Experimental investigation of bio-butanol laminar non-premixed flamelets

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 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 anti-correlate with temperature across the non-premixed flame, in agreement with non-premixed flame theory. Finally, the possibility of estimating the scalar dissipation rate at the stoichiometric surface χ_stoich was investigated through a measurement of the mixing layer thickness δ, performed with an intensified CCD camera and a modest-power laser.