Experimental values of critical wind velocity

Note (l)The content of the hemp eoal shows an additional percent. (2)The line under figures shows the composition which continues burning even under 10 mm of water. 

The decrease of the atmospheric pressure decreases the stability of combustion on the contrary, the increase of the pressure increases the stability. Therefore firework pieces must be constructed so that the burning pressure increases as far as possible. This is especially important in the case of ignition. For example, in Fig.28 A is more ignitable than B, when they are moving in high speed. 

With regard to the shape of firework pieces, burning is more stable at the concave surface of a composition rather than a convex one, because if the fire is partially put out for some reason, the burning is recovered instantaneously from the fire of the neighbouring parts on the same surface. Stability is especially high in a hole (Fig. 26, C). On the contrary, spherical pieces like the stars of a chrysanthemum give the lowest stability. It is a most interesting and important problem for us to be able to conquer this difficulty, which is described later (Fig.29 and 30).  

There are some compositions which burn without flame, e.g. smoke compositions. In this case the burning is generally quite stable because the burning surface is covered by generated ash, and the combustion proceeds independently of environmental conditions. Even when an amount of water is poured on the burning composition, the water cannot reach the burning surface. Accordingly, to put out the fire, the ash must be removed from the surface before the water is placed on it. 

The burning surface is sometimes destroyed by a mechanical action, e.g. shock or vibration, which strips off the burning layer from the composition to stop the combustion. Such an accident often occurs in the case of shooting stars the burning surface is dug off by the propellant gas. To protect the surface from the mechanical action, we use a punched metal 

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Tabic 5. Experimental values of critical wind velocity (n>/scc)... 

Classification of firework light sources 2 Standard diameters of round flowers 3. Experimental values of critical wind velocity Detonation velocities of report compositions 5. Observed flame temperature for representative fuels... 

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