Earlier research performed by Shell Research sought to compare the performance of fuels in the Jet Fuel Thermal Oxidation Tester (JFTOT) with that in a simulated engine oil cooler. However the agreement between the rigs was poor and initial attempts to improve the correlation by modifying various JFTOT operating parameters were ineffective. Now, those same operating parameters have been readdressed in more detail, in order to determine the physical and chemical factors which control fuel response in the JFTOT.
Flowrate experiments and activation energy measurements have indicated not only that the JFTOT's response to a fuel depends on the relative roles of chemical reaction and physical transport, but more significantly, the contribution of the two effects is fuel dependent.
Studies of test section metallurgy reveal that whilst differences between aluminium and stainless steel are clearly discernible under certain conditions, such differences become irrelevant as fuel degradation proceeds and the metal surface becomes lacquered.
The findings provide an explanation as to why no improvement could be made in the correlations exhibited by the earlier experiments. In addition, they enable us to offer tentative design criteria for a new small scale thermal stability test.