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Post by madpatty on Jul 14, 2020 0:58:17 GMT -5
Hello All, So I recently got my hands on a "BIG??" sized jet engine that is supposed to make ~160 lbs of thrust at full throttle. The unit uses hybrid ceramic ball bearings so startup should be relatively easy. BUT it is having difficulty to start. The details about the engine are as follows- Compressor Inducer- 100mm Exducer- 148mm Turbine (Standard Holset HX82 shaft) Inducer- 129mm Exducer- ~111mm Flametube Outer diameter- 183 mm Inner diameter- 65mm Outer wall Length- 70mm (The NGVs have a curved outer-wall to which outerwall attached to thats why it is shorter) Inner wall length- 70mm Holes (Before modification)Primary RegionDome region 39 x 4mm holes 39 x 3.2mm holes Outer wall 12 x 5mm holes Evaps 8 x 10mm bores Secondary ZoneOuter-wall 15 x 5mm holes Inner wall 8 x 6mm holes Tertiary zoneOuter-wall 30 x 7mm holes Inner-wall 16 x 9mm holes Problems1. Startup problemsI am using a leaf blower to start the engine.Its a gas start unit so first you have to light the startup gas and then slowly ramp up the starter power along with the fuel till the engine self sustains. The flame doesn't seem to remaining inside the flame-tube and most of fuel seems to be burning outside the turbine with long flames shooting out of the back. As a result the engine does not accelerate any further. So my initial thoughts were the primary zone is not able to HOLD the flame during the startup and thus most the liquid fuel is being blown out through the nozzle. This made me change the startup procedure a bit. this time preheat gas was lit off without almost any air flowing through the engine and then the blower along-with fuel was ramped up. This SUCCESSFULLY STARTED the engine up. 2. HIGH EGTThe engine seemed to be running fine BUT the egts were extremely high, in range of 900-1000 degrees celsius. THE CATCH HERE-Now at 1000 deg.C the turbine is mostly glowing almost yellow BUT in my case it was nowhere near that and wasn't even showing any colouration. I know the turbine colour is not a good indicator of exact EGTs BUT 1000 degrees C and no color is sure as hell a good observation. MY OBSERVATION- As in previous unsuccessful startup attempts I noticed liquid fuel being blown out the back, methinks some amount of liquid fuel is just escaping the combustion chamber and just burning in the nozzle after the turbine thus registering insanely high egts. Modification Made
After the previous observations, I thought maybe adding a bit more air to all the zones should help and by the way these zones were way off of JETSPECS that many of us have successfully followed. So I added extra holes to primary and secondary zones and also enlarged the tertiary zone holes. Holes (After modification)Primary Region Dome region 39 x 4mm holes 39 x 3.2mm holes Outer wall 48 x 5mm holes Evaps 8 x 10mm bores Secondary Zone Outer-wall 30 x 5mm holes Inner wall 8 x 6mm holes Tertiary zone Outer-wall 30 x 11 mm holes Inner-wall 16 x 9mm holes Problems AgainStartup problem exacerbated Now the fuel is totally burning out of the engine. The Engine won't accelerate at all no matter what I do and how I light the preheat gas. Adding any fuel shoots big long flames through the back. Some engine pics attached- Before hole modificationAfter hole modification
ANY help is appreciated or prior such experience if anyone can share. Thanks. Patty
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Post by racket on Jul 14, 2020 4:28:04 GMT -5
Hi Patty LOL........so you're the one who purchased it off Ebay , its been there a while. OK , its very similar to my 9/94 engine www.youtube.com/watch?v=8Y8jpaDTkEY , 9 inch case with a TV94 comp ( 98 mm inducer) ., now in Andy's bike jetandturbineowners.proboards.com/thread/385/gasturbine-second-quarter-drag-bike?page=16The reason for the lack of hole area in the flametube was to increase the pressure drop across the wall, and along with that , increase turbulence because they were having combustion problems. The cross sectional area of the flametube is reasonably OK. The vapouriser tubes are my concern , you mention 8 X 10 mm ID , so lets assume thats 12mm OD .................how long are they, what shape ?? Theres might not be sufficient surface area for heat transfer, I work on at least 6 X inducer area. Flow area at 8 X 10 mm dia is ~8% of inducer area , I like to be closer to 10-12% and prefered to use 3/8" OD tubing so that the surface area to flow area ratio is better for heat transfer , theres 18 tubes in the 9/94 engine at ~ 90mm long . I'm also concerned about the Tertiary hole positioning as the distance from front wall back to the Tertiary holes is shorter than I used as my holes were basicaly over the NGV . A few more pics please , so we can find a solution and get her fired up :-) Cheers John
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Post by madpatty on Jul 14, 2020 6:35:05 GMT -5
Hi Racket. Since you mentioned "they were having combustion problems" that makes me ask, Were you a part of the design process for this engine by any means? Do you have any other background on the engine? I did a quick calculation and their initial overall hole geometric area at just ~55% of inducer area implies rather large Pressure loss at about ~10% through the combustor. The evaporator are straight type and 40mm long each. There a small metallic piece welded inside the evap to prevent the fuel from directly shooting down the evap. The injector needles have opening towards the side so that fuel exits perpendicular to length of the evap and impact its side. Here are the few more pictures, hopefully that will help Regards.
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Post by racket on Jul 14, 2020 17:08:28 GMT -5
Hi Patty Thanks for the extra pics . Nope , had nothing to do with this engine , but made my comment based on the fact that the hole area was so small. At 40mm long those evap tubes will only have ~1.5 inducer areas of heating surface ............not enough , thats only a quarter of what I use , there'd be virtually no evaporation of the fuel in that time/distance , if you look at my 100 mm long tubes ibb.co/k0sDHp1 the first half is barely coloured despite being immersed in the hot gases going over into the NGV whereas yours are mounted in a "cool corner" of the flametube. Also the 10/98 flametube jetandturbineowners.proboards.com/attachment/download/7 had more combustion distance between the front of the FT and the dilution holes which gave a tad more time for combustion to be completed before things were "chilled" and combustion ceasing . I'm assuming the engine is fitted with a standard length turbine shaft , unlike a lot of the "micro" engines using turbo turbines where the shaft has extensions to increase combustor length, is this the case ?? Who made the engine ?? What fuel are you using ?? What sized leafblower as a starter , it'll need one with ~3 HP simply to get sufficient airflow rate , my leafblower was only marginal for starting with its 26cc motor A pic of the 9/94 flametube cheers john
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Post by madpatty on Jul 14, 2020 19:47:25 GMT -5
Hello Racket. Yup i seem to agree with you on the evaporators design. BUT at this point I won’t be able to change it unless I totally discard this combustion chamber and make a new one. YES, it uses a standard HX82 shaft without any modifications. I am using High speed diesel Mixed with 5% 2T oil for bearings. The leaf blower that i am using is a 32cc unit and the fact that It was able to successfully start the engine twice ,before I changed the hole area and ran into combustion problems, makes me think that leaf blower may be good for the job. While I don’t have enough history on this engine but i was told that it was made by Microjet Engineering UK which means it’s a Phil Heward design. Also I think this engine can work in its present configuration because there’s an exact same engine working like a charm in this video here- youtu.be/7po10b9ulIkRegards.
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Post by racket on Jul 14, 2020 20:18:34 GMT -5
Hi Patty
Diesel probably not the best fuel to use , not volatile enough , mix 2 parts petrol to 1 part diesel might work better , that more like I use in the 12/118 , 2 petrol 1 kero, the diesel won't burn quick enough .
Yep , blower should be up to the job.
Thats Rob O'Brien ( Obilaser) I use to correspond with him , I think he said Garrett turbine and Holset comp for the 150 lb engine , 90mm jet nozzle and 74,000 rpm
Cheers John
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Post by madpatty on Jul 14, 2020 20:50:49 GMT -5
Hi Racket.
Yup Robert,O Brien at Obilaser.
I think I read at some forum that he is or was at some point a US representative so that’s why.
Mine is a HX82 shaft similar part number to what Andy M is using in his “Money Pit” engine.
What do you think about me going back to original configuration on the combustion chamber holes( that is reducing the hole are) and then test run with 2:1 petrol diesel mix?
Regards.
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Post by racket on Jul 14, 2020 23:56:30 GMT -5
Yep , I'd recon that would be your best solution at this point of time, at least it fired up with those holes , just need to get the combustion happening a bit quicker and some petrol should help there , the flametube undoubtedly needs the higher pressure drop to work, not ideal , but necessary .
Cheers John
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Post by madpatty on Jul 16, 2020 22:40:57 GMT -5
Hi Racket. So I went ahead and reduced the flametube hole area. BUT the question was how small is too small. To test that I drilled slightly smaller holes that the “original” configuration hole diameters. The configuration tested was (~52% inducer area as compared to original ~55% inducer area)Primary Region Dome region 39 x 4mm holes 39 x 3.2mm holes Outer wall 12 x 4mm holes ( originally 12 x 5mm holes) Evaps 8 x 10mm bores Secondary Zone Outer-wall 15 x 5mm holes( same as original) Inner wall 8 x 6mm holes Tertiary zone Outer-wall 30 x 6.6mm holes ( Originally 30 x 7mm holes) Inner-wall 16 x 9mm holes ResultsThe engine did start in the first attempt itself. BUT the temperatures are higher than the original configuration. Observations and further testing One thing is for sure that this engine needs smaller hole area to work successfully BUT how small is the question. The recent test shows there’s a sweet spot for combustion at ~55% inducer area “Maybe”. I am thinking of getting the hole sizes to exactly as original configuration and test again so that atleast I can replicate the original performance. what do you think racket? Regards.
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Post by racket on Jul 16, 2020 23:20:46 GMT -5
Hi Patty
Did you use your orginal diesel fuel or the petrol/diesel mix for this latest test ??
I wouldn't think a 3% difference in hole area would make much difference , all it would do is slightly increase the pressure drop and/or maybe decease the mass flow a tad .
When you say , "The engine did start" .............what P2 or RPM did you achieve??
Have you tried checking the thermocouple for accuracy ?? ...........perhaps add another thermocouple and thermometer at the jet nozzle exit to get a "second opinion" .
What diameter is your jetnozzle ??
Cheers John
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Post by madpatty on Jul 16, 2020 23:41:46 GMT -5
Hi Racket.
The P2 was about 7 psi. Can't go higher because of high EGTs.
The thermocouples are matched/tested with 4 different ones that I have. Fuel is original diesel. Idea is to make 1 change at a time just so that we can characterize the engine behavior.
Jet nozzle is ~89mm diameter.
Regards.
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Post by racket on Jul 16, 2020 23:48:39 GMT -5
Hi Patty
Should be OK at 7 psi .
Thermos crossed off list .
Same fuel.....same problem :-(
Jet nozzle about right .
Yep , change the fuel and see what happens
Cheers John
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Post by madpatty on Jul 17, 2020 0:01:15 GMT -5
Hello Racket.
At this point I am also inclined towards changing the hole area to "original" and then do another test just so that I can replicate the original performance. Reason being the exacerbated problem with this new reduced hole area. Then test it with the new Fuel mix as well. We will have two datasets to compare too otherwise the doubt that this engine maybe too sensitive to any hole area change still remains.
Further to your theory of using fuel/petrol mix, There's one thing that I noticed in today's test. At some point when i turned off the starter gas during the startup fuel appeared to be not burning too efficiently inside the combustion chamber as flames were being shooting off of the back but as soon as I started injecting some "starting gas" inside the primary zone flame sort of rescinded inside the chamber and engine spooled up.
Fuel has some problem burning in the primary zone is my observation.
Ideally I want to do 3 tests at this point.
Test 1- Change the tertiary area to origin al and test with normal diesel. Test 2- Change the primary area to original so that we are in original hole area configuration and test. (original performance should be back) Test 3- Test NEW FUEL mix.
What are your thoughts on this testing sequence.
Regards.
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Post by racket on Jul 17, 2020 0:38:25 GMT -5
Hi Patty
Yeh , I'll go along with your 3 test route , the more data the better .
Interesting that the extra start gas coaxed the engine into life , I tried similar with the 12/118 by installing multiple propane injectors around the outer wall at the Primary Zone to produce a "flame bed" across the FT front wall that the evap tubes discharged into , results were inconclusive , my "air caps" were a better solution along with the petrol/kero mix instead of just straight kero
Cheers John
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Post by madpatty on Jul 19, 2020 6:34:26 GMT -5
Hi Racket.
I did 3 tests snd the results are as follows.
Test 1(Changing Tertiary Zone flow area) Modification- Opening up the 30 tertiary zone holes from 6.6mm to 7mm diameter(original config.)
Results- Immeasurable change in performance as expected because hole area didn't change much.
Test 2(Changing Primary Zone flow area) Modification- Opening up the 15 primary zone holes from 4mm to 5mm diameter(original config.). Now the combustion chamber is at same config. as when NEW.
Results- Improvement over the previous test run. Temperatures came down a bit but still in 900's deg C. I think it's very close to original performance as when engine was new. Still very small visible flames coming out of the nozzle
Test 3(Fuel mix 2 part gasoline and 1 part diesel) Result- Temperatures went slightly up. I would not consider this fuel mix a helpful in my case.
The behavior of this engine has responded best to change in primary zone hole area. At this point I am tempted to increase the primary zone hole area slightly. Like changing hole diameter from 15 x 5mm holes to 15 x 6mm holes BUT some suggestions before going that route will be really helpful.
My idea for this change is maybe there's some kind of a "BELL CURVE" with hole area. We know too much area is bad as from previous tests. Too little is bad either.
How do we know 5mm holes are best. Maybe there's a sweet-spot somewhere.
At this point I am also certain that the combustion chamber design is the main culprit BUT before going for full redesign I will want to better optimize this combustion chamber. Other reason is, Since this is company built engine I would expect it to run a LOT better with current configuration whatsoever. I definitely doesn't look to me an engine unit made by a noob with it's CNC machined parts etc.
Regards.
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