Impact of the operating conditions on the OH* distribution and its correlation with the heat release rate in hydrogen–air flames

IF 6.2 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame Pub Date : 2025-09-12 DOI:10.1016/j.combustflame.2025.114452

Francesco G. Schiavone , Marco Torresi , Sergio M. Camporeale , Davide Laera

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引用次数: 0

Abstract

OH* chemiluminescence is widely used as heat release rate (HRR) marker in combustion experiments. Still, its suitability for hydrogen–air flames has not been extensively assessed for a wide range of operative conditions and flame archetypes. In the present work, correlations between OH* and HRR spatial distributions are first investigated in one-dimensional unstretched laminar premixed flames at variable pressure ([1; 20] atm), unburned gas temperature ([300; 900] K), and equivalence ratio ([0.3; 3.0]). At atmospheric pressure and unburned gas temperature, two main differences are observed: a characteristic shift between the OH* and HRR peak positions and, for equivalence ratios close to stoichiometry, the presence of a non-negligible concentration of OH* in the post-flame zone, where the HRR value is zero. When pressure and unburned gas temperature are increased, the peak shift is attenuated, while the OH* concentration in the burned gases is favored.

For lean (

ϕ = 0.35

) and stoichiometric mixtures, the effects of strain and curvature contributions of flame stretch are analyzed in one-dimensional counterflow flames and two-dimensional expanding flames. Higher strain rates slightly affect the peak shift, but sensibly enhance the production of OH* in the burned gas region. Stretch strongly impacts on expanding lean flames, for which the onset of intrinsic instabilities worsens the OH*-HRR correlation, in terms both of distribution shape and intensity.

Finally, nonpremixed one-dimensional counterflow diffusion flames and a more complex two-dimensional triple flame are analyzed. In both configurations, a significant reduction of the peak shift is observed when the combustion occurs in diffusion-controlled regimes, sustaining the adequacy of OH* as HRR marker for hydrogen–air diffusion flames under various operating conditions.

Novelty and significance statement

This work presents a systematic investigation of the OH* distribution and its correlation with the heat release rate in several canonical premixed and nonpremixed laminar hydrogen–air flames under various operating conditions, extending the current literature on the subject.

The chemical pathways leading to the peculiar behavior observed for stoichiometric flames are investigated, and the interaction of OH* with intrinsic thermodiffusive instabilities in lean flames is analyzed, showing how the correlation with the heat release rate is worsened.

A coherent methodology to quantitatively assess heat release surrogates, which can be extended to other measurable quantities, is provided too.

This knowledge is significant as it underlines how the parametric variation of operating conditions can differently affect the correlation between the OH* and the heat release rate distributions, highlighting the limits of OH*chemiluminescence as a combustion diagnostic technique to validate numerical simulations.

查看原文本刊更多论文

操作条件对氢-空气火焰中OH*分布的影响及其与放热速率的关系

OH*化学发光在燃烧实验中被广泛用作热释放率（HRR）的标记。尽管如此，它对氢气-空气火焰的适用性还没有在广泛的操作条件和火焰原型中得到广泛的评估。本文首先研究了一维未拉伸层流预混火焰在变压力（[1;20]atm）、未燃烧气体温度（[300;900]K）和等效比（[0.3;3.0]）下OH*和HRR空间分布之间的相关性。在大气压力和未燃烧气体温度下，观察到两个主要的差异：OH*和HRR峰位置之间的特征位移，对于接近化学计量的当量比，在火焰后区域存在不可忽略的OH*浓度，其中HRR值为零。当压力和未燃气体温度升高时，峰移减弱，而燃烧气体中的OH*浓度升高。对于精益（φ =0.35）和化学计量混合物，在一维逆流火焰和二维膨胀火焰中分析了火焰拉伸的应变和曲率贡献的影响。较高的应变速率对峰值位移影响较小，但显著提高了燃烧气区的OH*生成。拉伸对扩张的贫火焰有强烈的影响，其内在不稳定性的发生使OH*-HRR相关性在分布形状和强度上都恶化。最后，对非预混一维逆流扩散火焰和更复杂的二维三重火焰进行了分析。在这两种结构中，当燃烧发生在扩散控制状态时，观察到峰移的显著减少，在各种操作条件下维持OH*作为氢-空气扩散火焰的HRR标记的充分性。本文系统地研究了几种典型的预混和非预混层流氢-空气火焰在不同工况下的OH*分布及其与放热速率的关系，扩展了现有的相关文献。研究了导致化学计量火焰中所观察到的特殊行为的化学途径，并分析了贫火焰中OH*与固有热扩散不稳定性的相互作用，表明其与放热速率的相关性如何恶化。还提供了一种定量评估热释放替代物的连贯方法，该方法可以扩展到其他可测量的量。这一知识是重要的，因为它强调了操作条件的参数变化如何不同地影响OH*和热释放率分布之间的相关性，突出了OH*化学发光作为一种燃烧诊断技术来验证数值模拟的局限性。

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.