K-PT 07c thrust fix -- K-PT 07X release

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mk
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K-PT 07c thrust fix -- K-PT 07X release

Post by mk » Tue Jul 18, 2006 6:49 pm

Hello all,

After having burned-out the prototype duct almost entitely, and as I found the time to put together the most basic information, I do now release the K-PT 07X pulsed combustor. Which can be considered as a developed counterpart of the UFlow1D-derived K-PT 07c engine (indeed, the K-PT 07X shows nice graphs as well).

While having theoretically estimated data for max. thrust, TSFC and others at hand, I do only present those which I actually were able to verify or measure on my own. Everybody else rebuilding the motor, and doing such and missing measurements might be encouraged to publish those data (with (probable) error). However, it might be his/her opinion whether to do so.

I would especially invite people having the time and capabilities to sort a way better propane injector, which may not exclude a way better fueling system in general, even allowing the usage of liquid fuels.

A few last notes wrt. starting:
I did not have the time anymore to sort a fixed starting-air setup, which means the development of an half-automated starting procedure. In part by solely turning on the spark source, air, and fuel-flow. Therefore some "fiddling" is still needed, while I did not find it very difficult.
However, I would adwise everyone to watch for flame outs when the duct is flooded with fuel vapour, and thereof missing oxygene to initiate combustion. Make sure the ports do point in the direction the wind on your test field is blowing, or do at least stay away from the ports as far as you can!
Furthermore, I found it helpful to "choke" the induced air-flow a bit, which also means adding additional turbulence. This may be achieved by putting some kind of turbulator the starting air supply pipe, or to insert the "air-pistol" of a compressor at an angle into the inlet.

Okay, that basically was it.

EDIT:
The file to be found below contained minor, but confusing mistakes. Now they have been fixed.
Attachments
K-PT_07X_release.pdf
Additionally and related, the "Esc-FIL-2005.pdf" file would be worth a look.
(465.53 KiB) Downloaded 583 times
Last edited by mk on Wed Jul 19, 2006 3:48 pm, edited 1 time in total.
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re: K-PT 07c thrust fix -- K-PT 07X release

Post by pezman » Tue Jul 18, 2006 11:55 pm

Wow, nice plans (60+ Newtons -- not too shabby)

Any estimates on tsfc?

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Re: K-PT 07c thrust fix -- K-PT 07X release

Post by milisavljevic » Wed Jul 19, 2006 12:59 pm

mk wrote:Okay, that basically was it.
What? That's it? Where are the pictures? (^_^)

Btw., good luck with your exams!
M.
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for ye merchants who do the prop'r t'ing only if
ye be haul'd-up on charges b'fore ye ship-mates
an' threat'nd wit' forfeiture of all ye precious loot
hear this - so-called stand-up guys YE BE NOT

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re: K-PT 07c thrust fix -- K-PT 07X release

Post by larry cottrill » Wed Jul 19, 2006 1:25 pm

Yes, Marten, very nice! A wonderful thing to share with the forum.

One thing I'm not understanding, though, is your notation "U-BEND" on the 140mm section. Is that meant to be the location where you START to make the U-bend (if used)?

Nice work.

L Cottrill

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Re: re: K-PT 07c thrust fix -- K-PT 07X release

Post by mk » Wed Jul 19, 2006 3:47 pm

Larry Cottrill wrote:[...] One thing I'm not understanding, though, is your notation "U-BEND" on the 140mm section. Is that meant to be the location where you START to make the U-bend (if used)? [...]
Well, perhaps picture may have helped. Indeed.

As you may see from the attachment, it was ment that the U-bend section employed was 140 mm long. It started immediately behind the combustion chamber.
Attachments
K-PT_07X_09-2005.png
Finished duct.
K-PT_07X_09-2005.png (77 KiB) Viewed 6189 times
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K-PT 07X in action

Post by milisavljevic » Wed Jul 19, 2006 4:31 pm

Here is another photo of the K-PT 07X, in radiant action --

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re: K-PT 07c thrust fix -- K-PT 07X release

Post by larry cottrill » Wed Jul 19, 2006 4:55 pm

Great stuff, gentlemen - very nice, indeed!

Sorry I doubted that you could shoehorn the U-bend into that 140 mm!!!

L Cottrill

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re: K-PT 07c thrust fix -- K-PT 07X release

Post by mk » Wed Jul 19, 2006 5:56 pm

Well, it just became those 140 mm, due I could not get any other ready-made 90° bends, and due everything alligned nicely, I could cancel putting an intermediate cylindrical section between both. It might be worth mentioning, that those employed are of about 3 mm wall-thickness.

EBay offers quite some opportunities. In my region it is not that simple to get only a few pieces of such metalwork for a desirable price.
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re: K-PT 07c thrust fix -- K-PT 07X release

Post by mk » Thu Jul 20, 2006 9:59 am

I have not ignored your post "pezman", but it just came to my mind today, that I only once did some rough measurements to obtain a TSFC value.

So, well, after searching for those few notes in my files, I finally found them.

I must admit that the real thrust measurement, i.e. as consequence of the throttle setting, is a bit obscure due to my stand inaccuracies. When interpretingmy notes correctly today, I would go for an estimated thrust setting of roughly 5.5 kgf.

Having done the calculation I'm getting:

f = (1.14 +- 0.23) kg/kgf/h

Where f equals the TSFC value.
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Re: K-PT 07c thrust fix -- K-PT 07X release

Post by milisavljevic » Thu Jul 20, 2006 11:59 am

mk wrote: Having done the calculation I'm getting: f = (1.14 +- 0.23) kg/kgf/h

Where f equals the TSFC value.
Hello, Marten!

In normal usage, TSFC is often represented by the symbol wf and with the letter f actually being a subscript. Silly, no?

If your measurements are correct, then the TSFC range that you have provided is wf = 0.91-1.37 kg/kgf/hr at a thrust
level = 80% of maximum. Let's call it wf = 0.9-1.4, in keeping with the likely number of significant digits. This is superb!

This is also somewhat better than my model had predicted for the K-PT 07X; however, the upper half of your range
is within the predicted limits. Having said this, I hope that you will find another opportunity to measure these values.

This data presents your K-PT 07X as a ground-breaking example of an enthusiast pulsejet - having attained the
acoustic temperature of 752 K and a TSFC of less than 1.3, if not 1.0, all in 2005. As I said, a superb performance!

Thank you, for allowing me a small role in you projects. (^_^)

Best regards,
M.

Edit: I failed to mention that Marten's K-PT 07X was capable of developing 100% thrust saturation, i.e., Cj =100%.
no safe haven for merchant scum


for ye merchants who do the prop'r t'ing only if
ye be haul'd-up on charges b'fore ye ship-mates
an' threat'nd wit' forfeiture of all ye precious loot
hear this - so-called stand-up guys YE BE NOT

avast!
Cap'n M.

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re: K-PT 07c thrust fix -- K-PT 07X release

Post by pezman » Thu Jul 20, 2006 1:31 pm

Wow, anything in the neighborhood of 1 is well worth building.

If others can copy this plan and replicate that kind of performance, then I agree that this is a breakthrough. Maybe not the first PJ to hit the "1.0" mark, but it seems to be the first published design that a hobbyist could use to build a pj w/ that kind of performance.

Thanks again for posting that.

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re: K-PT 07c thrust fix -- K-PT 07X release

Post by mk » Thu Jul 20, 2006 1:36 pm

Indeed I wondered about the pretty low number. I'd have expected somewhat more. To paraphrase your theoretical lay-down of the duct:
I would have expected a value of (roughly) wf = 1.6 kg/kgf/h*. Because of the duct was running less then max. throttle, the range was enlarged to both sides. However, I could hardly believe it myself, besides I already did hang to rather large error magnitudes. I would think that the real value should be somewhere in the "+-error-range". At least theoretical and measured ranges do intersect.

In any event, the throttle setting which was present will remain unknown.
Measuring it again would need a significant thrust-stand fix. And that's a problem for me actually. Time-wise and equipment-wise.

So, if somebody does not believe the stated value I could post the small calculation. Besides I do invite anybody to verify or falsify this measurement.


*) This was the lower boundary suggested for operating at maximum throttle, which means at 100% of max. throttle/max. thrust.

EDITed to avoid confusions with an above term wrt. "thrust saturation".
Last edited by mk on Thu Jul 20, 2006 2:29 pm, edited 1 time in total.
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re: K-PT 07c thrust fix -- K-PT 07X release

Post by milisavljevic » Thu Jul 20, 2006 2:14 pm

Marten --

With the K-PT 07X operating at or near 100% thrust, we can expect that the equivalence ratio will be at least 1.0,
and more likely approaching 1.2, considering your injector setup and choice of fuel, i.e., propane vapour.

With the duct operating at 80% thrust, or at least well below 100%, the equivalence ratio will be less than 1.0,
and in your specific case, I would estimate the equivalence ratio to be between 0.70 and 0.90.

What this means is that the attained value of TSFC will be less at the 80% setting than at the 100% setting.
Even the upper-range limit of 1.37 kg/kgf/hr represents an exceptional accomplishment.

Best regards,
M.

Edit: the model yields TSFC values of 1.13 and 1.45 for equivalence ratios of 0.7 and 0.9, respectively.
no safe haven for merchant scum


for ye merchants who do the prop'r t'ing only if
ye be haul'd-up on charges b'fore ye ship-mates
an' threat'nd wit' forfeiture of all ye precious loot
hear this - so-called stand-up guys YE BE NOT

avast!
Cap'n M.

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re: K-PT 07c thrust fix -- K-PT 07X release

Post by Mike Everman » Thu Jul 20, 2006 6:05 pm

Sweet work, Marten. It's a joy to follow along. I have not much to add, but I'm impressed mein freund!
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re: K-PT 07c thrust fix -- K-PT 07X release

Post by mk » Fri Sep 08, 2006 1:50 pm

Update.

Having heavily improved my thrust stand, I re-measured TSFC of the K-PT 07X duct. Thrust was measured with a fish scale, with the spring being under pre-load. Please note the pictures attached, due they will tell you more than a lot of words could.

The observed max. sustainable power level was 5 kgf (instead of the >6 kgf theoretically max.), with the TSFC-measurement done at 4 kgf that day.

Besides that above downside, for those who follow(ed), a few things need to be addresseed:
(1) Even with my first generation pendulum-type thrust stand, it was obvious that the K-PT07X duct was more powerful than the former K-PT 07c iteration.

(2) The simple 4x1.5mm propane vapour injector may without much doubt be considered as sub-optimal. It was felt that a more advanced injector could have offered the opportunity to (a) further reduce TSFC, and (b) allow for a larger max. and max. sustainable throttle level. However, it was nothing changed to the at first derived design, so that possible errors are of the same magnitudes and effects, which may not be underastimated as case of holding variables constant.

(3) The still used, and used for the latest tests, K-PT 07X prototype duct, which has been made from mild steel sheet, suffered and of course suffers from deterioration in several ways, like:
- "flaking" (Fe(II)-oxide),
- rust (Fe(III)-oxide),
- alignment alterations and bending, because of gravitational force effects during hot runs, which then also make exact mounting for exact thrust measurements somwhat difficult or even impossible - of course, that error might be of very small magnitude,
- dimension changes of sections, also because of gravitational effects, as well asdue to uncareful handling and/or fixing to a support structure, esspecially the latter being critical during runs.

(4) It is also likely, that the ultimate error of the pendulum stand was not linear, or rather, unidirectional. It may have shown a tendency towards too-large indications up from some point, or down from some point. Suitably because of one or the other construction improperty. We will never know 100 percently.

The above might thereof explain the felt reduction in power output to earlier, but different tests of the same duct, which were performed with pendulum stand. While the latest measurements IMO can be considered as way more accurate than those measurements done with the pendulum stand.

Finally, the TSFC value for the performed tests of the K-PT 07X duct, measured over a usage of about 1 kg propane*:

wf = (1.5 +- 0.2) kg/kgf/h

(@ 4 kgf, propane vapour fueling, layout properties identical to the published version)


*) There was only offered the possibility to measure propane usage via the differencel methode using a bathroom scale. This, as anybody may agree it, makes it difficult to keep the error range low without using lots of of propane. In fact the range of max. possible relative error, which was calculated to ca. 11.5%, was by some >85% caused by that bathroom scale's error. It is not too easy to get a scale which could cary a load of a propane bottle while still being exact to 100 g, rather 50 g or less.
Attachments
K-PT_07X_2006-09-04_2.png
Tests on 2006-09-04. Copyright Marten Klein
K-PT_07X_2006-09-04_2.png (217.94 KiB) Viewed 5521 times
K-PT_07X_2006-09-04_1.png
Tests on 2006-09-04. Copyright Marten Klein
K-PT_07X_2006-09-04_1.png (214.28 KiB) Viewed 5522 times
mk

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