New Spark Plugs Pass First Tests
(3) CommentsOur new spark plugs, which we hope to be far more rugged than the old, automotive ones, have passed their initial tests.
Production of the spark plugs was slowed during May, partially because of redesigns needed as we went along. In addition, our first designs, tested in late May, did not work well. Based on recommendations from our colleagues at Princeton Plasma Physics Laboratory, as well as our own investigation, we had selected Macro, a tough ceramic, as the insulator for the spark plugs. In addition, we tried to isolate the insulators from the new tungsten pins by leaving a 1/100 inch gap between them. The tungsten expands slightly, but very rapidly during the current pulse as it is heated by the current. If the tungsten is in contact with the insulator, the sudden expansion will cause a sharp shock to the insulator. So the idea was to keep the tungsten and the insulator apart, as well as using an impact-resistant ceramic.
However, this idea did not work. Even a slight curvature of the tungsten pin caused it to come into contact with the insulator. In our initial tests, all four insulators broke after two shots. It seemed possible that more careful alignment might succeed in isolating the pin, but we thought that we needed a much more rugged and reliable solution. Dr. Subramanian suggested Lexan plastic. Lexan is extremely hard to break, being used for bullet-proof glass, but melts at low temperatures. So here we could have a snug fit to the tungsten, since we would not worry about impact, but needed to isolate the insulator for the extremely high temperatures generated at the tip of the tungsten pin by the plasma. We decide to end the insulator 0.15 inch from the pin tip. In addition, we also would try another plastic, PEEK, which has a much higher melting point, but is somewhat less impact resistant.
After an initial eight shots at 24 kV with three new spark plugs, two using Lexan and one using PEEK, (plus one old spark plug for symmetry) no wear was visible on the insulators, although there was very slight pitting of the tungsten tip. Since we don’t know how the insulators will react at higher voltages, we have decided to make half the insulators from one plastic and half from the other. We’re confident this will not affect how fast the switches fire. We were able to get the three switches we tested to fire with 50 ns of each other, which is acceptable and can be improved with further adjustment of the spark gaps.
We expect to have all 12 spark plugs working by the end of this week.
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Comments
For a more in depth discussion, start a thread in the forums.Maybe these plastics are also good candidates for the insulators:
https://www.inventables.com/technologies/steel-like-plastic
https://www.inventables.com/technologies/strong-durable-polymer
https://www.inventables.com/technologies/strong-resistant-plastic
https://www.inventables.com/technologies/long-glass-fiber-reinforced-thermoplastic-composites-replace-metal
https://www.inventables.com/technologies/thermally-conductive-plastic-compounds-dissipate-heat
The site inventables.com informs about innovative materials. You might have used it already, but I’m posting it here just in case.
The link to the site was provided by QuantumDot http://focusfusion.org/index.php/forums/viewthread/522/P15/#5236
We’ve already successfully designed/built and trialed a few different “styles” of plasma plug, and you don’t really need to re-invent the wheel to make them work.
When I say “styles”, I refer to plasma plume shapes, in that you will need to design your plug with this feature incorporated in order to avoid premature wear(vaporization)issues.
Most people will recognize that a typical plasma plume is “golf ball” shaped, alas, this is detrimental to any plug design as it basically means that you’ll be vaporizing anything within the “golf ball”.
Of course plasma energy levels play a part in this too, and we’ve had no plug issues whatsoever with 4.7uF through to 10 Joule.
The idea is to protect the firing points from self vaporization by forcing the plasma plume to project away from these areas, and with a little bit of thought you can actually “model” the plume shape to a degree as well.
Think Lorentz Force…then apply a bit of liberty.
A certain firing point design will give you a bullet shaped plume, another will give orb shaped plumes, and yet another will give you stacked orbs(like bubbles) projecting away from the plug base.
All of these plume shapes are handy as they see the actual plasma plume manifest away from the firing points and with a suitable tinted lense and using high speed camera, you can actually see that in some instances, with certain designs, the plume doesn’t even make contact with the firing points, but manifests a couple of millimetres above them, thus self protecting the plug base.
Apply a little bit of forsight when designing your plug, and do try to think outside the box, for plasma isn’t spark, as many people commonly mistake it for, thus it behaves differently in a lot of other circumstances too.
The first thing you MUST do is build yourself a suitable pressure chamber with viewing window, in order to watch the plumes under pressure. You need to pressurize the chamber to whatever compression ratio your engine has, and design the plug to operate at these pressures. Failure to do so may result in a situation where the plug fires nicely at ambient, but physically inverts the plasma under pressure, meaning the plasma will be sucked back into the plug in some cases. The air you use in the pressure chamber must be flowed through, otherwise you will simply be firing in ionized air, again, not ideal.
It would be a shame to have wasted your time going through all the motions of designing and then making a plug, only to have the disappointment of a failure when trials in a real live engine present, all diu to not thinking it through as well as you could have.
We’ve been lucky, we’ve not had a single failure, perhaps due to our design approach, and build methods.
I sincerely hope others share the same successes.
Just think it through and you should be fine.
Oh yeah, we refer to the electrode interaction with the center ceramic during operation(in engine) as “chatter”, and this isn’t a big deal once you know what you’re doing during plug assembly.
The main problem with the center ceramic is that during its initial “firing” in the kilns, it often warps slightly. Certain steps need to be taken to eliminate the “chatter” issue prior to actually inserting the electrode.
Plasma plugs are fun.
I must urge caution, please be very careful which materials you opt to use, for you could inadvertantly choose a material which has serious consequences when interacted with plasma.
I strongly urge close study of “transmutation” with the various metals.
Ensure you have suitable Alpha/Beta/Gamma detection devices, along with a suitable 3D mapping capable spectrum analyzer and a decent earth leakage detector.
NEVER use materials normally used with common spark plugs, study the above to learn why.
Be safe folks!
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