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Double action Propane Combustion Airsoft gun Design

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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Double action Propane Combustion Airsoft gun Design

Unread postAuthor: auxiliary » Fri May 02, 2008 11:46 pm

I have come up with a design for an airsoft gun that uses propane combustion to load and shoot a BB all in one pull of a trigger (on shot per trigger pull)

The way it works is you pull the trigger which pushes back the piston releasing a controlled amount of propane, and at the end of the trigger pull, the button for the battery igniter is pressed, igniting the mixture.

When it explodes, the expanding gases push the blow forward mechanism forward on the top part of the gun. When the blow forward mechanism reaches a far enough point, the first o-ring is tripped and the gases can rush through the rod into the air nozzle. The second and farther up towards the barrel o-ring retains the blow forward mechanism and prevents leak during combustion.

While the blow forward mechanism is moving forward, the air nozzle loads the BB and hits the hop-up seal (Hop-up is not shown it will probably be a typical airsoft hop-up) right before the first o-ring is tripped so the gases will rush directly down the barrel propelling the BB.

I have a few questions about my design though. What would be the optimal ration of propane and air for the best combustion to take place? Will I have to come up with a way to exhaust the remaining gases after ignition? Will I have to make a way to draw in atmospheric air every time before combustion or will the entrance of air through the barrel be sufficient? Will the build up of heat be significant enough to make a water coolant tank necessary if the combustion chamber is about 100ml volume and made of copper? Also, will I have to worry about o-ring and Delrin(Turquoise colored) parts melting under the combustion? And lastly, will the piston that feeds the propane into the combustion chamber be a sufficient block from the rest of the fuel and the tank blowing up? (the piston housing will be a 1cm diameter aluminum tube in the 1.5cm copper tube housing) http://www.putfile.com/pic/8085321

Here is the diagram of the Tippmann C-3 for reference:
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Last edited by auxiliary on Sat May 03, 2008 10:44 am, edited 1 time in total.
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Unread postAuthor: Lentamentalisk » Sat May 03, 2008 12:39 am

well it wont burn if you use a 1:5 propane ratio, you need a ~1:20 ratio for good combustion.
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