Gelling in Diesel Fuel – What It Is and What To Do About It.
Diesel fuel contains paraffin wax in two forms. These two forms are liquid wax floating in suspension in the fuel and wax seed crystals that are floating throughout the fuel. You can’t see wax without a microscope in temperatures above the fuel’s Cloud Point (CP). At the Cloud Point, the wax begins attaching to itself, making it large enough to see with the naked eye. This wax appears as a cloud-like formation floating in the fuel. As fuel temperatures drop, the wax crystals continue to get larger and will begin to further stick to each other.
At this Cold Filter Plug Point (CFPP) or Gel-Point, the fuel will have difficulty passing through fuel filters. This is the critical point at which it can become difficult or impossible to operate an engine or burner – otherwise known as gelling in diesel fuel. As the temperature continues to drop, the fuel can become a semi-solid. This is known as the Pour Point (PP), or the point at which fuel no longer pours. “Gelling” occurs when diesel fuel reaches its Cold Filter Plug Point.
You can prevent from fuel from gelling in three ways:
- Keep the fuel temperature above the CFPP.
- Blend with a fuel such as kerosene that has less wax in order to spread out the wax and wax crystals.
- Use a Cold Flow Improver (or “Anti-Gel”) to prevent wax crystals from growing and sticking together.
#1 can be difficult if not impossible. #2 can be very expensive and reduces your fuel’s lubricity and BTUs (see our article covering ULSD for more information on kerosene). #3 can be done reliably and inexpensively, and is the best way to deal with these issues.
Cold flow improvers or “anti-gels” are a co-polymer that coat the paraffin wax crystals of diesel fuels. This helps to prevent the wax crystals from getting any larger and sticking to each other (gelling). This anti-gel material is quite thick and must be blended with solvents to allow it to be mixed properly with fuels. It is important to understand that even anti-gels blended with solvents will thicken at temperatures below 40°F. Anti-gel fuel additives should be stored above 40°F. If stored below 40°F allow them to warm up before adding them to the fuel.
How does anti-gel work?
An analogy of what happens to anti-gel is what happens with coolant antifreeze. By itself, antifreeze will thicken in cold weather to the point of being nearly solid, but when mixed with the correct amount of water it will prevent freezing to -40°F or more. Anti-gels work in a similar way – when mixed with the correct amount of fuel they effectively prevent gelling, lowering the gel-point by as much as 40°F (found in Complete Fuel Treatment™).
Another important note about anti-gel additives is that you must treat the fuel before it begins to gel. Complete Fuel Treatment™ is designed to prevent gelling, but after the fuel has gelled, these products won’t help.
Some anti-gel additives don’t thicken in freezing temperatures; you should understand why this is the case. One reason is the additive doesn’t actually contain any anti-gel. The other reason is the additive contains a smaller amount of anti-gel with large amounts of alcohol to prevent thickening. Alcohol is one of the worst things to put in an additive.
For already gelled fuel, see our article on reliquefying already gelled fuel.