Investigating NO emissions, stability, and flame structure in co-fired premixed NH3/CH4/air swirling flames

IF 5.8 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame Pub Date : 2025-02-01 DOI:10.1016/j.combustflame.2024.113892

Ayman M. Elbaz , Zubayr O. Hassan , Alfaisal M. Albalawi , Mahmoud MA. Ahmed , Marwan Abdullah , Emre Cenker , William L. Roberts

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引用次数: 0

Abstract

Ammonia combustion poses challenges due to low reactivity and high NO_x emissions, requiring optimization of combustor designs and fueling strategies. This study examines NO emissions, flame stability, and structure in co-fired premixed NH₃/CH₄/air flames using a double-swirl burner. The inner swirl stream consists of NH₃/CH₄/air mixtures with varying ammonia mole fractions (x_NH3: 0 to 1) and equivalence ratios (Φ_in: 0.4 to 1.4), while the outer stream contains CH₄/air mixtures with Φ_out ranging from 0.5 to 0.8 and Reynolds numbers (Re_out) of 4350, 5250, and 6000. NO emissions varied significantly with Re_out, Φ_in, and Φ_out, prompting further investigation of flame structure using OH-NO PLIF and PIV diagnostics for three flame sets: FA (Φ_in=0.4), FB (Φ_in=0.8), and FC (Φ_in =1.4). Far-rich (FC) and far-lean (FA) flames exhibited an early conical OH layer followed by a V-shaped OH layer, while NO dispersed across the flame, forming a thin layer at the OH boundary with a V-shaped distribution downstream. Higher Re_out facilitated V-OH/NO formation through enhanced mixing, increased recirculation, and more effective ammonia cracking in rich mixtures. At Re_out=4350, the absence of a V-OH layer in FA resulted in reduced NO emissions. Flame FB showed a broader, positively correlated NO and OH structure along the central region of the flame, indicating enhanced NH_i oxidation to NO. Overall, co-firing ammonia with methane in the outer stream was crucial for improving flame stability. To minimize NO emissions, it is important to lower Re_out, increase Φ_out, and avoid premixing NH₃/CH₄ in the inner stream. At high Re_out, limiting rich Φ_in to 1.2 or leaning it out, combined with increasing Φ_out, was the most effective strategy for reducing NO emissions.

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来源期刊

Combustion and Flame 工程技术-工程：化工

CiteScore

9.50

自引率

20.50%

发文量

631

审稿时长

3.8 months

期刊介绍： The mission of the journal is to publish high quality work from experimental, theoretical, and computational investigations on the fundamentals of combustion phenomena and closely allied matters. While submissions in all pertinent areas are welcomed, past and recent focus of the journal has been on: Development and validation of reaction kinetics, reduction of reaction mechanisms and modeling of combustion systems, including: Conventional, alternative and surrogate fuels; Pollutants; Particulate and aerosol formation and abatement; Heterogeneous processes. Experimental, theoretical, and computational studies of laminar and turbulent combustion phenomena, including: Premixed and non-premixed flames; Ignition and extinction phenomena; Flame propagation; Flame structure; Instabilities and swirl; Flame spread; Multi-phase reactants. Advances in diagnostic and computational methods in combustion, including: Measurement and simulation of scalar and vector properties; Novel techniques; State-of-the art applications. Fundamental investigations of combustion technologies and systems, including: Internal combustion engines; Gas turbines; Small- and large-scale stationary combustion and power generation; Catalytic combustion; Combustion synthesis; Combustion under extreme conditions; New concepts.