New rules for diesel cold flow problems: reasons to be concerned

Today's professional diesel users are aware of the changes to the fuel properties of diesel. The movement to more environmentally-friendly diesel fuels with extremely low sulfur levels has been great for the environment, but not so great in the context of preventing fuel issues with the equipment.

A big change with ULSD was in the realm of cold flow operability.  Most diesel users in climates outside of Florida are well aware of the poor cold weather tolerance that ULSD has.  This is primarily a result of how the refinery processing of the diesel fuel changes the chemistry of the soluble waxes that normal coexist in the fuel without a problem.  Back in 2005-2006, industry leaders expected that removing the sulfur would change the fuel chemistry such that the effective temperature at which diesel fuel gelling would be experienced would be noticeably higher. 

And indeed that's what happened. As fleet and bulk fuel users started switching out their higher sulfur fuels for the legally-required low sulfur ones in the winter of 2007, it so happened that the coldest weather in five years was also hitting the country. Combine the two and big-time diesel gelling problems arose.  And the industry took notice, realizing that cold weather problems with this new diesel fuel were no joke.

If you’re unfortunate enough to have neglected cold flow treatment of your diesel fuel before gelling temperatures arrive, you can experience the phenomenon of Wax Dropout.  This is slightly different from fuel gelling, and happens when the temperature outside sits below the fuel’s gelling point for an extended period of time – more than 72 hours.   If the diesel fuel hasn’t been treated with a cold flow treatment that keeps the wax dispersed, you can see a point when the (previously dissolved) wax all suddenly sticks together and drops out to the bottom of the tank.  The effect of such a sudden dropout is seen in plugged fuel lines and filters.

Wax Dropout At Higher Temperatures Than In The Past

Citing this phenomenon is relevant to ULSD because, in the field, they’re finding that Wax Dropout is happening at temperatures higher than traditional cold filter plug point temperatures (CFPP).  If a diesel fuel has a CFPP of -15 degrees F, it’s not unusual to see Wax Dropout happening 23-25 degrees above that, which mean it was happening at 8 degrees F instead of minus-15.  And if you’re in charge of diesel trucks in a place like Chicago, you can expect the temperature to reach 8 degrees a lot more often than -15 degrees.

Add this consideration to the fact that newer diesel engines are utilizing fuel filters with small tolerances than before.  The old 10 or 20 micron filters are being replaced by filters taking out 7 or 5 or even 2 microns.  They have to be smaller to protect the common-rail diesel engines up to the standards spec’d by the engine manufacturers.  For the diesel user, it means they have to pay even closer attention to diesel cold flow issues.  A five micron fuel filter is going to plug up at a higher temperature than a ten micron filter will.

So take these facts as you will. Today’s lower sulfur diesel fuels require more care and consideration if your aim is to prevent cold flow problems that may lead to massive headaches for you.

Learn more about cold flow problems in these related posts:

• New diesel advances mean more cold flow problems
• Budget busters for municipalities - cold flow problems

Image Credit: EmmiP Morguefile