It Lives ! well its halfway alive. And found great fuel.

Boom! The classic potato gun harnesses the combustion of flammable vapor. Show us your combustion spud gun and discuss fuels, ratios, safety, ignition systems, tools, and more.
Rob748
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Mon Mar 02, 2009 8:58 pm

Guess what. I got $25 and put together my cannon. It has a 2 spark gaps that I made exactly like Burntlatke.com. I also found a ver very very bopomy fuel. Old spice aersol works wonders. All the other fuel I used burned slowly when I sprayed some into the chamber and ignited it with the end cap off. Old spice however has like a explosion reaction. and its fairly loud for the end cap off. It Looks like a Atom Bomb explosion lol. It burns very very fast. Other than that. I still need like $30 for the metering system. Tommorow I will have a fan.

Specs
C Chamb. 15 in by 3 in
Barrrel 32in by 1in
Soon to be metered =fan
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Radiation
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Mon Mar 02, 2009 9:07 pm

Good that you started something finally. I hope you like the burnt stench of ol' spice because once you use it that smell never leaves your cannon.
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Rob748
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Mon Mar 02, 2009 10:08 pm

O I could get use to it. Am I right though ? its a very good fuel ?
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starman
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Mon Mar 02, 2009 11:13 pm

Not any better than a metered propane system would be. I would limit the Old Spice shots to testing and some "what the heck shots". Your real shootin' happens with metered propane.
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Tue Mar 03, 2009 1:25 pm

Rob748 wrote:O I could get use to it. Am I right though ? its a very good fuel ?
Any fuel that works for you is a "good fuel".

Beyond ease of use, availability and cost there is really very little difference in fuels. The energy in the various fuels is nearly identical. So close in fact that you can't tell the difference unless you carefully measure the muzzle energy. In a spray-n-pray fueling mode the error in fuel ratio is a much larger affect than is the small differences in the energies of various fuels.

Your observation that Old Spice burns faster is almost certainly an artifact of how you fuel the chamber. Just about any flammable fuel, when properly measured, will give a fast burn rate in an open chamber. Almost any fuel when improperly measured will give a slow burn rate. Same in a closed chamber (or working spudgun). Get the fuel ratio correct and all fuels behave about the same. Get the fuel ratio incorrect and all fuels perform poorly. Poor mixing of the fuel with the air is equivalent to having an incorrect fuel ratio.

The burn rate of propane in an open tube is highly dependent on the fuel ratio. The difference in burn rate between properly measured and mixed fuel and a fuel ratio near the upper combustion limit is huge. Near the upper combustion limit the flame propagation rate is only about 1 foot/second. You could "outrun" the flame front just by walking away from it.
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