Determination of Cold Weather Fuel Operability

 

There are various means used to theoretically predict whether a particular diesel fuel will function properly when used at reduced ambient temperatures. Some of these methods are "good predictors" and some are not. The following describes the most widely used testing techniques to assist fuel marketers and fuel users.

 

Research Laboratories Inc^® has always believed that the best possible way of proving winter time viability (operability) of a diesel fuel is to actually use the fuel in vehicles (or engine) applications during the cold months of winter. This testing should be completed over several different winters at different temperatures with different types of equipment and various different engine/equipment operating conditions.

 

Absent the above (1) ability, the second best means to prove diesel fuel winter time operability is to test the fuel in an actual vehicle placed in a Cold Chamber. The climate conditions can be controlled to closely match specific parameters the vehicle operator expects to encounter during winter time use of the diesel fuel. Again, different engine types and operating applications and various tests should be done.

 

Without the above (1 & 2) choices, the third best means of determining winter time operability of a diesel fuel is to flow the fuel through an O.E.M. fuel filter unit placed in a cold room using an O.E.M. diesel engine fuel pump with the fuel temperature lowered to typical winter time operating temperatures. This simulated engine fuel system operation testing should be done with different types of fuel filters at various fuel temperatures in order to verify the actual operability of the fuel.

 

   

                                              Cold Room chamber                                                                   pumps and OEM fuel filters

 

If the previous (1, 2 & 3) options are not available, the fourth best means of determining winter time operability of a diesel fuel is to laboratory test the fuel for Wax Dispersancy using Research Laboratories, Inc new Wax Dispersancy Filterability Test (WDFT). The WDFT examines 100ml of fuel from the "top" and 100ml of fuel from the "bottom" of a fuel sample placed in a freezer for 24 hours at 10 degrees F below the base fuel Cloud Point. If the ASTM Cloud Point test performed on the two 100ml samples is within 1.0 to 1.5 degrees F of the base fuel Cloud Point, the solidified paraffin wax content in the fuel is determined to be fully suspended. If the solidified fuel paraffin content can be fully suspended (and the wax crystals kept smaller than the fuel filter micron rating), the diesel fuel should flow through the engine fuel filters and likely not cause any cold weather operability issues.

5. INDEPENDENT LABORATORY TESTING:

Finally, if previous tests procedures (1, 2, 3 & 4) for determining cold weather fuel operability are not used, the only remaining options are laboratory testing for CFPP - Cold Filter Plugging Point., LTFT -Low Temperature Filterability Test, CP - Cloud Point and PP - Pour Point using automated test equipment for each parameter. These four tests provide limited verification of the actual field operability because of their respective testing techniques.

 

The CFPP test has been and still is used in numerous countries around the world as the chief evaluation parameter for winter time operability. These countries have an established specification requiring precise CFPP test results for stated ambient temperatures or stated calendar time periods. Unfortunately, there currently is no required CFPP specification for diesel fuels sold in the United States.

Research Laboratories, Inc believes automated CFPP testing can be used to effectively determine diesel fuel operability:

(a) if the solidified paraffin content/wax is properly suspended in the diesel fuel at fuel temperatures below the fuel Cloud Point and

(b) if the solidified paraffin wax crystals are kept very small and prevented from agglomerating together at temperatures below the fuel Cloud Point.

Three CFPP Testing Units

 

 

 

LTFT - Low Temperature Filterability Test

The LTFT laboratory test was created in 1981 by Exxon Chemical (now Infineum) in an attempt to:

 

(a) Provide an alternative laboratory test to the Cloud Point test being used to determine diesel fuel operability during cold weather and

 

(b) Sell a new chemical additive product offered at that time by Exxon Chemical that was advertised to improve diesel fuel operability during cold weather.

 

Exxon Chemical compared their new LTFT additive (and test procedure) to the manual CFPP test which was becoming popular in America in the 1980's. Exxon Chemical used field vehicle tests to show the LTFT test (with a +/- 9 degrees F repeatability) superior to the manually tested CFPP test (with a +/- 18 degrees F repeatability) in predicting diesel fuel operability. However, since the invention of new automatically computer controlled CFPP testing equipment (with +/- 2 degrees F repeatability), the validity of the 1981 LTFT test results showing superior operability prediction are seriously questioned.

 

LTFT results may questionably provide a more realistic winter time diesel fuel operability prediction than the fuel Cloud Point for diesel fuels that do not contain cold flow improver additives. But like the fuel Cloud Point test results, the laboratory LTFT results (with +/- 8 degrees F current reproducibility between labs) does not accurately predict diesel fuel operability for diesel fuels that contain new generation chemical additives that have been specifically formulated to improve winter time diesel fuel operability. Such treated fuels will operate successfully well below the LTFT result.  LTFT laboratory results (from the same laboratory) can vary widely in diesel fuels treated with the same winter operability improving additives if different crude oils are used to make the diesel fuel and if different manufacturing processes are used to make the diesel fuel. LTFT is also very labor and time intensive.   There are very few laboratories that provide this testing service.

 

While the laboratory Cloud Point test can be used to predict engine operability for diesel fuels that do not contain cold flow improver additives, the fuel Cloud Point does not accurately predict engine operability for diesel fuels containing new generation chemical cold flow improver additives.

 

The fuel Cloud Point (the temperature at which the fuel paraffin first changes from a liquid to a solid wax) is not changed by these new cold flow improver additives. However, these new additives DO lower the temperature at which the fuel can be effectively used in a diesel engine.

 

These new chemical additives disperse the solid paraffin wax and limit wax crystal agglomeration. And, these new generation additives also reduce the size and change the shape of the formed wax crystals which allows the solid wax crystals to flow through fuel filters at temperatures below the Cloud Point.

 

Absent any cold flow improver chemicals in a diesel fuel, the engine will fail at or near the Cloud Point temperature. With proper new generation cold flow improver chemicals added to the diesel fuel, the engine can be successfully operated at temperatures several degrees F below the Cloud Point.

 

 

 

The laboratory Pour Point test determines the temperature at which the diesel fuel is completely solid and will not flow. Accordingly, the Pour Point is only a measurement of the flow capability (movement) without any limitations and without any filtering restrictions. Therefore, Pour Point cannot be used to predict engine operability. The engine will fail because of filter or delivery line or pump plugging long before the Pour Point temperature is reached with or without chemical additive treatments.

Six Place Cloud & Pour Point Test Unit

 

 

 

The above discussion reviews the best testing options currently available for determining winter operability of on-highway and off-highway diesel fuels.

It should be noted that all of the above tests' results (and any operability determination) will be negatively affected if:

 

(a) An excessive amount of moisture is present in the fuel being tested.

 

(b) The physical properties of the diesel fuel being tested do not meet the recommended ASTM Quality specifications and   guidelines for the area in which the diesel fuel is being used. (Example: higher than recommended CP for northern climates during December, January, and February.)

 

(c) Fuel filter micron rating restricts fuel flow due to its mesh size.

 

(d) Fuel contaminate levels (such as microbial growth agglomeration, particulate accumulations, etc.) that impede fuel flow through the fuel system.