Spectrally resolved, 1D, mid-infrared imaging of temperature, CO₂, and HCl in propellant flames

This work presents a high-speed, spectrally resolved, mid-infrared imaging diagnostic for providing 1D measurements of gas temperature and relative mole fraction of ${{\rm{CO}}_2}$ and HCl in flames. An imaging spectrometer and a high-speed mid-infrared camera were used to provide 1D measurements of ${{\rm{CO}}_2}$ and HCl emission spectra from 2386 to ${{2402}}\;{{\rm{cm}}^{- 1}}$ with a spectral resolution of ${0.46}\;{{\rm{cm}}^{- 1}}$, and simulated emission spectra were least-squares fit to the data to determine the aforementioned gas properties. Measurements were acquired in HMX and AP-HTPB flames burning in air at 1 atm. This diagnostic was applied to characterize how the path-integrated gas temperature of HMX flames varies in time and with distance above the burning surface. Additionally, Abel inversion with Tikhonov regularization was applied to determine the radial distribution of temperature and relative concentration of ${{\rm{CO}}_2}$ and HCl within the core of AP-HTPB flames. The results demonstrate that this diagnostic has potential to further our understanding of propellant combustion physics by quantifying thermochemical flame structure at rates up to 2 kHz.