Spectral Assessment of Interferences to Two-line Atomic Fluorescence (TLAF) in Turbulent Sooty Flames

Abstract

Two-line Atomic Fluorescence (TLAF) using seeded atomic indium is a promising technique for two-dimensional temperature measurement in turbulent non-premixed sooty flames. However, it is desirable to reduce measurement uncertainties, which in turn depends on the fluorescence signal relative to background noise and interference. This paper reports a spectral assessment of interferences to both the Stokes and Anti-Stokes fluorescence signals in turbulent sooty flames undertaken with a spectrometer. Flame emission spectra were measured to assess the effects of various interference sources on indium fluorescence signals as well as to evaluate the efficacy of two techniques with potential to enhance the signal-to-noise ratio. Three types of interferences have been identified: laser Mie scattering from soot particles, laser-induced fluorescence from polycyclic aromatic hydrocarbons species (PAH-LIF) and laser-induced incandescence (LII) from soot particles. The feasibility of applying a correction for interferences by comparison of simultaneous images collected on- and off-resonance was assessed by collecting images at 430 nm and the fluorescence lines (410 and 450 nm). The correlation between the intensity of corresponding pixels from two instantaneous on- and off-resonance images was compared. This correction scheme was found to have limited value. The alternative scheme, which incorporates narrow-band filters, is considered to have much greater potential to be effective.