C2Production and Excitation in Sooting Flames using Visible Laser Radiation: Implications for Diagnostics in Sooting Flames

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Abstract
Swan band emission of C2, which had been produced and excited (d3 πg← u3 πu Δv = 0) by focused, tunable, visible laser radiation, was studied in sooting ethylene flames. The C2 signal from the sooting regions of the flames was found to be proportional to the measured volume fractions of soot, indicating laser-vaporized soot to be the source of the signal, and as such it can be used as a diagnostic tool for point measurements of the volume fraction of soot. C2 emission was detected for all incident wavelengths between 485 and 540 nm, with a C2, signal 1-2 orders of magnitude higher when the wavelength was tuned to a C2 resonance than when tuned to a wavelength between the Swan bands. High concentrations of laser-produced C2, and emission from C2, Swan bands can, through interference effects, limit the applicability of laser diagnostic techniques to sooting flames.