SURFACE EFFECTS ON DEPOSITS FROM JET FUELS

Flow experiments in a single-pass heat exchanger using JP-8 and certai n additives were initiated under controlled conditions to explore the effects of a metal surface on deposition. The experimental apparatus p ermitted a unique viewing of the time evolution of deposits at differe nt axial locations under conditions of limited oxygen availability som ewhat similar to those in jet aircraft. Scanning electron microscopy w as used to examine deposit microstructure. In addition, x-ray photoele ctron spectroscopy and Auger electron spectroscopy determined the chem ical composition of the deposits. Oxygen concentration measurements in the bulk flow were also performed, and the observed transient oxidati on behavior was related to measured time-dependent changes in the depo sit. Increasing dissolved oxygen levels and large changes in depositio n were characteristic of the induction time. Mechanisms of fouling in the heated and cooled sections were different. Spectroscopic analysis indicated that deposits formed in the heated section had chemical comp ositions different from those formed in the cooled section. Scanning e lectron microscopy revealed differences in microstructure between the heated and cooled sections. More uniform deposits formed in the cooled section as a result of once-soluble species becoming insoluble at low temperatures. In addition, the JP-8 additives significantly reduced f ouling in the heated section, but their effectiveness in the cooled se ction, especially after long periods, was unclear.