Method for absolute OH-concentration measurements in premixed flames by LIF and numerical simulations

We present and apply a methodology for the single-shot measurement of absolute concentrations of the OH-radical in a turbulent, premixed natural gas/air flame. The method is based on a combination of detailed numerical simulations of the turbulent flame and an experimental approach using planar laser-induced fluorescence (LIF). The numerical simulation is used to predict LIF intensities. It shows the existence of a sharp correlation between the LIF signal after excitation of the A-X(3,0) P-2(8) transition near 248.45 turn and OH concentrations for a wide range of conditions, including stationary and instationary laminar flames of different strain rates, with different models to treat molecular transport and different degrees of heat loss. This correlation allows the transformation of measured OH-LIF intensity images into absolute OH concentration maps.