PJ Alternators and Microwave PDE

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PJ Alternators and Microwave PDE

Post by Mike Everman » Thu Nov 13, 2003 7:40 am

So the Javfe Redux thread started to get into some good stuff going with regard to electrical power generation from pulse-jets, Bruce chimed in, I can't stop thinking about it, and Viv is reading 23 megs of magnetohydrodymic power generation report out of NASA Marshall (I only went as far as the abstract, sounds like a bust in terms of useful current, and it was a PDE chamber, which we're unlikely to play with, but perhaps Viv can paraphrase after reading the thing?) I believe Viv’s plate type thermocouple has great promise (supporting calcs, Viv?).
I'd like to start a discussion about how to do this easily, without regard to too many in-flight uses, but I would like to debate the possibility of triggering detonation cycles with microwaves.
Seems to me that the current PDE cycle is extremely difficult to deal with. Finicky multiple fuel/air mixtures, laser spectography in active mixture control loops, and on and on. OK, so there are a lot of PHD's on this case, but I've seen these guys all too often miss the forest for the trees; the more complicated their solutions, the better. They are stuck on a supersonic shock wave detonating the larger chamber’s charge, and all I’ve seen so far (please tell me if I’m wrong) are variations on this theme. Jeez, next thing you know they’ll all get together and the only cosmology taught in schools is big bang theory (ooops, too late).
I’d like to do some experiments, so I’m proposing tearing into a microwave oven, pulling the guts and directing the wave-guide into a chamber with various fuel air mixes, perhaps the radiation directed into the middle of a common tee fitting in form of a pulse, with plastic caps on the ends. How will I know it has detonated and not just burned really fast? Or is this just sillyness?
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Post by Bruce » Thu Nov 13, 2003 11:27 am

Why not just stick a jam-jar, complete with its pool of methanol, in the microwave and see if it detonates :-)

This is the "suck and see" testing methodology :-)

Note, use your neighbor's microwave -- no point in wrecking your own.

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Post by Mike Everman » Thu Nov 13, 2003 1:46 pm

Yeah, I'll try that right now.
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Post by Mike Everman » Thu Nov 13, 2003 1:48 pm

MY EYES! MY HANDS!!! OH, THE HUMANITY!!!
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Post by Viv » Thu Nov 13, 2003 2:48 pm

Well a couple of small problems with the MHD idea.

First they had a real hard time to get the electrodes to couple in to the ionised stream of gas in their engine, now that may be just down to the supersonic shockwave screwing things up as they did mention another problem about the shockwave being way in advance of the ionised combustion wave, but it would mean a very large area electrode, so large in fact that in a pulse jet it would probably start heating up and acting as an ignition source.

Second problem is the amount of magnetic field reqired from the coil and the field density, they are working with 0.6T , point six of a Tesla is a frigging lot to try and produce in the average shed.

They also ended up having to put a rocket nozzle on the end to try and concentrate the field and improve the coupling.

So I think we can drop the MHD idea apart from the diehards:-) it was a nice idea but the devil was in the details as useal:-)

But having said that the paper is worth reading! 23Mb is down to bad production it has some interesting details about PDEs in general.

EDIT Just ading a note
In the conclusions part of the paper he mentions using a microwave beam firing across the exhaust to measure the electron density, when the shockwave passes it attenuates the signal! "the cause of this unanticipated effect remains unresolved".

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Post by Viv » Thu Nov 13, 2003 3:13 pm

Oh by the way Mike, the PDE MHD engine is rectangular!

I thaught you would like that:-)

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Post by Mike Everman » Thu Nov 13, 2003 3:32 pm

viv wrote:when the shockwave passes it attenuates the signal! "the cause of this unanticipated effect remains unresolved".
Wow, they are baffled that a supersonic shock front travelling through the medium in which their signal travels; with it's inherently huge pressure gradient attenuated the signal? Frankly, I'm shocked, too. ((:-D))
using a microwave beam firing across the exhaust to measure the electron density
But that's an idea. there's a lot of free electrons in the CC, impinging on the walls, what if the CC is insulated electrically from the rest of the engine? Wouldn't it collect a humongous static electric charge? Usable, convertable in some way?

Or, forget any conversion and complicated microwave radiation for detonating the main chamber, perhaps it's able in the right configuration to build up and discharge a fat lightning bolt up the middle of the engine, detonating it quite nicely, with a much less finicky band of mixtures possible...
That should appeal to bruno's need for the thing's "heart to beat as it will", a fully passive system.
Very cool.
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Post by Viv » Thu Nov 13, 2003 4:27 pm

Well I allways wondered what the bastard child of a pulse jet and a gas dynamic laser would perform like:-)

but I think your new homeland security department would not like it:-)

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Re: PJ Alternators and Microwave PDE

Post by Viv » Thu Nov 13, 2003 4:49 pm

Mike Everman wrote:So the Javfe Redux thread started to get into some good stuff going with regard to electrical power generation from pulse-jets, Bruce chimed in, I can't stop thinking about it, and Viv is reading 23 megs of magnetohydrodymic power generation report out of NASA Marshall (I only went as far as the abstract, sounds like a bust in terms of useful current, and it was a PDE chamber, which we're unlikely to play with, but perhaps Viv can paraphrase after reading the thing?) I believe Viv’s plate type thermocouple has great promise (supporting calcs, Viv?).
I'd like to start a discussion about how to do this easily, without regard to too many in-flight uses, but I would like to debate the possibility of triggering detonation cycles with microwaves.
Seems to me that the current PDE cycle is extremely difficult to deal with. Finicky multiple fuel/air mixtures, laser spectography in active mixture control loops, and on and on. OK, so there are a lot of PHD's on this case, but I've seen these guys all too often miss the forest for the trees; the more complicated their solutions, the better. They are stuck on a supersonic shock wave detonating the larger chamber’s charge, and all I’ve seen so far (please tell me if I’m wrong) are variations on this theme. Jeez, next thing you know they’ll all get together and the only cosmology taught in schools is big bang theory (ooops, too late).
I’d like to do some experiments, so I’m proposing tearing into a microwave oven, pulling the guts and directing the wave-guide into a chamber with various fuel air mixes, perhaps the radiation directed into the middle of a common tee fitting in form of a pulse, with plastic caps on the ends. How will I know it has detonated and not just burned really fast? Or is this just sillyness?
Ok so microwaves, ripping the magnetron form an oven and pointing the waveguide in to the chamber will not do as much as you would like.

Microwaves is funny things! have a look in the average microwave receaver and you will see a couple coils a diode and inexplicably nothing connecting them together but it all works!

Your combustion chamber has to be resonant for accustic frequencys as well as microwaves, if the impedance does not match then vertually no power will be transfered from the magnetron, a bigger problem will be VSWR (voltage standing wave ratio) if you have done any CB radio you may have come across this when tuning an aerial.

What it means is the engine is now going to be a microwave resonator so it will have to be tuned to get the highest Q factor (Q=goodness:-) and impedance matched to the magnetron.

Not hard as microwave tuning in the real world is a screw wound in to the side of the wave guide, the main thing is to get the dimensions right.

I would suggest a quick look at the ARRL web site.

Viv
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Post by Mike Everman » Thu Nov 13, 2003 7:42 pm

I refuse to believe that the food won't cook without the proper size box! But I did find it disturbing the other night when I put a brick of butter next to a bowl of broccoli for a minute and a half, the butter didn't melt, and the broccoli was steaming. the butter alone is bubbling inside of 30sec.
It started me looking for spectrographic analysis of various fuels to find the strongest absorbtion frequencies and tune our microwave frequency accordingly. Nicely, the magnettron is a pulsed output, around here being 60hz, line frequency, and easily changed to the resonance of the PJ!!!
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Post by Viv » Thu Nov 13, 2003 8:12 pm

Mike Everman wrote:I refuse to believe that the food won't cook without the proper size box! But I did find it disturbing the other night when I put a brick of butter next to a bowl of broccoli for a minute and a half, the butter didn't melt, and the broccoli was steaming. the butter alone is bubbling inside of 30sec.
It started me looking for spectrographic analysis of various fuels to find the strongest absorbtion frequencies and tune our microwave frequency accordingly. Nicely, the magnettron is a pulsed output, around here being 60hz, line frequency, and easily changed to the resonance of the PJ!!!
Well the water in the brocali absorbs the energy and butter has a very low water content:-)

And yes the box is matched to the manetron and the magnetron runs at 2.4Gz pulsed at 60Hz

To change it is a bit harder as it is a cavity resonator so to change the frequency you have to change the size of the cavity.

I am off for two days to sunny Bristol to meet up with 1/3 of the Albion team so I will catch when i get back on Saterday night.

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Post by Bruno Ogorelec » Thu Nov 13, 2003 9:25 pm

[quote="VivI am off for two days to sunny Bristol to meet up with 1/3 of the Albion team[/quote]


Does that mean we can expect some loud bangs from the direction of Bristol or what?

Bruno

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Post by Mike Everman » Fri Nov 14, 2003 7:11 am

Bruno, got no juice (pun intended) for this idea?
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Post by Mark » Fri Nov 14, 2003 3:25 pm

Mike Everman wrote:Bruno, got no juice (pun intended) for this idea?
I'd go for that nifty arcing effect that happens with gold trim dishes.
Mark

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Post by Mike Everman » Fri Nov 14, 2003 3:28 pm

Got to make power to wield it!
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