PJ Alternators and Microwave PDE

[Mike Everman]

To my way of thinking, there is no polarity change with direction. There is just a lot of free electrons in the engine that need collecting on an insulated conductive surface (the engine metal becomes the cathode). Just insulating the engine surely does not work as is, though, or Bill Hinote or others with engines up on trailer whees would have already gotten a nasty shock and reported it. The difference I wanted to try was the insulated centerbody to act as dielectric and anode, of course, could also be a recipe for death by experiment!!

[mk]

I still think the potential will be between the entire engine tube and an insulated central shaft or centerbody. I don't understand the front to rear logic...

As far as I understand the problem, you are trying to give the engine some kind of "extra thrust" by extra acclerating charged particles in direction of the airflow. Though you need a "front-to-rear-accleration-field".
But I'm a little bit confused now, because it seems you are "just" wanting to produce some big sparks in the engine for starting some (chemical) reactions.

What's right now?

[Mike Everman]

The point was electricity generation with a minimal of extra stuff. A suggestion of coils around the engine led to ideas about generation by the reverse of magnetohydrodynamic fluid moving-for-thrust, but discounted.

I'm passingly interested in static electricity generation which I believe can be accomplished easily. It's usefullness is in doubt, but I started this thread with the thought that a passive power generation approach could power a microwave transmitter to ignite a whole volume of fuel/air at once, volumetrically, at normal engine frequencies; detonations which would have great advantages for thrust and efficiency.

[mk]

Well, multiple sparks at different places of the engines inside could then be more advantageous. I think that igniting at multiple places the same time shortens the burning time of the whole mixture and might though create a (little) shockwave. Therefor you would need some seperated and, of course, charged inlets with a relatively low electrical potential. But perhaps a single, really long spark could have the same effect by demanding a much higher electrical potential.

[Mike Everman]

Reports I've read by people that have tried this very thing say that it does not have any advantage. Flame propagation from a spark is much slower than the pulsations you want.

[El-Kablooey]

On the subject of generating electricity using a pj, has anyone considered a Peltier device? like in camper refrigerators, and those little cooler/warmer units for travel. If you give it electric current it removes heat energy from one side causing that side to be "cold" and the other to be hot. it also works in reverse i.e. if you heat one side and keep the other cool it will generate current. I don't know much about the capabilities of these things though. have to do some research. I do have a travel-trailer though, and the refrigerator works with one of these, the rear wall is a big heatsink, and this sucker is COLD. the freezer is frozen of course, and if you turn the temp all the way down in the fridge part, it freezes everything solid also. If you had one of these close to a PJ in motion, with proper heatsinking on the "cold" side it would surely generate some current.

[Mike Everman]

Yeah I've got a few component level devices I keep meaning to experiment with. not especially high temp capable, though, but insulate them a bit and get a decent heat sink going...

[El-Kablooey]

Stepping it up is no problem at all. and this is a guess but i'd imagine the voltage would be somewhat higher using larger thermocoupled plates instead of wire. possibly even integrated into the construstion of a jet with the propane feed keeping the cold side cold.

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[Greg O'Bryant]

what if you put a trigger electrode in a pulse jet kind of like how a strobe light works but larger? The electrode would be charged to 5 kv for only a brief second just long enough to ionize the gas around it. With the intention to not creat any spark or to ignite the gas but to add energy to it so when the flame front travles along it it would be excelerated? It would be easy to use a pot to tune the frequency of the trigger to the PJ's. You could also do this with your microwave idea just don't get it hot enough to ignite the propane, or what ever your going to use. For generating electricy what about the piezo efect you could step it down to a workable voltage or leave it how it is to charge a cap for the next trigger phase? or even having a magnet by the exhaust that is forced through a coil whith each blast wave?

[pezman]

Interesting to see such an old thread come alive.

Greg's ionization idea is essentially identical to the idea of using corona discharge to trigger a PDE pulse. The interesting thing about those ignitions is that they send out multiple streamers and ignite much more of the mixture than a traditional spark plug does. Also, since the ignition pulse is very brief, the energy per pulse is relatively low.

The problem with these ignitions is that they need to switch a very high voltage at several amps for a very short time. Here's a link to a paper that describes corona discharge ignitions and the GALCIT lab even has a paper that shows detailed plnas for construction of a unit -- however, this is not a simple device (uses a pseudo-spark switch and needs careful design for critical damping of the pulse). My guess is that anyone attempting to purchase a pseudo-spark will receive an unpleasant visit from the FBI.

http://www.galcit.caltech.edu/EDL/publi ... -24455.pdf

[Mark]

I think I posted something on that ignition topic awhile back, but I don't remember when.
Mark

[larry cottrill]

Stepping it up is no problem at all. and this is a guess but i'd imagine the voltage would be somewhat higher using larger thermocoupled plates instead of wire.

El-K -

The size of thermocouple wire has no bearing on the voltage, though it does limit the maximum current you can carry. The voltage of a thermocouple is determined by the electron shell characteristics of the metals chosen, and the temperature applied. The way to get higher voltage is to use a bank of thermocouples in series. The problem with this is that all the "hot junctions" have to be electrically insulated from one another, just like the cells in a battery. Also, it is necessary to keep the "cold junctions" cold, so they don't buck the current from the hot junctions.

possibly even integrated into the construction of a jet with the propane feed keeping the cold side cold.

I have suggested this before; again, the difficulty is keeping the cold junctions electrically insulated from each other while you accomplish this.

While these details make things more difficult and expensive, such a thermocouple battery is certainly doable. If we could perfect the art of making durable ceramic pulsejets with embedded metal parts, we'd have a near-perfect setup for this.

L Cottrill

[Mark]

Some corona discharge topics. See page 21 on the power point page for the furry electrode. Interesting terminology such as electron cascade and rise time I read somewhere.
Mark
http://carambola.usc.edu/research/coronaignition/
http://carambola.usc.edu/research/coron ... ition.html

[Mark]

Corona Beer and corona discharge in the same article. ha
Mark
http://www.eere.energy.gov/de/pdfs/conf ... ronney.pdf
Corona beer page 5. Someone has a sense of humor and probably a few limes.

[Greg O'Bryant]

Thanks for the input on corona ignition. To be honest I have never heard of it before, so if I sound like an ass forgive for what I'm about to say. My idea was similar to corona ignition but I didn't want to actually ignite the fuel with an electrical discharge. What I was thinking of was having a central spike go into the CC and down the tail pipe to creat a high voltage field, not strong enough to ignite the gases but strong enough to make them uneasy. Then the mixture would ignite in normal PJ style; however now the area in the CC would be more energetic, and hopefully the flame front would propagate at a faster rate, and becuase a PJ cycles it would be easy to time when the field would be present in the engine to save energy. I am trying to think of a ways to increase the energy in the reactants so that they would burn more eficiently and maybe even detonate. I do like the microwave idea. What molecule in the reactants would you be trying to ressonate?