Your engine’s tiny problem

Government mandates to reduce diesel engine emissions without severely hampering performance and fuel economy have spurred on big advances in fuel system design. Today’s engines are quieter, more powerful, and yet much more environmentally friendly.
But there’s a small problem: it doesn’t take much to foul the precision high-pressure fuel systems engines use. It doesn’t take much at all.

Fuel system pressures on the latest highway diesels engines can be as high as 30,000 psi, 10 times greater than a decade ago. Ultra-fine particles in the fuel that had not been a problem at lower pressures can hastily grind down component life at high pressure. Learning how to keep your engine as contaminant-free as possible is a huge challenge, one that starts at the refinery. There, the final fuel output filtration is typically 30 microns, leaving smaller particles in the fuel. Worse, after the fuel leaves the refinery it goes through several transfers until it ends up in your truck. By this time, the fuel has picked up even more contaminants.

All this ultra-fine, unfiltered crud can reduce the life of high-pressure fuel pump and injectors. Silently and gradually the fuel system degrades and the truck uses more fuel, creates more pollution, develops less horsepower, and becomes less efficient. Particles in the 5- to 10-micron range are the most abrasive.

You can take steps to protect sensitive fuel systems. First, test fuel at its source. Diesel fuel is the trucking industry’s No. 1 commodity cost of operation. Yet few companies regularly test their diesel quality. The recommended fuel tests should be for cetane index plus a cleanliness code set by the International Standards Organization.

If you use your own fuel storage, run tests for both incoming and output fuel from the tanks. Often, fuel is contaminated by dirt that’s already in the storage tanks. Poorly maintained tanks can also contain lots of water, resulting in microbe and algae growth that can clog fuel filters. The acidic by-products of microbe life cause inner-wall corrosion on the tank, further increasing contaminants.

On the engines themselves, finer filters may be an answer. While Caterpillar has reduced its filtration size all the way down to 2 microns, and Volvo’s is at 5 microns, Cummins is bucking the trend to finer filtration. Injection specialist Ray Amlung says the Celect fuel system used on earlier Cummins engines had secondary filtration down to 15 microns. But with the early ISX, this was relaxed to 25 microns, although it is now back down again to 15 microns. Amlung says the new HPI injection system is designed and tested to withstand the assault of available fuel, although there could be some edge erosion on metering ports.
“Lots (of people) run 25 microns with no issues,” he says, and the fuel injection system is designed to last the life of the engine.

Ironically, it was a Cummins N14 with Celect injection that was the basis for new research into particle size and engine wear. According to SAE paper 980869, “The Fuel Filtration Cooperative R&D program has determined that the critical particle size in a high-pressure Celect injection system is 6 to 7 microns.”

Diesel fuel will, over time, become contaminated with asphaltenes, which drop out and cause sludge. According to Cummins’ Amlung, asphaltenes are formed when diesel fuel is heated and pumped, so any injection system–especially one with a high return flow-will create these heavier ends of the diesel fuel. In his experience these are more likely to cause fuel filter clogging problems rather than debris and dirt.

This is also described in the Detroit Diesel Engine Requirements manual 7SE70 0209. Diesel fuel oxidizes in the presence of air, it says, resulting in the formation of undesirable gums and black sediment. Such undesirable products can cause gumming and lacquering of the injection system components, with reduced engine performance and fuel economy.
The asphaltene sludge can be mistaken for bacterial contamination, but it obviously will not be eliminated by a biocide. Accordingly, says Dieselcraft sales manager John Nightingale, if you experience filter plugging, test to see what is causing the problem.

To that end, Dieselcraft is just now launching a test kit that can be found at diesel hard parts stores. The “Fuel Bug” kit is simple to use and will indicate whether a maintenance manager should treat fuel for bacterial contamination. Fuel is merely added to a culture medium in a test bottle. If bacteria are present, growth will be apparent within 30 hours. After 72 hours, mold or fungus can be seen.

Nightingale says there is a general lack of understanding and little concern for these problems, even though fuel condition can cause significant loss of performance, roadside service calls, and long-term fuel pump and injector damage.

Acknowledging the problem of injector erosion, Detroit Diesel offers a tune-up kit for the Series 60 under the Power Pack name. Promoted in a small brochure, there are electron micrographs of typical injector tip hole erosion. It recommends replacing all six injectors when the rocker cover is removed for a single bad injector, because the time taken is only two hours more to “restore the original power and performance engineered into your Detroit Diesel engine.”

Detroit endorses the use of the Fuel Pro 382 and recommends it be installed at the same time as injectors are replaced. With the Detroit Diesel branded filter element, the unit is claimed to double the life of the on-engine filtration. Stanadyne, too, is offering a filter that is used on off-road equipment with 2-micron filtration and water separation to protect the high-pressure injection systems featured on construction equipment from Ford, John Deere, and LiebherrBecause of the fine filtration, a
2-micron filter can clog easily. Dealing with this problem, fleets simply increase the filter screen–at the risk of fuel system deterioration that will manifest itself as poor engine performance, fuel dilution of lube oil, failed pumps and, more frequently it seems, failed injectors.

Typically, injector failure from solids contamination is progressive, so you may not even notice a loss of performance and increase in smoke. As the injector spray holes erode, the precise combustion is degraded. Ultimately, wear in the injector leads to slobbering and increased fuel in the lubricating oil. At the same time, fuel economy falls.

Water contamination, though, may well be more dramatic, resulting in the tip of the injector being blasted off.

And over the years, the cost of an injector has escalated in parallel with its increasing complexity and closer manufacturing tolerances. An electronic unit injector is a big-ticket service item. Some maintenance managers are saying injector maintenance is a new line-item in their budgets, with replacement at lower mileages accounting for as much as a 75-cents-per-mile increase in operating costs.