Soot formation in iso-octane counterflow diffusion flames

This study investigates soot formation in laminar iso-octane counterflow diffusion flames (CDFs) under varying strain rates and fuel mass fractions. Spatially resolved measurements of temperature, major and minor gas-phase species, including polycyclic aromatic hydrocarbons (PAHs) up to three fused aromatic rings, as well as properties of the formed soot particles, such as volume fractions, primary particle sizes, and optical properties, i.e., refractive-index function for absorption in the near-infrared spectral region E ( m , λ N I R ) , were conducted using both intrusive and non-intrusive diagnostics. With increasing fuel mass fraction, the concentrations of C 1 to C 3 hydrocarbons and soot precursor molecules increase. This in turn results in higher soot volume fractions and larger particle sizes in the investigated CDFs of iso-octane. The evolution of the nanostructure and maturity of soot particles can be tracked via E ( m , λ N I R ) , which increases with rising fuel mass fractions and indicates extended basic structural units and a decreasing carbon-to-hydrogen ratio. Similarly, increasing strain rate reduces PAH concentrations, thereby affecting soot volume fractions, particle sizes, and maturity due to shortened residence times. The unique dataset aims to better understand the effects of alkane branching on soot formation by systematically investigating laminar iso-octane CDFs, and to elucidate the transition from precursor molecules to primary soot particles, including their molecular fine structure. In addition, the dataset is intended to contribute to the validation and development of kinetic mechanisms and soot models.