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Post by finiteparts on Jun 9, 2024 20:59:52 GMT -5
John,
I built curves for the inlet temperature at the nozzle guide vanes as a function of swallowing capacity, and also the exhaust nozzle. The numbers seem to approach realistic gas temperatures between 5.5 lbm/s and 6.0 lbm/s. Once the mass flow goes above this, the turbine inlet temperature would have to fall below 1500 deg F to be able to pass through the NGV's, assuming the combustor has a 5% pressure drop and a P2 = 5.5 bar (absolute). At this range also, the reheat gas temperatures fall in a 3100 to 3500 deg F range, which I haven't checked out yet. I will run a reaction solver to see what should be expected for AB exit temperatures and get back to you on this.
It is really tough to nail down a value without knowing a mass flow...but some measurements are always better than no measurements!
- Chris
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Post by racket on Jun 9, 2024 23:14:00 GMT -5
Hi Chris Yep , it often seems to be a case of fumbling around in the dark. I've reinstalled the dry nozzle and added a static pressure pickup on the same plane as the total pressure pitot entry to see if I can get more info . Years ago with my TV84 engine I fitted static/total probes but could never reconcile the results to determine mass flow, theoretical mass flows were always too large , probably because I assumed even flow velocities across the duct whereas there'll be a gradient due to wall friction . Hopefully another test this week :-) Thanks for the help Cheers John
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Post by racket on Jun 14, 2024 21:07:46 GMT -5
Hi Guys
Its a crappy cold and wet winters day here so have been reading over the last couple of years "developments??" and have come to the conclusion that I got lost after changing comps :-(
The 350 lbs of thrust test with the Chinese comp wheels was successful , temps were OK , so what went wrong when I had to change comps .
Instead of leaving the hot end alone and concentrating on the cold end only, I started to fiddle with too many things , some worked and some didn't , thankfully the flametube is now a better design .
The 350 pounder test ran 12 mm NGV throats , but I've since been playing with 11, 10 and 9 mm ones instead of leaving things as they were, the 12 mm NGV and turb wheel with 40 degree clipping were doing their job , even though the theory indicated I needed tighter throats at the higher PRs I was now running .
Problems with battery power affecting fuel pumps created "unknowns" which influenced changes which were unnecessary :-(
The recent test with the A/B using 9 and 10 mm NGV throats have made me think that the comp is capable of running out of full blown surge until pushed hard with the 9mm NGV throats at 5.5:1 PR on full afterburn , its possibly been running "unhappily" but not indicating it other than in the P2 gauge fluctuations .
As the teststand is ready for a testrun I'll do a dry nozzle test then pull the engine apart and increase the NGV throats to 11mm to see what happens, if theres an improvement I might even go back to the 12mm I had for the 350 pounder test :-)
Cheers John
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Post by enginewhisperer on Jun 14, 2024 22:56:23 GMT -5
ahh the fun of R&D!
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Post by racket on Jun 14, 2024 23:22:05 GMT -5
Fun fun fun ;-)
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Post by racket on Jun 16, 2024 0:29:44 GMT -5
Hi Guys Conducted a dry test run this afternoon , ~270 lbs of thrust , well within the design :-) Will get some vids up on Youtube . Heh heh ....Found a nice burnt patch of grass from last weeks A/B testrun when I arrive at the test site, probably from the glowing A/B when it disengaged itself youtu.be/v4394zeoNj8youtu.be/FOB_vbH38bEyoutu.be/bYa-d44IjosCheers John
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Post by racket on Jun 18, 2024 4:31:30 GMT -5
Hi Guys
Bit of an update , IGV angle back from 25 to 20 degrees and NGV throats increased to 11mm from 10mm, a couple of broken air deflector mounts that will need securing but everything else seems OK .
My jetpipe static pressure gauge has me concerned , it only registered ~4 psig whilst total pressure was at ~14 psit, so ~10 psi of dynamic pressure ( velocity) , this shouldn't be happening as it represents very high velocity possibly entering the A/B ....................a new line of investigation seems in order :-)
The dry nozzle diameter was increased by a couple of millimeters to 127mm , but its now got to be the shortest jet nozzle in history , the engines exhaust stub has an ID of 130mm , so the jet nozzling is only 3 mm :-(
Cheers John
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Post by racket on Jun 19, 2024 2:20:59 GMT -5
Hi Guys
Engine nearly back together , slow process as the air deflectors needed a lot more securing , but hopefully they'll hold together now , the surge at full power places a lot of load on them , I should have made them from thicker material instead of the 0.5mm stainless sheeting , it was easier to cut and shape ...............lazy me :-(
Cheers John
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Post by racket on Jun 20, 2024 4:02:10 GMT -5
Hi Guys
LOL.............nearly got the engine back on the test stand until I noticed the engine mounts were cracked :-( ..............more welding required .
Did a comparison of engine test data between the A/B run and the latest dry one and numbers weren't all that different , but theres a problem with the thrusts , 270 lbs dry but only ~300 lbs wet whilst consuming 8 lpm of fuel and running a rather warm afterburner , 30 lbs difference when it should be ~100 lbs , both tests had P4t of ~0.95 Bar so same energy level for making velocity , the other component , temperature is a little hard to work with as its impossible to measure the A/B temp going into the nozzle, we can only really go by the colour of the A/B and what its radiation level is , and both of those were at the extreme .
Cheers John
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Post by enginewhisperer on Jun 20, 2024 22:27:56 GMT -5
maybe something binding up in the test stand and reducing the measured thrust?
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Post by racket on Jun 21, 2024 1:05:53 GMT -5
Hi Andrew
Don't think there is, theres only the spring balance stopping things from rolling forward .
The P4t and Temps were both high on the wet run , similar to the dry run ,similar also with the manometer readings which should mean the similar amounts of air going in/through.
The one glaring inconsistency is the nozzle sizing, the dry run was using a nozzle area of ~10,935 sq mms , now if we do the usual , times 2 for decrease in density due to doubling the temp , and divide by 1.4 , the increase in velocity from the square root of temp change , then I'd need a nozzle of 15621 sq mms , but I have one 20% bigger in area at ~18870 sq mms , it would actually be more than that after extra expansion from the A/B temp.
BUT , oversized nozzles reduce temperatures and P4t in a jetpipe , neither of which is happening , only the thrust is low .
I guess I've just answered myself :-)
There appears to be a "problem" at the exducer exit, but whats causing it ??
Engine is back on the test stand ready for another run , time to recharge the camera batteries :-)
Cheers John
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Post by finiteparts on Jun 21, 2024 18:41:22 GMT -5
John, I made a quick plot of the required engine mass flow to achieve 270 lbf thrust as a function of exit plane Mach number: I took a SWAG at reading the measure exhaust temperature from you gauges video and it looked like maybe 867 deg C when you were at full power....is that correct? I assumed that the measurement was closer to the static gas temperatures so that I could estimate the gas acoustic velocity. Then, by sweeping the exit Mach number, we get the exhaust velocity component for the thrust equation. Then we can solve for the mass flow needed to meet that 270 lbf gross thrust. From your static and total pressure measurements that you quoted as Pt = 10 psi and Ps = 4 gage, and assuming a gamma of 1.33, it suggests an exit plane Mn = 0.658. Reading this from the above curve, that approximates a mass flow of roughly 6.2 lbm/s. Now, are the static pressure and total pressure measurements accurate? Maybe not, but some numbers are better than nothing and at least can indicate trends. Let me know if you would like me to plug in any other temps or pressures to make a new curve or exit plane Mn approximation. By the way, since you had the tachometer in on one of the recent tests, I compared the tachometer vs the approximation from the acoustic spectrum analyzer based approach...pretty solid! Tach Calc'd 49045 48900 56991 57116 63385 63431 I might try to change how the spectrum analyzer bins the measurements to see if it changes it any direction. - Chris
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Post by finiteparts on Jun 23, 2024 10:59:21 GMT -5
John, I realized I made a mistake on the last post. I had misread your pressures and so had used a Pt = 10 psig, when that was your dynamic pressure.
So I fixed it and put the Pt = 14 psig and thus got a much higher Mach number....Mn = 0.92.
That suggests that your engine's mass flow is more like 4.3 lbm/s.
Now the way this calculation is structured, there is some wiggle room in that exhaust velocity as this uses the bulk average value....so you might have a section of choked flow and some low velocity flow, but they should average out to around Mn = 0.92.
I just wanted to follow up on the mistake as it makes a big difference.
- Chris
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Post by racket on Jun 24, 2024 0:26:23 GMT -5
Hi Chris Thanks for the clarification :-) Test run this afternoon .............290 lbs of "dry" thrust youtu.be/-Ynf7tjGK1QCheers John
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Post by racket on Jun 24, 2024 1:08:01 GMT -5
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