The du Pont F21 149°C (300°F) Accelerated Stability Test has been used for many years to monitor stability properties of distillate fuels. The test (or variations of it) is the most commonly used in the petroleum industry because, of the many tests available, it is easiest to carry out. A small fuel sample is heated to 149°C (300°F) for 90 min or more, cooled, and filtered; degradation is qualitatively determined by visual or instrumental evaluation of the filter pad—without the need for gravimetric procedures. In our laboratory it is usually the first of several tests to evaluate fuel stability; results guide further work. The test is also used to monitor fuel stability during production, distribution, and storage.

Variations, refinements, applications, and limitations of the test are discussed. Severity is modified by varying the 149°C (300°F) aging period from 90 min to 4½ h. Sensitivity is varied by changing the porosity of the filter paper. Test results are precisely rated by measuring filter pad light reflection. The reproducibility of the test is considered, along with factors which affect results.

Data are presented which show the relationship of test results with actual long-term storage stability of fuels.