Introduction
Thermobaric explosives generate their characteristic effects through the coupling of detonation, metallic-fuel combustion and subsequent interactions with oxygen in the surrounding environment. Yet the role of aluminum post-combustion in sustaining the high-temperature blast field has remained difficult to quantify.
In a study published in Energetic Materials Frontiers , Wen-xiang Bian and co-workers compared two CL-20-based thermobaric formulations containing different potassium perchlorate contents with volume-equivalent TNT charges. Their experiments tracked fireball temperature, morphology and hotspot migration, while pressure sensors captured the corresponding blast-wave response. A theoretical model was established to connect fireball temperature and aluminum particle size with combustion completeness.
“Our analysis indicated that the thermobaric effect is not determined solely by the initial detonation,” shares Bian. “Instead, the subsequent combustion of aluminum provides an important source of energy that modifies both the thermal field and the development of the blast wave.”
The results suggested that controlling the balance between oxidizer-driven early combustion and later oxygen-assisted afterburning is central to understanding the performance of thermobaric formulations.
A concentrated fireball reveals the distinctive nature of thermobaric combustion
Infrared imaging shows that thermobaric explosives develop a concentrated and relatively localized hotspot, maintaining a volumetric explosion character throughout the evolving fireball. "This behavior contrasted with the more fragmented combustion observed for TNT,” says Bian. “The difference is also reflected in temperature evolution: immediately after detonation, thermobaric fireballs can exceed same-volume TNT fireballs by more than 1500 °C, while remaining hotter as the fireball expands.”
Oxidizer content determines the balance between early combustion and afterburning
The comparison between TBX30% and TBX5% revealed a clear temporal crossover. During the first 30 ms, the higher-oxidizer TBX30% maintained the higher fireball temperature because more oxidizing products promote rapid ooxygen-deficient combustion of aluminum. After approximately 30 ms, however, TBX5% became hotter as its larger amount of unreacted aluminum participated in secondary combustion with entrained ambient oxygen. After about 60 ms, the temperature histories of the two systems converged. TBX5% also showed more pronounced secondary afterburning and greater hotspot migration, highlighting the different roles of oxidizer-rich and oxidizer-lean formulations.
A temperature-based model identifies a route toward stronger thermobaric output
The team's theoretical analysis provided a quantitative link between fireball temperature and aluminum consumption. The Average Fireball Temperature model predicted mean temperatures of 2863 K for TBX5% and 3001 K for TBX30%, corresponding to aluminum burn-off times of 88 and 43 ms, respectively. “The model predicted that more than 95% of the aluminum can undergo complete combustion in both systems,” says Bian. “The hotter TBX30% fireball enabled a faster and more intense reaction, showing how increasing the early thermal environment can broaden the range of aluminum particles capable of reacting during secondary combustion.”
These findings provide a practical framework for understanding how post-combustion contributes to sustained blast-wave energy, particularly in the far field.
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Contact author details:
School of Chemistry and Chemical Engineering, Nanjing University of Science and Technology, Nanjing, 210094, China. E-mail address: lyn_00446@163.com (Y.-n. Li)
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Energetic Materials Frontiers
A post-combustion reaction model for aluminum in thermobaric effects field
The authors declare the following financial interests which may be considered as potential competing interests: the author Hai-junZhao is currently employed by Ansteel Industrial Micro Fine Aluminum Powder Co., Ltd. The other authors declare that they have no competing interests.