ASTM D3241-19 Standard Test Method for Thermal Oxidation Stability of Aviation Turbine Fuels

The standard "ASTM D3241-19 Standard test method for thermal oxidation stability of aviation turbine fuels" published by the American Society for Testing and Materials (ASTM) describes the procedure for rating the tendency of gas turbine fuels to accumulate decomposition products within the fuel system. Differential pressure values ​​in mm Hg are defined for this test method only. No other units of measurement are included in this standard.

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

• Deposits refer to oxidative products that are deposited in the test area of ​​the heater tube or captured in the test filter, or both. Fuel deposits tend to predominate in the hottest part of the heater tube, i.e. between the 30 mm and 50 mm positions.
• The heater tube refers to the aluminum coupon, which is controlled at high temperature and into which the test fuel is pumped. The tube is resistively heated by a thermocouple placed inside and its temperature is controlled. The critical test area is the thinner part between the shoulders of the tube, which is 60 mm long. The fuel inlet to the tube is at the 0 mm position and the fuel outlet is 60 mm.

This test method for measuring the high-temperature stability of gas turbine fuels uses an apparatus that subjects the test fuel to conditions that can be associated with those occurring in gas turbine engine fuel systems. The fuel is pumped through a heater at a constant volumetric flow rate and then enters a precision stainless steel filter where fuel degradation products can be trapped.

The device used in the tests ideally uses 2,5 mL of test fuel during a 450-hour test. The key data obtained are the amount of sediment in an aluminum heater tube and the clogging rate of a 17 µm nominal porosity fine filter located immediately downstream of the heater tube.

Test results are indicative of fuel performance during gas turbine operation and can be used to assess the level of deposits formed when liquid fuel comes into contact with a heated surface at a given temperature.

The equipment used in these tests includes:

• Aviation fuel thermal oxidation stability tester: eight suitable equipment models can be used as specified in the table provided in the standard. Some parts of this test can be automated. For a detailed description of the procedure, the appropriate user manual for the model of equipment to be used should be consulted. A manual is provided with each test rig. The equipment should not be operated without an understanding of all components and their function. Certain operational parameters used with the equipment are critical to obtaining consistent and accurate results. These are listed in a table.
• Heater tube deposit grading device: This device includes: visual tube grader, standardization of metrology requirements (the number of measured points is 1200 in the gradeable area of ​​the tube, the circumferential resolution is 24 equally spaced points, the longitudinal resolution is 50 equally spaced points), interferometric tube grader, ellipsometric tube grader and multi-wavelength ellipsometric tube grader).
• Since the thermal oxidation stability of jet fuel is defined only in terms of this test method, which is dependent on and cannot be separated from the specific equipment used, the test method should be conducted with the equipment used to develop the test method or with equivalent equipment.

In this standard, the standard operating conditions are specified as follows:

• Fuel quantity: Minimum 450 mL for testing plus approximately 50 mL for the system.
• Fuel pretreatment: Filtration through a single layer of general purpose, retentive, qualitative filter paper, followed by 12 minutes of aeration at an air flow rate of 1000 L⁄min for a maximum of 1,5 mL of sample using a 6 mm coarse borosilicate glass gas dispersion tube.
• Fuel system pressure: 3,45 MPa (500 psi) plus/minus 10 percent gauge.
• Thermocouple location: at 39mm.
• Fuel system pre-filter element: Filter paper with 0,45 µm pore size.
• Heater pipe control temperature: Preset as specified in the applicable specification.
• Fuel flow rate: 3,0 mL⁄min plus/minus 10 percent.
• Minimum fuel pumped during testing: 405 mL.
• Test duration: 150 min plus/minus 2 min.
• Coolant flow: approximately 39 L⁄h or the middle of the green range on the coolant gauge.
• Power setting: Approximately 75 to 100 for non-computer models, internally set for computer models.

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