An exploratory modelling study of chemiluminescence in ammonia-fuelled flames. Part 1

Abstract

The present exploratory study is aimed at the modelling of the chemiluminescence signature of premixed laminar NH3+H2+air flames. The detailed kinetic mechanism of the author was extended by reactions describing the formation and consumption of excited NO2*, NO(A), NH*, and NH2* mostly relying on previous analyses of chemiluminescence processes from the literature. The lowest-lying excited state of molecular nitrogen, N2(A) is also invoked to analyse its possible impact on the formation of these emitting species. In the present model, the formation of NO(A) and NH* in NH3+H2+air flames is governed by the energy transfer from N2(A) to the ground state NO and NH, respectively. The new model predictions are compared with available experimental data obtained by Zhu et al. in laminar counterflow NH3+H2+air flames (PROCI 39 (2023)). Good agreement with the measurements was demonstrated for NO(A), OH*, and NH*, both in terms of their variation with equivalence ratio and the amounts of ammonia in the fuel. Moreover, the model qualitatively captures the ratios of chemiluminescence intensity of OH*/NO(A), NH*/OH* and NH*/NO(A). Further analysis revealed that the bimodal behaviour of chemiluminescence in the spectral regions identified by Zhu et al. as “blue”, “green”, “yellow”, “orange”, and “red”, can be explained by the interplay of emissions from NO2* and NH2*, while emission in the “violet” spectral band could be assigned to excited H2O*.