不同压力和氧气条件下并流火焰蔓延率的相关性:地面实验以及与以往微重力、部分重力和正常重力实验的比较

IF 5.8 2区 工程技术 Q2 ENERGY & FUELS
Robin Neupane, Ya- Ting Liao
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引用次数: 0

摘要

环境压力和重力是浮力流中影响火焰向上蔓延过程的重要参数。基于压力建模的概念,本实验研究调查了热稀薄固体燃料在不同压力和氧气条件下的熄灭和火焰向上蔓延过程。实验在不同压力(从 10 kPa 到 100 kPa)和不同氧气摩尔分数(9%-21%)环境下的空气燃烧室中进行。随着压力的增加,观察到不同的燃烧行为:不着火、部分火焰蔓延、稳定火焰蔓延和加速火焰蔓延。随着环境氧摩尔分数的增加,也观察到类似的趋势。在分压条件下(如 25-50 kPa),火焰表现出通常在微重力和分重力环境下观察到的特征:蓝色和暗淡。在不同的压力和氧气水平下,火焰蔓延率和样品燃烧长度均可推导和比较。总体而言,燃烧强度和火焰蔓延率随着环境压力和氧气含量的降低而降低。压力降低时火焰蔓延率降低的原因是火焰间距增加和固体对流传热减少,而氧气摩尔分数降低环境中火焰蔓延率降低的原因是火焰温度降低。最后,利用火焰对峙距离(δf)的概念将目前和以前在不同环境下进行的研究联系起来,而火焰对峙距离是利用理论粘性边界层厚度(δv)估算出来的。研究发现,对于在微重力、部分重力和正常重力条件下获得的数据,在远离熄灭极限的各种环境条件下,近似地计算强制流的δf∼δv 和自然流的δf∼1/3δv 可以合理地预测火焰蔓延率。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Correlating concurrent-flow flame spread rates in different pressure and oxygen conditions: Ground experiments and comparisons with previous micro-, partial, and normal gravities experiments
Ambient pressure and gravity are important parameters in buoyant flow that governs upward flame spread process. Based on the concept of pressure modelling, this experimental study investigates extinction and upward flame spread process of a thermally-thin solid fuel in different pressure and oxygen conditions. Experiments are performed in a combustion chamber in air at different pressures (ranging from 10 kPa to 100 kPa) and different oxygen molar fraction environment (9–21 %). As pressure increases, different burning behaviors are observed: no ignition, partial flame spread, steady flame spread, and accelerating flame spread. Similar trend is observed as the ambient oxygen molar fraction increases. In partial pressure conditions (e.g., 25–50 kPa), flames exhibit characteristics that are typically observed in micro- and partial gravity environments: blue and dim. Flame spread rate and sample burnt length are deduced and compared between different pressure and oxygen levels. Overall, the burning intensity and the flame spread rate decrease with the decrease in ambient pressure and oxygen. The decrease in flame spread rate at reduced pressure is attributed to increase in flame standoff distance and decrease in convective heat transfer to the solid, whereas the decrease in flame spread rate in reduced oxygen molar fraction environment is attributed to decrease in flame temperature. Lastly, current and previous studies performed at different ambient environments are correlated using the concept of flame standoff distance (δf), which is estimated using the theoretical viscous boundary layer thickness (δv). It was found that approximating δfδvfor forced flow and δf1/3δv for natural flow can predict the flame spread rate reasonably well for data obtained in micro-, partial, and normal gravities, for a wide range of environmental conditions away from extinction limits.
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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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