Insight into NH3 formation characteristics at rich conditions in 70/30 VOL% NH3/H2 flames

Alnasif, Ali, Jójka, Joanna, Mashruk, Syed and Valera-Medina, Agustin ORCID: https://orcid.org/0000-0003-1580-7133 2024. Insight into NH3 formation characteristics at rich conditions in 70/30 VOL% NH3/H2 flames. Presented at: The 19th Edition of the International Conference on Numerical Combustion, Kyoto, Japan, 7-10 May 2024.

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Abstract

Recent studies have highlighted that in fuel blends with a 70/30 vol% ratio of ammonia/hydrogen, the ratio of final to initial mole fractions of NH3 is notably high. This finding underscores the importance of comprehensive understanding of the product gases, especially the residual NH3, in NH3/H2 laminar flames. Such understanding is critical for designing NH3-fueled combustors to comply with the stringent emission regulations. Understanding of the underlying chemistry in the oxidation of NH3/H2 mixtures is a pivotal factor for the flexible utilization of these mixtures in various applications, including propulsion systems and power generation. In this context, the current work investigates 70 kinetic reaction mechanisms from the literature in atmospheric conditions. This study aims to evaluate the effectiveness of these mechanisms in predicting the mole fraction of unburned NH3 in a volumetric fuel mixture of 70% NH3 and 30% H2. The findings revealed that the Lamoureux kinetic model yielded reliable estimations of the unburned NH3 within the equivalence ratio (ϕ) range of 1-1.2. However, its accuracy decreased around 1.4 of ϕ. Notable variations were observed in the reaction steps and rate parameters among these tested mechanisms. Predominantly, NH3 was converted to NH2 radicals through reactions with OH across all temperatures, with a secondary role played by O radicals at low to intermediate temperatures. At higher temperatures, NH3 dehydrogenation also occurred via H radicals, as evidenced in the NH3+H⇌NH2+H2 reaction. Additionally, at the combustion exit, NH3 regeneration was primarily driven by the NH3⇌NH2+H reaction at a temperature of 504 K.

Item Type:	Conference or Workshop Item (Paper)
Status:	In Press
Schools:	Engineering
Funders:	EPSRC
Date of First Compliant Deposit:	10 June 2024
Date of Acceptance:	19 January 2024
Last Modified:	14 Jul 2024 20:50
URI:	https://orca.cardiff.ac.uk/id/eprint/169624

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