FREEZING POINT OF AVIATION FUELS (AUTOMATIC FIBER OPTICAL METHOD): ASTM D7154
(Equivalent Test Method: IP 528)
EXPLANATION
The freezing point 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. Typical aviation fuel has freezing point temperatures in the -60 to -40° C range. Petroleum blending operations require precise measurement of the freezing point. The measuring range of the apparatus used in this test method is from -70 to 0 ° C. This test method expresses results with a resolution of 0.1° C. This test method eliminates most of the operator time and judgment required by Test method ASTM D2386. However, when the specification requires the use of Test Method ASTM D2386, do not substitute this test method or any other method.
TEST SUMMARY
A 25 mL portion of the test specimen is inserted into a test chamber, after which it is cooled while being continuously stirred and monitored by a fiber optical system. The temperature of the specimen is measured with an electronic temperature measuring device. When crystal formation is detected in the specimen, the temperature is recorded and the specimen in the test chamber is warmed, while being continuously stirred and monitored by the optical system, until the crystals in the specimen completely disappear. The temperature of the specimen when the last crystals disappear is recorded as the freezing point of the specimen.
TEST PRECISION
Repeatability: 0.5° C
Reproducibility: 1.9° C
Because there are no liquid hydrocarbon mixtures of known freezing point, which simulate aviation fuels, bias cannot be established. No relative bias between Test Method ASTM D2386 and this test method was observed.
