Comparative evaluation of extinction through strain among three alcoholic butanol isomers in non-premixed counterflow flames

Butanol isomer diffusion flames were studied experimentally in a counterflow burner configuration with an emphasis on establishing a difference in extinction strain rate among three fuels with practically identical thermochemistry. An effect of molecular structure on the extinction strain rates of butanol isomers was observed and analyzed in terms of bond dissociation energies. The results indicate that although all isomers share essentially the same adiabatic flame temperature, n-butanol flames can sustain a consistently higher extinction strain rate than the flames of other isomers (isobutanol and sec-butanol). Extinction strain rates of isobutanol and sec-butanol were equal, within experimental error. Numerical simulation of n-butanol diffusion flames produced results consistent with those measured experimentally and provided insight into the distribution of major species and combustion intermediates. Stable annular flames were observed for all three isomers as a temporary step before extinction.