Diesel Knowledge

Diesel fuel is a complex mixture of hydrocarbon molecules derived from petroleum crude.

Over time stored fuel will darken due to oxidation, repolymerization and agglomeration of certain components. The darkening is accompanied by the formation of sediment that plugs filters and causes poor combustion.

Gums and sediments in the fuel that develop over time do not burn in the engine very well, this can lead to carbon and soot deposits on injectors and other combustion surfaces which may lead to more serious problems.

Fuel vendors know what time can do to fuel quality and they suggest that if diesel fuel is stored it should be replaced with fresh fuel within a year unless special precautions or cleaning actions are put in place.

Another diesel quality problem is algae which is a bacterial or fungal growth. There are several forms, but they all live in water and feed on fuel. Generally algae are a living slime that will plug / block fuel filters. Water is the key catalyst for this algae issue. It is not possible to stop water from getting into fuel as the tank must always be vented to atmosphere, water naturally condensates on the insides of the tank walls with temperature changes.

Under normal storage conditions diesel fuel can be expected to stay in a useable condition for:
  • 12 months only at an ambient temperature of 20ºC.
  • 6–12 months at an ambient temperature higher than 30ºC.
Most diesel engine problems start out as poor fuel quality but end up as expensive repairs and out of service equipment. The source for 90% of all engine failures is poor diesel fuel quality.

Removing and disposing of contaminated diesel fuel and purchasing new fuel is a very expensive proposition, even when contaminated fuel is removed you still have a contaminated tank and just refilling the tank with new fuel does not solve the problem. Unless the tank insides are thoroughly cleaned the new fuel becomes contaminated by the remaining contents in the tank from the old fuel.

When failure is not an option on your diesel powered equipment clean fuel is paramount to you. Any application of fuel in storage will need extra special considerations. A diesel engine will not run if it is exposed to old or contaminated fuel. The use by date of fuel is limited and must be considered in any regular diesel maintenance program. Diesel fuel maintenance is often forgotten and can cause significant problems for your equipment reliability.

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Dirt and water in diesel

Water molecules will form in the bottom of fuel cans, tanks or drums. These are formed when fuel is stored for even short periods of time. The free water formation is due to condensation in the air and or the separation of water molecules from fuel.

Water may be emulsified in fuel by vibration or by emulsifying additives such as alcohol, or detergents.

Dirt and water are practically unavoidable in stored fuel, causing microbial growth, corrosive acids, electrolysis and rust. These contaminants can plug filters, corrode components, and decrease efficient combustion and cause engine shutdown or system failure.

Fatty Acid Methyl Ester (FAME)

Standards: The European FAME standard EN 14214:2009 provides minimum quality requirements and limits relevant side products and tramp chemicals from FAME processing. In order to reduce the risk of premature failure of the fuel system, FAME must conform to EN 14214:2009, regardless whether used as 100 % fuel (B100) or as a blending component.

The European diesel fuel standard EN 590:2009 includes diesel blends with up to 7 % FAME (B7). The agreed position of all FIE manufacturers undersigned is to limit release of injection equipment for admixtures up to a maximum of 7 % FAME (meeting EN 14214:2009) with the resulting blend meeting the EN 590:2009 standard.

A more extensive revision of both the EN 14214 and EN 590 standards will be required to facilitate blending of up to 10 % FAME (B10). For future revisions FIE manufacturers support the development ofCEN standards, rather than those of individual member states, and do not approve national decrees.

FAME Stability: The reduced stability of FAME is of particular concern. Aged or poor quality FAME contains organic acids like formic acid and polymerisation products. The acids attack many components, and the polymers can lead to plugged filters, sediments and sticking moving parts drastically reducing the service life of the FIE. Long standstill periods bear the risk of reaching the point when the ageing reserve of the fuel inside tank and FIE is depleted. Extra measures are recommended like well-timed monitoring of fuel stability or precautionary fuel exchange, followed by an idling operation when such extended periods of inactivity are anticipated. This affects also seasonally operated equipment like harvesters or emergency generators and vehicles to be exported to overseas. For this reason FAME-free EN 590 fuel is highly recommended for “first fill” or extended inactive periods.

Fuel stability is best described by the parameter ‘ageing reserve’, determined as induction period (IP) according to the EN 15751:2009 test method. B5 with an IP of ≥ 20 h has been demonstrated to be sufficiently stable for standard usage conditions in the European market. The stakeholders of CEN/TC19/WG24 considered it essential to maintain this fuel stability level of EU-B5 also for B7 and agreed to adapt EN 590:2009 accordingly.