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Spark Plugs

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: Fnord » Wed May 02, 2012 5:22 pm

yes a electric grill ignitor is a little less expensive, but its doesnt give you 100,000 volts or more like a stungun


You won't get 100,000 volts with a stungun either. Those numbers are taken from what the circuit can theoretically put out with no load applied. Add a spark gap and it'll go way down.
If you can't jump a 3.5 inch gap with your stungun, it's not putting out 100kv.

Grill igniters, seventeen dollars at walmart. Appears to be designed for two gaps and comes with a battery.
http://www.walmart.com/ip/Backyard-Gril ... t/19581268
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Unread postAuthor: Bowman » Wed May 02, 2012 6:14 pm

@Fnord Thanks for the link it's a great find. I just have one more question and if the answer is yes then I think I have some more designing and testing to do. Anyway, how could I get around shorting the circuit out. Because, if you just take an aluminum combustion chamber drill two holes in the side and attach two screws (spark gap) then the circuit will short out because the bolts in the spark gap will be touching the aluminum so the chamber itself will short out the circuit. I had an idea of just maybe wrapping some rubber tubing around the bolt or something that way it won't touch the aluminum. It looks like on that grill igniter they already have that so would it work?
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Unread postAuthor: Fnord » Wed May 02, 2012 6:22 pm

Notice the white cylindrical parts on the electrodes- it's a ceramic insulator similar to what is found in spark plugs. You could either drill a hole to epoxy them into, or go with sparkplugs as in your original idea
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Unread postAuthor: Bowman » Wed May 02, 2012 7:07 pm

Alright drill a hole and just insert them and they'll be fine. I know I said no more questions but are you sure epoxy will hold a seal. You see, the cannon will be powered by propane. So, it has to seal, I was thinking of attaching them with JB weld, plumbers goop, or epoxy putty. Or even all of them combined.
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Unread postAuthor: Fnord » Wed May 02, 2012 7:39 pm

JB weld will hold and seal fine for a normal 1x combustion. It's rated for temperatures of around 500F also. Don't try to mix different adhesives.

Spark plugs will be a little more durable, but take more work to install. It's a trade-off.
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Unread postAuthor: Bowman » Wed May 02, 2012 8:53 pm

By 1X combustion do you mean single shot? Because this design is semi automatic. Oh well, I guess I'll end up going with the grill ignitor because it's easier to install and the design has it to where the gun can be easily disasembled.
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Unread postAuthor: jsefcik » Wed May 02, 2012 9:36 pm

Fnord wrote:
yes a electric grill ignitor is a little less expensive, but its doesnt give you 100,000 volts or more like a stungun


You won't get 100,000 volts with a stungun either. Those numbers are taken from what the circuit can theoretically put out with no load applied. Add a spark gap and it'll go way down.
If you can't jump a 3.5 inch gap with your stungun, it's not putting out 100kv.

Grill igniters, seventeen dollars at walmart. Appears to be designed for two gaps and comes with a battery.
http://www.walmart.com/ip/Backyard-Gril ... t/19581268



still junk in my eyes
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Unread postAuthor: Bowman » Wed May 02, 2012 11:00 pm

still junk in my eyes


Coming from the guy who said to hook up a stun gun to a pvc pipe.......
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Unread postAuthor: mackconsult » Thu May 03, 2012 12:46 pm

Built up an aluminum spud gun out of spare material. Tapped the end plate for 14 mm spark plug and wired a BBQ light to it.

It is sparking but no combustion for some reason.

Any thoughts .... the BBQ lighter was one of those cheap disposable ones ($1) at walmart.
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Unread postAuthor: jimmy101 » Thu May 03, 2012 1:13 pm

mackconsult:
Most likely cause is a bad fuel mixture, usually too rich. For propane in air the volume of propane must be between about 3% and 8%. Percentages outside that range won't ignite regardless of the spark source.
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Unread postAuthor: Fnord » Thu May 03, 2012 5:12 pm

Bowman wrote:By 1X combustion do you mean single shot? Because this design is semi automatic.


1x, as in one chamber volume of air/fuel.
A 2x combustion would mean pumping in another volume of fuel and air, or adding additional oxygen. It would be considered a 'hybrid'.

Basically I was just saying it'll be fine for low pressures, but for anything else such as propane/pure oxygen, used threaded fittings.
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Unread postAuthor: natas » Thu May 03, 2012 5:35 pm

if u want easy to install. id say this one is really easy :-)

http://ultimatespudgun.com/30kv-igniter-p-219.html
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Unread postAuthor: Bowman » Thu May 03, 2012 5:41 pm

natas wrote:if u want easy to install. id say this one is really easy :-)

http://ultimatespudgun.com/30kv-igniter-p-219.html


There aren't any electrodes so I assume you use these: http://ultimatespudgun.com/electrodes-c ... p-273.html

Also, I found something even better (more expensive) but in my mind better.
http://ultimatespudgun.com/pistol-grip- ... p-274.html

I'll probably end up using these. I have no further questions. I guess this thread is done?
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