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Numerical studies on intrinsically unstable H2/CO2 flames: Effect of CO2 dilution, equivalence ratio, temperature and pressure

IF 6.2 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame Pub Date : 2025-07-01 DOI:10.1016/j.combustflame.2025.114307

Mayank Pandey, Krishnakant Agrawal, Anjan Ray

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引用次数: 0

Abstract

Direct combustion of H

_{2}

/CO

_{2}

gas mixtures obtained from the gasification and steam reforming processes can help avoid CO

_{2}

separation costs and safety concerns associated with the fast combustion of pure hydrogen as a fuel. This work studies the effect of varying CO

_{2}

concentrations in hydrogen-air flames through detailed numerical simulations (DNS) as well as canonical flame calculations. The species transport budget calculated using one-dimensional freely propagating flames shows dominance of diffusion against convection with increase in CO

_{2}

percentage. Similarly, an increase in reaction rate and negative Markstein length is observed for flames under strain, suggesting enhanced thermodiffusive response. Quantification of thermodiffusive instability in linear and non-linear flame propagation regimes has been performed for CO

_{2}

-rich hydrogen-air mixtures using two-dimensional freely propagating flames in a classical inflow, outflow and periodic domain for a range of equivalence ratios (0.8–1.1), unburned temperatures (300 K–700 K) and pressures (1 atm–8 atm). The growth rate of perturbation amplitude increases with decreasing the equivalence ratio and temperature, and increases with CO

_{2}

dilution and pressure, enhancing intrinsic instability. The flame propagates with a finger-like structure with increasing propensity of subadiabatic and superadiabatic regions for mixtures corresponding to higher growth rates. These findings will further the understanding of burning characteristics of H

_{2}

/CO

_{2}

/air mixtures when used in practical combustion devices.

Novelty and significance statement

Direct combustion of H

_{2}

/CO

_{2}

fuel mixtures can provide different low-cost pathways for grey hydrogen utilization. Such mixtures are known to exhibit intrinsic flame instabilities, especially of a thermodiffusive nature. This work presents a one-dimensional assessment of the convective, diffusive, reactive balance of H

_{2}

/CO

_{2}

fuel-air flames and their response to flow-stretch, which confirms the sensitivity of their thermodiffusive nature towards instabilities. The main novelty lies in the demonstration of thermodiffusive instabilities in H

_{2}

/CO

_{2}

fuel-air mixtures using two dimensional direct numerical simulations (DNS) and assessing sensitivities of instability growth rates and overall consumption speed to mixture equivalence ratio, unburnt temperature and pressure. Further, the relative impact of flame wrinkling and local differential diffusion on consumption speed enhancement for such mixtures has been quantified for the first time. Such insights make this study significant for understanding the combustion of H

_{2}

/CO

_{2}

/air mixture when used in practical applications.

查看原文本刊更多论文

本质不稳定H2/CO2火焰的数值研究：CO2稀释度、当量比、温度和压力的影响

直接燃烧从气化和蒸汽重整过程中获得的H2/CO2气体混合物可以帮助避免二氧化碳分离成本和与纯氢作为燃料的快速燃烧相关的安全问题。本文通过详细的数值模拟（DNS）和典型火焰计算，研究了不同CO2浓度对氢气-空气火焰的影响。利用一维自由传播火焰计算的物种输运收支表明，随着CO2浓度的增加，扩散对对流占优势。同样，在应变下火焰的反应速率和负Markstein长度增加，表明热扩散响应增强。在等效比（0.8-1.1）、未燃烧温度（300 K - 700 K）和压力（1 atm - 8 atm）范围内，利用经典的二维自由传播火焰，对富二氧化碳氢-空气混合物在线性和非线性火焰传播机制中的热扩散不稳定性进行了量化。扰动幅度的增长率随当量比和温度的降低而增大，随CO2稀释度和压力的增大而增大，增强了内在不稳定性。火焰以手指状结构传播，随着混合物的亚绝热区和超绝热区倾向的增加，相应的生长速率更高。这些发现将进一步理解H2/CO2/空气混合物在实际燃烧装置中的燃烧特性。新颖性和意义陈述直接燃烧H2/CO2燃料混合物为灰氢利用提供了不同的低成本途径。已知这种混合物具有固有的火焰不稳定性，特别是具有热扩散性质。这项工作提出了对H2/CO2燃料-空气火焰的对流、扩散、反应平衡及其对流动拉伸的响应的一维评估，这证实了它们的热扩散性质对不稳定性的敏感性。主要的新颖之处在于利用二维直接数值模拟（DNS）证明了H2/CO2燃料-空气混合物的热扩散不稳定性，并评估了不稳定性增长率和总体消耗速度对混合物等效比、未燃烧温度和压力的敏感性。此外，首次量化了火焰起皱和局部微分扩散对这种混合物消耗速度提高的相对影响。这些见解使得这项研究对于理解H2/CO2/空气混合物在实际应用中的燃烧具有重要意义。

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.