PAH formation in one-dimensional premixed fuel-rich atmospheric pressure ethylbenzene and ethyl alcohol flames

This study addresses health-hazardous emissions from combustion of aromatic and oxygenated components of engine fuel blends. An investigation was conducted on the evolution of polycyclic aromatic hydrocarbons (PAH) and other pollutants (soot, CO, unburned light hydrocarbons) emitted from one-dimensional ethylbenzene and ethyl alcohol flames. The study of ethylbenzene combustion is also pertinent to that of waste polystyrene, as past work has indicated that ethylbenzene may be a surrogate for initial products of polystyrene pyrolysis. Both liquid fuels were prevaporized in nitrogen, mixed with oxygen and additional nitrogen, and upon ignition, premixed flat flames were stabilized over a burner. Temperature measurements and product sampling were conducted at various heights above the burner. Results showed that ethyl alcohol combustion generated small yields of PAH, even under the adverse fuel-rich conditions of this study (ϕ=2.5ϕ=2.5). PAH mole fractions in the ethyl alcohol flame were 2–5 orders of magnitude lower than those in the ethylbenzene flame at the same location. PAH mole fractions often peaked in the postflame region and remained at relatively high levels thereafter. PAH mole fractions in premixed fuel-rich benzene, ethane, ethylene, and methane flames, published in the literature, were typically in between those found in the two flames of this study. Computations were conducted using a currently developed detailed kinetic model, allowing for the prediction of formation and depletion of major PAH and soot particles of different sizes. The computed chemical flame structures were compared to experimental data obtained in the present work. Predicted mole fractions were often close to the experimentally obtained values or, at worse, within the same order of magnitude for both fuels. Reaction pathways are discussed.