Visible chemiluminescence of ammonia premixed flames and its application for flame diagnostics

We report a spatially resolved spectroscopic study of the visible chemiluminescence emission from different premixed ammonia-air-oxygen flames stabilized on a laminar flat flame burner, with equivalence ratio ranging from 0.7 to 1.35 and an O 2 /N 2 ratio of 0.4. In the reaction zone of the observed flames, the visible emission was recognized to be the chemiluminescence of excited NH 2 * radicals, while in the post-flame zone, two types of chemiluminescence were observed: NO 2 * chemiluminescence dominated in the fuel-lean flames and NH 2 * chemiluminescence dominated in the fuel-rich flames. The high-resolution spectra of the NO 2 * and NH 2 * chemiluminescence in the visible region (400-700 nm) were recorded. The intensity of both spectra increased gradually with wavelength. However, the NO 2 *-chemiluminescence spectrum appeared to be continuous and unstructured, while the NH 2 *-chemiluminescence spectrum consisted of groups of distinct emission lines. Based on the spectral feature, the ratios of the integrated chemiluminescence intensities over the 598-603 nm wavelength range to the intensities over the 586-592 nm range and 447-453 nm range were used to sense equivalence ratio. In addition, slightly different colors of the fuel-lean and fuel-rich flames were observed, due to the fact that NO 2 * chemiluminescence had a relatively stronger signal in the blue region than NH 2 * chemiluminescence. The difference was used to infer flame equivalence ratio using the flame images recorded by a RGB digital camera, where the ratio of the signal from the red channel to the signal from the blue channel was calculated.& COPY; 2022 The Author(s). Published by Elsevier Inc. on behalf of The Combustion Institute. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )