Ignition Inside Ballistics Gelatin in Slow-Motion Video

Can someone explain what's happening with regards to the ingnition in the gelatin in this video?

https://www.youtube.com/watch?v=fX4ODh1g4eM

The guy that made the video took a whack at an explanation.

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The flash/explosion in the gel hasn’t been very well explained so far. The best explanation I have is that the hot bullet vaporizes some of the gel (which is flammable) and between the friction, heat of the bullet, and air being sucked into the temporary stretch cavity, as the TSX collapses it acts like a diesel engine and compresses the mixture of heated gel vapor and air until it explodes.

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There are actual ballistic experts around here, so I'm curious if this is a known phenomenon, or an anomaly.

I have no idea about the flammability of the gelatin but not only do you have friction from the bullet entering the gelatin, you have a bullet that is spinning very fast, typically over 100,000 RPM which will generate a large amount of heat.

Edited to add: It could also be hot unburnt powder.

There's been a discussion on arfcom that seems to give the correct answer.

Here are a few pertinent quotes.

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I agree that it is likely dieseling of vapor gel material.

At the apex of cavitation pressure in the bubble must drop really low. Some gel material turns to vapor. Bubble collapses, pressure rises and eventually the now-compressed and heated vapor ignites.

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Hydrocarbons in the gel igniting from during compression of the TC. Similar to engine knock.

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Chemist here. It is definitely "dieseling." From my research I am reasonably confident that those blocks are composed of a mineral oil gel. Mineral oil is a petroleum derivative that is to diesel what diesel is to gasoline. It's not flammable under normal conditions but would be under these extreme conditions.

ETA: The geek term is adiabatic compressed ignition.

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I'd be curious to hear from Doc whether he thinks the explosive expansion caused by ignition could be making the permanent wound channel look worse than it otherwise would be by tearing the gel further than the bullet impact alone would do.

10mm_ in the linked thread didn't think so but it seems crazy that channels which the bullet fragments have created wouldn't tear further from the violent expansion caused by the ignition.

Sonoluminescence

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Originally Posted by X9VlmF8m

Sonoluminescence

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That isn't a terribly satisfactory explanation for the smoke.

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Originally Posted by X9VlmF8m

Sonoluminescence

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I agree that this probably can't explain it, but I suppose a resourceful person could measure for X-ray emission.
http://www.nature.com/news/2008/0810...008.1185-1.jpg

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Originally Posted by JAD

That isn't a terribly satisfactory explanation for the smoke.

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Very true. I'll retract that. I've seen slo-mo video of underwater shots showing mild flashes, but that was rather extreme and created smoke.