Evaluation of the alternative fuel thermal-oxidation stability within the European Swafea program

The thermal stresses imposed on aviation fuels by aero-engines can lead to the formation of deposits within engine fuel systems which, in turn, can reduce their performance and necessitates extra maintenance to rectify. As modern and developing aero-engines subject fuels to ever increasing levels of thermal stress, the significance of fuel thermal stability is becoming more important. Therefore, it is increasingly beneficial to use fuels which minimize the formation of these undesirable deposits at high temperature. Different fuels demonstrate varying levels of thermal stability, largely due to their chemical composition. The presence of dissolved oxygen plays a major role in the degradation of the fuel and in the formation of insoluble products. The standard test method used to estimate the thermal oxidation stability of aviation turbine fuels is the JFTOT Procedure. All the fuels tested in the European Swafea project pass the test. Thus, it was not possible to observe any thermal stability difference between the selected fuels. In order to get more information on their oxidation behaviors, three specific tests are used. The sensitivity of the fuels to oxidation stability is determined. The most sensitive fuel is the blend 50% HVO Camelina/50% Naphtheno-aromatic cut followed by the blend 75% HVO Camelina/25% Jet A-1. This result is confirmed as these fuels contain the highest quantity of oxidized products observed in the liquid phase after 72 hours of degradation. Whereas these two blends produce the lowest quantity of deposit. On the other hand, the Jet A-1 and the blend 90% Jet A-1/10% FAE seem to be the least sensitive to oxygen, conversely it produced the highest quantity of solids. Thus, the thermal stability is directly linked to the fuel composition. The neat fuels (HVO Camelina and Naphthenic-aromatic cut) do not contain natural oxidant. So when blended, they show the lowest oxidative stability but they demonstrate the highest thermal stability as they do not produce deposit.