• Method adopted/last revised: 2023
• Method reapproved: None
• REF/ISBN:
• Status: Current
• First printed in STM books: 2017

This standard specifies a procedure for the assessment of the relative stability of middle distillate fuels under high temperature ageing conditions with limited air exposure. The test method applies to kerosines and gas oils, excluding aviation kerosine, having a flash point determined using a closed cup tester exceeding 38 °C. It is not applicable to fuels containing residues from petroleum processing.1
This test method provides an indication of the thermal oxidative stability of middle distillate fuels when heated to high temperatures that may occur in engine or burner systems, and can be used for investigations of operational problems related to fuel thermal stability2). It has not been substantially correlated to engine or burner operation. For storage stability, longer term storage tests, such as IP 378, or intermediate temperature tests, such as IP 388, are likely to give better predictions.
The test method uses a filter paper with a nominal porosity of 11 μm, which will not capture all of the sediment formed during ageing but allows differentiation over a broad range. Reflectance ratings are also affected by the color of filterable insolubles, which may not correlate to the mass of the material filtered from the aged fuel sample. Therefore, no quantitative relationship exists between the pad rating and the gravimetric mass of filterable insolubles.