Airborne Powder Fuels

[LGM]

This would get locked on Spudfiles for the use of solid fuels, and it doesn't feel like it would fit in on science madness, so here I am...

I had an idea to use powered fuels like flour, sawdust, or very fine charcoal in a spud gun (partially inspired by the flour into the tube with a candle at the bottom trick) and I was wondering if anyone here had input or has tried this before.

I'm thinking I could spread the fuel in the chamber with a 1-3 gram BP charge which would also provide ignition for the fuel. I would probably have to do this in a metal cannon but that is not a huge issue, I plan on making one this summer. Maybe with a smaller cannon I could try this with some aluminum powder once I get a better ball mill going.

Suggestions or stories are welcome.

[NightHawkInLight]

Maybe in a metal cannon that would work without blowing it to shreds. Although still very dangerous. I did start a thread on this on the old spudtech forum before it closed. Your best bet is probably charcoal. I have never made a cannon like this, but if you watch this video:

http://www.youtube.com/watch?v=Vy6PT03AVvc

You'll see I have done some experimenting on the subject. I believe it to be far to dangerous to implement in a cannon.

[LGM]

Nice video, I have to try that as soon as I can make some more BP. How fine was the charcoal in those?

The cannon I will be making has a chamber of 3.5" steel piping with a little over a quarter inch thickness. I think that it would be relatively safeish.

The aluminum powder idea might be a little much, recreating a thermobaric bunker buster in my backyard has it's potential problems.

[TheSidewinder]

Hmmm......

 

I want to be encouraging, but I also have to drag out the Moderator's Cane and wave it at you.

 

What you're proposing has the potential to be very dangerous, I hope you understand?

 

Just as you said, you'd effectively be creating a small-scale FAE (Fuel-Air Explosive).

 

I'm sure you've seen all the same videos I have, of large-scale ones the Military uses. I particularly like that MOAB. Best "insurgent reduction device" I've ever seen.

 

(For those who don't know, they're powerful beyond BELIEF, given how little "fuel" they actually use. Naturally, they've researched them to death to get the maximum yield, so the comparison isn't exactly fair.)

 

BUT... my point is, just HOW effective your small-scale one would be, is something I can't predict.

 

AND NEITHER CAN YOU. Not shouting, but it needs emphasis.

 

Consider what might happen, if that small-scale FAE works considerably BETTER than you thought it would.

 

With an open end, that pipe you mentioned PROBABLY would be ok, but can you be sure?

 

Maybe some folks who have cannons will pitch in here?

 

(Where's that one-eyed old goat when I need him...)

 

Please wait until you know more, for your own sake, ok?

[marks265]

I have a cannon. It is a replica flint lock black powder Brown Bess which is .75 caliber and has a long ass barrel. It takes a big man with big gonnads to fire this puppy from the shoulder when well packed! It's breech is at least 1/4" wall. I don't think a big gun should be taken lightly either. I bet Charlies' toys come on wheels for a reason called damn heavy or else he has a lot of kids. If Charlie and The Sidewinder started shooting at each other and used bad powder I might have holes in my roof! So play nice please and keep your powder dry!

[TheSidewinder]

*****SNIP****

If Charlie and The Sidewinder started shooting at each other and used bad powder I might have holes in my roof!

*****SNIP****

Unlike the esteemed Monsieur Cheney, I don't shoot at my friends....

 

 

 

 

 

 

 

M

[marks265]

Now THAT was funny!!!!!!!!!!!!!!!!!!!!!

[LGM]

I understand the potential danger here. I would start off with a smaller gun with a 2" welded steel chamber to a 1" steel barrel, fired remotely in a small bunker pointed away from things that I wish to remain intact. Maybe with 3/4" steel threaded plug at the back to place the charges in.

[TheSidewinder]

OK, just making sure you understand what you might be getting into.

 

And it looks like you do, given your testing plan.

 

You might consider making some sort of blowout plug in the chamber for relief, if things go badly wrong, to save the main gun.

 

Something like the old pop-valves you'd find on pressure cookers?

 

Good luck and be sure to reposrt results back here if you do, eh?

[TheSidewinder]

I have a cannon. It is a replica flint lock black powder Brown Bess which is .75 caliber and has a long ass barrel.

Hey, sounds nice! I love the old (and actual replica) BP Sporting Arms. Modern BP Rifles just aren't the same.

 

M

[Mumbles]

I thought the valves on pressure cookers were temperature and not pressure dependant. They're proportional to one another, but I want to say the principle the release valve works on is temperature. An alloy disk that melts. This doesn't make sense though as it would be a one time use thing. Still something to check.

[LGM]

Some pressure cooker valves are pressure dependent, some aren't. I don't think that a small hole in the side of a chamber the size of the full sized one I want to make will really make a difference, with what would probably be a 2.5-3" barrel opening.

 

My only fear is that something would get jammed somehow in the barrel, but I could make a preventative measure for that by making the first four or five inches of the barrel out of PVC, probably sch.80, and have the ammo stop before that point. That way the barrel will come off if pressures get way to high.

 

Maybe today I will make some smaller charges like I will use in the gun, just to get an idea of how much I will need to use in the smaller and larger ones. The large chamber has about 290 cubic inches. I can make the smaller scale one as soon as I can get to a hardware store, I'll probably have some results from that in a few days.

[hst45]

I'm borrowing technology from firearms design here. In a modern center fire rifle there are gas vent relief ports cut/drilled/cast into the receiver/bolt, assembly so that in the event of an over-pressure situation in which the the brass cartridge ruptured, the excessive pressure would be vented away from the shooter. Perhaps you could utilize this practice and drill a vent hole to relieve over-pressure, and wrap a band of sacrificial metal around the vent that would contain the pressure in "normal" operation but blow out in the event of excessive pressure. The obvious problem is developing a device that will not blowout prematurely but WILL blow when pressures rise to excessive levels. Perhaps a hose clamp would work for low pressure tests?

[LGM]

What about drilling some holes into the back of the gun and putting some thin sheet metal over them on the inside, that would probably work in the event of an overpressure.

 

Unfortunately it looks like more miserable snow for the midwest, and I'll be gone for tomorrow and the next day, so I doubt that I'll have the results on the smaller version back as soon as I had hoped. Maybe over the weekend.

[GalFisk]

I think you're overestimating the power of a FAE. A certain volume of BP is much more destructive than the same volume of fuel/air, the reason a FAE bomb is so powerful is that the sheer volume of explosive mixture is very large (many m^3). Inside a cannon chamber the explosion is limited by the available amount of oxygen in the air. In BP the oxygen is in solid form and much more compact, I'd be more worried about having too mcuh BP inside the chamber.

[LGM]

You're right, the charcoal alone probably won't be enough to burst the cannon, but if there is a little too much BP or if I want to try something like adding oxygen to the chamber or throwing a dash of aluminum powder in with the fuel, I want to have some sort of safety mechanism.

 

I still need a threaded plug to finish the small scale, curse leaky bike tires…

[jacob]

If you want something really powerfull you could try some 2 micron atomized Magnesium powder, be EXTREMELY carefull though, I've never used the stuff but Lloyd sponenburgh had a bad accident with it when mixing it with cabosil in a Ballmill (he wasn't milling it, only mixing) it ignited blasting the jar cap across his shop and shooting out a huge (about 3' by 8') tongue of fire.

 

the really crazy part is that he was atleast 6' away, perpendicular to the flame path and still got quite badlly burned just from the massive amounts of UV and infra-red light emitted, and it was only 100 grams that did all this.

 

It's also pyrophoric, I've heard that when scooping it out of a drum, the scoop gets warm before it clears the top, nasty nasty stuff.

 

Anyway, umm, have fun

[LGM]

@Nighthawk: Did you have small stars or metal shaving in your spreader charges in that video?

 

I ask because I just made several small charges like the ones I want to use in the cannons, and I can't get the charcoal to ignite. The first two were a central charge surrounded by charcoal, these both had too much charcoal with too little BP and I just ended up with black patches on my lawn.

The recent ones, which are more like what I originally planned, were .5" paper tubes with a small amount of bp in one end and filled the rest of the way with charcoal with a thin paper barrier between them.

 

I think some of the problem is losing power through the fuse hole, I found them enlarged considerably, and the barrier, which might be preventing flame from being easily passed to the charcoal.

[NightHawkInLight]

@Nighthawk: Did you have small stars or metal shaving in your spreader charges in that video?

 

I ask because I just made several small charges like the ones I want to use in the cannons, and I can't get the charcoal to ignite. The first two were a central charge surrounded by charcoal, these both had too much charcoal with too little BP and I just ended up with black patches on my lawn.

The recent ones, which are more like what I originally planned, were .5" paper tubes with a small amount of bp in one end and filled the rest of the way with charcoal with a thin paper barrier between them.

 

I think some of the problem is losing power through the fuse hole, I found them enlarged considerably, and the barrier, which might be preventing flame from being easily passed to the charcoal.

Well no I didn't have any stars in it, but it did take about a 1.5g kno3 flash salute. It also makes it quite a bit easier to ignite if you mill the charcoal with about 25% kno3 added. It's cheating a bit, but it really ensures a good burn.

[Ralph]

The bp would not nesisarily ignite the flour in these kind of conditions, i would recomend using some of my long time fuse penut butter based(have a look in the fuses thread) as it would continue to burn for quite some time after you bp has burned up, because from what I have seen and experienced these fuel air mixtures tend only to ignite once they are at a good saturation point (here are some examples watch closely as to when the plume ignites

) i know that the last two are compressed air ones but the fuel is exposed to the flare the since launch but only ignites once the fuel has nicely spread. so if your bp is very fast it may not work to well especially in a tube where an ideal saturation point may never be reached (especially if to much flour is used)

 

hope it works out well for you

[Dr Boom]

I'm not against experimentation- far from it, and I'm not going to say "don't try this at home" because anyone with an itch is going to do just that.

 

But I must stress the fine line between FAE and thermobaric explosions here. No- i'm not going to detail how to get a thermobaric to work: that has no place in the "cannon" thread and would raise questions anywhere else. FAE in cannons are fine to experiment with if you are fully aware of everything that could go wrong.

I don't want to sound like the old man across the street shakin' his cane at a bunch of kids making noise but jeez- are we really weighing the pros and cons of FAE in cannons, really?

Because the moment you don't respect that FAE combo you are messing with- that could unintentionally turn into a thermobaric bomb and you would have a bad day real quick. (not to mention you just blew up your cannon!)

 

Thermobarics occur at a rate just below the deflagration velocity of flash- but there is that age old debate about whether or not flash deflagrates quickly or dets. But that isn't what I'm trying to say here.

 

Using flash as your base charge and any powdered fuel is pushing your luck when in a cannon. Unless you have some "mad skillz" in metallurgy and can design a cannon again such potential blast pressures, you should reconsider just how far you are trying to shoot something (if anything) out of that cannon.