Diesel engines in vehicles and diesel powered equipment run better on clean uncontaminated diesel fuel. If diesel fuel has been in storage for longer than a few months there is a danger of contamination. The usable quality of diesel fuel becomes progressively worse the longer it is in a fuel storage tank. Most high quality diesel fuel suppliers will only guarantee their fuel for six months when in bulk fuel storage.

Diesel Fuel Contamination
Water Contamination of Diesel Fuel
The most common form of diesel fuel contamination is water. Water in stored diesel fuel is normally formed from condensation over time. Water contamination in the fuel storage system can lead to corrosion of the storage tank (depending on the materials used). This corrosion can lead to further contamination of the fuel.

Diesel fuel tainted by water can reduce the performance and fuel efficiency of diesel powered vehicles, generators and equipment. Water pollution can cause filter blockages and serious damage to parts of your generator or engine such as the injectors, pipelines, seals or gaskets. For standby generators water in fuel can reduce the effective life of its engine, increase the risk of internal corrosion and worst of all, result in equipment failure when it is needed most due to the fuel being too hydrolysed (tainted by water) to work at all.

Petroleum diesels typically hold 60ppm of suspended water. At this level, the water is almost insignificant as long as it is regularly used and replenished (and microbial contamination does not occur). Bio-diesels typically hold up to 25 times more suspended water than petroleum diesel. In recent years the worldwide introduction of bio-diesel has brought what was mainly a mariner’s fuel problem to every diesel fuel user. Bio-diesel is a perfect habitat for vigorous microbial growth.

Consequently the amount of exposure to natural condensation over time in an undisturbed storage tank before micro Bacteria proliferation begins is dramatically reduced. Deterioration in modern biofuel is much faster than for petroleum based fuels.

Bacteria Contamination of Diesel Fuel
Growth of microorganisms in petroleum products has been recorded since 1895. Water contamination of diesel fuel leads to the build up of microbes, bacteria and sometimes fungi. These Colony Forming Units (CFUs) of microorganisms feed on the fuel at water-fuel interface (where the water meets the fuel) until becoming too heavy and floating to the bottom of the tank, quickly forming bio-films and sludge. Both aerobic and anaerobic bacteria can produce corrosive acids and sticky residues. These undesired chemicals (broken down carbon chains) can further affect engine performance by reducing the combustible properties of the fuel and shortening the life of both engines and storage tanks. The resulting sludge and sticky residue within the diesel fuel can cause blocked filters, fuel lines and damage the precision fuel injectors that are vital to the efficient running of a diesel engine.
Other fuels
With the introduction of biofuels into petrol in the form of bio-ethanol, petrol, a once unaffected fuel, has now also become subject to the consequences of microbial contamination.
Lloyds technical paper
The Lloyds Register published a technical paper (Paper N.4, Session 1994-95) highlighting critical levels of bacteria in fuel.
less than 500cfu (colony-forming units) per litre is acceptable.
at 500-1000cfu, Lloyds warns “microbial proliferation occurring”
over 1000cfu “microbial proliferation; operational problems; investigate thoroughly; use anti-microbial treatment”.
Evidence of degraded fuel is
the presence of black smoke from the exhaust,
unacceptable engine performance and reduced power output
poor starting (or failure to start at all)
shorted fuel filter life,
incorrect fuel gauge readings (caused by sludge and residue contamination).
Using the Metcraft Smartank Fuel Polisher system as part of your Fuel Management plan can prevent diesel fuel degradation during long term storage leading to lower costs and provide a more efficient, reliable fuel supply.