ASTM D7153-22 Standard Test Method for Freezing Point of Aviation Fuels (Automatic Laser Method)

The American Society for Testing and Materials (ASTM) standard "ASTM D7153-22 Standard Test Method for Freezing Point of Aviation Fuels (Automatic Laser Method)" describes a test method for determining the temperature at which solid hydrocarbon crystals can form in aviation turbine fuels. This test method was designed to cover a temperature range of minus 80 degrees to plus 20 degrees, however, the interlaboratory study cited has only demonstrated the test method with fuels having a freezing point in the range of minus 60 degrees to minus 42 degrees.

For the purposes of this standard, the following terms and definitions apply:

• Freezing point, in aviation fuels, refers to the fuel temperature at which the solid hydrocarbon crystals formed during cooling disappear when the fuel temperature is allowed to rise under specified test conditions.
• The automated laser method refers to the procedures of automatically cooling a liquid aviation fuel sample until solid hydrocarbon crystals appear, followed by controlled heating and recording the temperature at which the hydrocarbon crystals completely redissolve into the liquid phase.

In the test method described, a sample is cooled at a rate of 10 degree⁄min plus/minus 5 degree⁄min while continuously illuminated by a laser light source. The sample is continuously monitored by optical crystal and opacity detectors for the initial formation of solid hydrocarbon crystals. After hydrocarbon crystals are detected by both sets of optical detectors, the sample is heated at a rate of 3 degree⁄min plus/minus 0,5 degree⁄min. Once the initial opacity in the sample has disappeared, the sample is heated at a rate of 12 degree⁄min plus/minus 1 degree⁄min. The sample temperature at which the final hydrocarbon crystals detected by the crystal detector return to the liquid phase is recorded as the freezing point.

In certain cases, the sample is reheated to approximately 10 degrees Celsius, as measured by the instrument, then cooled at the rate described above until hydrocarbon crystals are detected by the crystal detector. The sample is then heated at a rate of 12 degrees Celsius plus or minus 7 degree Celsius until the last hydrocarbon crystals return to the liquid phase. The sample temperature at which the last hydrocarbon crystals detected by the crystal detector return to the liquid phase is recorded as the freezing point.

The freezing point of an aviation fuel is the lowest temperature at which the fuel remains free of solid hydrocarbon crystals. If these crystals are present in the aircraft fuel system, they can restrict the flow of fuel through filters. The temperature of the fuel in the aircraft tank normally decreases during flight, depending on the aircraft's speed, altitude, and duration of flight. The freezing point of the fuel should always be lower than the minimum operational fuel temperature.

Petroleum blending operations require precise measurement of freezing point. This test method expresses results to the nearest 0,1 degree and eliminates much of the operator time and judgment required by the “ASTM D2386-19 Standard Test Method for Freezing Point of Aviation Fuels” standard.

The main equipment used in these tests includes:

• Automatic instrument: This instrument consists of a microprocessor-controlled test cell capable of cooling and heating the sample, a dual optical detector to monitor the appearance and disappearance of crystals and opacity, and to record the temperature of the sample.
• The equipment is equipped with a sample chamber, optical detectors, laser light source, digital display, cooling and heating systems, and a sample temperature measuring device.
• The temperature measuring device in the sample chamber can measure the temperature of the sample between minus 80 degrees and plus 20 degrees with a resolution of 0,1 degrees and an accuracy of 0,1 degrees.
• The device should be capable of cooling the sample at a rate of 10 degree/minus 5 degree/min, heating at a rate of 3 degree/minus 0,5 degree/min, and heating at a rate of 80 degree/minus 20 degree/min in the temperature range of minus 12 degree to plus 1 degree.
• A standard syringe that can inject approximately 10 mL plus/minus 2 mL of sample and has a tip or adapter tip that will fit into the inlet of the test cell. A disposable 10 mL syringe with a Luer-type cone connection is considered suitable.
• A waste container that can collect the overflow when the sample is injected into the test cell. A standard 400 mL glass beaker is considered suitable.

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