1. Biodiesel Cold Flow Basics
Information for Petroleum Distributors, Blenders, and End-Users on Issues Affecting Biodiesel in the Winter Months
Prepared by the National Biodiesel Board
2014
The purpose of this presentation is to provide producers, petroleum and biodiesel distributors, and end-users with background information on cold weather operability when using conventional diesel fuel and biodiesel in a variety of applications to insure proper operation.
This material is to be used in the public domain and is intended to be shared openly. However, portions of this material have come from a number of sources and individual slides are marked as copyrighted by particular companies that provided information on those slides and they are not to be used with express permission of the company or without proper reference.
Questions concerning information contained in these slides should be addressed to: National Biodiesel Board

2. Diesel Fuel & Cold Weather Operability
Operability is defined as the lowest temperature a vehicle will operate without loss of power due to waxing of the fuel delivery system.
Types of Diesel Fuel Used in the United States
Number 2 diesel fuel (#2-D): Most diesel fuel sold in the U.S. is #2-D. The cold flow properties of #2-D available in one geographic area can vary significantly throughout the year. Additives can be use to improve those properties.
Number 1 diesel fuel (#1-D): #1-D is a kerosene-like fuel, and has better cold flow characteristics than #2-D. In cold weather, it is often blended with #2-D to improve low temperature operability, or used by itself.
Premium diesel fuel: Premium diesel fuels are typically “enhanced” fuels that exceed minimum specifications. These specifications may include cetane number, heating value, stability, lubricity, detergency, and low temperature operability. These could count as “winterized diesel.”
Blends of #1-D and #2-D fuels: These fuels are often used during cold weather. The cold flow properties of these blends are dependent on the properties of the fuels used to make the blend, and can vary significantly.
All diesel fuels contain wax, and below a certain temperature, will undergo changes such as crystallization, gelling, or viscosity increase. These changes can reduce the ability of the fuel to flow and create filter plugging concerns, adversely affecting the operability of vehicles.

3. Diesel Fuel Background Information Relevant to Biodiesel
Diesel fuels composition and cold flow properties vary greatly across the United States. Cold flow characteristics of diesel fuels are influenced by the source of the crude oil they are made from, how they are refined and if they are blended to improve performance during cold weather.
The cold temperature properties of diesel fuel vary across the country depending on the time of year the fuel is produced and the climate. Generally, diesel fuels used in cold climates have better cold flow characteristics than diesel fuels used in warmer regions.
Both of these statements have a direct impact on the operability of biodiesel blends in cold weather

4. Cold Filter Plugging Point
Three Important Cold Weather Parameters that Define Operability for Diesel Fuels & Biodiesel
Cloud Point
Temperature where wax crystals first appear
Cold Filter Plugging Point
The lowest operating temperature in which a vehicle will operate
Pour Point
Lowest temperature where fuel is observed to flow
Cloud Point: The temperature at which small solid crystals are first visually observed as the fuel is cooled. This is the most conservative measurement of cold flow properties, and most fuel can be used without problems below the cloud point but above the cold filter plug point. Although not 100 % failsafe, it is the most appropriate test for applications that can not tolerate much risk.
Cold Filter Plug Point (CFPP): The temperature at which fuel crystals have agglomerated in sufficient amounts to cause a test filter to plug. The CFPP is less conservative than the cloud point, and is considered by some to be a better indication of low temperature operability.
Pour Point: The temperature at which the fuel contains so many agglomerated crystals it is essentially a gel and will no longer flow. This measurement is of little practical value to users, since the fuel has clogged the filter long before reaching its pour point. Distributors and blenders, however, use pour point as an indicator of whether the fuel can be pumped, even if it would not be suitable for use without heating or taking other steps.

5. Understanding the Cold Flow Mechanism in Diesel Fuel and Biodiesel
NUCLEI
VISIBLE CRYSTALS
Cloud Point
CRYSTALS GROW AND BEGIN TO ADHERE TO ONE ANOTHER
LARGE CRYSTALS
ADHERE, TRAPPING LIQUID. POCKETS ARE FORMED SIMILAR TO A HONEY COMB. FUEL GELLED.
Pour Point
Diesel Fuel & Cold Weather Operability
When diesel fuel or biodiesel fuel is cooled, it reaches a temperature where wax molecules precipitate out, agglomerate, and form large flat crystals that can quickly plug fuel lines and fuel filters. The base composition of the diesel fuel has a significant impact on the degree and magnitude of crystal formation.
Wax Settling can result in:
Non-uniform delivery of fuel
Elevation of fuel cloud point in storage tanks
Delivery of high concentrations of wax suddenly to a
fuel filter
More wax precipitates as the temperature decreases

6. Typical Treatment of Diesel for Cold Weather Operation
Additives
Commercial cold flow additives can help winter operability by modifying the wax crystal structure during crystal formation when cooling occurs.
Dosage level (expressed in parts per million (ppm)) of individual commercial additives varies depending on wax content and temperature.
Key Point: Additive must be added to fuel before it reaches cloud point temperature to be effective.
Screening your fuels with appropriate additives and biodiesel blends is recommended.
Before Additive
After Additive
(modified crystal structure)
A number of additives are available for improving the low temperature operability of diesel fuels. These additives include pour point depressants, filterability or flow improvers that lower CFPP, and wax anti-settling additives. The effectiveness of the additives is dependent on the properties of the fuel.
If fuels treated with flow improver are stored at temperatures below their cloud points, the modified wax crystals will tend to settle to the bottom of the tank leading to:
Inconsistent fuel quality.
Field problems associated with the wax
enriched lower portion of the tank.

7. Typical Treatment of Diesel for Cold Weather Operation
Kerosene (#1-D)
#1-D has excellent cold flow properties and is generally blended with #2-D in the winter months across the United States to meet customer cold flow specifications, improving / insuring operability. Cloud and pour points, and CFPPs of some #1-D can be well below
-30º F.
Impact of Kerosene Blending
Kerosene/#1-D is also used with biodiesel blends to help improve cold flow operability primarily by modifying the cloud or pour points temperatures. However, kerosene/#1-D has less energy content than #2-D and biodiesel and in some cases costs more than #2-D so there are trade-offs to be considered when deciding to utilize kerosene/#1-D or additives with your winter fuel supply.
Adding 10% kerosene reduces the fuels BTU value (power & economy) by roughly 1,500 BTU, but biodiesel blends eliminate lubricity issues that kerosene causes.

8. Biodiesel and Cold Weather Operability
Basic Facts about Biodiesel & Cold Weather
B100 freezes faster than most US petrodiesel.
Untreated B20 freezes about 2-10° F faster than #2 petrodiesel, depending on:
the cold flow properties of the biodiesel
the cold flow properties of the petrodiesel
at blend levels of 20% and less (< B20), the cold weather parameters of the diesel fuel will dominate
The same precautions need to be taken with biodiesel and biodiesel blends that you are currently taking with generic diesel to ensure trouble free winter operations.
Traditional cold weather solutions for diesel work well with biodiesel - kerosene, block and filter heaters and in-door garaging of vehicles.
Introduce cold flow additives when fuel temperature is above cloud point and treat the kerosene percentage as well to eliminate dilution.

9. Biodiesel Feedstock Composition and Cold Weather Operability
The cold flow properties of biodiesel fuels are dependant on the feedstock (specific type of oil, fat or grease) from which they are made and are a strong function of the level of saturated fat.
Animal fats, palm and coconut oils are more highly saturated— traditionaly higher Cetane Number, higher cloud point.
INCREASING CETANE NUMBER (CN) AND STABILITY
BETTER COLD FLOW PROPERTIES
Thirteen different, but common biodiesel feedstocks are represented in this slide and the data demonstrate the variability in three main fats and the impact on cetane number and fuel stability. As evidenced here, as the amount of saturation increases, the cetane and stability rise, but the cloud point rises as well.
Reference: McCormick, Robert L., Michael S. Graboski, Teresa L. Alleman, Andrew M. Herring, and K. Shaine Tyson "Impact of Biodiesel Source Material and Chemical Structure on Emissions of Criteria Pollutants from a Heavy-Duty Engine." /Environmental Science & Technology/. 35 (9):
For many biodiesel feedstocks the pour point of B100 is usually only a few degrees lower than the cloud point, so once biodiesel “begins to freeze,” gelling can proceed rapidly if the temperature drops only a few degrees further.

10. Cold Soak Filtration Test…
Under conditions prescribed by ASTM D7501, a 300mL test sample is chilled, warmed and filtered.
The time required to pass through a specific filter is measured.
The entire sample volume must pass through the filter within 360 seconds.
If vehicle performance is expected at or below -12o C / 10.4o F then a max of 200 seconds must not be exceeded.

11. Blending Biodiesel In The Cold
Common Cloud Points
for B100
Cold Weather Considerations:
When blending, the temperature of the biodiesel should be a minimum of 60oF or…
15oF above the cloud point.
In-line blending ensures the best mixing
If in-line blending for loading trucks is not available in cold weather, first add half the diesel (warm if possible). Followed by warm biodiesel at high pressure and volume to enhance thorough mixing followed by the other half of the diesel.
Avoid introducing biodiesel directly into a cold and empty tank.
CP Feed Stock Dependent
Plant Oils
Water Freezes
Recycled Grease
(UCO, WVO)
Cloud point and pour point for biodiesel are inherently affected by the type of feedstock used to produce the biodiesel (i.e. Monoalkyl esters of long chain fatty acids .)
Biodiesel usually has a much higher cloud point/pour point than petroleum diesel fuel.
Cold flow additives are common to meet operability requirements.
Success in cold temperatures requires a combination of
Fuel Quality
Fuel Blending
Cold Flow Additives
….and may require Heated Transfer and Storage Capabilities
Animal Fat
Safe blend temp 60oF
Resource: “A Biodiesel Blend Handling Guide”.  Minnesota Department of Agriculture.
“Room” Temperature

12. ASTM D6751-12 Cloud Point & the ASTM D 6751 Specification
This is the latest ASTM D 6751 specification (Winter 2007/2008). This specification will be updated as needed.
Neither ASTM D975 (the fuel specification for conventional diesel fuel) nor ASTM D6751 has a specific requirement for the maximum cloud point as shown above by the word ‘Report’ under the Limits category, but the cloud point should be provided to the customer by the distributor for all loads during winter months of operation. The cold flow properties needed depend on where it is being used (i.e. Michigan or Texas) and what time of year the fuel is being used (i.e. January or July). A petrodiesel or biodiesel fuel with a cloud point of 20°F may be just fine for a Texas summer, but would not be fine for a North Dakota winter.

13. Cold Weather Performance with Biodiesel
Establish a benchmark for cold flow protection based on the ASTM D975 “Tenth Percentile Minimum Ambient Air Temperature.”
the lowest ambient air temperature which will not go lower on average more that 10% of the time
Make sure the petroleum distributor is aware of this and incorporates it into blending operations
The 10th percentile minimum ambient air temperature is derived from an analysis of historical hourly temperature readings recorded over a period of 15 to 21 years from 345 weather stations in the United States.
These are values for January – reference ASTM D 975 Standard Specification for Diesel Fuel Oils (figure courtesy of ASTM).

14. Biodiesel Blending and Cold Weather Operability
The impact of blending biodiesel with diesel fuel is dependent on the characteristics of the base diesel fuel and the methyl ester.
How biodiesel is blended and the level (%) of blend has a direct influence upon cold weather operability.
Basic Blending Facts
Biodiesel can be blended with any kind of distillate fuel, diesel, kerosene, heating oil etc.
The more mixing, the better
Biodiesel is slightly heavier than diesel fuel, (0.88 SG compared to 0.85 SG)
Post Blending Facts
Once blended thoroughly with diesel, it stays together as one fuel and does not separate over time
Once blended the finished blend is treated like conventional middle distillates
Know your specifications before the fuels are put together because no testing is available to point out a problem area once they are combined
It is always better if the temperature of the fuel can be maintained at least 10-15° F above the reported Cloud Point of the product

15. Biodiesel Blending and Cold Weather Operability
Generally, the better the cold flow characteristics of the base diesel fuel, the greater the effect of blending biodiesel on its cold flow properties. Blending biodiesel with #1-D and premium diesel fuels tends to affect cold flow properties more than blending biodiesel with #2-D.

16. Biodiesel Blending and Cold Weather Operability
Concerns arise when the fuel temperature falls below the cloud point of either fuel, independently, or as a finished blend fuel.

17. B100 Cold Weather Storage and Delivery Precautions
B100 stored in cold temperatures must be heated to at least 15 degrees higher than the biodiesel feedstock being used prior to distribution or blending into middle distillates of any grade.
If pumping biodiesel in cold weather through a conventional fuel pump, keep the hose and supply line to the pump equally protected with heat. An option to heating the systems is to blend B100 with 50% kerosene to dilute the cold weather properties of the biodiesel.
Take precautions so B100 stays 10 – 15 ºF above the cloud point. Feedstock dictates cloud point temperature – know the feedstock(s) the biodiesel was made from.
Putting B100 into a cold empty truck can cause the B100 to gel which prohibits mixing properly
Require that B100 is hauled in insulated tankers during the winter months
Tanks, pipes, and pumps should be heated and insulated to insure B100 is 10 – 15 ºF above the cloud point of the biodiesel.
When designing a system for cold weather biodiesel storage tanks and fuel lines should be designed for the cold flow properties of the biodiesel being used and the climate they will see. Make sure that fuel pumps, lines, and dispensers are protected from cold and wind chill with properly approved heating and/or insulating equipment.

18. Cold Weather Blending Options and Precautions
With any type of blending (splash, in-tank or bottom loading), putting B100 into a cold empty truck can cause the fuel to gel, prohibiting proper mixing.
Always maintain biodiesel at 15º F above its cloud point prior to blending with diesel fuel.
If crystals form during blending they should go back into solution as long as the temperature of the blended fuel is above the cloud point of the blend.
Blending with kerosene can be utilized in situations where heated B100 is not available.

19. Low Blends of Biodiesel and Cold Weather Operability
Blends of 2% and 5% biodiesel with diesel fuel have little impact on cold flow properties. Only small increases in cloud and pour point are observed
Blends of biodiesel, even as low as 2%, and diesel should be stored at temperatures at least 5 – 10 ºF above cloud point of the blended fuel

20. Low Blends of Biodiesel and Cold Weather Operability
As long as the B2 or B5 blend is made using an appropriate “winter grade” diesel fuel, no special provisions are required for storing, transferring or using the fuel.

21. Biodiesel and Cold Flow Additives
Most cold flow additives essentially work only on the diesel portion of the biodiesel blend as U.S. oils and fats contain too high a level of saturated compounds for most additives to be effective.
The cold flow additive effectiveness can also change dramatically depending on the exact type of biodiesel and the processing it has undergone; much like the situation found with diesel fuel.
Most cold flow additives reduce the size of crystals or inhibit crystal formation in some way. Blending biodiesel with petroleum diesel moderates cold flow problems by dilution
When biodiesel is blended with diesel fuel, the key variables are the cold flow properties of the diesel fuel you blend with, the properties of the biodiesel, the blend level, and the effectiveness of cold flow additives

22. Conclusions Cold flow properties of petrodiesel fuel vary widely.
One MUST be aware of the cold flow properties of both the biodiesel AND the petrodiesel.
With blends of 20% and below, petrodiesel is dominant
Prepared properly, blends of B5 or less do not appear to be appreciably different from the base petrodiesel.
Contact the National Biodiesel Board at
with any questions.

23. Conclusions
Blending biodiesel with #2 petrodiesel in blends of 20% (B20) does have an impact on the cold flow properties.
Saturated oils and fats have more of an effect on cold flow properties.
Blending biodiesel with #1 petrodiesel in blends of 20% (B20) results in more of an impact on cold flow properties than with #2 petrodiesel.
But the resulting #1 blend still has better cold flow values than #2.

24. Cranmore Mountain Resort
Cool Customers
How others use biodiesel in cold climates
Cranmore Mountain Resort
When snow falls at a rate of several inches per hour and all signs point to perfect weekend ski conditions, this ski resort has a lot riding on successful operation of its snow grooming equipment.

25. Cool Customers
How others use biodiesel in cold climates
City of Brooklyn Park, MN
The city has used biodiesel blends since 1999 in its fleet of over 100 vehicles— including fire trucks, utility and police vehicles.

26. Cool Customers
How others use biodiesel in cold climates
Yellowstone National Park
Biodiesel powers about 300 vehicles, boilers and other diesel equipment at the crown jewel of America’s National Park System.