Viscosities at Flight Altitudes

Viscosities at the temperature of flight are relevant to performance, and accordingly review of a study of the viscosities of jet fuels at such temperatures will be commence this section. Assigning for the purpose of this summary the descriptors Fuel X and Fuel Y to two of the fuels which feature in, viscosities and supplementary data are given in the table below.


Fuel X was further studied for wax deposition behaviour. At the cloud point temperature of -52.6°C the bulk liquid was free of wax, but wax was becoming evident at the interface of the fuel and the container wall. On further cooling to the pour point of -58.0°C wax appeared in the bulk liquid after 37.5 minutes, and the inside container wall was coated with wax. Wax in the bulk liquid had become much more abundant after another five minutes and had consolidated in parts of the sample after another five minutes.

When a proprietary corrosion inhibitor was present the cloud point of Fuel X was found to rise to as high as -40°C. This is believed to be due to the provision of nucleation sites for incipient wax by the constituents of the additive.