ASTM D7153 Test Method for Freezing Point of Aviation Fuels (Automatic Laser Method)
4. Summary of Test Method
4.1 A specimen is cooled at a rate of 10 °C/min +/- 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 °C/min +/- 0.5 °C/min. When initial opacity in the specimen disappears, the specimen is then warmed at a rate of 12 °C/min +/- 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.
4.2 In certain circumstances, as measured by the apparatus, the specimen is reheated to approximately 10 °C, then cooled at the rate in 4.1 until hydrocarbon crystals are detected by the crystal detector. The specimen is then warmed at a rate of 12 °C/min +/- l °C/min, until the last hydrocarbon crystals return to the liquid phase. 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.
5. Significance and Use
5.1 The freezing point of an aviation fuel is the lowest temperature at which the fuel remains free of solid hydrocarbon crystals which, if present in the fuel system of the aircraft, can restrict the flow of fuel through filters. 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 shall always be lower than the minimum operational fuel temperature.
5.2 Petroleum blending operations require precise measurement of the freezing point.
5.3 This test method expresses results to the nearest 0.1 °C, and it eliminates most of the operator time and judgment required by Test Method D2386.
5.4 When a specification requires Test Method D2386, do not substitute this test method or any other test method.
