Experimental and kinetic analysis of laminar flame speed in hydrogen-enriched highly branched iso-alkanes: A comparison of iso-octane and iso-dodecane

Highly branched alkanes, critical components of sustainable aviation fuels (SAFs), significantly influence the efficiency and emissions of aircraft engines. With the increasing global demand for low-carbon aviation fuels, a deeper understanding of the combustion kinetics of highly branched alkanes is essential for optimizing fuel design and reducing carbon emissions. In this study, the laminar flame speeds of iso-octane (2,2,4-trimethyl pentane), iso-dodecane (2,2,4,6,6-pentamethylheptane; PMH) and their blends with hydrogen were investigated over equivalence ratios ranging 0.7 to 1.4, pressures from 0.5 to 1.0 bar, and temperatures of 353 and 395 K. Results indicate that iso-octane exhibits consistently higher laminar flame speeds than PMH across all equivalence ratios, with a more pronounced difference under lean conditions. Reaction pathway analysis reveals that PMH generates a higher yield of dienes, which consume a substantial amount of H radicals in further reactions, resulting in chain inhibition and a reduction in overall flame propagation. In contrast, iso-octane predominantly produces tert‑butyl and iso-propyl radicals, which further decompose into H and iso-butene/propene, thereby enhancing flame propagation. Hydrogen blending enhances flame speeds for both fuels, with a more pronounced effect on iso-octane. This is mainly due to the increased concentrations of key radicals (H, O, and OH), which accelerate chain reactions. This study presents the first experimental dataset of PMH laminar flame speed, addressing a critical gap for validating chemical kinetic models and enhancing combustion simulations. Additionally, the findings provide valuable insights into the combustion behavior of highly branched alkanes in hydrogen-enriched environments, supporting the development of low-carbon, high-efficiency clean fuels.