ASTM D7153 Test Method for Freezing Point of Aviation Fuels (Automatic Laser Method)
10. Procedure
10.1 Draw 10 mL +/- 2 mL bubble-free portion of sample into a syringe. Connect the syringe to the inlet port (Fig. 1). Rinse the test cell by injecting 10 mL +/- 2 mL of specimen into the test cell; the specimen excess will flow into the waste receiving container (Fig. 2)
10.2 Rinse the test cell a second time by repeating 10.1.
10.3 Draw a 10 mL +/- 2 mL bubble-free portion of sample into a syringe.
10.4 Connect the syringe to the inlet port (Fig. 1). Dispense the specimen into the test cell; the specimen excess will flow into the waste receiving container (Fig. 2). Leave the syringe connected to the sample inlet for the entire duration of the test.
10.5 Start the operation of the apparatus according the manufacturer's instructions. From this point through Section 11, the apparatus automatically controls the procedure.
10.5.1 Cool the specimen at a rate of 10 °C/min +/- 5 °C/min while continuously illuminating with a polarized laser light source. Monitor the specimen continuously with two optical detectors, an opacity detector and a crystal detector (Fig. 3), for the first formation of solid hydrocarbon crystals.
10.5.2 Once the appearance of the first crystals (Cd) is detected on the crystal detector and opacity (Co) is detected on the opacity detector, warm the specimen at a rate of 3 °C/min +/- 0.5 °C/min until the disappearance of the opacity (Do) is detected on the opacity detector. At that point, warm the specimen at a rate of 12 °C/min +/- l °C/min while it is still monitored by the crystal detector. When the disappearance of the last crystals is detected on the crystal detector, record the specimen temperature at which the last hydrocarbon crystals return to the liquid phase. Refer to A1.2.12 and Fig. A1.5 for detection curve examples.
10.5.3 Compare this recorded temperature with the temperature at which the first crystals were detected (Cd). When the recorded temperature is warmer than the (Cd) temperature, it is recorded as the freezing point.
NOTE 3 - In most cases, 10.5.3 is considered the termination of the test. (See 10.5.4.)
10.5.4 In certain circumstances, as measured by the apparatus, perform a second test cycle as follows in 10.6.
NOTE 4 - This circumstance may indicate the presence of contamination of the specimen with material other than aviation fuel and the stated precisions may not apply.
10.6 Second Test Cycle:
10.6.1 The original specimen is warmed up to approximately 10 °C and then cooled at a rate of 10 °C/min +/- 5 °C/min while continuously being illuminated by a polarized laser light source. Monitor the specimen continuously with the optical crystal detector (Fig. 3) for the first formation of solid hydrocarbon crystals.
10.6.2 Once the appearance of the first crystals (Cd) are detected on the crystal detector, continue to cool the specimen an additional 5 °C and then discontinue the cooling.
10.6.3 Warm the specimen a rate of 12 °C/min +/- l °C/min while it is still monitored by the crystal detector. When the disappearance of the last crystals is detected on the crystal detector, record the specimen temperature at which the last hydrocarbon crystals return to the liquid phase as the freezing point.
NOTE 5 - When condition described in 10.5.4 is encountered, this indicates that the sample may be contaminated. In that case, in order to minimize the test duration, only the 12 °C +/- 1 °C warming rate is used.
10.7 Once the freezing point is recorded, the test cell is warmed up to ambient temperature. Fig. A1.5 gives two examples of the testing process: one with a neat jet fuel, and one with a contaminated jet fuel.
10.8 The freezing point value will be automatically rounded to the nearest 0.1 °C and displayed by the apparatus.
10.9 Disconnect the injection syringe from the sample inlet. The cleaning of the test cell will be carried out during the performance of the next test.
