Near-infrared emission spectrometry measurements for nonintrusive soot diagnostics in flames

The present study focuses on measurement of line-of-sight emission intensity spectra in the near-infrared range by Fourier-transform infrared spectrometry for use in tomographic soot diagnostics. Measurements are carried out on an axisymmetric, laboratory grade, ethylene/air diffusion flame within the 1.1-1.7 μm (9000-6000 cm−1) spectral range. Presentation of the measurement and calibration methodology is followed by the description of noise and uncertainty assessment procedures. A novel noise characterization approach that accounts for both spectral and spatial fluctuations is introduced. Measured intensities are utilized to infer soot temperature and volume fraction profiles from an inversion technique based on gray refractive index assumption. Predictions at flame axis are found to be in reasonable agreement with properties reported in literature for similar flames, but steep volume fraction peaks at the flame edges are not sufficiently captured due to the expected effects of large beam diameter, suggesting that the present configuration requires improvement in terms of spatial resolution.