Simultaneous multispectral imaging of flame species using Frequency Recognition Algorithm for Multiple Exposures (FRAME)

Imaging the interaction between different combustion species under turbulent flame conditions requires methods that both are extremely fast and provide means to spectrally separate different signals. Current experimental solutions to achieve this often rely on using several cameras that are time-gated and/or equipped with different spectral filters. In this work we explore a technique called Frequency Recognition Algorithm for Multiple Exposures (FRAME) as an alternative solution for instantaneous multispectral imaging of flame species. The method is based on exciting different species with different spatial “codes” and to separate each signal component using a spatial frequency-sensitive lock-in algorithm. This methodology permits the signal from several different species to be recorded at the exact same time with a single camera. Furthermore, since the signals are recognized based on the superimposed spatial codes, there is no need for spectral separation prior to detection. The entire fluorescence envelope from each species can thus, in principle, be detected. In the current work, we present simultaneous planar laser-induced fluorescence imaging of OH and CH2O in a turbulent dimethyl ether (DME)/air flame.