For water removal, many filter manufacturers will use an absorbent technology to literally absorb water from the fuel. Once the absorbent can no longer absorb and hold water, the filter must be replaced. The Aquacon diesel filters from Parker Velcon use an absorbent technology called Super Absorbing Polymer, which is in the same family of chemical products as diapers. “It actually chemically bonds the water to a polymer and it’s no longer water at that point,” says Muzik.
In conjunction with more absorbent filtration media, water separators and coalescers can be used to further enhance water and particulate removal. The SWK-2000 Series of fuel water separators from Separ Filter, for example, use five stages of filtration to separate water and the majority of particles prior to the fuel passing through the filter media. Coalescers, on the other hand, continually remove water by gathering droplets of water from the fuel and dropping them into a sump. Unlike an absorbent, which requires users to replace the filter once it is no longer able to absorb and hold water, coalescers have a sump that needs to be drained on a periodic basis.
“Effectively, customers can have continuous operation of [a] filter system without having to change elements due to water,” says Thomas.
Changes in fuel
Though fuel quality has improved within recent years, there are still many places around the globe where fuel quality is questionable. According to Loftis, 50% of the world’s fuel supply does not meet current ISO fuel cleanliness standards.
“In many of our field experiences [we] have seen fuel samples 30 times dirtier than the ISO 18/16/13 specified by the fuel injection equipment manufacturers,” adds Barry Verdgan, research fellow at Cummins Filtration. ISO 18/16/13 states no more than between 1,300 to 2,500 particles greater than 4 micron can be present in the fuel.
Some fuel suppliers have also been known to dilute their diesel fuel with water in order to trick customers into thinking they’ve received more fuel than they actually have. Because of practices like this, Muzik notes the importance of filtering fuel before it enters a vehicle in addition to using onboard fuel filtration systems.
Along with poor fuel quality, filter manufacturers have had to contend with the introduction of biofuels and ultra low sulfur diesel (ULSD).
Biofuel is challenging because it is hygroscopic, which means it attracts water into the fuel. “It’s actually like a magnet and it pulls water [in] from the atmosphere and surroundings,” says Bigelow.
As biodiesel grades increase, so does the aggressiveness of those fluids, requiring different metallurgy and filter media binders to be used in fuel filters. For example, Bigelow notes that Separ Filters had to change the type of materials used in the O-rings, seals and other components in its filtration systems to ensure compatibility with up to B100 biodiesel.
Poor quality biofuels can also be an issue, notes Muzik. If a biofuel is not refined properly, a byproduct called glycerin will become present in the fuel. Glycerin is basically the same thing as soap, and it will coat fuel filters as well as potentially deactivate coalescers, inhibiting their ability to remove water from the fuel. Muzik says this was more of an issue in the past. “ [People] are being more diligent in specifying the quality of the biofuel they’re putting into their engines,” he states.
With ULSD, water removal is also a challenge because the chemistry of the fuel changed from the previous low sulfur version of diesel. ULSD contains 15 parts per million (ppm) of sulfur, whereas low sulfur diesel contains 500 ppm. According to Thomas, the change in fuel chemistry changed the surface tension of the diesel and made it harder to get water out of the fuel.
Challenges with ULSD can also arise from the additives used in them. Verdgan says some blends use additives that can precipitate out as soaps when metal ions are present, causing injector sticking and, in extreme cases, plugged filters.
Filtration demands will increase
As engine technologies continue to progress, many engine manufacturers foresee injection pressures doubling again, causing injector openings to decrease in size even more. This will further emphasize the need to have cleaner fuels running through a vehicle.