[lazide]

Cite?

Butane and propane can easily produce > 100 psi when used in engines, and are commonly used as replacement for gasoline and other hydrocarbons in generators and fork lifts to do just that.

In a confined enclosure (potato gets stuck or the like), it’s a pipe bomb.

[grogenaut]

by engines I'm assuming you mean something with a stroking piston which is going to reduce the total volume by somewhere from 4:1 to 13:1, so that's going to increase major pis increases by itself even before explosion. You don't have compression with butane into a potato gun, just the efffects of the rapid combustion. So it wouldn't really be a fair comparison.

[lazide]

Here is a nice declassified paper on using butane and propane in unconfined fuel air explosives. [https://apps.dtic.mil/sti/tr/pdf/ADA084367.pdf]

Quite effectively too.

There is also some nice research on proper high explosive detonation of similar mixes when using proper detonators.

It requires rather extreme amount of willful ignorance to think lighting a mixture of oxygen and butane or propane inside a enclosed space is only going to be 30-40 psi maximum, instead of ‘thank god it only hit that maybe because the potato moved’.

[https://colab.ws/articles/10.1134/s0010508211010114]

There was a good research paper I found that had a quantified set of numbers, but it required paying for it. Meh.

Still waiting for that cite.

[fkyoureadthedoc]

You're asking for citations when your whole premise is based on a wet potato getting stuck in a smooth plastic pipe. And then the potato being a durable enough seal to create a bomb. That's goofy as hell.

[lazide]

No. I’m asking for citations when your assertion is that flammable hydrocarbons mixed with oxygen in an enclosed container and ignited can not exceed 30-40 psi, or the bursting force of said (often brittle) plastic enclosed container. Especially since garden variety Schedule 40 PVC in the sizes we’re talking about are rated (non-shock) for over 180 PSI and many into the 200+ PSI range but there are easy to find videos of them bursting in spud guns.

[https://parts.spearsmfg.com/sourcebook/SCH40TECH_40WHTPIPE-1...]

And as noted in the prior declassified paper, shock fronts from these mixtures can easily move in excess of 280 meters/second even unconfined in air, with the right mixes.

Goofy? Perhaps. Life altering? Perhaps [https://youtu.be/KqstP9ics2A?si=Omtp8N7xPW91A5TU] - and yes, while many of those failures in the video are clearly due to improper glued joints (which is a big hint at the pressures involved, and way better than other kinds of failures!), many also involve the PVC shattering. Several in the first few minutes, actually.

I made a ton of potato guns as a kid, btw. Typically using propane. But I always respected the forces involved, because I wanted to not lose an eye, kill anyone, etc.

Looks like some enterprising MIT alumni + the air force academy did some internal ballistics reseaerch [https://arxiv.org/pdf/1305.0966].

Note - I highly recommend against using acetylene, which they did for some of the tests, as it will perform a proper super-sonic detonation [https://www.icheme.org/media/10611/iv-paper-08.pdf] under the right conditions and turn your potato cannon into an IED even if the projectile moves, or potentially even with no projectile at all. Per that paper - “It appears that Acetylene is unique in that it will propagate a detonation at initial pressures below those of which it is capable of sustaining deflagration”. I would have checked this paper which even more directly addresses the topic [https://link.springer.com/article/10.1007/BF02671917] (because I love this kind of thing, obviously), but $40. :(

So looks like as long as everything goes well, they are in the approximate range of 20 psi while driving the projectile, except for acetylene which hit a hair under 90 psi. They used stoichiometrically ‘perfect’ mixes.

My guess is the failures in the videos (and anecdotally) were driven by too lean fuel mixtures, easy to do in some conditions. But this paper [https://www.scientificbulletin.upb.ro/rev_docs_arhiva/full14...] seems to indicate the opposite, and also pressures >= 120 PSI. So I don’t know.

I also saw MAPP gas apparently being used in one of them too (the yellow cylinder attached to a plumbing torch), which would also be unwise.

[bobmcnamara]

> You don't have compression with butane into a potato gun

Maybe not yours, but we tapped ours. This held the potato near the chamber after compressing the gasoline-air mix. I have no idea how well it held, but if you didn't seat the potato into the threads it would push the broom back out. You'd hear a poor seal leaking.

[lazide]

I just want to say, this is gloriously crazy. Kudos.