Diesel Contamination

Diesel contamination is inevitable in the biodiesel blends the world has started to use. If left untreated, contamination will cause problems for diesel-powered generators, vehicles and equipment.

Our short video explains why fuel becomes contaminated and what can happen if the issue is ignored.


The diesel we buy in Europe is a blend of 93% petrochemical diesel and 7% biodiesel. Biodiesel – or FAME (Fatty Acid Methyl Ester) to give it its technical name – has been added to petrochemical diesel since 2011. This biodiesel blend contains less sulphur than pure petrochemical diesel and reduces CO2 emissions by up to 50%. However, the presence of biological organisms in diesel provides the ideal environment for contamination to occur.

Bacteria in Fuel - Diesel Bug

Contamination never used to be a serious problem. But since diesel was quietly blended with the biodiesel known as FAME, it has become an issue.


What is diesel contamination?

As it gets older diesel suffers from 3 main types of contamination:

  • Water contamination
    • Dissolved Water: water that is chemically dissolved or absorbed into water and distributed molecule by molecule. Think of sugar in tea.
    • Emulsified Water: very small droplets of water are suspended in the diesel. Think of oil and vinegar in a salad dressing.
    • Free Water: water that falls out of suspension in the diesel and gathers at the bottom of the tank. Whilst dissolved water can affect diesel’s stability, it is free and emulsified water that are more problematic. Not only can it cause fuel system and engine damage but it also promotes microbial growth (aka the diesel bug) in diesel storage systems.
  • Microbial growth (aka diesel bug). Microbial growth within a diesel storage tank is commonly known by the generic term ‘diesel bug’. Diesel bug isn’t a single type of organism. There are up to 100 different types of bacteria, moulds and yeasts that have been found inhabiting diesel systems.
    • Bacteria: single cells, typically 1-10 micron in size, with a 20-30 minute generation time (i.e. the time it takes for the population to double). One cell can multiply into 2 million in 7 hours in warm temperatures. Bacteria will degrade diesel over time.
    • Mould: a type of fungi with long multi-cellular filaments. There is little indication that they degrade diesel but due to the long strands are effective at blocking filters.
    • Yeast: a different, slow-growing type of fungi. Yeasts are typically 3-4 micron in size.
    • Biofilms: complex structures of microbes that adhere to the walls of the diesel storage tank. A biofilm begins to form when free-floating microbes land on a surface and attach themselves to it. This attachment is initially reversible. If they are not removed they start to change their structure and become irreversibly attached. These microbes then start to divide and attract other microbes to join the colony. Biofilms are complex structures that, given time, can grow to millimeters thick and contain billions of microbes. Sometimes, perhaps following tank turbulence, chunks of the biofilm will slough off and will block fuel filters. The bugs in biofilms also excrete acid. This acid will erode a metal fuel tank. Many holed tanks are a result of biofilm formation.
  • Solid particulate contamination
    • Asphaltines: present in all petro-chemical diesel fuel to a greater or lesser extent. Their presence tends to increase with changes to diesel temperature and oxidation. They are hard, brittle particles that are not soluble in diesel. They are generally less than 2 micron in size making them relatively harmless to a fuel injection system. They can agglomerate into larger particles which can easily block engine filters or damage injectors. These particles tend to collect at the bottom of a fuel tank and can form an oily sludge that is often confused with microbial contamination.
    • Gums and other Organic Contaminants: the oxidation stability of biodiesel is inferior to that of petro-chemical diesel. As the fuel comes into contact with oxygen, chemical reactions break down the diesel into peroxide, organic acids and gummy sediment. These soft, sticky substances can stick to fuel filters and engine components and cause acid erosion.
    • Other Particles: such as road dust and grit, soot, fuel tank rust, engine wear particles. All particles, regardless of source have the potential to cause wear or damage to the fuel injection system or engine.
    • Sludge: it is often claimed that ‘sludge’ is found within diesel fuel systems. It is often interpreted as being one of the above contaminants. In reality it is likely that it is formed from a combination of many of the above contaminants.


Why is contamination a problem?

Modern engines are incredibly sensitive to fuel contaminants. Engine filters can block and fuel injectors can suffer damage, resulting in total engine failure. This can have huge implications if the engine drives a generator providing emergency power to a hospital, data centre or bank.

Standby generators are a building’s last resort if mains power fails. They have to be 100% reliable. No backup strategy can accept the possibility of contaminated fuel derailing the power supply.


How can you prevent diesel contamination?

The key to keeping your diesel clean and dry is a comprehensive fuel conditioning programme. This should include four steps:

  1. Regular testing.
  2. Fuel and tank cleaning.
  3. Fuel polishing.
  4. Fuel stabilisation.
  5. You can enhance the effectiveness of the programme with products such as vent traps, bulk filters and normal fuel filters.
Fuel Conditioning Programme

IPU’s Fuel Conditioning Programme contains 4 stages: Testing, Cleaning, Polishing and Stabilisation.

But rather than go to 4 or 5 different suppliers for these services IPU is a one-stop shop for fuel conditioning. We can provide you with a complete 4-step programme. Our short video explains the four stages of the programme and how that can keep your diesel clean and dry.



IPU DieselCheck

IPU’s DieselCheck fuel tests alert you to contamination caused by tainted deliveries or tank breaches.

A DieselCheck fuel test highlights the types and levels of contamination in your fuel. We then provide you with a simple report to explain what we found and importantly, how to treat it.


IPU ClearTank

IPU’s ClearTank cleaning service is a one-time process that prepares your fuel for long-term conditioning.

Cleaning is an important step that needs to take place before fuel polishing – just like you wouldn’t polish a dirty car. IPU’s ClearTank service simultaneously cleans both the fuel and the tank, leaving your fuel clean and dry.


IPU Diesel Defence

Unfortunately, clean fuel doesn’t stay clean for long. IPU’s Diesel Defence on-tank and mobile polishing units maintain fuel to EN590 and ISO 4406 standards, ensuring it’s ready to power your critical applications.


IPU Fuel Stabilisation

IPU’s ADV Regulator neutralises the tiny molecules of water and contaminants that are too small to be removed mechanically during cleaning and polishing. This helps to starve bacteria of the ingredients they need to grow, saving money in the long term on regular filter replacements.


IPU Vent Traps

A storage tank’s breather vent is its weakest link. It is the easiest route for moisture the reach your diesel. At night, the air at the top of the tank cools and contracts. Fresh air is drawn into the tank through the breather. This new air brings moisture with it. Some of the moisture is absorbed into your diesel. After some of the air is expelled in the heat of the next day, the process repeats itself the following night.

IPU’s vent traps prevent moisture entering through the breather vents. Moisture is captured by the filter during the tank’s inhale cycle. During the exhale cycle moisture is purged from the filter back into the atmosphere. It is a self-maintaining system.


IPU Fuel Purifiner

Every engine has a fuel filter to remove contaminants. The filter is the last line of defence before diesel enters the combustion chamber. It removes fine particulates and some water.

But normal fuel filters have a limitation. They are not designed to remove massive quantities of diesel contamination. They clog in particularly harsh environments. Replacing filter elements is expensive, disruptive and time-consuming.

IPU’s Fuel Purifiner is your first line of defence for engines working in harsh environments. Engines in mines, quarries or on ships benefit from the Purifiner’s ability to remove heavy particulate and water contamination.


Parker Racor fuel filters

Parker Racor fuel filters are the gold-standard for on-application diesel filtration. IPU have been Racor distributors for over 30 years and can offer an unrivalled combination of expert service, competitive pricing and value-added services.