Study of reaction rates through a local extinction point in nonpremixed flames

A laminar co-annular counterflow flame is used to generate a stable local extinction point in a nonpremixed flame sheet. Measurements of hydroxyl planar laser-induced fluorescence (PLIF) and formaldehyde PLIF were made through the local extinction point and were used to estimate the OH+CH₂O forward reaction rate. In addition, two-dimensional numerical simulations of the flame and extinction point were completed using a comprehensive chemical kinetic model. Since the local temperature at the extinction point decreases strongly, the measured PLIF profiles include significant dependence on Boltzmann fraction, particularly for CH₂O. The simulated species concentrations were modified to include the temperaturedependent variations that could not be removed from the measurements. The simulated and measured profile shapes are in good agreement, but the simulations show a stronger quantitative increase in the OH+CH₂O reaction prior to extinction and a thinner reaction rate at the centerline than observed in the measurements. In addition to the direct comparison of OH+CH₂O reactions, the simulations are used to examine other important reactions at the extinction point.