Studies of jet fuel autoxidation chemistry catalytic hydroperoxide decomposition & high heat flux effects

Jet fuel has been used as an aircraft and engine coolant for decades. However, one problem associated with heating the fuel is the occurrence of deposition reactions that foul critical fuel system components. If left unchecked, these fuel system deposits can cause catastrophic failure. The chemical pathways leading to fuel oxidation and deposition are not fully understood. In order to better understand these pathways, the kinetic parameters of hydroperoxide decomposition, relevant to jet fuel oxidation, have been measured in the presence of potential homogeneous catalytic sources, i.e., dissolved metals and naphthenic acids. The addition of dissolved metal alone was found to increase the decomposition rate of hydroperoxides, while the addition of naphthenic acids alone was found to have little effect on the rate. However, the combination of dissolved metal and naphthenic acids is shown to synergistically increase the decomposition rate of hydroperoxides. The catalytic effect of metal and naphthenic acids on real fuel deposition rates was explored, and in general followed similar trends to the hydroperoxide rate data. Separate thermal oxidation experiments were conducted with jet fuel to explore advanced cooling schemes, e.g., regenerative cooling. Regenerative cooling schemes are often characterized by large heat fluxes and high wetted wall temperatures. Due to the complex experimental fluid flows and severe heat transfer conditions, computational fluid dynamics (CFD) with chemistry was used to predict chemical reaction rates and species concentrations. Some of the resulting kinetic data for hydroperoxide decomposition was incorporated into a revised pseudo-detailed chemical kinetic model, which was used in the CFD with chemistry computations. The relatively severe heat transfer conditions: heat fluxes of 0.26 and 0.49 Btu/s-in2 (43 and 81 W/cm2), wall temperatures of up to about 660°C, and bulk fluid temperatures as low as 27°C, caused the formation of large radial thermal gradients. In one case, heating of the fuel was sufficient to transition the flow from laminar to turbulent, which enhanced the reaction rate for some reactions. The large thermal gradients and high wall temperatures, coupled with flow conditions, created unique zones of chemical activity within the flow field. These zones of chemical activity included the localized depletion of dissolved oxygen within the boundary layer. CFD with chemistry was able to provide spatial resolution to the complex flow field to assist with experimental analysis