By: Enertech Labs, Inc.
The Ultra-Low Sulfur Diesel (ULSD (S-15)) that we started to receive in mid 2006 has shown some dramatically different cold weather characteristics from the earlier High Sulfur (HSD (S-5000)) and Low Sulfur Fuels (LSD (S-500)).
These new characteristics including higher temperature gelling, change in wax seed crystal, wax dropout, icing, and difficulty in treating have provided some significant challenges to distributors and end users during cold weather.
Due to these new characteristics, users in areas of the US where they have not seen cold weather problems in the past, are now and will continue to see serious issues with gelling, wax dropout, and icing. Here are the main issues known today.
Wax in diesel fuels - Paraffin wax is a natural and important part of diesel fuel. This wax provides several beneficial characteristics including high energy content (Btu's), lubricity, stability, and viscosity. The negative characteristics mainly revolve around cold weather operation and include gelling and something new we refer to as wax dropout.
Let's start by defining a few terms that will help in the discussion of the effects of cold weather on diesel fuel.
Traditionally the two main considerations for diesel fuel have been Cloud Point (CP) and Cold Filter Plug Point (CFPP).
Cloud Point (CP), ASTM D2500. – Fuel reaches its Cloud Point when liquid wax in the fuel has begun attaching itself to the seed wax crystals in the fuel, making them large enough to be seen with the naked eye. This wax will appear as a cloud-like formation floating in the fuel.
Cold Filter Plug Point (CFPP) or Gel Point ASTM D6371. - As the fuel temperature drops the wax crystals continue to get larger and will begin to stick to each other. At this Cold Filter Plug Point (CFPP) or Gel Point the fuel will have difficulty passing through fuel filters. This test is a more complicated procedure involving using a vacuum to draw a 20cc fuel sample through a 45 micron screen within a 60 seconds. This is the critical point at which it can become difficult or impossible to operate an engine or burner.
There is generally but not always a spread between Cloud Point (CP) and Cold Filter Plug Point (CFPP) of 2°F to 8°F. CP is a first indicator of cold weather operability temperatures for diesel fuels. It is a visible indication of paraffin wax in diesel fuels. Prior to the introduction of Ultra-Low Sulfur Diesel (ULSD, S-15) into the US market, the importance of CP was often discounted by many due to fact that diesel engines could generally successfully operate at temperatures many degrees below the Cloud Point (CP).
Up until the introduction of ULSD many if not most operators used CFPP to provide a reference temperature for cold weather operability with diesel fuels. This is however a complicated and imperfect test. As mentioned above, CFPP uses a vacuum to draw a sample of the fuel through a 45-micron screen within a given time. The point at which the sample fails to go through the screen in 60 seconds is the CFPP.
The main issue is that up until recently most fuel filters used a 10-micron filtering media. The significant difference 10 microns and 45 microns caused a disparity between the test and real world operations. However many in the industry felt that this differential was consistent and that provided a reliable guide for cold weather operability.
For example if you had a CFPP of -30°F, you could feel reasonably confident that you could operate to -20°F.
However three new factors need to taken into account due to changes in fuels and engines.
1. ULSD fuel does not appear to provide the same consistent differential between CP and CFPP as we had come to expect with High-Sulfur Diesel (HSD, S-5000) and Low-Sulfur Diesel (LSD, S-500).
2. The new phenomenon of Wax Drop Out (WDO) where under periods of extended Cold Soak, (48-72+ hours) the wax in the fuel suddenly drops out of the fuel. This can happen at temperatures above the CP. This problem appears at this time to be independent of CP or CFPP. Wax Drop Out - When the fuel gets to the Wax Dropout temperature, say for example 8°F and stays there for 48 to 72 hours, the wax will suddenly agglomerate and fall to the bottom of the container. This wax plugs filters and fuel lines until it is removed or until the fuel temperature is raised to a point where the fuel will reabsorb the wax. Again there is a further complication, in that the "old" HSD and LSD wax would gradually start to reabsorb as the fuel temperature rose. With ULSD when wax dropout has occurred the wax does not begin to reabsorb until the fuel reaches fairly high temperatures, often above 40°F, 50°F or even higher. This can make the process of getting an engine with gelled fuel to run properly far more challenging than we have ever seen before.
3. As diesel engines have become more sophisticated there has been a rise in fuel injection pressures. In order to obtain these higher pressures OEM’s have had to manufacture pump and injector parts to ever-closer tolerances. Today many injectors have tolerances in the 2-micron range. These tight tolerances and the very high cost of making and replacing these components have caused manufacturers to use fuel filters with smaller media to protect these components. Where in the past fuel filters typically were 10 microns, today we are seeing filters of 7, 5, and even 2 microns.
This makes the problems associated with ULSD even more difficult. Cloudy fuel that would easily pass through a 10-micron filter can often plug a 5 or 2-micron filter. This makes correcting the cold weather operability issues of ULSD like hitting a moving target. Today you need to adjust your fuel treatment to reflect the engines and filter arrangements in your fleet.
What can you do?
You can improve the cold weather characteristics of diesel fuel in several ways. You can remove some or even most of the wax. This lowers lubricity, reduces Btu's (causing lower mpg and engine power output), lowers the fuels viscosity, and raises the refining cost.
Prior to the rules regarding Ultra Low Sulfur Diesel, you could add #1 Diesel, Kerosene, or Jet A to the #2 fuel. This would lower the CFPP and PP by approximately 5°F for each 10% of the lighter fuel added to the #2 Fuel. You could also treat with additives commonly referred to as an anti-gel (cold flow improver, wax modifier, or solvent) to the #2 fuel to lower CP and CFPP. You can also use a combination of two or more of the above to achieve the necessary reduction in gel point.
Under the EPA mandated ULSD rules you can no longer use High-Sulfur Kerosene, High-Sulfur #1 Diesel, or Jet-A for winter blending of diesel. You can only use Ultra Low Sulfur Kerosene (ULSD #1 Diesel) or an additive containing 15 ppm or less of sulfur.
This ULSD #1 has significantly different characteristics than the fuels previously used for blending. It has lower aromatic content and much lower solvency. These new characteristics mean that blending 10% of this fuel will improve CP and CFPP by only 2°F or sometimes 3°F. In the past you would have expected a 50-50 blend to reduce CFPP by 25°F. With today's new fuels a 50-50 blend will reduce CFPP by only 10°F to 15°F and in many cases there can be even less improvement. It is also very expensive, ranging anywhere from $.30 to $1.00 more per gallon than regular kerosene.
In the Northern States fuel suppliers offer Winter Blended Diesel Fuels for use during cold weather. This is a poorly defined term that can mean almost anything. Unfortunately there are a few fuel suppliers that take advantage of these poorly defined terms to the detriment of their customers. As winter spec #2 ULSD fuel is generally safe to 0°F.
It is very important that you learn which form of blending your supplier is using. If they are using ULSD #1, you should ask for documentation that this fuel was actually loaded at the rack. Many customers require that this fuel be delivered in a separate compartment in the delivery vehicle to ensure that they actually are getting what they order. If the supplier is using an additive, you should ask which additive, how much is being used, and obtain the specifications on that product. As with all businesses most fuel distributors are honest and strive to provide the best products and services possible. The honest ones will have no problem with you asking questions that protect your interests.
In most cases the best way to be sure you are getting what you need and what you pay for is to purchase and add the additives to the fuel yourself. This will help you to know that you are getting the maximum protection available and that it is in the fuel when you need it.
When treating with a cold flow improver (anti-gel), using the recommended treatment ratio provides a certain level of protection, using twice the recommended ratio may improve the gel point a little, however if you go beyond that level it will actually raise or worsen the gel-point. At treatment levels beyond 3-4 times the recommended ratio, you will begin to saturate the fuel and can actually plug a filter full of anti-gel additive. This is generally indicated by a reddish or pink colored wax-like substance covering the filter as much as 1/4" thick. This wax-like substance will not readily melt at room temperature unlike paraffin wax that melts above 32°F.
Water is more of a problem than ever before. Diesel and biodiesel fuels hold water dissolved in them. The amount of water that ULSD is able to hold is greater than that of HSD or LSD. One of the characteristics of fuel is that its ability to hold water in solution diminishes as the temperature decreases. Fuel delivered at 70°F with 200 ppm of dissolved water will as the temperature drops begin to push that water out of the fuel into droplets. These droplets can be seen floating in the fuel and as temperatures reach and go below 32°F those droplets freeze becoming ice crystals.
As a result many of the cold weather problems where people believe they have fuel gelling problem are actually a fuel-icing problem. If you have operability issues in temperatures above 0°F you should check to be sure that you aren't dealing with ice.
Customers are regularly reporting situations where they have no water in storage tanks, no water in vehicle or equipment tanks, but they constantly have water in filters and separators. This is due to dissolved water falling out of solutions.
How can you greatly reduce these problems - You can prevent fuel from gelling in three ways.
- Keep the fuel temperature above the CFPP or Gel Point,
- Blend with a fuel such as kerosene that has less wax to spread out the wax and wax crystals
- Use a Cold Flow Improver or Anti-Gel to prevent the wax crystals from growing and sticking together.
Number one can be difficult, if not impossible. Number two can be very expensive and with ultra low sulfur diesel no longer being reliable; it can require so much ultra low sulfur kerosene as to be impractical. Number three can be done reliably and inexpensively and is the best way to deal with these issues.
Cold Flow Improvers or Anti-gel are a co-polymer that coats the paraffin wax crystals normally found in all diesel fuels to prevent the wax crystals from getting any larger and to prevent them from 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. Fuel additives containing anti-gel should be stored above 40°F. If stored below 40°F allow them to warm up before adding them to the fuel.
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-Gel's 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 35°F.
Another important thing to remember about anti-gel additives is that you have to treat the fuel before it begins to gel. Anti-gel additives are preventatives designed to prevent gelling. Once the fuel has gelled anti-gels won’t help you until the fuel has thawed.
If someone tells you they have an anti-gel additive that does not thicken when cold you should know and understand that there are two types of additives that don’t have this problem, one doesn’t actually contain any anti-gel, the other contains a smaller amount of antigel with large amounts of alcohol to prevent thickening. Alcohol is about the worst thing to put in an additive.
So when the cold weather is approaching look for products that will:
- Reduce the cold filter plug point by adding Anti-Gel, Anti-Icing, and Wax Anti-Settling agents.
- Disperse water from the fuel to help reduce the risk of freezing of your fuel system.
Also look for products that will:
- Add lubricity to your fuel system for reduced engine wear.
- Improve fuel atomization for improved fuel economy.
- Improve cetane.
- Clean injection and fuel systems.
- Stabilize fuel and reduce oxidation.
Enertech Labs will work with you to ensure that you have fuel that meets your needs and the requirements of your high tech equipment. If you have any questions or comments please contact Ron Greene @ (716) 597-5761.