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Sealing off the combustion chamber mid combustion...?

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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Sealing off the combustion chamber mid combustion...?

Unread postAuthor: broken_system » Wed Dec 02, 2009 12:22 pm

I have posted a few topics on here asking various things about combustion cannons. There is one more thing that I have thought about that I wanted to get some feedback about.

A note before reading: i am firing smaller rounds through about a 3/4" barrel. Fuel source: propane/o2

Suppose I had a combustion chamber followed by a barrel (duh lol), however inside I had a bolt system between the barrel and combustion chamber that would propel forward and allow gas to launch the projectile. Attached to this bolt would be a "door" type disk that would close off the combustion chamber from the barrel.

Now, suppose this happened mid combustion, would the expanding gas have enough time to travel out of the combustion chamber through the barrel?

The reason I ask is because I want to have a fast r.o.f therefor need a fast cycling rate of the combustion/venting the combustion chamber/adding more fuel.

My idea is that if I can shut the barrel off from the chamber, this would allow the remainder of the gas in the chamber to be harnessed and used to help vent the chamber, after this I would have some mechanical process to tap a valve to allow fuel to enter, ready for the next shot.

In my mind it seems that it would work given that the bolt only gets shoved forward after the gas expands, allowing it to launch the projectile. This would happen very quickly so even if I seal the chamber the projectile should be close to exiting the barrel (which would be max 1-2' long).
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Unread postAuthor: kenbo0422 » Wed Dec 02, 2009 1:45 pm

It sounds like a typical blow forward design. The valve is closed until it reaches a point where the magazine is closed off and the projectile can fire. The return spring would push back and close off the chamber again. With a propane/O2 system I don't know if the pressure will sustain long enough to give you the leftover effect to mechanically purge the chamber. I believe it may have been tried here before, but don't quote me on that.

There are others here who will have more experience with this concept. Just wait, someone will surely chime in.... 3 2 1
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Unread postAuthor: Lockednloaded » Wed Dec 02, 2009 5:54 pm

well for the "door type disk" you could use a butterfly valve, but i don't know how you could mod it do so. I'm no expert, so like kenbo said wait for someone with experience with this to help work out the details.
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