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The problem with mounting two turbos in sequence is the "loss" of power during the transition between the smaller and larger turbo.
To avoid the transition problem the smaller turbo should feed the larger one --- with a small leap of logic this requires the two turbo shafts to be mounted concentrically.
So
we have the following....
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The problem with this setup is controlling the inner turbos rotational velocity --- with a small leap of logic this requires a viscous coupling between the concentric shafts. Without a transfer of rotational energy from the inner to outer shaft the smaller turbo will easily spin out of control, destroying the impeller and pretty much everything else...
Ideally the roatational velocty of the outer shaft will converge to that of the inner shaft.
Hmmm
Amended:
The inner and outer shafts will be coupled using an electromagnetic clutch. When current is applied the shafts will be locked together (via the pressure plates). Current will be applied as the inner shaft reaches its operating maximum and the current strength will be modified to increase or decrease the coupling effect as required.
The shafts will be decoupled when the turbo goes "off boost".
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Perhaps this is asking too much of a viscous fluid --- the viscosity needs to increase as the inner shaft reaches its maximum rotational velocity. |
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A better solution has to be a progressive centrifugal brake between the inner and outer shafts. |
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I don't see how your proposed solution solves your stated problem. |
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I suspect the end result will simply be ineffectuality of the first, smaller turbo. |
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Oh well never mind it will come clear. I would have thought the major objections would be to a viscous coupling that operates around 100 thousand rpm.. |
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At that kind of speed, wouldn't air suffice as a viscous coupling? If not, then how about stages of vanes projecting out from the inner, and in from the outer shafts, to increase the coupling effect, and a captured atmosphere of CO2 or some similarly heavy gas. |
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Given the tight radii you're asking from your high-velocity fluid flows, I think whatever losses you might eliminate from the original setup, you reintroduce in this one. If you couple the two turbos together - even in my proposed air coupling, they're going to act more like one big, heavy, laggy turbo. This whole idea looks iffy. Neat concept, tho. |
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Yip --- in a viscous coupling there is always drag placed on the inner turbo shaft. |
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I recently learned that the air conditioning compressor (in cars) is engaged and disengaged using an electromagnetic clutch. This sounds like a better coupling mechanism... |
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So I will amend the idea... |
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turbochargers go through such wide thermal operating ranges and such high rotational speeds, thoughts about improving their efficiancy would do well spent on simplifying them, and making the axels/blades out of stronger/lighter/more temperature resistant material. adding complexity to the existing moving parts will always be a bad idea. note: "existing moving parts" VGTs are cool since they basically change the way the incoming gas hits the turbine. furthermore, any 2 turbos in series will be problematic due to cativation of air resulting in turbo surge, where the blades' inertia causes them to out-spin the air flowing through them (like a very small sonic boom). the system becomes too fluid dynamically complicated. radical thinking is appreciated and can lead to innovative inventions, but i dont think adding any type of weight/restriction to a turbochargers blade-axel assembly could ever do much good. |
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What is the benefit or point of having two turbo's in Series? I think you are following on the line of smaller one for quick spinnup and bigger one for more power, unfortunatly these are not independent variables. they are shared variables of a single component that are inversely proportional to one another. This is one of the fundmental issues with turbos. In general the only benefits come from lighter turbines, reduced drag and increased efficiency. |
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