bluerussetboy wrote:as in the above post, air and fuel will be mixed before injected into chamber
Sorry to burst your bubble, but unless you're building a hybrid, this isn't going to work.
In a normal metered propane cannon, there's a static volume of air inside the chamber, to which you add an exact amount of propane to create a stoichiometric fuel/air mixture.
If you intend to mix the air and fuel outside of the chamber, you either need to be injecting this fuel/air mixture into a vacuum, or you need to calculate in the amount of air inside the chamber, which defeats the purpose.
If you inject both air AND fuel into a chamber already containing air, your mixture will be far too lean, again, unless you're building a hybrid.
Additionally, you'd need to be able to seal off your fuel mixing/metering system from the chamber, to prevent combustion inside the mixing system, which could be catastrophic.
Also, any length of PVC or copper pipe and fittings, as you've drawn, would weigh significantly more than a small motor and battery, as several other people have pointed out. Perhaps you could somehow make your inside-chamber-gas-distribution-pipe also act as a spark strip.
My only other thought would be to use a venturi, much like the one on the tip of a propane torch, inside the chamber where the fuel comes in - this would effectively mix the fuel, and shouldn't weigh much.
Keep in mind a chamber fan has other advantages besides just mixing the fuel - it creates a hotter, faster combustion, and also aids in venting the chamber between shots.
Good luck with your build.
Peace,
Pete Zaria.
