The NH 3 /NO 2 /O 2 system: Constraining key steps in ammonia ignition and N 2 O formation

Amine/NO 2 interactions are important for ignition and N 2 O emissions in ammonia combustion. In the present work, reported results from batch reactors (580-690 K) and flow reactors (850-1350 K) for the NH 3 /NO 2 system were re-interpreted in terms of the present understanding of the amine chemistry. Furthermore, additional flow reactor results on the impact of O 2 on the NH 3 /NO 2 reaction were presented and analyzed. Based on the experimental results and the modeling analysis, it was possible to constrain the rate constants for reactions of NH 3 and NH 2 with NO 2 and for subsequent steps involving H 2 NO and HNO intermediates. The key reaction is NH 2 + NO 2 , forming H 2 NO + NO (R2) and N 2 O + H 2 O (R3). The results indicate that the yield of N 2 O in the NH 2 + NO 2 reaction decreases with temperature in the 850- 1350 K range, in agreement with the theoretical study by Klippenstein and coworkers. The fate of H 2 NO and HNO is important for the overall reactivity. In the absence of O 2 , formation of chain carriers is controlled by the sequence H 2 NO + NO 2 -> HNO + HONO, HNO + NO 2 -> NO + HONO, HONO (+M) -> NO + OH (+M). At higher temperatures, in the presence of O 2 , the sequence H 2 NO + O 2 -> HNO + HO 2 , HNO + O 2 -> NO + HO 2 , NO + HO 2 -> NO 2 + OH enhances radical formation and recycles NO 2 . The satisfactory agreement between experiments and modeling predictions, both without and with O 2 , supports the present rate constants for the reactions of H 2 NO and HNO with NO 2 and O 2 , respectively. (c) 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/ )

Automated summary

Amine/NO2 interactions play a crucial role in ignition and N2O emissions. This study reinterpreted the reported results from batch and flow reactors, and provided additional results on the impact of O2 on the NH3/NO2 reaction. The analysis constrained the rate constants for NH3 and NH2 reactions with NO2, as well as the subsequent steps involving H2NO and HNO intermediates. The experimental and modeling findings support the present understanding of the reaction kinetics.