An experimental comparison of non-premixed bio-butanol flames with the corresponding flames of ethanol and methane

Butanol non-premixed flames were studied in a counter-flow burner configuration in view of the emergence of methods of production of this fuel from biological agricultural sources. Major combustion species were measured using line-Raman imaging and K-type thermocouples were used in order to perform temperature scans across the flame. Also, extinction strain rates were measured as a function of overall stoichiometry. Of particular importance was the comparison with flames of methane (which is not oxygenated) as well as ethanol which is a currently widely employed bio-fuel. It was shown that butanol flames could sustain higher strain rates at extinction than ethanol flames but significantly smaller than methane flames. The extinction strain rate of methane-butanol mixtures were shown to be smaller than weighted averages of the extinction strain rates of the flames of the two pure components. No leakage of C-H containing species through the flame was measured for either of the flames. For the strongly diluted flames under consideration, it was shown that temperature followed a very closely linear relation with nitrogen concentration. For the same nitrogen concentration, butanol exhibited smaller temperature at the same overall stoichiometry and heat release, because of the higher average molecular weight of the fuel stream. Consistently with theoretical predictions, a decrease in mixing layer thickness was measured with increasing strain.