Proposed Design - Amphora with Single-Stage Tesla Valve Ring

[larry cottrill]

YAVPJFE [Yet Another Valveless PulseJet Front End] -

This time it's an amphora [or maybe just a streamlined cuspidor] surrounded by a single-stage Tesla valve, both of which serve to capture otherwise lost momentum from forward-firing gases.

What do you think?

L Cottrill

[Viv]

Nice! marvel of a drawing as usuel but F.J. Foa beat you to it I am afraid to say Larry.

His recuperators were on the out side though

Viv

[larry cottrill]

Viv -

Yes, of course, I am aware of the resemblance to the Foa engine, which is one of the nicest valveless front ends ever proposed ... and certainly, mine is not simpler to do. Not for the squeamish -- a real Troy Legner project. I should have acknowledged the Foa heritage.

However, this does try to go farther in limiting expulsion to the outside. I realized, too, that the outer ring isn't quite a Tesla valve, since the back-cycled flow doesn't help quell forward flow in the main forward stream. [Can you have a true, single-stage Tesla valve? I'd have to think about that a while longer to know for sure.]

Anyway, this is probably a bit hard to produce for most amateurs -- certainly not amenable to my 'basement blacksmith' methods.

L Cottrill

[Bruce]

There are two methods of addressing the reverse-flow issues surrounding most pulsejets:

1. try to stop the reverse flow using all manner of aerodynamic valving such as the Tesla valvular conduit.

2. forget about stopping the reverse flow and simply change its direction so that it contributes to the net thrust (like Lockwood has done)

After *much* analysis and experimentation I have come to the conclusion that option 2 is the only really viable choice for most applications.

Aerodynamic valves, no matter how they're designed or constructed, are way too soft to be useful.

Even the best are incredibly leaky and, as anyone who's ever built and run a regular valved pulsejet knows, it doesn't take much leakage (through burnt valves) to really kill the power output of a pulsejet.

The effect of a "soft valve" is also easily demonstrated by moving the fuel-injector in a direct-injection valved pulsejet towards the tailpipe. This leaves a buffer of air between the combustible mixture and the front of the engine. My experimentation has shown that as you move the injection point rearwards, the power drops off dramatically -- mainly because this wad of air absorbs a lot of the combustion pressure thus reducing the effective compression ratio during the deflagration process.

So, if you want a valveless engine that actually produces power you should focus not on stopping the gases from escaping out the front, but on turning them around to go out the back.

Of course I'm not saying that this turn-around can't be achieved through the use of some interesting characteristics of compressible mass-flows and pressure waves ;-)

[Viv]

I think the anular gap will be the critical part of the design, I cant at the moment see a lot of mass flow around the internal reflector.

It would be interesting to try it with and with out to see what happens, I am in that happy state of being able to argue it in both directions.

Myself and Bruno proposed a modified Foa last year so we have all ready visited the design in detail, as you say it is simple and elagant.

In a way you are looking at a choking nozzle so it will need a bit of high speed flow to get it to lock up, your inner reflector may interfere with that.

Viv

[larry cottrill]

Viv -

Ok, here's a mod I came up with as a real Tesla valve test version.

L Cottrill

[Viv]

Larry I cant see a pressure differance across the deflector ring to cause a mass flow?

I can see the anular gap choking like a `Delavel nozzle (good) but the extra internal deflector ring wont have any appriciable flow altering effects

Viv

[hinote]

There are two methods of addressing the reverse-flow issues surrounding most pulsejets:

Aerodynamic valves, no matter how they're designed or constructed, are way too soft to be useful.

Bruce, something HAS to be doing the job of rectifying the flow on the intake side of the L-H family.

This is NOT an aerodynamic valve, but a "plug" of relatively cool incoming air which is induced to flow in sufficient quantity and speed to allow the small compression wave returning from the other (exhaust) end to do its job.

The L-H family is a really amazing bag of tricks all working together to get the job done. Combining acoustic wavefronts and Kadenacy oscillations is as close to black magic as I can imagine.

Bill H.

[Bruce]

> Bruce, something HAS to be doing
> the job of rectifying the flow on
>the intake side of the L-H family.

Nope. The only concession to reducing the outflow through the intake pipe is the very small amount of taper in the intake tube.

The "rectification" of gasflows is done by the U-bend that turns the exhaust flow around so that it leaves the engine travelling in the same direction as that coming out the intake tube.

> This is NOT an aerodynamic valve,
> but a "plug" of relatively cool
> incoming air which is induced to
> flow in sufficient quantity and
> speed to allow the small
> compression wave returning from
> the other (exhaust) end to do
> its job

The returning gasflow from the exhaust cone doesn't provide much in the way of compression -- the LH is still a very low-compression engine, like all conventional pulsejets.

Sure, the plug of colder, denser air in the intake tube does provide a degree of inertial containment but this has more effect immediately following ignition when combustion pressures are climbing very rapidly.

The key role played by the tailpipe is that of promoting maximum evacuation of the combustion chamber and then promoting additional turbulence in the combustion chamber during the reverse-flow. This turbulence ensures that the flame-front propogates as quickly as possible and is another of the interesting synergies of design with this engine.

In a regular pulsejet design there are to goals that conflict in terms of design.

On one hand, we want to provide a very smooth, low resistance path for the incoming fresh charge of air -- that allows the engine to ingest the maximum amount of air and therefore create the largest possible volume of air/fuel.

On the other hand, in order to promote thorough air/fuel mixing and rapid combustion, we want the contents of the combustion chamber to be as turbulent as possible -- but in a regular engine the act of creating turbulence reduces the amount of air that can be ingested by creating additional drag.

The LH however, focuses the returning gasflow from the tailpipe into a stream that enters the combustion chamber as a narrow column but which very quickly breaks into violent vorticies that ensure maximum turbulence immediately prior to ignition.

As I've said before, I don't believe the LH is a pressure-wave engine -- it is a massflow engine.

Pressure waves alone don't provide significant compression -- just as ocean waves don't cause the sea-level to rise -- they're temporary and very localised changes in the pressure.

Sure, massflows must be accompanied by a pressure wave -- but it's the massflow behind the wave that is the driving force with the LH engine.

[larry cottrill]

Larry I cant see a pressure differance across the deflector ring to cause a mass flow?

I can see the anular gap choking like a `Delavel nozzle (good) but the extra internal deflector ring wont have any appriciable flow altering effects

Viv

Viv -

Nuts! I forgot to 'bucket' the inner ring. I'll get that fixed sometime later. As it is now, there is a second 'nozzle' opposing the intended one, though the unintended nozzle zone seems crude and inefficient. Hollowing out the ring into a second bucket will kill that effect, since it will reduce the instantaneous massflow moving around the 'amphora' toward the annular nozzle.

I think your criticism would be fully valid in a steady-state case; but here, the 'pressure' is really a pressure wave expanding outward and forward. The acceleration of the long outer 'recycling cone' will not only bump up the gas momentum before it bends back, it will get it to the rearward-facing outlet faster than the slower-moving explosion wave. Thus, there will already be flow mass with strong rearward momentum in the intake channel [just aft of the annular gap], which the forward flow will have to contend with. Exactly the desired Tesla valve action, this time.

L Cottrill
----------

[Viv]

Ok I will wait for the next drawing but in the mean time lets not forget that on the inlet part of the cycle the presant layout will cause a lot of turbulence and muck it up.

I only say this so you can include it in the next revision, I personaly like the Foa layout and this one, I cant work out why know one has ever had a go?

Viv

[larry cottrill]

Viv -

This is what I meant to do. I doubt that it will improve on your observation about turbulence, but at least it will carve out a clear difference between the momentum of the gas going straight out forward and that snaking its way through the recycling tube.

The higher molecular momentum wins!

L Cottrill

[Bruno Ogorelec]

Larry,

This last picture -- the thing may actually work in this configuration. I don't think the first approach would have worked, as it pitted the exhaust gas from one side of the ring against the same gas from the other side head on.

This one removes this and pushes hot gas from one side only. Or rather, the streams impinge on each other at an angle.

It will probably require VERY careful tuning to work, though. Much would depend on where the combustion would start. Instead of a 'volume mode' of ignition, you would want to have teh 'front mode' and have the front start from the 'cone' established between the 'ring' and the outer wall of the chamber. Maybe having the spark plug there would help by initiating the process in that cone. The outer wall might also be isolated to prevent it from cooling by outside air. At a later point in the process, this part will be a hot spot and that may act to start ignition in that part of the chamber. You might want to have the other hot spot -- the exhaust neck of the chamber -- cooled by fins to avoid having the igniton occur there.

I like it, but have to wonder about the way the shock waves would behave in that configuration. When we look at gases as flows it looks OK, but if you look at the shock fronts, the picture may get much more complex.

Bruno

[Bruno Ogorelec]

Another thing. To avoid having teh ignition start from the 'amphora' bucket, I would close it off. I know that you hope to use it as a reflector, but that idea is (in my opinion) doomed anyway and will prevent this new design from functioning properly. You just don't want ignition to start right in front of the bucket.

Bruno

[Andrew Parker]

I came across a Lockwood patent last week that uses what appears to be a modified cross section of a Tesla valvular conduit as a buffer between the pulse combustion chamber and a rotary valve. It is still being used in those massive pulse-jet dryers. Sorry, I didn't save the reference, but it shouldn't be too hard to look up. I believe he referred to it as an "air diode" and there was no mention of Tesla (good business approach) in his reference list.


Andrew Parker