Experimental investigation of strained, non-premixed butanol flames

Pure butanol as well as methane assisted butanol non-premixed flames were studied in a counter-flow burner configuration in view of the emergence of butanol production from biological agricultural sources. Major combustion species were measured across the flame using line Raman imaging and temperature measurements were obtained with K-type thermocouples. Of particular importance was the comparison of flames of the same heating value and equivalence ratio, as well as flames of the same overall equivalence ratio but varying reactant flow rates. Extinction strain rates were measured for a wide range of conditions. It was shown that there was a decrease of extinction strain rate with increasing overall equivalence ratio for both constant fuel flow rates and constant heat release of combustion and that butanol flames were more vulnerable to extinction compared to methane. Species concentration measurements indicated that N₂ concentrations varied linearly with temperature across the non-premixed flame. Finally, the possibility of estimating the scalar dissipation rate at the stoichiometric surface Xstoich was investigated through a measurement of the mixing layer thickness 5, acquired from the temperature distribution measurements as full width at half maximum. It was proven that this was not an appropriate method for the estimation of X_stoich. For certain cases, this was further investigated through an approximation of the gradient of the mixture fraction at the stoichiometric surface δZ_stoich.