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Abstract: Although the first efforts in understanding pyrotechnic whistles began over fifty years ago, there is still no firmly established mechanism that accurately describes their operation. This review describes the progress made and the current state of knowledge of combustion phenomena in whistle devices. In addition, investigations into identifying alternative safer fuels and additives to increase the striking audio-visual features of these devices are also reported. Finally, it is concluded that despite these great advances in understanding pyrotechnic whistles, there is still some doubt as to their true operating mechanism.

Keywords: pyrotechnic whistle, combustion mechanism, oscillatory combustion, acoustics

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Abstract: A study of the explosive output of rolls of paper toy caps, in variously sized assemblages, was conducted. The testing has shown that toy cap rolls are clearly capable of producing a powerful explosive effect if initiated with a sufficiently energetic event. TNT equivalencies based on toy cap composition mass ranged from approximately 10 to 80% for different sized configurations, with the largest equivalences being produced by the largest assemblages of toy caps tested. The results of this study are disturbing, considering that the toy caps (even in bulk packaging) have a UN classification of 1.4S, which by definition should not produce significant blast or fireball effects when initiated. Thus perhaps it is appropriate to consider whether the UN test protocol is adequate for this product.

Keywords: air blast, TNT equivalence, toy caps, Armstrong's mixture, UN test

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Abstract: The oxygen injector head in UALR's labscale hybrid rocket motor has been redesigned to include a coaxially located optical port. This port permits viewing directly into the space in front of the fuel grain where combustion is initiated. It is designed to allow a visible-imaging fiber optic, a UV-Vis fiber optic, or an infrared fiber optic to be aligned coaxially with the motor. The imaging fiber optic shows swirling and pulsating flow fields, which indicate that one-dimensional flow model assumptions are not valid. The quartz fiber optic is used with a UV-Vis spectrometer to perform spectral studies using fuels doped with metals. It is demonstrated that the same species that are seen in the plume can be detected in the combustion zone, which permits comparison of species at the two end points of the combustion process.

Keywords: hybrid rocket motor, spectroscopy, flow patterns, metal emission spectra, combustion diagnostics

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Abstract: A brief description of compressible fluid flow is presented to clarify and, hopefully, reduce the incorrect usage of the term "choked flow" in the fireworks community.

Keywords: choked flow, fluid flow, gas velocity, mass flow, rocket, sonic flow

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Abstract: The combustion chemistry of phosphorus and its compounds in pyrotechnic applications is discussed. Whereas red phosphorus (RP) and phosphorus sulfides can be used as fuels, the phosphates can be used as oxidizers in metal-containing pyrolants. Phosphorus combustion mainly occurs in the gas phase after volatilization of the parent phosphorus source, be it P₄ or P_red. The enormous sensitivity of RP and its mixtures is mainly due to high strain in red phosphorus building blocks and trace amounts of phosphoric acids formed in non-stabilized RP. The inherent danger of RP/chlorate mixtures is believed to result for the most part from acid-base reactions in non-stabilized RP mixtures leading to the highly reactive species ClO₂, which will trigger ignition.

Keywords: red phosphorus, phosphate, phosphide, white phosphorus, chlorate, smoke, Armstrong's mixture

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Abstract: Impact sensitiveness of pyrotechnic flash compositions consisting of mixtures of potassium nitrate (KNO₃), sulphur (S) and aluminium (Al) is experimentally analyzed using equipment similar to BAM (fall hammer) equipment. Results indicate that an increase in the sulphur content of the mixture raises its sensitivity to impact. The limiting impact energy (LIE) falls in the range of 5 to 8 J for the compositions studied, which may be categorized as class III explosives. The results obtained, using the statistical tool "Mixture Design", are helpful in correlating the characteristics of each component in the mixture with the overall impact sensitiveness. The model predictions and experimental results are found to match well within ± 0.5% error. Cost analysis and sound measurements are made for all compositions, and the results are compared with impact sensitivity to arrive at ratios of ideal compositions.

Keywords: flash composition, fireworks, impact sensitiveness, mixture design, pyrotechnics, potassium nitrate, sulphur, aluminum

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The high concentrations observed for these metals result in intensity versus concentration curves that alter from the expected linear progression for manganese, magnesium and strontium. The molecular band emissions observed for calcium, barium and copper in this study followed linear progression, as does the atomic line emission for barium. The line emissions for manganese, strontium and calcium lean toward the concentration axis. The curves are attributed to self-absorption or increased interactions among mixing species as metal concentration increases in the plume. A pattern-like combustion routine for each metal can be characterized with further study.

Keywords: combustion diagnostics, hybrid rocket, plume emissions, spectral signature, rocket exhaust, atomic spectroscopy, molecular spectroscopy, emission spectroscopy

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