Transient flameout process of boron-magnesium agglomerates during combustion in oxygen-rich atmospheres--颗粒学报PARTICUOLOGY

Duan, L., Xia, Z., Feng, Y., Chen, B., Ma, L., & Hu, J. (2024). Transient flameout process of boron-magnesium agglomerates during combustion in oxygen-rich atmospheres. Particuology, 88, 290-301. https://doi.org/10.1016/j.partic.2023.10.002

Transient flameout process of boron-magnesium agglomerates during combustion in oxygen-rich atmospheres

Lian Duan ^a, Zhixun Xia ^a, Yunchao Feng ^a, Binbin Chen ^a *, Likun Ma ^a, Jianxin Hu ^b

a College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073, China
b School of Mechanical Engineering and Mechanics, Xiangtan University, Xiangtan 411105, China

10.1016/j.partic.2023.10.002

Volume 88, May 2024, Pages 290-301

Received 23 July 2023, Revised 18 September 2023, Accepted 4 October 2023, Available online 28 October 2023, Version of Record 11 November 2023.

E-mail: chenbinbin11@nudt.edu.cn

Highlights

• B–Mg agglomerates of varying mass ratios were combusted under various O₂ contents.

• Transient flameout was found to occur, being promoted by higher Mg and O₂ contents.

• Upon fading of the flame intensity, a dark film coated the particles.

• This film inhibits surface and gas-phase reactions, leading to transient flameout.

Abstract

In this study, boron–magnesium agglomerates with varying mass ratios were prepared by drying a micron-sized boron–magnesium mixed suspension, and the combustion process of these agglomerates under different oxygen-rich concentrations were investigated using a laser ignition system. The test results showed that when the mass fraction of magnesium powder in boron-magnesium agglomerates exceeded a certain threshold (between 2% and 5%), flame extinction and reignition occurred after a significant reduction in the agglomerate volume during combustion. This process is referred to as the transient flameout process, which is affected by the magnesium content of the agglomerate and the oxygen concentration in the ambient atmosphere. An increase in the magnesium content or oxygen concentration makes this phenomenon more pronounced. During weakening of the flame intensity, a dark film gradually covered the particle surfaces. X-ray diffraction and elemental analyses of the cross-section and outer surface of the condensed combustion product suggested that the dark film is primarily composed of Mg-B-O ternary oxides. This film prevents direct contact between boron and oxygen, thereby inhibiting surface and gas-phase reactions and leading to the occurrence of the transient flameout phenomenon.

Graphical abstract

Keywords

Agglomerated particle; Boron–magnesium fuel; Boron combustion; Transient flameout process; Solid fuel ramjet

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