A Modeling Study of the Effects of Butanol Addition on Aromatic Species in Premixed Butane Flames

The motivation of the present work was to understand the mechanism by which alcohols produce less aromatic species in their combustion process than an equal amount of hydrocarbon with similar molecular structure does. Due to its numerous advantages over short-chain alcohols, butanol has been considered very promising in soot reduction. Excluding the influence of spray, vaporization and mixing process in engine cases, an adiabatic constant-pressure reactor model was applied to investigate the effect of butanol additives on aromatic species, which are known to be soot precursors, in fuel-rich butane flames. To keep the carbon flux constant, 5% and 10% oxygen by mass of the fuel were added to butane using butanol additive, respectively. Based on the soot reduction effects proposed in literature, effects on temperature, key radical concentrations and the carbon removal from the pathway to aromatic species were considered to identify the major mechanism of reduction in aromatic species. Reduction in aromatic species was observed in all cases compared with pure butane and the modeling results captured the trends in aromatic species with changes in oxygen content in the fuel. Analysis of the modeling results shows that in the condition of this study, temperature variation and radical concentration change generated by butanol additive have effects on reduction on aromatic species, but the effects are relatively small. The addition of butanol to butane reduces the aromatic species mainly by reducing the amount of carbon that is available to form precursor species.