A new propane line, Larry you better sit down for this :D

[Eric]

Unfortunately my camera needed a new burning laser which had to be ordered and still isnt back yet, so everyone will have to have that painfully long wait until I get some pics and video posted.

I finally got around to making a propane injector which could be attached to the high-er flow propane valve that I recently rediscovered, and made a crap load of noise today with my freshly filled propane tank.


First Ill start by saying that the jumbo chinese valveless engine finally got enough fuel to come close to full throttle, although if there is a higher throttle setting possible I dont want to be anywhere near it. If I had to guess how much thrust it was putting out, judging by how much the massive test stand was rocking even after cinderblocks were put on the feet, I would say probably 20-30 pounds thrust conservatively. A friend of mine who is 4 miles away by air ran outside because he thought a transport jet was flying really low over his house, then he realized it was a buzzing noise comming from my direction. If he could hear it that loud at 5 miles I would love to have seen the reaction of the small town 2 miles away from me in the same direction. The deleware river valley does a very nice job of channeling the noise .

If you stand at a 45 degree angle to the intake you are hit with so much sound energy that you can actually feel the air in your lungs compressing and expanding giving you a very very unpleasant buzzing feeling, as well as being so much vibrational energy transfered to your body that you cant stand at that spot at all. When you have your mouth open as you are breathing you get this weird sensation from the air rapidly flowing in and out. As soon as I discovered that spot I imediately ran away, and only breifly investigated this at farther distances. At any distance at the 45 degree line there is so much more force its mind boggling. You have to stand 15 feet away at the 45 degree line there is still at least 10 times more "sound" as standing 3 feet directly behind the engine which is quite a task on slipery snow.




Larry, the moment you have been waiting for:
I also got the big FWE to run today, it self sustained for about 10 seconds. I had to use my leaf blower on high, and had the fuel turned all the way up and in a pot of warm water to boost the pressure to the max. It just barely caught and self sustained but its still not getting enough fuel to really run. When its starting it makes some pretty impressive bangs creating a hell of a lot of instantenous thrust, one which actually nocked me on my ass thanks to the very slippery packed down snow. It ran but it wasnt getting enough fuel to fully sustain at a decent power level. Im going to try to find a propane line without any kind of regulation system so i basically just have a straight line coming from the high flow vavle at the tank. When that happens it should really roar.

With the amount of fuel its getting right now its not making much thrust at all, but it does release a lot of heat. Just like before when I tried to get it to run with even less fuel, the entire combustion chamber and cap got a cherry red color, with the previous attempts using the same ammount of propane as the small FWE. I have a feeling like the smaller FWE this engine is going to be very fuel hungry and not put out a whole lot of thrust. This time with more fuel the glow was quite visible durring the day and traveled some distance down the tailpipe, which is now entirely black.

Well I am hungry and not even going to attempt to check spelling or grammar and stuff. Now im gonna go eat and take a nap to get rid of my pulsejet induced headache/groggyness/incoherantness.

Oh yea, one of these engines is going to go on the tobboggan of death 2.0, which this time might actually be something other than a tobboggan this time.

Eric

[larry cottrill]

If you stand at a 45 degree angle to the intake you are hit with so much sound energy that you can actually feel the air in your lungs compressing and expanding giving you a very very unpleasant buzzing feeling, as well as being so much vibrational energy transfered to your body that you cant stand at that spot at all. When you have your mouth open as you are breathing you get this weird sensation from the air rapidly flowing in and out. As soon as I discovered that spot I imediately ran away, and only breifly investigated this at farther distances. At any distance at the 45 degree line there is so much more force its mind boggling. You have to stand 15 feet away at the 45 degree line there is still at least 10 times more "sound" as standing 3 feet directly behind the engine which is quite a task on slipery snow.

Eric -

You found a couple of points on the locus of complete reinforcement between the two wave sources: the intake and the tailpipe. The locus will not be a true straight line, but sort of a hyperbola with crossing lines as asymptotes. You should be able to find another such locus toward the front, though the intensities will be much weaker. It probably is not at exactly 45 deg to the engine centerline, although some point on the curve could be, of course.

If we knew a couple of exact points [angle AND distance from the tail end, let's say] and the exact air temp and frequency, we could diagram something interesting, i.e. the circles of wave fronts coming from the intake and tail. The wavelength will be determined by the speed of sound in cold air and frequency, of course. The locus of the curve will be where there are exactly one wavelength differences in the wave path distance between the two source points. You would graph the two points to the same scale as the waves traveling out from them in evenly spaced circles. Where the circles cross is a point of reinforcement. Once you've done that, you could predict where other such loci might be found - however, I would guess that our intake flare and tailpipe flare are less than one wavelength apart, even taking into account the radical shortening of the wavelength in cold air; that means that very few such loci would occur.

Our two noise sources are acting like two adjoining scratches on an optical diffraction grating, except it is a grating where the scratches are impossibly close together!

Here's another interesting thought: We could make such an engine almost quiet if (a) all the noise were confined to a rearward direction; (b) the intake noise were directed rearward through a duct whose internal gas temperature could somehow be adjusted; (c) the wave exit openings of the duct and the tailpipe were extremely close together; and (d) if the temperature of the duct could be adjusted so that the trough of the wave exiting it were precisely synchronized with the crest of the wave from the tailpipe. If we had sine waves of equal amplitude, the engine could be rendered completely silent. It also probably wouldn't run, due to pressure wave nullification!

L Cottrill

[Eric]

I have been noticing every time I run really loud engines that I am quite tired afterwards, I dont know if it has anything to do with the sound, or just playing around outside in the cold for 5 hours or so. Sometimes the sound is definatley the source of headaches, and tonight I am not quite with it.

I definately agree that finding those points would be very interesting, however I dont really want to be the guinie pig who has to sit at those points. Even at 8-10 feet the sound was unbearable for more than a second. When I was 5 feet away durring the first discovery it was down right painful, id imagine with enough exposure or getting closer might be very very damaging / fatal.... what was that post about hydrogen fed pulsejets being used as sonic weapons?, I'd imagine it feels something like that. So unless we get some pulsejet fans who are willing to donate themselves for science, I doubt I will be going anywhere near those points anytime soon, although a dB meter on a fairly long stick with a mapped grid may work..

I have also noticed that certian engines are disproportionatley loud at certian sizes. This beast is very loud.

I decided to sacrifice the one torch and use the hose and fitting as a straight through propane line, which will definatley be enough for the big FWE to roar away.

As for the making the engine nice and quiet, I was going for something along that line with the bullet jet design. Unfortunatley the pulsejets sound is non uniform, from my calculations back a long while ago I figured that even if you had equal intensities perfectly out of phase you would only get about 20-25% cancelation.

I forgot what else I was going to say, so i guess thats it.

Eric

[Ray]

You could always use several tanks plumbed in parrallel to increase the amount of fuel delivered...

[Bruno Ogorelec]

Eric,

Avoid the stress of strong pulsejet vibration. You are almost certainly tired due to the pummeling your body is receiving. Big pulsejets crumble masonry. You may have microscopic internal bleeding that manifests itself as tiredness because it is not located in any single spot but at many places inside your body.

I am not joking. Truly strong noise does bad things to your body.

[Bruno Ogorelec]

Here's another interesting thought: We could make such an engine almost quiet if (a) all the noise were confined to a rearward direction; (b) the intake noise were directed rearward through a duct whose internal gas temperature could somehow be adjusted; (c) the wave exit openings of the duct and the tailpipe were extremely close together; and (d) if the temperature of the duct could be adjusted so that the trough of the wave exiting it were precisely synchronized with the crest of the wave from the tailpipe. If we had sine waves of equal amplitude, the engine could be rendered completely silent. It also probably wouldn't run, due to pressure wave nullification!

Larry, it is much simpler to have two identical engines run side by side and have them work out of phase (which is very simple to do). The result would not be ‘completely silent’, however, because only the main ‘bang’ would be cancelled out. There’s plenty of other noise in a pulsejet. As a welder of some experience, you must have noticed that all combustion is noisy. Only the candle and the gas light at the lowest setting are quiet, and only because their ‘noise’ is so tiny that we don’t hear it.

A jet engine would be noisy even if it had completely silent combustion, because much of the jet noise is generated at the interface of the fast hot exhaust gas and relatively motionless cool ambient air. The smaller the speed and temperature gradient, the lower the noise.

But, coupled operation of two pulsejets would cut down noise to a considerable extent. It has been done and it works.

The problem is that it has not been investigated very thoroughly and some of its aspects are poorly understood. For instance, theoretically, such couple operation should boost the power. The two engines should ‘supercharge’ each other, so to say. Yet, the few experiments performed in that direction so far have resulted in the joint output that was _lower_ than the sum of outputs of the two individual engines.

I’ve thought about that a lot. The first thought is that something in the process is consuming energy. But, I can’t think of anything. Another thought is that the researchers have not isolated the flows well enough and that the exhaust of one engine was polluting the intake of the other. But, it would be such an obvious detail. One would have thought a smart researcher would eliminate that to start with.

I’ve come up with another theory. There is the possibility that the pulses are better at exerting thrust than the steady flows. This is certainly true for ejectors. Pulsating ejectors are notably more efficient than steady-flow ejectors. That would mean that we are robbing the pulsejet of some of its effectiveness if we eliminate the pulsation (which is the source of the greatest part of its noise).

Interestingly, this diminished output has not been noticed by the British team developing the BCVP. On the rare and all too brief occasions that the engine snapped into the ‘proper’ mode it really started kicking ass in comparison to the feeble puffing of its individual halves. But, the BCVP is rather different from two individual engines coupled together. And, it never ran properly for more than a few seconds.

[Mark]

Here's an old story involving air.
http://www.phschool.com/science/science ... _step.html
Mark

[Eric]

Avoid the stress of strong pulsejet vibration. You are almost certainly tired due to the pummeling your body is receiving. Big pulsejets crumble masonry. You may have microscopic internal bleeding that manifests itself as tiredness because it is not located in any single spot but at many places inside your body.

I am not joking. Truly strong noise does bad things to your body.

Yea, I knew that much, I didnt expect it to happen to this extent from such a small engine for the lenght of exposure.

What do you guys who have big lockwoods do? I dont even want to imagine how that guy with the 300 lb thrust lockwood gokart must feel after running it.

I wonder if I could make some armor to keep the sound from being transmitted to my body, kind of like a big full body ear muff. Whenever all the snow melts and everything dries up im going to have a parabolic pit dug and run everything in that so that the majority of the noise is reflected up into the sky, would be interesting to see what it does as far as a rain catylist on cloudy days.

Eric

[Mark]

I found this, it's kind of vague but might be of interest.
Mark
http://www.asosh.org/TopicSpecific/whol ... ration.htm
http://atiam.train.army.mil/portal/atia ... 01/ch7.htm
http://www.sma.org.sg/smj/4009/articles/4009e2.html

[Mike Everman]

Bruno,
I'm not so sure it's that easy to make two engines perfectly the same, nor do I think that the crossover tubes and such really get them all the way out of phase if they are made the same frequency. I'm pretty sure now that they truly want to get IN phase with each other.

I think the failing of the early attempts were that the engines need to be designed to run tandem, and tandem only. Think about how the ambient conditions change when they are run out of phase! The geometry needs to change, IMHO, and I do believe you'll get that supercharging you want.

I have two experiments coming up which will shed some light on this subject, which you know is very dear to me. All my wee hours have been spent on this particular subject for the last few weeks, and I'm almost ready to try. For some reason, I want to present the results more than the theory, so bear with me. It's helping me actually DO IT, instead of talk about it! I don't want to present the idea half baked.

[Eric]

Im actually building a valved engine(s) that will operate perfectly out of phase, or at any other portion of out of tune you want. But that will be for another day on the valved forum.

I got the camera back this afternoon and got some video and pics, unfortunately somehow the camera got set on 640x480 and I didnt even realize it. Oh well.

I decided to put one of the bar stool flares on it just for kicks, it starts almost instantly, but still wont sustain for more than 10 seconds. I have a feeling its due to the crapy intake internal geometry. Possibly the fuel probe could be put farther into the engine as well. Im just happy that im getting enough fuel for it to roar away like it does for the time being.

Here are some pics

Eric

[Eric]

Here is a short video clip. Im debating wether I should chop out the section where the intake is, patch a piece of metal over it, and convert the engine into a linear setup. I think it would run a hell of a lot better.

Eric

[Mike Everman]

Beautiful, Eric! Great vid. Can it possibly be that your propane tank cools rapidly enough to starve the engine in 10 sec? Got an electric blanket?

[Eric]

It very well could be, I have that pot the propane tank sits in filled with about a gallon of hot water, the tank is almost empty now and im always struggling to keep the whole thing above freezing. After a few attempted runs I usually pull the tank out to find a layer of ice from the formerly hot water. Cant wait until summer.

Eric

[Bruno Ogorelec]

Bruno,
I'm not so sure it's that easy to make two engines perfectly the same, nor do I think that the crossover tubes and such really get them all the way out of phase if they are made the same frequency. I'm pretty sure now that they truly want to get IN phase with each other.

Well, the lore and the documented experiments are all against you. For instance, Kentfield says that pretty much everything they tried to get two engines to work out of phase worked – connecting the intakes worked, connecting the exhausts, ditto, connecting both, ditto. I think connecting the combustion chambers also worked, but I can’t quite remember that one. The Israeli managed to synchronize two engines out of phase easily in a project of their own. [I have not managed to get them even to respond to mail, much less send a copy of the paper, so I don’t know the details, but I have seen reports that they did it.]

In contrast, it is extremely difficult to get two pulsejets to goose-step.

Put two pulsejets together at the right distance – even without physical connection – and they will slowly start synchronizing out of phase because it is their energy minimum. A pressure pulse from one engine will amplify the suction pulse of the other engine. Little by little, they will fall into this mutually helpful rhythm, like liquid finding itself the lowest spot on a seemingly flat plate.

OK, you can get them to help each other stay in phase, but the distance will have to be greater, the synchronizing ‘signals’ will be weaker and their strength will probably be overcome by the forces that try to push the cycles apart.

There are plenty of the latter. Look at what influences the functioning of pulsejets. Everything does. You fart near the engine and it will change the frequency, amplitude and wavelength a little bit. Thrust, too. The change will be minimal and it will only last for a few cycles, but it will be there. A pulsejet never, never, never ever, has two identical pulses in a row.

That means that it does not want to beat to a particular rhythm. It must have help to do that. There is no help to push two phases together, but there is a small but definite force trying to keep the phases apart. So, that’s what they do. You help them do that with some simple ducting and bingo! – you get coupled pulsejets. They have to be reasonably identical, but not fanatically so. They will probably always ‘hunt’ a little hither and yon, jumping in and out of tune like a Gypsy’s violin, but overall, the tune will more or less stay where it should be.

I also have this on a higher theoretical authority (I think Foa or Zinn, or Reynst or all three) but damned if I can find it very quickly. I’ll find it if it’s terribly important.

I think the failing of the early attempts were that the engines need to be designed to run tandem, and tandem only. Think about how the ambient conditions change when they are run out of phase! The geometry needs to change, IMHO, and I do believe you'll get that supercharging you want.

Well, the mutual supercharge is obviously a different problem. Yes, it differs from mere synchronization. I agree that you probably have to design the engines specifically for the new (markedly different) conditions. The Albion team will tell you that it’s not easy, especially when you want to achieve it with a valveless engine, but those tantalizing few seconds of proper operation let you know that it might well be worth the trouble.

I have two experiments coming up which will shed some light on this subject, which you know is very dear to me. All my wee hours have been spent on this particular subject for the last few weeks, and I'm almost ready to try. For some reason, I want to present the results more than the theory, so bear with me. It's helping me actually DO IT, instead of talk about it! I don't want to present the idea half baked.

Please bake it well. I can hardly wait to hear the verdict – even if it goes against everything I know. I find this very exciting.