Experimental study of hydrodynamic instabilities in laminar normal and inverse diffusion flames under elevated pressures

IF 5.8 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame Pub Date : 2025-04-09 DOI:10.1016/j.combustflame.2025.114165

Raul Serrano-Bayona , Tao Yang , Peng Liu , Xuren Zhu , Carson Chu , Ibrahim Alsheikh , William L. Roberts

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引用次数: 0

Abstract

Understanding hydrodynamic instabilities in coflow diffusion flames is essential for enhancing operational stability and safety. This study presents the first experimental investigation into the effects of pressure, flow rates, coflow/central jet velocity ratio, and O₂ concentration on hydrodynamic instabilities in laminar normal and inverse diffusion flames (NDFs and IDFs). Methane (CH₄) diluted with carbon dioxide (CO₂) was used as fuel, whereas oxygen (O₂) diluted with nitrogen (N₂) was the oxidant. The spatial-temporal features of these flames were captured with a high-speed camera, luminous flame height was characterized for flame dynamics, and oscillation frequency was quantified using the Fast Fourier Transform (FFT) method. Results demonstrate that flame configuration significantly influenced instability modes. Unstable NDFs consistently exhibited the sinuous mode, while unstable IDFs were predominantly under the varicose mode. This distinct trend could be attributed to the density difference between the central jet and the coflow stream. Instability modes are found to be highly sensitive to the gas velocity and O₂ concentration since these parameters could displace the point of toroidal vortices formation (upward displacement with higher coflow velocity and lower jet velocity) and affect the flame height (reduction at lower jet velocity or higher O₂ concentration). Pressure had a minimal effect on the instability modes, although stable flames were mostly observed at higher pressures with high

R e_{c o f l o w}

. Instead, oscillation frequency increased with pressure in buoyancy-driven flames (

F r < 1

) but was more influenced by jet flow rate in momentum-driven flames (

F r > 1

). A power-law relationship between the non-dimensional numbers

S t

and

F r

was observed with two different slopes for momentum-driven flames (

n < 0.5

) and for buoyancy-driven flames (

n > 0.5

). A single correlation with Re described frequency behavior at each pressure level. These findings offer practical conditions for optimizing ATR burner stability.

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高压下层流法向和反向扩散火焰的流体力学不稳定性实验研究

了解共流扩散火焰的水动力不稳定性对提高操作稳定性和安全性至关重要。本文首次对压力、流量、共流/中心射流速度比和O2浓度对层流正扩散火焰和逆扩散火焰（ndf和IDFs）流体动力不稳定性的影响进行了实验研究。用二氧化碳（CO2）稀释的甲烷（CH4）作为燃料，用氮气（N2）稀释的氧气（O2）作为氧化剂。利用高速摄像机捕捉火焰的时空特征，利用快速傅立叶变换（Fast Fourier Transform， FFT）方法对火焰的振荡频率进行量化，并对火焰的发光高度进行动态表征。结果表明，火焰构型对不稳定模态有显著影响。不稳定的ndf一致表现为弯曲模式，而不稳定的idf主要表现为静脉曲张模式。这种明显的趋势可归因于中央喷流和共流之间的密度差。不稳定模态对气流速度和O2浓度非常敏感，因为这些参数会使环形涡的形成点发生位移（共流速度高、射流速度低时向上位移），并影响火焰高度（射流速度低或O2浓度高时降低）。压力对不稳定模式的影响很小，尽管稳定火焰大多在高反流的高压力下观察到。在浮力驱动的火焰中，振荡频率随压力的增加而增加（Fr<1），而在动量驱动的火焰中，振荡频率受射流流速的影响更大（Fr>1）。在动量驱动火焰（n<0.5）和浮力驱动火焰（n>0.5）中，观察到无量纲数St和Fr之间的幂律关系具有两种不同的斜率。与Re的单一相关性描述了每个压力水平下的频率行为。这些研究结果为优化ATR燃烧器的稳定性提供了实际条件。

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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.