New Engines Demand Finer Fuel Filtration; Suppliers Use Nanofibers to Protect Systems
Tightening federal standards for truck emissions, including particulates, nitrogen oxides and, most recently, carbon dioxide, have led to higher-pressure fuel-injection systems that require finer fuel filtration than ever before to prevent engine problems.
With fuel pressures reaching as high as 44,000 pounds per square inch in the latest heavy-duty diesel engines, modern injection systems now call for filtration of particles as small as 2 or 3 microns. That is less than a tenth of the thickness of a human hair.
Failing to filter down to these microscopic sizes can lead to injector wear and failure. These, in turn, can cause catastrophic engine failures such as aftertreatment poisoning through overfueling, cylinder wall scuffing or even melted pistons, Russ Bretell, training and technical sales manager for Cummins Filtration, said in a video presentation.
Filtering for such tiny particles, however, has the potential to reduce filter life.
To address this challenge, filtration suppliers are using new synthetic materials to prevent their filters from plugging prematurely — a problem that tends to occur more frequently in the winter.
At the same time, expectations continue to rise for fuel filter efficiency, which refers to the percentage of particles of a certain size captured by the filter.
“Four- and 5-micron filters have been used for many years. However, what was considered high efficiency in the past may not cut it today,” said Scott Grossbauer, global director of clean fuel and lubricant solutions at Donaldson Co., a supplier of filtration products.
“In the past, 95% or 98% efficiency may have been considered good enough at 4 microns. Today, however, we are measuring high efficiency closer to 99.9%,” he said, adding that a fraction of a percentage point can make the difference on whether a filtration system can achieve the fuel cleanliness levels needed for the high-pressure, common-rail components on current engines.
In fact, some manufacturers now are looking for high-efficiency filtration of 2- to 3-micron particles, even though industry standards for cleanliness measure down only to 4 microns, Grossbauer said.
The filtration industry has been fighting the problem of filter plugging by introducing new types of filter material, generally referred to as “filter media.”
Synthetic nanofiber-based filter media can capture more particles while providing additional holding capacity for those contaminants because the fibers take up less volume within the filter, said Gary Bilski, chief engineer at Fram Group, which provides the Luber-finer line of filters.
But the additional efficiency, capacity and finer filtrating does mean added cost, Bilski said.
Bretell of Cummins Filtration also recommended synthetic media using nanofibers.
He pointed to the NanoNet and StrataPore technologies used in Cummins Filtrations’ Fleetguard filters. Those materials are stronger than the paper, cellulose and glass media that have been common in the past, he said.
“NanoNet results in a fully synthetic multilayer media that results in 10 to 13 times cleaner fuel out of the filters,” Bretell said. “Being fully synthetic, NanoNet filter media is not susceptible to water damage.”
The fibers also occupy less space in the filter body.
“The nanofibers are smaller than the cellulose, so as well as being more efficient in stopping the particles, they also offer more capacity within the filter,” Bretell added.
Donaldson’s Grossbauer reiterated that point: “Newer technologies have helped filters increase contaminant holding capacity within the same package size. However, that is not without challenge. As you pick up finer and finer contaminants with a fuel filter, plugging prior to your service interval can be a concern. What may have passed through a filter in previous years may be a contributing factor to plugging a tighter filter today.”
He said newer technologies such as the Synteq XP media included in Donaldson Blue filters have been designed to meet the protection requirements of high-pressure, common-rail components.
In addition to efficiently capturing debris, it also is important for filtration systems to retain contaminants while facing the wear and tear of trucking operations, Grossbauer said.
“The real-world challenges for filters come when they are subjected to engine and equipment vibration, fuel-flow surges and fuel-pressure pulsations,” he said.
The potential for fuel filter plugging is a frequent topic of discussion among members of American Trucking Associations’ Technology & Maintenance Council.
Darry Stuart, who is a past TMC chairman and co-leader of the popular Shop Talk sessions at TMC meetings, said the proper solution to that problem should not be to switch to less stringent filtration.
“Whatever anyone says, you must always filter down to a minimum 3 to 5 microns and never increase the media size to extend filter life,” said Stuart, who is president of DWS Fleet Management Services, which provides management services to fleets. “The filter is doing what it’s there for — to protect the fuel system and injectors.”
He is a strong proponent of providing extra filtration and recommends to the fleets he manages that they upgrade the fuel system by adding an external pre-filter such as those offered by Davco Technology. That increases the amount of filter media on the truck and prevents fuel filters from loading up between preventive maintenance intervals, Stuart said.
“More and more, it’s the need to change fuel filters that is determining the [preventive maintenance] interval,” he said.
To address this topic in greater depth, TMC has proposed a recommended practice, “Fuel Filters: Complaint, Cause & Correction.”
Task force Chairman Brian Mandt, who is the engineering manager for liquid filtration at Donaldson, said the document was assembled from industry resources and fleet input over a period of five meetings.
“We wanted to compile the information into a summary of things to look at when dealing with short filter life,” he said. “The new high-pressure, common-rail fuel systems have tighter clearances, so they need finer filtration. But the task force found short filter life is not from hard particles but more from soft content. This is fallout [from the fuel] caused by temperature changes.”
Michael Hoffman, vice president of fleet maintenance and facility services at FedEx Freight, said filter problems are more likely during cold weather.
“As fleets enter the coldest months of the winter, challenges with filtration tend to rise,” he said. “For any fleet of tractors, notifications about low power and engines not starting may require technicians to change fuel filters outside of preventive maintenance intervals in order to keep the fleet moving. At other times during the year, fuel filter changes usually last with no problem over scheduled intervals.”
In the end, a plugged filter also can been seen as a sign that it has been working.
“A filter gets plugged up because it is doing its job and removing the extra contaminants in the fuel,” Hoffman said. “The cleaner the fuel is kept through all stages of storage and transportation, the less likely it is that the onboard fuel filtration will plug up before its change interval.”
FedEx Freight is the less-than-truckload unit of FedEx Corp., which ranks No. 2 on the Transport Topics Top 100 list of the largest U.S. and Canadian for-hire carriers.
Aside from the filter technology, fleets also should pay close attention to the fuel being pumped into their equipment, suppliers said.
Fram’s Bilski said plugged filters often are caused by a problem with the fuel going into the truck’s fuel tanks rather than a problem with the filtration itself.
Grossbauer also advises maintenance managers to look to the fuel when filter plugging is an issue.
“The first step is to learn more about the diesel fuel you are putting into your equipment,” he said. “Ensuring that your fuel is clean and dry makes a big difference, but it’s sometimes not enough to be free of hard particles and water.”
Many problems can stem from the improper use or blending of fuel additives, he said.
“End-users sometimes use additional additives with the misconception that more is better, which can cause premature filter plugging because the total additive dose was too high,” Grossbauer said. “As a result, what can appear in fuel is a soft contaminant that will quickly plug filters, drastically reducing the expected service interval.”
Biofuels also introduce their own issues.
“Another example of potential contaminant is glycerin from biodiesel blends,” he said. “Buying biodiesel with lower free glycerin levels, keeping your fuel dry and protecting it from extreme temperature swings are all ways to mitigate this issue.”
Bulk fuel filtration also can prevent filter plugging by increasing cleanliness before the fuel ever reaches the truck, Grossbauer said.
Donaldson’s Clean Fuel Solutions business unit offers a bulk filtration product line designed to clean fuel prior to being pumped into fleets’ equipment, he said. “By stopping any of the contamination that may compromise equipment filter life, service intervals can be met and operations never disrupted.”
