High-temperature oxidation and pyrolysis of 2,4-dimethylhexane: Experimental insights into Iso-alkane decomposition and aromatic formation

Iso-alkanes are key constituents of sustainable aviation fuels (SAFs) due to their favorable combustion characteristics, including high energy density and low soot formation. They are therefore widely used as model compounds to study the fundamental reaction kinetics relevant to SAF combustion and decomposition. Experimental data for such fuels and systematic studies are scarce, but crucial for the development of detailed chemical kinetic models. Speciation measurements for the oxidation and pyrolysis of 2,4-dimethylhexane were performed in an atmospheric laminar flow reactor to investigate the high-temperature chemistry of a branched C₈ isoalkane. Around 35 quantitative mole fraction profiles per experimental condition were obtained in temperature ranges from 770–1273 K for pyrolysis, 770–1073 K for lean, and 770–1123 K for stoichiometric, and rich oxidation conditions. The data analysis reveals that fuel consumption begins at similar temperatures for all cases, whereas oxygen consumption strongly depends on equivalence ratio. Lean and stoichiometric mixtures exhibit comparable oxidation-dominated behavior, while rich conditions lead to delayed oxygen depletion and extended persistence of hydrocarbon intermediates. The initial fuel decomposition is consistent with β-scission of the weakest C-C bonds, forming primarily C₄H₈, C₅H₁₀, C 6 H 12 and C₇H₁₄. The dominance of C₄ species indicates a product distribution shifted toward smaller, thermodynamically stable olefins. Small differences between oxidation and pyrolysis are observed. Oxidation promotes the formation of oxygenated species and rapid decomposition of intermediates, whereas pyrolysis favors the accumulation of unsaturated hydrocarbons and larger species. Aromatic formation is significantly enhanced under pyrolysis conditions, with higher mole fractions of benzene, toluene, and naphthalene. The observed trends indicate the onset of aromatic chemistry and early progression toward soot precursor formation, while oxidizing environments suppress this molecular growth. These measurements provide new experimental constraints for kinetic mechanism development and improve the understanding of structure-reactivity effects in branched isoalkane combustion.