So your particle count is high, with "fines" being your biggest contributor. Usually hoses and lines breaking down generate larger particles, at least from what I have seen.

Stainless tanks and lines causing issues should show iron and nickle in the sample, your's shows zero for both. Depending on your engine's fuel system wear metals from fuel system components are typically iron, chrome, and sometimes nickle, lead, tin and copper. Since you didn't provide any engine details had to determine exactly which are likely in your case.

What is interesting is that you appear to show traces of elements of lube oil additives, Calcium, Phosphorus and Zinc are present, as is Silicon, but all a very low levels.

Your Sulphur number is high, are you running ULSD as the remaining 95% of the fuel, or road diesel with a higher sulphur content?

Filter plugging on biodiesel blends has usually been the result of poor quality biodiesel fuels not meeting ASTM 7467, here is a link to some reference info, https://www.dieselnet.com/tech/fuel_biodiesel_std....

The black particles could be from your hoses, or could be soot if someone is mixing used crankcase oils into the fuel, there was no test done for soot so hard to tell. Usually for B5 fuels tests don't include looking for Glycerin, Ester or carbon residue, but these can be culprits in filter plugging.

A single test may not provide a realistic view of the actual fuel, can you get some additional samples over several intervals to establish a trend?

Have you opened a filter and inspected it, closely looking at the filter pleats could give you a better indication of what is going on with your engine. Are you using secondary filters with a 2 micron rating, or something else? What is the rating of your primary filters?

Hope that helps, MikeL.

What is the source of the biodiesel? If it's from Rapeseed then the Rapeseed Methyl Ester will cause breakdown of many elastomers. The fuel lines and seals need to be specially compounded to handle it.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

when the fuel filters get clogged quite rapidly, the first thing to think of would be the fuel quality as delivered and eventually how it changes while in the tank. one of the things that can contribute heavily to a shorter filter life is the development of microbiological fouling of the fuel in the tank. under certain conditions, especially when there is some moisture in the tank as well, there can be a fast growth of microorganisms at the interface of the fuel and the settled water at the bottom of the tank. simple cleaning of the tank usually is not sufficient to clean the system, a temporary use of a biocide may be necessary.

i suggest you contact the fuel supplier to see whether additional analyses can be made to check if any changes have occurred in the fuel. also analyzing the clogged filters might give a indication what type of fouling is predominant.

another question to ask is whether all the buses experience problems or that the complaint is limited to certain types, whether a particular refuelling depot is used etc. the problems may well stem from not so perfect housekeeping somewhere along the line before the fuel ends up in the buses with problems.

Here are some links discussing the OP's issue, hope you find them helpful,

www.arb.ca.gov/fuels/diesel/altdiesel/biodieseldur...

http://www.baldwinfilter.com/literature/english/10...'s/06-1.pdf

http://www.intertek.com/biofuels/biodiesel/fuel-fi...

http://www.biodieselmagazine.com/articles/1566/the...
Note, this website has a lot of good info on dealing with biodiesel with lots of info some places other than North America

http://biodiesel.org/docs/ffs-basics/adm-fact-shee...
Note, this is another group that has a lot of good info on using biodiesel as well.

MikeL.

Did the operator change their filter supplier? We operate a gearbox with absolute rated oil filters. We noticed filters started plugging rapidly. Red flags go up, we open the equipment and inspect everything we can for damage. Oil analysis results haven't changed. I cut the filter elements, which were aftermarket. I also cut open an OEM unit just out of curiosity. It turns out the OEM element has layers that act as stages. The construction was essentially the same as the Parker Microglass iii element. The aftermarket filter only had a single media layer resulting in a 50+% reduction in life.

Also, know that when oil samples are done they tend to get filtered to a 10 micron or so before processing the sample. Larger particles, the kind that may be clogging your filters, may not even register during an analysis as they get filtered out prior to any testing.

Considering that fine particles of carbon black and silica are common rubber fillers, and there is a lot of S in rubber I believe that your thoughts about hose degradation maybe correct.

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P.E. Metallurgy, Plymouth Tube