2006-09, 2006-10 -- K-PT 07X-2 build and test

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2006-09, 2006-10 -- K-PT 07X-2 build and test

Post by mk » Wed Oct 18, 2006 3:15 pm

INTRODUCTION

The following paragraphs and attachments summarize, approximately, the build and first test of the K-PT 07X-2, the further developed K-PT 07X duct.


Building and running the -07x-2 duct was attempted just three, or rather, two weeks before my current winter semester started because of various reasons. At first, it was by no means a plan of mine to built an engine in the semester holidays. Only by chance I got a cheap CO2 bottle for my MIG welder in late September, so that the "old" -07X-2 change became an option.

The basic -07X-2 layout dates back about one year, and has been adapted in one or the other direction prior to the building process in order to fit, test, or prove newest theory. Thus "Milisavljevic" may get the main part of the theoretical credits for this one. If there have been other main influences, he might be your source of referrence, and be able to address the credits accordingly.



CONSTRUCTIVE ISSUES (IN COMPARISON TO THE K-PT 07X [->])

According to dimensioning, the -07X-2 re-employed the same diametrs and diametric ratios as -07X. I.e. the inlet was only reduced in length, the combustor front-end and the U-bend wese reutilized, and the final, cylindrical tailpipe section was reduced in length.
Thereof, only the combustor back, and the frustum ("megaphone") were altered such as they demanded a new build. Furthermore, the small diameter, cylindrical tailpipe section was both, reduced in length and demanded a rebuild, because of extensive oxidization effects ("flaking"), besides heavier-than-thought cross-sectional deterioration effects because of improper mountings in the past.

BTW So especially the latter may explain a noticed decrease/loss in max. thrust during the -07X's last test.

Well, because of the above, it was decided to take larger care about mounting issues. Looking at the attached photographs, you will notice certain parallels to other mountings or support structures. Most likely to Bill Hinote's and Eric Beck's solutions. Both came up with, or successfully demonstrated reusage of such designs. Being published, I did not bother with general features. The final solution for thermal-expansion-allowing mount, oppossed to proper and secure thrust and gravitational force deflection may not be optimal for propulsed systems, e.g. mount on a RC aircraft, or other constructive properties, e.g. thinner walls (especially a thinner-walled U-bend).



FUELING ISSUES (IN COMPARISON TO THE K-PT 07X [->])

The unadvanced 4 x 1.5mm radial "swizzle-stick" injector setup and location was kept the same. Being favourable or not might be in question, but I did not have the time to sort those variables as well, and again. This might be achieved in future tests. But that decision offers the possibility to compare preformance for a couple of fixed parameters, which is not too bad for a, so to say, alternativeless option.



FIRST TEST RUN RESULTS (IN COMPARISON TO THE K-PT 07X [->])

Sadly, significant things went wrong during the test run on the last weekend of the smester holidays. Which means, further tests will have to be delayed to another date, and maybe another location, too.

To avoid any confusion: Neither the duct, nor any major constructive issue failed. Rather it was somewhat trivial:
One time a plugging bolt of the headplate broke lose. Having had this solved, it did not last long and someone came complaining about the noise - I performed the tests on an expert-opinion-prooved ground not quite near any houses. However, it is none of my goals to get people set up with pulseed combustors, so I abandoned for the location that day. After all, it got too late to drive somwhere else, besides I would not have had enough propane left, anyway. During the weekend, no other date was possible because of the semester start.

Thereof, I could barely measure any data accurately enough, because of the two short runs that could be made only, and which were supposed to get a TSFC figure for 4 kgf power output. (The latter for comparisons to -07X, and evaluation of my new paket scale.) So because of the problems explained above, I could not even get a proper video record, a proper measurement of min. and max. power output (- all for my taste -), and related statements.

However, in advance to await better overall test conditions, even if it might be in spring 2007, the following can be stated:

(i) Having a properly working trolley-type thrust stand at hand, power output of -07X-2 could be judged to be overally equal to -07X duct's, if not even higher. That's no trivial evidence, IMO! While propane vapour pressure was large enough, i.e. the bottle warm enough, the -07X-2 easily achieved 5+ kgf, i.e. something inbetween 5 and 6 kgf. I did neither take a close look, nor did I throttle it up to any of the possible operation-stopping events. It only represented a quick estimation.
With further injector size, layout and location improvements, some power output might be gained.


(ii) Having had a scale available similar to the one Bill Hinote used during the meet in 2005 in California, for the two runs TSFC could be meaured to the following:

[1] missing screw: wf = (1.5 +- 0.2) kg/kgf/h @ 4 kgf*, 3.0 to 1.8 bar propane pressure**, 2:10 min, local daily atmospherical conditions of 2006-10-06

[2] properly assembled: wf = (1.5 +- 0.3) kg/kgf/h @ 4 kgf*, 3.0 to 1.8 bar propane pressure**, 1:20 min, local daily atmospherical conditions of 2006-10-06

The maximum relative errors for both runs are well above 10 %, but with the possibility of attempting a longer run, it was estimated to be possible to get the maximum relative errors down to atleast somwhere inbetween 5 and 7 % without changing the current setup.
___________
*) Power output may have been larger temporarily, in part up to 4.5 kgf, but only seldomly below 4.0 kgf. It is referred to continous thrust extraction measured with a spring scale. Its spring base frequency wrt. the assembly is at roughly 4.5 Hz; thereof failure due to exciting events seem unlikely.
**) Propane pressure decreased rapidly from the larger figures stated down to its equilibrium or stady-state value of about 1.8 bar.


(iii) The overall caracteristic frequency (OCF) was measured to be at about 223 Hz. Together with an overall acoustic length of about 1272 mm, the overall acoustic temperature (OAT) would be about 799 K, at least for an assumed open-pipe solution.
"Milisavljevic" may add further information with respect to this paragraph.


(iv) It it is likely that it relates to fueling issues, which means injector issues especially, that -07X-2 showed a more difficult starting behaviour than -07X. Namely the tendency to a sudden stop was increased as long as the engine had not settled near the final state of equilibrium wrt. (wall) temperature distribution. In fact, it seemed that the time demanded for reaching the final, dissipated equilibrium state lasted longer for -07X-2 than it did for -07X. Well, I must admit, that I can only guess, because I never measured that time explicitly. However, once the walls were glowing a little, the pulsed combustor behaved admissible (- might be a bit too degrading -) in the means of stable operation at various throttled power settings.


(v) It was also felt that sound intensity in the near field behind either of the ports was larger than it was for -07X. Which means especially perpendicular to the centerline, inbetween the two ports. While this might again be considered as a guess.


Well then, I hope those where the significant points.
Attachments
K-PT_07X-2_run[1].png
Copyright Marten Klein 2006.
K-PT_07X-2_run[1].png (221.4 KiB) Viewed 7387 times
K-PT_07X-2_ready.png
Copyright Marten Klein 2006.
K-PT_07X-2_ready.png (216.96 KiB) Viewed 7385 times
K-PT_07X-2_con_2.png
Copyright Marten Klein 2006.
K-PT_07X-2_con_2.png (72.53 KiB) Viewed 7387 times
K-PT_07X-2_con_1.png
Copyright Marten Klein 2006.
K-PT_07X-2_con_1.png (74.38 KiB) Viewed 7386 times
Last edited by mk on Wed Oct 18, 2006 5:16 pm, edited 2 times in total.
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re: 2006-09, 2006-10 -- K-PT 07X-2 build and test

Post by Eric » Wed Oct 18, 2006 3:33 pm

What you need is a parabolic pit to run the engines in.

Neighbors can be a real pain. Hope you get to test it again soon!
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re: 2006-09, 2006-10 -- K-PT 07X-2 build and test

Post by mk » Wed Oct 18, 2006 3:56 pm

Too true, Eric.

If it has not been due to bad soil (and wind) conditions for testing, I would have put the stuff a couple of meters further down in the old gravel pit, which is an MX aerial right now. Hmmm...it is not that deep anyway. Just unlike the open-cast mining holes, which will finally run over the small ex-gravel pit in a few years. Weird somehow.

Else, I could try to get one or the other test done at the airfield in Rothenburg/Neiße. If you remember, the "Days of Thunder", the 1st German pulse-jet RC flight camp took place there in may of 2006. The expense in driving to that location would be the downside, but it still is not comparable to common distances in other countries or locations in the world. E.g. it's not that far. !)

It is way better to find one or the other interested guy, than setting up all the people around. And because of the pulse-jet event, and the aircraft museum, interested and helpful people could be around. Though, I would not consider a Chesna to be quite, as well as (pros') dirt bikes.
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re: 2006-09, 2006-10 -- K-PT 07X-2 build and test

Post by Mike Everman » Thu Oct 19, 2006 2:17 am

I have cleaned up Marten's wonderful thread.
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Re: 2006-09, 2006-10 -- K-PT 07X-2

Post by milisavljevic » Thu Oct 19, 2006 2:45 am

mk wrote: (iii) The overall characteristic frequency (OCF) was measured to be at about 223 Hz. Together with an overall
acoustic length of about 1272 mm, the overall acoustic temperature (OAT) would be about 799 K, at least for
an assumed open-pipe solution.

"Milisavljevic" may add further information with respect to this paragraph.
I must point out that Marten was careful to write that an OAT of 799 K was applicable only if one assumed that
an open-pipe solution correctly described this pulsejet. This is not the case for pulsejets similar to K-PT 07X-2.

In fact, the measured open-pipe acoustic temperature for K-PT 07X-2 matched its modeled target of 682 K.
The closed-pipe equilibrium flame temperature was also found to be within 30 K of its design target, 1975 K.

K-PT 07X-2 is the first pulsejet designed such that both its open- and closed-pipe fundamentals will synchronise
at the same frequency, in this case about 206 Hz. The measured characteristic frequency of 223 Hz represents
a VFT synthetic frequency, which is something new, and will not be explained further at this point in time. The
point to be made here is that it is a mathematically unsupported practise to take the characteristic frequency of
certain pulsejets and "work the maths backwards" to calculate acoustic temperatures in excess of about 750 K.*

I have other comments to make about Marten's test results and our purposes in converting K-PT 07X to the "-2"
specification, but I felt that it was important to jump in now and try to stop more misinformation from spreading.

Congratulations Marten!

Best regards,
Störgröße M.

*This "ceiling" applies to classical, self-aspirating pulsejets combusting near-stoichiometric air-propane mixtures.
Last edited by milisavljevic on Fri Oct 20, 2006 12:16 am, edited 1 time in total.
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re: 2006-09, 2006-10 -- K-PT 07X-2 build and test

Post by Eric » Thu Oct 19, 2006 3:03 am

Ok then...

Any type of pit that would reflect the sound upwards would greatly reduce the noise.

If you are out at the ocean and shoot a gun you just hear pooof because the sound doesnt have anything to bounce off of and just kind of goes out.

With the pit a majority of the sound goes up into the sky where the people nearby cant hear it.

I run some of the bigger engines at a rock quarry some times and just up over the top of the edge people dont even really hear it, just kind of sounded like someone was mowing their lawn.

Eric
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re: 2006-09, 2006-10 -- K-PT 07X-2 build and test

Post by mk » Thu Oct 19, 2006 5:21 pm

Seems like I missed what was going on.

Anyway, thanks for the replies!
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re: 2006-09, 2006-10 -- K-PT 07X-2 build and test

Post by Fricke » Thu Oct 19, 2006 7:19 pm

Nice looking engine Marten!

I like your test stand! It´s much nicer looking than my 'hack'.

I´ve finally rebuildt my Super Balrog.
All that is left is to make a better fuel nozzle, so SB will reach it´s full specs.

//Fricke

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re: 2006-09, 2006-10 -- K-PT 07X-2 build and test

Post by Mike Everman » Thu Oct 19, 2006 7:51 pm

Beautiful work, Marten! I finally got to read your post after all the hullaballoo (that's a rare English term for BS) ;-)
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re: 2006-09, 2006-10 -- K-PT 07X-2 build and test

Post by pezman » Thu Oct 19, 2006 10:01 pm

That is a nice looking engine ...

The water mark in the photographs intrigues me ...

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re: 2006-09, 2006-10 -- K-PT 07X-2 build and test

Post by Mark » Thu Oct 19, 2006 11:06 pm

Being Mr. Off-Topic, I would just like to say I like all the protrusions sticking out of it, like the spark plug and other projections. It makes the engine look intelligent in some way if that makes sense.
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re: 2006-09, 2006-10 -- K-PT 07X-2 build and test

Post by mk » Fri Oct 20, 2006 12:05 pm

Thanks again!


Mike,
Figuring out what hullaballoo could mean was not too difficult.

Whatever happened, I think you have done a good job wrt. moderating yet again.


Fredrik,
Good luck with the "SB"!
Your build-quality was, or rather, is very good. Thus, it should not be an issue. Personally, I can hardly wait to hear from its first run. =)


"Pezman",
The water mark is a ZIME. A graphical decoder from Latvia, which employs the patterns or principles of traditional decoration textile look.
Because of the decoding technique there are billions of possibilities given. E.g. more than a couple for every human on this planet.


Mark,
In short terms: lol. !)

Do not take it too hard, but "looking intelligent" sounds like directly taken from an article about the fashion week.
Last edited by mk on Fri Oct 20, 2006 7:50 pm, edited 1 time in total.
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re: 2006-09, 2006-10 -- K-PT 07X-2 build and test

Post by Fricke » Fri Oct 20, 2006 4:55 pm

Fredrik,

Good luck with the "SB"!
Your build-quality was, or rather, is very good. Thus, it should not be an issue. Personally, I can hardly wait to hear from its first run. =)
Thank you!

This incarnation is a bit uglier on the outside. The next one will have better workmanship put in it... Too many modifications shows in the apperance...


You and a 'M' will be the first to know how it worked!

BTW: I´m now also with a ZIME! =)

//Fredrik

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Post by mk » Thu May 24, 2007 8:48 pm

Regarding:Rothenburg, "Days of Thunder", 2007-05-18.


Introduction

Due I want to keep everything regarding the K-PT 07X-2 engine to a single thread, I decided not to encapsulate it under the "Days of Thunder" topic.

At first it is worth to mention that I was able to demonstrate -07X-2 successfully. Even more, I could take a little more data. Unfortunately not differing much in precision from the tests in 2006. But OTOH, I am else missing a suitable location and time.


Run no. 1 of 2

There is not much to write about this one. At first I was pleased, that I got the engine started without much problems since the last time I run it (Oct. 2006). Second, I wanted to get an specific fuel consumption (SFC) reading, but somehow the time measurement failed. Thus only maximum static thrust (STH max.) and operation/throttling characteristics could be observed, besides overall characteristic frequency (OCF).

Throttling characteristics were quite acceptable, i.e allowing for minimal throttle settings that would hardly produce any thrust, and almoste immediate response to fuel flow alterations. I did not take any numbers here.

OCF: 221 Hz. A few Hertz below the 2006's measurement. However, I did not take a detailed look at the record of the run so far.

STH max.: ~5.5...6 kgf @ injector back-pressure of ~1.3 bar; probability for sudden extinction after exceeding 5.5 kgf increased dramatically.


Run no. 2 of 2

Same procedure as above. After some warm up the SFC reading (wf) could be taken. Sadly I could not let the engine run longer than about two minutes, so that the relative error of time and weight differences are quite large.

OCF: 220.78 Hz over 11 samples, 35.5 sec runtime, fixed perspective (depicted below).
Interesting wrt. the OCF is, that some samples show a split of a few Hz. E.g. the first peak f = 221 Hz, f' = 214 Hz; or the second (strongest split) f = 440 Hz, f' = 427 Hz. It will have to be discussed whether it is a phenomenon, or just a matter of the recording position.

SFC: wf = (2.3 +- 0.2) kg/kgf/hr @ STH = (4.0 +- 0.2) kgf, over t = (110 +- 1) sec, injector back-pressure ~1.2 bar; propane vapour pressures: beginning ~ 8.2 bar -- end ~ 6.4 bar.


Overall discussion & conclusions

(i) Due the wheather was warm & sunny, together with short run times, it must be said that the propane pressure was rather on a "too large side" for injector assembly -- namely the simple four-hole injector depicted in the K-PT 07X release sheet.

We may specify the problems briefly:

- In part tough starting & sudden extinction even with a warm duct, just until the vapour pressure fell under a superior level. Likely to be somewhere inbetween 7...7.5 bar. With the tests done in 2006 such problems were less of an issue. Especially when the propane pressure just decreased under 6 bar, and did not go much below 4 bar.

- Sudden extinction when reaching and/or exceeding 5.5 kgf power level, and a larger SFC (> 2 kgf/kg/hr @ 4 kgf) then observed in 2006 with the same assembly. Reasons might be the following:

[a] Mixing of fuel and air is too inadequate (local in homogeneities) with four radial holes.

Mixing efficiency decreases with increasing ("off-range") injection pressures, i.e. higher particle velocities at the orifices. Now this corelates to par. [a] by making the injector layout even worse by introducing an induced-related parameter.

Thus [a] and summing up in a lower mixing efficiency. Which means to get the same results as in 2006, more fuel was necessary. Back then, vapour pressures where most often aound 4 bar, and injector back-pressures at roughly 1 bar sometimes even below, and OCF of ~ 223 Hz. But in Rothenburg ~ 1.2 bar back-pressures were present. So there was more fuel passing the engine without making "practical" use, which might be supported by the lower OCF of ~ 221 Hz. Maybe additionally by the "peak splits" to be seen in the sound record. Those were new to my eyes.
These seem to be a resonable arguments, supported especially by Eric's reports about injector developments & affects, which can be found all-over the forum.

Therefore, a percentual gain in SFC regarding the the latest -07X-2 tests, if not in power output as well, might be observed when employing a better injector. Having different pressure readings and engine performance data at hand, it appears valuable to develop a liquid fuel injection. Which would more more easily allow to overcome the problems of injector layout vs. possible injection pressure ranges.


(ii) With all the tests done so far, it is obvious that the relative error could not lowered much below 9%, so there is still room for improvements. A better scale (electronic fishscale, more precise scaling) could help, as well as a longer run times.
Nothing further to it, I discussed it a few months ago.


######## Edited due to readability reasons. ########
Attachments
K-PT_07X-2_rohenburg_run[2-5]_wf.png
Waveforms. Graphs extracted with Audacity.
(19.83 KiB) Downloaded 175 times
K-PT_07X-2_rohenburg_run[2-5]_prsp.png
Perspective of the record.
K-PT_07X-2_rohenburg_run[2-5]_prsp.png (160.3 KiB) Viewed 5428 times
Last edited by mk on Mon May 28, 2007 10:53 am, edited 1 time in total.
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Re: Latest test results

Post by milisavljevic » Mon May 28, 2007 10:09 am


Hello Marten --

It is good news indeed that you were able to break away from your studies long enough to drop in
on the goings on at Rothenburg. I have read through everything that you were able to report here.

In a nutshell: K-PT 07X-2 operated at an OCF of approximately 221 Hz, and exhibited a "split" about
F1 (dF = -7 Hz) and F2 (dF = -14 Hz); SFC was measured to be 2.3 +- 0.2 kg/kgf/hr at 4.0 +- 0.2 kgf,
a value much greater than the previous measurements for both the old K-PT 07X and the new "X-2".
___

A. Acoustic Analysis

From the most recent version of the predictive model, the open-pipe (OF1) and closed-pipe modes
(XF1) for K-PT 07X-2 are 205.8 Hz and 233.8 Hz, respectively. These figures correspond to testing
at sea level on an ICAO standard day (15 C); I have yet to adjust these for your test-site weather
and elevation. If we apply a "50-50" split to calculate the VFT (synthetic) frequency, we find 219.8
Hz as the predicted OCF. The strong secondary peaks (F1-F2 splits) you discovered in your sound
recording indicate that the open-pipe mode is slightly dominant: this makes sense considering the
K-PT 07X-2 is a valveless pulsejet (the closed-pipe properties of this motor are created out of the
combustor geometry, e.g., employing a headplate in lieu of a conical transition section). If you will
send me the sound files that you have collected, I will be happy to extract the partial frequencies.

The model's corresponding acoustic temperatures are found to be EAT = 682 K, and EFT = 1980 K;
if we ignore VFT (and thus the closed-pipe properties), we find that the (deprecated) EAT = 785 K.

Even without adjustment, the modeled OCF value and the measured value are in good agreement.

If anyone is wondering just what a 'synthetic frequency' is, please consider the running frequency
of a valved pulsejet, e.g., the Argus AS-014 (or the Dyna Jet): as its intake valves open and close,
the duct alternates (acoustically) between open- and closed-pipe resonance 'modes'. In the case
of a valved pulsejet, the open-pipe resonance frequency is generally greater than the closed-pipe
frequency; the perceived running frequency (OCF) is approximately the average of the two values.

Valveless pulsejets are not so easily described. In more trivial cases, the open-pipe properties are
completely dominant, thus the OCF closely matches the predicted open-pipe resonance frequency.
For designs that feature headplates (as an example), the closed-pipe properties may no longer be
neglected, thus the OCF will be a 'composite' of the open- and closed-pipe resonance frequencies.
___

B. Performance Analysis

I believe that your assessment is spot on - the combination of a limited injector and excessive fuel
supply pressures resulted in poor SFC performance. It is clear from the supply and back-pressures
that you have reported here that minimal injector modulation was possible; moreover, the injector
design itself (i.e., multiple small orifices) does not lend itself to (predictable) modulation and linear
throttle performance (e.g., stepwise throttle response at low delivery pressures). What remains is
to compare your thrust and SFC measurements to the model's predictions. In this respect, we find
that K-PT 07X-2 behaves in real-life (testing) very much as was predicted during the design phase.

Maximum continuous thrust is predicted at about 5.2 kgf (NOC method; OCT yields almost 5.6 kgf);
both values are within the limit of experimental error. To demonstrate a high SFC = 2.3 +- 0.2, we
may assume localised, inhomogeneous fuel-air mixtures permitted the overall equivalence ratio to
approach rich-extinction (i.e., greater than 1.20:1). In fact, when K-PT 07X-2 is modeled with 'soft'
boundary layer effects (BLE) we find SFC (at 4.0 kgf thrust) yields 2.3 kg/kgf/hr when EER* = 1.07.
On the other hand, we already knew that K-PT 07X-2 is better described by using 'hard' boundary
layer effects; in this case we find that SFC (at 4.0 kgf thrust) yields 2.3 kg/kgf/hr when EER = 1.25.

As you have already concluded, a new fuel injector design is needed. You can also consider trying
a pressure-reducer that will allow the injector to sense a lower pressure than the bottle pressure.

Thank you very much for taking the time to post another thorough report: the data is appreciated!

Cheers!
M.

*Effective Equivalence Ratio
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for ye merchants who do the prop'r t'ing only if
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avast!
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