Running a line from the exhaust into a tesla turbine

[Argon317]

Hi I'm working on a project that involves powering a home made tesla turbine with a valveless pulsejet engine. The engine is designed for 4 lbs of thrust and we've been able to get it running successfully. The problem is how to to connect the exhaust to some sort of hose that feeds into the turbine. Any suggestions on how to do this and if its even possible? The tesla turbine works by using high velocity fluid. I was reading up on augmenters and wondered if a converging augmenter can be used to feed into a hose that feeds into the turbine... could this or another solution work?

[Viv]

Hi, the exhaust is a functioning part of the overall engine so you cant just connect some thing to it and expect it to carry on working the same way, a valveless pulse jet is an acoustically tuned device, if you alter its length in any significant way it will stop working (or work differently), imagine a musical instrument such as a trumpet, now imagine what happens to its sound (musical note) if you connected ten feet of hose to it and connected the end of that to your ~Tesla turbine.

Viv

[Argon317]

Appreciate the fast response. What if the line wasnt directly connected to the exhaust but to a converging augmenter of sorts? naturally we would minimize the line and put the turbine as close to the pulsejet as possible

[Viv]

Hi, again i would point to the musical instrument analogy (remembering its only a simple analogy) and ask you to imagine what your convergent cone and short linking pipe would do to the sound of your trumpet?

The tail pipe of a valveless pulse jet actually has a pretty complex number of process going on, one of these (possibly the deal breaker) is the so called suck back effect, basically what this means is that a large cold plug of air is drawn back in to the end of the tailpipe during the normal operation of the engine (it does not exactly coincide with the intake phase)(but close) the cold plug can fill up to 8 inches of the tailpipe for some engines.

Your cone (reverse augmenter et al) would have to allow for this cyclic reverse flow and the effect it would have on the pressure/flow delivery to your turbine.

On the positive side your cone and the gap it creates between the exhaust and the cone lip helps lessen the acoustic effects (acoustic coupling)(bad) between the turbine nozzle and the pulse jet, but keep in mind your cone and pipe form another acoustic element (so has its own resonant frequency to add to the chorus).

Viv

[PyroJoe]

Is it a traditional tesla turbine?
Heat can quickly become a problem.
Pictures would be useful to get a feel for the setup.
Thanks, Joe

[Argon317]

Our capstone undergraduate mechanical engineering project.

This is a video of the pulse jet running http://www.youtube.com/watch?v=pg0pZvMerG8 As you can see the combustion chamber glowed orange (that is not the reflection of the table). Temperature could very well be a problem, so we are in the process of acquiring temperature and pressure measuring devices for the exhaust flow.

This is a solidworks model of prototype tesla turbine we designed to be made out of ABS plastic. Our eventual final product will be made from 7075 T6 Aluminum for the discs and 6061 T6 Aluminum for the housing. The current inlet (brown) is made to operate under a compressed air source and will have to change if we want to feed the pulse jet exhaust into it. The turbine exhaust ports are shown in red. http://oi52.tinypic.com/14y0zp.jpg

This is the same angle with the blue endplate and some hardware hidden http://oi53.tinypic.com/6y0is2.jpg

This is the back of the turbine showing the exhaust ports a bit clearer. http://oi53.tinypic.com/vfa2dc.jpg

Finally this is a picture of the nozzle inlet geometry and a transparent stator that will house the discs and shaft. http://oi53.tinypic.com/ejsc39.jpg

[tufty]

This is a video of the pulse jet running http://www.youtube.com/watch?v=pg0pZvMerG8 As you can see the combustion chamber glowed orange (that is not the reflection of the table).

Nice. However, I'd just like to point out that, in that video, it's not running "hot". From video camera output (which usually overestimate in the IR spectrum), I'd expect to have seen it appearing to run bright orange to yellow, with patches approaching white hot. Something like this (courtesy of Eric):

*That's* hot.

Cooling your exhaust may cause problems, as it effectively adjusts the acoustics of the motor. Probably not enough to stop things working, though.

Simon

[PyroJoe]

Thin aluminum doesn't take high temps well.
I suspect there is somewhat a catch 22, in that you need to couple close to engine, yet this usually means a partially closed system that drives the heat up. Especially from the core gas, the gas that travels mostly on centerline of the jet.

To get a feel for how the core gas is going to affect the aluminum, may want to test some aluminum strip in the center of the exhaust stream, and see how well they hold up. Next try placing some steel or stainless steel wire just inside the center of the tailpipe.

Keep in mind that the ambient air will mix and cool this core gas not far from the tailpipe, and when a closely coupled augmentor is applied it will somewhat protect the core gas and allow it to travel farther out the jet without cooling.
(Of course this is a hazardous operation and each of us are responsible for our own safety.)

This also is dependant on if the tail has a expansion or not. (I am assuming not?)

I would go with steel all around if possible. Hope this doesn't sound to critical, but more like a heads up on what to look for.
Joe

[Argon317]

This is a video of the pulse jet running http://www.youtube.com/watch?v=pg0pZvMerG8 As you can see the combustion chamber glowed orange (that is not the reflection of the table).

Nice. However, I'd just like to point out that, in that video, it's not running "hot". From video camera output (which usually overestimate in the IR spectrum), I'd expect to have seen it appearing to run bright orange to yellow, with patches approaching white hot. Something like this (courtesy of Eric):
Simon

I dont believe we were running the pulsejet at full throttle. If it was then I'd imagine it would look something like that picture.

[Argon317]

Thin aluminum doesn't take high temps well.
I suspect there is somewhat a catch 22, in that you need to couple close to engine, yet this usually means a partially closed system that drives the heat up. Especially from the core gas, the gas that travels mostly on centerline of the jet.

To get a feel for how the core gas is going to affect the aluminum, may want to test some aluminum strip in the center of the exhaust stream, and see how well they hold up. Next try placing some steel or stainless steel wire just inside the center of the tailpipe.

Keep in mind that the ambient air will mix and cool this core gas not far from the tailpipe, and when a closely coupled augmentor is applied it will somewhat protect the core gas and allow it to travel farther out the jet without cooling.
(Of course this is a hazardous operation and each of us are responsible for our own safety.)

This also is dependant on if the tail has a expansion or not. (I am assuming not?)

I would go with steel all around if possible. Hope this doesn't sound to critical, but more like a heads up on what to look for.
Joe

We thought about using steel, but Aluminum is what we will be using considering our budget and the capabilities of our CNC machines.

[Mike Everman]

Hi argon,
Obviously there are troubles with this. We once made a tailpipe extension from aluminum, and once it got going, it literally dripped off like water.
viv I think is being too picky about acoustics, since once running, you can easily move a steel pipe with an elbow on it fairly near the tail and ram som exhaust into it. Get too close, and it will quit, of course. Make that tap tube long enough to get cooler gas, and it will no longer be going fast.

Your main problem on the turbine side is materials.
Your disks are going to warp enough for it to eat itself long before you melt it, though. I'd hate to see all that work go to waste in the first try. You may not want to hear that, but you're asking.

Maybe use a valve type motor and harvest the vacuum at the intake to draw through your turbine.

[Argon317]

Hi argon,
Obviously there are troubles with this. We once made a tailpipe extension from aluminum, and once it got going, it literally dripped off like water.
viv I think is being too picky about acoustics, since once running, you can easily move a steel pipe with an elbow on it fairly near the tail and ram som exhaust into it. Get too close, and it will quit, of course. Make that tap tube long enough to get cooler gas, and it will no longer be going fast.

Your main problem on the turbine side is materials.
Your disks are going to warp enough for it to eat itself long before you melt it, though. I'd hate to see all that work go to waste in the first try. You may not want to hear that, but you're asking.

Maybe use a valve type motor and harvest the vacuum at the intake to draw through your turbine.

I'm not sure what you mean by valve type motor could you clarify that? As far as radial strain goes, we've done a solid works analysis on the discs that are modeled using that Aluminum and all seemed fine. Factoring in temperature will be tricky yes, but inconclusive as of now until we get concrete temperature measurements. Don't worry I'm not going to run the exhaust without making absolutely sure it wont damage the turbine. Are there any other suggestions for harnessing the exhaust of the pulsejet?

[Mike Everman]

A dynajet or bailey, or any number of valve motors have mechanical valve. Look in the valve type forum for more. Your motor is acoustically valved, and hot gas as you know comes out both intake and exhaust. You need to harvest the kinetic energy of the gas, because there's not much in the way of pressure differential to work with.