Line-of-sight temperature and species profiles from an inverse analysis of spectral transmittances

Line-of-sight variations of temperature and concentrations of IR-active species within a simulated high-pressure flame are deduced using an inverse analysis. In this work, synthetic spectral transmittances, acquired by a Fourier transform infrared spectrometer along a single Line-of-sight, represent the experimental data. The theoretical basis of the inverse analysis is that spectral variations in the absorption coefficient contain information about spatial variations in temperature and species concentrations. An iterative approach based on the Marquardt- Levenberg method is utilized to solve for the temperature and species concentrations of CO and H₂O. The results show that accurate spatial variations of temperature and species concentrations can be recovered when changes in the spectral transmittances caused by noise are smaller than those changes caused by spatial variations in temperature and species concentrations. The recovered centerline temperatures and species concentrations are, respectively, within 5% and 20% of the actual values, when the variations in spectral transmittance caused by noise are about the same as that caused by spatial variations in temperature and species concentrations. As the flame temperature increases, the inverse analysis becomes more sensitive to the effect of noise.