Bugs Clogged Up Fuel System
Professional Skipper Magazine Issue 35 Sep/Oct 2003
I received a phone call a while back from one of my past customers, a charter boat skipper here in Auckland. He, the vessel's owners and their guests were sick and tired of the constant level of smoke coming from the vessel exhausts, especially during the boarding process and the guests' "welcome aboard" drinkies. The skipper was keen to use our diagnostic service to see what the root causes were and to see if anything other than stripping down the engines and rebuilding them could be done to reduce the smoke. The skipper also questioned why both engines were slow to kick into life as well as why the vessel had lost 3 to 4 knots top-end speed over the past 6 months or so.
From our point of view there were two main areas of concern. First off, oil samples would need to be drawn from both engines to check on the condition of the oil. Secondly, the fuel would need to be analysed for its microbiological content. This was especially important as the sight glasses on both Racor filter/separators units showed signs of a heavy microbial infection of some type.
We started by warming up the engines to operating temperature and the oil samples were then drawn. Fuel samples from both Racors were also drawn off and sent for analysis. Within two days we had received the oil analysis results, although the fuel samples would unfortunately take up to a week as the lab had to grow what we call "cultures" (the bugs).
The results from the lab analysis of the oil samples gave us our first clue as to what, in part, may have been the cause of the smoke, not to mention some of the other issues raised by the skipper. Fuel dilution! Unfortunately both engines had around 4-5% of diesel in the oil. The fuel dilution can be directly attributed to injector, internal fuel line or pump seal leakage. As a result of having diesel in the oil the viscosity (oil thickness) of the oil was lower, thus the oil was not providing the protection that the engine required. With the injectors leaking the lack of pressure and correct atomisation of the fuel in the combustion chamber would have made the engines harder to start. Fuel leakage into the oil can normally be put down to worn injector nozzles, which in this case was a little unexpected as the engines had only done around 1800 hrs.
Once we had the results from the microbiological lab we were able to determine the cause of the injector damage. Filamentous fungi or, to be more precise, Hormoconis resinae (Diesel Bug) and lots of it! The results were so high that they sat within the top recommended category (>10,000 cfu p/Ltr) of the Lloyd's Technical Register, Category D.
As a result of the Diesel Bug infection in the fuel tanks the damage to the injectors was severe. The size of the microbial mass that was getting through the filters not only stopped the injector nozzles from reseating properly, but also interrupted the spray pattern by enlarging the fuel droplets. The result was incomplete combustion of the fuel injected into the cylinder, with the carry over of the unburnt fuel being exhausted. The consequence of this was not only the resulting smoke but also the reduction in engine performance, thus the loss of speed and more than likely an increase in the fuel consumption as well.
Our recommendation to the skipper was to have the injectors from both engines pulled and serviced, the Racors cleaned out and the filters changed. Once all this was done the oil in both engines could then be changed. The fuel in the tanks would also need to be treated before it could be used again. The recommendation here was to use a product call Fuel Mag. The Fuel Mags were designed and manufactured in New Zealand and are distributed around the world. The product is fitted into the fuel lines between the tank/s and the filter/separators. The Fuel Mags are a permanent installation that requires no ongoing maintenance. They work by breaking the bond between the individual spores of the biomass (Diesel Bugs), thus breaking them down into single molecules small enough to pass through both the filters and pumps. The spores are then ejected from the system via the injectors without disturbing the spray pattern. The spores contained in the unused fuel, which is passed back to the tanks via the return lines are in a dormant state, reduced in size and unable to reproduce. As a result the microbiological growth in the tanks will slowly decrease over time until the infection becomes non-existent.
Once the Fuel Mags were installed and the remedial work on the engines fuel systems completed it was time to run the engines up. The level of smoke from both engines was noticeably lower. It was hard to say by how much, but it was certainly a lot lower than before. Also, noticeably, there were no longer large rainbow sheens of diesel appearing on the water which had been emanating from the exhausts. The skipper was happy not only with the reduction in smoke, but also with the cost of the exercise.
A couple of weeks passed before I received another call from the same skipper. The Racors were again full of microbiological growth. He wanted to know why the Fuel Mags weren't doing the job. I immediately rang the inventor of the product who was only too happy to come down and have a look at the problem.
Much head scratching went on until the skipper mentioned how he used his tanks. There were 6 x 1 thousand litre tanks, three a side, although the return lines only went back to the aft tanks. The skipper used each of his tanks individually as required to keep a good balance, however the balance lines between the tanks were at the top and hardly ever come into play. It was pretty quickly determined that the main problem was flow, in other words there needed to be a circuit. The return lines would have to be rerouted so that each tank was teed off the line. This would enable all the tanks to receive the same amount of fuel all of the time. Fortunately, a bit of luck made life a little easier. All the tanks had entry points in the top aft corners, with only the port and starboard aft tanks being used for the return lines. The rest had been plugged off at some stage in the past. To enable this system to work the skipper would have to leave all the fuel valves open so that an equal amount of fuel could be drawn off from each of the 6 tanks at the same time.
The issue of physically cleaning out the tanks was also brought up. Again, a stroke of
luck come our way. All six tanks had extremely good inspection hatches. Even better was that three of the tanks were all but empty. With the use of a large filter and pump mounted on a trolley we were able to pump the fuel from tank to tank via the filter. Once each tank was empty we were able to open them up and clean them out. As the inspection ports were large and on the side of the tanks we were able to wipe out virtually all of the fungus that was stuck to the bottom of the tanks.Two very long hard days graft were done to complete this work; however once it was finished the vessel was free of any major microbiological infections. The fuel now flowed in a complete circuit, which included the Fuel Mags and as a result the vessel's engines now receive clean non-infected diesel. The smoke is a lot less and the vessel is now back up to full speed. The sight glasses remained clear and still do today, some two years later.
Written by Kelvin Hieatt
Managing Director
Marine Diagnostics Ltd
