## Proposed CC design

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Ogge
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### Proposed CC design

I have been thinking about the hf ringing in most CC designs and have been working on trying to minimize the effects. The design goal is to provide the reflective surfaces of the CC in such a way as to allow any random directional vector from the chosen ignition point to have the fewest number of reflections before entering the exhaust tube.

Unfortunatly I have not figured out how to use UNIFLOW yet. Would anyone be willing to model the output?

My new CC design is bell shaped.

The front cap is a parabolic curve with a focal point at my chosen ignition point. This cap is the same size as the exhaust tube and directly opposite the exhaust opening at ~4x the focal distance. Any vector originating at the ignition point towards the front cap will be reflecting directly down the exhaust tube.

The exhaust side surface is spherical with the radius set at the ignition point (parabolic focus of front cap). This radius should be 3x or greather than the distance of the focal legth of the front cap. This will provide a mirror for any vector from the ignition point directly back to the same point and into the parabolic front cap.

The side walls of the CC should be gradually curved flare (like the horn of a trumpet) to provide any vector from the ignition point to be redirected at an angle into the exhaust. To determine the geometry of the side walls, draw lines from the exhaust tube inner walls to the front cap, also draw lines from the outer edge of the parabolic cap thru the ignition point to the spherical reflector wall. The side walls should intersect the spherical reflector at that point.

(corrected)
Calculation of Lamda (L) should be 2X the total length from the ignition point to exhaust exit + 2X the radius of the spherical reflector +2X the focal legth NOT just the total lenth of the engine.

Expected results of analysis:

The pressure wave from the CC will be tripple humped from the following paths. 1) direct wavefront from ignition point down the exhaust. 2) wavefront from reflection off parabolic cap then down the exhaust. 3) reflection from spherical mirror, back thru ignition point, reflected off front cap then down the exhaust. These will be followed by reflection off the side walls at an angle that will zigzag down the exhaust and dispell most of their energy as heat.

The 1st wave will be propogating thru the cold air mass in the exhaust and should be relatively small compared to the 2nd and 3rd waves so I am ignoreing it for calculation of timing. I am just assuming that it is providing a more consistant heating of the exhaust tube so the 2nd and 3rd waves are basicly traveling at the same speeds.

The 2nd wave reflected of parabolic front cap will travel to exhaust, reflect back the entire length of engine, pass thru the ignition point, reflect off the spherical mirror back to the ignition point at approximatly when the third waves is returning from the exhaust reflection, and has reflected off the front cap to the ignition point. At this time should be the maximum pressure to ignite the following cycle.

The resulting waves will all be driving straight at the ignition point compressing the mixture deposited by the intakes from both ends of the CC in a collapsing spherical wave.

Last edited by Ogge on Wed Jan 12, 2005 8:57 pm, edited 6 times in total.
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pezman
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### Re: Proposed CC design

Wouldn't your requirements describe a CC that is shaped like an egg?

Probably not a bad idea, btw.

edit: Just read more carefully -- not an egg. Has anyone experiment w/ "eggs"?

Ogge
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### Re: Proposed CC design

pezman wrote:Wouldn't your requirements describe a CC that is shaped like an egg?
Nope, you are curving the side walls the wrong way. Think of the Liberty Bell with a partial spherical section welded on the bottom. Or a blunt tipped arrowhead.

One advantage of this design, cheap bells may be purchased to use as the front cap. I have already found many on the net that may be usable for a few dollars. They are even available in different metals and sizes.
Last edited by Ogge on Wed Jan 12, 2005 6:29 pm, edited 1 time in total.
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mk
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### Re: Proposed CC design

Adam's design seems to be a bit like the Gluareff pressure jets in shape.

But: I dont know how the cap added to the comb. chamber can have the same diameter as the exhaust, when you don't want any sharp edges?
(look at a Gluareff picture to understand what I mean; max. cap dia.=max. comb. chamber dia.)

As Pezman wrote, I would think the nose of the egg shaped comb. chamber (I assume it here, too) points to the exhaust tube then, doesn't it?

Interesting, interesting.
I do mostly rather consider flow than acustics. Pezman and Adam, your opening my eyes to some rarely considered key details...
mk

Ogge
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### Re: Proposed CC design

mk wrote:But: I dont know how the cap added to the comb. chamber can have the same diameter as the exhaust, when you don't want any sharp edges?
Who said no sharp edges? There is a sharp edge at the flare to sphere junction.

I dont mean to be crude, but looking at my design the CC with exhaust tube looks just like a part of the male anatomy used for thrust. I guess God already designed the best shape for thrusting.
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mk
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### Re: Proposed CC design

Ogge wrote:Who said no sharp edges?
Well, as I said: My flow thinking...
Hmmm...but actually I'm defently not a friend of sharp edges. I do like smooth sections still a lot more (the reason could be my four or more years of understanding, analyzing and tuning of two-stroke engines).
Surprise me again.
mk

Ogge
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### Re: Proposed CC design

This CC is designed for a thermojet/chinese type engine. The intake(s) would be on the spherical mirror surface angled directly at the ignition point driving the fresh charge into the nose cap. I dont think an intake in the center of the nose cap would work at all.

The only wavefront that should exit the intake is any vector directly from the ignition point. This should be a very clean, single pulse. I prefer the thermojet setup with multiple intakes from 2-5 positioned arround the edge.

I would prefer a gradual curve on the intake instead of doing an abrupt angle like the FWE. The curve will induct vortex rotation just like the currents in a meandering river. The vortex will help draw more air in on the refresh cycle.

By using more than one intake with this swirling intake intersecting at the ignition point, mixing should be very good.
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Ogge
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### Re: Proposed CC design

mk wrote:
Ogge wrote:Who said no sharp edges?
Well, as I said: My flow thinking...
Hmmm...but actually I'm defently not a friend of sharp edges. I do like smooth sections still a lot more (the reason could be my four or more years of understanding, analyzing and tuning of two-stroke engines).
Surprise me again.
Marten,
If you look at the design and trace any vectors from the ignition point to the sharp edge at the spherical mirror, you will note it is directly perpendicular to it. NO vector is directed into the sharp edge. The only path into the sharp corner is by elastic collision of random molecules that the resulting vector heads into it. I can live with that.
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mk
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### Re: Proposed CC design

Ogge wrote:This CC is designed for a thermojet/chinese type engine. The intake(s) would be on the spherical mirror surface angled directly at the ignition point driving the fresh charge into the nose cap. I dont think an intake in the center of the nose cap would work at all.
I understood this point that the nose is kept "clean" from any pipes (from the outside and the inside. The internal to-focal-point facing intake fresh charge flow was part of my way of thinking, too.
I just wanted to mention that I rather would apply a curved or inclined shection/shape.

However, re-reading your posts partially made some more things clear to me that seemed obscure first, but...
Ogge wrote:The side walls of the CC should be gradual curved flared [...]
...is the only point were surely my "English decoding from words to imagination" isn't good enough. The aim is clear, but I cannot really imagine the comb. chamber walls shape - what does "gradual curved flared" mean (not the translation of the words, of course)? Can you send/post a drawing?
mk

Ogge
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### Re: Proposed CC design

The aim is clear, but I cannot really imagine the comb. chamber walls shape - what does "gradual curved flared" mean (not the translation of the words, of course)? Can you send/post a drawing?
Sorry, that was bad english on my part, I corrected the original post.

Im afraid all I have on my home PC is ms paint atm. But think of the horn of a trumpet or other musical instrument. You need to transition from a small diameter (at the nose cap) to a much larger diameter (of the spherical mirror) but you dont want a constant increase at a fixed angle. You want the flare to increase in angle faster as you approach the mirror. I havent determined the exact mathmatical bell curve function to use yet.

The really important parts of the design are the parabolic cap and the spherical reflection mirror. The spherical mirror being a much larger radius (3x+ or possible 4x+ to allow for better volume in cc). It should ack like a large telescope or directional microwave transceiver antenna.

If you used a constant increase (conical section) in size any vector from the ignition point angled toward the side walls would reflect off at a shallow angle, hitting the mirror at a wrong angle. This needs to be avoided. The goal is any vector angled at the cc side walls reflect into the mouth of the exhaust tube opening.
Last edited by Ogge on Wed Jan 12, 2005 10:15 pm, edited 1 time in total.
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larry cottrill
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### Re: Proposed CC design

What you're after is admirable. However, I can assure you of one thing of which I am absolutely certain: In this case, "optics" won't work. I don't mean that such an engine won't run - of course it can. It might even be very good! But even if it is, you will be deceiving yourself if you claim that performance is because of the careful curvature of the reflecting surfaces.

There are two basic reasons for this. The first is that once an explosion has taken place and you get the so-called 'constant volume expansion', what you would find at a microscopic level is that the molecular velocity vectors are chaotic - they will not resemble a set of rays emerging from a point source. In fact, they won't even come close to that. True, it won't be perfectly chaotic in some pure sense - but close enough that an "optical" focal point will lose all its intended meaning. So, none of the reflective surfaces will do what you want them to do. The action will be that of high-energy molecules reacting with the surface of an oven, not that of rays striking an optical reflector.

The second reason is difficult for many to fathom, but with your background you should have no trouble with it. It is this: Even if we had orderly aligned radiation, a reflector of small diameter in terms of the radiation wavelength can only disperse the incoming wave energy as a broadly scattered diffraction pattern. In telescope making, this was evident in the paradox that an optically perfect 4-inch diameter telescope produces star images THREE TIMES as big as an optically perfect 12-incher; i.e. the smaller the aperture, the bigger blob a stellar image will be, even if perfect optics are assumed. There is in fact a 'Rayleigh Criterion' that predicts the sizes of these diffraction images! It is literally physically impossible for a reflective or refractive surface a small fraction of a wavelength in width to focus energy of that wavelength. Really good imaging cannot be achieved until the optical surface is thousands of times the wavelength. Consider your microwaves vs short waves: which could you focus accurately with a three-foot paraboloidal reflector?

I am not trying to be discouraging - this kind of idea has come up many times, and I always have the same answer. The shape of the chamber is critically important - the FWE and other designs prove that. But it is not due to a behaviour that looks like optical or microwave reflection or refraction.

L Cottrill

Al Belli
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### Re: Proposed CC design

Hi Ogge,

I would try a simple exponential horn shape, X = Y^n , as a starting point. You may vary the exponent to increase or decrease the rate of flare.

Al Belli

pezman
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### Re: Proposed CC design

Well, I think that the shock waves have a relatively short wavelength that are more or less like a thin shell expanding spherically.

http://www.pulse-jets.com/phpbb2/files/ ... t1_140.gif

It should be possible to focus and aim these and make use of them -- BUT, the propogating medium is not homogeneous, and that is likely to mess with any efforts to aim it in any sensible direction.

Ogge
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### Re: Proposed CC design

Larry,
I understand your concerns but we are not talking about optical frequencies here, we are talking about microwave frequencies based on the molecular bonds of the reactants.

The way a microwave oven works is by energizing the molecular resonance of the hydrogen bonds of a water molecule adding energy which in term causes heat. When the chemical reaction of combustion occurs the energy in the molecules will vibrate due to the added heat energy.

The molecular frequencies of a given fuel reaction are given in the caltech explosives database. The frequencies are very well known to any PDE designer because it becomes a critical design element in sustaining detonation. The frequencies given off cause transverse wavefront angled off the leading edge of the shockwave forming cell structures in the explosive path. If your explosive waveguide is not able to propagate these cells, the frictions associated with traveling the waveguide slows down the wavefront. But if the transverse waves are allow to propogate and overcome your losses, the detonation can continue to accelerate supersonicly.

Pezman stated that the wavelength for a propane/air mixture is ~46mm. If you are talking about a hydrogen/air mixture is ~15mm. Granted the pressure also effects this frequency.

Microwave frequencies most certainly can be directed, focused or reflected.

It is not the individual molecules that all follow the propogation path, it is the net effect of the virbrations transmitted from molecule to molecule. Just like the molecules of water in the ocean above the earthquake zone where not the same molecules that washed up on shore.

But according to your statement, the Tital wave should have wandered aimlessly. Waves dont behave that way. They follow strict physical rules. They go in a straight line, they reflect and they impart energy on collision with other surfaces. Just ask any titalwave victim.
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larry cottrill
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### Re: Proposed CC design

Ah ... of course, you're right about the distinction between the wave energy and the molecular motion. I just never think of it in the terms of electromagnetics.

The only thing that bothers me now, though, is the question of whether such a phenomenon has a direct link to the pressure waves. If you're talking about energy at the microwave level, that's way higher frequency than any acoustic ringing we're usually concerned with. Why isn't the microwave phenomenon you're describing a totally separate issue from the mechanical waves that we usually deal with? I mean, I understand how the repulsion between nearby molecules can be electromagnetic in this case, but how can that influence the gross wave patterns we generally care about? I'm just not seeing the link.

And just so you'll know ... in my case, maths won't help!

L Cottrill