacuumed into a two-stage dust collection system with a HEPA filter. HEPA filters are designed to contain very fine particles.
Disposing of the ash and PM from the cleaned DPF must be done in an appropriate manner. Roy Horton, director of product strategy for Mack Trucks, a manufacturer of heavy duty Class 8 trucks, engines, and transmissions, advises fleets follow all local, state, and federal guidelines for all handling and disposal measures.
On the other hand, if you are looking for a facility to clean DPFs, then Clean Diesel Specialists’ Koukal suggests fleets “find a cleaning facility that has the knowledge and expertise to properly clean a filter. Beware of companies offering cleanings that are significantly cheaper than industry standard or offer unrealistic turnaround times.”
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.
At FSX Equipment, they perform three tests to ensure the DPF is in healthy, working condition. First is a visual inspection, Anderson says. If any black soot is coming out the outlet end of the filter, this could signify a crack or melt inside.
The next test can confirm whether there is a crack or melting inside with FSX’s bypass detection. If there is any particulate matter coming all the way through the filter, Anderson says, this will be observed in the first 30 seconds of cleaning, identifying it as a failed filter.
Lastly is the test flow bench, which will measure the pressure or breathability index of the DPF. The flow number is then compared with a baseline chart that will tell the operator if the filter is in the green, orange, or red range, Anderson explains. Green means the filter is in excellent operating service, orange means the filter is still good, but may require cleaning sooner, and red means the filter has sustained damage and should be replaced.
When replacing a DPF, fleets have three options available: OEM, aftermarket, and remanufactured.
OE filters
An OE or original equipment DPF comes from the original truck manufacturer.
“The nice thing about [OE 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 OE DPFs meet the efficiency standards set, Anderson advises they tend to be rather costly and may not always be available for purchase. He says this is because some OEM core exchange remanufacturing programs will prioritize use of these new OEM filters to replace failed filter cores, if the returned core is deemed unfit to reuse.
“When they get a filter back and it's bad, they have to seed that with a new filter, so some of the remanufactured [DPFs] out there end up being brand new filters because [with] a failed part, you'd have to bring a part in to replace that, otherwise you run out of filters eventually,” Anderson says.
Aftermarket
An aftermarket filter can come from a number of suppliers who have replicated the filter, says Kelly Gedert, vice president of on-highway market development for Daimler Truck North America, a heavy duty truck manufacturer. Aftermarket filters are typically less expensive than OEM filters, and there are more options to choose from, but aftermarket DPFs are banned in California unless CARB has approved the aftermarket DPF and waived the anti-tampering restrictions.
Additionally, DPF performance may be hindered.
“The consequence of using aftermarket DPFs that don’t meet OEM specifications may result in system performance fault codes,” Volvo’s Moore says.
Reman
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 expectancy as an OE 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 unless CARB has given them approval. 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 ignoring 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 questionable results. The term ‘remanufacture’ itself is a misnomer as there are no parts replaced as there are with [other] remanufactured products.”
Conclusion
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.
