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help on combustion chamber

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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help on combustion chamber

Unread postAuthor: sean.gale13 » Wed Mar 27, 2013 1:43 am

hi i have just built a spud gun with a combustion chamber made of 50mm PVC and barrel 16mm aluminium, i have completely seal the end cap and installed a valve so that a fuel cell from a pasload nail gun injects a limited amount of gas into the chamber. As the trigger is pulled the gas is released then ignition but not combustion, it will fire roughly every 30 attempts. Im sure the problems is that there is not enough oxygen, i am wondering if there is any other small fuel cells that are self sufficient without oxygen and will fire consistently? Or if i need to install a small fan that will create a constant flow or external air to give it the right ratio? any help would be really appreciated
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Unread postAuthor: jsefcik » Wed Mar 27, 2013 6:24 am

A fan would certainly help between shoots to vent out spent fuel,, also to mix the fuel while its inside
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Unread postAuthor: jimmy101 » Wed Mar 27, 2013 5:54 pm

You inject and then ignite in one go? Even if you fuel ratio is OK I would expect it not to ignite since the fuel won't be properly mixed.

Separate fuel injection from firing by at least a few tens of seconds, of by a few seconds if you have a chamber fan.
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Unread postAuthor: sean.gale13 » Wed Mar 27, 2013 7:52 pm

I can control the time between injection and ignition( pull trigger half way to inject gas, pull trigger all the way to ignite) this system allows me to do more than one injection of gas before ignition if I need to, where can I find plans on a fan system that will not be destroyed from firing ??? Thanks guys
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Unread postAuthor: jsefcik » Wed Mar 27, 2013 9:46 pm

sean.gale13 wrote:I can control the time between injection and ignition( pull trigger half way to inject gas, pull trigger all the way to ignite) this system allows me to do more than one injection of gas before ignition if I need to, where can I find plans on a fan system that will not be destroyed from firing ??? Thanks guys


For a fan just use an old 12v computer fan, hook it to a project box, fans dont get destroyed cause of the combustion being so quick it doesnt melt or it
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