IN PRINT: Keep it Clean — The art of aftertreatment maintenance
Posted: November 30, 2017 by Jim Park
This is a good news/bad news kind of story. The bad news is that aftertreatment system maintenance is still required, and will be for years to come. The good news is that it’s getting easier. Original Equipment Manufacturers have improved the efficiency of these devices, and in some cases the packaging. Those changes mean some trucks will see fewer regen events on their Diesel Particulate Filters (DPF’s), and their cleaning intervals have in many cases been extended. Maintenance of the Selective Catalytic Reduction systems (SCR & DEF) remains minimal.
It’s good news, not great news.
Several factors have combined in recent years that help alleviate some of the maintenance burden. Low-ash oils such the American Petroleum Institute’s CK-4 and FA-4 have been available for about a year now, and they are having a positive impact on ash accumulating in DPF’s.
“These newer oils contain less ash than older oils, so there’s less chance of DPF fouling,” says Jim Nachtman, Navistar’s heavy duty product marketing director. “The new cleaning intervals we publish for our A26 engine are based on these new oils. You can continue to use older oils, like a CJ-4 or CI-4, but you’ll have to dial back the DPF cleaning interval.”
Engine lubricants are typically the single largest source of ash in the filter. Specifically, it is certain additives in the oil such as metal-based detergents, anti-wear additives, and anti-oxidants that were developed before DPF’s came along. The new oil classifications contain less of this material, which means that if you’re using a CK-4 or an FA-4, there will be less of that type of ash winding up in the DPF.
When choosing oil, be sure you’re using the right product for your engine. The CK-4 oils are for current and older engines, and are backward compatible with CJ-4, CI-4 with CI-4 PLUS, and CH-4 oils. The FA-4 oils are designed for newer engines (2016 and beyond) and are not backward compatible because of lower high-temperature/high-shear properties.
Oil has other ways of making it into your DPF as well, such as leaks and internal oil consumption. Any liquid, such as fuel, oil or coolant that makes it into a cylinder and eventually into the exhaust stream, will foul the DPF and lead to premature plugging, and perhaps permanent damage to the Diesel Oxidation Catalyst (DOC), the DPF, or worse, the SCR.
“Contamination of the SCR can interfere with NOx conversion,” says John Moore, Volvo Trucks’ product marketing manager – powertrains. “Once they have been damaged by coolant or oil contamination, they have to be replaced. They cannot be cleaned or repaired.”
Since the SCR is downstream of the DPF, the likelihood of contamination is slim, but if a severe problem goes unchecked for a long time, the risk is higher.
“Oil and/or coolant consumption all play a factor with DPF contamination and will result in the engine controller commanding more frequent regenerations due to the excessive backpressure created by the oil/coolant contamination,” says Kenworth marketing director Kurt Swihart. “Drivers should monitor oil and coolant usage and notify their maintenance department immediately if usage increases.”
Longer cleaning intervals
A combination of better technology and better monitoring has allowed engine makers to extend DPF cleaning intervals. Either a predetermined number of kilometers or hours, combined with fuel consumption, are reliable predictors of how heavy the engine is working, and how likely the DPF is to need cleaning.
“Since 2007 we have learned a lot, and with the addition of SCR in 2010 we have been able to tune the engine system differently, which is allowing us to reduce ash accumulation,” says Russ Poling, Cummins’ on-highway marketing communications manager. “We are now producing more torque at lower engine RPM, which reduces the amount of fuel we burn, and that is producing higher exhaust temperatures and steadier flow. All of which lead to more effective regenerations.”
More effective regens mean longer intervals between cleanouts.
Speaking of new technology, Volvo and Mack are now using what they call the Wave piston design, which they claim improves the completeness of the combustion and produces less soot. Moore told Today’s Trucking that Volvo is looking at extending its cleaning intervals to 600,000 kilometers or 10,000 hours for on-highway trucks.
Challenges will persist, though, for vocational trucks, fleets that run lighter loads, and those with lots of stop and go operation, like residential refuse collection trucks. “That’s a 50-yard dash, 1,000 times a day,” says Scott Barraclough, Mack technology product manager. “They will require a regen at least once a week.”
Doug Baker, fleet maintenance supervisor at St Mary’s Cement and CBM Ready-Mix in Toronto, says his fleet consists of brand new trucks and many that are 10 and even 20 years old. “Much of what we do is city work,” he says. “We don’t often get enough drive time between the plant and the customer to complete a regen while driving. Wet concrete has a limited shelf life, so we can’t just stop anytime we choose for 45 minutes to an hour and do a regen.”
He says they rely heavily on dealers to service aftertreatment systems because there’s just too much going on to keep his technicians trained on all the latest and greatest updates.
One trend we’re seeing that might please guys like Baker is smaller aftertreatment modules. It seem counterintuitive that a smaller DPF would go longer between cleanings than a larger one, but that’s what manufacturers claim.
“The name of the game is heat,” says Polling. “Enabling closer placement to [the] engine, retaining more heat inside the module, and better distribution and storage of the soot and ash are all in-concert contributors to higher efficiency and effectiveness.”
Polling says overall, servicing a Cummins aftertreatment system has become simpler. There’s easier access to the DPF, which saves time and money in the repair shop. “In addition, our dosing system no longer requires the use of coolant lines and our Single Module aftertreatment [system] has a single electrical connection, reducing hardware and software complexities.”
While owners of older equipment can’t yet take advantage of the newer DPF technology, they can sleep a little easier knowing things will only get better. Still, there are a few proactive things they can do to ensure the truck itself isn’t working against them:
Verify there are no exhaust leaks where heat can escape and dust or grit can get in.
Minimize idle time, especially in winter.
Train drivers to not ignore the dash lamp warnings, to report fluid top-ups, and not to overfill the crankcase when adding oil.
Use approved oils and never mix oil into fuel tanks.
Spec’ trucks with adequate engine size and gearing to operate with medium-to-high load levels to leverage passive regeneration.
Consider performing a manual regen during the Preventive Maintenance inspection to reduce the need to perform unanticipated and inconvenient parked regens.
The SCR side
Here’s the rest of the good news – there’s practically no maintenance required on the SCR system, including the Diesel Exhaust Fluid tank or the dosing system.
Navistar’s Nachtman says the only scheduled maintenance for that company’s SCR system (the Cummins’ Single-Module AT) is changing the DEF tank neck filter, which is in place to keep grit and debris out of the tank. “It’s a scheduled item at 500,000 kilometers,” he says. “That’s all. If there’s a problem with the DEF line return pump, you replace it. There’s really no other maintenance except to clean the tank if it becomes contaminated with something like diesel fuel.”
Volvo and Mack have added a DEF quality sensor to the tank to alert the driver to a potential contamination problem. “That came with the onboard diagnostics updates in 2016,” Moore says. “Previously the system would not detect bad DEF. Instead, it would guess at the source of the problem, sometimes targeting a sensor. You’d get some incorrect fault codes and possibly an engine derate because it wasn’t seeing the proper conversion rate. Now, you’ll see a code for bad DEF.”
Mack and Volvo have a scheduled DEF filter and pump filter replacement at 240,000 kilometers.
Many of the gains, of course, involve new equipment. Those with older trucks have to stay on top of the aftertreatment system. They are expensive critters to repair or replace. And for those buying used equipment, a thorough inspection of the aftertreatment system is highly recommended.