Secrets of the Dead: The Reynst Pot and the Hinote Criteria

[larry cottrill]

You may recall that when I posited the 'Hinote Criteria' with the 'Reynst Point' [then mis-named the 'Logan Point'] at the L/8 station, an interesting question was mentioned: If these criteria are so meaningful, why doesn't the classic Reynst Pot fit these proportions? It has been suggested that one reason is that unlike most of our valveless pulsejets, the Reynst Pot has no resonant intake.

I would submit to you for criticism and comment that both the lack of fit to the Hinote Criteria and the absence of a resonant intake pipe in the Reynst Pot are abject nonsense.

Using Bruno's classic Reynst Pot scale drawing, we may approximate the acoustically corrected end points of the central "cone" as shown in the first drawing, using .6 x the inside diameter [but ignoring the slight 'end flares']. What I claim is that acoustically, the top of the pot surrounding the "cone" doesn't exist, and the "cone", with end corrections, forms almost exactly the L/5 tuned intake observed on typical "Reynst breathing" engines. The forward acoustic point is almost exactly at the L/8 Reynst point I deduced for such engines. The pressure trough returning back through the exhaust funnel is almost entirely focused through the "cone", and virtually all the Kadenacy breathing to support combustion is down through its center, NOT around it.

If these points are preserved in situ, we can modify the engine practically at will, as shown in the second drawing. I have preserved the inner "venturi-like" contour of the inside of the "cone", but that is totally unnecessary if a reasonably proportioned intake flare is used.

Not only can the intake be attached to the tailpipe of a "Reynst breathing" engine [a la Fo Mi Chin], it can in fact be completely surrounded by the exhaust duct! This is exactly the case in the Reynst Pot.

The classic Reynst Pot meets the Hinote Criteria and the L/8 Reynst Point virtually perfectly, with the central "cone" acting as a resonant intake pipe, providing practically all the intake flow for the Pot. Prove me wrong if you can ...

L Cottrill

[Mike Everman]

Absolultely faaaascinating. Nice work. No criticism that I can think of. Must test that second one!

[Bruno Ogorelec]

Larry, at first glance, I'm impressed. I am sure that having so many numbers fit the criteria cannot be a coincidence.

So, there's acoustic logic to the thing.

I'm not so sure about the flow logic, as Reynst put the diffuser there so that the mixture would cavort around it.

Your 'equivalent' forces a different kind of swirl. I wonder what effect that would have on the cycle.

Lots to think about.

[larry cottrill]

I'm not so sure about the flow logic, as Reynst put the diffuser there so that the mixture would cavort around it.

Your 'equivalent' forces a different kind of swirl. I wonder what effect that would have on the cycle.

Lots to think about.

Bruno -

Yes, I remember you describing that swirling action before, and I'm sure that is important. However, I'm only saying the two are equivalent in terms of wave mechanics, not in the flow details.

What needs to be reiterated is that the wave mechanics control the action of these engines. Wave mechanics [what we keep calling 'acoustics'] is not the entire picture - but it provides the basic timing which is the foundation of the whole cycle. I would probably be astounded at how many different "engines" can be built on this pattern - but probably equally astounded at how poorly many of them would perform even though they can be started and will self-sustain!

What the Criteria do for us is give us a basic framework on which to hang the various subtleties of how to move masses around in response to the pressure forces. Basically, they give us one less "mystery" to solve: the basic length proportions of [or looking at it another way, the critical stations in] our engines.

I wish I could see how these proportions could apply to successful linear engines, but I haven't "snipered" that one yet. Maybe someone else will beat me to it.

L Cottrill

[larry cottrill]

Must test that second one!

I seem to remember that there used to be big bottles [maybe perfume or cologne bottles] proportioned just like that! Just add a stack of appropriate length, and you've got it.

More realistically, the chamber and intake stack could be much more conventionally shaped and built out of ordinary pieces. Taking a 'Fo Mi Chin' type approach, there are those stubby little spray cans of model enamel you can get for outrageous prices at hobby shops, for instance - the height of the cylindrical side is only about the same as the diameter. So, with some delicate welding with your Henrob, a small model could be easily tried. You might need to make the gap adjustable, at least for preliminary testing, to get the flows to work right.

The Cottrill Screechodyne(TM) or something.

L Cottrill

[mk]

Cool, Larry, very cool.

Larry, at first glance, I'm impressed. I am sure that having so many numbers fit the criteria cannot be a coincidence.

So, there's acoustic logic to the thing.

I'm not so sure about the flow logic, as Reynst put the diffuser there so that the mixture would cavort around it.

Your 'equivalent' forces a different kind of swirl. I wonder what effect that would have on the cycle.

Lots to think about.

That would also prove that seperation of wave mechanics/acoustics and mass flow do have or rather are in some ways necessary for getting "nice" results. Seems like Reynst also knew what he did...
People beeing deeply in this theme might be able telling us s.th. to the why? and when? questions.

[Mike Everman]

And if? and really? and faaaaascinating! LOL

[Bruno Ogorelec]

That would also prove that seperation of wave mechanics/acoustics and mass flow do have or rather are in some ways necessary for getting "nice" results. Seems like Reynst also knew what he did...

My thoughts, exactly. Reynst developed a non-acoustic model of aspiration and then added the acoustic resonator as an amplifier. It is wonderful how the two mechanisms complemented each other.

When you read his works, you get the impression that he paid greater attention to gas speeds than to gas pressures. Very interesting. The Reynst pot is all about the preservation of gas speed, rather than boosting the pressure. A completely different mechanism from the conventional tubular engines like the Lockwood or the Escopette.

Secrets of the dead, indeed.

[Ray(in England)]

Hello Larry,
Thanks for another insight.
Sorry if it seems Im asking self explanatory questions but.......
Where is the fuel fed into this 'pot' engine?.

What has to be placed at those black/white quarter circle symbols?
I know they usually show centres of mass and force on aeroplanes.
Thanks Ray.

[larry cottrill]

Hello Larry,
Thanks for another insight.
Sorry if it seems Im asking self explanatory questions but.......
Where is the fuel fed into this 'pot' engine?.

What has to be placed at those black/white quarter circle symbols?
I know they usually show centres of mass and force on aeroplanes.
Thanks Ray.

Ray -

It seems from much previous discussion that there were several ways to fuel the Reynst Pot, but the current favorite seems to be to let fuel pool evenly around the intake lip and get drafted in all around [the original Reynst pot stood vertical, not horizontal as in the drawings here]. What I would do on an actual engine, I think, is bring the fuel pipe in through the front flare of the tail cone, aimed forward right at the center of the "little cone" in the case of the Pot, or right at the center of the intake flare in the intake stack of the "engine" in the second drawing. There's still a lot to be learned about exactly where to feed fuel, I'm afraid ...

The fancy targets are to show the REAL pressure nodes of the cone and the "Reynst Point" of the engine as a whole. The pressure node of the INSIDE end of the intake pipe must be at, or very close to, the Reynst Point for good breathing of the engine. The pressure node of an open pipe is always beyond the open pipe end! It is located at approximately 0.6 ID away from the cut edge - trimming the pipe back from this actual node position is what I'm calling the "end correction". A sudden flare at the pipe end is not considered in determining the correction, because it's too short to have much effect on the wave mechanics.

This reminds me that something I failed to show is that there would be an end correction to the rear end of the tailpipe as well! However, the location of the two critical points of the little cone don't seem to take this into account. Probably, the final design was tuned experimentally and lengthened a bit from the theoretical. The few jets I've "measured" [meaning, from supposedly scale drawings] don't seem to make any allowance for any end correction at the tail end, and often don't seem to honor end corrections at all. This is probably because the pipe IDs are so small compared to the lengths that the corrections are too small a fraction of a wavelength to be critical. With the little cone in the Pot, though, you can see the huge difference it makes between the position of the nodes and the physical ends of the tuned element!

Incidentally, the Reynst Point should not be viewed as a single point on the engine centerline, but as a transverse plane going across the entire tube section. Where the nodal point of the intake duct touches this plane and in what direction the intake CL is aimed are more properly matters of mass flow than wave mechanics. Thus, a Logan intake which joins the shell at right angles to the engine CL would join right at the L/8 station, theoretically.

L Cottrill

[Bruno Ogorelec]

It seems from much previous discussion that there were several ways to fuel the Reynst Pot, but the current favorite seems to be to let fuel pool evenly around the intake lip and get drafted in all around [the original Reynst pot stood vertical, not horizontal as in the drawings here]. What I would do on an actual engine, I think, is bring the fuel pipe in through the front flare of the tail cone, aimed forward right at the center of the "little cone" in the case of the Pot, or right at the center of the intake flare in the intake stack of the "engine" in the second drawing. There's still a lot to be learned about exactly where to feed fuel, I'm afraid ...

This is the logic of Reynst fueling.

The central mechanism of the Reynst pot is the toroidal (doughnut-shaped) swirl of the incoming mixture. The fresh charge streams from all sides over the lip of the pot, surges into the internal diffuser, and aims for the bottom of the pot. Hitting the bottom, it curls to the sides and back up. When it gets back to the lip of the pot, it is turned back into the central diffuser by the incoming charge, so it all revolves like a doughnut, downwards through the center and upwards along the pot walls.

If you were making the fuel supply, where would you add fuel to this swirling torus?

The only logical place is the lip of the pot. That way, the mixing begins immediately. If you feed fuel into the pot, the mixture is uneven, as the back of the incoming flow is without fuel. It's pure air. There's not that much time for the pot to refill and there is less local turbulence than in the ordinary pulsejet, so that the poor initial mixing would never get completely corrected.

The reason for the low local turbulence is the preservation of speed. Unlike other pulsejets, which induce immediate turbulence upon the entry to the chamber, the Reynst pot preserves the speed of the incoming mixture. It does not break up the flow into myriad little vortices, but curls it into the big vortex. The mixture continues to travel fast, but does it in the swirl, rather than in a straight line.

That means that the flow is still quasi-laminar. You don’t get the usual local turbulence, but only the internal shear that takes place in a vortex due to the fast sequence of expansion and contraction of gas. (It expands as it gets to the outside of the swirling torus and contracts as it gets inside.) This shear will only homogenize the mixture that already has fuel in it, but will not introduce new fuel. So, your best bet is getting the fuel in as early as possible.

As you do get shear, the fuel does not have to be finely atomized. In fact, the Reynst pot ingests fuel in relatively big droplets. The shear quickly tears them to pieces, so to say. That’s why it will work even with relatively heavy fuels, like diesel, and burn them amazingly cleanly.