Not too many things in life are a sure bet except for death and taxes as the saying goes, but maybe we can add one more to the list. It would be this one fact: diesel fuel is inherently unstable. That’s right, and with each transfer from one storage outlet to another in the supply chain, the fuel can become contaminated.  Diesel fuel is subject to water incursion, microbial and bacterial growth and particulate contamination. So what exactly does that mean? Well, if you are storing diesel for any purpose like an emergency back up generator, an above or below ground storage tank or diesel that goes unused for prolonged periods of time in power equipment or marine vessels then you have problems waiting to happen. 

    Like what?  Maybe a little diesel fuel history and chemistry are in order to put things into perspective.

    In an effort to reduce diesel fuel emissions, The United States adopted new emissions standards for “Low Sulfur Fuel” for all on-highway applications in 1994 as determined by a standard from ASTM, the organization that establishes these standards.  This new diesel fuel standard for sulfur content was reduced from the previous 0.5% to 0.05%, or not more than 500 parts per million.  Fast forward to 2006.  ULSD (Ultra Low Sulfur Diesel) became widely available in the United States. Because of stricter clean air standards and engine manufacturer’s requirements, a full transition to ULSD with a maximum sulfur level that is currently only 15 parts per million applies to 100% of on-highway and off-road diesel fuel.

    Sounds great, right? Well, yes and no.  This is good news for Mother Nature.  Less sulfur in the air means less pollution and a cleaner and healthier planet for all of us.  Unfortunately, not such good news for diesel engines because in the process of removing the sulfur, much of the lubricity fuel systems require was removed. Diesel engines were designed to run on oil (fuel oil #2), which has as inherent slipperiness referred to as lubricity.  This lubricity is required for the injection pump and injectors themselves. Why is lubricity important?  Because without lubricity the engine is compromised causing premature equipment failure from high wear or scarring between contacting metal parts resulting in possible catastrophic failure. Definitely not good.

    So, in order to correct this problem, biodiesel is now added during the refining process, which provides this essential lubricity. But… biodiesel creates its own set of problems, like water.  Water is arguably diesel fuels’ worst enemy and can be in the form of free, dissolved or emulsified states. Biodiesel reduces the molecular surface tension where water and diesel fuel meet allowing for water present in fuel to more readily disperse throughout the fuel thereby becoming entrained into the fuel.  This will appear as hazy fuel.

    Water also enters fuel tanks through ill-fitting, missing or corroded caps and openings or vents in the tank’s top. Humid air entering through vents and daily temperature fluctuations cause water droplets to condensate on the inside tank walls even with a "full" tank. There is always a 10% or more headspace that allows for fuel expansion/contraction. Water droplets form on the tank walls in this space and settle on the tank bottom. The more interior tank wall exposure, the more potential for water accumulation.

    Water in its free state settles on the tank bottom where acids form causing corrosive damage to the sides and bottom potentially causing bottom structure failure and/or leaking.  Water is also the number one culprit for creating the perfect environment for microbial growth, often called diesel bug or “algae.” These microbes can grow with less than 0.25 inches of water present in the tank bottom.  These toxic bacteria, mold and fungus feed off of the fuel hydrocarbons and reproduce exponentially forming additional waste products and acids at the bottom of the tank. They can also coat the walls and baffles of the fuel tank, clogging fuel filters, producing dark smoke exhaust and damaging engine components such as injectors and fuel pumps. Biocides are the common remedy if microbial growth is present but use of these can actually aggravate the situation and turn bio-film into solids which is a filter plugging nightmare!  Biocides have limited effectiveness.  They do not kill all microbial growth so the unaffected bugs will continue to reproduce establishing a continuous cycle of only short-term relief with their use.  The bottom line is that no matter how vigilant the steps taken are, water contamination in fuel tanks is a fuel systems’ number one enemy that can lead to a cascade of costly and potentially catastrophic events. If there is no water present in the fuel there is nowhere for microbes to live, survive and thrive. Period.

    Other contaminants from the natural degradation of diesel fuel wreak havoc on the entire fuel system as well.  Wax-waxes in diesel can solidify if temperatures fall below a certain point and cause filter blockage.  Dirt and Particulates-inorganic substances like dirt, sand, rust and dust cause damage to the fuel systems injectors and other components resulting in increased engine wear, abrasion and potential engine failure.

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    Solids-asphaltenes are naturally occurring and are not soluble in fuel and tend to cluster forming solids or sludge that settle in the tank bottom.  This sludge is composed of asphaltenes as well as microbes,  organic/inorganic waste compounds and other contaminants.