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pressurized hydrogen spark gap

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Microwatt

Thu Feb 17 2011, 09:44PM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
Location:
Posts: 224

take a look at my spark gap i just designed. It uses two automotive spark plugs threaded into a machined block of plastic. the hydrogen is made by acid onto zinc. pressures above 20 bar are possible and rise times in the ten of picosecond range. can switch jundreds of kilovolts please add comments or suggestions.

Nah

Thu Feb 17 2011, 11:07PM

Registered Member #3567 Joined: Mon Jan 03 2011, 10:49PM
Location: USA, 1960s
Posts: 260

How are you going to refuel this thing? Wouldn't it be much easier to just connect this to a tank of H2? Also, wouldn't the spark arc through the acid, causing this think to go BAM?

Just saying, I'm not trying to be mean or anything.

Adam Munich

Thu Feb 17 2011, 11:54PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Ftr, a car battery can make a lot of H2 in a short amount of time.

Dr. ISOTOP

Thu Feb 17 2011, 11:58PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Why spark plugs? Why not regular round spark gap terminals?
Also, I second the use of a tank of H2.

Newton Brawn

Fri Feb 18 2011, 01:41AM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

Whatt the purpose of this spark gap ??
Remember that the auto sparg gaps may have a serie resistor inside, that causes adiverse effects in the switching...

Microwatt

Fri Feb 18 2011, 03:03AM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
Location:
Posts: 224

hydrogen gas helps reduce the jitter. I can show research that pressurized hydrogen gas has a breakdown limit of a milion volts per cm. Getting a tank is too much trouble. whats wrong with making a reaction chamber and having that feed through to the spark gap?

Xray

Fri Feb 18 2011, 05:24AM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

Microwatt wrote ...

hydrogen gas helps reduce the jitter. I can show research that pressurized hydrogen gas has a breakdown limit of a milion volts per cm. Getting a tank is too much trouble. whats wrong with making a reaction chamber and having that feed through to the spark gap?

Hydrogen gas is EXTREMELY explosive when mixed with O2 in the air. BE CAREFUL!

jpsmith123

Fri Feb 18 2011, 06:34AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843

Hmmm let's see, first of all, you'll have not pure hydrogen, but a mixture of H2, HCl and H2O vapor, resulting in a conducting, corrosive mess.

But even if you could somehow fill it with pure hydrogen, your device, as shown, wouldn't work very well, if it would work at all, that is.

I realize that it's just a quick sketch illustrating a concept, but if anything remotely resembling that device as shown was built and filled with high pressure gas, it would simply flash-over on the outside (and/or possibly on the inside).

If a spark gap is to be operated in the open air, the creep distance along the outside surface has to be sufficiently large to prevent flash-over.

Also, as per your sketch, the device as shown would have lots of inductance and a very low switching speed due to the very large inductance and also due to the relatively large resistive phase component of switching. Getting a fast switching speed (especially into a low impedance load) means operating the spark gap at a very high field intensity (i.e., having a very short gap at high pressure).

Then there's the mechanical design which has to be safe at high pressure; the thermal considerations; internal and external creep distances; electrode material considerations and the issue of evaporated electrode material depositing on the walls; etc.

Lastly, IIRC, the highest pulse rep rate for a H2 filled spark gap that I recall seeing in the literature was maybe 1 kHz or something like that.

I am certianly no expert on spark gaps, but I've looked into it a little bit - enough to realize that while spark gaps are seemingly simple devices, designing a high performance spark gap is anything but trivial.

If you go to the web sites of commercial spark gap manufacturers, and look at some of the literature they have, e.g., data sheets and application notes, you'll get an idea of what's involved.

Here's a paper on an electromagnetic pulser that uses a specially designed spark gap operating with H2 at 300 psi. On page 10 you can see a picture of the spark gap and get an idea of all the careful design and construction work that went into it:

cedric

Fri Feb 18 2011, 12:01PM

Registered Member #2941 Joined: Fri Jun 25 2010, 08:08AM
Location:
Posts: 143

Grenadier wrote ...

Ftr, a car battery can make a lot of H2 in a short amount of time.

with oxygen ...

Proud Mary

Fri Feb 18 2011, 02:59PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Might not the vigorous effervescence in your hydrogen generator produce an aerosol of conductive fluid in your spark chamber, or at least increase the humidity in a leaky way? Acid exhalations from the gas generator might develop a taste for the sparking plugs' steel parts, while chloride ions set up house in your spark chamber, awaiting a super speedy escape into the outside world.!

What temperature and pressure do you expect in the spark chamber on ignition, and how have you calculated the maximum internal wall temperature and maximum safe shock load and deformation stress that your 'machined block of plastic' can withstand?

Assuming you can sort these problems out, you'd have to design the device as a transmission line element if switching speeds of 'tens of picoseconds' are to be achieved, so the gap geometry and impedance can not be chosen arbitarily.

How will you measure the length of your picosecond pulses?

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