New diesel advances mean more cold flow problems

I had a friend who moved to North Dakota and she would post updates on what the temperature is like on a given day once she got there. She's been posting in October and they would be looking at wind chills in the single digits.

If you live in Illinois or New York or basically anywhere except Florida and the Deep South, you’re nodding your head right now. The weather has been crazy the last few years, maybe even the last decade.  Really hot in the summer, with lots of winter storms, and frigid cold in the winter.

This is concerning if you’re in charge of diesel equipment or a stored diesel fuel supply, you may already be making (or have made) plans to treat the fuel for cold flow improvement.

But what you may not know is that the traditional measures and expectations for cold flow temperatures of diesel fuel are changing. And not for the better. You can account for these if you're willing to change the way you think about cold-weather diesel treatment. Otherwise, you run the real risk of winter fuel problems when you don’t expect them.

Better Diesel Filters Mean More Problems In The Cold

When making decisions about what to do on the cold flow end, it’s most common to rely on experience when it comes to judging the problem temperatures for fuel.  All fuel has a cloud point – the point at which stuff formerly dissolved in the fuel starts to become undissolved.  It's been common to base the timing of winter fuel treatment on how the anticipated ambient temperatures compare to the fuel's cloud point. 

Enter the new diesel engines.

The newer generation of diesel engines is forcing operations personnel to rethink the conventional wisdom on this because the newer diesel engines use secondary filters with the necessary ability to filter out smaller and smaller particles.  Today's common rail diesel engines need this added protection.

It used to be that 10 microns was the standard filtering size.  Now, these engines are spec’ing 7 or 5 or even as low as 2 microns.  The purpose of the change is to filter out as much of the smallest particulates from the fuel as possible, to protect expensive parts.

The secondary consequence of this is what it does to the effective gelling temperature. Filters that used to let fuel with a cloud point of 15 degrees would let the fuel pass without a problem. To put it another way, enough wax would make it through the filter above that temperature, that you'd get a cold filter plug point at around 10 degrees or so. This would have been a normal expectation that fleet managers would have been able to account for.

Today's filters with smaller holes, in those situations, more and more of these fuels are going to plug filters at temperatures higher than before - because they catch more paraffin. This changes the effective gelling temperature for the fuel used in those engines.

The recommendation now is to use the fuel's cloud point as the fuel's new effective gelling temperature. For the typical diesel fuel, that's going to be a difference of about 5 degrees. But five degrees in this context isn't a small difference by any means.

What Temperature For cold flow problems?

Professional fuel users have a good idea when they need to add a cold flow improver because they generally know the cloud point and plug point temperatures of their fuel. And they keep track of outside temperatures so that they have an idea ahead of time when they need to break out the cold flow improver (since it needs to be in the fuel before the fuel gets too cold).

Generally, satisfactory operation should be achieved in most cases if the blended fuel is 6 degrees C above the "10th percentile minimum ambient temperature" for the fuel's area. This term may not mean anything by itself, but it's supposed to be the temperature that isn't below for more than 3 days out of a given 30-day period.  This is different for different areas and different times of the year. For example, Long Island's 10th percentile temperature in December is -14 degrees C. For Alabama in December, it's -6 degrees C. 

As a user, you want to start considering cold weather treatment when the temperature starts coming within 5 degrees of your fuel's cloud point. This means, if you're tracking the ambient temperatures for your area when the forecast starts projecting lows that approach 10 degrees above the normal 10th percentile minimum ambient temperature, that is the time for you to get your cold flow improver into the fuel.

The new recommendations are to adjust your expectations higher towards the cloud point temperature and away from the plug point temperature.  The smaller the filter, the higher the temperature that you’re going to experience shutdowns in cold weather.

If you use a 7-micron secondary filter, they recommend expecting problems about halfway between the cloud point and plug point temperatures.

If you use a 5 or a 2-micron filter, they recommend just using the cloud point as the “new plug point”.  That means you should expect to have plugging problems at temperatures maybe ten degrees higher than before.

Anything else you can do?

Sure. Just make sure you’re getting your cold flow treatment into the fuel early enough in the season.  Cold flow treatments (like Cold Flow Improver) only work if they’re present in the fuel before the cloud point causes paraffin to start dropping out. 

So you’ll want to be treating the fuel for cold flow earlier in the season if you could be having plugging problems ten degrees higher than before. 

You may be interested in these other posts:

• What to do When Your Diesel Fuel Starts to Gel
• Diesel engine problems: black smoke explained
• Cleaning Diesel Injectors - What you need to know