M1E Preview

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Viv
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Re: M1E Preview

Post by Viv » Sat Oct 02, 2004 7:05 pm

hinote wrote:
Graham C. Williams wrote:
Why did you move away from the flat plate entry to the combustion chamber?
Graham:

Thanks for your suggestions.

The flat front plate appeared (in Uflow) to be more effective, giving a sharper cutoff for the intake gases (turbulence) and possible aiding in rectification at the intake.

But it's more critical to find the correct intake length with a flat front--and I'm already in trouble with finding the right value for that.

I need all the help I can get.

Also, it's a great place to mount the fuel injectors.

BTW I'm getting enough induction effect from the propane nozzles to eliminate the need for any starting air. Just turn on the spark, and valve-up the propane, and she lights every time.

When I get this thing running, we can plug-in the results and see how it conforms with the rest of the model.

Bill H.
Acoustic Propulsion Concepts


".......some day soon we'll be flying airplanes powered by pulsejets."
Sorry Bill I tripped up over your fueling comments, it does not sound right, I cant see how you are getting enough air from entrainment of the propane.

I cant see that giving you enough air to form an explosive mix with that much propane flow, the result would be well over rich.

And please nobody quote pressure jet intakes at me unless you want to get biten! they are a lot more complex than the rubbish written about them.

Bill can you give more of a discription at to whats happening and what your procedure is, have you tried a lot of forced air? was it a blower or compressed air?

Viv
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hinote
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Re: M1E Preview

Post by hinote » Sat Oct 02, 2004 7:38 pm

Viv wrote:
Sorry Bill I tripped up over your fueling comments, it does not sound right, I cant see how you are getting enough air from entrainment of the propane.

I cant see that giving you enough air to form an explosive mix with that much propane flow, the result would be well over rich.

Bill can you give more of a discription at to whats happening and what your procedure is, have you tried a lot of forced air? was it a blower or compressed air?

Viv
Viv, you've certainly given me food for thought here.

The appearance of the flame in the combustion chamber is a nice, clean blue--but I'm getting some sooty orange out the tailpipe--so there's obviously an over-rich problem (at least at higher fuel flows--this doesn't occur at lower rates).

I haven't (yet) tried to induce additional airflow with an external source--but I will.

You can definitely hear a rumbling effect from the engine when it's burning fuel, and I assumed there was enough turbulence to induce resonance--but maybe that's not the case.

Reviewing my start procedure so far--I just start the spark, and then turn up the fuel flow until it starts to burn. No supplemental air (so far).

What do you think?

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

Viv
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Re: M1E Preview

Post by Viv » Sat Oct 02, 2004 8:05 pm

hinote wrote:
Viv wrote:
Sorry Bill I tripped up over your fueling comments, it does not sound right, I cant see how you are getting enough air from entrainment of the propane.

I cant see that giving you enough air to form an explosive mix with that much propane flow, the result would be well over rich.

Bill can you give more of a discription at to whats happening and what your procedure is, have you tried a lot of forced air? was it a blower or compressed air?

Viv


Viv, you've certainly given me food for thought here.

The appearance of the flame in the combustion chamber is a nice, clean blue--but I'm getting some sooty orange out the tailpipe--so there's obviously an over-rich problem (at least at higher fuel flows--this doesn't occur at lower rates).

I haven't (yet) tried to induce additional airflow with an external source--but I will.

You can definitely hear a rumbling effect from the engine when it's burning fuel, and I assumed there was enough turbulence to induce resonance--but maybe that's not the case.

Reviewing my start procedure so far--I just start the spark, and then turn up the fuel flow until it starts to burn. No supplemental air (so far).

What do you think?

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."
Bill, the just having a flame burning in the cc will induce a fair amount of acoustic noise that will drive the overall system in to low power resonance (rumbling) but weather that will trip the whole thing over in to high power oscilation depends on the "Q" of the resonator, or how good a resonator it is.

Its not just the engine geometry that needs to be right for this it includes the fuel system delivery rate and the heat release rate of the fuel, the tendency for the fuel system to oscilate in time with the engines acoustics is a definate plus point as long as it is all adding heat in the right phase with the engines overall cycle.

It does sound from what you have said though that you are in low power Lockwood rumbling mode, basically you need to give it a good kick up the arse to get it to the next power level.

Its all a feedback loop if that helps:-) I think a good draft of air blowing through and then trying diferant fuel levels is next, you want some bangs as they will drive it over the edge.

Viv
"Sometimes the lies you tell are less frightening than the loneliness you might feel if you stopped telling them" Brock Clarke

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Stuart
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Re: M1E Preview

Post by Stuart » Sun Oct 03, 2004 3:20 pm

hinote wrote:
Graham C. Williams wrote:
Why did you move away from the flat plate entry to the combustion chamber?
Graham:

Thanks for your suggestions.

The flat front plate appeared (in Uflow) to be more effective, giving a sharper cutoff for the intake gases (turbulence) and possible aiding in rectification at the intake.

But it's more critical to find the correct intake length with a flat front--and I'm already in trouble with finding the right value for that.

I need all the help I can get.

Also, it's a great place to mount the fuel injectors.

BTW I'm getting enough induction effect from the propane nozzles to eliminate the need for any starting air. Just turn on the spark, and valve-up the propane, and she lights every time.

When I get this thing running, we can plug-in the results and see how it conforms with the rest of the model.

Bill H.
Acoustic Propulsion Concepts


".......some day soon we'll be flying airplanes powered by pulsejets."
Here's something I agree with Bruno on: Why not just run the fuel up the middle of the intake? In fact, I think it makes sense to create a propane driven liquid fuel carburetor. That is, a small venturi pipe around your propane tube which also has an inlet for liquid fuel. The propane makes a cheap fuel pump and indusces startup flow.
I'm writing an automated airplane designer in java, useful later when you guys get ready to bolt a p-jet onto some wings

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Re: M1E Preview

Post by Mike Everman » Sun Oct 03, 2004 5:37 pm

I'm surprised that you've gone to cutting the intake when it wouldn't "instant start", Bill. I'm sure by your food for thought comment that you'll be considering resetting the intake to the starting length and using starting air, so I won't bother suggesting it. ;-P
Mike
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hinote
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Re: M1E Preview

Post by hinote » Sun Oct 03, 2004 6:38 pm

Mike Everman wrote:I'm surprised that you've gone to cutting the intake when it wouldn't "instant start", Bill. I'm sure by your food for thought comment that you'll be considering resetting the intake to the starting length and using starting air, so I won't bother suggesting it. ;-P
All right, all right--I was going to keep quiet for a day or two, but since you commented:

Please see the attached (which I have labeled "Blunderbuss"). I found a spare intake (just lying around, waiting!) that was considerably longer than necessary, and decided to start 'way too long and then cut it down, about 1/2-inch at a time. Looks a lot like the namesake rifle, I think.

Yes, I'm using start-air (compressed air through a blow-gun, with a tube extension on it). The engine resonates nicely with the right amount of air, but it isn't (yet) sustaining. I'm working through quite a long set of length reductions, so it's likely to take several days before I can make any further judgement.

Stay tuned (standard pun).

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."
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Anthony
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Re: M1E Preview

Post by Anthony » Sun Oct 03, 2004 8:02 pm

Wow, if you put this thing in the air you'll ingest birds and shoot em' toasted at the end! Nice engine, can't wait to see thrust figures, T/W ratio and TSFC, looks promising!

Good luck!
Anthony
Image

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Re: M1E Preview

Post by Mike Everman » Sun Oct 03, 2004 8:45 pm

Very cool, Bill, should make for some ear shattering bangs! I must wonder though, if you aren't focusing on length overmuch, and not considering the impedence other than as a byproduct of intake length. In my opinion you're attacking the finer point of intake resonance when (I feel) it has little to do with getting it sustaining. The inlet area will determine all (if the heat release time and over-all length allow it), if the intake length is within a reasonably large range. My often wrong, but never uncertain opinion is that it looks ready to go if you choke down the inlet; then work the finer points on a running engine and thrust stand.

Perhaps try introducing a tapered stinger in your inlet to choke it down some, to find a running impedence, then play with intake resonance.

I've said it before, but I'm still not certain if our local intake mode should be in or out of phase with our main cycle, or at some odd harmonic that enforces one and draws out the other. If it's in, of course you get a bit (I mean 2%) more high and low pressure extremes in the CC; if it's out, you get it to dwell longer at the extremes, which may help with ingestion more than anything. Who's to say without a serious experiment? What do you think, M.? Ha,Ha.

Come down in a few weeks and we'll drink beers and try some of this on a smaller engine! This baby might break our windows. ;-P
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Re: M1E Preview

Post by Graham C. Williams » Sun Oct 03, 2004 11:41 pm

Dear Bill.
I'm sure everything Viv and Mike are saying is correct. Introducing air to the front end changes at least two variables. The induction pipe appears longer to backflow; the confinement increases. The total heat and the heat release rate probably increase as well. If you still cannot get enough energy from combustion to increase the induction velocity to the point when it sustains but it will resonate with forced air it's time to squash the induction pipe a little and force up the mach number during backflow.

Best Regards
Graham.

hinote
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Re: M1E Preview

Post by hinote » Mon Oct 04, 2004 1:50 am

Mike Everman wrote: I must wonder though, if you aren't focusing on length overmuch, and not considering the impedence other than as a byproduct of intake length. In my opinion you're attacking the finer point of intake resonance when (I feel) it has little to do with getting it sustaining. The inlet area will determine all (if the heat release time and over-all length allow it), if the intake length is within a reasonably large range. My often wrong, but never uncertain opinion is that it looks ready to go if you choke down the inlet; then work the finer points on a running engine and thrust stand.

Perhaps try introducing a tapered stinger in your inlet to choke it down some, to find a running impedence, then play with intake resonance.

I've said it before, but I'm still not certain if our local intake mode should be in or out of phase with our main cycle, or at some odd harmonic that enforces one and draws out the other. If it's in, of course you get a bit (I mean 2%) more high and low pressure extremes in the CC; if it's out, you get it to dwell longer at the extremes, which may help with ingestion more than anything. Who's to say without a serious experiment? What do you think, M.? Ha,Ha.
OK--I'll go along with the recommendations of some of our more active participants here. I'll try a variable area "stinger" to see if we can find an improved impedance. This can be combined with my effort to find an optimum length, at the same time. Each length will be tested with the stinger, to see if a change in inlet area might create a sustaining engine

I'm not sure I completely agree with this approach, but since I lack any convincing argument to the contrary I'll give it a go.

My line of reasoning is that a properly designed intake provides its impedance through correct acoustic matching, and good plugging from the cold-air inflow velocity. A reduction in intake diameter may create a running engine but will sacrifice the breathing necessary to give it the higher performance the designer aspires to.

Having said that, I've observed that the Uflow sim shows an increase in end-of-cycle pressure in the combustion chamber as the intake tube is increased in length, up to a very obvious value--after that, the pressure falls off rapidly as the intake mismatch increases in value.

I have chosen to start with an intake tube length that is well above the indicated value and then shorten it until I get to the range where Uflow says it should be optimum.

I only have 2 hands (like regular people) so I can only handle that many variables at once. Since one hand is on the throttle (propane flow), I'll need to combine the proposed variable-diameter stinger with the start-air supply. The attached drawing shows a simple solution for this device. It's formed from a piece of straight metal tube and is pushed through a tapered piece formed from a length of hardwood dowel, and fastened (glued?) into place.

Does anybody else have a different (and possibly better) solution?

One of my goals here is to try and educate myself as well as others here about the problems associated with getting a new design to run. I would like to encourage as much participation in this discussion as we can get.

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."
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hinote
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Re: M1E Preview

Post by hinote » Mon Oct 04, 2004 4:34 am

Mike Everman wrote:
I've said it before, but I'm still not certain if our local intake mode should be in or out of phase with our main cycle, or at some odd harmonic that enforces one and draws out the other.

Come down in a few weeks and we'll drink beers and try some of this on a smaller engine! This baby might break our windows. ;-P
Damn, Brother---

there's an interesting subject to argue about (no, NOT the beer!).

I'd love to hear more arguments about this particular aspect of pulsejet engine component phasing.

I (again!) wish we had a more sophisticated program to help with our analysis. I still think Uflow may be useful here--it reflects the relationships between the important parts when they're correct, and when they're not.

I think I've seen a definite relationship between the intake tube resonance and the combustion chamber working in-phase; this means that both the intake tube and the combustion chamber length are important, and must be adjusted to reflect their participation with overall length/frequency of the engine. In the Ecrevisse, one must also add the "E-cone" (my term) into the relationship.

Comment-es-vous??

Poorly Written,

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

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Re: M1E Preview

Post by Graham C. Williams » Mon Oct 04, 2004 1:39 pm

Mike Everman wrote:I've said it before, but I'm still not certain if our local intake mode should be in or out of phase with our main cycle, or at some odd harmonic that enforces one and draws out the other. . ;-P
Dear Bill and Mike.
I'm not so sure it can ever be any more than an approximation. During start-up all the variables are changing. During steady running things are anything but steady.
To say that for a straight induction pipe the induction pipe length should be approximately equal to 1 cycle of the induction pipe resonance and for a tapered induction pipe it seems to work for 2 or 3 cycles of the initial resonance, can only be an approximation. I'm reasonably happy about saying the first (2nd or 3rd) induction pipe reflection (expansion wave) should approximately coincide with the low pressure in the combustion chamber. Should we also say that until the induction velocity is above some figure specific to that motor you cannot achieve the degree of mechanical confinement needed to tip the balance in our favour?

Graham.

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Re: M1E Preview

Post by Mike Everman » Mon Oct 04, 2004 4:13 pm

Graham C. Williams wrote:SNIP Should we also say that until the induction velocity is above some figure specific to that motor you cannot achieve the degree of mechanical confinement needed to tip the balance in our favour?

Graham.
Absolutely, Graham. You sent me the attached at some point, it's an excerpt from Queens Belfast 820953, very appropriate, I think:
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Re: M1E Preview

Post by Graham C. Williams » Mon Oct 04, 2004 11:11 pm

Dear Bill.
That's exactly how the tapered induction pipe works. Under backflow the induction pipe is pushed up the M curve.
I'm not too happy about this set of curves application to non-steady flow but it illustrates the point.

Graham.

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Re: M1E Preview

Post by Graham C. Williams » Mon Oct 04, 2004 11:36 pm

Dear Bill.
Another small point.
Viv commented on the Q of the system. I'm absolutely with him on this point and was about to start a thread on this.
Over a small number of samples 'Easy starting' motors have all had a Q less than about 1. Larry’s motor is a fine example of such a soft motor.
Higher Q (Q>1) motors offer better potential performance; the wave structure being more focussed on the combustion area. I hope he does not mind me saying this but Mikes 50mm E motor is a super example of something in this class; needing a bit more care to find the tune initially but once found it goes very well and starts easily. This is all conjecturing based upon little data. I think your motor has a high Q.

Graham.

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