A Study of the Combustion Behaviour of Pyrotechnic Whistle Devices (Acoustic and Chemical Factors)

M. Podlesak and M. A. Wilson

ABSTRACT: Pyrotechnic whistles have long been used in both civilian and military applications. It is known that, under certain conditions, these compositions burn in an oscillatory manner and have exhibited a tendency occasionally to explode with great power during combustion. Based on the results of experimental work and a study of the thermochemical properties of whistle fuels, a hypothesis is proposed that attempts to account for the observed high levels of explosive and acoustic power of pyrotechnic whistles. The formation of < 10 μm diameter hollow carbon spheres was observed in laboratory experiments involving the thermal decomposition of potassium benzoate (a whistle fuel) in a reducing atmosphere. At the moment of formation, the spheres may possibly be filled with combustible hydrocarbon gases and would be extremely reactive. If formed during the quiet cycles of an operating whistle device, their existence may explain the higher than expected acoustic power of pyrotechnic whistles. Such a hypothesis may also lead to an understanding of other hitherto unexplained  explosions, where under conditions such as ‘cook-off’, the thermal decomposition of organic fuels used in some other pyrotechnics would result in the formation of new substances which are more reactive than the parent chemicals.

Keywords: whistle, combustion, acoustics, oscillating burning, pyrotechnics

Ref: JPyro, Issue 17, 2003, pp19-34

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