Asphaltene's and Plugged Fuel Filters

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.

Diesel Doctor

Copyright 2009©

Black Fuel Filters - Asphaltenes - Re-polymerization

Black Fuel Filters – Asphaltene Production and

Re-polymerization in ULSD Fuels

Have you seen filters that look like this.

There is a difficult new problem with ULSD fuels. Today most ULSD is derived using the process of catalytic cracking. This form of refining uses very high temperatures, high pressures, and chemicals known as catalysts to refine crude oils into various fractions including Ultra Low Sulfur Diesel. The fuels derived using these processes suffer from a wide range of problems including a lack of oxidative and thermal stability.

This lack of stability manifests itself in many ways including an increased ability to hold dissolved water, an increased negative reaction with oxygen, and a far greater inability to handle high temperatures over time. Different refining processes and catalysts can make these problems better or worse. It appears that certain refineries produce fuels which are far less stable than that of others.

Diesel engines recirculate fuel to lubricate and cool the fuel system and engine components, In the past fairly large volumes of fuel were recirculated and this tended to keep temperatures lower, generally in the 140°F to 160°F. Today some of the newer engines can heat that fuel to temperatures that can exceed 200°F or even 220°F.

When some catalytically derived fuel is exposed to temperatures above 100°F for extended periods of time such as when fuel is recirculated in a diesel engine, the catalytic process starts up again re-polymerizing parts of the fuel. This results in rapid deterioration and darkening of the fuel. In this process small droplets of asphaltenes (heavy oils) are formed.

When the fuel is again pumped from the tank, the fuel filters will pick up the tiny asphaltene droplets, agglomerating them until the filter or filters are plugged. This can happen in 3000 to 5000 miles with some instances of plugging in less than 1000 miles.

While there are additives that can add thermal and oxidative stability to fuels, they are not commonly used by refiners or fuel distributors. These additives are not found in most aftermarket additives.