Do you know the failure rate for your aftertreatment systems? You’d be surprised how many fleets don’t.
“It used to be that exhaust was way down the line items on expense for a fleet. Now it’s up there with oil and tires and fuel,” says Randy Griffith, sales and tech manager for Emission & Cooling Solutions.
Emission & Cooling Solutions works with fleets to implement training and DPF service programs for heavy duty aftertreatment systems.
“We preach total aftertreatment cost. It’s not about the cost of the cleaning as much as it is how much is it costing to maintain your entire fleet on this segment?”
Overview of the aftertreatment system
Beginning in calendar year 2007, heavy duty diesel-powered vehicles began using exhaust aftertreatment technology to meet more stringent U.S. Environmental Protection Agency (EPA) on-highway emissions standards.
The updated emissions standards included a significant reduction in particulate matter (PM) and nitrogen oxide (NOx) emissions emitted from heavy duty diesel vehicles. PM includes soot, unburned hydrocarbons, ash or sulfate.
The PM emission standard took full effect in 2007. The NOx standard was phased in for diesel engines between 2007 and 2010.
Diesel engines with aftertreatment systems must use ultra-low sulfur diesel (ULSD) — which was another U.S. EPA standard designed to help reduce pollutants in conjunction with limiting emissions. If a higher concentration of sulfur is in the fuel, it could cause damage to the aftertreatment system.
Heavy duty diesel engine aftertreatment systems were introduced as a solution to aid in reducing both PM and NOx emissions since the pre-2007 fuel system, air handling and combustion technologies were unable to complete this task up to government standards.
Generally speaking, the heavy duty diesel engine aftertreatment system has two primary components: the exhaust aftertreatment technology — which includes the diesel oxidation catalyst (DOC) and diesel particulate filter (DPF) — to reduce and mitigate PM; and a select catalytic reduction (SCR) system to reduce NOx emissions.
“Diesel-powered commercial equipment manufactured beginning in 2007 contained the DOC and DPF only,” Denso’s Gilbert Ramirez, manager, heavy duty product management, explains. “The EPA introduced the [2010 greenhouse gas emissions] requirements to eliminate NOx from the emission stream in 2010, which led to the inclusion of the SCR to the aftertreatment system.”
Denso, a supplier of OEM and aftermarket vehicle parts, and AP Emissions Technologies, a global manufacturer and distributor of vehicle emissions control systems and products, have partnered to manufacture and market a new line of OE-quality DPF and DOC products for heavy duty on-road and off-road vehicles and equipment.
“What the DOC does is it changes the chemistry in the exhaust stream, and utilizes heat to burn the soot into ash, and the DPF stores the ash until it’s time to clean and have it removed,” says John Lightner, Cummins technical sales support manager. “The SCR system, through a chemical reaction, by the introduction of the diesel exhaust fluid (DEF), changes the chemistry and eliminates the NOx and greenhouse gases, so that you have (a little water and nitrogen) coming out of the tailpipe. You’re not having the carbon dioxide coming out that gives you the greenhouse gas.”
Cummins designs, distributes and services diesel and natural gas engines and related technologies, including fuel system, controls, air handling, filtration, emission solutions and electrical power generation systems.
The Technology & Maintenance Council’s (TMC) Recommended Practice (RP) 355 on Maintenance and Inspection Guidelines for OEM-Installed Exhaust Particulate Filters for Diesel-Powered Vehicles provides details on the numerous original equipment diesel particulate filter (DPF) technology for heavy duty commercial vehicle diesel engines. In addition, RP 355 offers information about how the DPF works, and details on how to maintain the system and diagnose issues.
According to RP 355, the aftertreatment system can help reduce PM through a number of methods, including:
- Improved air management (e.g. optimized turbocharger)
- Improved combustion system (e.g. combustion bowl shape and location)
- Improved oil control (e.g. piston ring design and cylinder bore honing)
- Improved injection system (e.g. optimize injection duration, optimize injector hole size)
- Rated speed optimization (e.g. rated engine speed)
Find the root cause of aftertreatment issues
While traditionally many have pointed to the DPF as the cause of aftertreatment issues, fleets should note problems with the DPF are typically symptomatic of an issue further upstream in the system.
“If your engine is not running correctly, then it’s going to emit more emissions and can plug up your filter and create more maintenance,” says Cummins’ Lightner.
There are two areas to address when it comes to servicing the aftertreatment system: proper diagnosis, and routine maintenance. Emission & Cooling Solutions’ Griffith advises setting a proper preventive maintenance (PM) schedule for the aftertreatment system is vital to the efficient operation of the vehicle.
When addressing what’s thought to be a filter issue, “everybody does one of two things: they either point at the filter and say, ‘that filter’s bad,’ or they do a manual regen to try to get the truck back up and running and send it down the road, and they don’t address the issue that’s going on with the truck,” advises Griffith.
A regeneration is completed on the DPF when the filter has reached a certain saturation level, monitored by the engine control unit (ECU).
There are three types of regeneration that can be done: a passive regeneration automatically completed by the vehicle, an active regeneration manually initiated by the driver, or a forced regeneration done by a technician in the shop using a scan tool. Regardless of the type of regeneration, there are two requirements for proper regeneration of the system: adequate air volume and proper temperature.
When in the shop, a scan tool can be used to confirm air measurements and proper temperature for diagnosing issues with the aftertreatment system and DPF.
Air volume aids in pushing the PM through the DPF; a hot enough temperature allows the system to burn the soot into ash.
Griffith notes that air intake issues, such as a leak, can cause a decrease in air volume further down the system. A high-pressure smoke machine can aid in diagnosing an air leak, he says.
“The number-one thing that we find that causes premature issues [with engine aftertreatment servicing] can be pointed back to an intake or exhaust leak,” Griffith says. “Or, a leak in the system with clamps and gaskets.”
“It used to be, you could find an exhaust leak really easily because you had a whole bunch of black soot around wherever it was that was leaking,” Griffith adds. “That’s not so much the case anymore. Making air visible using a smoke machine to make sure that your clamps and gaskets seat well is really important. If you get air in the system that hasn’t been heated through the DOC or a loss of back pressure due to the leak, you’re going to have problems.”
When it comes to high enough temperatures, Griffith says some fleets may see a drop in system temperature if they do not properly re-insulate the exhaust pipe after service.
Conversely, the system can also run too hot, particularly when there may be a leak upstream, according to Denso’s Ramirez.
If more oxygen is accessible to the system through these leaks, it “can result in an overly rich mixture reaching the aftertreatment equipment,” Ramirez says.
“This causes higher-than-normal heat, which can lead to destroying the PM coating and melting the substrate,” he adds.
Temperature readings, measured with exhaust temperature sensors, are a key indicator in diagnosing an issue within the aftertreatment system.
“We don’t want to have too big of a temperature drop across the face of the DPF,” Griffith says. “As far as diagnostics go, DOC outlet and DPF inlet sensors are the first place to check to ensure a proper regen is taking place.”
“A lot of times we can start diagnosing by looking at the temperature sensors,” he explains. “On a DOC, you have to have a temperature of 600 degrees F to get the ramp up and the catalyst effect, to get that exhaust really hot. We’ll use the front temperature sensor to make sure that we’re getting that temperature that we need to make the ramp up happen, then after the DOC on the inlet of the DPF, we look at that temperature and make sure we’re getting enough heat — somewhere around 1,000 degrees F on the inlet side of the DPF — and then we look at the outlet side of the DPF to make sure we’ve got some temperature coming through there.”
Also as it relates to sensors, additional sensors used in the aftertreatment system include the pressure differential sensor, used to measure the current capacity of the DPF, and the NOx sensors.
“You have one [NOx sensor] at the turbo outlet, and you have one at the tailpipe outlet of the SCR,” explains Cummins’ Lightner. “What those are doing is measuring how much oxygen is in the exhaust flow, as well as how much NOx is in the exhaust flow, and it determines how much [DEF] needs to be injected to eliminate the NOx level at the tailpipe.”
“The number-one sensors that we’re seeing people having problems with are the NOx sensors,” Griffith adds. “[There’s one] on the inlet side and one on the outlet side, and there’s been some talk in the industry about having problems with the NOx sensors on the outlet side being caused by water that falls in the stack if it’s got a vertical exhaust … If you get a lot of water in the exhaust — of course, water and electricity don’t really work together very well.”
Proper DPF management and maintenance
As part of a regular preventive maintenance program, DPF management can be handled through four options: filter exchange programs, cleaning the filters in-house, cleaning with a service provider, or replacing with new filters.
DPF exchange programs are designed to allow fleets to send used filter cores to be remanufactured. This can help alleviate cost, but Emission & Cooling Solutions’ Griffith suggests understanding the details of the exchange program to be aware of the history of that remanufactured filter.
“The primary benefit of the exchange program is uptime, assuming the exchange unit is available,” adds Denso’s Ramirez. “The risk is the unknown history of the core which could contain multiple cleaning events.”
“When you get a reman filter, there’s no way to know what happened to that filter along the way,” says Griffith. “You don’t know how many miles are on it, you don’t know any of that.” Griffith suggests confirming the cores sent in are the same cores sent back, and that is done through a service provider like Emission & Cooling Solutions. “They can tie it back to a unit, and they know if there was an EGR cooler that leaked on that truck (for example). Or, if you’re having trouble with a specific truck, you can track that filter through your fleet.”
When utilizing an exchange program, Duane Bratvold, western regional sales manager for Webasto suggests confirming the core is still intact before sending it in for remanufacturing.
“‘When you send these filters in, before you send them, take a wire, go down into the cells to make sure it’s not melted in the middle,” he says.
Webasto offers cold-start and idling solutions for the commercial vehicle market.
When it comes to setting a PM schedule for DPF cleaning, Griffith stresses it’s important to consider the operating environment of the fleet. But, as a general rule of thumb he has seen success with recommending a cleaning after 250,000 miles, when the vehicle will typically still be under warranty. During this PM, Griffith suggests more than just air to clean the filter, instead opting for a thermal, or even liquid, cleaning.
“With the newer filters, it’s a lot harder to get all of the ash out of those filters, so we’ve found where actual liquid cleaning (or thermal cleaning) is the way to go,” Griffith says.
“Of these cleaners, the aqueous types have proven far more effective than the ‘bake and blow’ method, at removing a higher percentage of ash from the DPF,” Ramirez confirms.
When completing a PM for the aftertreatment system, Griffith also suggests replacing the clamps and gaskets.
“If you think about it, you’ve got maybe 1,200 degrees F in the exhaust, and you have metal there,” Griffith says. “Metal expands and contracts with heat, so we recommend always replacing the clamps as well as the gaskets, just to make sure you get a good tight seal.”
Griffith’s final suggestion for preventive measures is to employ the use of a smoke machine when the system is disassembled for the PM “so you can verify that everything upstream is tight and you’re getting all the air volume and temperature you need to make sure that truck continues to regen for another 100,000 or 200,000 miles without having to touch the system again.”
An alternative to cleaning is always to replace the filter with a new unit. Replacement of the DPF may be the most cost-effective solution, depending on the overall cost of the aftertreatment program for the fleet.
Looking for signs and analyzing the filter itself can also prove useful to understanding issues on the vehicle.
“The more that these trucking companies can get educated at what the DPF is doing, what the markings are or the contamination that’s on the filter - then it gives them a little better fight to try to offset these issues,” Bratvold says.
Regardless of the method employed for handling DPFs, an analysis is critical to understanding the full cost of an aftertreatment program, stresses Griffith.
For instance, if a fleet implements a filter cleaning program in-house, he suggests the company not look only at the cost of the cleaning process itself.
“If you can get a better cleaning process and you can reduce the number of filters you’re having to replace, you actually save money in the long run,” Griffith explains.
“(Fleets may not) take into account the other factors around it, like what is the failure rate of the filter? If you get a really good cleaning process and you can bring the failure rate down, but the cost of cleaning goes up, you still actually win, because you’re not replacing $2,000 filters as often,” he adds.
All systems are not created equal
Vehicle idle time plays a significant role in aftertreatment system performance. In addition, duty cycle is an important consideration for the service frequency of aftertreatment systems.
“Depending upon how much idle time they have, whether the engine is consuming engine oil, the duty cycle — are they over the road or are they stop-and-go; the environment such as the ambient temperature — all those play a factor into how often the aftertreatment needs to be maintained,” says Cummins’ Lightner.
Idling is detrimental to extending the life of DPFs, says Webasto’s Bratvold.
“Idling at a truck stop, or when they’re out doing their normal job during the day just ... absolutely destroys a DPF. The DPF is so cold, all it is is like a garbage can collecting soot, and then it gets to a point there’s too much soot and it can’t overcome it,” Bratvold explains.
This is because the engine aftertreatment system works most optimally at highway speeds, when a vehicle’s engine gets hot enough to complete a regeneration cycle. Any extended idling means the vehicle’s engine is not
burning hot enough. This causes excessive soot to collect in the DPF, versus allowing the system to heat up to an optimal temperature to
burn off the soot into ash. Technicians can complete forced regenerations, using a scan tool in the shop, to complete this service. But that takes the vehicle out of service as well.
Preventative measures to consider
Bratvold recommends, based on studies conducted at Webasto, that a coolant or engine heater can aid in reducing the service requirements on an aftertreatment system.
“We’ve proven that in some of the tests that we’ve done in the laboratory, where we’ve preheated an engine and start it up, and we measured the soot in that cold startup area,” says Webasto’s Bratvold. “Just by preheating the engine you can reduce that soot by 60-plus percent. If you can stop that cold, wet, dense soot from going into the DPF, until the DPF warms up to where it can start to regenerate, you’ve beaten half the battle right there.” This can be done through an engine heating system, either specified at purchase or installed as an aftermarket option.
If you can preheat (the engine) every day, depending on your duty cycle, you can extend those intervals — you can probably cut out three to five cleanings per year, depending on what your duty cycle is,” Bratvold says. “Every time that DPF gets full, if you do not deal with it then, right at that time, then you run the risk of a contaminant getting in there causing a catastrophic failure.”
There are different options to heat up the engine, including a coolant heater and a plug-in block heater. The heater must be turned on about 45 minutes before the driver gets in the cab to start his or her route. This gives the system enough time to warm up before the vehicle is turned on.
For maintenance on the engine heater, Bratvold advises to turn it on at least 20 minutes per month, even in warmer months, to ensure continued operation. In addition, the fuel filter on the engine heater should be changed annually.
With that, driver education is critical to ensure system issues are addressed as quickly as possible.
“Operator error is probably the number-one failure of a DPF,” Bratvold says. “A lot of these guys will drive down the road and the light will come on and they don’t want to stop so they’ll just keep driving it until something goes wrong and they’re forced to pull over.”
“If a light comes on you have to deal with it immediately,” Bratvold adds. “You need to understand who is cleaning your filters and make sure they have the expertise to find issues and not just send you back the filter.”
If a fleet employs a filter exchange program, Emission & Cooling Solutions’ Griffith also suggests going through a single-source provider to service DPFs. This allows for complete data collection of all filters through one provider, versus going through multiple vendors.
“All that data comes into one place,” Griffith says. “And it should be compiled and it should be presented as quarterly, monthly, yearly, however they want it.”
It is also critical to ensure proper technician training when it comes to coding maintenance and service of the aftertreatment system.
“If you have a DPF failure and you’re sending the filter out for cleaning and you’re not getting that (filter) back, finding a way to code that as a failure is really the only way to do it - making it a data point, basically,” Griffith says. “With the systems out there now, everybody runs their own proprietary kind of system, from what I understand, just making sure that people are recording it the correct way, so you can identify that part as a failed filter will lead to a better understanding of failure rates.”
Takeaways and next steps
Emission & Cooling Solutions’ Griffith recommends every fleet look at the total cost of aftertreatment - not just the price of the replacement filter, but the cost of cleaning, replacement programs and all aspects of the service.
“There are very few people who have a good grasp on exactly how much their aftertreatment is costing them,” Griffith says. “We’re using data analytics to really help people understand what their failure rate is, as well as identifying ‘this truck has a higher failure rate than this truck.’ In the future, some people will probably be using that when they spec their trucks.”