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