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Post by racket on Oct 4, 2017 16:01:05 GMT -5
Hi Matt LOL, doesn't that tell you something about the best design to use , the good old "sore thumb" combustor is the best, I've seen some of those pretty fluid dynamic tests of right angled bends, not nice But having said that, because you'll be needing a large combustor of at least 9-10" dia positioned over a pretty large comp scroll housing , the bend going into the turb scroll can be of fairly large radius , you'll need to have the combustor axis in the same axis as the rotor so that the gases enter your turb scroll without bias to either side of the NGV stator. Theres a couple of my large vapouriser engines on site here for you to checkout jetandturbineowners.proboards.com/thread/40/2-shaft-turbine-kart-buildjetandturbineowners.proboards.com/thread/78/garrett-gt6041-powered-kart the GT6041 isn't flowing much less than your turbo , a 10% scaleup of the combustor would be adequate Cheers John |
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mjb777
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Joined: September 2017
Posts: 22 
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Post by mjb777 on Oct 4, 2017 21:47:51 GMT -5
Yes it certainly does say a lot about the sore thumb config John, I knew I was walking into that response! haha I was thinking that the large 5" or so diameter, large radius 90 degree feed to the turbine housing would minimise losses in the turn, and am thinking hard about the 5" compressor housing to combustor housing ducting and interface to minimise bends and losses at that end to help make up for it. There is beauty in symmetry so you bet the combustor will be right down the engine center line! The center entry turbine housing works out well.  I checked out your build threads and they have the juices really flowing now, and plagiarism is running amok! To reduce the complexity and diameter of the combustor a bit, is it appropriate to reduce diameter and increase length to maintain the same combustor volume? Also I would be keen to keep manufacture simple and use a parallel walled flame tube, with a cone at the end to match the turbine housing feed pipe, over your large diameter and heavily tapered design used for the GT60 engine? Matt. |
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Post by racket on Oct 5, 2017 1:20:54 GMT -5
Hi Matt
LOL........Copying is the sincerest form of flattery ..............go for it ..................I've never been shy to copy shamelessly ;-)
DO NOT SKIMP ON FLAMETUBE/COMBUSTOR CROSS SECTIONAL AREA ............it CANNOT be compensated for by adding length ..................you will need at least a 7.2 - 7.5" dia flametube in the Primary Zone to reduce air speeds for combustion to be stable, you're going to be flowing massive volumes of air, it needs a big area to slow down in , 3 times inducer area is my ratio for the flametube cross section , it could be reduced a tad , maybe 10% , but any less than that and you're on your own , I've see too many "skinny" flametubes that have given, at the very least, nothing but combustion troubles to the engine builder, worst case scenario is generally a dead engine from flames going through the turbine wheel and cooking it :-(
Those skinny flametube failures by guys on the Yahoo DIY Gas Turbine Site led to the creation of Jetspecs
Cheers
John
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mjb777
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Posts: 22
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Post by mjb777 on Oct 5, 2017 2:13:13 GMT -5
It certainly is the highest form of flattery! Anyone copying me will be copying a copy!  Current version of Jetspecs output for combustor flame tube dimensions and hole size and number is appropriate? Matt. |
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Post by racket on Oct 5, 2017 2:34:02 GMT -5
Hi Matt
Because you want to use vapouriser rather than a single spray nozzle , theres some differences with flametube wall hole sizes/placement in the Primary Zone , Secondary holes are also affected though Tertiary are "standard" .
Jetspecs will give you some "generous" dimensions , these can be "massaged" a bit to reduce size.
Cheers
John
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mjb777
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Posts: 22
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Post by mjb777 on Oct 5, 2017 5:24:34 GMT -5
Okay that makes sense with the additional air that will be arriving through the vaporisers I'm guessing? I think I'll heed your advice and stick with the Jetspecs flame tube dimensions as closely as I can or perhaps even increase volume to compensate for the displacement of the vaporiser assembly. I'll see what I can read from your example vaporiser can pics as far as adjustments to hole position etc are concerned. Thanks so much for all your input so far John. Time to go over my thoughts on paper all over again and then it'll be materials ordering time! Hope you won't mind me bugging you further downrange....... Matt. |
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CH3NO2
Senior Member
Joined: March 2017
Posts: 455
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Post by CH3NO2 on Oct 5, 2017 9:42:53 GMT -5
.... Hope you won't mind me bugging you further downrange....... Matt. John probably wont mind. He puts up with me blowing up his PM's with countless questions too. 
I may be able to help you a bit here. I highly recommend you go to Johns profile and read just his posts. You, we, can learn a lot by doing this. Since you are thinking about vaporizers this is what I have found by reading John's various forum posts. Evaporator flow area should be ~10% of the the Primary zone flow area. Then make the vaporizer tube total heated surface area ~6X the compressor inducer area. Do this and you will have a working evaporator system. John has made it vastly easier for us n00bs to get started. Tony |
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mjb777
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Joined: September 2017
Posts: 22
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Post by mjb777 on Oct 5, 2017 13:09:10 GMT -5
.... Hope you won't mind me bugging you further downrange....... Matt. John probably wont mind. He puts up with me blowing up his PM's with countless questions too.
I may be able to help you a bit here. I highly recommend you go to Johns profile and read just his posts. You, we, can learn a lot by doing this. Since you are thinking about vaporizers this is what I have found by reading John's various forum posts. Evaporator flow area should be ~10% of the the Primary zone flow area. Then make the vaporizer tube total heated surface area ~6X the compressor inducer area. Do this and you will have a working evaporator system. John has made it vastly easier for us n00bs to get started. Tony Thanks a bunch Tony! I am very grateful for the vast amount of knowledge and support here, and also the fact that the sheer numbers of guys who also enjoy this pursuit means I'm not that abnormal after all! haha Those numbers for the evaporator are great and very much appreciated! I hope you realise that you have just been placed on my "people to pester" list! Matt. |
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CH3NO2
Senior Member
Joined: March 2017
Posts: 455
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Post by CH3NO2 on Oct 5, 2017 15:42:15 GMT -5
LOL! I think our persuit of making turbines means we are very abnormal! I'm a n00b too but I'll help any way I can. Tony |
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Post by racket on Oct 5, 2017 15:57:37 GMT -5
Hi Tony
I have to correct your "10% of Primary air" figure , thats incorrect , it should be "total hole area ".
For the "walking stick" type vapourisers I used ~15% due to their poor "aerodynamics" from the 2 right angle bends , I use the 10% for our "straight through" ones in our "micro" type engines.
For the GT6041 I used 0.75" OD tubing of 0.050" WT , ID of 0.65 " , area 0.33 sq ins , with 6 of, it comes in at ~2 sq ins of inlet flow area ,or 15% of the 106mm inducer area, first axial arm 110 mm long , radial arm 70 mm , and third arm 55mm
The flametube wall has Primary holes adjacent to the vapouriser outlets , 2 for each , there are other holes positioned to produce as much turbulence/recirculation as possible .
Matt
I'd suggest you try and source Inco tubing rather than the stainless I had to use , Smithy found a couple of the 6 vapourisers had failure of the tubing , which was unexpected as every endeavour was made to provide as much symmetry of components as possible to minimise any bias of airflows etc etc , all we could put it down to was poor quality tubing in a couple of the vapourisers even though they were all made from the same length of material.
The GT6041 flametube would work on your engine though with a tad more pressure drop , a slight scaleup of the diameter/s is all thats required for your 10% greater airflow .
Cheers
John
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mjb777
Member
Joined: September 2017
Posts: 22
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Post by mjb777 on Oct 5, 2017 22:34:22 GMT -5
All noted guys! Excellent stuff!
I have sourced and tig welded Inconel material before and definitely agree that it would be a good idea to make the vaporisers from it. Id hate to have one of the tubes or material going through my nice big NGV and turbine.
Matt.
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ripp
Veteran Member
I'm sorry, I don't speak english, so I torment you (and myself) with a translation program,Sorry
Joined: January 2013
Posts: 237
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Post by ripp on Oct 6, 2017 1:19:44 GMT -5
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mjb777
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Post by mjb777 on Oct 6, 2017 7:00:18 GMT -5
Thanks Ralph, I hope I can build my engine to some of the KJ66 type, and "turbo" type engine builders standards! A good percentage of the point of this is to have another gleaming addition to my noisy fuel consuming man cave art collection...... John, Would the 10 - 15% of the total flame tube holes area used for calculating the vaporizer tubes area then be subtracted from the area of holes required in the flame tube, specifically the primary holes, due to the fact that there is additional air being delivered into the flame tube primary area via the vaprisors? Or would the vaporiser tube area be an addition to the calculated required flame tube holes area total? Matt. |
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Post by racket on Oct 6, 2017 15:59:30 GMT -5
Hi Matt
Yep , that 10-15% vapouriser area is part of the Primary Zones allotted 30% of total hole area , its the equivalent of the ~10% that would go through the air swirler surrounding a single spray nozzle.
The GT6041 flametube was a 50% scaleup of the Tv84 flametube used in the 2 shaft kart , 6 vapourisers instead of 4 , mass flows were ~2.75 lbs/sec vs ~1.8 lbs/sec , so a lot of the Primary and Secondary holes were of similar size , just 50% more of them , I looked at the 6041 flametube as having 6 segments , each segment was treated as a "flametube" with regards trying to get good air/fuel presentation/mixing for each vapouriser discharge .
I've looked around for any written info I have on the build but can't seem to find anything , I must have simply "made it" .
LOL...............I thought I'd better check my pile of drawings just in case , and there she is , a plan drawing of the setout of the vapourisers and a drawing of the flametube sidewall with all the "small" holes , guess I wasn't too concerned about the layout of the Tertiary holes in the top of the tapered section.
Cheers
John
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mjb777
Member
Joined: September 2017
Posts: 22
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Post by mjb777 on Oct 6, 2017 18:16:35 GMT -5
Makes perfect sense! Thank you. Glad you found the drawing. Bet it brought back some memories! Guess I'm approaching the hard bit now, for me anyway...... Waiting to be able to really get into this!!!... Am still overseas on this current work rotation and looks like I won't be back home until November. Blah! Good thing eBay never sleeps and I'll get into the new calcs and do some drawings for you all to cast your experience over. Matt. |
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