DPF Retrofits Growing Due to California Rule

This story appears in the May 27 print edition of Transport Topics.

Retrofits of diesel particulate filters onto older vehicles that never had them will take a jump in 2014, when California’s rule requiring DPFs on all pre-2007 trucks takes effect, forcing owners to pay close attention to engine problems that produce clogged units.

California’s DPF requirement applies to “virtually every truck with a gross vehicle weight rating of 26,000 or more pounds carrying capacity,” said Mike Tunnell, director of environmental affairs for American Trucking Associations. Tunnell is based in Sacramento.

The requirements affect vehicles in use throughout the state, as well as most entering from out of state.

“Any truck that travels on a California road needs to be in compliance, no matter where that truck came from,” Tunnell said. “Limited exemptions exist, including some for rural areas” and for longhaul trucks driving less than 1,000 miles in the state.

California’s Air Resources Board estimates that the number of trucks in the state that need aftermarket DPFs will triple, from more than 35,000 in 2013 to 105,000 in 2015, plus about 10,000 trucks in neighboring states that will have to have retrofits.

Growth in retrofitting isn’t limited to California. Demand for the process is expected to grow as jurisdictions across the country seek to cut the amount of particulate matter, or soot, from diesel exhaust by mandating DPFs.

Parts of Texas, Georgia, the northeastern states from New York to Maine and most of California — which has six of the nation’s 10 most polluted areas — are likely to see retrofit requirements for older trucks.

Tony Brasil, chief of the CARB’s heavy-duty diesel implementation branch, said those jurisdictions with more pollution are the most aggressive in reducing emissions, because while EPA’s air quality standards are uniform nationally, areas not meeting them must take extra steps to ensure compliance.

DPFs have been standard on heavy trucks since 2007, and while they are sometimes blamed for poor engine performance, manufacturers said most DPF problems — clogging with unburned fuel or accumulated ash — arise either with the engine itself or result from the truck’s duty cycle.

“Examples of engine issues that could cause DPF clogging are problems with fuel injectors, [exhaust gas recirculation] systems or turbos,” said Simon Guest, global marketing leader for Cummins Emission Solutions in Columbus, Ind. “Less frequently, premature DPF plugging can also be caused by external sources such as fuel additives or oil in the fuel.”

Joselyn Rendon, a spokeswoman for Ironman Renewal LLC, a diesel retrofit installer based in Corona, Calif., agreed that out-of-tune engines can create DPF problems.

“A poorly maintained engine may result in DPF failure due to various factors, such as emitting much heavier smoke, release of worn-out materials into the exhaust stream, excessive ash from the engine oil, etc.,” she said.

“A failure of the turbocharger could allow engine lube oil into the exhaust stream and subsequently coat both the diesel oxidation catalyst and the DPF with that oil,” which would require removal and cleaning, said David McKenna, director of powertrain sales for Mack Trucks, a Volvo Group subsidiary based in Greensboro, N.C.

While there are some problems, Ironman’s Rendon said a retrofit could extend the life of an old truck by keeping it on the road after the 2014 regulation kicks in.

“In most cases, if a fleet were to retrofit all their vehicles by year-end, instead of replacing them with newer, more expensive models, the life span of those trucks would be extended to up to 10 years, meaning [owners] don’t have to worry about replacing their vehicles with a 2010 or newer model-year engine until 2023,” Rendon said.

She said a DPF retrofit runs  $10,000 to $15,000, while a new truck costs upward of $100,000 for a 2011 or later model truck and $35,000 to $55,000 for a used truck made between 2008 and 2010.

In fitting a DPF to an older truck, the owner has to decide whether to use “active regeneration,” which uses an injection of fuel to the exhaust to clean unburned soot from the filter, or a “passive” unit, which depends on higher exhaust temperature to do that cleaning.

“It comes down to three things: engine model year, duty cycle and driver operation,” she said. “Vehicles with older model-year engines will expel higher levels of diesel exhaust emissions and therefore will most likely not qualify for a passive device. Also, if the candidate engine does not meet the required temperature criteria of the passive systems, then an active system will be assigned instead.”

Rendon added, “The operation style of the driver will have some influence on how the engine runs and the emissions output.”

Another factor that fleet managers must pay attention to, especially with older engines, is that DPFs tend to mask engine problems.

“With a DPF in place, the major disadvantage that the maintenance staff has is that the visual black soot trail or white smoke coming out of the tailpipe — which was previously the method of determining an engine problem — is now replaced with a DPF system warning light [that] requires a system download” to see it, Rendon said.

Because it consumes fuel, active regeneration costs more than passive regeneration.

“A typical active regeneration event consumes approximately three U.S. gallons of fuel. There are engine designs that require or demand an active regeneration every five hours. So in a typical day, there may be demand for two to three events at three gallons of fuel per event. That translates into six to nine gallons of diesel fuel at $4 per gallon, which amounts to $24 to $36 per day in fuel expense,” McKenna said,

“A highway tractor will produce a significant amount of quality high- temperature passive exhaust heat. Constant speeds . . . produce less soot and can be oxidized completely” through passive regeneration, McKenna added.

He said the U.S. Environmental Protection Agency certification year and sometimes the DPF model also factor into which vehicles need which type of regeneration, due to the effect of selective catalytic reduction used on most 2010 model-year engines. EPA’s 2010 emissions rule required virtual elimination of nitrogen oxides emissions.

While higher engine heat cuts down on soot, it also increases NOx emissions. Most truck and engine suppliers went to SCR to deal with NOx, allowing the engines to run hotter. Engines using only exhaust gas recirculation, to cool combustion temperatures and keep NOx low, tend to produce more soot.

“For a 2007-certified typical highway application, we would require an active regen about every 11.5 engine hours. The same application for a Mack ClearTech 2010 certification could be as long as never. I have seen Logged Vehicle Data reports that have tractors with greater than 150,000 miles with no requests for an active regen. This is a direct result of selective catalytic reduction and reduced [exhaust gas recirculation].” McKenna said.

He added, “We have highway tractors with 180,000 miles that have never had a demand for an active regeneration event. The EGR-only designs consume a great deal of fuel just to keep the DPF clean.”

Even DPFs on longhaul trucks that use passive regeneration may eventually accumulate so much soot that they need to be cleaned out.

“When chassis mileage accumulates to around 250,000 miles, the DPF is starting to reach its design limit for ash loading,” McKenna said. “After the soot is oxidized, trace amounts of residual ash are left over and stored in the DPF. As the DPF fills with the ash, the effective surface area for soot collection is reduced, and demands for active regeneration [soot removal] events increase.”

While early experience with DPFs may have resulted in decreased fuel economy, more recent models and further emissions changes have improved efficiency.

“Most of the issues related to the DPF in 2007 were due to unfamiliarity with the system,” which often resulted in a DPF that had to be cleaned by an external machine because of the thick soot level, said John Moore, manager of powertrains for Volvo Trucks .

“With the advent of SCR and the EPA 2010 engines, active regeneration was replaced with passive regeneration along with lower exhaust gas recirculation rates due to DEF elimination of NOx, paving the way for a 5% increase in fuel efficiency versus 2007 engines,” he added.

“Depending on the engine/aftertreatment system design, adding particulate filters may impact fuel economy,” said Zornitza Pavlova-MacKinnon, senior manager of aftertreatment and applications for Daimler Truck Group North America, which owns Freightliner Trucks and engine maker Detroit Diesel Corp. “For example, a significant increase in back pressure can affect fuel economy, but it can be managed by system design considerations.”

Vehicle exhaust piping modifications to accommodate the running board, soot accumulation in the DPF, ash accumulation in the DPF, among others are among those considerations, she said.

“DPFs can certainly impact fuel efficiency,” said Elissa Koc, a spokeswoman for truck manufacturer Navistar Inc., based in Lisle, Ill. “As soot and ash build in the filter, the engine must work harder to run the DPF. Therefore, maintaining cleaning and service intervals maximizes fuel efficiency.”

The right type of engine oil can prolong the useful life of a DPF, Koc said.“In addition, oil type can impact maintenance intervals. For example, CJ-4 lube oil extends the recommended cleaning interval by almost 100,000 miles.” CJ-4 is a high-alkaline oil considered essential to a DPF’s operation that is recommended by the American Petroleum Institute because it is designed to produce low amounts of ash.

However, the oil is expected to go out of use when a new oil is introduced around 2016, Koc said.

Truck makers Kenworth Truck Co.; and Peterbilt Motors Co. declined to comment for this article.