H₂O and temperature measurements in propagating hydrogen/oxygen flames using a broadband swept-wavelength ECQCL

We present experimental results using a swept-wavelength external cavity quantum cascade laser (swept-ECQCL) diagnostic to measure broadband absorption spectra over a range of 920-1180c m ^-1 (8.47-10.87 µm) with 2 ms temporal resolution in premixed hydrogen/oxygen flames propagating inside an enclosed chamber. Broadband spectral fits are used to determine time-resolved temperatures and column densities of H ₂ O produced during combustion. Modeling of the flowfield within the test chamber under both equilibrium conditions and using a 1D freely propagating flame model is compared with the experiment in terms of temporal dynamics, temperatures, and H ₂ O column density. Outputs from the numerical models were used to simulate radiative transport through an inhomogeneous combustion region and evaluate the performance of the spectral fitting model. Simulations show that probing hot-band H ₂ O transitions in the high-temperature combustion regions minimizes errors due to spatial inhomogeneity. Good agreement is found between the experimental and modeling results considering experimental uncertainties and model assumptions.