Fuel system icing inhibitors (FSII) are added to jet fuel to prevent freezing of the water content at flight altitude. Their concentration in water and therefore their freezing point correlates with the refractive index.
Jet fuel contains up to 30ppm 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. In aviation, the addition of a FSII to jet fuel is mandatory, depending on flight route, altitude, season and aircraft.
FSII, like Diethylene Glycol Monomethyl Ether (DiEGME), have to be added to jet fuel in a final concentration of 0.10 – 0.15% v/v. To analyse absolute FSII content in jet fuels, ASTM standards require the use of refractometry for measuring water extracts. The preconfigured scale, FSII ASTM D 5006, in Anton Paar´s Abbemat refractometer will automatically adjust the prism and the sample to 20°C with an accuracy of up to ±0.03°C. Compared to other methods used for DiEGME determination, the advantage of refractive index determination lies in the rapid sample preparation and measurement.
Abbemat refractometers analyse the refractive index with a highly precise accuracy of up to 0.00002nD, therewith meeting the required repeatability for FSII detection within 0.005 volume %. This is specified in the application note available online.
Contact: Andre van Zyl