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Fuel’s #1 Enemy Is All Wet

High-pressure common-rail (HPCR) systems are precise but complicated pieces of machinery that require the cleanest possible fuel to function without breakdown. The old “clear and bright” visual inspection of fuel is no longer good enough when inspecting fuel for cleanliness; even microscopic contaminants can cause engine failure and costly downtime.

But HPCR engines have been around long enough that OEs and operators alike are largely aware of the problems caused by dirt and other hard particulate in fuel, and there’s a general understanding of the importance of effective filtration both on the vehicle and in bulk fuel tanks.

Hard particles aren’t the only fuel-related threat to these engines. In a survey* of on- and off-road service centers conducted by Donaldson Filtration Solutions, it became clear that water can play a major role in HPCR fuel system reliability, especially in regions with high humidity and/or poor fuel quality. “Some of the mechanics we surveyed told us that water-related issues are the largest challenge they face,” said Doug Lundstrom, product manager at Donaldson. “Issues with water can be quite complex, and equipment owners might not be aware that they are having water issues or how to deal with the issues effectively.”

Maintenance Intervals Aren’t Hitting the Target

The general rule of thumb is that, in perfect filtration conditions, an operator can expect to get a million miles out of an HPCR engine before the “lifetime overhaul” milestone that usually consists of injector replacement. It’s expected (or hoped for) that the injectors at least reach the 805,000 km / 500,000-mile mark, when most engines receive a mid-life overhaul. But in humid climates or anywhere that water in fuel is a reality, users are consistently getting much less than the expected mileage before injector replacement.

“Our survey indicated that 565,000 km / 350,000 miles is a more realistic mileage that many operators are getting out of their engines before replacing HPCR fuel system components such as high-pressure pumps and injectors,” Lundstrom says. “Largely due to fuel issues, Southern shops especially are so used to changing injectors after such a short lifespan, that’s it’s just accepted as reality.”

But this doesn’t have to be reality.

Understanding is the First Step

It’s hard to think of water as a bigger threat than dirt and other solid particulates, but what you can’t see can hurt you. Water is, quite simply, an incredibly destructive contaminant that can infiltrate fuel, which is why OEs typically specify that minimal free water reaches the HPCR system. Water can cause damage in so many ways. If it comes in contact with iron and steel components, rust particles can enter the fuel stream and etch or abrade the system. Water droplets can cause abrasive wear due to water’s inherent lack of lubrication compared to the fuel itself. Water can dissolve certain contaminants in fuel, creating harmful deposits in the fuel stream. Pitting and spalling can occur when water is exposed to heat and pressure in tight spaces. And in colder climates, water in fuel can turn to ice, which then becomes the hard particulate that we all know can ruin an engine or its injectors.

Injector wear due to water in the fuel.

And those are just the direct complications that water can introduce into a fuel system. If left unchecked, water can interact with certain chemicals in fuel and create a “soft solid” that can rapidly plug onboard filters or even cause deposits that can act as hard particulate. The presence of free water in any bulk or onboard tank can cause microbial growth that quickly plugs filters and an acid that corrodes metal components.

Any way you look at it, water in fuel is bad news for an engine. So what can be done about it?

Technology Is Evolving, and Testing Needs to Evolve With It

While “barrier-style” filters remain prevalent, this technology might not offer the needed protection against water in all operating conditions. As the industry has moved to ultra-low sulfur diesel (ULSD) and more biodiesel, removing water from fuel has new challenges. First, many of the new additives and biodiesels can change the fuel chemistry, making it much more difficult to remove water from the fuel. These new chemistries (including surfactants and soft contaminants that didn’t exist before) can coat filter media fibers and lessen their ability to repel water. 

To combat these increasing difficulties with water, the on- and off-road industries are starting to move to multi-stage coalescing filters which can be more effective in removing water throughout the life of the filter. Multi-stage coalescing fuel filters actually allow water droplets to accumulate and grow in size before being repelled by a hydrophobic screen into a water collection area. While they’re proven to be more effective at water removal, some OEs are hesitant to adopt the new technology, especially in off-road equipment. This is in part because testing and research methods vary, and this leads to misunderstanding of the problem.

“Current ISO test standards for water removal really exist to compare one new filter to the next,” Lundstrom says. “They are not effective in predicting how a filter will perform in real-life applications. A filter is only new once; the effectiveness of a filter changes throughout its lifetime.”

To further complicate matters, most testing is done in a lab setting as opposed to field conditions. “Lab testing is accurate, but sometimes not the full picture,” Lundstrom says. “Out in the field, the challenges are almost endless. Field tests help add understanding of all the contaminates we’re facing, and only by understanding those contaminates can we develop technology to deal with them.” Filtration companies that conduct real-world testing on filtration products have a leg up when it comes to protecting today’s advanced engines, both on and off road.

Protect Your Supply, Protect Your Equipment

The easiest way to protect your HPCR engine is to prevent water from ever getting into your fuel. “When it comes down to it, it’s a lot easier to keep water out of fuel than it is to remove it later,” Lundstrom says. “There are many ways that water can get into your supply, so we recommend that you control what you can control.”

While onboard filtration with robust water removal is a must on most HCPR engines, it’s also not the place to start. For example, if you utilize any sort of bulk fuel storage, it’s vital to protect that supply. Water can enter your bulk tank in three primary ways: when delivered by your fuel supplier, from the atmosphere, and through condensation. This is why effective bulk filtration is key. Even the smallest bulk tank should have filtration at the inlet to the tank to prevent pre-contaminated fuel from mixing with the existing supply. There should be filtration at your pump, to strip out any free water that made it into the supply. And there should be a filtration system on any vents or breathers of your tank, to prevent water (and dirt) from entering through the atmosphere.

And even this triple layer of protection on bulk fuel storage, combined with effective onboard filtration, isn’t enough. Tanks need to be inspected and cleaned on a regular basis. No cracks, loose fittings or broken seals. All transfer points should be regularly inspected, and fuel in the tank should be tested consistently.

Worth it in the End

Keeping water out of your fuel and, in turn, your HPCR system isn’t easy or simple. But it’s worth it, especially if you have that million-mile mark in mind.

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*This article was written for, and originally published in Diesel Progress.

**Survey was conducted with service centers representing 90,000 repairs annually throughout the U.S. and Brazil, with particular focus on the southern U.S. due to humid climate conditions.