Updated information on Ultra-Low Sulfur Diesel Fuels

December 2007

The Ultra-Low Sulfur Diesel (ULSD or S-15) fuel story continues to unfold and there is not much good news to be told.

ULSD is causing more and more problems in the field, with little explanation and no help from the major refiners.

Burying our heads in the sand will not solve any of these problems. They will not go away on their own, and unless forced by customers or legislation the major refiners are very unlikely to make any changes.

Some ULSD basics:

ULSD is hygroscopic, it actually holds more dissolved or suspended water (up to 2X as much) than Low Sulfur Diesel (Non-Road, Locomotive, Marine (NRLM), LSD, or S-500) or High Sulfur Diesel (HSD or S-5000).

This dissolved water causes several problems.

It causes higher levels of gum formation, varnish formation, and carbon deposit formation.

This water will corrode (rust) fuel tanks, pumps, injectors, and any other metal it touches. We have seen dozens of examples of engines stored for a few weeks to few months that have significant corrosion in the injectors and other fuel system components even though they are immersed in fuel.

Dissolved water encourages and increases oxidation, speeding the breakdown (destabilization) of the fuel. We are seeing fuel destabilize due to oxidative and thermal breakdown much quicker than ever before. This destabilization takes many forms including darkening of the fuel and formation of asphaltene droplets which blacken and plug filter in a few hundred to a few thousand miles.

Dissolved water is affected by the temperature of the fuel. ULSD at 30˚F can only hold approximately 35% of the water it can at 75˚F. As fuel cools it loses its ability to hold dissolved water. The water is actually pushed out of the fuel into tiny droplets. These droplets explain why you can look at fuel in a tank and see no water and yet a fuel separator or filter can constantly be accumulating water. Furthermore at temperatures below 32˚F those water droplets turn to ice crystals. These ice crystals will quickly plug a fuel filter with a white ice that looks remarkably like wax to the uninformed. We regularly hear from people who believe their fuel is gelling at temperatures of 32˚F or just below it. This icing was a major problem last winter and is already causing problems this season. To add to the problems caused by this high water content, bacteria and fungi can and do actually grow in fuels with little or no visible free water in the tank.

The size and shape of the paraffin wax seed crystals have changed dramatically in ULSD as compared to previous fuels. In ULSD these crystals are larger and regularly shaped than in the LSD and HSD fuels. These larger crystals cause a series of problems for users of ULSD.

First ULSD will “gel” several degrees sooner (warmer) than the previous fuels. The larger crystals are harder to ?treat? to prevent gelling.

Next, there is a new cold weather operability problem that was previously unknown and until recently undefined. This is “Wax Dropout”, an occurrence that happens when ULSD is subjected to a “Cold Soak” period of approximately 48 to 72 hours. When the fuel is continuously at or below a given temperature for an extended period of time (Cold Soak); the larger heavier wax crystals agglomerate and drop to the bottom of the storage container. This paraffin wax has the further problem that it is not readily reabsorbed by the fuel as the temperature rises.

On Monday February 5th of 2007 in the Northeast we had had a weekend where the temperature dropped to approximately 8˚F and stayed there all weekend. On that Monday morning after approximately 72 hours of 8˚F or colder we saw a massive region-wide problem with WDO. We have now tested for and seen this problem happen at temperatures between 12˚F and 0˚F.

The temperature where this WDO phenomenon occurs does not appear to directly correlate to any of the commonly used cold weather operability measures such as Cloud Point (CP), Cold Filter Plug Point (CFPP), Low Temperature Flow Test (LTFT), and Pour Point (PP) traditionally used to discuss and rate diesel fuels.

The traditional method for improving cold weather operability for diesel and heating fuels was to blend with Kerosene (#1 Fuel) or Jet A. Depending on ambient temperature, cost, and availability, blends of 10%, 20%, 30%, 40%, 50%, and even higher have been used to lower the CP, CFPP, PP of fuels.

Due to a combination of factors including EPA regulations, Catalytic Cracking, and Severe Hydrotreating ULSD has a lower aromatic content and less solvency. The EPA regulations requiring the fuel to be delivered to the vehicle with a Sulfur content of 15 ppm or less have eliminated High Sulfur Kerosene and Jet A as blending agents.

This situation has theoretically forced refiners to create an ULSD #1 (Ultra-Low Sulfur Kerosene) for blending purposes. There are however a number of significant problems with using ULSD #1 for winter blending. For one thing, the major refiners don?t want to produce this product. There are several reasons including but not limited to; limited demand, the need for segregated storage, the inability to use ULSD #1 for other uses, and high cost of production.

In short, the biggest problems are nobody wants to make ULSD #1, nobody has any place to store it, it is much more expensive than regular Kerosene, and last but not least, it doesn?t work anywhere near as well as the old high sulfur Kerosene.

The old industry “Rule of Thumb” for winter blending HSD and LSD was that for every 10% Kerosene or Jet A that you blended in you would improve (lower) the CP, CFPP, and PP by 5˚F.

An example would be if you had LSD with CFPP of 10˚F and you blended in 50% Kerosene you could expect to lower the CFPP to approximately -15˚F. This standard has been used since before World War II.

Today using ULSD and ULSD #1 for blending the new “Rule of Thumb” is that for every 10% ULSD #1 you blend into ULSD you only improve CFPP by 2˚F or less.

An example today would be starting with ULSD with CFPP of 10˚F and you blended in 50% ULSD #1 you might lower the CFPP to approximately 0˚F. We say might because we have seen a high number of instances where 10% ULSD #1 provides a 1˚F or less improvement.

In order to successfully operate using ULSD an Anti-Gel product formulated to work with ULSD must be used. Many if not most of the old-line anti-gel products that have been on the market for 10, 20, even 30 years do not work effectively on Catalytically Cracked fuels including ULSD.

To successfully treat ULSD requires new formulations that include an Anti-Gel additive with “Seed Crystal Wax Modifiers”, Cold Flow Improvers, Wax Anti-Settling Agents, and Anti-Icing agents that have been modified to work with this new fuel.

Enertech Labs offers a wide range of products including Complete Fuel Treatment, Polar Flow, and the Matrix products with chemistry formulated address these and the many other problems found in today’s fuels. They are designed to remove (Disperse) water, including dissolved water; stabilize fuels, and provide extreme cold weather operability (Anti-Gel) improvement for ULSD, LSD, NRLM, HSD, IFO, and MFO.