LIF thermometry in sooty flames using NO D2Σ +← X2Π(0,1) and OH A2Σ +← X2Π(3,0) bands

Abstract

A new method for temperature measurement in sooty flames was developed using laser-induced fluorescence (LIF). NO and OH rotational temperature measurements of a propane diffusion flame were tried on an excitation scan. Tunable, narrow band ArF and KrF excimer lasers were used to excite the D 2Σ +← X 2Π(0,1) band system of NO and A 2Σ +← X 2Π(3,0) band system of OH. Emission spectra of the induced light from the flame were obtained by a spectrograph. In the case of OH excitation in a propane diffusion flame, the observed spectrum consisted of OH fluorescence and off-resonance emissions. OH fluorescence and off-resonance emissions appeared in the same wavelength region. Therefore, it could not be applied to the OH excitation scan of temperature measurement for a sooty flame. In the case of NO excitation in the propane diffusion flame, the emission spectrum also consisted of NO fluorescence and off-resonance emissions. However, NO fluorescence was mainly observed at shorter wavelength region compared with that of off-resonance emissions. By these spectrum data, it was found that the ε(0,3) band of NO was free from the fluorescence of another species and off-resonance emissions. Rotational temperature of NO was measured by the excitation scan based on the ε(0,3) band. In order to check the validity of this technique, OH rotational temperature in the methane premixed flame was measured, and its temperature was compared with the NO rotational temperature. Both temperatures were mostly in agreement.