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 (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 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).

– On top of the aforementioned filtration modes, Clean Diesel D.E.B.U.G. system 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 are the main diesel fuel contaminants?

There are many different types of contaminants that could adversely affect, damage or even destroy a fuel injection  system. Bacteria, fungus, water, suspended microscopic particles, additives, wax are some of the main contaminants.



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. 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.

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.
  9. Reduces risk of external contamination on refuelling with the dispensing function.
What is the point of difference for Clean Diesel technology?

There are several points of difference but the 2 main ones would be:

– No other machine or human service can remove microbial growth, particulates and water without trucks, humans, chemicals and environmental impact.

 – No other technology is capable of measuring in real time the absolute level of contamination in a diesel tank and clean the fuel to the desired ISO Level of fuel cleanliness.

What makes the technology so special?
  1. The F.A.C.T. cleaning algorithm.
  2. The proprietary wavelength modulation of 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.

What is the main benefit?

Diesel fuel generators are the only global options for backup power to go from total darkness, to full megawatt power delivery in minutes. No battery system, solar system or wind system will deliver instant, real time backup of this size.

The highest risk for the end user is engine failure, and the highest risk for engine failure is dirty fuel.

We solve that problem!