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Frequently Asked Questions

1. What is diesel fuel "algae"?

Algae are a life form found in water, similar to algae growing in an aquarium. Algae do not live in fuel and it requires sunlight to grow. For years, people have been referring to tank sludge and the jelly, slime and other contaminants found in fuel filters as “algae”. The colloquialism “diesel fuel algae” is widely used and understood. However, there is no relationship between the “algae” growing in your aquarium and the sludge “growing” (forming) in your fuel tank and showing up on your filter elements.


There are three basic areas of concern about contaminants in fuel and oil:

1. Water

2. Inorganic debris (sand, dust, rust, etc.)

3. Organic debris (fuel breakdown products and waste products of fuel deterioration and re-polymerization)


The organic debris represents more than 90% of all contaminants found in fuels and oil. It is this organic debris, the sludgy, slimy, acidic material that people refer to as “diesel fuel algae”. It could also be called a polymer, tar, wax or asphalt!

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2. What is diesel fuel?

Diesel fuel is a very complex mixture of thousands of individual compounds with carbon numbers between 9 and 23 (the number of carbon atoms per hydrocarbon molecule). Most of these compounds are members of the paraffinic, napthenic or aromatic classes of hydrocarbons (HC).

These three classes have different chemical and physical properties. The different relative proportion of these three classes is one of the factors that make one diesel fuel different from another. It influences fuel properties and affects its performance.

Up until 35 years ago, refineries used only about 50% of a barrel of crude oil to make distillates such as gasoline, jet fuel and diesel. The remainder of the barrel of crude oil went to “residual oil”. Today, as a result of different refining techniques and additive packages, the refinery uses 90% or more of the same barrel of crude, which clearly has consequences for fuel stability.

More than 90% of the debris on filter elements and the sludge in your fuel tank is organic material, fuel and oil breakdown residue. In most cases, this debris is acidic and not good for your engine. It causes corrosion in injectors, pumps and storage tanks.

The solids that form as a result of the inherent stability of the fuel and the natural process of degradation will accumulate in the bottom of your tank. The sludge will form a coating or bio-film on the walls and baffles of the tank, plug your filters and impact combustion efficiency. Eventually it will clog fuel lines and ruin your equipment.

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3. What is the stuff that clogs my filter?

Filter clogging can have several causes. For example, low temperatures can cause wax crystallization, which can lead to filter clogging. An example would be using summer diesel in cold weather. Wax or paraffin is part of the diesel fuel.


Chemical incompatibility may cause dramatic filter clogging. This may happen when fuels with incompatible additive packages are mixed together.


Contaminant build up resulting from excessive microbial growth and bio-degradation of fuel can cause filter clogging. Microorganisms, bacteria and enzyme activity, fungus, yeast and mold cause fuel degradation and the formation of waste products.  The process is similar to milk turning into cottage cheese, a different form of milk.


Even though microbes may cause and accelerate the process of fuel degradation, it should be noted that the waste products clogging your filter are not the microbes, but fuel components which have formed solids.


Frequently, the application of biocides aggravates the situation and turns bio-film into solids creating a real fuel filter nightmare. Bio-film develops throughout the entire fuel system. It grows in the water/fuel interface and on the walls, baffles and bottoms of storage tanks. An unlucky end user may be filling up his tank and getting this debris delivered as part of the fuel, for the same price as the fuel.


Poor thermal fuel stability can clog filters. Fuel will form particulates (solids) when exposed to pumps and the hot surfaces and pressure of the fuel injection system. This will result in an increase in asphaltene, agglomerations, polymerization and a dramatic loss of combustion efficiency.


Fuel systems, in general, are designed to return a significant portion of the fuel, not used for combustion, back to the tank. The return fuel is very hot and will promote polymerization and fuel breakdown. Eventually, more and more solids from the tank will reach the filter and over time clog the filter. These problems continuously occur in commercially operated engines, such as trucks, heavy equipment, shipping, and power generation; but will also appear in recreational boats, RV’s and all types of fuel storage tanks.


Short filter life is symptomatic of polymerization, increase in the size of the fuel droplet, agglomeration of asphaltene and the formation of solids in the fuel system. The consequences are carbon build up in engines and exhaust systems, higher fuel consumption and excessive smoke.

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4. Can diesel fuel clog my filter?

Yes, it can. The stuff that clogs your filter is actually fuel in some way, shape or form. In excess of 90% of this organic debris is fuel breakdown products. It is not sand, dust, stones, rust or inorganic matter that blocks your filter.


The inorganic material like sand, dust and other particles will not cause your filter to clog. In fact, a lot of sand in a fuel filter would act as extra filtration. The pores between the sand particles are much larger than the pores in a standard fuel filter element. Sand filters are commonly used to filter water. A hair is approximately 80 microns in diameter, and fuel filter elements range all the way from 30 microns for a prefilter to 2 microns for a fine filter.

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5. How does fuel stability affect me?

Fuel stability is a serious concern to the diesel fuel user.


The chemistry of diesel fuel instability involves the chemical conversion of precursors to species of higher molecular weight with limited solubility. The conversion process often involves the oxidation of the precursors.


We all realize that fuel is an unstable, organic liquid that goes “bad”. Your vendor will always sell you the highest fuel quality possible. However, due to a variety of circumstances fuel may have “aged”, oxidized and contain water. It may have been contaminated before it was delivered to you by your vendor.


Fuel has to travel from the refinery to you. It is pumped through pipelines, barged, trucked and stored in tank farms. Daily changes in temperature and exposure to the atmosphere will cause condensation and water in storage systems. None of this will help improve fuel quality.


When your fuel is finally used, it is exposed to the heat and pressure of the engine injection system, centrifuges, pumps and heaters causing an increase in asphaltene agglomerations, which negatively impacts combustion efficiency and emissions.

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6. What is "bad" fuel?

Fuel is made to certain ASTM specifications. When it does not meet these specs, we could refer to it as “bad fuel”. However, we tend to refer to fuel as “bad fuel” when we see symptoms such as:


-          Dark, hazy fuel

-          Filter clogging

-          Sludge build up in tanks

-          Poor engine performance

-          Excessive smoke and emissions


We refer to fuel and “good fuel” when it is clear and bright. Or rather in that case, no reference is made at all to our fuel. We simply use it and take fuel quality and peak engine performance for granted. Bad fuel is fuel that does not meet ASTM specifications.

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7. Is "dark" fuel the same as "bad" fuel and can I still use it?

This is a question that many of us have asked more than once. And what we really want to know is, “Will the stuff damage my engines?” Engines are expensive, ruining an engine is costly and operating an engine on bad fuel is not wise.


We all know that most engine failures start in the fuel tank. When all the mechanical parts are in good operating condition, the cooling and lube systems are working, the lube oil clean and there is a sufficient supply of clean air getting to the combustion chamber; a diesel engine could run almost forever. The only limiting factor is fuel quality. Dark fuel is symptomatic of poor quality and even though, in most cases it can be used, fuel in this condition will provide poor combustion and filtration problems.


Dark fuel is in general indicative of oxidation and the process of fuel degradation is in a far advanced stage. Hazy fuel is indicative of water emulsified in the fuel. In general, dark hazy fuel will not damage your engine. It indicates however, poor fuel quality, which will definitely not provide you with peak engine performance.


Using less than optimal fuel quality negatively impacts engine efficiency and accelerates the process that makes new engines old.


Diesel fuel ranges from colorless, to amber or light brown color, depending on the crude oil and the refinery process used to produce it. In addition, dyes may be added to change the fuel color for tax identification purposes.


In time, stored fuel will darken due to oxidation, repolymerization and agglomeration of certain components. The darkening is accompanied by a formation of sediment that clogs filters and causes poor combustion. Fuel and oil distributors suggest that if diesel fuel is stored for emergency use, it should be replaced with fresh fuel within a year, unless fuel conditioning is used.

The University of Idaho conducted tests on the life expectancy of fuels to determine the time line of degradation of stored #2 diesel fuel. The results indicated 26% degradation after 28 days.

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8. How does my engine negatively affect fuel quality?

A diesel engine uses only some of the fuel it pulls from the tank. All of that fuel goes to the high pressure fuel pump and to the injectors operating under enormous pressure and high temperatures.


The surplus fuel the engine is not using goes back to the tank. The fuel is continuously re-circulated and exposed to extreme pressure and heat, which results in the agglomeration of asphaltenes, the high carbon content and heavy fuel molecules. It leads to the formation of larger and larger clusters of solids, which are very difficult to completely combust. These solids may grow so large that they will not pass through the filter element and become part of the polymer and sludge build up clogging the filter.


In addition, hot fuel coming back to the tank will raise the fuel temperature in the tank, cause condensation and contribute to microbial contamination, fuel breakdown, bio-fouling and the build up of sludge and acid.


Large fuel droplets and high asphaltene concentrations 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.


Any device in the fuel system exposing fuel to heat and pressure, such as pumps, heaters, or centrifuges will increase the formation of asphaltenes and negatively impact combustion.

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9. Isn't my filter supposed to keep my fuel system clean?

Filtration simply cannot and will not do that. At best, filters, separators and centrifuges remove debris suspended in fuel before fuel reaches the engine. Stopping, preventing or reversing the process of fuel breakdown is a completely different matter that can be addressed by and resolved with a combination of magnetic and chemical fuel conditioning.


It is not very likely that filtration (either an external filter or a filter on the engine), will remove the sludge coating from the walls and baffles of your storage tank and the use of biocides will almost always aggravate the situation. Filtration has no effect on the fuel break down processes whatsoever.


Filters are primarily designed to remove inorganic debris from the fluid stream and they become clogged with organic debris, resulting from fuel degradation. The water separator is designed to remove free water. However, a separator and filter combination or a centrifuge cannot remove emulsified water. But a filter and water separator combination is essential in any diesel application. Most of the debris you see on the filter elements, the stuff that clogs your filters, is the result of the fuel having begun to form solids.

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10. How can I protect stored fuel for a long time?

Temperature, humidity and condensation are very important factors in managing fuel integrity. The presence of free water provides a medium for microbiological growth that result in the formation of slime and acids causing corrosion of metal surfaces such as storage tanks, pumps and injectors. Therefore, good housekeeping and purchasing clean, dry fuel from a reputable supplier are definitely the first steps.


It is recommended to start out protecting stored fuel with a chemical conditioner to stabilize the fuel in the tank. This chemical conditioner is a fuel catalyst that also contains corrosion inhibitors and lubricity enhancers to not only preserve fuel integrity, but also to protect your engine equipment. Periodically, additional chemical conditioner is added to keep the fuel stabilized.


You also need to remove water from storage tanks on a regular interval. This can be done with a mobile tank cleaning system. It is used to remove water from the tank bottom and works as a fuel polishing system. Storage tanks can also use a “water eliminator”. A “water eliminator” is a small nylon or larger stainless steel cylinder, containing a special polymer. The polymer will absorb the water, and not the fuel, for easy removal.


The use of an adequate fuel quality management program and service, regular fuel testing to monitor fuel integrity are an absolute necessity and will save money. In applications such as emergency power generation, installing a fully automated fuel recirculation and fuel filtration system is recommended.

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