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Problems with my Combustion Cannon

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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Problems with my Combustion Cannon

Unread postAuthor: cavalkaf » Tue Nov 07, 2006 7:03 pm

Well, first of all, I live in Brazil, so I don't have access to most of your tools/fuels, and my English isn't perfect.......
Anyway, my project was to make a cannon out of PVC to use with the locally available fuels - in other words, Gasoline, Alcohol, and other things (I know you guys are going to call me crazy, but I took all precautions necessary).

Ignition-wise, I chose to basically use a spark plug salvaged from an old car (couldn't find any BBQ igniters here). It allowed me to fire from a safe distance, which is important when dealing with fuels like gasoline 8)

My problem: I got it to fire 3 or 4 times out of the 100 (or more) I tried it. I know the spark plug system is working (I can see the spark), the fuel/oxygen ration seems fine (I can get it lit up using a lighter - however, the chamber is open when I use the lighter, so fuel/air ratio might be a problem), and I know I have a fairly thing seal on the barrel. My guess is that the spark plug isn't igniting the fuel because its liquid, not a vapor, and it isn't under pressure or high temperature (call me crazy again, but I tried heating up Gasoline/Alcohol to about 60 celcius, no luck). I also tried putting in some butane on the mix, but my only source was a lighter - no luck either.

Well, I hope you guys can help me trouble-shoot my cannon. Here are the specs/drawings/photos:
The combustion chamber has a height of 50cm and a diameter of 3 inches (sorry for mixing up the units)
The barrel has a height of 70cm and a diameter of 2 inches
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Diagram

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The final product

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The cannon set up along with electrical system

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A high-res view of the cannon, with the electrical.

BTW, I forgot to take pictures of the internals/the covering cap on the end of the cannon, as well as the projectiles, but I guess what I posted should be enough for some basic troubleshooting.
Oh, and this is my first combustion cannon. I also built a pneumatic one a, and had great success with it - fires well every time, and can hold fairly high pressures losing about 1 PSI an hour :D

Thanks in advance for your help!

EDIT: Forgot to say how I am loading it. I am using a medicine spray bottle filled with the fuel. Plan on posting a picture soon...
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Unread postAuthor: Spyider » Wed Nov 08, 2006 4:49 pm

ok well if you cant get the parts at a local store why not jjst order them so the gun works correcly. anyways ide get some propaine off line im sure you can order some. if you cant get propaine just use hairspray now i now they got that over their... sure it might gunk the chamber up a little but ittle shoot better that a gas one! :twisted:
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Unread postAuthor: rna_duelers » Thu Nov 09, 2006 1:45 am

Well do you have a computer fan to your desposal?They work very well at increasing perfomance and also mixing the fuel and oxygen together.I have a gun that when the fuel is put in it it will not fire very well unless the fuel and oxygen is mixed.So give that a try.

If you do get a computer fan place it at the back of the chamber forcing air down towards the barrel,and turn the fan on for about 4 seconds before fireing.

Let me no if it works.Also you could try some arosol can sprays like spray cooking oil or anything else wiht flammable gasses.

Your English is fine,far from shocking like some people on this forum that have it as there first language.
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Last edited by rna_duelers on Thu Nov 09, 2006 4:44 am, edited 1 time in total.
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Unread postAuthor: killagorrila99 » Thu Nov 09, 2006 2:36 am

I know how you feel, I've recently had a combustion fail on me (AGHHHH!) Just scrap it and build a bigger one.
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