The structure of diffusion flames burning pure, binary, and ternary solutions of methanol, heptane, and toluene

Abstract

The structure of counterflow diffusions flames burning heptane, toluene, binary solutions of methanol and toluene, and heptane and toluene, and ternary solutions of methanol, heptane, and toluene is characterized in the vicinity of extinction. Composition profiles of stable species were measured in these flames by use of gas sampling with quartz microprobes and analyzed by use of on-line, two column gas chromatography. Temperature profiles were measured by use of coated thermocouples. A number of compounds were observed during pyrolysis of the fuel. Experimental results were analyzed by using the mixture fraction (conserved scalar) as the independent variable. Results show that for a diffusion flame burning heptane the approximation that the Lewis numbers for all species are approximately equal to unity is valid. When the composition profiles for major chemical species and temperature profiles are plotted with mixture fraction as the independent variable, the maximum value of the concentration of the major stable species and the maximum value of the temperature were found to occur on the rich side of stoichiometry. For diffusion flames burning solutions of methanol, heptane, and toluene, the compositions of the hydrocarbon fuels were observed to extrapolate to a value of zero at nearly the same location; however, methanol was observed to extrapolate to a value of zero at a different location. It is suggested that a previously developed theoretical analysis which did not allow the fuel concentrations to attain a value of zero at different locations may give slightly inaccurate results, when used to predict flame extinction.