Degradation and contamination of diesel (diesel, fuel oil, fuel oil ...): causes and remedies

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Degradation and contamination of diesel (diesel, fuel oil, fuel oil ...): causes and remedies




by Christophe » 27/11/19, 12:47

Same as for degradation and aging of gasoline but for diesel ...

A good fuel is good combustion (with a little water is even better but not in the fuel!) : roll: : roll: : roll:

Contamination of diesel fuel, cause, consequences and remedies

The diesel tanks of the ships show contamination by micro-organisms. The effects of this contamination can prevent an engine from starting and cause severe damage.

What are the origins, effects and solutions to combat this contamination?


Microorganisms are living organisms invisible to the naked eye. Those likely to contaminate diesel and fuel oil are bacteria, yeasts and molds. They are contained in the ambient air that naturally carries these germs.

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Where do these microorganisms come from?

The "breathing" of the storage tanks is at the origin of the appearance of water in which the micro-organisms will proliferate. They will then find, at the water-hydrocarbon interface, the three elements necessary for their development: water, mineral salts and carbon contained in diesel and fuel oil.
The day / night temperature differences, the "hot" gas oil in return of injection increases and promotes the risk of condensation which, remember, occurs when air loaded with moisture comes into contact with a cold wall.
The water thus generated will therefore be found in the bottom of the tanks and in the filters. The presence of water and the high temperatures then favor the proliferation of micro-organisms which find there a dream medium.

How to detect the presence of contamination?

Untimely stops engine operation when the boat is sailing in waves. On this occasion, the deposits are "brewed" and thus reach the height of the suction strainer.

Increased frequency of change of the filters.
Presence of gelatinous deposits on the filters.
Strong smell.
The diesel fuel is turbid and has suspended solids.

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What are the consequences of diesel contamination?

1. Deterioration of additives: Some additives, especially those rich in nitrogen and / or phosphorus are consumed by microorganisms. This results in the loss of all or part of their properties.

2. Corrosion: The hydrogen sulphide produced by bacteria is particularly corrosive because of its acidic nature, causing serious damage to tanks, piping and engines.

3. Sludge formation: Microbial wastes settle to the bottom of the tanks where they form a layer of sludge promoting the creation of an anaerobic environment conducive to corrosion. This land also represents a shelter for viable microorganisms brought with each fill. Unless physically eliminated, this sludge is a potential source of infection.

4. Odor: One of the problems that often goes hand in hand with microbial contamination of fuels is the appearance of a very strong odor (rotten egg). This simply reveals the presence of hydrogen sulphide.

5. Clogging filters: Some microorganisms attach to the filters, where they find again the water and the hydrocarbon necessary for their development. The production of biopolymers by a specific class of bacteria amplifies this phenomenon. This results in a reduction of the flow or a complete clogging of the filters and pipes. This can have serious consequences, such as breakdowns or total deterioration of the engines. This biofilm (bottom of tank) strongly adherent can reach several centimeters of thickness. It is resistant to steam and the majority of solvents. Only a specific biocide can eliminate it.

6. Mechanical Deterioration: The micro-organisms will increase the water content, reduce the detergency and lubricity characteristics of the fuel and produce corrosive substances. The mechanical consequences lead to corrosion and / or seizure phenomena, at the level of the supply and injection circuits, which can go as far as the breaking of pumps and injectors.

How to prevent diesel contamination?

Purge, where possible, the bottom of the tanks.
Also regularly bleed the separators / decanters of water when they exist on the fuel line (wintering-wintering).
Limit the empty volume in the tank. Fill the tanks at the end of the season.
Avoid, in case of mounting additional tank, the low points where water can accumulate.
Always close the tank cap tightly.

How to get rid of this contamination?

Thoroughly drain the tank to remove accumulated water as well. Diesel, lighter than water stratifies above it in tanks.
Indeed, water offers on the one hand a privileged environment for the development of micro-organisms and its presence is formidable in the injection circuits.
Finally, treat with a biocide that will destroy microorganisms.

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Check the filters after 48 hours to avoid clogging with organic matter (the remains of microorganisms).

What are the aggravating factors to the development of contamination in diesel?

Stagnation in a tank half full.
A half-full tank offers a large contact surface of its walls with moisture-laden air. The more the tank is filled, the less it offers exchange surface.
Thus, a full tank contains little air and offers little contact surface to the condensation.

Bio fuels
Part of the esters composing biofuels constitute a privileged nutrient medium for colonies of microorganisms.

Low sulfur content
The low sulfur content of current fuels would favor the development of yeasts in reservoirs.


Source: http://www.actunautique.com/2019/11/car ... medes.html
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