Abstract
Raman spectroscopy is a powerful technique that allows for simultaneous measurements of multiple species; however, it suffers from low signal intensity and, in diagnostics of ammonia (NH3) combustion, strong flame fluorescence. The current work re-introduces a multipass setup to perform enhanced quantitative Raman spectroscopy measurements of major species and nitric oxide (NO) in a premixed laminar lean (φ = 0.9) NH3 flame. A way to deal with the strong flame reaction-zone fluorescence is proposed and validated. The measurements were performed using both the second (532 nm, NO detection) and third (355 nm, major species and temperature) harmonics of an Nd:YAG laser. The acquired data sets were compared to the simulation data obtained with two chemical kinetic mechanisms. The reported average post-flame concentration of NO reaches a plateau at 3900 ± 120 ppm, and the detection limit is 700 ppm. The 355 nm excitation wavelength proved to provide close to no flame fluorescence, which allowed for measurements across the entire flame from reactants to products. Thus, major species profiles were acquired, and the concentration and temperature results are in good agreement with the simulation data. Lastly, possible error sources are estimated and ways to minimize them are proposed.
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