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Post by azwood on Feb 21, 2018 13:47:38 GMT -5
John, please explain your "tight" turbine scroll comment. My understanding is for our DIY turbines we want the highest A/R (largest doughnut) to give us maximum power. I understand that the turbine scroll flow factor must be compatible with the compressor trim. If the turbine scroll flow factor is too low it will force the compressor into surge. If the turbine flow factor is too big it will result in a choked compressor. If one has a factory turbocharger the turbine scroll should be compatible with the compressor trim. My hot side is a ar128 |
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Post by racket on Feb 21, 2018 14:36:25 GMT -5
Hi Azwood
Thats a nice matching of wheel sizes , turb exducer area ~20% bigger than comp inducer , potential for a ~1.5 lbs/sec flow and 90 HP from a suitable freepower turb stage .
Cheers
John
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Post by racket on Feb 21, 2018 15:02:02 GMT -5
Hi Ron
Nope , most of the Garrett range of "automotive" turbos have undersized turbine wheels that require a wastegate to be fitted to a SI engine exhaust to prevent overboosting the engine , these turbos are unsuitable for us to use .
The diesel CI engine turbos are a better proposition as they generally run high boost levels , but they have "cold" exhaust gas temps with less energy so the turb stage is generally a free floating type without wastegate , this minimises backpressure and maximises fuel efficiency .
A bit of a history lesson .............my Garrett TV84 came off a 475 HP Detroit Diesel engine , turb wheel 110/96 mm , there were 4 turb scroll housings available a 1.23 , 1.39, 1.60 and a 1.84 , I tried all 4 housings at various times , I started with the 1.84 , it was too big and the comp choked , the 1.60 was better and I probably should have tried the 1.39 before I got to the turb exducer and removed a fair chunk of it because it was choking .
After the "surgery" on the exducer , the 1.60 was far too big , the 1.39 was still a bit too large allowing the comp to flow into the less efficient regions , but the 1.23 was "just right" , it kept the comp flow under control whilst producing the right turb wheel power to drive it .
In hindsight the 1.39 scroll with the unbutchered exducer would have been the right combination , with a more even split of pressure drop/s across the stage .
When I talk about a "tight" scroll, I'm indicating a size that would hopefully choke and keep the comp flow under control when the turbine wheel is "oversized" with regards its potential flow .
Diesel turbos come in a huge range of configurations depending on the engine manufacturers requirements , a large number have oversized turb wheels for a gas turbine conversion , though this could be compensated for by the use of water injection to "fill out" those oversized passageways with steam whilst increasing power .
Cheers
John
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Post by azwood on Feb 21, 2018 16:04:20 GMT -5
Hi Azwood Thats a nice matching of wheel sizes , turb exducer area ~20% bigger than comp inducer , potential for a ~1.5 lbs/sec flow and 90 HP from a suitable freepower turb stage . Cheers John That's more power than I thought I'd get.thanks John for you help what a great forum this is no haters just good people that like jets awsome. |
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Post by azwood on Feb 21, 2018 16:45:55 GMT -5
Hi Ron Nope , most of the Garrett range of "automotive" turbos have undersized turbine wheels that require a wastegate to be fitted to a SI engine exhaust to prevent overboosting the engine , these turbos are unsuitable for us to use . The diesel CI engine turbos are a better proposition as they generally run high boost levels , but they have "cold" exhaust gas temps with less energy so the turb stage is generally a free floating type without wastegate , this minimises backpressure and maximises fuel efficiency . A bit of a history lesson .............my Garrett TV84 came off a 475 HP Detroit Diesel engine , turb wheel 110/96 mm , there were 4 turb scroll housings available a 1.23 , 1.39, 1.60 and a 1.84 , I tried all 4 housings at various times , I started with the 1.84 , it was too big and the comp choked , the 1.60 was better and I probably should have tried the 1.39 before I got to the turb exducer and removed a fair chunk of it because it was choking . After the "surgery" on the exducer , the 1.60 was far too big , the 1.39 was still a bit too large allowing the comp to flow into the less efficient regions , but the 1.23 was "just right" , it kept the comp flow under control whilst producing the right turb wheel power to drive it . In hindsight the 1.39 scroll with the unbutchered exducer would have been the right combination , with a more even split of pressure drop/s across the stage . When I talk about a "tight" scroll, I'm indicating a size that would hopefully choke and keep the comp flow under control when the turbine wheel is "oversized" with regards its potential flow . Diesel turbos come in a huge range of configurations depending on the engine manufacturers requirements , a large number have oversized turb wheels for a gas turbine conversion , though this could be compensated for by the use of water injection to "fill out" those oversized passageways with steam whilst increasing power . Cheers John I'd like to learn more about water/meth injection on jets I use it on my turbo bike |
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Post by racket on Feb 21, 2018 19:11:42 GMT -5
Yep , we don't tolerate anyone who disturbs our peaceful Group ...........we're here to enjoy ourselves and help one another.
Water/alky can be a help in a hot dry environment , but theres a limit to its uses at the "front end" , but water can be injected into the combustor to increase mass flow , which then means less pressure drop required through the turbine stage and more pressure/energy downstream for thrust/HP production .
I never tried water/alky injection on my turbocharged bike ............there wasn't much room for it .
Where are you based ??
Cheers
John
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Post by turboron on Feb 21, 2018 20:16:39 GMT -5
John, your comments are very helpful. They explain why a couple of the Garett T4's I bought have T3 compressor wheels with a T4 turbine. They seemed like a strange combination until I received your comments. I think this is the first time the group has been told that you can have a turbine scroll that is too big. You usually just say it should be 20% bigger now we know that there is a sweet stop in a area range about 20% larger than the compressor inducer. The idea is to choked (reach sonic velocity) in the turbine scroll rather the turbine wheel. I think in an axial turbine you want the turbine IGV to choke and control the flow.
Thanks, Ron
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Post by azwood on Feb 21, 2018 20:58:20 GMT -5
Yep , we don't tolerate anyone who disturbs our peaceful Group ...........we're here to enjoy ourselves and help one another. Water/alky can be a help in a hot dry environment , but theres a limit to its uses at the "front end" , but water can be injected into the combustor to increase mass flow , which then means less pressure drop required through the turbine stage and more pressure/energy downstream for thrust/HP production . I never tried water/alky injection on my turbocharged bike ............there wasn't much room for it . Where are you based ?? Cheers John Cool I'm in the Yarra valley Victoria Australia |
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Post by racket on Feb 21, 2018 21:19:52 GMT -5
Hi Ron
Theres some strange combinations out there .
Probably ideal to choke the scroll throat from a comp output point , but from an efficiency direction maybe a bit of scroll and a bit of turbine wheel expansion , but as we want to run our engines at highish power settings the turbine inducer tip is going kinda fast so we pretty much need a choked nozzle to produce sufficient velocity to keep up with the blade once the inlet radial velocity is added to the vectors .
The 1.84 A/R "fat doughnut" on my TV84 really was FAT , the flow passageway increased in area once past the rectangular inlet port in the mounting foot , the velocity produced at the scrolls throat wouldn't have been as fast as the turb tip , most of the turb power came from the choked exducer deflection ................heh heh , I soon fixed that when I cut 1/2" axially off the exducer at the tip and 1/4" at the root , the wheel was unchoked and producing minimal power so I had to go to a "tight" scroll with high velocity gases to restore power.
I had a frustrating scenario happening , the choking of the exducer matched the comp flow nicely , so even with that fat doughnut in place the engine ran relatively OK without excessive T2 temps , thrust didn't change much despite changing scrolls and even jet nozzle sizes , it didn't behave as the theory books said an engine should , but once the exducer was unchoked , it did .
So yes , a turb exducer area ~20-25 % larger than the comp inducer area , and a reasonably tight A/R , ...............A/Rs get a bit confusing because they aren't really a size/area , we can have the same A/R "number" but with very different actual throat areas as it depends on the "R" , which depends on the size turb wheel which in turn dictates the scroll dimensions., we might have say a !.23 A/R on a 60 mm turb wheel and on a 120 mm turb wheel , but flows will be massively different .
Cheers
John
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Post by racket on Feb 21, 2018 21:24:49 GMT -5
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Post by azwood on Feb 22, 2018 0:37:30 GMT -5
Great I'm not for from there I'd like to see more jet bikes I mean what's better than jet turbine bike😂 |
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Post by azwood on Feb 22, 2018 0:38:35 GMT -5
I like to add one to the collection lol  |
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Post by racket on Feb 22, 2018 3:03:58 GMT -5
An interesting collection ;-)
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Post by azwood on Feb 22, 2018 17:38:43 GMT -5
An interesting collection ;-) Thanks |
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Post by azwood on Feb 22, 2018 17:42:05 GMT -5
Been on a few sites that calculate flame tube dimensions and get different answers on the holes.tube size said 164mm
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