FYFD

Tag: deflagration

  • Ignition

    Ignition

    Shown here are the first instants after a bubble full of methane gas is ignited via laser. Using the schlieren optical method and a high-speed camera, scientists recorded the deflagration at 10,000 frames per second. Because schlieren imaging is very sensitive to small changes in density, we see not only the expanding flame front as the methane ignites but also the subtle waviness of the methane expanding into the surrounding air as the bubble bursts. (For comparison, check out what bursting a water balloon looks like at high-speed.) Be sure to head over to ScienceTake for the full schlieren video, and also check out this award-winning video of a match lighting made by the same researcher.  (Image credit: V. Miller et. al.; full video: The New York Times; submitted by Rebecca M.)

    ETA: An earlier version of this post mistakenly said the demo used a balloon full of methane rather than a bubble. Thanks to jump-first-think-later for the correction.

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    Water in Oil

    Pouring water on an oil fire is a quick way to cause almost explosive results. Since water is denser than oil, it quickly sinks to the bottom of a container, heating up as it does. When the water reaches its boiling point, it evaporates and expands as steam. That phase change involves a huge change in volume, a fact made especially clear in the video below. The steam expands and rises, throwing droplets of oil upward and outward. These smaller atomized droplets are easier to combust, which, in the case of the video above, causes a veritable cloud of flames if a fire has already started. 

    (Video credits: The Slow Mo Guys and N. Moore)

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    Fire-Breathing

    In this high-speed video, the Slow Mo Guys demonstrate fire-breathing. Rather than using a liquid fuel like kerosene, they utilize cornstarch, which is both easily flammable and non-volatile thanks to its powdered form. Blowing out the cornstarch creates a turbulent jet of cornstarch and air. Combine that with a combustion source, and the cornstarch quickly deflagrates, meaning that the flame propagates via heat transfer. When neighboring regions of cornstarch become hot enough, they ignite and the flame front expands. You can observe this in the flame growth shown in the video; just after ignition the cornstarch jet is much wider than the fire and it takes some time for the flames to catch up with the jet. Although a liquid-fueled fireball operates by the same principles, it can look rather different. For comparison, check out this high-speed video of a WD-40 fireball. And, hopefully it goes without saying, but don’t try this stuff at home. (Video credit: The Slow Mo Guys)