Stainless FWE with small intake runs at -3 F !!!!!!!!!!!!!!!

[Bruno Ogorelec]

Standing waves DONT move from the tailpipe! Standing waves DONT MOVE, they are standing! ONLY, only, only traveling waves move down the axis!

I agree. I just thought we did not have to go back that far. I thought this was a given.

The traveling waves are the only axial moving energy source. Standing waves generate transverse mechanical vibration of the walls. The standing waves is dampening the energy of the traveling waves by radiating it externally where it energizes the air boundary arround the tube. This tube vibration creates longitudinal waves (in the air) perpendicular to the waveguide on the OUTSIDE of the waveguild as SOUND.

Um… We do need to go back, it seems. There’s a misunderstanding here that needs to be resolved. The term ‘standing wave’ is a contradiction in terms. It really is standing, but it is not a wave.

But – and it is a big ‘but’ -- it is the indication that real, moving waves are about. We are talking of the standing wave, all the time knowing that it is just a representation of something else – of a certain combination of waves moving to and fro along a conduit. It’s a kind of shorthand.

This is nothing unusual. We employ the same kind of shorthand when we talk of the centrifugal force, which does not really exist either, but is just a representation of something else.

I find it strange to hear of the standing wave described apart from the traveling waves, as if one were transversal and the other axial. We have just concluded that there is no such thing as a standing wave, haven’t we? It is just a concatenation of moving waves.

Furthermore, those moving waves are anything but axial. They may look axial while they are moving down a conduit, but they are really spherical. Given the chance, they will move in all possible directions. Look at a Schlieren photo of a blast coming out of a pulsejet tailpipe and you will see a perfectly spherical bubble.

There is no movement from node to antinode to node

I agree. Better to say, there is plenty of gas movement – otherwise there would be neither thrust not aspiration -- but it is not attributable directly to the passage of the wave. The major movement of gas is the result of equalization of gross imbalance of pressure along the conduit. There’s great pressure at one end of the duct and no pressure at the other. So, gas flows from the high-pressure end to the low-pressure end.

That said, however, the standing wave (i.e. the combination of moving waves!) still plays a great role. It regulates the process, setting its timing and giving it additional energy. It takes energy from the combustion process, stores it and releases it back into the process. It is like the flywheel on the piston engine.

The real picture of events is very complex. We are watching at least three interweaving phenomena. One is the process of combustion in a vessel of quasi-constant volume. This generates the second phenomenon -- the cycle of heating-expansion-cooling-condensation of gas in a duct. This, in turn, generates the third – the establishment of resonance. The latter is amazingly similar to sound-wave resonance, only involving much greater pressure amplitudes than normally associated with sound and taking place under great changes in temperature.

Now, those three phenomena (and no doubt a few others besides) are bundled tightly together in a process in which they are not only coexisting but also interdependent.

This takes us back to the thing you said before, which made me respond vehemently in the first place. You simply cannot say that one of those aspects is a byproduct of another. It is like saying that you just need muscle to lift weights. No, you also need the bones to lend muscles support and you need joints to allow articulation and you need cartilage to keep them all together. Neglect one of those elements and the whole structure will start creaking and will soon collapse.

In other words, dampen the vibration, as you suggest, and you will dampen the pulsejet cycle. Do it too well and the cycle will collapse. The oscillation that you find superfluous is the very reason the thing works at all.

Standing waves cause the entire length of the tube to vibrate this is resonance. Resonance is the vibration of a waveguide. Its a mechanical force. These oscillation travel radially out from the axis of the tube. A pipe organ or tuning fork does not emit sound from the end of the tube, it is radiated outward down the entire length.

We may be talking at cross purposes here. Please note that I am not talking of the resonance of the duct itself, but of the resonance of the gas column in the duct. The standing wave I am talking about would be established even in a duct carved in a block of something completely non-resonant. It has nothing to do with the properties of the duct material.

Maybe one can talk of dampening the vibration of the duct without affecting the vibration of gas. Maybe that would reduce the noise without reducing the gas pressure swings. If that can be done, I’d certainly welcome it. I don’t know enough about the problem to say anything. Maybe you know more.

Noise is certainly an unfortunate by-product. It is more intense here than in many other jet engines, precisely because of the nature of the pulsating combustion. I agree with any effort to dampen noise, but dampening its origin -- the very oscillation that makes the pulsejet function -- is a bit counterproductive, don’t you think?

BTW – I am far from certain that what you say of organ pipes is true. I vaguely remember hearing somewhere that the material used for organ pipes is picked precisely for being non-resonant, so that the resonance of the pipe does not interfere with the resonance of the air inside it. But, as I said, I know next to nothing about the resonance of solids.

[Al Belli]

Hi Bruno,

Organ pipes have classically been made of lead for two main reasons. Lead is non resonant, and is easily made into sheets by casting onto a flat surface. The reason that movie house organs were/are harsh sounding, is that the pipes were made of harder materials ( like zinc ), and the blower pressures were much higher than " church " organs. High pressure makes the organ louder with a reduced number of pipes. For the best voicing, You need many pipes at low pressure, with the higher "harmonics" added by ranks of 1' pipes in fundamental, tierce and quint combinations. These " little squeakers " make an amazing difference in the voicing of the organ.

Al Belli

[larry cottrill]

Forget all this business about Standing waves.

Graham -

My friend, you are a learned man. I HATE IT when I find something to disagree with you about, because I am not. But hear me out on this one, for I beg to differ ...

The high frequency "standing waves" in the chamber are important in a way that led directly to my design of the FWE chamber. What I noticed when running UFLOW1D in a simulation of the Elektra I and II engines is that when you look at the graphic analysis, you see an incredible amount of pressure thrashing up and down in the chamber during most of the pressure part of the cycle. Now, realize that the UFLOW model of these engines substitutes a cylindrical chamber with two flat ends for the electrical "octagon box" [really a flat square box with somewhat rounded corners] - so this high frequency oscillation, in the model, comes from the reflective containment of the cylindrical wall and the flat ends.

What I realized is that this "standing wave" action is what in the radio realm is called a "parasitic oscillation" - that is, a resonance which uses up energy without contributing to the useful work of the apparatus as a whole. It just consumes energy, wasting it ultimately [and in our case, quite directly] as heat.

The reality of the Elektra I and II chambers is far WORSE than the UFLOW model, because the chambers are the worst possible acoustic configuration - six flat sides, in parallel groups, broken only by a couple of holes. There are actually FIVE pairs of parallel reflectors to set up the standing wave after the blast, at three DIFFERENT high frequencies, NONE of which are in any way harmonically related to the fundamental frequency of the pipe as a whole! You have the two big octagonal faces for a very high frequency [only about 36mm apart], the four flat edge faces for a frequency somewhere around half that, and a slightly lower frequency from the opposed corners [a bit farther apart than the four flat sides]. ALL of the energy reflected by these faces [except for the small fraction that leaks out through the exhaust hole and intake] is wasted heating up the walls of the chamber! That's all it accomplishes, with the possible exception of slightly aiding mixing and ignition.

The design of the FWE was spurred on by this discovery, trying to find an "ideal" shape that would show no evidence of the parasitic oscillation discovered in the Elektra models. Of course, this was done without modeling the effects of the penetrating intake pipe, which has plenty of influence on what happens inside the real engine.

This, in my opinion, almost entirely explains why the thrust of the Elektra series is so pathetic, contrasted to the arguably excellent performance of the FWE. It is also the reason I claimed that the Elektra I would be very good as a heater, because of its "low efficiency" - meaning, of course, its low thrust development for the fuel consumed, not lack of thermal efficiency, which is another issue.

Of course, I agree that the "standing waves" themselves are not waves, but simply evidence that the "ringing" waves are traveling back and forth, creating alternate zones of wildly varying pressure and dead nodes. But my observation so far is, there is no comparison between an engine where parasitic oscillations are highly developed and an engine where they are purposefully avoided - the very same thing that can be observed in amateur radio transmitters designed and built at varying levels of skill.

If this observation is faulty, I need an awfully good explanation of why.

L Cottrill

[mk]

Don't you get a resonance (standing-wave) frequency for every system that will be set? Of course you do (do also think of De Broglie waves...)!

So standing waves (built up through reflection of travelling waves) have to be a fundamental "thing", a self-setting/self-organizing phenomenon just as they are a kind of by-product as well. They are containing/ recovering energy, for sure, it is their job if you will. But through this recovery of energy the next cycle is being driven (increasing the amplitude after setting a succesful cycle one time, like you do at starting). Interesting is the paradoxon: The higher the energy recovery ratio, the higher the energy output ratio can get (think of two-stroke engines and the effects adding different tuned pipes). You cannot take as much energy out of the cycle as you want to, the engine might die thereof (take the pictures postet by Forrest ["WebPilot"] under the "heart of a pulse combuster" topic in the "pulse jet forum" part to get an idea of what I mean).

Any disagreements, suggestions etc.?

Of course everything is IMHO. Don't feel offended. It's not only interesting getting so many different opinions to know.

[Eric]

I figure a picture is worth a thousand words. I modified the drawing Eric posted.

I find that funny since it seems like you didnt even read anything from my post, or my picture, and then you say I am confused about standing waves because I drew arrows of the flame path on my picture, yet you decided to take the flame path as the nodes and anti nodes of some standing wave.

After looking at the drawing and Eric's reference to the flame patterns. I have to agree that the standing wave is the key feature that triggers ignition and sustaining.

Well its good that you finally "saw the light" about this much at least, although lets wait for you to revert to some other diluded way of thinking, ok guess I wont have to wait very long:

As to what I said earlier about wanting to minimize the standing wave effects. I was not implying trying to do so with any of the current designs. I was refering to efforts on ONLY my own designs.

Bruno wrote:

The fact that PDEs are not really pulsating, but are single-shot machines has clouded your thinking. Pulsejets pulsate. Their cycle is recurring, a self-excited relaxational oscillation.

I understand and agree. My designs will be self-exciting constructive feedback oscillation.

Ah! FINALLY! Someone with a noble cause: To achieve What NASA, Boeing, CalTech, MIT, and countless other institutions can not! I like your style Ogge.

I hope the drawing helps to illistrate what im talking about with standing waves.

yes it obviously illustrates something, unfortunatley I dont think it has anything to do with the subject of pulsejets

[/quote]

[Ogge]

Um… We do need to go back, it seems. There’s a misunderstanding here that needs to be resolved. The term ‘standing wave’ is a contradiction in terms. It really is standing, but it is not a wave.

But – and it is a big ‘but’ -- it is the indication that real, moving waves are about. We are talking of the standing wave, all the time knowing that it is just a representation of something else – of a certain combination of waves moving to and fro along a conduit. It’s a kind of shorthand.

Yes, we are getting some where. I totally and wholeheartedly agree.

I find it strange to hear of the standing wave described apart from the traveling waves, as if one were transversal and the other axial. We have just concluded that there is no such thing as a standing wave, haven’t we? It is just a concatenation of moving waves.

Furthermore, those moving waves are anything but axial. They may look axial while they are moving down a conduit, but they are really spherical. Given the chance, they will move in all possible directions. Look at a Schlieren photo of a blast coming out of a pulsejet tailpipe and you will see a perfectly spherical bubble.

Here I have to disagree and here is my reason. Standing waves do exist, there cause is the traveling waves but the intersection of high pressure waves does have an external effect.

Yes they are spherical (if no pulseshaping is used) but when spheres collide, they start off intersecting at a single point on the axis, as they move towards each that intersection becomes a circle that continues to expand until the overpressure region starts to decay or the expansion reaches the outer boundary wall. It is this region of extreme over pressure that is creating a new transversal wave perpendicular to the axis. This new wave (resulting from 2 high pressure spherical regions) can be propogated thru the wall. Granted, it appears pipe organs try to use non-resonant matterial to try to dampen this. We are not, steel will propogate that waves. Some will be converted to heat in the walls, and some will be carried forward into the new medium (outside air) generating longitudnal waves in the air (NOISE).

I agree. Better to say, there is plenty of gas movement – otherwise there would be neither thrust not aspiration -- but it is not attributable directly to the passage of the wave. The major movement of gas is the result of equalization of gross imbalance of pressure along the conduit. There’s great pressure at one end of the duct and no pressure at the other. So, gas flows from the high-pressure end to the low-pressure end.

Oh, I absolutely agree. There has to be movement due to pressure. My statement was that there was no movement force imparted by the standing wave. It is not contributing to movement forces.

That said, however, the standing wave (i.e. the combination of moving waves!) still plays a great role. It regulates the process, setting its timing and giving it additional energy. It takes energy from the combustion process, stores it and releases it back into the process. It is like the flywheel on the piston engine.

Again I agree but I would like to make a point. This is the process I mean to replace with a different mechanism. It appears obvious to me the role its playing. Just by looking at Eric's drawing, if the flame patterns seen inside are the outline of the standing wave. Here is what I think (opinion) is happening.

The standing wave is helping to move the new mixture plug and compress it towards the walls as it oscilates. This concentrates mixture under pressure against the hot walls scrubbing lose the free radicals/hot gas molecules that allow a self-sustaining renewed combustion.

I mean to replace this aspect of the combustion cycle. I want to use a pulse that only occurs once, timed to compress and trigger the re-ignition process without relying on a standing wave to provide that trigger.

The real picture of events is very complex. We are watching at least three interweaving phenomena. One is the process of combustion in a vessel of quasi-constant volume. This generates the second phenomenon -- the cycle of heating-expansion-cooling-condensation of gas in a duct. This, in turn, generates the third – the establishment of resonance. The latter is amazingly similar to sound-wave resonance, only involving much greater pressure amplitudes than normally associated with sound and taking place under great changes in temperature.

As far as the first two aspects, combustion ,over expansion ... thats a given for any repeating cycle.

Again a nearly total agree but I do not think the process is similar, I personaly would say it IS sound-wave resonance exactly but you are correct about being greater amplitude. Amplitude = volume. Amplitude of a wave is the indication of the wave energy. An increase in amplitude is a increase of energy SQUARED.

Now, those three phenomena (and no doubt a few others besides) are bundled tightly together in a process in which they are not only coexisting but also interdependent.

Bruno, yes the cycles are interdependant on each other, but NOT on the presence of the standing wave. I know, current designs DO require them for re-ignition.

The point I am making is IF you remove the need for the standing wave to initiate re-ignition and whatever help to aspiration. The other parts of the cycle are still present. You still get gas expansion, you still get over expasion then induction then compression IF you can re-ignite it with as well or better ignition source then the standing wave provides.

This takes us back to the thing you said before, which made me respond vehemently in the first place. You simply cannot say that one of those aspects is a byproduct of another. It is like saying that you just need muscle to lift weights. No, you also need the bones to lend muscles support and you need joints to allow articulation and you need cartilage to keep them all together. Neglect one of those elements and the whole structure will start creaking and will soon collapse.

I am stating that the standing wave is a function of 2 things. The lengths of the tubes and the magnitude of the reflection wave.

1) You need the exhaust tube to be able to set up resonance with your source frequency to initiate a standing wave.

You stated earlier that the combustion is like a noise generator. Here I disagree. There are very discint frequeny components based on the gasses pressent. The primary frequency will be based on the fuel reaction this is a dominant feature in PDE designs. Similar techniques can be used in pulsejets.

2) You need reflections being the same amplitude as the incident waves.

What I am doing in my designs is trying to MINIMIZE these aspects. Primarily I want to make the incident waves >>> reflection waves. If that is done, a standing wave cannot be created.

Maybe Mike can generate the waveform combination with his tool that will show say 2 sinewaves traveling in opposite directions with incident wave say 3x the reflection wave. The resulting waveform will be dominated by the incident (outbound) wave. This will turn the exhaust into a High speed pump! Instead of giving out puffs of expansion gasses impeeded by the reflections, it will use the energy to drive them from the exhaust thus greatly increasing thrust.

I have heard it stated that only 1/7th of the cc volume leaves the exhaust per cycle. I have no idea if this statement is correct. I was shocked it was so low. I want to get as near as 100% exhaust as possible setting up a near vacuum in the CC then allow refresh cycle to begin. This is one of the reasons I proposed my bellshaped CC design. It tries to maximize energy in such a way as to direct it all at the exhaust in a much more controlled invironment and allowing rapid exhaust by preventing alot of waves from being trapped in the CC.

In other words, dampen the vibration, as you suggest, and you will dampen the pulsejet cycle. Do it too well and the cycle will collapse. The oscillation that you find superfluous is the very reason the thing works at all.

Bruno, I am trying to separate the need to rely on the standing wave. I believe it can be done.

Noise is certainly an unfortunate by-product. It is more intense here than in many other jet engines, precisely because of the nature of the pulsating combustion. I agree with any effort to dampen noise, but dampening its origin -- the very oscillation that makes the pulsejet function -- is a bit counterproductive, don’t you think?

Again, I believe we can do it! Oscillation will not be impeaded. You are explicitly linking the standing wave presence with oscillation. You can have oscilation without standing waves. You just replace the feedback mechinism with an alternate source. That alternate souce in my design is the BCI.

BTW – I am far from certain that what you say of organ pipes is true. I vaguely remember hearing somewhere that the material used for organ pipes is picked precisely for being non-resonant, so that the resonance of the pipe does not interfere with the resonance of the air inside it. But, as I said, I know next to nothing about the resonance of solids.

Agreed, the air column is also oscilating. That cannot be damped unless you damp the standing wave or totaly prevent resonance. Resonance is a form of aplification, one of my design goals is to get rid of that amplification. The engine will still make noise, but at a greatly reduced volume.

Im not crazy. I truely think we can do this.

On last thing. I realize the current engine designs will not operate without the standing waves, they are designed to use and require them. I think we can design engines that will operate without them even better.