pulse jet theory V o.1

[paul fellows]

Hi Joe
(IMO?)
it is an interesting idea, build pressure then release it in a controlled way.
what I meant by fleshed out is how is the system controlled?

It sound like you have built quite a few jets, do valveless engines sound higher pitched than a comparable sized valved engine.

Re the quote, this is attributed to Confucius but it might not be.
“an intelligent man learns from his mistakes, a wise man learns from other peoples mistakes.”

[PyroJoe]

what I meant by fleshed out is how is the system controlled?

The controls that I use are relative to the dimensions of the components involved. My own "recipe", that balance the attitude of the engine.

do valveless engines sound higher pitched than a comparable sized valved engine.

I would say of comparable sizes (which is a very lose term) valved engines cycle faster. The shorter tail pipe and short intake length help the CC to ingest air and blow down more quickly.

Though it is not a very good comparison, as valved engines differ greatly amongst themselves, and a well designed valveless can have a very quick, well contained cycle.

[larry cottrill]

I'm afraid I'm not seeing three reversals (positive to negative and back) which of the of the four graphs should I be concentrating on. :(

All the views are important and interesting in some way. To me, the Mass Flow graph (lower right} always looks like an exaggeration of the Mach No. graph (upper right) because they are functionally related by working density into the mix. The interesting thing about these graphs is that you can clearly see the "velocity node" -- the point where nothing moves. In the fast-moving animation, it looks like a "fulcrum" around which these graphs see-saw up and down. Note that this point lies on the widest diameter of the chamber. It is exactly the point where the two quarter-wave sections butt together, as if there were a solid wall there. Ha.

Looking across at the pressure graph (upper left) you can see that this very same point is covered by the large regions of high and low pressure during the cycle. The "velocity node" is also the "pressure antinode" -- the point where the pressure swings are maximum. However, in the Lady Anne (as in every well-developed pulsejet design), the maximum pressure swings, both high and low, are widely spread through the engine interior. This is evidence of (at least potentially) high power development for the engine's size (volume). If you look carefully during the slow motion part of the animation, you will see the pressure wave from the initial explosion divide and move outward until it disappears near the intake and exhaust pipe apertures (it is impossible for the wave to stay high as it nears the open ends, which always have a pressure near atmospheric). Then you will see the depression coming back toward the center. This is the Kadenacy effect in action -- as this low trough moves inward, reversal of flow begins in earnest (glance at the Mass Flow curve at the same instant). When the pressure is lowest throughout the middle of the engine, inflow is about maximum from both ends. This low trough now spreads out toward the ends, and ultimately the pressure curve swings high again, from the ends inward toward the center. Once the pressurization of the center zone is maximized, the new explosion takes place, and the cycle is re-born.

Looking at the density graph (lower left) clearly shows what is hot and what is cool. Basically, high density = cool air from the outside, low density = hot air (and exhaust gas) developed inside. Breathing of the intake end and formation and ejection of the tailpipe "piston" can be clearly seen.

An interesting detail of the pressure graph is the very brief but very deep downward spike that develops near the rear of the intake pipe during the early breathing phase of the cycle. This intense low pressure hiccup coincides nicely with very rapid inflow of air in that part of the intake. The exact location and intensity will vary from one design to another, but it pays to know where this is located if you're interested in low-pressure vapor or liquid fueling. It is what I have called the "carburetion point" of the engine. It is the "sweet spot" to pour in fuel if you're not wanting to use a highly pressurized fuel system.

L Cottrill

[metiz]

Hey Larry

I never tried Uflow but the graphs are near identical to what NUDiS produces. Does Uflow have the same core functionalities as NUDiS?

[larry cottrill]

I never tried Uflow but the graphs are near identical to what NUDiS produces. Does Uflow have the same core functionalities as NUDiS?

NUDiS is more fully developed. They are both basically 1-dimensional analyzers, and I assume the same underlying fundamental gas equations are used. Only Graham Williams knows for sure ;-)

L Cottrill

[PyroJoe]

For my own use I look for a design that supports a little more action through the tail.
I probably have brought to much mud to the forum over the last couple of years, so this will probably be the last few offerings of what I see as important in the design of the engines. Will be posting four shots from Uflow, the first is the inital condition:

[PyroJoe]

Here the the main pressure volume is starting to split, notice the development of the leading edge of the tail pressure wave, and density wave. The intake has already started its blow down cycle, which is one reason I like the idea of loading the intake to delay the pressure drop from the intake. This intake pressure drop begins well before the pressure wave reaches the tail expansion.

[PyroJoe]

Notice the density wave has traveled with the pressure wave, also this tail is conservative as there is plenty of pressure remaining as the wave approaches the end of the tail. This pressure won't completely disappear after passing the end of the tailpipe. Notice also that the mass flow has picked up here without complete loss of the pressure wave. The intake is still exhausting, depleting much of its own pressure and the effect has pulled the backside of the tail pressure wave down considerably.

[PyroJoe]

If the intake is loaded this would be the condition right before the intake starts its blow down at the end of a recuperator, and the tail wave reaches the expansion.

[larry cottrill]

Paul -

In comparing Pyro's example with mine, keep in mind that his is set up with the intake on the left end, mine with the intake on the right end. I set mine up that way because the intake is usually where I change things most often, and with UFLOW it is much easier to make changes on the right end.

L Cottrill

[paul fellows]

Joe
what type of engine did you use, paticularly the 'loaded' one. number 4

Larry
i'v just noticed that the lady Ann dose not have its intake and tailpipe on oposit sides of the of the combustion.
i'm trying to pin down a theory for the simpler Lockwood type befor moving on to the more complex type,
the tailpipe of the lady Ann is obviously and quater wave, as is the intake, and there is a half wave beteen the opening of the inlet and the end of the tailpipe.

i was still thinking organ pipes .of cause its one frequency but two diferant wavelengths, for the intake and tailpipe

[PyroJoe]

I call the engine a Midway, as its CC volume is midway between a volume that is large/"relaxed"with plenty of throttle range, and one that has almost no throttle range and cycles fast to the point of being rather unstable and difficult to start. This gives it the characteristics of being easy to start, but obtain a quick cycle after up and running.

The loaded version is a midway with a recuperator added to the intake length. It is supposed to breath in like a short engine, but loads up like a longer engine on the outflow. The Escopette has been doing this for some time. The Kraken is based on the midway dimensions and should eventually have the same outflow cycle as the above loaded version. Although I think UFLOW is missing parameters for cavity resonance, so in my views it is showing only 1/2 of the story.

[paul fellows]

im gonig to end this post for now

i'v come across the idea of thermoacoustics, and it looks like it might provide the right answer once in understand it
when i first came across it i posted to see if it was of interest.
and Metiz replide that it is old news

los alamos are giving away free softwear called DeltaEC for designing acoustical ducted systems,
unfortunatly the engines that they design have heat exchaingers where the CC should be.
you can pick it up here http://www.lanl.gov/thermoacoustics/

[Irvine.J]

There's only 1 thing in this world we know for sure... I... AM... AWESOME!!!!!