Proposed Design: 'Mushroom' Wave Engine

[larry cottrill]

Here's what I was describing to Bruno on the most recent Elektra I thread - what he calls the 'pancake' chamber configuration. To me the engine looks like some kind of mushroom. As described on that thread, this is a single-port wave engine - highly experimental, and no guarantee that it will sustain at all. But it's cheap and fairly easy to build, so it should be worth a try.

UFLOW1D shows some fairly impressive theoretical performance for this design, with a really good value for massflow and an operating frequency somewhere around 285 hz [if I've predicted the temps anywhere near reality], so it would be an interesting one to get going. I have repeated the UFLOW curves here so they'd appear together with the drawing.

Good luck!

L Cottrill

PS: Something that should be obvious but that I forgot to note on the drawing: All dimensions are in mm.

[mk]

Hey, where's the tailpipe?

Just kidding.

[Bruno Ogorelec]

Thank you very much, Larry!

Remember, Reynst was saying that the shallower the pot, the better (but the more difficult to start). For some reason, he never seems to have considered the 'snorkeler' layout. I wonder what he'd have thought about the 'Cottrill Mushroom'.

[mk]

"Tasty, but a bit too 'salty'." -- ?

[steve]

Larry, while I'm comfident that the engine could work based on your U-flow analysis, I'm a little concerned with how it would be started.

Between Mark and myself, I'd say we have a lot of combined experience when it comes to getting propane fueled reynst snorkelers not to work. As a matter of fact, I'm not sure anyone on this forum has gotten one to start! (please correct me if I'm wrong- If someone has successfully done it, I'd love to hear how!)

I think that I might be able to make the claim that one of the main purposes of the tailpipe is to make startup easier. For example, starting a high performance pulsejet like the lockwood is a cinch when compared to the complicated mess Reynst had to go through to get his monsters running. (OK that was very general, but interesting to think about nonetheless.)

perhaps you could use a thin tailpipe to get it running, then close the tailpipe with a setscrew or something else valvelike. hmmmmm, might be worth a try.

[El-Kablooey]

or maybe input starting air through a small air line directly into the CC instead of blowing it in through the intake/exhaust stack??????????? I don't know,, just a thought.

[mk]

Steve,
then it might be worth a try to just insert a suitable piece of pipe concentric into the inlet/exhaust. Just the same as Larry did with "Mr. Plugging Rod" and the "Elektra".

The assembly would be similar to the current Reynst re-iterations posted under the "metal jam jar experiments" topic. Only having a resonant inlet as well.

Where did I see a similar drawing?

At least the inserted pipe would also make for a chimney effect, leading to an improved re-charging or aspirating, when in Vertical position, of course. One of the things that are used when starting the improved Reynst combustors as described under the "metall jam jar" topic.
Well, the original inlet/exhaust tube would also make for a second, maybe counter chimney effect. I'm not sure if it might play a role then.

[Bruno Ogorelec]

Marten, but then it would not be the same engine. I think what El-Kablooey has proposed -- a separate starting device blowing mixture directly into the chamber -- would be better.

Larry is sticking to his guns -- he provided one of his unique comcentric air-and-gas jets at the intake. Maybe another one, hugging the intake tube and with the end poking into the chamber, would do the trick.

[larry cottrill]

Larry is sticking to his guns -- he provided one of his unique comcentric air-and-gas jets at the intake. Maybe another one, hugging the intake tube and with the end poking into the chamber, would do the trick.

Obviously, starting is going to be the tough issue here. There doesn't seem to be any established design rule for reliable starting of single-port engines. But, if we think an engine will run, there certainly has to be some conceivable way to start it!

What happens to prevent starting of single-port devices is that the entire engine becomes slightly pressurized, so that the starting air no longer forms a jet into the chamber and therefore the dead air in the chamber cannot be displaced by good air/fuel mixture. This is most obvious in the case of trying to start these things with some kind of external blower, almost certainly a futile endeavour.

I really don't think that the air pipe I have shown can be the best answer, but I was working quickly and had to draw something! I would certainly hope that a beginner wouldn't try to build from this drawing [of course, occasionally beginners have good luck in the absence of accumulated prejudices about how things "should" work]. In its defense, however, remember that our starting air doesn't have to be a steady flow - we could work in quick pulses at very low frequency [say once or twice per second, like starting a Dynajet]. What that would do is allow pressurization to neutralize so the next blast of air would make it in. As I see it, the air nozzle would be quite small and the air pressure pretty high, maybe 50 or 60 PSIG so that the stream velocity would be high. That, coupled with pulsed delivery technique, might do it.

Thinking about this later, I also thought of Bruno's suggestion, as well as some 'cross-feed' designs down near the chamber [high speed air flows angling across the throat]. The trouble with putting the fuel spout in close, however, is that good mixing may not be achievable in such small distances and times, once the engine tries to run. I even speculated that there might be an advantage to having the fuel stream and starting air stream cross as they go in [i.e. rather than be concentric flows], the idea being that you would at least achieve excellent mixing of the starting air/fuel stream.

What it amounts to is, if you decide to build this, be aware that a large part of your experimental effort is going to be in figuring out a reliable starting air scheme and/or technique. The good news is: If you come up with a really good method, it could benefit everyone who wants to build any kind of single-port engines, Reynst pots, etc. and perhaps help even those interested in designing 'concentric intake' types!

L Cottrill

[Mark]

I was thinking if you had a smallish air tight vessel with strong walls, perhaps you could go back to the burst disk philosophy for starting, something Schmidt tried I guess. For me, I was imagining something simple in the way of a jam jar with an obstruction over the snorkel that would burst free. Then you could start out by just amplifying the pressure in the tank with a few pumps of air from a tire pump, and then spark the apparatus. This would create a stronger starting impulse, air would race out and then in on the first cycle somewhat faster, not only improving compression but also turbulent mixing hopefully.
Maybe even an oddly designed jam jar would run more forcefully than a typical jam jar, if you conjured the genie from the bottle with a rousing starting blast, this again brought about by pre-pressurizing the vessel with enough energy/air to start "the effect" in motion.
With my simple straight tubed valved pulsejet I could only start it by corking the tail to get enough impulse to get feedback to sustain. While a pulse detonation jam jar sounds funny or rather far-fetched, maybe there is some other stronger phenomenon that lurks in a jam jar that will come out and play if given a chance.
Mark

[El-Kablooey]

I think what El-Kablooey has proposed -- a separate starting device blowing mixture directly into the chamber -- would be better.

Holy crap! Did Bruno actually agree with ME on something?? ;) JK
I think that means that I must be learning a thing or two from reading all of you guy's posts! I promise to build some engines and get some real experience with these things, hopefully one day I'll actually be able to have some positive input in this forum. I'm darn sure interested, and am a tinkerholic for sure.

just out of curiosity, is the CC at the optimum volume for this kind of engine? or would maybe 2 boxes welded together, instead of a cover plate, provide more space for the explosion/vacuum effect to operate more smoothly? or am I way off on this one? (lemme have it Bruno!)

[Bruno Ogorelec]

Holy crap! Did Bruno actually agree with ME on something??

Ouch! Have I really been such a jerk? Have to reset my jerkness options.
OK. Intensity to 'mild'. Special options: 'increased kindness to new members'. There; it's done. The next time I reboot, I'll be a lot easier to take.

just out of curiosity, is the CC at the optimum volume for this kind of engine? or would maybe 2 boxes welded together, instead of a cover plate, provide more space for the explosion/vacuum effect to operate more smoothly? or am I way off on this one? (lemme have it Bruno!)

No one really knows. The single port engines are still a bit of a mystery. (As if the two-port engines weren't; ha-ha-ha...) What can be gleaned from old literature is that the bigger the chamber, the easier it is to start. The smaller it is (while still able to work), the more efficient.

The inventor of this kind of combustor, F.H. Reynst, made his with a sliding bottom, like a piston that could be moved up and down a little. You’d set the bottom for a big chamber for start-up and once the thing caught, you’d move it forward to make the chamber smaller. Very cumbersome, but he designed it as a very efficient combustor for furnaces, so it didn’t matter.

BTW. I watched El Kabong (and dozens of others) with my daughter, maybe 15 years ago or more. Good fun. He’s a horse, isn’t he? Was there a fencing turtle involved somewhere? Or am I mixing it up with something else? My daughter’s favorite was the Professor Gadget. And there was some kind of a Super Teddy Bear with spots. At about that time, the first anime were starting to appear. My daughter and I hated them profoundly. Today, they are considered an art form. We just couldn’t take them.

[steve]

bruno, just be glad that you don't live in the US- more then half the cartoon shows on nowadays are anime. talk about outsourcing! ;-)

sorry for hijacking!

[El-Kablooey]

Naw man, not a jerk at all!! I was only kidding, you have done nothing but stated your opinion, which you definately should do! I never once thought of you as a jerk, only someone older and wiser than myself. And I definately greatly appreciate your answers to my questions, you and the other fellows on this site have given me a great wealth of information, and alot of new things to think about and tinker with that I wouldn't have dreamed of previously. Thanks!

I have all the stuff laying around the shop to build this engine, not sure I have the know-how to get it running right away though. Let me get out here and cut some grass while it's dry, and maybe I can be the gineau pig (SP?). I'll check back in when I get finished.

Oh, yeah El-kabong was a horse and his sidekick was a little jackass named bubba louie. I kind of relate to El-kabong sometimes, so thats where I got the name.. It was him or Wil-e Coyote. ;)

[Greg O'Bryant]

Larry:
I can't help but notice that the shape of your engine looks a lot like the actual pattern the fire,combustion zone, has in a jam jar. I was just wondering if you think the higher power output and properties of the electra, compared to a jam jar, may be due to having the CC actually fit the combustion zone. This seems to agree with what Bruno says when he says that the larger CC Ryenst are easier to start but the shallow CC Reynst perform better, and didn't you say yourself that a larger CC is more forgiving but doesn't perform as good as one that is actually in tune with the engine?
P.S. I think your idea on how to start it looks fine to me, but?