Even the Cheapest Jet Should Breathe Like a Reynst!

Moderator: Mike Everman

Postby Mike Everman » Tue May 11, 2004 2:50 am

Larry,
Very interesting... If you need to extend the tail, I've had good luck with some aluminum flashing wrapped tight around, and held with a pipe clamp. I'll have to look back and see what length you started with, but it would be prudent to start with 6x the cc length. I say this because most LH types have thier exhaust throat (another place you could use a little pinch, I'm thinking...) at 25% of the over-all length; so when the intake is roughly the same length as the CC, the tail is 6x the CC length.
Thanks again for the "kick in the pants" re: Kazooenstein!
Mike
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Postby larry cottrill » Tue May 11, 2004 3:20 am

Mike Everman wrote:I'll have to look back and see what length you started with, but it would be prudent to start with 6x the cc length. I say this because most LH types have thier exhaust throat (another place you could use a little pinch, I'm thinking...) at 25% of the over-all length; so when the intake is roughly the same length as the CC, the tail is 6x the CC length.

Mike -

The tailpipe length is almost exactly 22 inches, and its ID is just a hair over an inch. The chamber is 3.5 inches 'square' [outside] and 1.5 inches wide. The rounded corners reduce the volume significantly, of course.

The contrast between rich and lean running is interesting, and very easily studied with the needle valve. At the richest setting you can run, the noise is very loud, but deep and rough. The tailpipe flame is ragged and balloons out and flies around from side to side -- it has the appearance of coming out in 'feathers' or 'chunks'. The flame you see by looking down through the intake is various shades of blue, boiling sort of like white water rapids. When you lean it out, with plenty of air running of course, you reach a point where the sound 'cracks' [astonishingly like leaning out a two-stroke piston engine!] and it immediately smooths out into the fine 'pulsejet sound'. The tail flame is clean and straight, projecting maybe five or six inches from the pipe. A look down the tube again shows various shades of blue, but set out in straight, parallel streams going rearward.

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Postby larry cottrill » Tue May 11, 2004 6:05 pm

Mike -

I just realized that there are other things that should be mentioned or reiterated: The full length of the intake pipe is almost exactly seven inches [probably .75 inch longer with the flare attached]. Also, though I didn't measure it after I built it, the pipe centerline at the bottom end of the pipe must be approximately 2.5 inches aft of the front chamber wall.

The 22-inch length of the tailpipe may be badly tuned, acoustically speaking. Recall that this length was decided upon on the basis of volume -- I was working from the volumes in the Dynajet, not the lengths! If you believe in masses dominating the process, this makes sense, but not if your thinking is acoustically oriented; in that case, the tailpipe should be cut way back, so the whole engine would be about the length of the Dynajet. [Recall that the length and volume of the chamber are almost exactly Djet sized, though the cross-section shape is radically different.] The 'venturi' flattening you proposed for the intake seems astonishingly close to the throat area of the Djet, though I haven't worked out the math to verify it.

Another interesting thought is that everything about this engine is doing what it's supposed to when it's forced to run right -- the flow must be curling up from the bottom of the intake so the explosion takes place right up front; the explosion drives the blast right past the pipe into the intake; and, I'm convinced that the explosions are now solid blasts that ought to carry the cycle! I really think that the geometry is basically working -- it must be a defect in the wave timing that's killing her.

Perhaps the blast mass is getting completely past the intake way before the pressure trough can get back there to set up a good draw; so, when it valves open, there's little pressure difference. Then, the air just slowly fills in the pressure drop as the wave finally makes it to the chamber. Too soft an action to create the sharp, forward curling blast of air needed to feed the intended combustion zone at the front end.

What do you think? Is that scenario possible, or based on misunderstanding how the mass should behave in relation to the wave?

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Postby Mike Everman » Wed May 12, 2004 1:55 am

Larry-
I don't know what to think, frankly. Too many variables. The snorkeling into the CC of the intake is a trouble spot in my mind. The short length and it's demands for high frequency operation is another. I think the only hope is if you can get every other rarifaction wave to start the next cycle, and your straight pipe isn't accelerating this return wave, nor do I think it could possibly be a clean, well defined wave after two circuits. Remember when Bruce put the aerovalves on his valve-type body? It barely ran and very anemic. It was much larger than this, and therefore with a better chance to run(?)
I hope you prove me wrong, but I'm just not sure this can possibly ever be more than a blowtorch. I am not quite there with my understanding of flows, and definitely don't know where to begin with Electra, but acoustically I'm getting a bit on firmer ground and it doesn't seem to have the right length proportions. I haven't a clue as to what acoustically happens with the snorkel intake.

OK, that was a long way to say "I don't know Jack". I'm just happy to be here! :-(|)
Mike
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"I've Seen the Lightning Flash ..."

Postby larry cottrill » Wed May 12, 2004 3:55 am

Mike Everman wrote:Larry-
I don't know what to think, frankly. Too many variables. The snorkeling into the CC of the intake is a trouble spot in my mind. The short length and it's demands for high frequency operation is another. I think the only hope is if you can get every other rarifaction wave to start the next cycle, and your straight pipe isn't accelerating this return wave, nor do I think it could possibly be a clean, well defined wave after two circuits. Remember when Bruce put the aerovalves on his valve-type body? It barely ran and very anemic. It was much larger than this, and therefore with a better chance to run(?)
I hope you prove me wrong, but I'm just not sure this can possibly ever be more than a blowtorch. I am not quite there with my understanding of flows, and definitely don't know where to begin with Electra, but acoustically I'm getting a bit on firmer ground and it doesn't seem to have the right length proportions. I haven't a clue as to what acoustically happens with the snorkel intake.

OK, that was a long way to say "I don't know Jack". I'm just happy to be here! :-(|)

Mike -

Ah, you wouldn't say such things if you'd been here to see and hear it run last night. Yeah, even taking into account all the air I was pouring in.

Even if Elektra I turns out to be a total dud, the 'snorkel' is a wonderful experience. How many living persons have witnessed, with unaided eye, the flow of combustion gas WITHIN a pulsejet chamber. Yes, Hank has observed pulsing inside jam jars and Rossco has probably peered into the front end of his designs to see the gases fleeing like pursued robbers, but I've seen it through a porthole into the heart of the beast -- stood and watched it streaming by like the cars of a blue-hot freight train in the night. Only a foot of distance between the wall of lightning and my eye, without so much as a quartz window in the way. If the Lord calls me home tonight, I can ask St Peter at the gate, "Hey, man ... did you see THAT?"

All right, that settles it ... the next thing to try is to cut it back to Dynajet length, overall, and see what it does! To not try it would be ridiculous; I can weld the piece of tube back on there in about four minutes flat if I don't like what happens.

I actually doubt very much that the pressure wave reacts to the presence of the 'snorkel' as though it were some second pressure node. There is certainly no indication of that in the frequency you get when you force the thing into full grease pulsation. Then again, even if that's true, it could look a lot different to the rarefaction wave coming back. Of course, a lot of things could look different than expected, with that velocity of air pouring in, so who knows?

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Postby Rossco » Wed May 12, 2004 10:00 am

Larry, STOP.
Dont cut the tail off. Extend it first if anything, in my experience itll run too long but never if too short.
I built a similar engine, well, in the way of intake angle. And yep, she is a beutiful sight. The other thing that you really should do is get a shop air compresser air sorce in there. Then you can really see the fire when at full blast. I was going for spinning dense intake air and straight outgoing blast. The tank effect of the intake air streem coming to a dead stop was in theory giving me some pre-combustion compression. Could still work, just a lot of bugs to be ironed out and absticals to get around.
Its one of two engines of mine that would not and will never run. Three if you count the twin engine, but i may just get back to that one day. With out dampening your project at all, my engines would not run with any amount of variables or changes. Now that i have more of an understanding of the beast, i just look at them and shake my head. Proportions are just all out there. But they did get me to were im at today, so they arnt all bad.

You mentioned that i may have peered up the intake of my engines when running to see their fiery belly in full action. Well, yes, and if i could, i would watch it all day.
My test rig is the best at the mom. From the intake you can see right out the tail, through an iridesent blue veil. Bus the most exiting is from the tail. With a full face mask on, battering into your face, you can get nearly right to the end. Looking up there at full blast is something else. The first thing that catches your eye is the red/white hot fuel ring, that is wrapped around the intake. Looking closer you see the bright blue of the combustion zone around the outside of the intake, forcing itself inward to fit through the restriction at the end of the CC. Then at that throat, you see the glowing walls of the engine, with the insides of my welds being the brightest. This is where sparks tear of and come racing in a streak of light into your face mask.
VERY EXITING to say the least! so i know your satisfaction, even if you only get that far with electra. Again, im not saying that that is all that you will get, you seem to be way more patient that myself.

I tried looking into the tail at starting once, tho the shock wave that came out in one of its big starting booms tore the mask off, so that idea was short lived!

Mike or others, where do you get your dimentions from? Is this just a common sort of ratio or do you coulculate them somehow? I know that there has(is) been calculators developed(ing) But can these be applied to different engine types with any accuracy?. My undersanding of mass flow and wave mechanics is poor to put it politely, and would really like someone of the likes of M. to go over some of my dimentions to see what could be done. All mine are off the top of my head and then tuned to work. This is very frustrating tho, let alone timestaking.
Thanx in advance.

Rossco
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Postby larry cottrill » Wed May 12, 2004 1:27 pm

Rossco wrote:Larry, STOP.
Dont cut the tail off. Extend it first if anything, in my experience itll run too long but never if too short.
I built a similar engine, well, in the way of intake angle. And yep, she is a beutiful sight. The other thing that you really should do is get a shop air compresser air sorce in there. Then you can really see the fire when at full blast. I was going for spinning dense intake air and straight outgoing blast. The tank effect of the intake air streem coming to a dead stop was in theory giving me some pre-combustion compression. Could still work, just a lot of bugs to be ironed out and absticals to get around.
Its one of two engines of mine that would not and will never run. Three if you count the twin engine, but i may just get back to that one day. With out dampening your project at all, my engines would not run with any amount of variables or changes. Now that i have more of an understanding of the beast, i just look at them and shake my head. Proportions are just all out there. But they did get me to were im at today, so they arnt all bad.Rossco

Rossco -

I understand you're concern -- yes, I know that lengthening the pipe will often improve results. One important aspect is that you're working against a more massive 'piston', and that's usually good.

HOWEVER ...

Getting workable gas masses is only one aspect of the problem. The real issue with the location of the 'snorkeled' intake is this: Its location must be where the overexpansion immediately behind the main blast mass coincides, both in time AND space, with the arrival of the main trough in the reflected negative pressure wave. That's what you must have for such an engine to work. It happens, more or less correctly, in the Chinese [although Bruno has pointed out that this design may not be optimized]. The Chinese is a very long engine, with a very large piston to drive the suction phase. But I question whether it is really a 1/4 wave engine; in all likelihood, it seems to me that it may really operate in a 3/4 wavelength mode. Of course, I'm just guessing, and changing that in a way that leaves it properly tuned would be a major undertaking.

Now, look at the Reynst Pot -- arguably, the most optimal valveless design ever. The piston mass is huge [especially when you consider that part of it is always cool air pulled in through the gap!] but it is SHORT -- the stack is only a little more than twice the length of the chamber. That, my friend, is a picture of a GOOD design, where mass balance and acoustic resonance are in as near-perfect balance as might be humanly possible to attain.

The Elektra I idea is similar, except that a lot of the rear-end piston mass has been sacrificed, so it is somewhat de-tuned from the classic Reynst, right off the bat. Nevertheless, it is NOT going to be properly tuned by making it work as a 3/4 wave device. It's only going to be really good [or, as close to really good as it can be] as a 1/4 wave engine. [I'm talking, of course, about the fundamental wavelength seen in isolation.]

Such things are difficult to deal with in a system that's just thrown together out of 'off the shelf' parts. The flow scheme from the intake into the explosion zone of the chamber would be easier to get right if the chamber were, say, twice as long [still shorter than the Chinese!] Nevertheless, that very short front end dictates that, from an acoustic standpoint, longer will not necessarily be better. If more mass is needed to get all the power we can, the way to do that would be to replace the 1 inch ID pipe with a larger one, once the optimal length is established.

So, what the heck ... I can add extensions until it works. But once I get an extension that works, the next thing I would do is cut the original pipe back to achieve an end-to-end length of one THIRD of the total I end up with [after all, 1/4 wave is one third of 3/4 wave!]. So, yes, that might be a plan for going forward, and would certainly be easy enough to do.

Such engines are inherently weird. The 'snorkeled' end has to be located where it will have no significant effect on the blast phase, yet where it will have maximum sensitivity to the rarefaction wave when it hits, just at the time the valving action of the blast mass has ceased. It's hard to get something like that exactly right. Yet, the fine performance under forced air tells me that the geometry of the front end has a realistic chance of working -- all that's missing is the natural production of the quick blast of air 'down the chute' that I'm now 'faking' with the blower.

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Elektra I Testing -- Photos At Last!

Postby larry cottrill » Wed May 12, 2004 5:45 pm

I finally finished my last roll of film. The last two are from the very last tests [note the 20 lb Propane tank beyond]. The second photo of it running does not show the engine at full heat -- after 30 seconds, most of the flat sides of the chamber were glowing, as was the whole front half of the tailpipe.

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Attachments
Flare_and_bottle_crop1.jpg
The temporary intake flare, cut from the neck of a polythylene bottle like the one shown. Photo Copyright 2004 Larry Cottrill
Flare_and_bottle_crop1.jpg (63.04 KiB) Viewed 5749 times
Starting_with_blower_crop2.jpg
Starting, fairly rich mixture, with blower input. The Intake flare is visible just below the blower snout. Photo Copyright 2004 Larry Cottrill
Starting_with_blower_crop2.jpg (268.95 KiB) Viewed 5748 times
Running_with_blower_crop2.jpg
Running, lean mixture, with blower input, shortly after leaning it out with the needle valve. This is pulsing at about 200 hz, but dies immediately without forced air. Photo Copyright 2004 Larry Cottrill
Running_with_blower_crop2.jpg (99.29 KiB) Viewed 5748 times
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Postby Mike Everman » Thu May 13, 2004 2:41 am

Larry, great pictures, thanks! I hope you get it to sustain.

Rossco,
I don't want to hijack Larry's thread, so I'll start another re: dimensions.
Mike
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Postby Mark » Thu May 13, 2004 2:56 am

I'd like to see if it would run with the side port not extending into the combustion chamber, but rather flush with the wall and out of the way of the turbulence inside the center. Just an idea if you run out of other things to try. Nice pictures, I always think pictures add so much.
Another thing to try would be to inject the fuel straight in line with the intake tube, cocked so it was right in the center of the side port tube, the tip aimed straight in the direction of the combustion chamber, like how a typical Logan does it.
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Postby larry cottrill » Thu May 13, 2004 3:35 am

Mark wrote:I'd like to see if it would run with the side port not extending into the combustion chamber, but rather flush with the wall and out of the way of the turbulence inside the center. Just an idea if you run out of other things to try. Nice pictures, I always think pictures add so much.

That makes it just a shortened Chinese. It would avoid the design element I was trying most heartily to validate.

Another thing to try would be to inject the fuel straight in line with the intake tube, cocked so it was right in the center of the side port tube, the tip aimed straight in the direction of the combustion chamber, like how a typical Logan does it.
Mark

Actually, this is what I do. I'm sorry this wasn't made clear earlier. The top of the fuel tube takes a gentle bend [not to be confused with TV re-runs of a big bear] out to the left at the top. At the bottom, it is aimed slightly inward so it projects fuel flow to a point approximately in the center of the lower rim of the intake tube. The bend at the top simply serves to get the threaded fitting out of the way. The fuel tube itself is 1/8-inch OD copper, and is probably less than 1/16 inch ID. This sounds tiny, but appears to be adequate for all the flow needed, at least so far.

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Postby Mark » Thu May 13, 2004 2:29 pm

I can certainly see/understand your desire to do something new and not just make another old tried and true design, like those old Chinese electrical box pulsejets. I don't know how many times I have said to myself out loud in some distant soliliquy way, "... if only someone would try something new with the side intake on those old boxy Oriental valvleless designs, if somehow one could re-orientate that side port to make it more electric, some gentle method to lead the air right into the center of that combustion chamber....."
Thanks for the clarification on the gentle bend, I wonder if you could get it to run on honey, something akin to Bruno's butter jet proposal?
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Postby Mark » Thu May 13, 2004 5:47 pm

In all seriousness, I think your pulsejet looks pretty good so far, it just needs more love. I thrive on finding or seeing common objects turned into clever pulsating combustion devices. Keep up the good work.
I was running an old oxygen tank jam jar style, a pint at least of methanol in the bottom, a 5 by 14 inch tall tank, and I lit it with a short length of 3/4 inch tubing screwed in the top. I lit it with a small propane torch and and the combustion was popping away, I swung the flame from the torch near the tip where the gases were being ejected and fresh air drawn in, each time just that little interference dampened the resonance greatly, on the last try the flame of the torch kind of bent, "a gentle bend", as if being drawn in and then I had killed the effect, the popping combustion stopped dead. It's funny how fragile a robust running snorkeled vessel can be. For a jam jar, it can be kind of loud, so sometimes I wear muffs, especially when first lighting it off, the initial hiss can be annoying too.
Stay tuned for when my newly won bigger tank arrives from eBay world.
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More Recent Photos

Postby larry cottrill » Fri May 14, 2004 2:47 am

My Elektra I Page 2 [Test Journal Page] now features the photos I posted here earlier, plus a few more:
http://www.cottrillcyclodyne.com/Elektr ... raI_2.html

The wide view of the overall test setup and the valve/regulator assembly for torch-size propane and MAPP cylinders may be of particular interest to some. Especially note the Safe Science(TM) NoDump Propane Cylinder Stand, procured at great personal expense.

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Postby Mark » Fri May 14, 2004 3:25 am

I was thinking you might like to try a coil of 1/8 inch or 1/16 inch is it, that really small copper tubing you can buy at some hardware store, it even comes with fittings for it too,anyway if you could coil it around some region that gets hot, preheating the propane can go a long way to getting a peachy keen flame. The added heat not only gives the fuel more velocity which aids in mixing, but also the propane will react with the oxygen much faster too.
Best of luck whatever you come up with. The one picture of your jet looked kind of strangely stylish sitting on its little stand.
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