Research on Characterization Methods and Uncertainty Evaluation for Freezing Point Reference Materials

Jet fuel, commonly known as aviation kerosene in China, is primarily represented by No. 3 jet fuel. The freezing point is a crucial indicator of jet fuel's low-temperature fluidity. During flight, as jet fuel temperature decreases, solid hydrocarbon crystallization can occur, potentially blocking filters and compromising flight safety. According to GB 6537-2018, the freezing point of No. 3 jet fuel must not exceed −47°C. Two methods are specified for determining the freezing point: GB/T 2430-2008 "Standard Test Method for Freezing Point of Aviation Fuels" and SH/T 0770-2005 "Standard Test Method for Freezing Point of Aviation Fuels (Automatic Phase Transition Method)," with GB/T 2430-2008 designated as the arbitration method. This study investigates the effects of various factors, including sample volume, cooling bath temperature, and stirring rate, on freezing point measurement results. It also examines the consistency between the two methods and evaluates the uncertainties introduced by the characterization method. Results indicate that a 0.01 mL change in sample volume leads to a 0.07°C variation in test results. Stirring rates between 1 and 1.5 revolutions per second cause a 0.2°C change in measurements. Cooling bath temperatures ranging from −60°C to −80°C have minimal impact on freezing point results. Experimental validation shows a maximum deviation of 0.7°C between the two methods, surpassing the reproducibility requirements of the standard method. The uncertainty components introduced by sample volume, stirring rate, method selection, and data rounding are 0.040°C, 0.058°C, 0.20°C, and 0.14°C, respectively. The expanded uncertainty of the characterization method is 0.50°C (k=2).