FREEZING POINT OF AVIATION FUELS (AUTOMATIC LASER METHOD): ASTM D7153
(Equivalent Test Method: IP 5290)
EXPLANATION
See explanation in Test Method ASTM D7154.
This test method covers the temperature range -80 to 20° C.
TEST SUMMARY
A specimen is cooled at a rate of 10 +/- 0.5° C/min while continuously being illuminated by a laser light source. The specimen is continuously monitored by optical crystal and opacity detectors for the first formation of solid hydrocarbon crystals. Once the hydrocarbon crystals are detected by both sets of optical detectors, the specimen is then warmed at a rate of 3 +/- 0.5° C/min. When initial opacity in the specimen disappears, the specimen is then warmed at a rate of 12 +/- 1 ° C/min. The specimen temperature at which the last hydrocarbon crystals return to the liquid phase, as detected by the crystal detector, is recorded as the freezing point.
In certain circumstances, as measured by the apparatus, the specimen is reheated to approximately 10° C, then cooled at the rate mentioned above until the hydrocarbon crystals are detected by the crystal detector. The specimen is then warmed at a rate of 12 +/- 1 ° C/min, until the last hydrocarbon crystals return to the liquid phase. The specimen at which the last hydrocarbon crystals return to the liquid phase, as detected by the crystal detector, is recorded as the freezing point.
TEST PRECISION
Repeatability: 0.6° C
Reproducibility: 0.9° C
Because there are no liquid hydrocarbons mixtures of known freezing point, which simulate aviation fuels, bias cannot be established. A systematic bias was observed between this method and Test Methods ASTM D2386 or IP 16.
Mean of the result by ASTM D2386 or IP 16 = X - 0.347 where X is the mean of result by ASTM D7153. However, the relative bias is within the reproducibility of both test methods.
