Measurement of Fuel Concentration Distribution in a Sooting Flame through Raman Scattering

Abstract

Spontaneous Raman spectroscopy with KrF excimer laser was applied to obtain a fuel concentration distribution in a sooting flame. In the case of sooting flame, fluorescence from polycyclic aromatic hydrocarbons (PAH) and laser-induced incandescence (LII) from soot particles appeared with Raman scattering. These background emissions overlapped on the Raman scattering. In order to separate the Raman scattering and the background emissions, polarization property of laser-induced emissions was utilized. Since the background emissions were depolarized whereas the Raman scattering was highly polarized, it is possible to subtract the background emissions from the overlapping signal of the Raman scattering and the background emissions. Subtracting the emission signals for the electric vector of the laser light perpendicular and parallel to the direction of observation allows to extract the precise Raman signals. By using this technique, detailed fuel concentration distribution in sooting flames could be obtained based on Raman scattering.