Anybody have data/experience on tube-in-tube engines?

[vhautaka]

Does anyone know workable dimensions or the needed equations for a Tharratt engine or similar? Patent numbers, anything?

Or, if these have ever been tried with a full-length augmentor shroud?

As it is arguably the easiest engine to build (even for non-welders), I would think there have been some experiments among enthusiasts?

Yep, I'm looking for usable opening areas and part lengths for the intake-and-augmentor-inside version I want to build.


- ville

[hinote]

Does anyone know workable dimensions or the needed equations for a Tharratt engine or similar? Patent numbers, anything?

Or, if these have ever been tried with a full-length augmentor shroud?

As it is arguably the easiest engine to build (even for non-welders), I would think there have been some experiments among enthusiasts?

Yep, I'm looking for usable opening areas and part lengths for the intake-and-augmentor-inside version I want to build.


- ville

I have considerable experience with the tube-in-tube concept--all of it unsuccessful.

I too would love to see someone make this concept work. Be prepared for a lot of cut-and try, though.

Bill H.
Acoustic Propulsion Concepts, Inc.

[vhautaka]

Bill,

Unsuccessful in which way? Run erratically, never pulsate at all, explosions..?

May I ask you more about these experiments? What fuels, what engine sizes approximately? Big, small?


Cutting and trying will commence in one week, and I'll post any results.


- ville

[Mike Everman]

Ville-
I'll be watching with great interest!

[tufty]

Does anyone know workable dimensions or the needed equations for a Tharratt engine or similar? Patent numbers, anything?

http://v3.espacenet.com/textdoc?DB=EPODOC&IDX=GB793239 looks likely

Simon[/url]

[Stephen H]

Ville-
I'll be watching with great interest!

same here! On the valveless section im guessing you are talking about where it says Tharratt. Aparently its not and that was a mistake, i havnt finished reading about it yet though!

Time for the new valveless section yet kenneth ??

Stephen

[Mike Everman]

Bruno and I worked on some configurations with both Kentfield and Lockwood proportions, and the exhaust throats are very small differences in diameter, depending on what tube you consider, but one we looked at was only 1.5mm gap!
Thermal expansion of the central pipe must be considered carefully: if you have enough gap to reach the right geometry when hot, it may not start ever. If it is right to begin with, it will choke itself in the first few seconds.
I suggest, even though it's more difficult, that the two sections be conical so if you move the intake tube axially, you can adjust the intake total area while running, perhaps automatically with temperature so the engine is happy through it's wild temperature excursions.

If it were steel, and I don't have my calculator, but if it were 10" in diameter, and went to say 1,000F, a 1.5mm annular gap will be almost gone. (I don't even have paper and pencil, so I'll do this in more detail later).

That's the main problem with tube-in-tube, if you want it to be easy cylinders, the temperature will change the geometry too much to deal with. Perhaps Tharratt had it worked out somehow, but his annular intake areas seem whacky big compared to L-H or Kentfield.

[vhautaka]

Thanks guys! Great!

Mike, about heat expansion:

It only now occurred to me that the expansion is so severe.

The patent suggests using heat resistant steel, ceramic coatings and whatever... the most accessible suggestion is using longitudinally corrugated tubes.

This might be yet another reason (I've already lost count) to look into inside-out annular designs. If the intake area is inside the engine, it's subject to proportionally less thermal expansion changes, right?

In addition, the structure could be quite possibly designed so that thermal expansion actually makes the intake area larger and even helps it stay in proportion with the expanding tailpipe area.


Ok.. it's weekend, I'm not drunk, not asleep, not in front of TV... but pondering these voodoo machines. :) Damn.


- ville

[Mike Everman]

re: http://v3.espacenet.com/textdoc?DB=EPODOC&IDX=GB793239 looks likely...

Remember folks that patents are granted to things that do not work all the time. The machine's actual functionality is not a prerequisite for getting a patent!

[vhautaka]

Mike, looking at those Tharratt contraptions, they seem to have isolated the intake area pretty well from the ignition / combustion area. Probably that helps with thermal expansion trouble.

Also the huge size of Tharratt intake may be compensated by the 180 degree turn.

Also I know their patent could be full of crap... well I couldn't machine such nice engine heads anyway :)


Ok. Here's how I think I should proceed with my engine.

First, I'll make the "annular" engine straight. This will be just like a straight valveless with a tuned intake in front, except there's some pipes / cones inside to simulate everything being in annular configuration.

The intake/cc transition looks real ugly like that, and will probably need some rounding in order to make the intake take something in. On the other hand, the sharp turns could be beneficial during combustion, possibly allowing for a shorter intake.

Intake, CC and tailpipe will be tuned and modified until it runs, and further to get some range of usable values for the relationships. Thrust is not an objective here, just reliable and reproducible pulsating combustion in an annular combustor with a minimum of work. The intake must be such that it fits inside the empty space in the center of combustion chamber / tailpipe.

Then it's time to "really go annular" with at least some of the problems already solved.

I hope to get at least some ear shattering blasts next weekend... hope this simple idea doesn't turn into one of those "full of cans of worms" things.

In that case, at least I'll be able to give pictures and exact specifications of things that would NOT run... all good and educational. ;)

[Mike Everman]

Ville-
I like #2 with some thought given to an exhaust throat and diffuser. Once again though (it may run but), since you're "folding back", you have the thermal expansion problem with the intake sharing a wall with the combustion chamber. the intake area will increase in this case with temp.

Enjoy your can of worms!

It's rare that someone posts a drawing of what does not work, they usually just stop talking about it and move on. I think a whole section should be devoted to "what does not work". good idea! Though practically speaking it's much more fun to work the next great idea than document the failure!

[vhautaka]

It's rare that someone posts a drawing of what does not work, they usually just stop talking about it and move on. I think a whole section should be devoted to "what does not work". good idea! Though practically speaking it's much more fun to work the next great idea than document the failure!

Documenting failures may save someone else some work and propane, not to mention frustration ... or, in some drastic cases, such less readily available resources as hair, eyes and fingers. :)

Also, then others, or my own future self, will know where to start improving on a "failed" invention.

For example, your thermal expansion comments made it pretty obvious that annular intakes and exhaust throats must be placed as close to the center of the engine as practically possible in order to reduce the relative expansion changes.


My whole idea started from "how would I make a simple engine breath through way more air than it needs for the combustion cycle?" and an opening through the middle, with both intake and exhaust working as ejectors, seemed pretty obvious.

Now, mostly just reading this forum, I've gathered some more ideas and some solutions to common problems or deficiencies that would be feasible with a layout like this.

Like drag caused by outside air rushing into the tailpipe during intake phase. I think it would be much better to fill the tailpipe with warm, expanding air from the center of the engine, even if that's not so good for tailpipe cooling. At least it'll recycle some of that heat into compression and drag reduction.

In an ideal case, the engine would continuously suck in air at the front and blow from the back, so that all backflows would be contained inside the casing and aided by heat expansion of the extra intake air. How that augmentor should be shaped, I think nobody knows.

And then there's the neverending quest for a donut vortex, which will very likely require some sort of annular configuration. So something like this just has to be built, tested and documented in order to get closer to even more interesting things.


Well, I guess I'm already stockpiling them worm cans. Extremely tasty food for thought, these wriggly little guys...


- ville