RCA Brand

Centre Tank Services Ltd (ENGLAND)

CTS Brand


Picture shows badly contaminated
fuel tank in a New Zealand based Ship

Purifiner Distributors (NZ) Ltd commissioned the School of Ocean Sciences of the University of Wales to carry out a scientific experiment to determine the effect of a magnetic field on diesel fuel contaminated by bacterial growth.

The methodology of the test was devised by the School of Ocean Sciences in accordance with Lloyds Register of Shipping Type Approval Department of Engineering Services, Ref. TA/40397/67488/94/REL.

These studies carried out by the University of Wales were funded by Purifiner Distributors NZ Ltd and were reviewed by two anonymous referees. The report was published in BIOFOULING, 1999, Vol.14(3), pp 197-211, the premier journal in its field.

This report is available on request


One of the first symptoms of microbiologically contaminated fuel is filter blockage.

The experiment was conducted to verify our claim that the unit changed the structure of microbiological growth to the extent that the biomass broke down, became dormant and would pass through the filter element into the engine and burn in the combustion chamber.

The object, therefore, was to continuously circulate contaminated fuel through a protected and an unprotected filter of the same construction and to monitor developments.


The experiment was conducted over a total period of 38 days using a closed system of contaminated diesel fuel in a 114 litre reservoir, being simultaneously circulated through a parallel series of two units and two 30mm Separ fuel filters. One of the units contained a magnetised core, the other an unmagnetised core.
The diesel fuel used for the experiment was first analysed to ensure that it was free of biocide contamination. To this was added 20 litres of clean seawater fortified by a suitable nutrient.

The fuel was maintained at a stable temperature consistent with practical applications 25°C – 30°C.
The biocidal contamination of diesel oil degrading micro-organisms were laboratory cultured in a medium similar to that in the experimental set up.

Two methods of test were established. The first, to provide an early indication of filter blockage, was to shut down the circulation system and close off the pump discharge to the reservoir. Then, by isolating the magnetic and non-magnetic legs in turn the time taken for 2 litres to flow through each of the legs was measured. The sample drawn off was returned to the reservoir.
The second method of test was carried out with the circulating pump stopped and the isolating valves in each leg closed.

Samples were taken from the three sample points A, B, C

They represent the following:

  • A. The fuel that had passed through each entire leg i.e. magnetised unit plus filter and non-magnetised unit plus filter.
  • B. The fuel that had passed through the magnetised and unmagnetised units.
  • C. The fuel entering both units.


These samples were examined for the distribution and number of particles larger than 12 micron.

These initial tests established the uniformity of flow rates and conditions in each leg.
after the sample of the controlled contaminant was added to the reservoir, daily sampling from points B & C took place.

The method used to determine the level of microbiological presence was a technique called “most probable number”. This technique is based on the volume of biomass and the average particle size.

The system was operated for 6 days prior to the addition of microbial culture. This test indicated that there was relatively uniform flow through both legs of the flow path with a higher resistance in the magnetised leg. This was later found to be due to an increased filter element thickness.

Microbiocidal culture was added. In the period day 1 – 17 the only flow rate difference in each leg, either due to gravity or when the pump was switched on, was attributed to the greater filter element thickness in the magnetised leg.

At the completion of flow measurements on day 17 the air supply was turned on, the diesel contaminated water was agitated and caused to mix with the diesel in the reservoir.
On day 18 quantities of seawater started to appear in the filter bowls of each leg and a small reduction in flow rate was measured. At this time aeration was adjusted to reduce the amount of water being carried through the test rig and to produce a level of agitation of the contents experienced in a practical situation.
As the experiment progressed from day 20 to day 38 blockage of the non-magnetic leg of the rig increased significantly.

The left image: SEM Photomicrographcs of the surface of clean filter medium prior to use (A), a sample showing the upstream surface of the filter associated with the magnetic device after use (B) and a sample showing the upstream surface of the filter associated with the non-magnetic device after use (C). B and C indicate similarly fouled surfaces yet the filter associated with the magnetic device was much less resistant to flow at the termination of the study.

The rates of blockage indicated that the unmagnetised leg would be totally blocked at day 41 whilst the magnetised leg would show no significant reduction in flow rate.

The experiment was terminated on day 38 and it was found that the filter from the magnetised leg was 35% blocked but had continued to function normally, whereas the unmagnetised leg was 75% blocked and would achieve total blockage had the experiment continued to day 41.

The image to the left: SEM photomicrographs of the downstream surface of the fouled filter medium from filters associated with the magnetic device (A and C) and the non magnetic device (B and D).  Differential fouling is evident, being greater on that from non-magnetic leg.



It means that a fuel system protected by a Purafiner unit will enable the micro-organisms to pass through the filter to be consumed by the engine combustion process.

This extends the filter life while at the same time removing the biological contamination.


It means that the level of proliferation will be significantly reduced whilst the draw off from the tank and subsequent replenishment will reduce the level of contamination in the tank.

It means that the fuel being dispensed will be in a condition where the particulate size of the micro-organisms will enable them to pass into a diesel engine fuel system without causing persistent premature filter blockages.

Once again the micro-organism will be sufficiently small to be consumed in the engine combustion process


The effect of a cleaner fuel without large particulate size and without the presence of biofilm or exopolymer will improve injector performance, giving a cleaner and more efficient combustion cycle.

The control of the microbiological media reduces wear on injector equipment, thus extending component life.

Control of microbiological acidic secretions dramatically reduces the corrosive compounds deposited in the storage and fuel systems.

The fuel shelf life is extended by the prevention of biological souring of the stored fuel


  • Cleaner, more efficient combustion cycle (more bangs per buck)
  • Reduced wear of fuel injection equipment (lower maintenance costs)
  • Elimination of corrosion of fuel storage tanks (lower maintenance costs)
  • Extension of fuel shelf life
  • Prevention of fuel being converted by cell enzymes into non-combustible by-products. Stop trying to burn stuff that wont. It takes heat and fuel to do this and the result is unburnt residues and smoke, etc.