Asphaltenes and Plugged Fuel Filters
Asphaltenes in diesel fuels are becoming a much larger problem since the introduction of Ultra-Low Sulfur Diesel (ULSD - S-15) fuels.
There are actually several problems that have come together to cause the filter plugging black slime we so often see today.
Asphaltenes are highly polarized long chain components in crude and the heavier refined oils. Under certain circumstances these compounds associate themselves to form complex colloidal structures.
In Low Sulfur Diesel (LSD – S-500), High Sulfur Diesel (HSD – S-5000) and heating and bunker fuels the higher aromatic content of the fuel tends to discourage the formation of the complex colloidal structures limiting the problem.
However the EPA mandated reduction in aromatic content in ULSD has allowed this problem to happen sooner, more often, and in cooler temperatures than had been seen previously.
Asphaltenes agglomerate into an oily sludge. This problem is made worse when water is added to mix.
Petroleum and bio-derived fuels all hold water suspended in them, ULSD unfortunately holds approximately twice as much as the LSD and HSD fuels we had seen prior to June of 2006. Biodiesel (B100) can hold ten (10) times as much water as LSD and HSD, so even small amounts of biodiesel blended with diesel fuels dramatically increases the amount of dissolved water present.
Blending of fuels refined from different crude stocks further exacerbates this problem. Also, warmer temperatures in storage or due to the recirculation of fuel by the engine fuel system speeds the process and thickens the sludge.
Fuel that looks perfect going into a clean tank can develop tiny asphaltene droplets in a matter of hours when recirculation temperatures exceed 140°F (note: some newer engine fuel temperature as it exits the head exceeds 210°F). These pin-prick sized droplets can plug a 10 micron fuel filter in 3ooo to 4000 miles or less 50 hours of operation.
Many people mistakenly see this as a biological (bacteria and fungi) problem, however in the majority of cases the accelerated biological growth is the result of near perfect growing conditions that allows this rapid growth after the filter plugging asphaltene material has blocked the filter(s).
Keeping the water out helps, but the real solution is a thermal stability additive, a oxidative stability additive, together with a water dispersant.
Please comment with your experiences, suggestions, and or questions.