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Thursday, July 25, 2024

Biodiesel gelling

Posted by Krzysztof Lis on March 31, 2008

Winter is almost over on the northern hemisphere, so you probably experience increasing temperatures. Biodiesel gelling is a serious concern in cold climate, or during cold winter months.

Why is biodiesel gelling important to be avoided? At cold temperatures, biodiesel becomes cloudy. When temperature drops down more, the biodiesel it gels — it becomes solid. Somewhere at this point (perhaps a little earlier) your fuel filter will be clogged with solid biodiesel snots. Fuel will not be pumped to injection pump and your engine will not work.

So you better make sure your biodiesel doesn’t gel in your fuel tank, or you’ll have trouble starting your engine!

First most important thing you need to know is when (exactly) your biodiesel starts gelling. Unfortunatelly there’s no easy answer to that question. Some biodiesel batches become cloudy at 15°C (59°F), some at -5°C (23°F), depending on the oil used for transesterification (that’s a smart name for biodiesel making process — I’ll explain it in one of the future posts). Here’s a few examples of different biodiesels and cloud points.

  • -15°C (14°F) – biodiesel made from low erucic acid varieties of canola seed [2].
  • -5°C (23°F) – biodiesel made of some waste vegetable oil [1].
  • 16°C (61°F) – biodiesel made from tallow [2].

Cloud Point (CP) and Cold Filter Plug Point (CFPP)

CP is the temperature when some crystals of solidified fuels start to form. The fuel is still liquid, so it’ll go through your fuel filter and you can probably use it in your car even below this point. CFPP is the temperature when fuel filter in your car will become clogged by those crystals. The fuel is still liquid and can be pumped by your fuel pump (but has greater viscosity!), but will clog your fuel filter. This point is considered by some as a very good indication of low temperature operability [3].

How to overcome biodiesel gelling?

The first answer that comes to mind is: do not use biodiesel in winter. But that may not be as simple as that. If for some reason you need or want to use biodiesel in cold time of the year, consider:

  • mixing it with winter petrodiesel,
  • mixing it with kerosene,
  • adding some anti-gelling additives,
  • using two-tank system with heat exchanger to warm your biodiesel (exactly the same as kit for vegetable oil).

You’ll find some interesting tests here and here, and some additional info here.

If you have some good information or test result for your biodiesel batch, feel free to post it in comments. Very big thank you in advance! :)

[1] Biodiesel in winter, article from Journey to Forever.
[2] Biodiesel, article from Wikipedia.
[3] Biodiesel: Handling and Usage Guidelines, U.S. Department of Energy.


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