Synergistic use of plasma and air staging for emission control in NH₃–air flames

Aravind, B., Wang, Ziyu, Mashruk, Syed and Valera Medina, Agustin ORCID: https://orcid.org/0000-0003-1580-7133 2026. Synergistic use of plasma and air staging for emission control in NH₃–air flames. Proceedings of the Combustion Institute 42 , 106657. 10.1016/j.proci.2026.106657

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Abstract

In this study, a detailed experimental investigation on the effect of gliding arc plasma on the emission characteristics of air staged (AS) ammonia (NH3) flames is conducted for the first time. Four AS configurations, AS-OI-L100, AS-OI-L200, AS-TI-L100, and AS-TI-L200 employing orthogonal (OI) and tangential (TI) secondary air injections at two axial locations (100 mm and 200 mm) were examined. For no-plasma cases, the results show that AS significantly reduces NO emissions compared to the no-staged configuration, with AS-OI-L200 achieving 73–77 % NO reduction while maintaining minimal NH₃ slip (<5 ppm). Tangential injection further enhanced NO reduction (up to 85 %) but increased NH₃ slip, whereas a shorter staging distance (L100) led to reduced performance due to limited mixing. Plasma activation markedly improved flame stability and radical formation, providing an additional 36–38 % NO reduction relative to no-plasma cases. Moreover, the combined plasma–AS operation achieved up to 96 % NO reduction under lean conditions, although excessive NH₃ slip was observed in some tangential configurations. Overall, the AS-OI-L200 configuration exhibited the most balanced performance, delivering high NO reduction alongside low NH3 and N2O emissions. Numerical analysis further reveals that plasma activation increases NH2 concentrations, shifting NO formation from the conventional Fuel-N pathway toward an N-activated oxidation route. When combined with air staging, reduced local O2 availability and enhanced NO consumption via N + NO = O + N2 lead to net suppression of NO formation. These findings demonstrate that careful control of secondary air injection orientation and staging location, in combination with plasma activation, provides an effective strategy for achieving stable, low-emission NH₃ combustion, thereby advancing the practical use of ammonia as a carbon-free fuel.

Item Type:	Article
Date Type:	Published Online
Status:	Published
Schools:	Schools > Engineering
Publisher:	Elsevier
ISSN:	1540-7489
Date of First Compliant Deposit:	19 October 2026
Date of Acceptance:	5 June 2026
Last Modified:	19 Oct 2026 11:33
URI:	https://orca.cardiff.ac.uk/id/eprint/190302

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