Dirty Fuel Causes Operational Problems
Professional Skipper Magazine Issue 39 May/Jun 2004 (unedited)
Sample of diesel from day tank
A while back I received a call from one of the more notable marine engineering companies here in Auckland. They had an issue with one of the visiting super yachts that had stayed back after the Americas Cup for a refit. The company had just competed work on rebuilding the vessels gen sets, however both were bellowing out a dirty light brown smoke.During the rebuilding process both sets of injectors and pumps were removed and serviced. However, as a result of the smoke the injectors were pulled again and retested. From what I understand more than half did not come up to spec. The injectors were re-serviced and put back into the engines. This time when the engines were run up the engineers used fuel from a 20 Ltr container, which they had bought from the local service station. Great they thought, beautiful clean burning engines, as one would expect. However, within only a few hours it was back to the dirty light brown smoke, bugger!!
It was at this stage I was called in to offer my two cents worth. It was concluded that the only common denominator was the ship's fuel. I took a sample of fuel from the vessel's day tank and sent it off for both chemical and microbiological analysis. When the results come back from the labs it was very easy to see what the issue was and what was causing the problem. The results received from both labs were as follows:
Chemical Analysis Results
Density @ 15°C: 0.8452 g/ml
Flash Point, PMCC: 74°C
Distillation IBP: 183.0°C
10% Recovery: 224.0°C
50% Recovery: 298.5°C
Calculated Cetane Index: 54
Calcium, as Ca: <0.5 ppm (Not detected)
Conclusions
These results are consistent with a "typical" quality diesel fuel. This result also indicates that there has been no oil contamination of the diesel fuel.Microbiological Analysis Results
The following were found per litre of diesel, the largest sample tested being 50 ml:
cfu per litre 4.0 x 103
ND
6.0 x 103
5.1 x 104
22%
Conclusion:
The diesel sample received is a Category D under the Lloyd's Register guideline limits for diesel fuel in storage tanks.
Hormoconis resinae. Represented by the dark growth on the plate.
What the microbiological analysis of the fuel showed was that the diesel was heavily infected with Diesel Bug. Category D is the top limit in the Lloyd's guidelines, which highlights the fact that operation problems are likely. Diesel Bug is more commonly known for blocking the primary fuel/water separator filters, however the particles of biomass that do get through can not only upset the injector nozzle sitting, but also the fuel's spray pattern, thus unburnt fuel is not uncommon.Draining and cleaning out the fuel tanks and lines is normally the first option here, but with quite substantial quantities of fuel onboard and very inaccessible tanks I advised that the fuel from all three tanks should be passed through a centrifuge and polished instead. Centrifuges are very good for removing water and impurities from the fuel, however Diesel Bug is thought to have a specific gravity similar to diesel, thus while the cause of the Diesel Bug infection is removed the result may not be. To deal with this issue I recommended that a Fuel Mag be fitted to the outlet of the centrifuge so as to break down and sterilize any of the biomass particles that did get through.
The process of polishing took up to three days non-stop as the large quantity of fuel had to be circulated through the centrifuge at least three if not four times. While this was being done the engineers fitted Fuel Mags to the gen sets and main engine fuel supply lines. The injectors were also re-serviced again. Once the work was complete the vessel went out for a good shake down after completing its refit. All ships engines performed up to expectations and at no stage was there any obvious signs of smoke.
Bacteria slide
A week or so later I went back on board to take another sample from the day tank. When the results were received from the lab we were left with no illusions that the work carried out was highly effective in dealing with most if not all of the offending Diesel Bug.
Microbiological analysis Results
The following were found per litre of diesel, the largest sample tested being 50 ml:
cfu per litre Aerobic bacteria 100 Anaerobic SRB (cfu per litre after 5 days) ND Yeast ND Total Filamentous Fungi ND % Cladosporium resinae (Hormoconis) 0%
Conclusion:
The diesel sample received is a Category A under the Lloyd's Register guideline limits for diesel fuel in storage tanks.While this method worked well for this particular vessel it's not always this easy. One of the main things that was of great assistance was that the two main tanks and the day tank were all fitted with drain or what we call stripping lines. This meant that the fuel could be drawn from the exact bottom of the tanks, something that is not able to be done on most vessels. This is because the only access to draw off diesel is the fuel supply pick up lines, which unfortunately for this type of work are normally two or three inches above the floor of the tanks, thus leaving the area where most of the water sits inaccessible. I leave that thought with you when you are building your next vessel or reconstructing your vessels fuel tanks.
Good Sailing
Written By Kelvin Hieatt
Managing Director Marine Diagnostics Ltd
