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On the segregation of NH₃ and H₂ within the flame front in premixed turbulent combustion of NH₃/H₂/N₂ blends

Lookup NU author(s): Professor Nilanjan ChakrabortyORCiD, Dr Hamid Kavari

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).

Abstract

© 2025 The Author(s). The study analyses the segregation of NH3 and H2 in globally lean premixed turbulent flames of NH3/H2 fuel blends using direct numerical simulation (DNS) data of statistically planar turbulent flames. Turbulent premixed flames for two fuel blends, 60%NH3/25%H2/15%N2 and 40%NH3/45%H2/15%N2, with an equivalence ratio of 0.81, were examined in the thin reaction zones regime. Differences in chemical reactivity and differential diffusion between NH3 and H2 lead to local variations in equivalence ratio within the flame, significantly affecting species distribution compared to one-dimensional (1D) laminar premixed flames. The equivalence ratio variation within the flame causes locally either stoichiometric or fuel-rich pockets despite the globally lean condition in the cases considered here. This also enables localised diffusion mode burning, which is stronger for H2 in the 60%NH3/25%H2/15%N2 blend, whereas it is stronger for NH3 in the case of 40%NH3/45%/15%N2 H2 blend. The transition from lean premixed to non-premixed combustion at the rear end of the flame leads to the misalignment of the normal vectors of NH3, H2, and temperature isosurfaces, impacting reaction-diffusion balance. The displacement speeds of H2 isosurfaces exceed those of NH3, leading to differences in effective normal strain rates, which along with local equivalence ratio variation, influence the behaviour of the scalar gradient magnitude. These findings suggest that the modelling of premixed combustion of NH3/H2 blends must account for variable equivalence ratio combustion and non-premixed burning mode, even for globally lean mixtures.

Publication metadata

Author(s): Chakraborty N, Khamedov R, Kavari H, Hernandez-Perez FE, Im HG

Publication type: Article

Publication status: Published

Journal: Combustion and Flame

Year: 2025

Volume: 281

Print publication date: 01/11/2025

Online publication date: 05/09/2025

Acceptance date: 01/09/2025

Date deposited: 16/09/2025

ISSN (print): 0010-2180

ISSN (electronic): 1556-2921

Publisher: Elsevier Inc.

URL: https://doi.org/10.1016/j.combustflame.2025.114455

DOI: 10.1016/j.combustflame.2025.114455

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