Coupling regimes of premixed laminar flames with thermal radiation absorption in fresh gases. Application to H2O-/CO2-diluted mixtures

IF 5.8 2区 工程技术 Q2 ENERGY & FUELS
J. Ben Zenou, R. Vicquelin
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引用次数: 0

Abstract

In the context of decarbonizing industry and transportation, the combustion of hydrogen and oxycombustion of methane play a pivotal role. Hydrogen combustion can use steam (H2O) to mitigate pollutant emissions, while methane’s oxycombustion involves recirculating burnt gases (EGR or Exhaust Gas Recirculation process), particularly CO2. This paper investigates the complex role of thermal radiation in premixed laminar flames, in particular in such H2 AirH2O and CH4 O2 CO2 mixtures. It highlights how radiation assumes a significant role in flames diluted with radiative participating gases, through both emission and reabsorption. The main objective is to achieve a comprehensive physical understanding of the coupling between thermal radiation and combustion, examining its effects on flame structure and burning velocity and how it varies with different parameters (equivalence ratio, dilution level, pressure, and domain size). The study employs detailed 1D premixed laminar flame simulations by coupling a fluid and a radiative solver. Both a grey gas approximation for preliminary understanding and realistic radiative gas properties (CK model) are considered. Coupling numbers derived from characteristic time ratios for convection, chemistry, and radiation, are presented. These metrics facilitate the classification of radiation-combustion coupling into three distinct regimes that represent distinct qualitative physical phenomena. The regimes are defined as follows: WeakAbs, where the effects of thermal radiation absorption are minor; RadConv, where thermal radiation competes with convection in the fresh and burnt gases but does not interact directly with chemistry within the flame front; and RadChem, where thermal radiation also competes with chemistry within the flame front. For the investigated conditions in both H2 and CH4 flames, thermal radiation also quantitatively alters the flame speed, with an acceleration that can be significant. Furthermore, the paper presents an iterative two-layer model to efficiently estimate the impact of thermal radiation on flames, which shows high accuracy except in the RadChem regime. Lastly, it introduces a predictive model that quickly determines a flame’s coupling regime using only an adiabatic simulation, helping in deciding to neglect, approximate, or fully integrate radiation in premixed diluted flame simulations.
新鲜气体中预混合层流火焰与热辐射吸收的耦合机制。在 H2O-/CO2 稀释混合物中的应用
在工业和运输业去碳化的背景下,氢气燃烧和甲烷富氧燃烧发挥着举足轻重的作用。氢气燃烧可以利用蒸汽(H2O)来减少污染物排放,而甲烷的富氧燃烧则涉及燃烧气体的再循环(EGR 或废气再循环过程),尤其是二氧化碳。本文研究了热辐射在预混合层流火焰中的复杂作用,特别是在 H2 AirH2O 和 CH4 O2 CO2 混合物中。它强调了辐射是如何通过发射和再吸收两种方式在被辐射参与气体稀释的火焰中发挥重要作用的。研究的主要目的是全面了解热辐射与燃烧之间的物理耦合,研究其对火焰结构和燃烧速度的影响,以及如何随不同参数(当量比、稀释程度、压力和域尺寸)而变化。研究通过耦合流体和辐射求解器,采用了详细的一维预混层流火焰模拟。既考虑了用于初步理解的灰色气体近似,也考虑了现实的辐射气体特性(CK 模型)。介绍了根据对流、化学和辐射的特征时间比得出的耦合数。这些指标有助于将辐射-燃烧耦合分为代表不同定性物理现象的三种截然不同的状态。这三种状态的定义如下弱吸收(WeakAbs),热辐射吸收的影响较小;辐射对流(RadConv),热辐射与新鲜气体和燃烧气体中的对流竞争,但不直接与火焰前沿内的化学反应相互作用;辐射化学(RadChem),热辐射也与火焰前沿内的化学反应竞争。在所研究的 H2 和 CH4 火焰条件下,热辐射也会定量改变火焰速度,其加速度可能很大。此外,论文还提出了一种迭代双层模型,用于有效估算热辐射对火焰的影响,该模型除在 RadChem 体系外均显示出很高的准确性。最后,论文介绍了一种预测模型,该模型仅使用绝热模拟就能快速确定火焰的耦合机制,有助于决定在预混合稀释火焰模拟中忽略、近似或完全整合辐射。
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来源期刊
Combustion and Flame
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.
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