FWE with increased Throttle Range?

[PyroJoe]

2 weeks ago I was building a small draft engine similar to Grims style, with the intake directly over the CC. The mind often drifts between engines, of what can be applied between engines. The one characteristic of the basic FWE, is how specific the throttle range is, very specific. Very much different from the Deacon engines. Even on the smallish one I was building, the range was good.

I tested several FWE in the past and found Larrys fairing style provided better starting and range with less fuss. So I took it a step further in thought, opened up the port, basically blending a Deacon engine with the FWE. If my hunch is correct, this should open up the throttle range some.

The CC and the rest of the jet posted, is a blend of the Lady Jane, Anne, and the small Deacon engine. Anne is at the bottom for reference.
Joe

[larry cottrill]

Joe -

To my eye, this is a sort of "extreme" form of my Smooth Lady and Sveldt Lady engines (except for their straight tails, of course). I always did like this "straight-in" approach to the intake, and those Ladies really did start and run well. I did nothing about testing for throttle range, of course -- at that point, I was just glad to get something that would run. These were derived (in terms of the intake) from my briefly successful Fo Mi Chin II engine, if I'm remembering the chronology properly. The only basic deviation from your plan is that in all those cases I did tweak a little of the upper lip downward to deflect the incoming stream a bit more toward the chamber centerline.

This is one of those geometric layouts that I think is a good solution for small engines but (I speculate) probably not for large ones, where I think the mixing turbulence and collision with the dome might be too localized in the "top" of the chamber, and/or not sufficiently forward. But, who knows?

It appears that your engine volume will be quite a bit larger than the Lady Anne plan. Should be interesting to try.

As always, good luck with it!

L Cottrill

[PyroJoe]

Here is the revised version. Stripped out the LJG values and hedged more towards the draft engines. Hope it thumps, who knows. I found the tail dim. 2.66 very critical, a couple of hundredths this way or that will add 1 cubic inch to the tail. Didn't realize how crucial that measurement was. ha, live and learn.
Joe
(note to self: don't attempt to scale this one down.)

[PyroJoe]

wow, kind of out there.

[PyroJoe]

Here it is scaled up to a 5" front plate with LJG.

[PyroJoe]

She doesn't lock in yet, but not sure on the intake length. If you half the exhaust length should you also half the intake length?

Slowly cutting small slices from the intake for now. Since the intake pours into the chamber over such a long length, it is difficult to judge what length should be close to normal. Started out with the length similar to the 3" CC that will lock in.

Did find the signature horn sound of the short FWEs, not nearly as loud as Anne. The latest (single intake) Anne sounds similar to four air horns going at full pressure. Strange thing is, this big CC one wasn't locked in. The injector was at the approx. area that Anne runs, when the horn sound started, very clear and defined.

She jam jars fine with the injetor out at the flare. Tested some charcoal fluid in her with the tail vertical, she jars at somewhat slow pace but, interesting. May try methanol tomorrow.

On propane there is a double burn effect in the tail. It runs somewhat like a cross between the half-wood jar and a FWE.

First signs indicate she probably lacks enough containment and lack of tail pump to lock in airless. May try air tomorrow, then a smaller ID intake pipe, then back to straight pipes.

Oh yeah, almost forgot to mention that the glow on the chamber starts just next to the intake pipe transition. from about where the weld is to 1/2" on the chamber. Not at the usual CC to Tail transition/weld.

Joe

[PyroJoe]

She would lock in for brief periods, just fractions of a second. Tested a straight tail config also. Tested a swap between the the intake and tail. The feel of it was the pulse was much to short, after a review of the design I concluded the 26 degree angle on the CC is well over what is needed.

Was aware of this angle early in the design but chose to ignore it. The larger angles are approx. 20 degrees (including jars).

Another game of whack a mole, next design has a small cylinder section at the front to balance out the volume and bring it within the 20 degree mark. All in all very pleased with the throttle, with the exception that it failed to lock in and sustain.

The bustle tail made a strange noise, one not heard before. Best I can describe it is a very, very high pitched tweet.
Joe

[larry cottrill]

Joe -

Yes, the narrower the angle (meaning, the gentler the side slope) the longer the pressure wave will be stretched, and the more forgiving that phase of the cycle will be. That's why it was what it was with the Short Lady, etc. The shorter you make that cone, the "harder" the emerging wave pulse will be -- good for energy, I guess, but possibly trickier to synchronize with the rebounding wave pulses (which will be shortened, too, naturally) later in the cycle. Putting a cylindrical segment in front will greatly change the situation, of course.

Interesting, nonetheless.

L Cottrill

[Graham C. Williams]

Hi Larry and Joe.

Detached flow, related to conical half angle and the operating conditions, appears to be a limiting factor to design. 5 degrees + or - 1 degree is about as much as you can do. At first sight, this consideration seems to be more important in the tailpipe than the CC back cones. Looking at Mikes work would suggest that it may infact be of equal importance in the CC. Until recently it's always been assumed that a CC back cone half angle of 45 degrees was all you needed (No reasons given, non needed. If you like, I'll suggest that it was thought that a detachment in flow when the gas returns from the tailpipe promotes good mixing with the fresh charge). Work published here by James, James, Mike, myself and others is asking serious questions about this.

The Type 07 Derived FWE Tailpipe designs I worked upon never had Throttle Range as any consideration. The design allows me to approach what I consider to me the minimum acoustic length for a motor and still have good efficiency. I believe that one way of looking at it is 'the Type 07 section in the motor effectively lengthens the motor in some respects'

Happy Christmas.
Graham.

[larry cottrill]

Hi Larry and Joe.

Detached flow, related to conical half angle and the operating conditions, appears to be a limiting factor to design. 5 degrees + or - 1 degree is about as much as you can do. At first sight, this consideration seems to be more important in the tailpipe than the CC back cones. Looking at Mikes work would suggest that it may infact be of equal importance in the CC. Until recently it's always been assumed that a CC back cone half angle of 45 degrees was all you needed (No reasons given, non needed. If you like, I'll suggest that it was thought that a detachment in flow when the gas returns from the tailpipe promotes good mixing with the fresh charge). Work published here by James, James, Mike, myself and others is asking serious questions about this.

I think it is usually assumed that separation and the resulting turbulence instill a desirable "randomness" to the internal structure of the flow, and that this will be beneficial for mixing (which is probably quite true). What is often missed is that you gain randomness in molecular motion simply by achieving smooth flow from a narrower to a wider section, as in a diffuser. This is because of the static pressure gain. Both the gain in static pressure and the temperature rise are indicators that the molecular velocities have become more "outward reaching" than along the general line of flow. This is exactly the desired action of a diffuser, and it is highly effective as long as smooth flow is maintained; the effectiveness of this breaks down if roughness (or too steep a side slope, or misalignment of flow, or ??) causes separation.

Actually, I doubt that there is such a thing as truly laminar flow through the full length of a properly developed diffuser, simply because of the increasing randomness of the molecular paths as the increase in pressure (and temperature) takes place. I'll bet a point is reached where laminarity breaks up into a fog of practically microscopic drifts and eddies. This action would be quite different from what we normally think of as turbulence, however. I could easily be proven completely wrong, of course, with a carefully designed wind tunnel test or something.

None of this means that macroscopic turbulence is never useful. I think that particularly in small engines, where the mixing path length is necessarily short, turbulence in the chamber during the intake phase may be quite necessary to get the explosion placed where we need it. In large engines, though, we probably need a different design approach for the intake transition area that relies more on good diffuser action (possibly along with some other flow principle, e.g. getting highly localized turbulence with an interfering "bluff body" as suggested to me by Graham long, long ago).

L Cottrill

[PyroJoe]

Next revision.

[PyroJoe]

Better CC, approx. the same volume.

[PyroJoe]

Wasn't able to make the expanded tail function with this CC. The extra length of the CC must have offset the tail tuning.

The good news: it works magnificent with the straight tail (1.5"IDx30"). Nice throttle range, clean, stable running. The injector can be placed from the flare all the way into the CC. It still has that same injector sweet spot, just off center towards the tail pipe.

Airless start. Place the injector just inside the flare, slowly bring the flow up, and once the tail is hot, push it right on up. Locks in early and easily.

The injector used was a three point, but not with the normally crimped edges. This one had the three holes, one in each section.

Larry,
Do you recall at what position in the tail pipe that pulse jets will melt mild steel? I am thinking about dividing the expanded tail with a steel plate just at the last 1/3 of its length.
Joe

[larry cottrill]

Larry,
Do you recall at what position in the tail pipe that pulse jets will melt mild steel? I am thinking about dividing the expanded tail with a steel plate just at the last 1/3 of its length.

Joe -

In an expanded tail section, you might be able to get away with that, since it should be significantly cooler than the same depth in a straight pipe. In the Dynajet, we started getting rapid oxidation and/or melting at about the halfway point. Up near the nozzle point, the effect was quite dramatic!

If there's anyone left out there who has never seen this, it's here at full speed:
http://www.youtube.com/watch?v=uqXiOnWk ... re=channel
... and at approximately one third speed:
http://www.youtube.com/watch?v=F8vqfphZ ... re=channel

L Cottrill

[PyroJoe]

Intake is slightly angled. Difficult to slice it just right.