The idea of the dispenser potato gun

[BORIS_ELCIN]

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

[jimmy101]

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).

[BORIS_ELCIN]

but all it is, good design, tried someone to repeat it?

[jimmy101]

Probably not since it just makes a puff of flame. Won't work with a barrel and ammo.

[mrfoo]

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.

[BORIS_ELCIN]

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?

[mrfoo]

[BORIS_ELCIN]

Something that should be cool. Somebody tried to use the arrows from a crossbow in such a device, which speeds can be achieved?

[jimmy101]

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.

[mrfoo]

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.

[jimmy101]

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.

[sharpshooter]

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)