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Micro combustion problems...

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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Micro combustion problems...

Unread postAuthor: qwerty » Sun Sep 19, 2010 5:12 am

Here's the scenario:

So i fill my syringe with 2ml of propane, i inject it into the chamber (which has a barrel on with a BB inside) i then pump the syringe 6 times without taking it out the chamber, when firing i dont take the syringe out and get constant ignition but the BB never exits the barrel it sounds and feels like it ignites, gets forced halfway down the barrel then gets sucked back in.
Almost like it's making its own vacuum.

Any ideas whats wrong?
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Unread postAuthor: jackssmirkingrevenge » Sun Sep 19, 2010 5:28 am

i then pump the syringe 6 times without taking it out the chamber


Por que?

What's your ignitor and how big is your spark gap? Are you injecting the correct amount of propane?
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Unread postAuthor: qwerty » Sun Sep 19, 2010 5:46 am

Ignition is a bbq pezio spark gap is about 4mm and i'm pretty sure it's at optimal ignition as i've tried others with no successful ignition

Basicly there is a hole in the side of the chamber where i inject the fuel, but i pump it up and down 6 times before i click the pezio.
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Unread postAuthor: jackssmirkingrevenge » Sun Sep 19, 2010 5:59 am

can you increase the gap to around 7mm and not pump the syringe?
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Unread postAuthor: ilovefire » Sun Sep 19, 2010 6:13 am

how long is the barrel because if it is was to long then the gas starts to cool before the projectile leaves the barrel sucking it back, i have experienced it before and i think it even sucked the projectile back into the barrel after leaving
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Unread postAuthor: jimmy101 » Sun Sep 19, 2010 9:58 am

We need to know the chamber and barrel volumes.

Is there significant leakage around the syringe inlet port?
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Unread postAuthor: qwerty » Sun Sep 19, 2010 11:01 am

Well i cut down the barrel and it fires now.

Just to make a mini hybrid now...

Off topic but is this right.

(not exact) for a 3x mix i would want %12 propane and 30psi?
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Unread postAuthor: jackssmirkingrevenge » Sun Sep 19, 2010 11:09 am

qwerty wrote:(not exact) for a 3x mix i would want %12 propane and 30psi?


pretty much ;)
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