E.S.R. Determination of atomic hydrogen distribution in oxy-fuel flames burning at atmospheric pressure

Abstract

Energy transfer from a high temperature flame to a solid involves the recombination of dissociated species near the surface, in particular of the hydrogen radicals. Paradoxically no known satisfactory measurement technique, exists for the determination of hydrogen radical concentrations in oxy-fuel flames burning at atmospheric pressure. We have derived an experimental technique, using ESR spectroscopy, that allows this determination. A quartz burner equipped with an appropriate cooling system is placed directly in the ESR cavity. We obtained the hydrogen resonance signal and studied its variation for different positions of the fame inside the cavity. Hydrogen concentrations cannot be calculated directly from experimental data; hence we proceed indirectly to deconvoluate the resonance signal. This allows us to overcome the present severe handicap in obtaining atomic hydrogen concentrations in oxy-fuel flames from ESR measurements. Data obtained in this work, after temperature correction, give us the axial distribution of hydrogen radicals for different oxy-propane and hydrogen-oxygen flames. These results show clearly that for all flames, the hydrogen radical concentration is maximum in a zone immediately above the inner cone. This maximum is very well pronounced for fuel-rich ratios, and the hydrogen concentration profile extends well away from the inner cone. Finally, the overall atomic hydrogen content of the flame reaches a maximum in the cases of, fuel-rich ratios, which agrees well with previous calculations.