Ruiz, H.J. Vargas, Naess, T., Aravind, B., Laera, D., Lartigue, G., Mashruk, S., Valera-Medina, A.  ORCID: https://orcid.org/0000-0003-1580-7133 and Gicquel, L.
2026.
Large Eddy Simulation Cell-by-Cell quantification of nitrogen oxide sub-mechanisms in premixed ammonia-air flames with differentiated hydrogen injection.
Combustion and Flame
292
, 115182.
10.1016/j.combustflame.2026.115182
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Abstract
Ammonia-hydrogen fuel blends are currently being investigated as a promising technical solution for gas turbine decarbonization, yet NO x emissions pose critical challenges for industrial deployment. In the present work, joint Large Eddy Simulations (LES) and experimental investigations are proposed to study the NO x formation mechanisms in premixed ammonia-hydrogen swirled flames enriched with separate hydrogen injection. The target configuration is the experimental setup developed at Cardiff University. Four test points operated at atmospheric pressure and characterized by the same global 70/30 NH3/H2 volumetric fuel composition but different equivalence ratios, i.e., 0.65, 0.8, 1.0, and 1.2, are compared. LES performed using the multi-fuel Thickened Flame turbulent combustion model (MF-TFLES), coupled with finite rate chemistry, show good agreement with experimental PLIF NO and OH* chemiluminescence measurements. This validates the capability of the numerical model to accurately reproduce both the flame structure and the emissions distribution. Cell-by-Cell (CBC) chemical analysis demonstrates that the fuel-NO pathways dominate NO formation despite hydrogen’s enhancement of local reactivity through preferential diffusion and superadiabatic effects under lean conditions. The HNO route constitutes the primary formation pathway, while the NH i and thermal NO contributions remain limited across all operating points. Hydrogen addition intensifies overall reactivity and locally increases NO production but does not alter the dominance of ammonia-derived chemistry over thermal pathways. Exhaust NO emissions peak at ϕ = 0.8 and approach zero at ϕ = 1.2 , driven by the presence of unburnt ammonia under rich conditions. The reburn mechanism actively consumes NO at all equivalence ratios but exhibits maximum effectiveness at ϕ = 0.65 , preventing the highest NO production rates from translating to peak exhaust emissions which are observed at ϕ = 0.8 . N2O formation occurs upstream in reactive zones before thermal decomposition to N2, with negligible exhaust concentrations except under very lean conditions at ϕ = 0.65 . Novelty and significance statement This research presents novel OH* chemiluminescence and NO PLIF measurements on swirling ammonia-hydrogen flames with differentiated fuel injection. The recently introduced multi-fuel thickened flame turbulent combustion model (MF-TFLES) is applied to LES of complex ammonia-hydrogen-air swirling flames with heterogeneous fuel composition obtained via a differentiated injection strategy. Based on a finite rate chemistry methodology, Cell-by-Cell quantification of individual reaction contributions allows to identify spatial distribution of pollutant formation sub-mechanisms. This understanding address the primary challenge of NO x control in ammonia-hydrogen combustion, enabling industrial adoption of carbon-free fuel systems.
| Item Type: | Article |
|---|---|
| Date Type: | Publication |
| Status: | Published |
| Schools: | Schools > Engineering |
| Publisher: | Elsevier |
| ISSN: | 0010-2180 |
| Date of First Compliant Deposit: | 11 September 2026 |
| Date of Acceptance: | 6 July 2026 |
| Last Modified: | 11 Sep 2026 08:45 |
| URI: | https://orca.cardiff.ac.uk/id/eprint/188807 |
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