ASTM D6811 Standard Test Method for Measurement of Thermal Stability of Aviation Turbine Fuels under Turbulent Flow Conditions (HiReTS Method)
12.1 Immerse the input tube and clean filter into a clean sample vessel filled with fuel aerated as in 8.2. The inlet fuel temperature shall be between 15 and 30°C as measured by the input fuel electronic thermometer.
12.1.1 Set the bypass valve to TEST, and start the test.
12.2 Use the bypass valve to purge the tubeways with the fuel sample. Reset the bypass valve to TEST.
NOTE 5 - The test can only start if all independent and computer-monitored safeguards have not detected a fault condition.
12.3 Visually check the system for leaks. If a leak is found, abort the test and vent the system by using the bypass valve. Tighten or replace any leaking fittings if necessary and repeat 12.3.
12.4 Close the capillary tube enclosure door, ensure that the bypass valve is set to TEST, and commence heating the capillary tube.
NOTE 6 - The pyrometer commences measuring the temperature of the capillary tube at the required positions when the fuel exit temperature, from the capillary tube, has stabilized to the prescribed value.
12.5 At the end of the test remove the sample filter and inlet tubing and clean by rinsing with heptane and then by backflushing with heptane, and then refit. Immerse the input tube and sample filter in heptane and clean the system in accordance with the manufacturer’s instructions. When this procedure has been completed, vent the system using the bypass valve.
NOTE 7 - Heptane draining out of the apparatus can be avoided by leaving a capillary tube installed or by capping the upper and lower unions, and ensuring that the bypass valve is in the TEST position.
12.6 The result of the test is automatically calculated. (See Section 13 for the derivation of the HiReTS Peak and Total numbers.)
13. Calculation of Result
13.1 The HiReTS Total number is the total of the difference between the minimum and final temperatures measured at the required positions, along the surface of the capillary tube, during the test.
HiReTS Total number = δT1 + δT2 + δT3 + δT4 + δT5 + δT6 + δT7 + δT8 + δT9 …… + δTn
δTn = difference between the minimum and final temperatures measured at Position n, °C during the test while the fuel exit temperature is maintained at a stable level.
13.2 The HiReTS Peak number is the largest of the differences between the minimum and final temperatures measured at any of the required positions, along the surface of the capillary tube, during the test.
13.3 Express the HiReTS Total and Peak results as whole numbers. Round up any fractions. Use the formats T65, T125, P65 and P125 to denote Total (T) or Peak (P) and the test time.