An exploratory modelling study of chemiluminescence in ammonia-fuelled flames. Part 2

The detailed kinetic mechanism of the author was extended by reactions describing formation and con-sumption of excited species which are formed in NH3 + CH4 + air flames, complementing the modelling effort s presented in Part 1. Currently the model includes the following excited species: O(1D), OH *, O2 *, CH *, CH2(1), NO2 *, NO(A), NH *, N2(A), NH2 *, C2 *, CO2 *, CH2O *, and CN *, among which many were ob-served in chemiluminescence signatures of ammonia-fuelled flames. The new model predictions were compared with the experimental data obtained in laminar premixed counterflow NH3 + CH4 + air flames (Combust. Flame 231 (2021) 111508). The overall agreement between the measurements and calculations was not as good as it was observed for NO(A), OH* and NH* in NH3 + H2 + air flames presented in Part 1. It was argued that both unquantified experimental uncertainties and remaining deficiencies of the model could contribute to the discrepancies found. Nevertheless, for OH *, NH *, CN *, CO2* and CH *, as well as for several ratios of chemiluminescence intensity of different excited species the predicted trends both in terms of their variation with equivalence ratio and the amounts of ammonia in the fuel are in qualita-tive agreement with the measurements. The most important inconsistency between the experiments and modelling is found for NO(A), which is the only species in NH3 + CH4 + air flames forming, according to the present mechanism, by the energy transfer from N2(A). This indicates that either formation of N2(A) precursors, namely NH and N, is not accurate due to missing interaction of nitrogen and hydrocarbon chemistry, or reactive quenching of N2(A) is incomplete and requires further development.(c) 2023 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/ )

Automated summary

The extended kinetic mechanism for NH3 + CH4 + air flames includes various excited species and is compared with experimental data. While the overall agreement between measurements and calculations is not as good as in NH3 + H2 + air flames, the predicted trends and chemiluminescence intensities of certain excited species are qualitatively in agreement with the measurements. The most important inconsistency is found for NO(A), suggesting potential inaccuracies in the formation of N2(A) precursors or incomplete reactive quenching of N2(A).