If you’ve been paying attention to the most recent engine announcements, you’ll notice that the engine companies have spent a good deal of time highlighting the features of the aftertreatment system (ATS). That’s no accident—the ATS is extremely important, and the systems have advanced significantly in recent years.
Before we dive into the details, here’s a quick refresher. There are three components to the engine aftertreatment system: the diesel particulate filter (DPF), the diesel oxidation catalyst (DOC), and the selective catalytic reduction (SCR).
The DPF has been the main focus of attention when problems come up, but it’s just as important to look at the DOC and SCR to make sure everything in the system is working properly with each other.
“The DOC is part of the regeneration process to burn the soot out of the DPF,” explained Dale Boone, director of product development for commercial vehicles with Eberspaecher, which manufactures aftertreatment systems for Detroit, Volvo and Mack engines. “In many cases, OEMs use passive regeneration, but there’s still the capability for active regeneration. Passive regeneration occurs naturally in the truck. Under active regeneration, the DOC is part of the process to increase gas temperature. Basically, in most cases, fuel is consumed and used within the DOC. That increases the gas temperature, and that higher temperature gas enters the DPF and helps to burn off soot.”
Aftertreatment systems have led to a significant reduction in the emissions pouring from the engine. However, they’ve acquired a reputation as a thorn in fleets’ sides thanks to significant maintenance costs. With this in mind, the newer ATS systems have been optimized and improved to avoid these kinds of problems, and there are also measures fleets can take on their end to help prevent DPF issues.
When asked if his fleet has run into problems with the DPF or the aftertreatment system, Dan Vander Pol, vice president of maintenance for Oak Harbor Freight Lines Inc., said that repair and maintenance costs related to the ATS are “out of control” and represent at least 30% of his fleet’s total maintenance costs.
“We run into most of our problems [with DPFs] on routes that don’t get up to highway speeds for at least a 30-minute consecutive period per day,” Vander Pol detailed. “Those routes will have to do a regeneration, which usually takes about an hour. That means a driver and truck are sitting unproductive while burning fuel for an hour—that’s very costly!
“We also do regens in the shop all the time to make sure the truck is cleaned out prior to going on the road. These usually don’t take that long since they are not usually due for one.”
Vander Pol did say that he thinks the systems have been getting better lately, with most OEMs releasing new system structures, but that “we really won’t know for sure for a year or two.”
Eberspaecher’s Boone weighed in from the perspective of the ATS manufacturer on the issues he’s seen with the aftertreatment system, and what his company is doing to mitigate those issues.
“A lot of what we see would be characterized as a leak out of the system, but you can also see on the ATS, there’s a series of sensors used for OBD. Those sensors could lead to failures,” Boone said.
“There’s also always a challenge with the mixing of the urea,” he continued. “The urea solution gets injected, typically, after the DPF in today’s conventional systems, and it has to be converted to ammonia gas for consumption in the SCR catalyst. If that’s not done properly, you can run into issues with efficiency of the SCR catalyst, and you can also run into issues with urea deposits.”
Boone explained that not completely evaporate the urea is a big problem that leaves a white deposit in the system, which can lead to additional backpressure. That has a negative impact on the drivability of the vehicle. It can also be highly corrosive. So manufacturers like Eberspaecher have to engineer the boxes to resist that corrosion.
Among more basic issues include failed DPFs or cracked DPFs that allows soot to bypass the filter. Sometimes, Boone noted, the problem is with other components of the engine, but still results in the need to replace the ATS. If there’s a faulty injector or a turbo fails, for example, those failures can lead to issues in the ATS. The ATS wasn’t the cause of those problems, but it still might need to be replaced afterward.
So how are manufacturers tackling the aftertreatment system’s biggest issues? According to Boone, one of Eberspaecher’s biggest priorities in putting together the ATS is making sure that it can last the life of the vehicle.
“When we work with the OEMs, what they’re really looking for is our expertise in providing a durable design,” he began. “One of the things that we can do is design the system in a way that the service time when the filter needs to be removed for ash cleaning is reduced. A good example of that is the Volvo aftertreatment system, which has a DPF that can be serviced in around 15 to 20 minutes, whereas a lot of the previous generation systems would take significantly longer. That all leads to more uptime for the vehicle, rather than having it sit in a shop.”
Boone said that one of the DPF’s biggest drawbacks is that it adds a restriction to the system that wasn’t there prior to the use of a filter. It’s gathering soot, which has to be turned off, and it’s gathering ash, which has to be physically removed. All of this leads to an increase in the backpressure of the system.
“So, while we can’t change the filter ourselves, what we can do in is find ways to reduce the overall backpressure of the system and try to mitigate that increased restriction that the filter gives you,” he said. “This goes back to urea mixing—we’re looking at how well this urea solution is being mixed with the exhaust gas and how it’s being consumed on the SCR face; making sure we’re using the entire SCR catalyst, not just a small zone of that catalyst.”
Boone said that overall, the aftertreatment systems being made now are “lasting a significant portion of the vehicle’s life.” Further improvements to the system include better performance in terms of gas flow, and a quieter ride that meets regulations on acoustics.
The engine OEM perspective
Engine manufacturers are well aware of the burden that DPF issues have become for fleets. We spoke with several engine manufacturers on what they are doing to minimize these issues in their new engines.
“The primary issues that put the DPF at risk are poor maintenance practices and any engine issue that could lead to excessive engine-out smoke,” said Dale Allemang, regional service director for Daimler Trucks North America. “Significant effort and progress has been made in on-board diagnostics to catch such issues before damage is done to the DPF, and a well-maintained engine and aftertreatment system are vitally important to minimizing DPF issues.”
“In the past, DPF issues have primarily resulted from the accumulation of soot and ash,” said Clint Garrett, product manager for Cummins. “Soot is produced almost the entire time that an engine is running, but is worst during hard acceleration or sudden increases in torque demand from the driver. With the 2017 Cummins X15 engine, improvements in engine breathing have led to drastic reductions in soot production and innovative controls that actively manage temperature in the DPF. This management is important because the only way to clean soot out is by a regeneration, which burns fuel to increase the DPF temperature.”
Garrett touted Cummins’ new Single Module Aftertreatment System, which he said is 60% smaller and 40% lighter than its predecessors and has better temperature retention because of the compact packaging design. This, Garrett said, results in more consistently managed regeneration events—meaning that regenerations will only become more frequent as the system fills with ash.
“Ash is present in both oil and fuel and cannot be burnt; therefore, the only way to remove it from the DPF is through a cleaning process or with a Genuine ReCon DPF replacement, which is the recommended option by Cummins,” Garrett continued. “Switching out a truck’s DPF helps expedite the service event and ensures that the truck gets back on the road faster. Liner and ring improvements resulting in reduced oil consumption, as well as improvements in fuel consumption, have reduced the amount of ash that reaches the DPF on the 2017 X15. This has extended time between maintenance intervals with trucks that average over 6.5 MPG experiencing DPF maintenance intervals of 600,000 to 800,000 miles, which in some cases extends beyond the first owner.”
International Trucks also uses the Cummins Single Module Aftertreatment System in its A26 engine. Jim Nachtman, International’s on-highway marketing director, said that the reduced weight and size of the single-canister system makes it much easier to work on and to remove from the vehicle, which improves serviceability.
“With the newer engines, we’ve also been able to greatly extend the DPF cleaning interval,” Nachtman said. “For the International A26, for applications better than 6.5 MPG, we have a DPF cleaning interval of 600,000 miles.”
With the average Class 8 truck trade cycle being less than that, this might mean that some fleets never need to incur the expense of a DPF cleaning, Nachtman pointed out.
“On the engine side, there’s a fuel doser which sprays fuel into the exhaust to heat up the exhaust during active regeneration,” he noted, “With that, the system uses compressed air to ensure the fuel doser remains clean, blowing out any remaining fuel and machining uptime.
“Also, both the A26 and the Cummins X15 [also offered by International] offer an anti-scraper ring or anti-polish ring, which are different names for the same technology,” Nachtman continued. “This is a part inside the engine that scrapes off any carbon deposits on the piston. It enables the oil consumption rate to remain extremely low over the life of the engine. For example, we have some N13 and now A26 customers who are going through their entire oil drain intervals without topping off oil. Not consuming oil helps to extend the DPF cleaning interval, because when you burn oil, you ultimately create ash in the aftertreatment system.”
Nachtman added that International and Cummins worked closely together on optimizing the Cummins ATS for the International A26. “To validate that system, both companies require millions of miles of real-world testing to be performed, as well as a certain amount of bench testing with the combined A26 and Cummins single can aftertreatment system working in conjunction with one another. That system we’ve had throughout the entire design and validation cycle over many years, and that’s what we’re in production with today,” he explained.
According to Darryl Oster, assistant chief engineer with Peterbilt, PACCAR’s 2017 MX line of engines made improvements to the ATS in reliability, weight and frame space. The ATS in the MX engines is 100 lbs. lighter than previous systems and packages in the same or less space than before. Oster said that Peterbilt specifically looked at sensors and wiring, which are often the culprits in aftertreatment downtime, and redesigned the systems using new chassis routings, which segregate air, fluid and electrical system routings on the frame rail. They also added wiring harnesses with improved connectors for prevention of water ingression and chaffing failures.
“Volvo invented the wave piston, introduced for GHG ’17 engines, which significantly reduces soot production,” noted John Moore, Volvo Trucks’ product marketing manager—powertrain. “Our one-box Exhaust Aftertreatment System regens more efficiently. It encases the DPF, SCR and DOC into one package. With the new design, the DPF is easier to access and lighter compared with the two-box version, allowing for quicker serviceability and increased framerail space.”
Engine and ATS manufacturers are working on doing what they can to mitigate the issues fleets see with the DPF and ATS system. But is there any preventative maintenance the fleets should be performing themselves to avoid these problems?
According to each member of our panel of experts, the simplest and most important thing for fleets to do is to understand and follow the OEM recommendations. Each engine and ATS is different, and the most important thing is to know what your system requires, be it oil drain intervals, DPF cleaning intervals, when to perform an active regeneration, or something else.
Peterbilt’s Oster added that it is also important to understand recommended maintenance intervals according to your operation’s duty cycle. As an example, higher idle times lead to more soot production in a diesel engine, which reduces oil drain intervals and DPF cleaning intervals. Making sure preventative maintenance is performed according to how your vehicles are used will ensure maximum uptime.
“Failing to do any maintenance that could lead to excessive engine-out smoke, high oil consumption or inefficient removal of ash from the DPF would put the DPF at higher risk of having an issue,” Daimler’s Allemang said. “In general, a well-maintained engine and aftertreatment system significantly reduce this risk. For example, we have seen things as simple as the engine air filter put the DPF at risk.”
Further maintenance recommendations included the following:
- Engine OEMs often require that when you service a DPF, you replace any of the gaskets or clamps that are used to hold that DPF in place. This will guarantee that you get a good seal of the DPF back in the system, and that there are no leaks in the system.
- Activating parked regeneration in a safe place when automatic regeneration requirements cannot be met will help ensure overall health of the entire aftertreatment system.
- It is extremely important to pay attention to the CEL/MIL lamps, which are put into place to notify the driver that actions need to be taken to ensure the health of the ATS. If ignored, damage to the system can occur, as well as derate conditions including torque and speed reductions.
- It is important to know what kind of oil your engine requires, especially in light of the recent introduction of the American Petroleum Institute’s FA-4 and CK-4 categories. The engines will require the correct oil in order for the recommended DPF cleaning intervals to be correct.
On the other hand, International’s Nachtman said that as long as every aspect of the engine and the aftertreatment system is running properly, there’s really no need for preventative maintenance—that is, as long as you stick to the recommended cleaning intervals.
“However,” he added, “if there is any issue going on with the hardware—for example, if your driver is needing to top off regularly with coolant or oil when those fluids are burned inside the engine—that can ultimately reduce the service interval of the DPF, and can cause damage to it. So you do need to make sure that your drivers don’t need to top off any of the fluids. If they do, then you want to bring the product in for service to protect the aftertreatment system from any potential issues down the road.”