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Stratigic Spark Placment

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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Unread postAuthor: joannaardway » Tue Aug 21, 2007 1:05 pm

paaiyan wrote:I agree with putting the spark in the back, though I like my own idea better. Build an induction coil capable of producing a spark that runs the entire length of the chamber. Place one electrrode at the front, one at the back. Problem solved!

You do better with a Marx Generator than an induction coil.

If you need a spark more than 54", your chamber is too big. If you need a spark hotter than that, you're using the wrong fuel.
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Unread postAuthor: paaiyan » Tue Aug 21, 2007 1:25 pm

joannaardway wrote:
paaiyan wrote:I agree with putting the spark in the back, though I like my own idea better. Build an induction coil capable of producing a spark that runs the entire length of the chamber. Place one electrrode at the front, one at the back. Problem solved!

You do better with a Marx Generator than an induction coil.

If you need a spark more than 54", your chamber is too big. If you need a spark hotter than that, you're using the wrong fuel.


Impressive as that is, I think it's a bit above my skill with electronics.
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Unread postAuthor: psycix » Tue Aug 21, 2007 8:03 pm

The pressure rises equally in the whole chamber during combustion, in, behind or before the flamefront rules the same pressure (flame fronts go fast, but pressured gasses equal MUCH faster)

in my oppinion the DIRECTION of the flame front DOESNT MATTER
the only thing that matters is the SPEED of the combustion

this would tell:
middle = best

but since we only go for the fastest combustion of all gasses:
place multiple electrodes in front, middle, and back wich will start multiple combustions burning very very fast raising the pressure the fastest
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Unread postAuthor: paaiyan » Tue Aug 21, 2007 8:25 pm

psycix wrote:The pressure rises equally in the whole chamber during combustion, in, behind or before the flamefront rules the same pressure (flame fronts go fast, but pressured gasses equal MUCH faster)

in my oppinion the DIRECTION of the flame front DOESNT MATTER
the only thing that matters is the SPEED of the combustion

this would tell:
middle = best

but since we only go for the fastest combustion of all gasses:
place multiple electrodes in front, middle, and back wich will start multiple combustions burning very very fast raising the pressure the fastest


Well if speed is what matters, then middle isn't best. A foot-long spark running the length of the chamber would ignite it all at once, there's your speed.
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Unread postAuthor: jimmy101 » Wed Aug 22, 2007 10:14 am

Rock, I've also always figured the center was best. It sure seems to me that two flame fronts will be better than one, even if one of the flame fronts is moving a bit slower than the other.
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Unread postAuthor: pyrogeek » Wed Aug 22, 2007 10:44 am

What about just shooting a bigass flame through the chamber to ignite it all? Like have a chamber with a union on it, and charge that with propane and compressed air. Then feed that into a pipe running the length of the chamber with multiple holes drilled. That could probably ignite it all really well.
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Unread postAuthor: jimmy101 » Wed Aug 22, 2007 1:10 pm

pyrogeek wrote:What about just shooting a bigass flame through the chamber to ignite it all? Like have a chamber with a union on it, and charge that with propane and compressed air. Then feed that into a pipe running the length of the chamber with multiple holes drilled. That could probably ignite it all really well.


DR on the old SPUDTECH forums tried something like this. It seems to work if there is a very light projectile (e.g., a paper towel) but it doesn't seem to do anything with a real projectile. Probably because you are injecting into a chamber that itself pressurizes, which slows down the injected gases very quickly.

This ignition mode has been fairly well studied in combustion engineering. Google "pressure piling", or take a look at this paper.

IIRC, the basic approach works sometimes with things like rocket engines but it doesn't work for things like internal combustion engines (which is basically what a spudgun is).
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Unread postAuthor: thespeedycicada » Wed Aug 22, 2007 1:21 pm

paaiyan wrote:
joannaardway wrote:
paaiyan wrote:I agree with putting the spark in the back, though I like my own idea better. Build an induction coil capable of producing a spark that runs the entire length of the chamber. Place one electrrode at the front, one at the back. Problem solved!

You do better with a Marx Generator than an induction coil.

If you need a spark more than 54", your chamber is too big. If you need a spark hotter than that, you're using the wrong fuel.


Impressive as that is, I think it's a bit above my skill with electronics.
Actually small ghettoish marx generators are cheaper and simpler than tesla coils in fact the first high voltage thing i did was a marx its really not that complex.
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