An experimental, theoretical, and kinetic modeling study of post-flame oxidation of ammonia

Jie Jian, Hamid Hashemi, Hao Wu, Peter Glarborg*, Ahren W. Jasper, J. Klippenstein

*Corresponding author for this work

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Abstract

The post-flame oxidation rate of ammonia was investigated in a novel atmospheric pressure flow reactor at temperatures of 1280±16 K and as a function of residence time and mixture composition (1-10% O2, dry and moist). The experimental results, as well as selected data from literature, were analyzed using an updated detailed chemical kinetic model. The medium temperature, very lean conditions enhance the importance of reactions of the nitroxyl (HNO) intermediate. High-level theory was used to calculate the rate constant for HNO + NH2, indicating that this step is significantly faster than values used in literature. Furthermore, a trajectory based approach was used to determine collision efficiencies for selected bath gases for HNO + M. The experimental results show that the NH3 oxidation rate increases with temperature and O2 concentration, while the presence of water vapor slightly inhibits reaction. Formation of NO and N2O was strongly promoted at higher levels of O2. Modeling results agreed well with the measurements, except at the lowest level of O2. The predicted oxidation rate of NH3 was shown to result from a delicate balance between chain branching and terminating steps nvolving NH2, H2NO, and HNO. Recent theoretical work on reactions of these species by Klippenstein and coworkers and Stagni et al. was instrumental in improving modeling predictions. After initiation, NO reached a pseudo-steady-state level, where the pathways to NO were largely balanced by the NH2 + NO reaction. Nitric oxide was partly oxidized to NO2, with the NH2 + NO2 reaction responsible for most of the N2O formation.
Original languageEnglish
Article number113325
JournalCombustion and Flame
Volume261
ISSN0010-2180
DOIs
Publication statusPublished - 2024

Keywords

  • NH3 oxidation
  • Flow reactor
  • Theory
  • Kinetic modeling

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