蒸汽稀释对NH3/O2/H2O预混火焰的物理化学影响

IF 6.2 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame Pub Date : 2025-02-24 DOI:10.1016/j.combustflame.2025.114074

Yu Zhang, Bo Han, Jinqi Zhu, Wenda Zhang, Linyao Zhang, Yijun Zhao, Shaozeng Sun

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The effects of steam dilution are decoupled into physical (dilution effect, thermal effect, transport effect, radiation effect) and chemical effects (direct reaction effect and third-body effect) to investigate the competitive and synergistic mechanisms between these effects on the kinetic scale. Results indicate that the NH3 primary decomposition and the H/O radical pools determine NH3/O2/H2O flame speed. H/O radical formation and NH3 staged dehydrogenation dominate the heat release and consumption, respectively. NO is mainly produced from HNO and NH radicals, and the reduction reactions of NHi(i=0–2) and NNH-N2O mechanism dominate NO consumption in NH3/O2/H2O flame. The dilution effect strongly inhibits SL, Tf, ENO, and κext of NH3/O2/H2O flames, as it reduces fuel concentration and leads to low active radicals. The thermal and radiation effects increase the reaction heat loss to decrease SL, Tf, and κext, while the transport effect helps the rapid reactant diffusion with contrast results. The thermal/radiation/transport effects extend the heat release and OH/HNO accumulation region to increase ENO at fuel-lean conditions. For chemical effects, the direct reaction and third-body effect synergistically suppress Tf and promote ENO, exhibiting competition on SL. Under most conditions, the direct reaction effect dominates the chemical effects, which are reversed at a high dilution ratio (ZH2O). For the extinction strain rate, the direct reaction effect and three-body effect transition from competitive to synergistic with increased ZH2O. 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引用次数: 0

摘要

NH3/O2/H2O燃烧将富氧强化燃烧与蒸汽相结合，控制火焰温度和NOx排放，是未来清洁高效发电的一种很有前途的氨燃烧技术。为了研究NH3/O2/H2O火焰中蒸汽稀释的调节机制，本研究采用预混合自由火焰和逆流动火焰模型，研究蒸汽稀释对层流火焰特性的影响，包括火焰速度（SL）、温度（Tf）、NO排放（ENO）和熄灭应变率（κext）。将蒸汽稀释效应解耦为物理效应（稀释效应、热效应、输运效应、辐射效应）和化学效应（直接反应效应和第三体效应），在动力学尺度上探讨这些效应之间的竞争和协同机制。结果表明，NH3初分解和H/O自由基池决定了NH3/O2/H2O火焰速度。H/O自由基形成和NH3阶段脱氢分别主导了热释放和热消耗。NO主要由HNO和NH自由基产生，NH3/O2/H2O火焰中NO的消耗主要由NHi（i= 0-2）还原反应和NNH-N2O机制主导。稀释效应对NH3/O2/H2O火焰的SL、Tf、ENO和κext有较强的抑制作用，降低了燃料浓度，降低了活性自由基。热效应和辐射效应增加了反应热损失，降低了SL、Tf和κext，而输运效应有助于反应物快速扩散，结果对比明显。在燃料稀薄条件下，热/辐射/输运效应扩大了热量释放和OH/HNO积累区域，从而增加了ENO。在化学效应方面，直接反应和第三体效应协同抑制Tf，促进ENO，在SL上表现出竞争关系。在大多数情况下，直接反应效应主导化学效应，在高稀释比（ZH2O）下则相反。消光应变率随ZH2O的增加，直接反应效应和三体效应由竞争效应向协同效应转变。为了平衡NH3/O2/H2O燃烧效率、燃烧器热阻、排放和火焰稳定性，未来的策略可能包括采用蒸汽分级喷射和RQL （Rich-Quench-Lean）燃烧组织，并结合等离子体辅助/多孔介质燃烧技术来提高燃烧效率、清洁度和火焰稳定性。

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Physical and chemical effects of steam dilution on premixed NH3/O2/H2O flames

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Physical and chemical effects of steam dilution on premixed NH3/O2/H2O flames

NH₃/O_2/H₂O combustion combines oxygen-rich enhanced combustion with steam to control flame temperature and NO_x emissions, and it is a promising ammonia combustion technology for future clean and efficient power generation. For investigating the regulation mechanisms of steam dilution in NH₃/O₂/H₂O flames, this study employed premixed free flame and counterflow flame models to investigate the impact of steam dilution on laminar flame characteristics, including flame speed (S_L), temperature (T_f), NO emissions (E_NO), and extinction strain rate (κ_ext). The effects of steam dilution are decoupled into physical (dilution effect, thermal effect, transport effect, radiation effect) and chemical effects (direct reaction effect and third-body effect) to investigate the competitive and synergistic mechanisms between these effects on the kinetic scale. Results indicate that the NH₃ primary decomposition and the H/O radical pools determine NH₃/O₂/H₂O flame speed. H/O radical formation and NH₃ staged dehydrogenation dominate the heat release and consumption, respectively. NO is mainly produced from HNO and NH radicals, and the reduction reactions of NH_i(i=0–2) and NNH-N₂O mechanism dominate NO consumption in NH₃/O₂/H₂O flame. The dilution effect strongly inhibits S_L, T_f, E_NO, and κ_ext of NH₃/O₂/H₂O flames, as it reduces fuel concentration and leads to low active radicals. The thermal and radiation effects increase the reaction heat loss to decrease S_L, T_f, and κ_ext, while the transport effect helps the rapid reactant diffusion with contrast results. The thermal/radiation/transport effects extend the heat release and OH/HNO accumulation region to increase E_NO at fuel-lean conditions. For chemical effects, the direct reaction and third-body effect synergistically suppress T_f and promote E_NO, exhibiting competition on S_L. Under most conditions, the direct reaction effect dominates the chemical effects, which are reversed at a high dilution ratio (Z_H2O). For the extinction strain rate, the direct reaction effect and three-body effect transition from competitive to synergistic with increased Z_H2O. To balance the NH₃/O₂/H₂O combustion efficiency, combustor thermal resistance, emissions, and flame stability, future strategies may involve adopting steam staged injection and RQL (Rich-Quench-Lean) combustion organization, as well as combining with plasma-assisted/porous media combustion technology to enhance combustion efficiency, cleanliness, and flame stability.

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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.