Sunday, January 11, 2009

Mythbusters accidentally create a reaction-diffusion-like system

This short video clip shows that the Mythbusters appear to have accidentally and unknowingly created a kind of reaction diffusion system in their "Trailblazers" episode when they ignited a trail of gasoline. If you look closely behind Adam you'll see waves propagating in a manner reminiscent of various reaction diffusion and cellular automata systems. I think what's going on here is that the gasoline vapor and the moving ignition creates a two dimensional amorphous relaxation oscillator. Remember that it is the vapor of gasoline that is flammable, not the liquid. As the fuel evaporates into vapor it takes a few moments before it reaches an ignitable fuel to air mixture. When it does, a wave of flame propagates over the area thus eliminating the vapor which then slowly re-accumulates until it ignites again when it encounters an ignition wave from some other region. The exact position of the flame is highly sensitive to the environment and initial conditions thus the system turns into a set of chaotic cyclically flammable domains that move around in a fascinating manner. Apparently without knowing it, Jamie and Adam have stumbled upon a quite lovely piece of science. I've got to try to reproduce this!

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