Radiometer measurements of the spectrally resolved radiative heat flux in a combustion chamber

So far ellipsoidal radiometers used in combustion environments have been limited to broadband measurements of total radiative intensity, converting the total incident thermal radiation into an integral electrical voltage signal while neglecting information about the incident radiation’s wavelength distribution. To preserve this spectral information, the novel radiometer concept presented in this study enables spectrally resolved radiative heat flux measurements inside a combustion chamber. For this purpose, the established design of ellipsoidal hemispheric radiometer cavities was extended by integrating hollow optical fibers as radiation guides. This combination allows the use of radiation analysis instruments, such as a Fourier transform infrared spectrometer, outside the chamber. Calibration measurements were conducted to determine the angular-dependent response of the radiometer and to perform a wavelength-resolved intensity calibration. These procedures enable a reliable interpretation of the collected radiation signals within the combustion chamber. Furthermore, the radiometer was applied at an oxyfuel-driven laminar flow reactor and a 1MWth test facility, investigating three different pulverized walnut shell flames – one under air and two under oxyfuel conditions. The obtained results allowed the identification of emission lines from water vapor, carbon dioxide and methane, emission lines, as well as radiative heat flux distributions at different measurement positions within the combustion chamber. Based on these distributions, an influence of radiation absorption effects related to varying gas temperature profiles inside the combustion chamber were observed.