… gunpowder, treason and plot!” Like many nursery rhymes in the UK, this is a glib ditty of pain, suffering, and death! If you’re born with a British sense of humor, the only logical consequence of a failed assassination attempt with gunpowder is to throw a party with the same material in the form of fireworks! Of course, Guy Fawkes night – named after the hapless assassin, is but one of many occasions where fireworks are used. Diwali, Independence Day, Bastille day, Hanabi Takai, New Year and Chinese New Year to name but a few more.

But what gives these pyrotechnics their lasting appeal?

The answer lies in the chemical composition used to control color and heat and its particle morphology to control the burn rate. Kosanke and Kosanke show that burn rate increases (burn time decreases) with finer meshed particles (Figure 1) and with irregular shapes (Figure 2)1, both of which control the surface area to volume ratio.

Figure 1. Burn times for flares made with varying magnesium particle size
Figure 2. Mass burn rates for a composition using different fuel particle shapes

The authors also describe that the ignition sequence can be controlled when the fuel burns in a linear fashion (Figure 3). Each disk representing a different fuel type, which could be used for explosion, incandescence or propulsion. The result is a visual and aural spectacle enjoyed in celebration by many cultures around the world.

Figure 3. Burning “propagating” along a stick of pyrotechnic composition.

Where much larger rockets are concerned, rocket engineers control the acceleration, speed, and duration of propulsion through the careful application of fuel, oxidizer, and heat. The Falcon Project is one such organization that designs rocket motors for military and commercial applications2. Here, the chemical and material properties of solid-state fuel and oxidizer are controlled to give the desired level of thrust for the specified projectile.

One such projectile is the Bloodhound Super Sonic Car, which is intended to travel at 1000 mph or Mach 1.3. That will get me to my local supermarket in just under 5 seconds – a considerable time-saving! Although at 13 meters long, parking will be an issue.

For the Bloodhound, a hybrid rocket motor is used which uses the ‘old-style’ Formula 1 V8 engine to pump in liquid oxidizer at 40 L/s to blend with the solid-state fuel and produce nearly 28,000 lbf of thrust. For a fascinating lecture on the topic by the Falcon Project co-founder, Daniel Jubb, watch the video below.

For F1 fans, like myself, I recommend skipping to 30 minutes 40 seconds where the glorious sound of the V8 supercharger can be heard, followed by rocket related carnage!

References

  1. B.J. Kosanke, K.L. Kosanke, Control of Pyrotechnic Burn Rate, 2nd International Symposium on Fireworks, 1994
  2. https://www.ukspacefacilities.stfc.ac.uk/Pages/Falcon-Project-Ltd,-Westcott.aspx