The NH3/NO2/O2 system: Constraining key steps in ammonia ignition and N2O 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/ )