Good housekeeping of diesel fuel requires constant attention to detail to avoid both short-term and long-term engine problems. If a preventive maintenance program for fuel is not begun and followed, the operational and maintenance costs related to the engine will increase, period.
Frequently, the tell-tale sign of microbial growth in fuel is filter plugging. As colonies of bacteria grow in the tank, they clog fuel filters to the point that the engine is starved for fuel. If the solution is just to put a new, clean filter in the filter housing, wait until it plugs up again, and then replace it again, then a lot of fuel filters will be needlessly used. Buying cases of primary and secondary fuel filters can quickly become an unseen budget buster.
Diesel fuel has a couple of jobs. One is to be the source of the hydrocarbon liquid that is turned into power by the engine. The other is to cool and lubricate the fuel injection system.
If fuel is contaminated with water, it will cause damage to injectors. Ideally, the water content in fuel should be well under .05 percent by volume. Above that level, injector life is reduced by about half. When water passes through an injector, it immediately vaporizes and is turned into steam. Because this occurs at high pressure, it will eventually damage the injector tips. This tip damage will prevent the injector from creating the desired fuel spray pattern. And as water content increases, the lubricity of the fuel decreases, causing excessive wear and premature failure of injectors and fuel pumps.
Water is also the culprit that spurs the growth of fungi and bacteria at the bottom of the fuel tank. Some of the bacteria in the tank release acidic byproducts as part of their life cycle. This acid causes corrosion within the fuel system, which leads to more repairs.
Inorganic debris such as rust, dust, sand and other particulates usually find their way into the fuel during the transportation and delivery process from the refinery to the fuel pump. This dirt is abrasive and causes excessive wear and tear on engine parts.
Asphaltenes, an oily black substance, makes its way into diesel fuel during the refining process and as fuel ages in the tank and deteriorates. Asphaltenes are larger carbon-chain molecules than diesel. High asphaltene concentrations in fuel require more time, more energy and higher temperatures to combust than is available in engines during the combustion cycle and before the exhaust valve opens. Therefore, asphaltenes in fuel reduce the efficiency of the engine, which translates into less power from every gallon of fuel.
According to the Chevron Diesel Fuels Technical Review, to maintain fuel integrity one should:
Ideally fuel should be polished and the tanks cleaned whenever the yacht is refueled, or on a monthly basis if the yacht is not fueled frequently. Diesel fuel is the lifeblood of the main engines and generators aboard every yacht.
Many captains believe that they cannot have fuel problems because their yacht is very active and the fuel in the tank is burned through regularly. The fallacy in this belief is that most of the contaminated fuel in the tank sits at the bottom. The fuel pick-up tube in the tank can be located as much as six inches above the bottom of the tank. Those six inches contain water, anaerobic bacteria, mold, asphaltenes and other compounds. This last dirty bit of fuel is never used, and is the exact purpose of having the pick-up tube located above the tank bottom.
But once new, clean fuel is bunkered and introduced into the dirty fuel at the tank bottom, the new fuel also gets contaminated. Then the level of the contaminants eventually builds up to a height high enough to enter the pick-up tube and start clogging filters.
Implementing and strictly adhering to a fuel preventive maintenance program is a simple and inexpensive alternative to the cost of repairing severely damaged high pressure pumps, injectors and pistons.
Capt. Jeff Werner has been in yachting for almost 25 years. Contact him through MyDieselDoctor.com.