Tomographic laser absorption imaging of combustion species and temperature in the mid-wave infrared

In this work, laser absorption spectroscopy techniques are expanded in spatial resolution capability by utilizing a high-speed infrared camera to image flow fields backlit with tunable mid-wave infrared laser radiation. The laser absorption imaging (LAI) method yields spectrally-resolved and spatially-rich datasets from which quantitative species and temperature profiles can be generated using tomographic reconstruction. Access to the mid-wave infrared (3-5 µm) enables imaging of fuels, intermediates, and products of combustion in canonical small-diameter flames (< 1 cm). Example 1D measurements and 2D reconstructions of ethane (3.34 µm), carbon monoxide (4.97 µm), and carbon dioxide (4.19 µm) in an axisymmetric laminar flame are presented and discussed. LAI is shown to significantly enhance spatio-temporal data bandwidth (∼400 simultaneously sampled lines-of-sight) and resolution (∼50 µm) compared to other tomographic absorption spectroscopy techniques, and with a simplified optical arrangement.