Re:The tragic physics of the deadly explosion in Beirut
by erdos4d on Tuesday August 11, 2020 @08:35AM
(#24119625)
I am not an expert and do not understand it fully, but I know that fuel/air mix does make a phase transition of sorts and becomes a high explosive when the compression ratio is high enough. At low ratios it burns, at high enough ones it really does detonate with a shock wave running through it and causing the whole charge to blow up almost at once. Ammonium nitrate does the same if there is a big enough kick to get a strong detonation wave going through it, though I think there is much greater chance of this if there is some sort of solvent (gas, diesel, etc) mixed in with it.
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Re:The tragic physics of the deadly explosion in Beirut
by throwaway0a5e on Tuesday August 11, 2020 @09:06AM
(#24119875)
> I think there is much greater chance of this if there is some sort of solvent (gas, diesel, etc) mixed in with it.
The fuel is what burns turning into combustion byproducts. Larger volume -> high pressure -> physics magic I don't feel like explaining -> shock wave. Burning pure AN is a waste, you're basically burning super lean. Add fuel and you get closer to stoic. More efficient reaction -> more output volume per input volume -> more bang.
It's like the difference between making a bunch of gas fuel (like propane or something) go up as a woosh vs a bang but with solid inputs instead of gasses.
Re:The tragic physics of the deadly explosion in Beirut
by brokenmachine on Wednesday August 12, 2020 @08:06PM
(#24138582)
I'm also no expert, but I thought that "detonation" in a gas engine just meant that there was too much fuel being injected, when the engine is at too low revs, so the piston can't move quickly enough to absorb the expansion and convert it to spinning the crankshaft - very similar to if the timing of the spark was too early.
Nothing to do with a transition to high explosive, although it will destroy an engine just the same.