NO formation/reduction mechanisms of ammonia/air premixed flames at various equivalence ratios and pressures

By A. Hayakawa, T. Goto, Rentaro Mimoto, Taku Kudo, Hideaki Kobayashi. 2015

244 citations recorded by the source corpus.

Ammonia is a carbon-free fuel and its application to internal combustion engines is expected. However, few studies on ammonia flames, especially at high pressures, have been carried out because ammonia has not been considered to be a fuel owing to its lower combustion intensity. Most of NOx, which is formed by ammonia combustion, is considered to be the fuel NOx. The objectives of this study were to investigate the fundamental characteristics of NOx experimentally, such as NO emission and chemiluminescence of ammonia/air flames not only at the atmospheric pressure but also under high pressures and to explore NO formation/reduction mechanisms using numerical simulation. Experiments were carried out using a nozzle-type burner. NH2 ammonia  band spectra were observed, and it was clarified that the color of ammonia flame is mainly determined by the NH2 ammonia  band and H2O spectra. Burned gas was sampled from ammonia flame stabilized at the burner. The mole fraction of NO decreased with the increase in equivalence ratio at atmospheric pressure. Reaction flow analysis was performed, and it was clarified that the decrease in the mole fraction of NO for rich mixtures was caused by NHi (i = 2, 1, 0). High pressure experiments were performed using a high pressure combustion test facility for stoichiometric ammonia flame. Consequently, the decrease in the mole fraction of NO was experimentally observed and its tendency was found to qualitatively agree with the results of the numerical simulation. It was clarified that the third body reaction of OH + H + M  H2O + M plays an important role in the reduction of the mole fraction of NO at high pressure.

Subfields: Computational Mechanics, Fluid Flow and Transfer Processes, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/b0b6d8e15b338d7a39add951ed7d503cb24ecce5

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Citations in the corpus

NO and OH* emission characteristics of very-lean to stoichiometric ammonia–hydrogen–air swirl flames (2020, result): “This non-monotonic trend was comparable with that observed in [22] for pure ammonia.”
Stability limits and NO emissions of technically-premixed ammonia-hydrogen-nitrogen-air swirl flames (2020, background): “However, while the HCN intermediate plays a large role in the formation of NO via fuel 472 NOx pathways for ammonia-methane blends [22,34], HCN is not present with ammonia-hydrogen 473 blends and pure ammonia and the HNO intermediate contributes instead [11,26,29,32].”
The regulation effect of methane and hydrogen on the emission characteristics of ammonia/air combustion in a model combustor (2021, background): “[26] Hayakawa A, Goto T, Mimoto R, Kudo T, Kobayashi H.”