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How to keep your aftertreatment system from ‘eating your lunch’


ORLANDO, Fla. — Complex emissions aftertreatment systems such as diesel particulate filters (DPFs) and selective catalytic reduction (SCR) have been attached to trucks for more than five years now, but still fleets are struggling with the maintenance and repairs of these items.

Kirk Altrichter, vice-president of maintenance with Crete Carrier Corp., asserted at the Technology & Maintenance Council’s fall meetings that, “Emissions-related problems are eating our lunch.”

He said 3-4% of the company’s 5,500 trucks are down at any given time and that a quarter of all maintenance is emissions-related. “That’s a lot of technician time and a lot of downtime,” he said.

While he acknowledged exhaust aftertreatment systems have accomplished their objective by reducing NOx, PM and CO2 emissions, he also said “Emissions systems create upstream problems and downstream woes.”

Some of the problems Altrichter has dealt with include: leaked coolant causing cracking of the DPF and fouling of the diesel oxidation catalyst, leading to catastrophic engine failures; fuel leaks that have melted the DPF and created the need for premature cleaning; oil leaks that have clogged the DPF; and misfilling of diesel tanks with diesel exhaust fluid (DEF) and vice-versa.

Getting DEF into the fuel tank leads to a $15,000 repair, Altrichter pointed out, and getting diesel in the DEF tank will cost $5,000. Usually, the driver doesn’t realize he has misfuelled the truck and will operate the vehicle, making the problem worse. Altrichter wondered why sensors aren’t on-board to provide an early warning when diesel has entered the DEF system or DEF has gone into the fuel system.

“Why are there no sensors to prevent the spread of DEF and vice-versa?” he wondered. “A sensor and a gate to close the flow of either would save a tremendous amount of cost. I’m generally not a proponent for adding a bunch more sensors, but there may be a case made for a few more.”

Altrichter also said questions remain about the best ways to service the DPF.

“What is the best recommendation?” he asked. “For me, the best recommendation would be that I wouldn’t have to touch it while I own the truck.”

Vic Meloche, manager, technical sales and support for Detroit and Kevin Otto, aftertreatment systems program leader with Cummins, said there are steps fleets can take to minimize problems related to the aftertreatment systems.

“Most aftertreatment issues stem from upstream issues,” said Meloche, who urged fleets to pay close attention to the maintenance of their engines. He said fleets should act promptly on malfunction indicator lights and be quick to install any hardware calibration updates as they become available.

“Do not ignore malfunction indicator lamps,” agreed Otto. “In the past, you might have been able to get away with this, but not today.”

Otto said fleets need to follow the troubleshooting procedures recommended by the OEM, noting, “Often a visual inspection isn’t enough to make an accurate repair. Follow the OEM’s troubleshooting and inspection guidelines.”

One of the more common problems a fleet may encounter is face plugging of the diesel oxidation catalyst – black deposits that form as the result of unburnt fuel collecting on the front end of the catalyst. This increases backpressure on the engine and requires exhaust gases to funnel through a smaller area than intended, Otto explained. As a result, the exhaust gas travels through the oxidation catalyst too quickly for processing and travels through to the particulate filter, which can become plugged prematurely.

“It leads to a cascading effect that causes components to fail,” Otto explained.

One way to prevent face plugging of the DOC is to spec’ lower horsepower engines, which must work harder, generating the higher temperatures the aftertreatment system needs to properly function.

“If the engine is not working hard, it won’t keep the temperatures up,” he said. It’s also best for trucks to spend at least some of their time in over-the-road duty cycles, which create the best conditions for DPF regenerations.

Otto also warned against installing winter front grille covers, which can confuse the aftertreatment system and cause false readings.

“It’s better to have a cooling system that’s working properly so a winter front is not necessary,” Otto warned.

When it comes time to clean the DPF, Meloche said the technique chosen is not important – as long as it achieves a complete cleaning.

“We don’t care how you clean the filter, as long as you get all the ash out,” he said.

If the filter isn’t properly cleaned, leftover ash can compete with soot for space, causing the DPF to overheat and potentially causing the substrate to crack. This will allow unfiltered exhaust gas to pass through to the SCR catalyst.

The results can include a poisoned catalyst and cracked DPF, both expensive problems to repair.

Starting next year, Meloche said trucks will require soot sensors installed at or near the outlet of the aftertreatment device, which will ensure the exhaust leaving the tailpipe is soot-free. This will help identify cracked or non-functioning DPFs, Meloche noted.

“Starting next year the EPA says we have to start catching cracked filters a lot sooner than we have in the past,” he explained.

Some of the most common aftertreatment system failures are caused by water in the fuel, which can cause deposits and rust to form on injectors, leading to sticking injectors.

“If an injector sticks open, now you have issues with an external fuel source, little air and crazy things happen,” Meloche warned.

Fuel filters should be changed as per OEM recommendations and water separators used. Meloche also warned that some fuel additives can hinder the effectiveness of water coalescent filters. Using too much cold flow additive can introduce sulfur into the aftertreatment system, leading to failures.

To avoid misfuelling mistakes, Meloche urged fleets to attach fuel tank stickers and to train drivers so they know not to put diesel in the DEF tank and vice-versa and if they do so, to fess up early so the tanks can be drained before more damage is done. Meloche also said to ensure air filters don’t become plugged.

“Proper airflow is key to a smooth-running and healthy engine,” he said. This also means checking the air system for rust and debris, which can be passed along the system where it will plug filters and potentially defeat the DEF system. One more thing fleets can do is to ensure they’re using quality DEF.

“It’s important that everyone only use certified DEF,” he said. “There are people taking fertilizer and mixing it with water and trying to make their own DEF. Only the certified DEF should be going into the tank.”


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3 Comments » for How to keep your aftertreatment system from ‘eating your lunch’
  1. Darren Burchill says:

    A fuel tank sticker should read do not operate this truck with scr system in functioning condition.

  2. PS says:

    What would happen if the SCR/DOC was filled with DEF with incorrect volumes or completely filled?

    We have had a 2013 Hino 338 that had a bad urea doser and it leaked DEF into the SCR over a 500 mile trip. Hino went into safe mode we had to tow it back to dealer ( at a very expensive tow) . Hino changed the urea valve, reset the computer and truck was good to go. Then shortly after the whole system collapsed both the DEF and the SCR filters were completly burnt and cost to repair is expensive.

    So would a bad DEF urea injector cause massive failure?

  3. E.knowles says:

    DEF stands for Diesel Engine Failure. I’m a one truck owner operator and this emissions system plagued with problems is about to put me out of business. No one can figure out how to keep my Volvo working. Every Volvo dealer just hangs 1000,s of dollars worth of parts on it. Driving otr is already a hard way to earn a living, now we have the added worry of these trucks going to derate soon in the middle of nowhere. I’ve got to hand it to the government and these truck manufacturers. They have finally made semi trucks as undependable as all the 4 wheelers running around with their check engine light on. But big trucks derate, imagine how much hell would be raised if people’s cars went into derate as soon as check engine light came on.

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