Extinction limit and NO/N2O formation of methanol/ammonia counterflow diffusion flames under elevated conditions

IF 6.2 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame Pub Date : 2025-10-11 DOI:10.1016/j.combustflame.2025.114520

Peng Ma , Shumeng Xie , Jinzhou Li , Samir B. Rojas Chavez , Hao Hu , Huangwei Zhang

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引用次数: 0

Abstract

To address ammonia’s low reactivity, the interest in co-firing with methanol, a conventional green transportation fuel in internal combustion engines, is steadily growing. However, the effects of methanol on ammonia flame extinction and NO_x are unknown. In this study, we examine the influence of methanol addition on ammonia flame stability under elevated conditions, based on the counterflow diffusion flame via numerical simulations using detailed chemical kinetics and chemical explosive mode analysis. Our analysis shows that methanol addition significantly extends extinction strain rate and introduces a two-stage explosive mode structure under high strain rate conditions. At 1 atm, a small methanol addition (energy fraction of CH₃OH in fuels E_CH3OH=5%) increases the extinction strain rate by 13%, and with E_CH3OH = 50%, the extinction strain rate is nearly 4.75 times higher than that of pure ammonia. This is primarily attributed to the enhanced OH radical production, which shows a strong positive correlation with flame extinction limits. Moreover, elevated pressures and oxidizer preheating further expands the extinction strain rate. Pressure effects are primarily linked to increased local heat release rate despite lower radical mole fraction. Methanol has minimal influence on the pressure–extinction relationship. Furthermore, methanol blending slightly increases NO formation via enhanced HNO and fuel-N pathways but simultaneously reduces N₂O emissions due to accelerated radical-driven consumption. Methanol addition significantly alters the radical chemistry by introducing CH₂OH as a key intermediate, shifting OH formation from the conventional O₂ + H pathway to a new dominant route via O₂ + CH₂OH → HO₂ → OH. This work provides new insights into the extinction characteristics and nitrogen chemistry of NH₃/CH₃OH flames under realistic conditions, supporting the design of cleaner and more efficient ammonia-based energy systems.

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升高条件下甲醇/氨逆流扩散火焰的熄灭极限和NO/N2O生成

为了解决氨的低反应性，人们对与甲醇（内燃机中传统的绿色运输燃料）共烧的兴趣正在稳步增长。然而，甲醇对氨灭焰和NOx的影响尚不清楚。在这项研究中，我们通过详细的化学动力学和化学爆炸模式分析的数值模拟，研究了甲醇添加对高浓度条件下氨火焰稳定性的影响。分析表明，在高应变率条件下，甲醇的加入显著延长了消光应变率，并引入了两段爆炸模式结构。在1atm时，少量甲醇的加入（燃料中CH3OH的能量分数ECH3OH=5%）可使消光应变率提高13%，当ECH3OH= 50%时，消光应变率是纯氨的近4.75倍。这主要是由于OH自由基的生成增加，这与火焰熄灭极限呈强烈的正相关。此外，压力升高和氧化剂预热进一步扩大了消光应变速率。压力效应主要与局部热释放率的增加有关，尽管自由基摩尔分数较低。甲醇对压力消光关系的影响最小。此外，甲醇混合通过增强的HNO和燃料n途径略微增加了NO的形成，但同时由于自由基驱动的消耗加速，减少了N2O的排放。甲醇的加入通过引入CH2OH作为关键中间体，将传统的O2 + H途径转变为O2 + CH2OH→HO2→OH的新主导途径，显著改变了自由基的化学性质。这项工作为现实条件下NH3/CH3OH火焰的熄灭特性和氮化学提供了新的见解，为设计更清洁、更高效的氨基能源系统提供了支持。

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.