Analysis of Measured Flame Transfer Functions With Locally Resolved Density Fluctuation and OH-Chemiluminescence Data

The goal of this study is to analyze flame transfer functions (FTFs) locally by quantifying the heat release rate with OH*-chemiluminescence and density fluctuation measurements using laser vibrometry. In this study, both techniques are applied to a swirl burner configuration with known FTFs acquired by multimicrophone-method (MMM) measurements for perfectly premixed and partially premixed cases. The planar fields of the quantities are compared to the FTFs in order to improve the understanding regarding the specific amplitude and phase values. On the global scale values of heat release expected from the MMM are satisfactorily reproduced by both methods for the premixed cases, whereas OH*-chemiluminescence data cannot be used as indicator for heat release in the partially premixed case, where equivalence ratio fluctuations are present. Vibrometry is not affected by fluctuations of equivalence ratio but additionally reveals the periodic oscillation of the conical annular jet of the cold reactants in the combustor filled with hot products.