Mesophase and pyrolytic carbon formation in aircraft fuel lines Original Research Article

Exposure of jet fuel to high temperatures in aircraft fuel lines triggers pyrolysis reactions which eventually lead to deposition of carbonaceous solids on metal surfaces. This is a particularly important problem for advanced future aircraft which may expose fuel to very high temperatures. Different optical textures were observed in samples of deposits formed in different sections of aircraft fuel systems. Deposits from a burner fuel line consist only of pyrolytic carbon, indicating that gas phase reactions were responsible for solid formation. Afterburner line deposits, on the other hand, contain both pyrolytic carbon and carbonaceous mesophase structures, implicating also liquid phase carbonization reactions. The FTIR data shows that solids containing mesophase consist of polynuclear aromatic hydrocarbons with a low degree of condensation and alkyl substitution. In contrast, solids with pyrolytic carbon structure are composed of highly condensed, large polyaromatic species. It is clear that jet fuels go through extensive cracking, aromatization, and aromatic polymerization reactions before solid deposition takes place in the fuel lines.