Displacement Fueling/Venting Concept

Boom! The classic potato gun harnesses the combustion of flammable vapor. Show us your combustion spud gun and discuss fuels, ratios, safety, ignition systems, tools, and more.
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auxiliary
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Thu Oct 06, 2016 4:20 pm

Hi Spudders!

I thought of a way to fuel/exhaust a combustion potato cannon is a simple way. I originally came up with the idea when I decided I wanted to build a cannon using a garden sprayer for a chamber like this one:

Image

The problem with this kind of chamber is that there is only one large hole and that would be used for the barrel. So the traditional method of using a fuel meter, exhaust valve, and mixing fan would not work as well. With the inspiration of ijahman's RR6 design http://www.spudfiles.com/combustion-can ... 19769.htmlI came up with a prototype to test the concept of displacing the exhaust out of the barrel using a propane torch. The torch acts as a Venturi nozzle that mixes the correct proportions of propane and air. This fuel/air mixture goes down a tube to the back end of the chamber and pushes the exhaust gas out of the barrel. So without having to use a fan or ball valve, a new charge is ready! I found that the cannon works in all orientations when fueling/reloading. Having it upside down or sideways doesn't affect the power (as measured by how load the bang is).

[youtube][/youtube]

Pros to this design:

-Simple
-Cheap (Less plumbing)
-Less holes in chamber
-Reliable
-Powerful
-No fan needed

Cons to this design:

-Have to count off seconds of fuel
-Increased fueling time
-Will not work if you load projectile then refuel.

I plan to go forward with my garden sprayer cannon idea utilizing this fueling method. Tell me what you all think!
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rna_duelers
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Thu Oct 06, 2016 8:01 pm

A carbie Fueling system,like the idea it's worked well for so many years in other applications why not spudding.

The chamber shape and placement of the intake would seem to have a big impact on performance,have you tried it with a non fluid shaped chamber? PVC pipe etc with voids/pockets of unburnt fuel or non exhausted gasses.

Keep it up.
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auxiliary
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Sat Oct 15, 2016 11:55 am

I have tested this set up with a water bottle chamber in the video and with my garden sprayer cannon (Chappy) only. And those chamber shapes seem to work just fine. I don't really have any measuring equipment that I could use to measure a performance difference between chamber shapes. My guess is that the pockets that come with pipe fittings wouldn't affect it too much. I think that bigger factor would be that aspect ratio of the chamber (long and skinny vs spherical). That's just my guess though.
jimmy101
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Sun Oct 16, 2016 5:17 pm

The advantage that carbide has over most others fuels is that it has a very wide combustion range making fueling much easier and misfires uncommon.

The disadvantage that carbide has over most others fuels is that it has a very wide combustion range making correct stoichiometry unnecessary but therefore limiting the amount of energy in the chamber.
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auxiliary
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Thu Oct 20, 2016 5:04 pm

Oooh now I'm confused. I think rna-duelers is talking about a carburetor fueling system like in an engine?
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rna_duelers
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Thu Oct 20, 2016 11:43 pm

I did mean carburetor fueling,sorry about the confusion...But,carbide carburetor fueling now there's something i haven't seen!

Have you started on the weed sprayer chamber?
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Sat Oct 22, 2016 6:16 pm

Ok Gotcha! Check out the thread below this one. I made the cannon it's it's called Chappy. I hydrotested the chamber though out of curiosity and it failed. See details in the thread.
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