Relationship between the formation of aromatic compounds and solid deposition during thermal degradation of jet fuels in the pyrolytic regime

The formation of pyrolytic solid deposit, or coke, in the fuel line can be detrimental to the operation of high-speed aircraft., Yet, the formation of coke from the fuel has not been well characterized. The present study has investigated the relationship between the formation of aromatic compounds a nd solid deposition for three candidates for high-thermal-stability jet fue ls at 482 degreesC (900 degreesF) with stressing periods up to 2 h. The fue ls include one coal-derived (JP-8C), one paraffinic petroleum-derived (JP-8 P), and one naphthenic petroleum-derived (DA/HT LCO). The DA/HT LCO, an ext ensiirely hydrotreated light cycle oil where virtually all aromatics have b een hydrogenated to cycloalkanes, suppressed the solid deposition to a grea ter extent than that of the more paraffinic petroleum-derived JP-8P and sho wed a comparable low solid deposition to that of the coal-derived fuel JP-8 C. Both GC/MS and solution-state C-13 NMR analysis on the stressed fuels co nfirmed that the paraffinic content is most likely to crack under thermal s tress, while cycloalkane structures are more thermally stable. Solution-sta te C-13 NMR and HPLC investigations of the overall structure of the stresse d Liquids indicate that the solid deposition is a function of the rise in t he aromatic content and also the amount and rate of development of the nonp rotonated aromatic carbons, giving mostly 2 to 4 rings aromatics. Furthermo re, solid-state C-13 NMR was used to follow the development of the aromatic structure in the corresponding solid deposit as a function of the buildup of aromatic compounds in the stressed Liquid fuel.