The continued development of more powerful aviation turbine engines has demanded greater thermal stability of the fuel as a high temperature heat sink. This in turn requires better definition of the thermal stability of jet fuels. Thermal stability refers to the deposit-forming tendency of the fuel. It is generally accepted that dissolved oxygen initiates the deposition process in freshly refined fuels. While there are many tests that are designed to measure or assess thermal stability, many of these either do not display sufficient differentiation between fuels of average stability (JP-8) and intermediate stability (JP-8+100, JP-TS), or require large test equipment, large volumes of fuels and/or are costly. This paper will discuss the use of three laboratory tests as “concept thermal stability prediction” tools with aviation fuels, including Jet A-1 or JP-8, under JP8+100 test conditions. The primary goal of the USAF JP8+100 thermal stability additive (TSA) program was to increase the heat-sink capacity of JP-8 fuel by 50%. Current engine designs limit fuel temperature into the nozzle to 325°F (163°C); JP-8+100 allows fuel temperatures to rise by 100°F to 425°F (218°C) into the nozzle without suffering serious fuel degradation. 1-2
The laboratory thermal stability tests discussed in the present paper are (1) the Isothermal Corrosion Oxidation Test (ICOT)3-4, (2) the Hot Process Liquid Simulator, in conjunction with a differential pressure measurement (HLPS-DP)4, and (3) the Quartz Crystal Microbalance (QCM). 5-6
The potential use of these tests as a predictor for additive performance in extended tests, such as the Extended Duration Thermal Stability Test (typically 96 hours, 100 USG of jet fuel) operated by the USAF, has been discussed in the past, and is beyond the scope of this paper.