PLIF measurements of non-thermal NO concentrations in alcohol and alkane premixed flames

There exists interest in using alcohols as renewable, lower emission fuels. It has been observed that alcohol flames generally produce lower concentrations of NO emissions and the cause of these reductions is attributable to a number of mechanisms. This work therefore investigates the relative contributions to total NO formation in alcohol fueled flames, relative to comparably sized alkane flames. Measurements of quantitative NO PLIF were conducted in two common premixed configurations: a conical, Bunsen-type flames and a lower peak temperature burner-stabilized McKenna flat flame. Additionally, these flames were modeled using a detailed NO x chemical mechanism and investigated to understand the primary contribution pathways to non-thermal NO formation. From this analysis, it was observed that alcohol fueled flames produced as much as 50% less non-thermal NO than alkanes. However, under lean conditions the non-thermal contributions increased to about 80-90% of those observed in alkanes due to a greater contribution to non-thermal NO in both alcohol and alkane flames from non-hydrocarbon radical related mechanisms.