What is diesel fuel contamination?

Contamination is simply the presence in the diesel fuel of unwanted materials such as rust, particles, water and biomass. The term contaminants include any unwanted matter that is found in diesel fuel. These contaminants affect the quality of diesel fuel and can cause damage to the diesel engine fuel system resulting in poor performance or even engine failure. There are many different types of contaminants that could adversely affect, damage or even destroy a fuel injection system. The most common types of diesel fuel contaminants are:

– Physical contamination: suspended microscopic particles, rust, dust particles, fibre material.

– Chemical contamination: water (moisture), gases, molecules of unwanted chemicals (such non-compliant fuel additives)

– Biological/microbial contamination: fungus, bacteria, viruses commonly known as DIESEL BUG.



What is the worse type of diesel fuel contamination?

Of all contaminants, water is the worse. Water causes damage to fuel tanks, fuel system components and engine. Water is also the breeding ground and the main food source for DIESEL BUG. Water can enter and be present in diesel fuel in 3 forms:

– Dissolved water – Also known as RH% (relative humidity) or moisture is the water in dissolved state inside the diesel fuel. It is indistinguishable with the naked eye the presence can only be confirmed with specialised sensors or by laboratory analysis.

– Free water – accumulates at the bottom of the tank and it is present on the walls above the fuel line as a consequence of condensation. Because water is heavier than diesel fuel there is a distinct line separation between the two so the presence of free water is clearly visible. Free water can also be detected with specialised water in fuel sensors.

– Emulsified water – When the free water is mixed mechanically with the diesel fuel forming a cloudy/milky in appearance mixture.

One way or another, the water will find its way in any diesel tank either by refuelling with water contaminated fuel, condensation, leakage, ingress from atmosphere (humidity) and sometimes human error.


Diesel bug, also commonly known as “diesel virus”, “algae” or “diesel fungus”, is the microbial contamination that develops in the new ULDS fuel in the presence of water. It is the water in the fuel tank that the diesel bug survives on, and allows it to reproduce at an extremely fast rate. Diesel bug additives and biocides have been designed to kill the bugs but they do not remove the dead bugs, relying on the engine combustion to burn them off. That leads to accumulation of the sludge at the bottom of your tank.

diesel microbial contamination

diesel bug

Diesel Bug was always a problem for diesel fuels, however, since the introduction of Ultra Low Sulphur Diesel (ULSD) it has become more and more evident, as sulphur was able to inhibit microbial growth in diesel fuels. The problem gets worse when biodiesel is added to ULSD and according to Australian Standard of fuel quality it can be up to 5%. The reason is that, compared to regular diesel, biodiesel is much more hygroscopic (attracts water). Studies found that biodiesel can absorb up to 25 more water than diesel and as the temperature increases above 35°biodiesel has an increased rate of 22.2ppm/°C – 9 times more than regular diesel. That is the reason why tanks situated in the engine room or in higher temperature areas have worse microbial contamination (up to few centimetres thick on the bottom of the tank). When that happens the primary fuel filters become constantly clogged.

diesel bug filters

diesel bug blocking filters


How was DIESEL BUG born?
  • In US in 1990 the Clear Air Act was amended to require stricter emission reductions of:

  • So what does this mean? Among other things, it meant reduction of sulphur content from 500-3000ppm to less than 10ppm and the birth of ULSD (Ultra Low Sulphur Diesel). Without sulphur in it, for the first time in history, diesel now had the ability to grow microbial bacteria, essentially contaminating itself from within.
  • Without protection a new type of contamination was created: THE DIESEL BUG 
  • Europe did the same few years later, in 2009, Australia followed suit.
How can you really tell if the fuel is clean?

It is done by the implementation of the international standard ISO 4406. This standard provides a framework for reporting the concentration of contamination particles in diesel fuel using an automatic particle counter (like the one used on our iCleanED autonomus intelligent cleaning machines)

As stated above, ISO 4406 is the reporting standard for fluid cleanliness. According to this standard, a code number is assigned to particle count values derived at three different micron levels: greater than 4 microns, greater than 6 microns and greater than 14 microns. The ISO code is assigned based upon Table 1 below:

Table 1 – ISO 4406 Fluid Cleanliness Guide

ISO code number Number of particles per ml
More than Up to and including
28 1,300,000 2,500,000
27 640,000 1,300,000
26 320,000 640,000
25 160,000 320,000
24 80,000 160,000
23 40,000 80,000
22 20,000 40,000
21 10,000 20,000
20 5,000 10,000
19 2,500 5,000
18 1,300 2,500
17 640 1,300
16 320 640
15 160 320
14 80 160
13 40 80
12 20 40
11 10 20
10 5 10
9 2.5 5
8 1.3 2.5
7 0.61 1.3
6 0.32 0.64

4µm / 6µm / 14µm and per / ml

For example: An ISO cleanliness code of 18/16/13 refers to the following:
18 = 4µm particles, 16 = 6µm particles, and 13 = 14µm particles.

By referring this information to the chart above, you can see the range of the actual particles within the index.
18 shows between 1,300 to 2,500 – 4µm particles, per ml of fluid sample
16 shows between 320 to 640 – 6µm particles, per ml of fluid sample
13 show between 40 to 80 – 14µm particles, per mil of fluid sample

It is recommended by most new diesel injector manufacturers to have an ISO Cleanliness Code in the range of 15/12/10 to 12/9/6.

Fuel Status ISO Code 4406 Comments
Fuel Supply ISO 22/20/18 Typical levels of incoming fuel (Primary source of contamination)
Tank Filtration ISO 18/16/13 Maximum level recommended by engineer manufacturer
On-Board Filtration ISO 15/13/10 Preferred by engine manufacturer
High Pressure Common Rails ISO 12/9/6 Fuel injector requirement


What is the difference between fuel filtration, fuel polishing and Clean Diesel D.E.B.U.G.?

Fuel filtration – applies only to fuel – (that is fitted either as a primary filtration between the diesel tank and the engine or secondary filtration on your engine) uses filters that remove free water (the water that accumulates at the bottom of the tank) and particle contamination (rust, dirt etc) to a certain size, usually 10-30 micron for conventional diesel engines. HPCR diesel engines (High Pressure Common Rail) require higher levels of filtration, usually 2 micron.

Fuel polishing – applies only to fuel – removes what conventional fuel filtering is not usually capable of (emulsified water that is suspended in fuel and doesn’t drop to the bottom of the tank to be drained).

Clean Diesel D.E.B.U.G. system – applies to both fuel and the storage tank – on top of the 2 aforementioned filtration modes,  offers additional 2 levels of microbial decontamination with a proprietary wave lengh modulation UV and the optional O3 injection for the inside of the tank ensuring 100% kill of diesel bug.

What is nominal filtration?

Nominal filter rating indicates the approximate size particle or water percentage, the majority of which will not pass through the filter. It is generally interpreted as meaning that 85% of the particles of the size equal to the nominal filter rating may be retained by the filter.

When it comes to nominal contamination level in a diesel tank it means the average level of contamination of fuel sample taken from top and bottom of the tank.

Because of the restricted access to where the samples are taken from (usually from a single spot such as filling port or fuel sender port), this level of contamination is more an indication of what type of contamination is in the tank rather than the actual level.

What is absolute filtration?

Absolute filter rating means that, for example, 99.9% of the particles larger than a specified micron rating will be trapped on or within the filter as well as water removed at the specified percentage.

When it comes to absolute contamination level in a diesel tank it means the percentage of evenly distributed contaminants throughout the entire fuel. 

The novelty of our technology is that iCleanED machines perform like “shaking” the tank to put everything in suspension and then measure and remove the contamination until it reaches the desired ISO 4406 level.

What are the advantages of Clean Diesel technology?
  1. Eliminates the need of expensive fuel replacement.
  2. Eliminates the need of periodic tank cleaning.
  3. Zero downtime during the cleaning process.
  4. Dramatically reduces labour input.
  5. Safer operation and reduced risk of injuries.
  6. Reduced risk of environmental contamination.
  7. Ensures true absolute ISO levels of cleanliness with F.A.C.T. technology.
  8. Eliminates microbial contamination without the use of chemicals by UV exposure
  9. Reduces risk of external contamination on refuelling with the dispensing function and inline treatment.
Can I use regular UVC germicidal light to decontaminate my diesel?

NO, NO and NO!

If diesel is exposed to UV light it will degrade as it is not UV stabilised because when absorbed by diesel, UV energy will excite photons. This, in turn, will create free radicals and then, in a very short period of time, degradation occurs, as catalyst residues will often act as receptors. 

What is the type of UV light used in Clean Diesel technology?

We have developed a special type of UV light, with a proprietary electromagnetic signature, we call it UVD (D from diesel) and has the same germicidal effect as UVC but is safe to use on diesel.

Part of the electromagnetic spectrum, ultraviolet radiation is split into three types.These are:

  • UVA
  • UVB
  • UVC

The wavelengths of visible light are tiny, measured in billionths of a meter. A billionth of a meter is called a nanometer, or nm. UVA has a wavelength range of 320-400 nm, while UVB has a range of 280-320. Meanwhile, UVC’s range stands at around 100-280. If we take skin as an example, UVA may result in a tanning of the complexion, while UVB may mean it burns. The common effect of UVC IS germicidal, which is the scientific term for killing or inactivating microorganisms by destroying nucleic acids and disrupting their DNA. This renders them useless when it comes to performing critical cellular functions.



What makes the technology so special?
  1. The F.A.C.T. cleaning algorithm.
  2. The proprietary electromagnetic signature of the UVD light within the D.E.B.U.G. system.
  3. The proprietary design of flow and return tubes and heads.

The algorithm is what took years to develop and allows the machine to self-sample, process, treat and repeat as required. The right wavelength modulation also took years to develop and keeps the fuel stable whilst using UV to kill microbial growth and all other living bacteria / fungus. The flow and return tubes and heads agitate all the fuel in the tank and ensure all particulates, water and microbes are passed through the machine and sanitised/filtered/separated.

The F.A.C.T. cleaning algorithm is a model based control application where multiple independently measured inputs are evaluated by a controller which then commands multiple outputs such as pump speed, fuel priming, flow direction, flow rate controller and the proprietary UVD fuel decontamination system.  The monitored inputs are fuel flow, fuel temperature, differential pressure in the multistage filtration system, relative humidity of fuel, water concentration and fuel contamination in accordance with the ISO 4406 international standard code for fuel cleanliness. The calculation is performed in real time to decide the flow control rate and direction and the intensity of the UVD fuel decontamination system in order to decontaminate and clean the fuel in the fastest time and the minimum amount of consumables while providing 100% guaranty compliance with the ISO 4406 and AS3570 for fuel cleanliness. This calculation is built on a mathematical model (the F.A.C.T. algorithm) considering the changes such as flow/viscosity with temperature, filter blocking tendency based on the differential pressure changes in real time with trends, water content and so on, rather than a simple feedback loop used in conventional filtration (e.g. filter blocked – pump stop – change filter). The advantage of this new innovative filtration technology gives iCleanED machines the ability to react proactively to changing input conditions rather than changing output conditions like a traditional filtration system.