The effect of long-term storage on Jet-Fuel in aircrafts

Although the long-term storage of Jet-Fuel in large storage tanks and depots has been extensively studied, little work has been conducted on Jet-Fuel stored in smaller containers. Because the surface area to volume ratio for fuels in small tanks is much larger than the ratio for large tanks, it was assumed that fuel aging and deterioration would be accelerated when stored in smaller tanks. In this study, JET A-1 grade fuel was stored in small, 30 liter, onboard aircraft fuel tanks. The fuel's physical and chemical characteristics were monitored for 24 months. Most of the fuel's characteristics showed no significant changes over the course of the study. Rises in both Initial Boiling Point and Flash Point were noted, as well as some fluctuation in Total Acidity and Water Separation. The only significant change in fuel properties found during the study was a drop in JFTOT Thermal Stability, which, for most of the systems monitored, went off-spec after a short 6 month period. In an attempt to identify the causes of this drop, further tests were conducted on the samples monitored in the program, as well as other samples taken from similar aircraft systems. No correlation could be found between off-spec JFTOT results and other parameters tested, such as: trace metal concentration, sediment, water content and microbial growth. Although the cause for off-spec JFTOT could not be determined, our assumption was that it was not caused by degradation processes in the fuel. Furthermore, it was found that for the aircraft fuel system being studied, poor fuel Thermal Stability has little impact on engine performance. In conclusion, our test program has shown that, for the particular fuel system being studied, no significant changes in the jet-fuel's properties and composition were noted over a 2 year period. The higher surface area to volume ratio of the fuel tanks studied did not have an adverse effect on the fuel's physical and chemical characteristics.