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The poor performance of some high purity jet fuels appears to be related to polar compounds in the fuel and not to viscosity, volatility, or sulfur and nitrogen compounds. Surface active additives such as corrosion inhibitors markedly improve lubricity. Results of laboratory tests correlate well with the field experience, where sticking fuel controls and pump wear at high temperatures have been reported. Highly refined fuels developed to meet new standards of thermal stability or purity are generally poor in lubricity compared with conventionally refined fuels and may require a lubricity additive to satisfy advanced fuel systems.

Fuel used as a coolant in the supersonic transport can degrade thermally and affect heat transfer surfaces. A heat transfer unit developed by Esso Research to follow the course of degradation reactions and to relate deposit formation to heat transfer rates has been used under a Federal Aviation Agency program to study fuels varying widely in quality. Data reveal that oxygen disappearance, peroxide buildup, and deposit formation are interrelated and can be roughly correlated with fuel composition. Deposit formation above a certain level generally results in loss in heat transfer; but in some cases increases in heat transfer have been observed. The temperature at which significant deposit buildup takes place and loss in heat transfer occurs in the HTU can be predicted by the fuel “breakpoint” measurement made in the ASTM-CRC Fuel Cokers.

The current incentive for safety fuels is due to excessive loss of aircraft in Vietnam due to fires. Evaluation of four classes of thickened fuels eliminates “canned-heat” gels, the visco-elastic Napalm type, and the polymer-thickened fluids. Emulsions-thickened fuels seem more compatible with aircraft systems. Points of superiority include ease of removal from tanks, good atomizing properties in engines, and constancy of rheological properties over a wide temperature range. Recent work on an Army-sponsored contract to develop emulsion safety fuels for Army helicopters and cargo planes has uncovered a number of formulations containing at least 97% fuel. Based on early laboratory data, these emulsions appear to have good stability at −30 to 130 F. The separation of JP-4 varies from 1-10% after several cycles of heating and cooling between these limits. One nonaqueous emulsion, WS-X-7063, has provided valuable background information.