Advantage of multiple ignition points?

Mr. Sir · Sat Oct 30, 2010 4:05 am

After searching through old topics, it seems that there is no definitive answer regarding the possible performance increase of multiple spark gaps vs. one well placed gap. The reason I am wondering is because I am thinking of building a cannon with several (6?) evenly spaced ignition points down the length of the chamber (4"x18"). The cannon is also going to have an onboard propane/mapp meter, mixing fan, and stun gun circuit. Given the mixture is stoichiometric throughout the whole chamber, the excessive spark gaps will cause the flame to propagate at six different places, allowing for quicker combustion and more power. This is just my guess. Let me know what you guys think.

Also I am new to the forum. I lurked for the last week just reading through all this great information. I hope to learn much more and contribute to this awesome community. Thank you for your time.

ilovefire · Sat Oct 30, 2010 4:41 am

welcome to spudfiles

yes you will get better performance with more spark gaps the quicker combustion will result in the projectile building up more speed in the given barrel length then a slower combustion would, will like to see how it works out for you and good luck

POLAND_SPUD · Sat Oct 30, 2010 5:12 am

But does this mean that multiple spark gaps are not that important on small volume combustions?

ilovefire · Sat Oct 30, 2010 5:24 am

POLAND_SPUD wrote:But does this mean that multiple spark gaps are not that important on small volume combustions?

on a small volume combustion you will also have a smaller barrel so to get it to reasonable speeds, the more spark gaps the better on whatever volume chamber

spudamine · Sat Oct 30, 2010 11:16 am

After searching through old topics, it seems that there is no definitive answer regarding the possible performance increase of multiple spark gaps vs. one well placed gap.

Try downloading HGDT and having a play, It allows you to model multiple spark gaps.
http://thehalls-in-bfe.com/HGDT/

Fnord · Sat Oct 30, 2010 12:08 pm

Jimmy did a study of this some time ago. It's about the most technical any of us have gotten.
Here:
http://www.spudfiles.com/forums/studies ... 12807.html

Mr. Sir · Sun Oct 31, 2010 12:07 am

Thanks for the info. I went ahead and built my chamber tonight. I threaded in five automotive spark plugs down the length of it. I know that the spark is way off center using plugs, but they look cool. It's not nearly the most efficient ignition setup but I want my cannon to be aesthetically pleasing. Hopefully the amount of sparks will make up for the fact that they are not centered.[/img]

Pete Zaria · Thu Nov 04, 2010 12:39 am

I believe the primary reason for multiple ignition points is to create multiple flame fronts inside the chamber during ignition, which theoretically deceases the time required to achieve peak pressure and helps to ensure complete combustion. However, I'd bet that the difference is only a few percentage points.

I used a long, thin piece of circuit board blank that runs the length of the chamber with small gaps etched (with a file) every few inches that create spark gaps.

Like a simplified version of this: http://www.burntlatke.com/strip.html

Ah, found some pics:

Peace,
Pete Zaria.