Finer Filtration: Is It The Answer?
While Caterpillar has reduced its filtration size all the way down to two microns, and Volvo's is at five 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 back down again to 15 microns now. 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 the SwRI research into wear particle size. In SAE paper 980869, Gary Bessee and others conclude 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 a sludge that may be mistaken as biological contamination. 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're experiencing filter plugging, you should 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 two-micron filtration and water separation to protect the high-pressure injection systems featured on construction equipment from Ford, John Deere and Liebherr.
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