NO formation in rich premixed flames of C1-C4 alkanes and alcohols

A comprehensive study of prompt nitric oxide (NO) formation is presented for rich (φ = 1.3) premixed flames of alkanes and alcohols. Measurements of the flame burning rate, the temperature, and the CH radical and NO species are performed in atmospheric-pressure laminar premixed stagnation flames. New data, obtained for all isomers of the C4 fuels, butane and butanol, are merged with existing data for C1-C3 fuels obtained by the same methodology. The combined dataset consists of all isomeric combinations of the fuel molecules, and provides a complete description of pollutant trends related to fuel type and branching structure for C1-C4 alkanes and alcohols. These data show alcohols produce less NO than alkanes of equivalent carbon chain length. This behavior is linked to the tendency of alcohols to produce lower concentrations of the CH radical, due to inhibition of the formation of methyl radicals. The results show a linear scaling of prompt-NO formation with the CH radical concentrations, when these are scaled by the characteristic residence time in the flame. This residence time depends on the burning velocity of the fuels, which decreases with increasing fuel branching. These data are useful for thermochemical model development using detailed simulations of the experiments and a comparative diagnostics approach. Further adjustments to all of the thermochemical models are needed to capture the observed trends. This dataset is made available and provides validation and optimization targets for future model revisions.