igniter placement inside chamber

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Postby FLONE » Mon Nov 27, 2006 4:58 pm

Any opinions? I'm a firm believer in dual ignition, mostly want to hear where people think they should be placed. Thanks!
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Postby Mr.Plow » Mon Nov 27, 2006 5:13 pm

About 3/4ths of the way to the rear. Single ignition point. There are a lot of variables to consider and there is no perfect place that applies to all cannons, but generally thats how mine go.
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Postby SpudStuff » Mon Nov 27, 2006 6:39 pm

For a dual ignition you should have one at the front and one 1/2 way back. That way the burning gasses don't push out the unburned ones. It burns from the front back.
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Postby SpudBlaster15 » Mon Nov 27, 2006 9:34 pm

SpudStuff, let me guess. You built your combustion cannon with a single spark gap placed in the center of the chamber. Then you decided to add an additional spark gap, and placed it in the front. You then needed a reason to justify your decision, and thus formed that explanation because it is what you WANT to believe. The reason I say this is due to the fact that your suggested placement will not provide optimal performance. The spark gaps should be placed at 1/4 and 3/4 from the end of the gun.
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Postby sgort87 » Tue Nov 28, 2006 1:36 am

Where are those flame front animations when you need em? I used to think how SpudBlaster does until I saw those animations that show the way the jet of flame shoots forward.

SpudStuff, the unburned gasses are not pushed out. A flame jet shoots out the center of the gun. Besides, whether the gasses in the fornt are the ones burning or not, it has no effect on the prjectile's motion. Overall, the pressure in the system is the same everywhere.
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Postby SpudBlaster15 » Tue Nov 28, 2006 6:54 pm

So your telling me that placing 2 spark gaps in the locations stated does not provide optimal performance? I have tested several different positions using single, double, and triple spark gaps, and this works the best.
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Postby jimmy » Wed Nov 29, 2006 2:41 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by SpudBlaster15
[br]So your telling me that placing 2 spark gaps in the locations stated does not provide optimal performance? I have tested several different positions using single, double, and triple spark gaps, and this works the best.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Care to post some numbers?

The question of the number and location of the sparks has been kicking around for a while. I don't recall ever seeing any hard numbers that support any of the theories.

Granted, two sparks would be <u>expected</u> to be better than one, and three even better still. And, <u>presumably</u> there is an optimal location for the spark(s). But can you <b><u>actually measure the difference</u></b> between the various configurations? Has anyone ever tried to do it?

The only data a quick search turned up is <a href="http://www.burntlatke.com/strip.html">BurntLatke's comparison of two versus three spark gaps</a>. Latke found no significant difference between two and three sparks.
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Postby SpudBlaster15 » Wed Nov 29, 2006 8:14 pm

No numbers here, just experience.

Drawing the 'three sparks made very little difference over two' conclusion based on Latke's tests comparing a spark strip to electrodes is invalid. First of all, the 3 sparks were all placed closer together than the two electrodes. The point of using 3 spark gaps is to ignite the fuel at 3 different location in the launcher. Also, the sparks created by the spark strip would ignite the fuel at one side of the chamber, and it would have to burn outward aswell as forward/backward. Despite these deficits, the spark strip did increase the projectile velocity by an average of 20mph, imagine what a properly set up 3 spark system could do.
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Postby jimmy » Wed Nov 29, 2006 9:30 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by SpudBlaster15
[br]No numbers here, just experience.

Drawing the 'three sparks made very little difference over two' conclusion based on Latke's tests comparing a spark strip to electrodes is invalid. First of all, the 3 sparks were all placed closer together than the two electrodes. The point of using 3 spark gaps is to ignite the fuel at 3 different location in the launcher. Also, the sparks created by the spark strip would ignite the fuel at one side of the chamber, and it would have to burn outward aswell as forward/backward. Despite these deficits, the spark strip did increase the projectile velocity by an average of 20mph, imagine what a properly set up 3 spark system could do.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

Fine, you don't believe Latke's data.

BTW, the spark strip did not increase the the muzzle velocity. The average increased by ~20 MPH but the SD of the numbers is more than twice the difference between the two sets. To put it crudely, the two averages are, within experimental error, identical. Heck, the range within the individual datasets is +/-140 MPH, so a ~20 MPH difference between the sets is not significant.

I don't believe "just experience" in the absence of any numbers. In the absence of actual measurements, everyone is just a "firm believer" in whatever their pet theory happens to be.
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Postby SpudBlaster15 » Thu Nov 30, 2006 7:33 pm

The only numbers I can give you are the distances my gun shot before and after adding an additional spark gap at the other end of the chamber. The additional spark gap increased the distance the projectile travelled by ~100ft.
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