Sparkling Fireworks

Chihiro INOUE
The University of Tokyo
Tokyo, Japan

Sparkling Fireworks 1
Chihiro INOUE (The University of Tokyo, Japan)

For over 300 years since the Edo period, a sparkling fireworks called Senkou-hanabi has been popular in Japan. This firework is made by simply wrapping a black powder (a mixture of potassium nitrate, carbon and sulfur) in a twisted paper. When we enjoy these fireworks in summer night, we hold the top end of the paper string and ignite the lower end. Then, a small fireball is produced at the lower end of the paper string, and beautiful streaks of light scatter from the fireball as shown in Figure 1 with soothing sounds. The formation of these streaks is attributed to sequential atomization and luminescence of droplets ejected from the fireball driven by a series of chemical reactions. A lucid scenario, however, has not been provided for the origination process of the streaks of light. While the fireworks has been so much popular in Japan, the physics behind its beauty was remained unexplained. In our study, by using a high-speed video camera, the origination of streaks of light from the fireball is clarified.

Sparkling Fireworks 2
Chihiro INOUE (The University of Tokyo, Japan)

Figure 2 shows self-luminous images of the fireball. At t=0.0ms, the fireball expands by the combustion gas produced inside. Suddenly, at t=0.8ms, the surface of the fireball bursts. Due to the surface tension, the rim of the hole is pulled into the fireball. Then at t=2.4ms, the flow induced inside the fireball simultaneously concentrates and produces a small convex shape. At t=3.2ms, the convex portion grows rapidly to become the thin liquid thread. Finally, after t=4.0ms, the thread splits into droplets, which are recognized as streaks of light. It was revealed that the beautiful streaks of light originate from the interior of the fireball, and not from its surface.

This research was kindly supported by Dr. Joji KUWABARA and Mr. Keiji JO (Photron Ltd), and by Mr. and Mrs. Tsutsui (Tsutsui Tokimasa toy fireworks factory).

Abstract Link

Gray Arrow G34.00004: Atomization in Sparkling Fireworks

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This image may be freely reproduced with the accompanying credit: Chihiro INOUE (The University of Tokyo, Japan)

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Dr. Chihiro INOUE
The University of Tokyo, Japan