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The idea of the dispenser potato gun

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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The idea of the dispenser potato gun

Unread postAuthor: BORIS_ELCIN » Fri Dec 02, 2016 11:12 am

Hello, I am writing through an interpreter, because I do not know English well.
I would like to know if someone tried to make the dispenser as in this video https://yadi.sk/i/aQy5KJ3Kzm68U
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Re: The idea of the dispenser potato gun

Unread postAuthor: jimmy101 » Sun Dec 04, 2016 2:54 pm

Looks like a cheap air pump pumping air through (a syringe body?) chamber that has a paper towel saturated with alcohol (or gasoline, or ... anything sufficiently volatile) into a bottle open at one end and ignited with a piezo (from a lighter or a BBQ).
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Re: The idea of the dispenser potato gun

Unread postAuthor: BORIS_ELCIN » Mon Dec 05, 2016 10:14 am

but all it is, good design, tried someone to repeat it?
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Re: The idea of the dispenser potato gun

Unread postAuthor: jimmy101 » Wed Dec 07, 2016 12:48 pm

Probably not since it just makes a puff of flame. Won't work with a barrel and ammo.
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Re: The idea of the dispenser potato gun

Unread postAuthor: mrfoo » Wed Dec 07, 2016 3:28 pm

I don't see why it shouldn't work on a larger scale if you can get the mix right; effectively it's a primitive (and not very tunable) carburettor. That kind of setup is probably going to give an over-rich mix for petrol, you'd really want something like methanol, I'd think, along with a reed valve on the fuel inlet into the "chamber".

Methanol's not enormously energy-dense. Methanol/nitromethane mix (glow plug engine fuel less the castor oil) might be a better bet. Or, given that the size (and thus volume of mixture) would need to be scaled up for "real world" usage, you might be better off with an actual carb scavenged off some piece of dead garden machinery, fed with a compressed air source and using a more dense fuel. Still wants a reed valve, though.
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Re: The idea of the dispenser potato gun

Unread postAuthor: BORIS_ELCIN » Wed Dec 07, 2016 6:16 pm

mrfoo wrote:I don't see why it shouldn't work on a larger scale if you can get the mix right; effectively it's a primitive (and not very tunable) carburettor. That kind of setup is probably going to give an over-rich mix for petrol, you'd really want something like methanol, I'd think, along with a reed valve on the fuel inlet into the "chamber".

Methanol's not enormously energy-dense. Methanol/nitromethane mix (glow plug engine fuel less the castor oil) might be a better bet. Or, given that the size (and thus volume of mixture) would need to be scaled up for "real world" usage, you might be better off with an actual carb scavenged off some piece of dead garden machinery, fed with a compressed air source and using a more dense fuel. Still wants a reed valve, though.

Please tell us if the use is as a video, and to use alcohol as fuel, whether the projectile can be given a larger energy?
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Re: The idea of the dispenser potato gun

Unread postAuthor: mrfoo » Thu Dec 08, 2016 3:53 pm

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Re: The idea of the dispenser potato gun

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Re: The idea of the dispenser potato gun

Unread postAuthor: BORIS_ELCIN » Fri Dec 09, 2016 9:31 am

Something that should be cool. Somebody tried to use the arrows from a crossbow in such a device, which speeds can be achieved?
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Re: The idea of the dispenser potato gun

Unread postAuthor: jimmy101 » Fri Dec 09, 2016 12:30 pm

mrfoo wrote:I don't see why it shouldn't work on a larger scale if you can get the mix right; effectively it's a primitive (and not very tunable) carburettor. That kind of setup is probably going to give an over-rich mix for petrol, you'd really want something like methanol, I'd think, along with a reed valve on the fuel inlet into the "chamber".

Methanol's not enormously energy-dense. Methanol/nitromethane mix (glow plug engine fuel less the castor oil) might be a better bet. Or, given that the size (and thus volume of mixture) would need to be scaled up for "real world" usage, you might be better off with an actual carb scavenged off some piece of dead garden machinery, fed with a compressed air source and using a more dense fuel. Still wants a reed valve, though.
The problem is that the fueling system requires air flow through the gun's chamber, which is kind of hard to do with ammo in the barrel. You would need another valve on the opposite end of the chamber from the air/fuel inlet point.
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Re: The idea of the dispenser potato gun

Unread postAuthor: mrfoo » Fri Dec 09, 2016 4:01 pm

jimmy101 wrote:The problem is that the fueling system requires air flow through the gun's chamber, which is kind of hard to do with ammo in the barrel.

True.
You would need another valve on the opposite end of the chamber from the air/fuel inlet point.

Not true. There's any number of reloading options that could be used to allow refuelling the firing volume whilst the chamber is empty, and loading the ammunition afterwards.

The simplest, and perhaps even most efficient if it also meant compression of the barrel volume into the firing volume (higher pressure, more mix), is refuelling followed by muzzle reloading. It would also be relatively simple to set up a revolving chamber for a multi-fire setup, a bolt or pump-action loading system (which could potentially also deal with the "pumping fuel mix into the firing volume" at the same time) and I can think of a few ways of going fully-automatic with (fairly) rapid fire.
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Re: The idea of the dispenser potato gun

Unread postAuthor: jimmy101 » Mon Dec 12, 2016 4:08 pm

mrfoo wrote:Not true. There's any number of reloading options that could be used to allow refuelling the firing volume whilst the chamber is empty, and loading the ammunition afterwards.

The simplest, and perhaps even most efficient if it also meant compression of the barrel volume into the firing volume (higher pressure, more mix), is refuelling followed by muzzle reloading. It would also be relatively simple to set up a revolving chamber for a multi-fire setup, a bolt or pump-action loading system (which could potentially also deal with the "pumping fuel mix into the firing volume" at the same time) and I can think of a few ways of going fully-automatic with (fairly) rapid fire.
Which is functionally identical to having a second valve in the chamber. Moving the barrel/ammo inline with the fueled chamber sure sounds like a valve to me, and a more complex one at that.
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Re: The idea of the dispenser potato gun

Unread postAuthor: sharpshooter » Fri Dec 16, 2016 2:22 pm

Why not just measure the correct amount of fuel with the syringe, and squirt that into the chamber? Would of course have to find a syringe of appropriate size for your fuel density (ie tiny fractions of an mL for liquids, something larger for gases)
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