紊流预混射流稳定氢火焰中低速条纹结合火焰的固有不稳定性引起边界层闪回

IF 5.8 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame Pub Date : 2025-06-04 DOI:10.1016/j.combustflame.2025.114236

P. Porath , L.A. Altenburg , S.A. Klein , M.J. Tummers , A. Ghani

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引用次数: 0

摘要

本文报道了用分辨良好的LES对紊流预混纯氢火焰的边界层闪回现象。本文的数值计算是基于TU Delft （TUD）射流火焰在雷诺数Re=11000时的闪回实验。闪回是一个高度敏感的过程，这就是为什么(i)湍流流入条件，（ii）化学建模和（iii）混合管壁温度是准确预测这一瞬态过程的关键参数。热扩散火焰不稳定性的存在是这种设置中闪回的主要原因。我们确定了混合管内的准相干湍流结构，即喷射事件，它将缓慢的、预热的富氢流体从壁面输送出去，并触发闪回事件。结果，火焰在管道出口上游形成一个指向未燃烧气体混合物的凸尖。在从无约束（火焰周围无壁面）到约束（火焰周围有壁面）边界层闪回的过渡过程中，该尖端进一步弯曲并向射流出口中心传播，同时其曲率和氢的反应速率显著提高了2倍。我们在不同的流动条件下重复了几次闪回模拟：所有情况都具有相同的FB特征，因此证实了结论的普遍性。此外，数值闪回机制证实了实验假设的过程。在确定影响火焰闪回的关键控制参数的基础上，我们进行了刘易斯数和壁面温度的参数变化。通过改变路易斯数，我们可以清楚地表明闪回是由热扩散不稳定性驱动的，而较热的壁面显著地恶化了这种设置的闪回行为。新颖性和重要性声明氢燃烧由于不排放二氧化碳，在各种能源应用中起着至关重要的作用。然而，稀预混氢/空气燃烧会带来安全挑战，特别是火焰闪回的形式，可能会导致燃烧室的灾难性故障。理解和控制闪回对于确保氢气的安全和有效使用至关重要，例如在燃气轮机中。通过这项研究，我们解决了一些悬而未决的问题：(i)湍流预混稀100%氢射流火焰边界层闪回的根本原因（ii）从无约束边界层到受限边界层闪回的转变（iii）研究控制火焰闪回的关键参数：刘易斯数和壁面温度。本研究首次证明了湍流预混稀氢燃烧中的闪回是由热扩散不稳定性的特征行为驱动的。

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Low velocity streaks combined with intrinsic flame instabilities provoke boundary layer flashback in a turbulent premixed jet-stabilized hydrogen flame

We report on boundary layer flashback of a turbulent premixed, pure hydrogen flame using well-resolved LES. This numerical work is based on flashback experiments of the TU Delft (TUD) jet flame at a jet Reynolds number of

R e = 11000

. Flashback is a highly sensitive process, which is why (i) the turbulent inflow conditions, (ii) chemistry modeling and (iii) the wall temperatures of the mixing tube are crucial parameters to predict accurately this transient process. The presence of thermo-diffusive flame instabilities is the main contributor for flashback in this setup. We identify quasi-coherent turbulent structures in the mixing tube, namely an ejection event, which transports slow, preheated and hydrogen-enriched fluid away from the wall and triggers the flashback event. As a result, the flame forms a convex cusp upstream of the tube exit pointing towards the unburnt gas mixture. During the transition from unconfined (no walls around the flame) to confined (flame surrounded by walls) boundary-layer flashback, this cusp further bends and propagates towards the jet exit center, while, at the same time, its curvature and the reaction rate of hydrogen significantly increase by a factor of two. We repeated the flashback simulations several times and also for various flow conditions: all cases feature the same FB characteristics and, hence, confirms the generality of the conclusions. Moreover, the numerical flashback mechanism confirms the process hypothesized by the experiments. Based on the identified governing key parameters that affect flame flashback, we performed parametric variations of the Lewis number and wall temperature. By varying the Lewis number, we can clearly state that the flashback is driven by thermo-diffusive instabilities, while a hotter wall significantly deteriorates the flashback behavior of this setup.

Novelty and significance statement

Hydrogen combustion plays a crucial role in various energy applications due to no CO₂ emissions. However, lean premixed hydrogen/air combustion can lead to safety challenges, particularly in the form of flame flashback, potentially causing catastrophic failures in combustion chambers. Understanding and controlling flashback is essential to ensure the safe and efficient use of hydrogen for instance in gas turbines. With this study, we address a number of open questions:

(i) root cause of boundary layer flashback in turbulent premixed lean 100% hydrogen jet flames.

(ii) transition from unconfined to confined boundary layer flashback.

(iii) investigate key parameters that govern flame flashback: Lewis number and wall temperature.

This study demonstrates for the first time that flashback in turbulent premixed lean hydrogen combustion is driven by the characteristic behavior of thermo-diffusive instabilities.

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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.