FREEZING POINT OF AVIATION FUELS: ASTM D2386
(Equivalent Test Methods: IP 16, ISO 3013, DIN 51421, JIS K 2276, and AFNOR M07-048)
GENERAL
The freezing of an aviation fuel is an index of the lowest temperature of its utility for certain applications. Solid hydrocarbon crystals can restrict the flow of fuel in the fuel system of the aircraft. The temperature of the fuel in the aircraft tank normally decreases during flight depending on aircraft speed, altitude, and flight duration. The freezing point of the fuel must always be lower than the minimum operational fuel temperature. Petroleum blending operations require precise freezing point measurements. The freezing point is a requirement of specifications ASTM D910 and ASTM D1655. Typical freezing point of aviation fuels is in the range -40 to -65° C.
There are three test methods available for this analysis. All three have been found to give equivalent results. However, when a specification calls for a specific test, only that test must be used.
A measured fuel sample is placed in a jacketed sample tube, also holding a thermometer and a stirrer. The tube is placed in a vacuum flask containing the cooling medium. Various coolants used are acetone, methyl-, ethyl- or iso-propyl alcohols, solid carbon dioxide, or liquid nitrogen. As the sample cools, it is continuously stirred. The temperature at which the hydrocarbon crystals appear is recorded. The jacketed sample is removed from the coolant and allowed to warm, stirring it continuously. The temperature at which the crystals completely disappear is recorded.
TEST PRECISION
Repeatability: 0.8° C
Reproducibility: 2.3° C
