Steven Zabarnick

Oxidation of jet fuels and the formation of deposit

Abstract Jet fuels and jet fuel surrogate were thermally stressed to simulate the time-temperature history of aircraft fuel-handling systems. The resulting fuels and soluble and insoluble products were analysed. The results are shown to be incompatible with previous mechanisms concerning the source of deposit precursors. In general, two important dependences on oxygen have been found: 1. (1) in agreement with previous research, the amount of deposit formed decreases significantly if oxygen is removed from the fuel before thermal stressing; 2. (2) fuels that oxidize easily are likely to be more stable (as measured by deposits). New evidence is presented to support the free-radical mechanisms of oxidation and deposit formation, in contrast to proposed ionic mechanisms of oxidation. A general theory of oxidation of hydrocarbons has been incorporated to account for the observed oxygen-dependences, involving a free-radical, autoxidation, chain mechanism. It is proposed that the presence of naturally occurring antioxidant molecules plays an important role in both inhibiting the oxidation of the fuel and forming deposit precursors. Some properties (concentration, reactivity) of these antioxidant molecules and the implications of the theory are discussed.

Flow and Chemical Kinetics Simulations of Endothermic Fuels

Advanced aircraft engines are reaching a practical heat transfer limit beyond which the convective heat transfer provided by hydrocarbon fuels is no longer adequate. One solution is to use an endothermic fuel that absorbs heat through chemical reactions. This paper describes the development of a two-dimensional computational model of the heat and mass transport associated with a flowing fuel using a unique global chemical kinetics model. Most past models do not account for changes in the chemical composition of a flowing fuel and also do not adequately predict flow properties in the supercritical regime. The two-dimensional computational model presented here calculates the changing flow properties of a supercritical reacting fuel by use of experimentally derived proportional product distributions. The present calculations are validated by measured experimental data obtained from a flow reactor of mildly cracked n-decane. It is believed that these simulations will assist the fundamental understanding of high temperature fuel flow experiments.Copyright

The Effects of Dissolved Oxygen Concentration, Fractional Oxygen Consumption, and Additives on JP-8 Thermal Stability

Since dissolved oxygen participates in fuel deposit formation, knowledge of the effects of dissolved oxygen concentration on fuel thermal stability is critical for fuel system design. In this work, the combined effects of dissolved oxygen availability and additives on jet fuel thermal stability are studied. Experiments with JP-8 jet fuel were conducted in a three-part heat exchanger which simulated a complex thermal and flow environment. The dissolved oxygen content at the flow inlet was varied, and deposition was studied under conditions of either fractional or complete oxygen consumption. The effects of a thermal stability additive package were also studied. An intriguing result found with JP-8 fuels is an increase in deposits formed in heated regions for decreased oxygen consumption, but inverse behavior with the additive package.Copyright