richardm
Senior Member
Joined: June 2022
Posts: 338
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Post by richardm on May 24, 2024 6:13:13 GMT -5
Telle me more about the bearings you re using.. I like terms like stretching the envelope , thinking outside of the box , pushing the limits.. That s what keep us moving.
Progressing very slowly here, so much to do all around... Almost done with the fuel and oil module Some final testing and then hooking it up to the engine Next is the instrument / control panel Some sheet metal work and lots of wiring..
Cheers!
Richard
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Post by racket on May 24, 2024 18:37:41 GMT -5
Hi Richard Standard turbo "brass" for the bearings Turbine end Comp in diffuser Comp end thrust bearing Rear side of thrust bearing All looking good , so they can go back together :-) Cheers John
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Post by racket on May 28, 2024 1:59:50 GMT -5
Hi Guys
All back together and on the trailer :-)
Reduced the NGV throats from 10mm to 9mm .
Adjuster the bent tip angle on the syringe fuel injectors to spray a little deeper into the evap tubes.
And had to reweld a couple of the diffuser outlet air deflectors that the surge had "stressed".
Left the IGV in place as the tighter NGV throats might cause problems .
Also opened up the A/B nozzle by a few more mms to ~146mm dia .
Just need to make up a fuel brew , charge all the batteries and I'll be ready for a test run
Cheers John
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Post by racket on May 30, 2024 21:25:14 GMT -5
Hi Guys Well , that was a waste of time and fuel :-( youtu.be/tNr2t2FSRzkAt least the afterburner colour improved even though the thrust was a disappointment . Went into surge too early , gotta go back and have a look at what I had a couple of years ago . Cheers John
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Post by racket on May 30, 2024 21:36:27 GMT -5
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Post by racket on May 30, 2024 22:38:29 GMT -5
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Post by racket on May 31, 2024 18:57:45 GMT -5
Hi Guys
After digesting the video data it looks like my changes to the NGV throats was the problem , by reducing the throats from 10mm to 9mm my red manometer readings were a lot higher , at 3Bar P2 it was at ~650 mm water head whereas on the previous test run it was only 275mm , so a lot more air being dumped.
The green manometer measuring inlet "vacuum" remained similar at 900mm yesterday whilst it was 975 previously , so a tad more air going in on the previous test .
Its starting to make sense?? , even though the theory and real world aren't in alignment with regards the NGV throat area requirements .
CONCLUSION. A change back to 10mm for the throats , the installation of the other couple of TOT thermocouples in the A/B transition tubing to get a more accurate reading of turb temps , along with the extra fueling I now have to the A/B and a bit more off the nozzle to increase its diameter so as to be able to handle the extra gas volume , and she might do what we want :-)
Cheers John
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richardm
Senior Member
Joined: June 2022
Posts: 338
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Post by richardm on May 31, 2024 19:39:50 GMT -5
Hi John! Ha ve a quesito here for you: How much fuel is your AB burning compared to the turbine running at full power? My question arises from this reasoning: Assuming about 1/3 of the available oxygen is used in the turbine, the remaining 2/3 can only sustain about twice the fuel burn of the turbine. How close to that ratio are you ?
Cheers!
Richard.
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Post by racket on May 31, 2024 20:09:38 GMT -5
Hi Richard
Yesterday I was dumping ~8 lpm into the A/B , this was a tad too much for the restricted airflow as there was a blue flame from the A/B where you could see combustion happening as ambient air was interacting with the over rich exhaust , previously I flowing ~6 lpm to the A/B which was ~twice what the gas producer was consuming , assuming 4.5 lbs/sec - 270 lbs/min of air , say 50:1 A/F ratio , so 5.4 lbs/min - 2.45 kgs/min of fuel , at my fuel density of ~0.76 = 3.27 lpm
Combustion efficiency is pretty poor in our relatively short afterburners , even 80% might be optimistic, 3.27 X 2 =6.54/0.8 = 8.175 lpm required.
Cheers John
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Post by finiteparts on Jun 1, 2024 18:26:04 GMT -5
John, It suggests that the compressor and turbine are not very well flow matched, but I think some of the testing may have made interpreting the results difficult. So the first thing is that you made these changes and then only checked them out at full power with the AB lit, is that correct? If it was me, I would have done a dry run (even with the AB duct on it) just to see if it behaves any different with the AB on or off. Secondly, the throttle movements are rather rapid. Slower, smoother changes allow the system to be closer to the steady state operating line. Rapid movements take the engine off of the steady state op-line and transiently push it closer to the surge boundary. The faster the throttle push, the closer it gets to the surge boundary. That last high power throttle movement is extremely fast, especially for a condition that will be working in the narrowest map width region. Third, if the AB is over-fueled, you could easily be back pressuring the rest of the engine and if there is no choked region between the turbine end and the compressor system, the light off pressure pulse could destabilize the compressor or diffuser into a rotating stall or surge condition. This is exactly what would happen to the early turbofan engines. The AB would light off with a sudden pressure pulse that would travel forward up the fan duct and cause the fan stage to stall. Some of them could only be cleared by shutting down the engine and restarting as rumor goes. Is your AB fueling system able to bring on the fuel slowly and ramp up as needed? Or does it just come on at a constant pressure? Lastly, if you do find the compressor is oversized, you might think about putting a throttling cone on the inlet to reduce the air coming in and move the map over to the left a bit. You can see a paper on that here: www.scribd.com/document/466350368/paper3Variable trim compressors were a hot topic for a moment a few years ago. There are other papers out there, but that is one of the first and should give you a good idea of how to implement it if desired. Good luck, Chris
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Post by racket on Jun 1, 2024 20:06:26 GMT -5
Hi Chris LOL.......they certainly aren't well matched :-( The comp needs a turb stage with much greater flow capacity , but this could be rather difficult due to the comp design , its made for tractor pulling where the engine can over ride any imbalance by forcing the gases through the turbine at higher pressures . If we scale the flow capacity of one of the newer high flow Garrett comps that are flowing >15 lbs/min per sq inch of inducer , then my 19.6 sq inches of inducer would be capable of ~300 lbs/min - 5 lbs/sec , and even with that flow my inducer tip incidence still isn't right , it needs to flow a tad more . For the last few tests I've had a 25 degree preswirl IGV stator fitted , during the previous test on 20 May www.youtube.com/watch?v=KXgQpgKQBvc&ab_channel=racketmotorman I was able to run the engine up to 4.5 Bar - 5.5:1 PR without it going into surge because of the 10 mm NGV throats , once they were reduced to 9mm during the latest test she surged whilst at similar P4t pressures , so backpressure wasn't a problem , the NGV was choking. The red manometer on that previous test was at zero when running 5.5:1 PR , so no dumping out the surge slot , what went in the front at a "vacuum "of 1100mm of water, went through the engine , www.youtube.com/watch?v=lsbC77keFXQ&ab_channel=racketmotorman I just need to replicate that with full A/B fuel flow . The previous test would have been successful other than the A/B fuel pump wasn't supplying enough pressure , barely 10 psi instead of 20 psi , the latest test had it up ~26 psi , because of the 10 psi fuel pressure the A/B combustion was erratic and causing bouncy gauges , I feel the engine was configured correctly during that test , it was only the A/B pumps which let me down . If I can "adjust" the A/B nozzle size to produce ~0.85 Bar of P4t whilst on full A/B fuel flow, the engine will perform . The A/B fuel system is either on or off , I could fit a bleed back to tank like the engines system , but at this stage I feel its not necessary . The last test was a "step backwards" , but it has illuminated a cause thats easily fixed , I'm pretty confident that the next test will be "the last " :-) I'm fitting a static pressure probe at the NGV throat exit to get an idea of whats happening inside . Cheers John
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Post by racket on Jun 4, 2024 0:30:36 GMT -5
Hi Guys Test this afternoon ................EPIC :-) Lotsa problems getting the A/B to light off , wasted lotsa fuel trying , it would only ignite once I ran the engine at 1.5 Bar rather than the usual 1 Bar , probably because of my 2 parts petrol to 1 part kero , the mixture strength is a tad more fussy . But once alight the engine was performing nicely until I was past 4 Bar P2 when the A/B started sucking air and its fuel pressure dropped away , but I was well past the 300 lbs of thrust point by then . A/B was radiating heat beautifully until the fuel ran out , a 20 ltr drum doesn't last long . Gotta cut more off the 146mm dia A/B nozzle to open it up as TOT temps and P4t still too high. I'll get some video up on Youtube , they'll be a bit longer and more boring than normal due to the troubles, be kind with the comments ;-) youtu.be/yRET5XiYFggyoutu.be/LQkSB9JeOg0youtu.be/AaUrqxNoTSkCheers John
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Post by enginewhisperer on Jun 4, 2024 18:42:19 GMT -5
that's looking pretty good!
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Post by racket on Jun 4, 2024 20:39:10 GMT -5
Hi Andrew
Yep , she was going well until the pumps started sucking air .
I've just cut an inch off the A/B nozzle , opened her up from 146mm to 155 mm dia , ~12.7 % increase in area which should drop my backpressure down enough to keep the temps under control .
The next test will be a full bore run only so that I have time to film all the necessary gauges.
I got a couple of odd numbers from the static pressure probe at the NGV throat outlet, at 2 Bar P2 I had 1 Bar , at 3 Bar P2 it was 1.8 Bar , I simply didn't have time during the last test to film the full throttle reading .
Gotta make up another drum of brew , batteries being charged :-)
Cheers John
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Post by enginewhisperer on Jun 4, 2024 23:09:18 GMT -5
looking forward to the results
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