Fuel-Structure Dependence of Benzene Formation Processes in Premixed Flames Fueled By C6H12 Isomers

Abstract

The fuel-structure-dependent significance of various benzene formation pathways is analyzed using data from rich (ϕ = 1.7) flames fueled by four C₆H₁₂ isomers: 1-hexene, cyclohexane, methylcyclopentane, and 3,3-dimethyl-1-butene. The isomer-resolved chemical compositions of the four premixed, laminar low-pressure flat flames are determined by flame-sampling molecular-beam mass spectrometry employing single-photon ionization by synchrotron generated vacuum-ultraviolet photons. Isomer-resolving photoionization efficiency curves and quantitative mole fraction profiles reveal the dominant fuel destruction pathways, the influence of different fuel consumption processes on the formation of commonly considered benzene precursors, and the contributions of several routes towards benzene formation. While propargyl and allyl radicals dominate benzene formation in the combustion of 1-hexene, contributions from reactions involving i-C₄H₅ and C₅H₅ radicals are revealed in the flames of 3,3-dimethyl-1-butene and methylcyclopentane, respectively. Close to the burner surface, successive dehydrogenation of the fuel is found to be important for the cyclohexane flame and to some smaller extent for the methylcyclopentane flame.