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Built a combustion cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: Ragnarok » Mon Dec 15, 2008 3:16 am

Xxplosive42o wrote:It is still hard for me to accept after 12 shots proving one had greater speeds than the other that the results are irrelevant.

The results aren't irrelevant, but they have to be taken with a pinch of salt - you can't just apply them as a hard and fast rule.

Some cannons would see minor benefits in power and consistency from such a thing, but it carries no guarantees, adds extra wiring, and isn't essential (as Crusader proves), so it's up to each individual user if they want to do it. No reason to push anyone.

It's a much debated subject. Some people claim single sparks in certain places have the edge, some will promote dual/triple sparks, some use spark nets, some people talk of jet ignition (one of my favourite ideas), among others.

Each to their own I say.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: Moonbogg » Tue Dec 16, 2008 6:06 am

Ragnarok wrote:Yeah, sure, but you'll have to hop back in time and post it somewhere over a year and a half ago, destroying the continuity of time, etc, etc.

Contest is long since over.

Damn, how rediculous of me.

Spudblaster15, his chamber cracked. Solid wall ABS? Damn. What happened there? Maybe PLASTIC isn't the best choice for explosion containment. I think i'll make a nice stainless combustion with good old welds and bolted/gasketed connections.
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Unread postAuthor: Radiation » Tue Dec 16, 2008 8:45 am

Or maybe just don't use unrated material.
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I void warranties.

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Unread postAuthor: mark.f » Tue Dec 16, 2008 12:42 pm

Just to chime in, but I found that spark gaps spaced evenly in the center of the chamber to provide multiple spherical flame fronts has improved performance for me, but there's no scientific testing to prove this.

*obligatory Slowpoke image*
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Unread postAuthor: Xxplosive42o » Tue Dec 16, 2008 6:39 pm

Well it should theoretically help because...

The combustion process in a spud gun without correctly placed spark gaps or only one does not happen instantaneously. This is because the combustion radiates in a progressive pattern away from the spark. The spark ignites gases nearest to the electrode which then propagates outward away from the spark in a spherical pattern. You'll often hear this combustion progression across the cylinder referred to as the "flame front". A proper spark placement is a way to get the best flame front situation possible. If you manage to create multiple spherical flames within the chamber it will burn the available gas much quicker; thus creating a more powerful expansion. But note, the distance between one gap and the next must be carefully measured and placed for this to be effective. Like Starman wrote, "For instance, 2 gaps placed within a couple of inches of each other in an 18" chamber isn't going to make any performance difference".

In addition, there are also other factor's that can influence the time it takes for combustion to be complete. These include: air/fuel mixture, density (temperature), volumetric efficiency of chamber, turbulence, physical shape of the combustion chamber.

Hope this clears up some confusion with new builders who are curious. 8)
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" Forget about all the reasons why something may not work. You only need to find one good reason why it will. "
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