Quantitative hydroxyl concentration time-series measurements in turbulent nonpremixed flames.

Quantitative hydroxyl concentration time-series measurements have been obtained by picosecond time-resolved laser-induced fluorescence in a series of methane-air and hydrogen-argon-air nonpremixed flames. The recovery of a quantitative time series is complicated by the need to account for fluctuations in the fluorescence lifetime. We have recently developed instrumentation that enables the simultaneous measurement of fluorescence signal and lifetime. The present research represents the first application of this technique to turbulent flames. The correction for hydroxyl lifetime fluctuations is shown to be significant for mean concentrations and thus probability density functions but negligible for power spectral densities (PSD's). The hydroxyl PSD's were found to vary slightly with radial and axial location in the flames and to vary significantly with Reynolds number. However, the PSD's in the H(2)-Ar-air flames are nearly identical to those in the CH(4)-air flames.