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Location:
Sydney
Registered:
July 2002
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Compound turbo
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Tue, 15 July 2003 07:12
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Does anyone have any info on "compound turbo"s? Not one turbo blowing into another, but a turbo with a belt driven supercharger on the front of it.
I think a lot of war planes used to have them. I know they also used to have a lot of twin-charged systems with a turbo blowing through a supercharger then into the inlet.
Can anyone tell me why they aren't done? If you could have a belt driven and exhaust driven turbo, then you could make the belt driven part give a lot of boost low down (a lot of gearing) and the turbo part to give a lot of boost at the top end (big exhaust turbine).
As for disengaging the supercharger as the boost rises from the turbo, it could be left on and produce positive energy directly onto the belt as well as pushing through more air.
I understand its a pipe dream, but surely someone has played around with the idea, and has some pics and info on the web.
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Location:
c'town, NSW
Registered:
May 2002
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Re: Compound turbo
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Tue, 15 July 2003 07:53
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sounds interesting..
but dont turbos spin at very high rpm so wouldnt the belt driven part only be able to spin 'only so fast'?
so wouldnt the belt part run out of puff in a matter of milliseconds being overtaken by the speed of exhaust gasses and be hardly anymore better than a well matched normal turbo setup?
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Location:
c'town, NSW
Registered:
May 2002
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Re: Compound turbo
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Tue, 15 July 2003 07:57
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hmm i spose u could gear the belt system, also there might be a possibility with this to be able to load the turbo before you launch the car.
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Location:
Ipswich
Registered:
July 2002
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Re: Compound turbo
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Tue, 15 July 2003 08:16
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why not use the compressed air from the supercharger instead of exhaust gas to spin the turbo?
Don't know if that is possible or makes sense.
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Location:
Brisbane
Registered:
October 2002
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Re: Compound turbo
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Tue, 15 July 2003 08:31
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but until the sc is making the same pressures as in the exhaust, wouldn't the exhaust gas back up in the inatke of the SC
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Location:
Sydney
Registered:
July 2002
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Re: Compound turbo
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Tue, 15 July 2003 08:37
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You can let the supercharger overboost, like what a twin-charger setup does.
And yes, pushing the supercharger more is not an issue as you definately need to gear it properly, similar to a centrifugal supercharger.
Just need a supercharger that is geared down low, but can take bigger rpm than its max boost.
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Location:
Brisbane
Registered:
May 2002
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Re: Compound turbo
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Tue, 15 July 2003 23:31
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The whole idea of a twincharge setup is to eliminate the inefficient supercharger at high rpm, when the far more efficient turbo takes over. Having a supercharger spinning past its efficiency range is going to sap a lot of power for no reason!
I gave a lot of thought to this idea a few years ago, and here's what I came up with. Consider a normal turbo setup, but with a positive-displacement supercharger pushing air into the turbo inlet. When the turbo spools up, a clutch disengages the supercharger and an air bypass opens so the turbo isn't trying to draw air through the supercharger. All the advantages of a turbo but without any lag!
It would be complex to set up and difficult to make the transition smooth, but I reckon that's the best compromise. So, anyone wanna try it? 
As for "compound turbos", that usually means two or more turbos joined in series. The idea is to get huge boost pressure without overspeeding a single turbo. I've never heard of it being used on anything but large diesels though.
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Location:
Sydney
Registered:
July 2002
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Re: Compound turbo
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Wed, 16 July 2003 00:05
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That would probably be better with a roots positive displacement supercharger. But a clutch would definately be needed.
But again we're getting back to the twin-charger discussion.
What about a mini gearbox inside the supercharger side of it? If you can get 2 or even 3 speed transmissions for 1/10th scale remote control cars, then its possible they can be that compact.
Do centrifugal superchargers have an efficiency rpm or an efficiency boost pressure? If you could build one that could keep spinning but not produce any extra boost (what does a supercharger do outside its efficiency range?)....
I'd imagine the power curve to be similar to Norbie's twin turbo curve, unless you got the supercharger/turbocharger matched up just right.
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Location:
West Aust
Registered:
October 2002
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Re: Compound turbo
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Wed, 16 July 2003 01:14
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There was a rolla in Hot 4s Dec 1999 that had a blower/turbo setup. It allowed him to use the blower off the line and a really big turbo with heaps of lag for up high.
Kev
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Location:
Sydney
Registered:
July 2002
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Re: Compound turbo
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Wed, 16 July 2003 01:15
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Yeah that was another twin-charger setup.
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Location:
was adelaide now newcastle
Registered:
February 2003
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Re: Compound turbo
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Wed, 16 July 2003 02:31
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i think it was mazda that used a weird setup on one of their deisel engines, it was called a pressure wave supercharger and acted as an exhaust powered supercharger, but also had a belt on the front of it, since i have only ever seen the actual unit and not the engine that it originally came from i cant tell you much more, you may see some of these things at jap import wreckers.
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Location:
Madrid - Spain
Registered:
August 2002
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Re: Compound turbo
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Wed, 16 July 2003 03:28
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As far as I know, there was never a compound charger fitted to an aircraft engine and I can't see why it would be needed. Sure some engines are fitted with turbo or super chargers but not both.
Aircraft forced induction has a different goal than automotive ones. In cars, they are used to increase power. In aircraft, they are used to maintain a particular power level at different altitudes. Lag is not a consideration as they are generally run a constant RPM.
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Toymods Club Treasurer
Location:
Sydney
Registered:
May 2002
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Re: Compound turbo
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Wed, 16 July 2003 03:28
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HKS made a turbo kit for the 4AGZE which came with controllers to disengage the factory superchargers clutch once the turbo spooled up, and an AFC.
The supercharger though had to blow through the turbo's turbine side, then through the factory intercooler, throttle, etc.
I think BD4's fitted it up as a trial, but it cost about $10 to buy the complete kit.
Been toying with the idea of adding a supercharger to my turbo diesel, to give it some punch between 1400rpm and 2200rpm while the turbo is still spooling up. It stills takes a lot of gas to make 13psi.
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Location:
Brisbane
Registered:
May 2002
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Re: Compound turbo
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Wed, 16 July 2003 03:53
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| HKSPete wrote on Wed, 16 July 2003 10:05 |
What about a mini gearbox inside the supercharger side of it? If you can get 2 or even 3 speed transmissions for 1/10th scale remote control cars, then its possible they can be that compact.
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Now we're getting pretty complex! It could be done but such a transmission couldn't be too compact when you consider the amount of power it has to deal with. The blowers on drag V8's require 100's of hp to turn at max power; obviously a normal road car wouldn't be that extreme, but we're not talking trivial amounts of power either.
Some manufacturers are experimenting with electrically assisted turbos, which is a much neater solution. Basically a high-rpm electric motor sits on the shaft of the turbo, and keeps the turbo spinning when there isn't enough exhaust gas to do the job. I'm not sure if there are any such units in production yet, but there's a bit of info on TurboDyne's web site:
http://www.turbodyne.com/
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Do centrifugal superchargers have an efficiency rpm or an efficiency boost pressure? If you could build one that could keep spinning but not produce any extra boost (what does a supercharger do outside its efficiency range?)....
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Centrifugal superchargers develop boost as an exponential function of rpm. If you overspeed them, boost goes through the roof!
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Location:
Canberra
Registered:
June 2003
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Re: Compound turbo
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Wed, 16 July 2003 03:56
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I looked into this and ended up with a system like Norbie described. I even made up the plumbing in PVC pipe to see if it was doable. The hardest part would be getting a smooth transition from SC to turbo. You would have to run the SC until the turbos air needs overcame what the SC could provide...more a case of flow than boost. A bit of dyno time would sort it out but pretty fiddly. With the new generation turbos they have these days it's just not worth the effort....anyone want the SC12 i have in the shed?
Pete - as for the turbo providing positibve gains to the belt once it takes over?? It just doesn't produce the torque to have any worthwhile benefit.
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Location:
Sydney
Registered:
July 2002
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Re: Compound turbo
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Wed, 16 July 2003 07:12
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| gold28 wrote on Wed, 16 July 2003 13:28 |
As far as I know, there was never a compound charger fitted to an aircraft engine and I can't see why it would be needed. Sure some engines are fitted with turbo or super chargers but not both.
Aircraft forced induction has a different goal than automotive ones. In cars, they are used to increase power. In aircraft, they are used to maintain a particular power level at different altitudes. Lag is not a consideration as they are generally run a constant RPM.
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http://rwebs.net/avhistory/opsman/geturbo/geturbo. htm
about halfway down is a great diagram
http://www.enginehistory.org/installations.htm
more good diagrams on this one
http://www.wpafb.af.mil/museum/engines/eng68.htm
nice airplane engine image on this one.
There are a heap of others. Thats where the compound turbos (one blowing into another) first came about - in aircraft. Which is also the same place that superchargers were born, and maybe turbos as well (not sure on turbos).
Norbie: If the RC cars can take 2hp through a 3 speed transmission that is less than an inch long, surely it can be scalable.
Electrically assisted turbos is still on my idea of a combined turbo supercharger. The rest of the ideas are still stuck on the twin-charger idea.
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Location:
Finland
Registered:
November 2002
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