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Answers to filter blocking issue faced by the UK’s farmers

14 August, 2020
AF has been working with the scientists at FAST exocet to establish what caused the fuel blocking issues in 2019, and how they can be prevented this coming harvest.

What Happened in 2019?
Adding biodiesel (fatty acid methyl ester - FAME) to petroleum diesel to increase the renewable content of the fuel and advance the green credentials of all interested parties has been happening for some time. The FAME content of road diesel (EN590) has been steadily increasing for more than 10 years. Until 2019, it was typically in the range 4-5% by volume.

Both the on-road fuel standard (EN590) and the off-road fuel standard (BS2869:A2) allow for up to 7% by volume of FAME to be added. This standard was set in 2011 and has not changed.

Running in parallel to the fuel standards is the Renewable Transport Fuel Obligation (RTFO). This is the government’s requirement of the fuel supply industry to include increasing volumes of renewable content in the UK’s fuel pool – collectively both diesel and petrol. The expectations are:

YEAR RTFO RENEWABLE VOLUME (%)
2011 5.75
2018 7.25
2019 8.50
2020 9.75
2032 12.40

The balance is made up by the volume of ethanol added to petrol as renewable content and the double counting of any recycled product used e.g. used cooking oil. Fuel suppliers can also pay for exemption certificates.

In 2019 compliance with the RTFO became an industry imperative, and fuel suppliers pushed the FAME content towards its maximum permitted limit.

For off-road fuel (BS2869:A2), the sudden increase in the FAME content caused many problems over a number of months nationwide. The main issues were fuel starvation and equipment downtime resulting from fuel filter blockages.

The filter residues and deposits were analysed by FAST and by an external laboratory in order to chemically identify the material causing the fouling. Results found the materials on the filter surface contained an unusually high amount of sterol glucosides and monoglycerides. FAST also identified stearic monoglyceride on a number of filters.
Biodiesel Precipitates
Sterol glucosides and monoglycerides are natural materials found in biodiesel (FAME) derived from plants. Once they have precipitated out of the fuel, these compounds will not readily dissolve back into solution with the bulk fuel unless the temperature is raised to around 40°C. Precipitation of sterol glucosides and monoglycerides is accelerated at lower temperatures, but, as experienced in 2019, can also occur at typical ambient temperatures during summer months.

After much discussion with industry partners and further research, FAST concluded that the most likely cause of the spate of fuel filter blocking issues was the agglomeration of these FAME component precipitates.

Fuel Testing
Approximately 15% of the fuels tested were in poor condition by appearance alone - they had free water and sediment visible and microbiological growth was observed.

It was concluded that filter blocking may have been due to microbiological growth and/or particulate and water contamination resulting from poor storage conditions.

As the fuel filter blocking issues became more widespread and fuel samples were continually being received without any obvious or consistent divergence from specification, FAST began to routinely measure the particle count distribution.

FAST exocet ® Fuel Additive Field Trials
FAST supplied dispersant-containing fuel additives for customers to carry out field trials with end users who were experiencing serious fuel filter blocking issues.

The field trials were immediately successful and exocet® Sludgebuster became the first additive recommended to treat the problem.
It also became apparent during 2019 that, those customers who had been routinely using exocet® Gas Oil Supreme prior to the FAME content increase, did not experience any fuel filter blocking issues even though their near neighbours were. exocet® Gas Oil Supreme, exocet® Gas Oil Conditioner and exocet® Diesel Supreme became the additives recommended to prevent the problem by routine addition to the bulk fuel.

Additional Laboratory Testing
Samples that had been received in August 2019 were re-visited in December. Some were now found to be hazy in appearance, having been recorded as “clear & bright” initially. This indicated a solid material was precipitating out of the remaining fuel sample.

exocet ® Fuel Additives
FAST’s exocet® fuel additives containing dispersants and deposit control additives which lead to free-flowing fuel are:
exocet ® Sludgebuster
exocet ® Diesel Supreme
exocet ® Gas Oil Supreme
exocet ® Gas Oil Conditioner XO1258GO


These exocet® additives will treat and prevent filter blocking problems caused by recipitated biodiesel (FAME) particulates. FAST recommends the use of a 10µm filter on all bulk storage tanks.

The Economics - Replacement Filters vs. Fuel Additives
exocet® fuel additives, at the recommended dose rates, add around one penny to the price of a litre of fuel.

In this context, we ask you to consider the following:
  • the price of new fuel filters for your vehicles

  • the price of new filters for your bulk fuel storage tanks

  • the labour charge to change these filters

  • the number of times fuel filters were changed during the peak of the crisis

  • the cost of downtime: people, lost production


No matter what your volume of fuel use, using fuel additives regularly is far more cost-effective than continually replacing filters.

The information above is an extract from the recently published Fast exocet Biodiesel, Particles and filter blocking report. If you would like a copy of the full report please contact the AF Fuel department who will be more than happy to assist.

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If you have any queries or would like to find out more please get in touch.
info@theafgroup.co.uk 01603 881881Honingham Thorpe, Colton, Norwich, Norfolk NR9 5BZ
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