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Flame dynamics of nonpremixed coflow DME jets in momentum-driven and buoyancy-momentum-driven regimes

IF 6.2 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame Pub Date : 2025-08-20 DOI:10.1016/j.combustflame.2025.114396

Dong Jun Kim , Jeong Park , Suk Ho Chung , Chun Sang Yoo

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引用次数: 0

Abstract

This study experimentally investigates the behavior of laminar nonpremixed flames of N

_{2}

-diluted Dimethyl ether (DME) in a coflow jet under varying fuel mole fractions (

X F, 0

), jet velocities (

U 0

), and temperatures (

T 0

= 300, 400, and 500 K). A wide range of lifted flame behaviors is observed as

U 0

increases, including three distinct trends in liftoff height (

H L

): Monotonically increasing (M.I.), Monotonically decreasing (M.D.), and U-shaped

H L

. In addition, two flame extinction modes (i.e., flame blowoff and blowout) are identified depending on the jet developing length (

Z f r e e

). The observed flame behaviors are classified into three different regimes based on the Richardson number (

R i

): Momentum-driven (MD), Buoyancy-momentum-driven (BMD), and Buoyancy-driven (BD) regimes. The monotonically decreasing

H L

behavior appears exclusively in the buoyancy-momentum-driven regime, where buoyancy effects remain significant. In contrast, the monotonically increasing

H L

behavior is confined to the momentum-driven regime, where jet momentum dominates. The U-shaped

H L

behavior emerges during the transition between the buoyancy-momentum-driven and momentum-driven regimes. To elucidate the underlying stabilization mechanisms, time-resolved flame edge measurements are conducted using laser ignition downstream of the nozzle, from which flame stabilization and blowout mechanisms are identified for each regime. In the buoyancy-momentum-driven regime, flame liftoff is influenced by a combination of buoyancy, jet momentum, and heat loss to the nozzle rim. In the momentum-driven regime, jet momentum is the dominant factor. Correlations for

H L

are developed in terms of the laminar flame speed (

S 0 L

U 0

T 0

X F, 0

, and

R i

, reflecting the regime-dependent influence of buoyancy and momentum. Finally, the flame blowoff and liftoff limits of attached flames are characterized using the density difference between fuel and burnt gas,

U_{0} / S_{L}^{0}

, and a heat loss parameter, revealing the role of heat loss in flame liftoff processes. These findings provide a unified understanding of lifted flame behavior and extinction mechanisms under various flow and thermal conditions.

Novelty and significance statement

This study establishes a unified regime-based framework for lifted flame behavior by introducing three regimes: the momentum-driven (MD) regime, the buoyancy–momentum-driven (BMD) regime, and the buoyancy-driven (BD) regime, all defined based on the Richardson number. Unlike prior studies limited to specific conditions, this study explains diverse lifted flame behaviors, including U-shaped, increasing, and decreasing variations with jet velocity, across a broad range of conditions. By identifying distinct extinction modes, such as flame blowout and blowoff, and revealing the role of nozzle heat loss in the BMD regime, this study advances the understanding of flame stabilization and limit phenomena beyond previously known mechanisms.

查看原文本刊更多论文

非预混共流二甲醚射流在动量驱动和浮力-动量驱动下的火焰动力学

本研究通过实验研究了不同燃料摩尔分数（XF,0）、射流速度（U0）和温度（T0 = 300、400和500 K）下n2稀释二甲醚（DME）层流非预混火焰在共流射流中的行为。随着U0的增加，可以观察到大范围的升力火焰行为，包括升力高度（HL）的三种不同趋势：单调增加（M.I.），单调减少（M.D.）和u型HL。此外，根据射流发展长度（Zfree）确定了两种火焰熄灭模式（即火焰吹灭和井喷）。根据理查德森数（Ri），将观察到的火焰行为分为动量驱动（MD）、浮力-动量驱动（BMD）和浮力驱动（BD）三种不同的模式。单调递减的HL行为只出现在浮力-动量驱动区，浮力效应仍然显著。相比之下，单调递增的高程行为仅限于动量驱动区，其中射流动量占主导地位。在浮力-动量驱动和动量驱动之间的过渡过程中，出现了u型HL行为。为了阐明潜在的稳定机制，使用喷嘴下游的激光点火进行了时间分辨火焰边缘测量，从中确定了每种状态下的火焰稳定和爆裂机制。在浮力-动量驱动状态下，火焰上升受浮力、射流动量和喷嘴边缘热损失的综合影响。在动量驱动状态下，射流动量是主导因素。HL的相关性是根据层流火焰速度（sol）、U0、T0、XF、0和Ri开发的，反映了浮力和动量的依赖状态的影响。最后，利用燃料和燃烧气体的密度差、U0/SL0和热损失参数表征了附着火焰的火焰喷出和上升极限，揭示了热损失在火焰升起过程中的作用。这些发现提供了对不同流动和热条件下火焰提升行为和熄灭机制的统一理解。本研究通过引入动量驱动（MD）、浮力-动量驱动（BMD）和浮力驱动（BD）三种机制，建立了一个统一的基于机制的升力火焰行为框架，这三种机制都是基于Richardson数定义的。与以往仅限于特定条件的研究不同，本研究在广泛的条件下解释了不同的提升火焰行为，包括u型，随着射流速度的增加和减少变化。通过识别不同的熄灭模式，如火焰喷灭和吹灭，并揭示喷嘴热损失在BMD机制中的作用，本研究推进了对火焰稳定和限制现象的理解，超出了先前已知的机制。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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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.