A comparative study on soot and PAH formation of C10 naphthenic ring-containing species in laminar coflow diffusion flames

Abstract

C10 naphthenic ring-containing species are important components in transportation fuels and have been widely used for surrogate formulation of diesel and jet fuels to represent cycloalkanes or aromatic fractions. In this study, experimental and modeling studies were carried out to compare the formation of typical polycyclic aromatic hydrocarbons (PAHs) and soot in coflow methane/air diffusion flames doped with n-butylcyclohexane, decalin and tetralin. The laser-induced incandescence (LII) and laser-induced fluorescence (LIF) techniques were applied to measure 2D maps of soot volume fractions and relative PAH concentrations, respectively. Yield sooting index (YSI) was obtained experimentally to indicate the fuel sooting tendency. It can be observed that the soot volume fractions, sooting tendencies and pyrene concentrations of C10 naphthenic ring-containing species follow the order of tetralin > decalin > n-butylcyclohexane. The chemical kinetic simulation reveals that decalin decomposes through two main pathways, including the H-atom abstraction route and ring opening route. Especially, the pathway of ring opening reactions coupled with dehydrogenation results in the strongest benzene formation process among the test components. In the reacting system of tetralin flames, ring opening reactions are suppressed, while the dominant decomposition way of tetralin is via H-atom abstraction reactions, which offer a more direct pathway to form naphthalene and indene without benzene formation, leading to the highest naphthalene concentration of tetralin flame and the strongest soot formation process among all the test components. This fundamental investigation aims to provide valuable data on sooting behaviors and PAH formation characteristics of typical C10 naphthenic ring-containing species and get insight into the kinetic pathways from fuels to soot precursors. Useful information has been obtained for soot reduction from the perspective of the fuel design and surrogate formulation in terms of the sooting tendency.