Measures of Fuel Thermal Stability — Which Answer is Correct?

It is highly desirable to be able to predict the degree of fuel thermal degradation within a jet engine fuel system from simple chemical parameters or rapid small-scale testers. However, given the complexity of the problem, which includes such variables as system components, fuel heat history, fuel flow regimes and residence times, it is likely that no one single measurement can hope to provide the answer. Shell Research's approach to investigating jet fuel thermal stability is proceeding along three parallel fronts:- • Large-scale rigs realistically simulating engine components, so enabling predictions of fuel performance in the real environment. • Critical examination of the JFTOT specification test, assessing its ability to predict service fuel performance unequivocally. • Fundamental mechanistic studies to provide the necessary chemical background for the studies. These include analyses of fuel composition and kinetic measurements of fuel oxidation. This paper describes each method, the advantages, disadvantages and nature of the measurement. The differences between the various types of measurement are explained. Finally, the results from each test are drawn together to yield a simple mechanism for fuel thermal degradation.