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Flame structure of single aluminum droplets burning in hot steam-dominated flows

Wu, Zhiyong LU orcid ; Ruan, Can LU ; Qiu, Yue LU ; Stiti, Mehdi LU ; Xu, Shijie LU orcid ; Jüngst, Niklas LU ; Berrocal, Edouard LU ; Aldén, Marcus LU ; Bai, Xue Song LU and Li, Zhongshan LU (2025) In Combustion and Flame 271.
Abstract

In this work, a specially designed experimental setup is employed to study the ignition and combustion of single aluminum droplets in hot steam-dominated flows. The transient burning behaviors of Al droplets of different sizes are characterized by simultaneously visualizing the flame incandescence and droplet shadowgraphs with two high-speed cameras at high magnification. The combustion process can be described in three stages: Al ignition and droplet generation, droplet evaporation and flame development, and steady combustion. During the steady combustion stage, a bright flame sheet, characterized by a narrow layer of dense nano-micron-sized alumina droplets, encapsulates the Al droplet core. The flame sheet composed of alumina... (More)

In this work, a specially designed experimental setup is employed to study the ignition and combustion of single aluminum droplets in hot steam-dominated flows. The transient burning behaviors of Al droplets of different sizes are characterized by simultaneously visualizing the flame incandescence and droplet shadowgraphs with two high-speed cameras at high magnification. The combustion process can be described in three stages: Al ignition and droplet generation, droplet evaporation and flame development, and steady combustion. During the steady combustion stage, a bright flame sheet, characterized by a narrow layer of dense nano-micron-sized alumina droplets, encapsulates the Al droplet core. The flame sheet composed of alumina droplets is located on a stagnation plane where the radial velocities relative to the droplet core are close to zero. The standoff ratio is around two, and it slightly decreases with the droplet size and increases with the oxygen content in the ambient gas. The thickness of the flame sheet (the alumina particle layer) is analyzed using Abel inversion of the projected profile of the flame incandescence and optical depth, revealing a thickness of about 50 μm for a burning droplet of a 550 μm diameter. Based on the shadowgraph images, the evaporation rate of the Al droplets is determined from the shrinking rate of the droplet projected area. Size-dependent evaporation rates are found to be related to different slip velocities, and the addition of oxygen to the oxidizer can significantly increase the evaporation rate. Finally, a conceptual model of a burning Al droplet in the steady combustion stage is proposed based on the experimental findings. The presented results provide novel datasets that contribute to model development and deepen the understanding of the physical and chemical processes involved in aluminum droplet combustion.

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author
; ; ; ; ; ; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Al/steam combustion, Aluminum evaporation, Flame structure, Spatiotemporal diagnostics
in
Combustion and Flame
volume
271
article number
113838
pages
11 pages
publisher
Elsevier
external identifiers
  • scopus:85208298972
ISSN
0010-2180
DOI
10.1016/j.combustflame.2024.113838
language
English
LU publication?
yes
additional info
Publisher Copyright: © 2024 The Authors
id
83e51454-3332-49a6-b7d6-14eed24fc875
date added to LUP
2024-11-16 21:55:16
date last changed
2025-04-04 14:43:52
@article{83e51454-3332-49a6-b7d6-14eed24fc875,
  abstract     = {{<p>In this work, a specially designed experimental setup is employed to study the ignition and combustion of single aluminum droplets in hot steam-dominated flows. The transient burning behaviors of Al droplets of different sizes are characterized by simultaneously visualizing the flame incandescence and droplet shadowgraphs with two high-speed cameras at high magnification. The combustion process can be described in three stages: Al ignition and droplet generation, droplet evaporation and flame development, and steady combustion. During the steady combustion stage, a bright flame sheet, characterized by a narrow layer of dense nano-micron-sized alumina droplets, encapsulates the Al droplet core. The flame sheet composed of alumina droplets is located on a stagnation plane where the radial velocities relative to the droplet core are close to zero. The standoff ratio is around two, and it slightly decreases with the droplet size and increases with the oxygen content in the ambient gas. The thickness of the flame sheet (the alumina particle layer) is analyzed using Abel inversion of the projected profile of the flame incandescence and optical depth, revealing a thickness of about 50 μm for a burning droplet of a 550 μm diameter. Based on the shadowgraph images, the evaporation rate of the Al droplets is determined from the shrinking rate of the droplet projected area. Size-dependent evaporation rates are found to be related to different slip velocities, and the addition of oxygen to the oxidizer can significantly increase the evaporation rate. Finally, a conceptual model of a burning Al droplet in the steady combustion stage is proposed based on the experimental findings. The presented results provide novel datasets that contribute to model development and deepen the understanding of the physical and chemical processes involved in aluminum droplet combustion.</p>}},
  author       = {{Wu, Zhiyong and Ruan, Can and Qiu, Yue and Stiti, Mehdi and Xu, Shijie and Jüngst, Niklas and Berrocal, Edouard and Aldén, Marcus and Bai, Xue Song and Li, Zhongshan}},
  issn         = {{0010-2180}},
  keywords     = {{Al/steam combustion; Aluminum evaporation; Flame structure; Spatiotemporal diagnostics}},
  language     = {{eng}},
  publisher    = {{Elsevier}},
  series       = {{Combustion and Flame}},
  title        = {{Flame structure of single aluminum droplets burning in hot steam-dominated flows}},
  url          = {{http://dx.doi.org/10.1016/j.combustflame.2024.113838}},
  doi          = {{10.1016/j.combustflame.2024.113838}},
  volume       = {{271}},
  year         = {{2025}},
}