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Post by paulthepilot5 on Jan 8, 2021 5:56:30 GMT -5
Hi, everybody.
Starting a turbo based turbine build on a Borg Warner turbo (probably sx200) and De Haviland Goblin combustor.
I have a few basic questions.
Is there a optimum size ratio I should be looking at with regards to compressor and turbine and turbine housing A/R.? Or is this a not so critical aspect?
If I want to predominantly use the turbine for a bleed air supply what other considerations should I look into? My understanding is bleeding off air will increase TIT/TOT accordingly dependant on volume, perhaps a larger compressor sizing compared to turbine, or smaller turbine housing would be more ideal considering?
Thank
Paul
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Post by racket on Jan 8, 2021 15:16:15 GMT -5
Hi Paul
The A/R of the turb stage is important especially when taken in conjunction with the turbine wheel size compared to the comp wheel size .
If you want to do a bleed air arrangement then you'll need an "oversized" comp wheel , the final arrangement will depend on just what you are wanting to achieve ................more info please .
Cheers
John
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Post by paulthepilot5 on Jan 9, 2021 5:26:39 GMT -5
Thanks for the quick reply. The overall plan is to use the turbine and it’s compressor in a turbine compounded engine, a small 2.8L turbo diesel. Bit of a wild idea but I’m happy to experiment. Pretty much using turbine compressor as the atmospheric stage on a compound setup, and making use of turbine exhaust to through a Venturi to help scavenge and reduce back pressures. This diagram gives a rough schematic of what I have planned, with some intercooling and valving omitted.  One of the turbos I was looking at was the borg Warner s200 series. Compressor: 51mm inducer, 77mm exducer. Turbine:70mm inducer, 56mm exducer. I’m not particularly set on sizing, I most likely need a bigger turbo for what I have planed. But will at least get the auxiliary systems and control setup running as a stand alone turbine and work from there. |
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Post by racket on Jan 9, 2021 16:52:30 GMT -5
Hi Paul
Is there a particular application for such a complicated setup ??
What are you trying to achieve ??
Hope the lockdown isn't causing you too much hassle , only another day to go :-)
Cheers
John
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Post by paulthepilot5 on Jan 9, 2021 17:23:41 GMT -5
Hi Paul Is there a particular application for such a complicated setup ?? What are you trying to achieve ?? Hope the lockdown isn't causing you too much hassle , only another day to go :-) Cheers John Hi John, lockdown is not a problem, gives me more time to build things 😆 Basically trying push as much power out of the little 2.8 diesel which I do a bit of drag racing with. already has a compound turbo setup on it. Was playing around with Antilag systems and ideas. The idea of running the atmospheric turbine came up purely because it would remove majority of the drive pressure from the engine exhaust, much less pumping losses through the engine and lower engine EGT, meaning more fuel can be injected. Has the potential to get s significantly more power out of the engine without as much thermal load (EGT,s and melting pistons is the biggest limitation to the fueling I can run. Plus it will be an interesting project thanks Paul |
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Post by racket on Jan 9, 2021 19:34:48 GMT -5
Hi Paul
OK , drag racing ............so not concerned about fuel burn rates , only making more horsepower, that simplifies things .
A diesel needs maximum boost with minimum exhaust backpressure to maximise expansion ratio within the cylinders , so get rid of the "turbocharger" and only have the "gas turbine" , but that will limit your potential peak boost level compared to your two stage system .
What boost are you currently running ??
I can see where you're coming from with the ejector exhaust , the "turbo" could run a larger A/R turb scroll ( lower backpressure) and still have the same pressure ratio across it to power its comp
Cheers
John
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Post by paulthepilot5 on Jan 9, 2021 22:02:21 GMT -5
Hi Paul OK , drag racing ............so not concerned about fuel burn rates , only making more horsepower, that simplifies things . A diesel needs maximum boost with minimum exhaust backpressure to maximise expansion ratio within the cylinders , so get rid of the "turbocharger" and only have the "gas turbine" , but that will limit your potential peak boost level compared to your two stage system . What boost are you currently running ?? I can see where you're coming from with the ejector exhaust , the "turbo" could run a larger A/R turb scroll ( lower backpressure) and still have the same pressure ratio across it to power its comp Cheers John I do want to retain the smaller turbo for some drivability only intending the turbine to be for short duration runs. I won’t get the pressure ratio with just the turbine, going to be running around 45/50psi psi I have some revised designs that keep it as a compound turbo/turbine utilising both turbos for higher P/R, will also mean functionality with turbine. Again intercooling is omitted from drawings. The idea of a scavenging Venturi could also be utilised.   |
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Post by racket on Jan 9, 2021 23:32:40 GMT -5
Hi Paul
Yep , I can see it as doable, getting the valves syncronised and the turbo matching just right, will be a challenge , not for the faint hearted .
Cheers
John
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Post by paulthepilot5 on Jan 9, 2021 23:50:40 GMT -5
Hi Paul Yep , I can see it as doable, getting the valves syncronised and the turbo matching just right, will be a challenge , not for the faint hearted . Cheers John My thinking is if there is a check valve flap style arrangement on the engine exhaust side and also in the compressor-combustor pipe the timing should be less critical. Im thinking I may not need to control the bleed air to engine, If I’m running a larger than optimum compressor and don’t have that air bleed off through the engine it might drive compressor into a surge condition. |
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Post by racket on Jan 11, 2021 15:50:17 GMT -5
Hi Paul
Yep , surge is going to be the big problem .
You mentioned a boost of 45-50 psi , is that the maximum you'll be running ??
If it is , why not only have a single stage setup ??
Cheers
John
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Post by paulthepilot5 on Jan 12, 2021 5:14:32 GMT -5
Hi Paul Yep , surge is going to be the big problem . You mentioned a boost of 45-50 psi , is that the maximum you'll be running ?? If it is , why not only have a single stage setup ?? Cheers John Given the small displacement of the engine, getting that PR isn’t really doable on the smaller size turbos I need to get any kind of performance down low. Not a great deal of RPM range to play with in a diesel, peak torque at 2600, peak power at 3600 and dies off after that 4250 red line. Getting boost on early before 2000rpm is pretty important to get the most out of peak torque of the engine. Any turbo big enough to manage that PR efficiently is too big to be usable. I’m not necessarily limiting it to that boost, I do want some headway to go further if need be if I can get the fueling required. cheers Paul |
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Post by paulthepilot5 on Jan 12, 2021 5:38:47 GMT -5
Just doing some really rough calculations, probably around 40-45 lb/min mass flow through the engine at 40boost pressure and max rpm. I’m thinking that is quite a large amount to supply from bleed air probably outside the scope of a turbocharger based turbine, what do you think?
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Post by racket on Jan 12, 2021 18:46:51 GMT -5
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Post by racket on Jan 12, 2021 19:14:34 GMT -5
Hi Paul
You don't need a fancy ball bearing turbo , just a regular cheaper "brass bush" one , it'll need to be pretty big , 98mm plus inducer , the bigger the better as your bleed will represent a smaller fraction of total flow .
The "average" Garrett turbo has an "undersized" turbine stage suitable for wastegate operation , but for your application it'll not be needed as your mass flow through the turb stage will be reduced by your bleed .
45 psi of boost won't be a problem with a large turbo, and at reasonable efficiency .
Cheers
John
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jetric
Veteran Member
Joined: December 2014
Posts: 149 
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Post by jetric on Jan 12, 2021 21:54:31 GMT -5
Hi John/Paul, The gas turbine air producer engine that was used in the manic beatie was manufactured by a UK company that was called TTL (turbine technology limited) and used the core (including bearing housing) from a Holset Hx82 turbo with a bespoke vaned compressor and turbine housing and a tiny combustion chamber. Personally I would use a microturbo saphir gas turbine air producer to produce the 45psi of boost pressure that you require as this engine will flow more air bleed volume than the TTL engine and is also more compact, Both types of engines are available from my pal at jetenginetrader.co.uk Hope this helps, Richard S. |
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