I got some questions.

Harness the power of precision mixtures of pressurized flammable vapor. Safety first! These are advanced potato guns - not for the beginner.
PracticallySane
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Thu Dec 31, 2020 11:56 am

I dont believe I am "pumping water" into my chamber. Water is a product of combustion, I believe that the moisture is coming from combustion rather than the atmosphere.

My thought was to remove the moisture created during combustion.

However the suggestion to direct the fill port at the spark plug sounds like it could solve my issue.
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mrfoo
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Thu Dec 31, 2020 12:26 pm

To a certain extent, you'll always be pumping water in, unless you live somewhere with absolutely 0% humidity. You're also adding water vapour through combustion, as you note. After combustion, the pressure in your chamber goes to its maximum, and then reduces as the projectile (if any) is pushed down the barrel. After the projectile has left the barrel, hot gases will continue to leave the barrel, with inertia these will "pump" the pressure in the combustion chamber to below atmospheric. This is known as the Kadency effect, and it's much beloved to those (like me) who make pulsejets. At the same time, the remaining gases in the chamber are cooling, lowering pressure further. The water vapour condenses at this pressure, and droplets form on the chamber walls and, annoyingly, on your spark plug.

Directing the fill port at the spark plug will almost certainly help enormously.

"Drying" the air coming in as mentioned above should help some as well.

You might also look into improving the cooling of the external walls of the chamber *except* where the spark plug is, or even actively heating around the plug, with the aim of making the condensate prefer forming everywhere other than the plug.

Glow plug ignition might help, I think you mentioned that, but it will likely slow down triggering.

Shortening the barrel might help by reducing the kadency pumping, but it's unlikely to help in terms of spud velocity unless your barrel is super overlong.
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Thu Dec 31, 2020 12:45 pm

I should have noted my pump has a small desiccant filter already on it. It definitely only happens if I let the gun cool down and "condense" I can fire repeated shots without a problem, however if I let the gun sit for an hour after if will not fire again.

I have even played with "dry firing" the chamber in an attempt to "purge" the moisture with some success.

I am also wondering if anyone has trouble with carbon build up? Maybe I am running rich, but holly cow this thing is a soot machine...
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Thu Dec 31, 2020 1:33 pm

Butane when burned releases a residue of water and carbon dioxide, which is what you say, referring to the "internal factor 1". The second internal factor is the pressure drop with respect to atmospheric pressure, which condenses moisture, as Mrfoo says. There is at the same time, the normal humidity of the environment, which is an external factor. A moisture filter at the pump inlet makes the external factor small, and blowing the water should solve the two internal factors.
I'm not going to say that connecting a few turns of conductive wire to the spark plug, and a small appropriate battery, is another option because you will fuck me! :o
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Thu Dec 31, 2020 1:37 pm

I like the ladies, I promise I won't "fuck" you. Lol 🤣
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Fri Jan 01, 2021 8:29 am

hectmarr wrote:
Thu Dec 31, 2020 1:33 pm
I'm not going to say that connecting a few turns of conductive wire to the spark plug, and a small appropriate battery, is another option because you will fuck me! :o
Oh Hector :lol: :lol: :lol:
hectmarr wrote:You have to make many weapons, because this field is long and short life
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