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Fuel Polishing

Diesel engines, in particular, are subject to premature wear and damage from "dirty" fuel. Furthermore, when fuel filters become occluded with impurities, restricted fuel flow negatively impacts filter―and engine―performance. Operators might assume that newer engines are more accommodating of fuel problems, since they are more advanced. In reality, the opposite is true.

Technology advances in recent years, including higher-pressure fuel injectors and pumps, make the use of clean fuel even more important. The reality is that for all engines―and newer engines in particular―a wide variety of unwanted agents, from water caused by condensation to oxidative particulates from the fuel tanks themselves, can cause serious problems. In this article, we'll detail some of the advanced processes and procedures that operators can use to ensure their diesel fuel is as pristine as possible when it enters the engine.

Why Does Diesel Fuel Degrade, and How Do the Fuel and Tank Interact?

Many generator operators have learned that diesel fuel, if kept clean, cool and dry, can be stored six months to one year without significant quality degradation. However, that's not the whole story for fuel stored in a tank under regular use, which is one of recirculating fuel, water, microbes and deterioration.

When a diesel engine pulls fuel from the tank, that fuel goes through a high-pressure fuel pump and enters the injectors, which operate under extreme pressure and high temperatures. Any fuel that the engine does not draw into the injectors returns to the tank. As a result, a large portion of a tank's fuel can be continuously re-circulated and exposed to extreme pressure and heat.

This behavior results in the agglomeration of asphaltenes. Asphaltenes―in the form of asphalt―make great paving materials on roads, for roofs and as waterproof coatings, but they are very hard on engines.

Over time, these asphaltenes aggregate into larger clusters and solids that are very difficult for engines to combust. They can grow so large that they will not pass through the fuel filter, instead adding to the sludge that builds up and can clog the filter completely.

Compounding the problem, the hot fuel coming back to the tank raises the temperature of the remaining fuel, causing condensation that becomes water (and eventually, algae due to microbial contamination), which mixes in with the fuel. Heating also expedites fuel break down. The result is fouling of the fuel and a buildup of sludge and acid in the tank. The water and acid cause rusting and corrosion of the tank, further exacerbating fuel deterioration. Most of these contaminants settle to the bottom of the tank, but only temporarily. Upon every refuel, they are stirred up and can become suspended in the fuel.

How Bad Is It?

Most engines cannot tolerate ongoing particulate contamination (prior to fuel filtration) greater than 50 milligrams per gallon (15 milligrams per liter). Injectors become clogged and damaged by particulate matter at a rate that corresponds to the size of the particles, but some damage is certain. Injectors damaged by impurities also cannot maintain correct fuel droplet size, which can prevent the fuel from firing properly when it enters the combustion chamber. Degraded fuel―especially if it is acidic, which is almost always the case―can also cause corrosion within fuel system components.

Regarding water, injector life and performance begin to be reduced when water content reaches the miniscule measurement of 0.05% (500 ppm). Water-tainted fuel (the water component of which becomes steam when it is heated in the engine's combustion chamber) damages injector tips, reduces combustibility and negatively impacts the ability of diesel fuel to lubricate the engine. In cold climates, especially if block heaters are not providing adequate heating, moisture also encourages the formation of ice crystals in the engine.

Simple Solutions Avert Major Issues

So, what should an operator do to counteract all these negative factors? Following are our recommendations, which are based upon WPP's experience cleaning and polishing fuel for its customers, working with thousands of generator engines and generator sets. These recommendations are in addition to (and often as a result of unsatisfactory or inconclusive results from) regular routine testing for acid number, cetane index, density, distillation range, flashpoint and viscosity.

  • Fuel Analysis

    Every six months, operators should have their fuel analyzed for contaminants.

  • Fuel Screening

    If contaminants are found during fuel analysis, or at least annually, fuel should undergo a heavy-duty screening process to remove large bits of sludge, rust scale and other contaminants from the tank.

  • High-Capacity Fuel Filtration

    After each completion of heavy-duty screening, the fuel should undergo high-capacity filtration, water separation and fuel conditioning.

  • Introduction of Fuel Catalyst

    Depending on the severity of the contamination (prior to screening and filtration), technicians may recommend adding a fuel treatment and catalyst to the tank, which removes engine deposits and prevents their future formation. Although the choice of catalyst is up to the operator, WPP has had good results with AFC-705, a concentrated, industrial quality, full-spectrum fuel additive and fuel-tank cleaning agent for use with diesel, gasoline, biofuels, kerosene and HFO. AFC­705 will stabilize fuel, prevent sludge build-up, improve combustion, reduce harmful emissions and eliminate the need for expensive and toxic biocides.

  • Introduction of Microbicide

    After removal of the asphaltene residue, rust and corrosive particulates, water, and other chemical agents, it's also beneficial to add a microbicide to kill microbe-producing algae and fungi.

Value-Added Benefits

If you are replacing fuel filter components and injectors prematurely, it's usually an indicator of poor fuel quality.

If your generator engines meet these criteria, don't despair. Regular fuel cleaning and polishing offers benefits beyond increasing engine performance and reducing wear and premature failure. Keeping the fuel as clean as possible also reduces fuel consumption up to 10% and lowers exhaust temperatures, which reduces NOx production. As a final bonus, asphaltene sludge and other noxious particulates that do not enter the engine also don't become a component of any emissions that enter the atmosphere.

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