Degradation mechanisms of n-Dodecane with sulfur and nitrogen dopants during thermal stressing

Abstract

Thermal stability problems are expected to become severe in the future due to the anticipated use of broadened specification and alternative fuels, and to increased demands on aircraft performance. Consequently, a fundamental thermal stability study was undertaken, wherein model fuels, n-dodecane and n-dodecane plus dopants, were stressed on a modified Jet Fuel Thermal Oxidation Tester facility between 200-400°C. The resulting samples were fractionated to concentrate the soluble products and then analyzed to identify and quantify the stable reaction intermediate and product species. The soluble products consisted mainly of n-alkanes and 1-alkenes, aldehydes, tetrahydrofuran derivatives, dodecanol and dodecanone isomers, C24 alkane isomers and dodecylhydroperoxide (ROOH) decomposition products. The relative amounts and shifts in the distribution of these species with dopant addition led to inferences about the reaction mechanisms. Dopant addition showed that the major soluble products were always the same, with and without dopants, but their distributions varied considerably. 3,4-dimercaptotoluene and dibutysulfide dopants individually added to n-dodecane interfere with the hydrocarbon oxidation chain at the alkylperoxy radical and the alkylhydroperoxide link, respectively. 2,5-dimethylpyrrole dopant, on the other hand, introduces cooxidation reactions involving dopant and oxygen, and consequently inhibits ROOH formation. Pyridine, pyrrole and dibenzothiophene individually added to n-dodecane showed few significant effects. © 1988 American Institute of Aeronautics and Astronautics, Inc.