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Combustion of particles, agglomerates, and suspensions - A basic thermophysical analysis

机译：颗粒，附聚物和悬浮液的燃烧-基本热物理分析

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Ignition and combustion of single particles, particle agglomerates, and suspensions are analyzed using a simple thermophysical approach that considers ideal, non-volatile fuel particles undergoing heterogeneous reaction controlled by a combination of diffusion and kinetic rates. This approximation is useful to describe the combustion behavior in suspensions of refractory metal-fuel particles, where the lack of significant premixing of fuel vapor with oxidizer can lead to combustion in a diffusion micro-flame enveloping the particle. The transition from kinetic heterogeneous-fuel oxidation to diffusion-controlled combustion occurs via thermal runaway, customarily called particle ignition. There is, however, a critical particle size below which an individual particle cannot ignite at any temperature, and the combustion will be controlled by heterogeneous kinetics at a temperature close to that of the bulk gas. While individual particles may not be able to ignite, the collective effect, which results from the self-heating of particle suspensions to thermal runaway, can enable fast reaction in suspensions. Micron- and sub-micron-sized fuel particles are used for their high reactivity, but such particles often agglomerate before combustion. The ignition and combustion behavior of an agglomerate can be drastically different from its isolated constituent particles due to a large internal surface area inside of the agglomerate that is partially accessible to oxidizer, while only the external surface area of the agglomerate is available for heat loss. It is shown that the interplay between the thermal regimes of reaction, the collective effects of the suspension, and the collective effects of agglomeration can lead to a wide range of observed ignition and combustion phenomena that are independent of the material-specific fuel and oxide properties. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
机译：使用简单的热物理方法分析单个颗粒，颗粒团聚体和悬浮液的点火和燃烧，该方法考虑了理想的非挥发性燃料颗粒，它们通过扩散和动力学速率的组合进行异质反应。该近似值可用于描述难熔金属燃料颗粒悬浮液中的燃烧行为，在这种情况下，燃料蒸气与氧化剂之间没有明显的预混合会导致包围该颗粒的扩散微火焰中燃烧。从动力异质燃料氧化到扩散控制燃烧的过渡是通过热失控发生的，通常称为颗粒点火。但是，存在一个临界粒径，在这个临界粒径以下，单个粒子在任何温度下都不会点燃，并且燃烧将通过异质动力学控制，温度接近于整体气体的温度。尽管单个粒子可能无法点燃，但粒子悬浮液自加热到热失控所产生的集体效应可以使悬浮液快速反应。使用微米级和亚微米级的燃料颗粒具有较高的反应性，但此类颗粒通常在燃烧前发生团聚。团块的着火和燃烧行为可能与团块的分离成分完全不同，这是由于团块内部的内表面积较大，氧化剂可以部分进入该团块，而只有团块的外表面积可用于热损失。结果表明，反应的热态，悬浮液的集体效应和团聚的集体效应之间的相互作用可以导致观察到的广泛的着火和燃烧现象，而与材料特定的燃料和氧化物性质无关。 （C）2018年燃烧研究所。由Elsevier Inc.出版。保留所有权利。

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