Visualization of unsteady combustion of single aluminum droplets: coalescence, eruption and fragmentation
Wu, Zhiyong LU
; Ruan, Can
LU
; Sun, Jinguo
LU
; Jüngst, Niklas
LU
; Aldén, Marcus
LU
and Li, Zhongshan
LU
(2025)
In Combustion and Flame
275.
- Abstract
- Detailed characterization of the unsteady combustion behaviors of individual aluminum (Al) droplets is scarce, due to the experimental challenges in resolving the transient phenomena at the micrometer scale. In this work, we spatiotemporally elucidate the complex interplay, including droplet coalescence, eruption, and fragmentation, of individually burning Al droplets and alumina (Al2O3) products, in a hot H₂O/N₂/O₂ flow. Flame incandescence and droplet shadowgraphs are simultaneously imaged using two high-speed cameras, and the surface temperature evolution is tracked in separate measurements via high-speed two-color pyrometry imaging. Initially, the Al droplet burns in a symmetric phase, during which a visible flame sheet fully... (More)
- Detailed characterization of the unsteady combustion behaviors of individual aluminum (Al) droplets is scarce, due to the experimental challenges in resolving the transient phenomena at the micrometer scale. In this work, we spatiotemporally elucidate the complex interplay, including droplet coalescence, eruption, and fragmentation, of individually burning Al droplets and alumina (Al2O3) products, in a hot H₂O/N₂/O₂ flow. Flame incandescence and droplet shadowgraphs are simultaneously imaged using two high-speed cameras, and the surface temperature evolution is tracked in separate measurements via high-speed two-color pyrometry imaging. Initially, the Al droplet burns in a symmetric phase, during which a visible flame sheet fully encapsulates the Al droplet. This is frequently followed by an unsteady asymmetric stage where the droplet locally breaks or entirely fragments. The transition from symmetric to asymmetric combustion is triggered by the coalescence of high-temperature Al2O3 satellite droplets with the parent Al core, forming a Janus droplet with two immiscible components (the Al2O3 cap and the Al core). This coalescence rapidly heats the interfacial surface to temperatures above the Al boiling point, causing a sharp increase in Al vapor pressure and high vaporization rates, i.e., Al vapor ejection. The ejection is driven by a temperature gradient between the Al2O3 cap and the contacted Al surface. The Janus droplet morphology is quantitatively analyzed to derive the interfacial tension between the liquid Al and Al2O3, enabling predictions of the droplet's cross-sectional geometry at various stages. Furthermore, ex-situ sample analysis shows that the eruption significantly enhances the formation of nanometer Al2O3 particles. These observations advance the understanding of the unsteady behaviors inherent to Al droplet combustion. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/0c22f831-bb76-4a68-a940-0dad9d981c9a
- author
- Wu, Zhiyong
LU
; Ruan, Can
LU
; Sun, Jinguo
LU
; Jüngst, Niklas
LU
; Aldén, Marcus
LU
and Li, Zhongshan
LU
- organization
- publishing date
- 2025-03-11
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- Aluminum combustion, Droplet coalescence, Eruption and fragmentation, Janus droplet, Optical diagnostics
- in
- Combustion and Flame
- volume
- 275
- article number
- 114103
- pages
- 13 pages
- publisher
- Elsevier
- external identifiers
-
- scopus:86000656510
- ISSN
- 0010-2180
- DOI
- 10.1016/j.combustflame.2025.114103
- language
- English
- LU publication?
- yes
- id
- 0c22f831-bb76-4a68-a940-0dad9d981c9a
- date added to LUP
- 2025-03-17 21:00:51
- date last changed
- 2025-06-05 04:07:01
@article{0c22f831-bb76-4a68-a940-0dad9d981c9a,
abstract = {{Detailed characterization of the unsteady combustion behaviors of individual aluminum (Al) droplets is scarce, due to the experimental challenges in resolving the transient phenomena at the micrometer scale. In this work, we spatiotemporally elucidate the complex interplay, including droplet coalescence, eruption, and fragmentation, of individually burning Al droplets and alumina (Al2O3) products, in a hot H₂O/N₂/O₂ flow. Flame incandescence and droplet shadowgraphs are simultaneously imaged using two high-speed cameras, and the surface temperature evolution is tracked in separate measurements via high-speed two-color pyrometry imaging. Initially, the Al droplet burns in a symmetric phase, during which a visible flame sheet fully encapsulates the Al droplet. This is frequently followed by an unsteady asymmetric stage where the droplet locally breaks or entirely fragments. The transition from symmetric to asymmetric combustion is triggered by the coalescence of high-temperature Al2O3 satellite droplets with the parent Al core, forming a Janus droplet with two immiscible components (the Al2O3 cap and the Al core). This coalescence rapidly heats the interfacial surface to temperatures above the Al boiling point, causing a sharp increase in Al vapor pressure and high vaporization rates, i.e., Al vapor ejection. The ejection is driven by a temperature gradient between the Al2O3 cap and the contacted Al surface. The Janus droplet morphology is quantitatively analyzed to derive the interfacial tension between the liquid Al and Al2O3, enabling predictions of the droplet's cross-sectional geometry at various stages. Furthermore, ex-situ sample analysis shows that the eruption significantly enhances the formation of nanometer Al2O3 particles. These observations advance the understanding of the unsteady behaviors inherent to Al droplet combustion.}},
author = {{Wu, Zhiyong and Ruan, Can and Sun, Jinguo and Jüngst, Niklas and Aldén, Marcus and Li, Zhongshan}},
issn = {{0010-2180}},
keywords = {{Aluminum combustion; Droplet coalescence; Eruption and fragmentation; Janus droplet; Optical diagnostics}},
language = {{eng}},
month = {{03}},
publisher = {{Elsevier}},
series = {{Combustion and Flame}},
title = {{Visualization of unsteady combustion of single aluminum droplets: coalescence, eruption and fragmentation}},
url = {{http://dx.doi.org/10.1016/j.combustflame.2025.114103}},
doi = {{10.1016/j.combustflame.2025.114103}},
volume = {{275}},
year = {{2025}},
}