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How to seal spark gap to for high pressure and what to use?

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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How to seal spark gap to for high pressure and what to use?

Unread postAuthor: boyntonstu » Sun Jul 19, 2009 2:09 pm

A few questions:

I am thinking of building a Hydrogen gun.

If the H2/O2 ratio is 3:1 not much of spark is require to cause ignition.

I believe that this Hydrogen spud gun uses way more voltage than necessary:

http://www.youtube.com/watch?v=uSXcV-r1Ifs

Seems that a spark plug would work and seal OK.

What other kind of insulated pass throughs are there?

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Unread postAuthor: Hotwired » Sun Jul 19, 2009 2:47 pm

Spark plugs work fine. Unless you're going off your head and doing very high compression ratio hybrids (at which point the ceramic insulation cracks on firing) then it's all good.

Yes, that cannon looked like it was using a stungun ignition for a basic hydrogen combustion. Overkill but no ones counting the wasted joules. A clicky piezo would work any day of the week.
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Unread postAuthor: boyntonstu » Sun Jul 19, 2009 3:18 pm

Hotwired wrote:Spark plugs work fine. Unless you're going off your head and doing very high compression ratio hybrids (at which point the ceramic insulation cracks on firing) then it's all good.

Yes, that cannon looked like it was using a stungun ignition for a basic hydrogen combustion. Overkill but no ones counting the wasted joules. A clicky piezo would work any day of the week.


Here's an idea: A couple of pass through diodes.

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Re: How to seal spark gap to for high pressure and what to

Unread postAuthor: jimmy101 » Sun Jul 19, 2009 3:21 pm

boyntonstu wrote:What other kind of insulated pass throughs are there?

Don't need insulation at all if you use two pass throughs. I prefer two fine thread drywall screws because of their nice pointy tip. Screws also have the advantage that it is easier to get the spark out near the center line of the chamber instead of up against the chamber wall.

If you are using a metal chamber then you might consider getting nylon screws and drilling a very small hole though'm for the wire. Since the gauge of the wire is pretty much irrelevant, you can use 30G magnet wire. Drill and tap suitable holes in the chamber to match the nylon screws.

Or, for that ghetto look, drill two small holes (<1/16"D), pass through 30G magnet wire and seal with just about anything. Heck, hot melt glue would probably work for holes that small. :D
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Unread postAuthor: KineticAmbitions » Sun Jul 19, 2009 3:50 pm

I've seen it accomplished nicely using two lengths 14 gauge solid copper wire wrapped in electrical tape. They are then both passed through a 1/2" brass cap with a 1/2" hole drilled through the top, and the cap is filled with JBweld or some other epoxy. The ends in the chamber are bent toward each other, leaving a 1mm or so gap, and the ends outside the chamber are bent away to prevent arcing. Pipe nipples can be used as well, but there is no lip to grip, and mixes any higher than 10x or so on large chambers tend to push the epoxy plug out.

Another good option is Model T sparkplugs - they use a 1/2" pipe thread and are thus easily adapted to chambers. Their failure point is somewhere around 30x in large chambers, from what I've seen, at which point the insulator breaks completely through the lip holding it in place, and fires out the back of the plug at dangerous speeds.

In a plastic chamber, machine screws with sharpened ends can be used - simply drill and tap the hole to the correct thread, and countersink the holes to provide a flat sealing face on which you can place an O-ring.
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Unread postAuthor: boyntonstu » Sun Jul 19, 2009 4:00 pm

How about using a Schrader valve?

Fill with it and spark though it.

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Unread postAuthor: Technician1002 » Sun Jul 19, 2009 4:23 pm

boyntonstu wrote:
Hotwired wrote:Spark plugs work fine. Unless you're going off your head and doing very high compression ratio hybrids (at which point the ceramic insulation cracks on firing) then it's all good.

Yes, that cannon looked like it was using a stungun ignition for a basic hydrogen combustion. Overkill but no ones counting the wasted joules. A clicky piezo would work any day of the week.


Here's an idea: A couple of pass through diodes.

BoyntonStu


In my many years in electronics, I've never head of them.. Could you possibly be thinking of pass through capacitors? In a spark application, they are not built for the pressure and they as a noise suppression device, will shunt an ignition pulse to ground.

Do you have a reference to the part you mention?

A feed through capacitor looks like this;
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Unread postAuthor: jimmy101 » Sun Jul 19, 2009 4:39 pm

Technician1002 wrote:In my many years in electronics, I've never head of them.. Could you possibly be thinking of pass through capacitors? In a spark application, they are not built for the pressure and they as a noise suppression device, will shunt an ignition pulse to ground.

Perhaps he is thinking about a stud rectifier. Only problem is that the body is one of the electrical contacts. For example http://www.allelectronics.com/make-a-st ... R/-/1.html .
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So I don't think it will work.
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Unread postAuthor: Technician1002 » Sun Jul 19, 2009 4:46 pm

jimmy101 wrote:
Technician1002 wrote:In my many years in electronics, I've never head of them.. Could you possibly be thinking of pass through capacitors? In a spark application, they are not built for the pressure and they as a noise suppression device, will shunt an ignition pulse to ground.

Perhaps he is thinking about a stud rectifier. Only problem is that the body is one of the electrical contacts. For example http://www.allelectronics.com/make-a-st ... R/-/1.html .
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So I don't think it will work.


That is a stud mount rectifier. It is true the case is one of the two leads. It is not a pass through part.
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Unread postAuthor: boyntonstu » Sun Jul 19, 2009 5:11 pm

I am sure that you guys are correct.

Thanks,

This would do it nicely with a 1/4 -32 thread:

http://tinyurl.com/nwageq

CHAMPION V-2 SPARK PLUG FOR MODEL CAR, BOAT, AIRPLANE ENGINES, NICE

HERE IS A CHAMPION V-2 SPARK PLUG THAT HAS BEEN INSTALLED AND FIRED BUT IS IN REALLY NICE CONDITION. THIS IS A ¼” - 32 THREAD LONG REACH PLUG. THIS IS THE SPARK PLUG THAT IS RECOMMENDED FOR USE IN MANY ENGINES INCLUDING THE FORSTER 29 IGNITION ENGINE, MOST O&R ENGINES, VIVELL 35, AND OTHERS.

Or perhaps a lawn mower engine spark plug.

The smaller, the better.



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