[M.D. Holloway]

Diesel Fuel has been an interest of mine as of late. Some fun facts about diesel...

No. 2 diesel fuel - Most common during warm and moderate seasons. Regulated in U.S by ASTM D975

No. 1 diesel fuel - Kerosene, Aviation turbine fuel (Jet A, Jet A-1), Military jet fuel (JP-5, JP-8) , Winter-grade diesel fuel, either neat or blended into No. 2 diesel fuel.


Off-Road Diesel #2 and Over-the-Road Diesel # 2 differ only in the tax applied at the time of sale. Off road is dyed red.

Kerosene #1 and #2 are lighter than #1 and #2 diesel fuel. Most kerosene is dyed red.
The old method of winter treatment using 1 gal of kerosene to 10 gal of diesel can get a driver into trouble unless it is dispensed as clear kerosene from a pump which charges road tax.

Any red dye in a tank of fuel is detectable by the sampler the DOT uses, even when diluted by a large quantity of undyed fuel. As little as 1/2 qt of ATF in a tank of fuel will be detected as untaxed fuel and can cause a major headache for the driver.

Number 2 Diesel Fuel Has A
- Higher initial boiling point
- Higher flash point
- Higher viscosity
- Less natural lubricity
- MUCH more wax (No. 1 diesel has virtually no wax)
Than Number 1 Diesel Fuel

It is the wax content of No. 2 diesel fuel that is the source of its potential cold flow problems in winter conditions.

Cold weather properties are important, remember that normal alkanes are desirable, but the desirable diesel fraction alkanes have melting points above 0C temperature, so special flow-enhancing additives and changes to the hydrocarbon profiles occur seasonally. That's why it's never a good idea to store diesel from summer for winter use.

Actual low temperature operability of specific equipment applications are approximated by using various established test procedures:

- Cloud Point: The temperature at which wax first begins to drop out of fuel as the temperature is lowered. A good indication of actual operability limits when using diesel fuel containing no cold flow additive

- Freeze Point: The temperature at which the last portion of wax, after it has begun to drop out, will re-melt and dissolve as the fuel is warmed - required to be no higher than -40 C for Jet A and no higher than -47 C for Jet A-1 (also JP-8)

- Pour Point: The temperature at which the entire fuel becomes immobile due to wax solidifying throughout the entire liquid phase. For fuels without cold flow additive, pour point will be about 2 – 3 C lower than cloud point. For fuels with cold flow additive, pour point can be 10 to 25 C lower than cloud point, depending on the fuel and the additive used. It is not a good indicator or real low temp operability since it usually over estimates real world performance limits.

- Cold Flow Plugging Point (CFPP): CFPP is the temperature at which diesel fuel may clog filters. For fuels without cold flow additive, CFPP is essentially equal to cloud point. For fuels with cold flow additive, CFPP will be between cloud and pour points. The wider the gap between cloud and pour points, and the closer the CFPP is to the pour point, the better the performance of the cold flow additive will likely be.


Cold Flow Additives: They co-crystallize out either with or just before and then with the wax as the fuel is cooled, disrupt the wax crystal formation, causing only very small wax crystals to form, prevent large plate-shaped wax crystals that plug fuel lines from forming.
Their performance can be fuel-dependent, that is, certain additives may work better in some fuels than in others.

It is best to have less wax in fuels so not as much wax can drop out as the fuel is cooled.
A wider distribution of wax molecular weight is important so that not all the wax drops out at once when the fuel temperature reaches the cloud point A gradual, skewed tail at the heaviest wax portion, so that only a small amount of wax drops out at first when the cloud point is reached.