Chemical interactions between 1,2,4-trimethylbenzene and n-decane in doped counterflow gaseous diffusion flames

The chemical interaction of the two-components of a jet fuel surrogate, n-decane and 1,2,4-trimethylbenzene (TMB), was studied by adding several hundreds ppm of each chemical to two counterflow diffusion flames, one using methane and the other ethylene as baseline fuels. The objective was to look into evidence of synergistic effects due to the interaction of these reference fuels, that are representative of normal alkanes and aromatics, respectively, making up the bulk of practical fuels. The dopants were added in the same proportions as in the Aachen surrogate of jet fuel. The flames presented two distinct environments: the permanently blue methane flame and the incipiently sooting ethylene flame provide well defined temperature-time histories and chemical environments, with the one based on ethylene being relatively more oxygen-deficient. Profiles of critical pyrolysis products and of some stable soot precursors were determined from GC/MS analysis of gas samples extracted from the flames and compared with results from the OPPDIFF model using a lumped chemical mechanism. Mechanistically relevant synergies among the two fuel components are highlighted considering the production rate of aromatics in both flames when adding the two components either simultaneously or separately. The principal observation is that the combined addition of the two components causes an overproduction of methane in the ethylene flame, a decrease in the concentration of acetylene in the methane flame and an acceleration of the aromatic destruction/growth pathways. The model for the most part fails to capture the principal evidence of synergistic effects. Most of the other quantified species reveal no synergy, their concentration being the sum of the contributions of each component used individually, partly because of the small amounts of reactants that were added to the flames.