Measurement of Ether-Type Fuel Icing Inhibitors in Aviation Fuels
Fuel system icing inhibitors are added to jet fuel to prevent freezing of the water content at flight altitude. Their concentration in water and therefore the freezing point correlates with the refractive index.
Getting ready for take off
Jet fuel contains up to 30 ppm water. The outside temperature at flight altitude is below -50 °C, so icing of water in jet fuel must be inhibited. Frozen water in jet fuel may cause blocking of the fuel feed system, which is what caused the crash of British Airways’ Boeing 777 at London Heathrow Airport on January 17th, 2008. In both military aviation and civil aviation, the addition of a fuel system icing inhibitor (FSII) to jet fuel is mandatory, depending on flight route, altitude, season and aircraft.
FSII, like Diethylene Glycol Monomethyl Ether (DiEGME), has to be added to jet fuel in a final concentration of 0.10 % v/v to 0.15 % v/v. To analyze absolute FSII content in jet fuels, ASTM standards require the use of refractometry for measuring water extracts.
Verifying FSII content in jet fuels with Abbemat refractometers
According to the international ASTM D 5006-03 "Standard Test Method for Measurement of Fuel System Icing Inhibitors (Ether Type) in Aviation Fuels", jet fuels have to be analyzed refractometrically at a defined temperature. The preconfigured scale "FSII ASTM D 5006" in Anton Paar´s Abbemat refractometer will automatically adjust the prism and the sample to 20.0 °C with an accuracy of up to ±0.03 °C and directly show %v/v of DiEGME in the prepared sample.
Compared to other methods used for DiEGME determination, like e.g. gas chromatography, the advantage of refractive index determination lies in the rapid sample preparation and measurement.
The determination of fuel system icing inhibitors according to ASTM D5006-03 is further specified in the corresponding Application Report.