Experimental measurement of temperature and H2O concentration distribution in particle-free flames using water vapor integrated spectral band emission

With the development of efficient and clean combustion technologies, particle-free flames become common, and their temperature and species concentration distributions are very useful for understanding the flame structure and optimizing combustion conditions. In this study, the integrated spectral band ratio (ISBR) method is applied to measure the temperature and H₂O concentration distributions in four laminar diffusion particle-free flames of oxy-combustion. In the experiments, the measurement of radiative intensity data with high spatial and spectral resolution is performed by an optical system consisting of a Gülder burner, a portable spectrometer and a translation stage. The integrated spectral emissions in two optimized bands near 1.5 μm are obtained and used to reconstruct the radial temperature and H₂O volume fraction distributions of the flame cross-sections. The reconstructed results well reproduced the combustion structure of diffusion flames, and the calculated spectra using the reconstructed results are in good agreement with the measured spectra. The reconstructed results are also compared with simulation results by CoFlame code. The profiles of temperature and H₂O volume fraction distributions are consistent with each other, and the biggest difference of peak flame temperatures is about 50 K. The comparisons indicate that the measured radial temperature and H₂O volume fraction results have good accuracy. Path-averaged results measured by the spectrometer are also reported and compared with the radial reconstructed results. The result profiles have obvious difference, and the peak temperature is significantly underestimated in the path-averaged results with the biggest difference of 133 K.