ISO 6249:2021

Overview

ISO 6249:2021 - Petroleum products: Determination of thermal oxidation stability of gas turbine fuels specifies a laboratory procedure to rate the tendency of gas-turbine fuels to form deposits when exposed to heated surfaces. Applicable to middle distillate and wide‑cut fuels, it is especially directed at aviation turbine fuels, including those with conventional and synthetic blending components (e.g., as referenced in ASTM D7566 and Def Stan 91‑091). The test simulates fuel contact with a heated surface under controlled flow and pressure to indicate thermal oxidation stability during gas turbine operation.

Key technical topics and requirements

• Principle of test: Fuel is pumped through a resistively heated aluminium heater tube and then through a precision filter. Fuel degradation products can deposit on the heater tube and trap in the filter; filter differential pressure is monitored for premature shutdown.
• Heater tube: Defined metallurgy and dimensions (aluminium 6061‑T6 with specified Mg/Si limits and precise center section length). Critical test area is a 60 mm centre section.
• Deposit measurement and rating:
  • Visual tube rating using a colour standard (10‑step scale from 0 to >4).
  • Quantitative measurement by interferometry, ellipsometry, or multi‑wavelength ellipsometry (Annexes C–E) to determine deposit thickness (nm) and deposit volume (mm³).
  • Standard spot and maximum deposit thickness definitions are provided.
• Apparatus and materials: Lists reagents (solvents, drying agent), filters, sparger, heater tube kit and maintenance/calibration requirements (Annexes A and F).
• Procedure elements: Sample preparation, apparatus assembly and cleaning, calibration, start‑up/pressurization, test profile, shutdown, disassembly, and reporting. Normative annexes give detailed apparatus and rating methods; informative annexes cover maintenance and bibliographic references.
• Safety & precision: Includes warnings about hazardous materials and describes precision/validation expectations and required test report content.

Practical applications and users

• Fuel quality control laboratories assessing thermal oxidative stability of aviation and gas‑turbine fuels
• Fuel producers and blenders validating formulations (including synthetic blends)
• Aircraft and engine manufacturers evaluating fuel‑system deposit risk
• Certification bodies and R&D groups comparing fuels and additives for deposit mitigation
• Test houses performing regulatory and specification testing referenced by aviation standards

Related standards

• ASTM D3241 (related rating procedures)
• ASTM D7566 and Def Stan 91‑091 (synthetic blending components scope)
• ISO 3170 / ISO 3171 (sampling)
• ISO 3274 / ISO 4288 (surface texture references)

Keywords: ISO 6249:2021, thermal oxidation stability, gas turbine fuels, aviation turbine fuel, heater tube, deposit thickness, interferometry, ellipsometry, fuel quality control.