Analysis of ammonia–methane stabilized flames in an optically accessible porous media burner through chemiluminescence imaging

Munoz-Herrera, Claudio, Aravind, B, Rojas, Paula, Hernández, Christian, Mashruk, Syed, Valera-Medina, Agustin ORCID: https://orcid.org/0000-0003-1580-7133 and Toledo, Mario 2026. Analysis of ammonia–methane stabilized flames in an optically accessible porous media burner through chemiluminescence imaging. Fuel: The Science and Technology of Fuel and Energy 412 , 138122. 10.1016/j.fuel.2025.138122

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Abstract

Porous media burners (PMBs) offer enhanced combustion efficiency and extended stability limits through heat recirculation, yet their limited optical accessibility has restricted experimental insight into pore-scale flame behavior. In this study, methane–ammonia premixed flames were investigated in a two-zone PMB with a downstream bed reduced to a single-sphere thickness to provide enhanced optical access. OH* and NH* chemiluminescence imaging was used to visualize interphase-stabilized flame fronts across equivalence ratios of 0.7–1.0, mass fluxes of 0.2–0.4 kg m−2 s−1, and ammonia fractions up to 50 % by volume in the fuel mixture. Stability maps showed that pure methane flames stabilized only at the highest mass flux, whereas increasing NH3 content displaced the flashback region toward lower mass fluxes and introduced blow-out or extinction zones under lean or low-reactivity conditions. A first-order stability indicator, defined using the ratio of filtration velocity to laminar flame speed, qualitatively delineated the stability regimes with 86 % overall accuracy. Chemiluminescence images revealed different stabilized flame-front morphologies which are proposed as a mean to explain mechanisms that are expected to be present simultaneously in conventional two-zone PMBs. These patterns reflect the complex thermochemistry inside the intricate geometries of PMBs. While conventional packed-bed burners may exhibit further distorted flame morphologies, this study provides valuable insights for advancing the understanding of pore-level combustion in PMBs.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Engineering
Publisher:	Elsevier
ISSN:	0016-2361
Date of Acceptance:	20 December 2025
Last Modified:	07 Jan 2026 10:45
URI:	https://orca.cardiff.ac.uk/id/eprint/183639

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