Impact of Reynolds number on the flow field structure and NOx emissions in turbulent NH3-CH4-air flames within a swirl burner

Wang, Ping, Shuai, Ruiyang, Zhang, Jinzhao, Zhang, Zeyu, Valera Medina, Agustin ORCID: https://orcid.org/0000-0003-1580-7133, Qian, Weijia, Ferrante, Antonio, Qi, Haotian and Wang, Yongzhi 2025. Impact of Reynolds number on the flow field structure and NOx emissions in turbulent NH3-CH4-air flames within a swirl burner. Applied Thermal Engineering 279 (Part F) , 127981. 10.1016/j.applthermaleng.2025.127981

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Abstract

Ammonia offers carbon-reduced combustion for gas-turbine systems but require precise control of flame stability and nitrogen oxide (NO) emissions. This study experimentally and numerically investigates the role of Reynolds number (Re = 14,600–37,400) in governing NH3-CH4-air premixed swirling flames (70 vol% NH3, equivalence ratio = 0.85) through chemiluminescence spectra detection, Large Eddy Simulations (LES), and NO diagnostics. While existing studies on Re effects in NH3 combustion are predominantly experimental, this work integrates LES with experimental diagnostics to unravel the underlying turbulence-flame-NOx formation mechanisms. Key findings reveal that flame stabilization exhibits a distinct Re-dependence: while flame topology remains largely unaffected by Re, both flame temperature and heat release rates within the combustion chamber increase with rising Re, significantly enhancing combustion stability. This trend is further corroborated by chemiluminescence intensity, which grows nearly linearly with Re—showing 1.5× and 2.4× higher values at Re = 26,000 and 37,400, respectively, compared to Re = 14,600. LES analysis of flow-thermal coupling indicates that turbulence intensity (defined as the ratio of velocity fluctuations to mean velocity) remains Re-invariant, yet the primary reaction zone experiences temperature rises of 27 K and 36 K at Re = 26,000 and 37,400 relative to the Re = 14,600 baseline. However, these stability gains come with NO emission tradeoffs: higher Re elevate flame temperatures while reducing fuel gas residence time, ultimately increasing outlet NO emissions by 1.4× and 2× for the Re = 26,000 and 37,400 cases, respectively, compared to the Re = 14,600 condition. LES and experiments jointly demonstrate Reynolds number’s competing effects in ammonia combustors − stabilizing flames yet increasing NOx − mandating careful Re optimization in ammonia gas-turbine designs to reconcile stability with emission requirements.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Engineering
Publisher:	Elsevier
ISSN:	1359-4311
Date of Acceptance:	19 August 2025
Last Modified:	01 Sep 2025 13:15
URI:	https://orca.cardiff.ac.uk/id/eprint/180786

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