Flame Concentration Measurements Using Picosecond Time-Resolved Laser-Induced Fluorescence

Abstract

Measurements of probability density functions (PDF^s) and power spectral densities (PSD_s) are needed to characterize minor species concentrations in turbulent flames. Current techniques can be used to measure PDF_s, but they have limited ability to measure PSD_s. We report here on a new strategy. picosecond time-resolved laser-induced fluorescence (PITLIF)), which can be used to simultaneously measure concentration PDF_s and PSD_s in turbulent flames. Knowledge of the local quenching environment, which is necessary to obtain accurate number densities, is obtained using a high-bandwidth channel capable of resolving individual temporal decays of the species of interest. In this initial investigation, we demonstrate the capabilities of the PITLIF instrument by studying fluctuating concentrations of sodium seeded into a laminar H₂/O₂/Ar diffusion flame. We show that PDFs and valid PSDs can be obtained for concentration fluctuations in the frequency range of interest for many studies of turbulent combustion.