Simultaneous single-shot laser-based imaging of formaldehyde, OH, and temperature in turbulent flames

Abstract

Single-shot formaldehyde (CH2O) laser-induced fluorescence (LIF) imaging measurements in turbulent flames were performed using XeF excimer laser excitation in the 410 transition of the Ã1A2-1A1 electronic system at 353 nm. Background contributions to the CH2O LIF detection were assessed in spectroscopic measurements. Simultaneous two-dimensional mapping of OH LIF, CH2O LIF, and temperature fields was carried out in a standard Bunsen flame. The zones of peak heat release rate localized via the product of OH and CH2O LiF intensities correlated with areas of intermediate temperatures. In addition, single-shot imaging of the transient formaldehyde distribution was performed in a 150 kW natural gas swirl burner. Formaldehyde distributions in strongly turbulent swirl, flames differed significantly from thin layers found in laminar and weak turbulent flames, indicating the presence of low-temperature chemistry in preheated gas pockets. The CH2O distribution measured in the swirl flame was compared with averaged fields of temperature, OH, and NO concentrations.