Visualizing CH* chemiluminescence in sooting flames

This investigation presents and validates a method to visualize CH* chemiluminescence in a sooting non-premixed flame. Excited-state CH radicals (A2Δ → X2Π, denoted CH*), upon relaxing, emit a photon in the visible portion of the electromagnetic spectrum, giving what is seen as a faint blue glow. Optical methods, especially those that rely on passive emission, provide a simple and non-intrusive means to characterize combustion; however, in the presence of hot solid particles – particularly soot – chemiluminescent emission can be obscured by blackbody radiation. This paper describes an image post-processing technique where flame emission is imaged through multiple filters near the CH* emission band in order to infer and filter the contribution of continuum radiation from soot in the CH* band. This information is then used to produce a soot-free image of CH* chemiluminescence.