Focused wave engine runs!

[Mark]

I remember Tharratt's article where he tromboned a loose fitting cap on the head of a valveless, he found thrust was relatively strongest at a certain sleeve length, but as you moved the cap up or down, I can't remember which, the thrust dissipated and then gradually increased once again almost up to the best thrust level.
In such a way, it seems you could also transition this effect in a Logan, gradually increase the side port and decrease the main exhaust tube so that the once small side port could transmogrify into an exhaust of equal length and diameter to the main exhaust tube.
I've seen designs where twin exhausts spit out equal amounts because they are symetrically the same in every way, the same proportions connected to the combustion chamber. Here we have a main body and two identical exhausts, some sort of valveless turned mutant if you will.
As we travel up and down in lengths and diameters, we can arrive at shapes that work and don't work, it just depends on whether you want to let go and toy with features that just don't work until you alter another feature to compensate/allow for the new tragectory.
Most valveless pulsejets have an asymmetric shape about them, yet I wonder what the benefit of asymmetry is over a main body with equal twin exhausts angled backwards, over a Lockwood shape for example? Must a valveless require asymmetry?
Mark

[larry cottrill]

Steve -

I think I have decided what road to take. It will not involve any cutting and patching now, and possibly not ever.

Think about it - what we're hearing is masses are wrong, impedances are wrong, and I think these are correct perceptions. But here's what's wrong with most of the recommended remedies: They alter two variables at once. That's not what we need now.

If we try to adjust masses by changing lengths of things, we also alter the acoustics. Now, consider what we've got here: the first engine most of us have ever seen that came off the drawing board and out of the blacksmith shop ready to start and run! Steve, if the mass balance is really poor, impedances are out of whack, etc., and if the engine will start and run right off the block what does that tell you? Here's what I think it tells you: The acoustics are right on the money! Man, whatever we do, we don't want to screw that up.

Tonight, I took out the Elektra II and again tried to start it. You may recall that I thought this was pretty close to running when I first tried it out, but it wouldn't quite catch hold and go. What I did tonight was try Graham's suggestion of applying a pinch to the intake, not too far from the flared end. I went through 3 or 4 gradual increases in pinch, and I can tell you quite honestly that there was a noticeable improvement at every stage. I ended up with an internal width of about .25 inch [6mm]! No, it still doesn't sustain, but then it doesn't have the carefully proportioned lengths of the Lady, either. It does have almost exactly the same overall length, the same intake tube diameter, and approximately the same tailpipe ID. So, other than the chamber, the masses are pretty close.

The difference is actually quite amazing: The intake flame is now a tiny wisp, blown easily to the side by the leaf blower, and disappears completely in any roaring mode of operation. You can get roaring with the leaf blower about a foot away from the intake flare! The pops and roars are FAR louder than the last time I tried it - the bangs from the tailpipe feel about like a slap in the stomach from a toddler; quite noticeable. The difference in roaring loudness is striking [I wear plugs AND muffs, typically]. It has obviously shifted the emphasis of the engine dramatically in favor of the tailpipe delivering most of the useful energy.

In all this, the operating frequency stayed exactly the same, as far as I can observe. When I build mine [Focused Wave engine, that is], this is the method I'm going to use to get it right. Yes, the tube ends up funny-looking - but I'll need some kind of narrow pinch to set up a spray bar / needle valve assembly for liquid fueling, anyway.

I think this is the way to go; if anyone can prove me wrong, let 'em.

L Cottrill

[Hank]

Hello- Steve, please keep posting on your engine as your line of inquiry grows.
Thanks, Hank

[Graham C. Williams]

Dear Larry.
Can you tell me exactly why the induction pipe extends into the combustion chamber?

Best Regards
Graham.

[larry cottrill]

Dear Larry.
Can you tell me exactly why the induction pipe extends into the combustion chamber?

Best Regards
Graham.

Graham -

I saw this hours ago, but was unable to sit down for a while to respond until now. I have been at work since 0630 yesterday morning, and it is now 0120, and I'm hours away from being done building up a Unix system to replace one that apparently suffered a SCSI controller crash. I am now at the stage where I can start rebuilding the data from the backup tapes, which I expect to take a few hours. About ten or fifteen people weren't able to work today [I mean, yesterday] because of this, and I don't want them to have a second day down while we continue to figure out what's really wrong. My general weariness may make the following not very lucid, but I'll do the best I can.

The short answer to your question is: To try to separate the wave from the mass flow, in the intake pipe. There is no point in trying to stop the pressure wave from exiting through the intake; however, it might benefit from minimizing mass flow, which doesn't gain a lot of momentum in the fairly short pipe and just causes heating of the tube. So, the bottom of the pipe is extended down in and cut off at an angle that discourages blast mass from getting diverted out through it. Rather, most will simply pass around on the way to the [relatively] low impedance exhaust. Of course, I'm assuming that even the short trip aft to the intake spout will add some momentum, and certainly the flow will be well directed by that time, so the diverting effect of any pressure deficit in the intake should be minimized.

Obviously, this will not be 100 percent effective. However, as indicated in my last post , this coupled with a strong pinch in the pipe really does seem to minimize the losses out through the intake. The pinch seems to make a world of difference, once you achieve lean running. The Elektra sisters had quite a spout of flame out the intake before pinching the intake pipe way down [from about 7/8 inch ID to a pinch 1/4 inch wide x just over an inch across, at the narrowest]. So, I thank you and Mike Everman for the suggestion to raise the impedance this way - it does have a profound effect on the flow balance of the engine in the blast phase, while leaving the acoustic proportions essentially unaffected.

The extension with the angled cut is a detail borrowed from the Elektra I and II, and hopefully improved upon somewhat in the present case. You may remember my enthusiastic report of actually witnessing the blast gas passing the port in the Elektra I, where you could look straight down the pipe into the bottom of the chamber. The difference between rich and lean burning in both the speed and character of the flame was actually quite astonishing to see.

So, would it work without the inner extension? Well, the Chinese does, but I really don't think the designer of that one cared how the flows proportioned out between the two exit paths, as long as the mass cleared the intake soon enough to let a good blast of air in! I wanted the main mass concentrated on accelerating the cold mass in the tailpipe, as much like the Dynajet as I can get. From the kind of thrust forces Steve just measured, we've got a way to go yet, to come close to that ...

L Cottrill

[Graham C. Williams]

Quote 'So, I thank you and Mike Everman for the suggestion to raise the impedance this way'. Quote.

No, I think we all have to thank Mike for this one. My only contribution was to help with some of the understanding but mainly as a sounding board for Mike's ideas.

Thanks for the explanation. I'd forgotten your report 'observations of the mass flow around the extended induction pipe'.

Best Regards
Graham.

[Mike Everman]

Graham, thanks for the nod, but I'm not sure that I didn't get the squash idea from Larry in the first place! (his shark was around when I came on the scene...), but enough of that ;-P

Larry,
I look at the snorkeled intake a bit differently, and am trying to see the advantage. I believe the engine would work exactly the same if it were the same length, with a conical entry, and moved toward the closed end so its entry is in the same lengthwise position. You mention the chinese' apparent ignorance of flow, but it really doesn't matter, to my way of thinking. The only flow worth worrying about is the intake flow, IMHO.

The best thing I see about the way you have done it is twofold:
You have reduced the intake's protrusion out of the engine, and could possibly go even further submerged, like perhaps the inlet is a conical opening in the exhaust transition (if there were one).
The next interesting thing is the angled cut. To my eye, it simulates a divergent cone on the end of the tube (if such a thing is needed here, I don't know). Makes me wonder if you can make a slightly angled cut on inlets or exhaust tubes to simulate a conical flare. Faaaascinating!

[Mark]

I vaguely remember something in Foa's book that comes to mind. Of all the various intakes on valveless engines, none had been found to be more effect than a straight pipe of a certain length. It turned out what you gain in one direction, you lose in the other.
By having the intake extend into the combustion chamber, you do inhibit outflow, by lengthening the blow down time, a jam jar having a really long blow down time with the awkward port.
Everything can't be attained, it is a trading game. You could inhibit backflow with a longer side port or a smaller side port too. But then your aspiration(s) goes south. I can't remember if it was Reynst, Foa, or Tharratt who started a sentence out with the phrase, "Vainly, many have tried ...." pertaining to flow rectifiers.
When I was around 11, I use to try and build perpetual motion machines using flowing water and air pressures. It seems funny to me now, the tubing and air pressure chambers. It all came back to wanting something to flow in one direction without thinking about the other half of the equation, in some way like our side port topic.
Mark

[Mark]

Here's a bit of literature from 1965, "The tube shapes which will resonate seem almost infinite (although it is hard to believe at times) if all other factors concerned are proper." "Even a simple straight pipe will run as a pulse jet, which may come as a surprise to some, but it is perfectly logical when ..." "This configuration is very poor on performance, however. The best all around performance seems to be produced when the tail pipe has about twice the volume as the combustion chamber." .....

Here was some stuff about valveless engines in the same article.

"First of all there are no moving parts in this type of pulse jet, consequently no maintenance is required. Along with this decided advantage valveless jets possess a lower thrust than a valve type unit of comparable size. This is due to a lower combustion chamber pressure. The length to diameter ratio is also much higher than valve type units. Even with these two drawbacks the overall advantages of the valveless units make them more desirable powerplants than the valve types.
We have run valveless units with an inlet area/combustion chamber area ratio as low as 10% and as high as 24%. Here again the best results must be arrived at by trial and error, because changing any one of the dimensions of the pulse jet tube produces an entirely different relationship between the other fundamentals of the tube."

Just some tidbits I thought were interesting.
Mark

[Hank]

Hello- I reiterate my belief that the exaust portion of the duct of Steves engine has too great a volume. There is an influx induced by the disproportionate volume that is acting against the thrust wave. The engine sustains combustion and produces thrust, it is just not producing as much as it might. Hank

[Mike Everman]

I respectfully disagree, Hank. The lack of tail heating must mean that it's volume is too little compared to the combustion chamber. The low pressure phase is enough to bring cool air (almost) all the way to the CC. That wouldn't be bad if the intake plugging were better at exhaust phase, like if it had valves. It's a trade-off as we all know, you can't have too good of plugging there and also have good injestion. All that cold air in the tail is a good plug indeed, and could make for some good internal augmentation.
I am still struck with how short this engine is!

[steve]

Larry- The cones were mailed out to you today (friday) so you should be recieving them soon! BTW don't worry if there is a thin coat of rust on them because it will all melt when the engine is run for the first time. however if you want to make it look pretty for construction photos, a little steel wool and oil will take it right off.

I have completed an augmentor using the same dimentions as the combustion chamber cone (for convienience) and will try to get an updated thrust measurement sometime in the next week (but be patient because I am VERY busy right now)

[Mike Everman]

Don't be afraid to give the Lady's intake a little pinch! If she gets offended, offer here a little strawberry candy!

[steve]

I have completed preliminary testing of the FW engine equiped with an augmentor. I mentioned earlier that I used the same dimentions for the augmentor as were used for the CC cone. I am still using the Bruno style injector with the nozzle flush with the inlet flare.

It was considderably more difficult to start the engine with the augmentor in place but once I started it I discovered that thrust levels actually decreased! They dropped down to a mere 400g at full throttle (a 200g decrease) Aparently I dont know jack when it comes to augmenting engines! Any suggestions? Comments? Tidbits of wisdom?

BTW: Larry did you get those cones yet? If not they should arrive in another day or two.

[Graham C. Williams]

Dear Steve.
Try this paper:
Nasa/TM-2002-211711
AIAA-2002-3915
Unsteady Ejector Performance: An Experimental Investigation Using a Pulsejet Driver.

Graham.