Ram Ejector Engine/Burner

[Rossco]

Ive made a new topic here for this project to live in for easier referance, as it is no longer a terbine, or even the same project.

It is now a cyclic ejection breathing.........burner/engine.

By way of a background, Larry and i discussed something of similar concept some years ago, both possesing quite similar personaly original own designs. Nothing was done about it then, as happens to so many interesting thoughts at any particular time in ones life, and it drifted of into... where ever such things go.
Recent findings and moreso ponderings have brought me back to the concept.
With a gift of some new odd items of steel that were given to me with the understanding that of coarse they could be usefull for something, im up and running with the project.

The start of the project as of 30mins ago, copied from the Ram Turbine thread...

Ejector system made, and tested!
Very simple! Very effective!!

A small flow through the intake and out the ejector mouth creates a great volume of air to flow, at some small pressure around the clean air intake piping growing exponatialy with input velocity. Very little mixing of the "exhast" stream air, and clean air which is great.

Results for the first 20 mins of work into the project are very satisfying indeed!

Combustor now/next, to get the intake air expanding and hopefully ejecting at a point where it will drive its own operation.

Rossco

[Rossco]

Ah, forgot to mention one other observation.
It is bloody loud!
So much for moving to a neibour friendly project.

Rossco

[Dave]

Rossco

Good to see you back.

"It is bloody loud!"

Now you have my attention.

Looking forward to seeing the picutures.

Dave

[Bruno Ogorelec]

It is bloody loud!

Well, you got my attention, too.

Guys, this way we will never break into the mainstream. We are supposed to make those things quiet! How are we going to do that if we enjoy noise so much? Will we ever find the inner strength of character to make our engines sound wimpy?

[larry cottrill]

Rossco -

Just remember, I still get to keep the name Cyclodyne if it works ;-)

Also remember: NASA said it couldn't be done:
http://www.cottrillcyclodyne.com/Cyclod ... ction.html

Ha ha! We'll show them yet ...

L Cottrill

[Rossco]

OK, thanks for that Larry.
Very interesting read from NASA!

I do remember more clearly now. We came to about this point last time (i thought that it was longer ago)? no diff.

You did offer something along the lines of the non disclaimer agreement, although i had no intention of going much, if any further with the project at the time.

I would be very interested in seeing the other stuff some time, although not yet.
I need to get a feel for my steel first. To be able to look at something and know the sound, speed, momentum, reactions even failure or missestimation that would be happening as if it were not just paper but alive.

Thankyou for the attachment, yes that is the one that i was thinking of.
I do remember now having to really scratch my head about that one, to try to get it all happening at the same time in my mind, when looking at three different dimentions on paper!
The biggest problem that i would hit when "running" it was keeping it all steady! Although i think i have that sorted, so ill keep you posted.

As always, ill keep you all posted here, although, maybe i could have a little yarn off line at some later date with you Larry, to ponder a couple of things. You look like a better ponderer than i?

The one thing that i would say though, i think that you would find it terribly diffucult to work with me on this project? I am a frustrating sort of person to one so controled, as yourself.
I jump around in development, do things only cause I feel they sould be a cirtain way, without "scientific backing" (or however NASA put it), and measure things with a handspan, or fingerwidth.
If its too big i bash it with a hammer untill its smaller, if its too small i take to the rest of it with a gas ax to make it proportional, and the plans are then drawn off the prototype not the other way around.
This is just a word of warning. Although i would be happy to discuss any findings of mine, or explore questions of yours with this project, out of interest sake, if nothing else.

Rossco

Im going out now to measure the sound out of this thing, ill let you know.
By the way, thats just the intake with compressed air. Im sure it could only get louder with combustion, hot/cold gas interfaces and the rest.
It has to be better than the stocatto hammering of a pulsed combustion tho!?

[Rossco]

Sound test.

Picked up 500mm to one side of intake. With no air blowing toward meter.
Compressor at 100psi (relativly low)
Air gun/nozzle, supposedly a quiet flow design.

Compressed air gun alone. 75db
Blowing into venturi and pipe without ejector action. 85db
Blowing in full ejector action. 150db

Bit of a step up!
Tearing the high velocity flow back away from the rest seems to be causing quite an upset! It is a reall tearing sound too.

enough for now...

Rossco

[Rossco]

Its built.
Ugly.
Dont know how it will go now its built. Doesnt look promising.
Sprayed some fuel into it and lit the exhast. It screamed, as a jar does, then i suppose the ejector action started working and it made an almighty bang. Thats it.
It doesnt have a flame holder in it, as i am going to put a big bung in the bottom to be able to add and change such things.
But i wasnt expecting such a big bang, so now im just not sure how to start the thing gently?
Im now glad that it isnt a turbine, as i think it would be busted already.

Rossco

[larry cottrill]

Rossco -

Great work! Get us a photo or two.

(Remember ... I never said it would be easy ;-)

L Cottrill

[Bruno Ogorelec]

I think you should do well to look up the Rijke tube.

I know of no reason why a Rijke tube should not be a loop, though it might require some thought about the actual layout, especially with ejector action added.

I don't remember enyone ever attempting to put an ejector and the Rijke tube together. Remember -- you heard it here first.

The reason to do it is simple -- the Rijke tube introduces resonance, which boosts combustion intensity, but keeps combustion constant. It is not intemittent, like a pulsejet.

(I've long thought that the pressure jet is some sub-variant of the Rijke tube. Maybe other variants are possible, like a cyclical flow engine.)

When I say 'putting the ejector and the Rijke tube together' it may just boil down to the right positioning of the ejector and the combustion zone in the duct, to take advantage of resonance. It may be more complex than that. I just don't know. But, I think it would be stupid to miss the opportunity if it's there. The Rijke thing offers something for nothing, which is a rare thing indeed.

[larry cottrill]

Rossco -

All right - I've thought about it enough to get an idea of why this is going to be so difficult. Well, I mean, you already KNOW why it's going to be so difficult: It's going to be hard to make an ejector that's good enough. Duh. However, that's not a very quantitative answer; just how good does it need to be, anyway? I think I can now answer that in a rough sort of way, working from some reasonable assumptions.

First, the assumptions. Suppose we proceed from the old truism that an air-breathing jet will operate most efficiently when the relative jet velocity [exhaust going out] is 2x the relative intake velocity [air coming in]. This "rule" supposedly applies to any pure jet drive [may not apply to turbofans or other hybrid types]. Unlike most "truisms", this one is supposed to be based on solid math, physics, etc., although I haven't done enough research to determine how it was derived. But, that's Assumption 1.

Assumption 2 is that, in a ramjet, the massflow is essentially constant throughout the whole engine, i.e. the massflow is exactly the same number of molecules passing ANY station in the engine per one second of time. In reality, of course, the fuel gets added in, but at a lean burn air/fuel mixture of 30 lb/lb, that's only an addition of 3 %. If anyone doubts that such an assumption can be true, answer this question: Where in the engine duct does gas mass accumulate over time? If the answer is 'nowhere', then the gas massflow has to be the same everywhere.

Assumption 3 is derived directly from 1 and 2: If the exhaust massflow is the same as the intake massflow, then ipso facto the entire increase in momentum must be the added VELOCITY caused by the heat of combustion [really, the part of that heat that can be used, i.e. after losses]. Obviously, if the velocity is doubled, the exhaust gas density must be 1/2 of the cold air density coming in.

So, in a normal ramjet what we have is an engine that throws the same volume of air that it takes in, but twice as fast, at half the density. Pretty basic so far.

Now, the classic textbook ramjet picture [for subsonic engines] shows an exhaust area about equal to the intake area. Since this is just a schematic drawing, not a detailed plan, let's just take Aout = Ain as Assumption 4, keeping in mind that it is probably only approximate.

The really important part to understand is that the intake and exhaust massflows are essentially equal. That one fact means that to derive significant net thrust, we will need a heck of a good ejector / augmentor, to wit:

An ejector trades off increased massflow [from entrained cold air] with decreased velocity, conserving total momentum [if losses are small enough to be disregarded]. Suppose we have an ejector that is capable of taking on as much free [cold] air massflow as the driving stream [engine exhaust in our case]. Suppose that we can find a position behind the ejector exit where the velocity will be 1/2 the exhaust velocity [here I am talking about a static running condition, of course]. At that location, we will have TWICE the massflow needed for combustion, at exactly the right velocity for the ramjet intake. Think this sounds pretty good? As ejectors go, it's probably not bad for an amateur effort. HOWEVER:

What this means is that we will neet an intake that accepts HALF the ejector output !!! This leaves only half thrown free of the engine to provide thrust. I would submit to you that this is not highly impressive. Also, we can assume that half the exhaust gas is going back into the engine intake, which is probably not too great either.

Of course, if we are clever enough to make a really good ejector, we could drag in TWICE the massflow of the exhaust stream. Maybe. Then, we would only need to collect ONE THIRD of the ejector output to recycle into the engine, and only 1/3 of that gas would be exhaust gases. This sounds much better.

Stretching the laws of physics [and overall credibility] even further, if we could somehow pull THREE times as much fresh air as the exhaust massflow [and still get half the exhaust velocity!] we would need only ONE FOURTH of it to ventilate our ramjet, and only 25% would be re-used exhaust. That nets a LOT left over for thrust.

And so on ...

So, how good an ejector / augmentor do you think we can build? I submit to you that getting one good enough to deliver four times what goes in at half the speed is probably not achievable in our remaining lifetimes. But, what do I know? The claims for those little 'air amplifiers' really make them sound pretty good ...

I have the sneaking suspicion that buried somewhere in the foregoing discussion lies the long-hidden reason these engines aren't flying people all over the globe even as we speak. Just a hunch, of course.

Now, the good news is: The ejector / augmentor stage should be helped considerably by forward velocity, although there will be a point of diminishing returns where drag effects will take over. But, there is a very good chance that we could have an engine that will run well enough statically to get us off the ground [though kind of a dog] and then pick up efficiency radically for a while until some reasonable speed is attained. If an engine is cheap/simple/maintainable enough, that would make it a contender for some serious applications! After all, you could provide JATO or something for the takeoff run.

L Cottrill

[matt512s]

Hello All;
I was wondering how a Rijke tube helps a jet engine.
As far as I can understand, it is just a heated tube that
makes noise. What and how does it give you "something
for nothing"?
Best Wishes:
Matt

[pezman]

Well, it's a thermo-acoustic phenomenon -- as is a pulse-jet.


Here's one link that I found. I just glanced through this and it looks like it uses mostly linear acoustics for analysis. Looks like the guy built some wailin' tubes though -- it must have been deafening in that lab.

http://scholar.lib.vt.edu/theses/availa ... thesis.pdf

[Rossco]

Larry.
Quite a thought provoking "little" essay there, as always.
I think that youve made a lot of good points, and i have been thinking along the same lines to some extent to try to envisage the operation of this thing actualy running.

Ben, youve really got your head stuck in the sand sometimes.
You are generalising hugely, again. A ram jet, does not need foward velocity to operate at all! Static running is quite feasable, and often succeded in the backyard lately by many an enthusiast.

By saying this i am only talking about engine velocity being static of coarse. A source of high speed air is needed, i agree. That energy is provided in most cases from an external pump, driven by separate power.

What are we achieving by feeding huge amounts of fuel into these engies tho? A small amount of global warming...and some burnt lawn and/or torn up garden. This energy output, minus losses, can easily drive the action of feeding itself the air required for sustainance, as any other static engine does! Its just a matter of making it do such a thing with out any machinary to transfer the energy.

Rant, rant, rant...

Back to the engine itself. (Burner, for Ben)

Just some notes for you to think over Larry, as your conservation of momentum argument has made it sound much too easy!

The biggest one, is the exhast velocity out of this thing??? Its got me totaly lost in where all the energy is going.

I made the cold air input direct into the bottom of the CC at a tangent to cyclone, for a couple of reasons... To possibly produce a vortex mixing and flame holding section? dont know about the feasability of that one? And the second, i was aiming to get this going as a BURNER on wood, dust or other solids, so it needed the air to be forced in and smash around in the "fuel" for even burning.
This action seems to be taking all the velocity out of my exhast exit.

Forget the ejector section for a while, and the burning.
Just blowing a compressed air gun into the open pipe intake at the bottom of the CC creates huge sucktion at the mouth, (ejection action again), presumably forcing a much larger volume of air in, at a lower velocity than the gun is dilivering. This is fine, that is what you would expect?
BUT, out of the exhast (at the top of the CC) there is only a gently waft of air coming out???????? Lots in, through a large opening, should produce the same amount out, although its a smaller exit, so it sould be at a higher velocity?

What do you think of that? What is the cyclone effect in there doing to the input air? Its not coming out any where, (its air tight) and there is no air pushing back out the intake, (you can feel it sucking). WTF.
In my mind, i see this being no different to blowing an air gun into a larger than nozzle pipe. A whole heap of high speed air comes out the other end.
My solution for testing this at the moment is get another CC (which i have many of) and build the same thing with the intake and exhast just at opposite ends. Straight, inline, without spinning that air.
There should be only a difference of pressure within the CC as apposed to the pipes and a velocity difference from inlet to outlet, both relative to CSA dimentions. RIGHT?

How would you think of intake to exhast diameters ratio? The build at the moment has much to small an exhast i think! About a third? I was aiming at a very high exhast velocity, to produce a high ejector action to counter the backpressure. (so much for that)

Youve got me thinking on this project again Larry, keep it up.
It really doesnt matter of usable left over thrust at this point. Im developing the action, not a flight engine. (or an engine at all for that matter) The thing at present weighs in at about 10KG...no, it would prob. be more than that!

Another thing that i was thinking from your post.
The ejector action i have no worries about.
With a compressed air gun, it produces an estimated twice the volume at half the velocity just out the intake pipe (open to air) with all the input air, and probably more, exiting the ejector. The ejected exhast has no noticable (by feel) loss in velocity, although it really must.

The ejector by the way, ejects the exhast OUT of the pipeing after generating a mass flow, rather that what i think your designs do, eject exhast into the engine to generate a flow? I get confused when you keep saying that there is a cirtain amount of exhast back into the engine. I dont think this is nessacary. (although for a wood burner could be benifficial?)

Bruno, what are your findings or thoughts in respect to your "swirl can" concept on "cycloning" using a large amout of energy?

Ive not given up on it, just some annoying underlying issues, nothing to do with the concept in question, have put it all on hold.

Rossco

[larry cottrill]

I made the cold air input direct into the bottom of the CC at a tangent to cyclone, for a couple of reasons... To possibly produce a vortex mixing and flame holding section? dont know about the feasability of that one? And the second, i was aiming to get this going as a BURNER on wood, dust or other solids, so it needed the air to be forced in and smash around in the "fuel" for even burning. This action seems to be taking all the velocity out of my exhaust exit.

Forget the ejector section for a while, and the burning.
Just blowing a compressed air gun into the open pipe intake at the bottom of the CC creates huge sucktion at the mouth, (ejection action again), presumably forcing a much larger volume of air in, at a lower velocity than the gun is dilivering. This is fine, that is what you would expect?
BUT, out of the exhaust (at the top of the CC) there is only a gently waft of air coming out???????? Lots in, through a large opening, should produce the same amount out, although its a smaller exit, so it sould be at a higher velocity?

What do you think of that? What is the cyclone effect in there doing to the input air? Its not coming out any where, (its air tight) and there is no air pushing back out the intake, (you can feel it sucking).

Well ... uh ...

Obviously, the energy you're applying is being taken up as mechanical or thermal losses somewhere. My only guess at the moment is that you are indeed achieving suction in most of the intake, but that there is air escaping around the outer surface, i.e. that entering and exiting air are passing each other, with the exiting air clinging Coanda-style to the intake wall. That would certainly qualify as a "mechanical loss"! You could test for this (perhaps with the help of a nearby Princess) using something that produces a thin smoking trail, such as a stick of incense. If this turns out to be true, it would be a good indication that the exhaust might be choking the flow you're expecting back there, and overpressurizing the chamber. Another possible cause could be the ejector throat being too large for the width of the driving gas stream being used. I have a strong feeling that efficient ejectors will have a throat not much larger than the stream nozzle, so that the driving stream practically fills the throat where it enters. But, perhaps someone will inform me that I'm just wrong about this.

My solution for testing this at the moment is get another CC (which i have many of) and build the same thing with the intake and exhaust just at opposite ends. Straight, inline, without spinning that air.
There should be only a difference of pressure within the CC as apposed to the pipes and a velocity difference from inlet to outlet, both relative to CSA dimentions. RIGHT?

Yes, that's what we would expect. That experiment would be a way of simplifying the problem, if the intake and exhaust are identical in size and shape to the one you're fighting with.

How would you think of intake to exhaust diameters ratio? The build at the moment has much to small an exhaust i think! About a third? I was aiming at a very high exhast velocity, to produce a high ejector action to counter the backpressure. (so much for that)

I would have the two areas practically identical. I think that an undersized exhaust is just going to overpressurize the chamber, making it hard to drive the intake.

The real secret to good ramjet operation is to have a really good diffuser section - really smooth, gradual density and pressure increase leading to the combustion zone. Remember, the pressure at the rear of the diffuser must basically balance the combustion chamber pressure, to keep combustion right where you want it (even with good flameholders in place). And, recall that it's basically just thermal expansion that drives tailpipe velocity - you're not going to achieve much velocity over that of the incoming air if your expansion is not well developed before the gas gets into the nozzle zone. (Probably "reminding you" of things you've already got securely locked down, but it never hurts to mention everything one can think of.)

Another thing that i was thinking from your post.
The ejector action i have no worries about.
With a compressed air gun, it produces an estimated twice the volume at half the velocity just out the intake pipe (open to air) with all the input air, and probably more, exiting the ejector. The ejected exhast has no noticable (by feel) loss in velocity, although it really must.

Unfortunately, 'feel' is, I think, a very subjective indicator of what's happening. The problem is that our 'feel' [meaning, by hand] is affected a lot by the air temperature. If a stream of air comes out at about skin temperature, it feels like MUCH less air than it really is, for example. High temp air tends to produce an exagerrated perception of the flow. What's really needed is a way to measure the actual flow momentum. About the simplest thing I can think of to do that would be a simple manometer. You could make one up from a U-shaped plastic tube with colored water in it, with the U bent around an ordinary wooden ruler or metre stick. That would tell you the truth in actual flow momentum terms. Your unit of measurement would be inches (or cm) of water, i.e. the difference in height between the sensing side and the open-air side.

The ejector by the way, ejects the exhaust OUT of the piping after generating a mass flow, rather that what i think your designs do, eject exhaust into the engine to generate a flow? I get confused when you keep saying that there is a certain amount of exhaust back into the engine. I dont think this is necessary (although for a wood burner could be beneficial?)

Well, one of the main saleable uses for the Cyclodyne engine was going to be as an industrial heater that could be started on natural gas and quickly shifted over to burning solid fuel delivered down a chute, such as pelletized wood waste. My reference to the recycling of exhaust was in relation to the ire-raising drawing I put up in the other post. Using the exhaust directly as precompression drive to the combustor was always a feature of the Cyclodyne design, as it invariably is in other cyclical-flow engines.

Remember that in turbocompressor engines, what the "compressor" stage does is mostly create high velocity air flow. Much of the increased pressure is attained by funneling that out through a fairly long diffuser that opens into the combustion chamber. I have a graph in my old book that shows 'compression ratio' as a function of air travel through the front end of an old turbojet. The big jump in compression ratio happens after the air leaves the moving parts of the compressor. So, just like in a ramjet, the classic turbojet relies on a long diffuser to slow down the air and achieve higher static pressure (and density) going into the combustion process. This is what the cyclical flow designs hope to achieve with ejector input. This principle should be clearly visible in the drawing I posted (in this case using a complete 'augmentor' rather than an 'ejector' per se), although I now think the proportions may be unrealistic - it would take VERY efficient ejector performance for a device of those proportions to work. [Of course, I was only trying to illustrate the principle, not lay out a plan that someone could build from and be assured of immediate success.]

L Cottrill