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Old 05-28-2008, 10:17 PM   #1 (permalink)
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Turbo to drive accessories?

Just a hairbrained thought.

Does anyone know how much power it takes away from your engine to drive a turbocharger? and what RPM you can start making usable power with them? I looked briefly for that but all I've come up with is efficiency numbers of the turbo itself. My idea is to use a turbo to drive the accessories via a pulley attached directly to the turbo instead of using the crank itself. You wouldn't actually use it to compress air back into the cylinders, simply to drive the accessories with exhaust gas and possibly make the engine more efficient through the elimination of the parasitic loss of the accessory belt. I say this is hairbrained because I know you have to spool up a turbo to get it to do anything, but maybe you can redesign the vanes to operate at different speeds and also not to compress the air, but rather turn a pulley... Just a thought. Opinions?

Edit: although the increased backpressure in the system, combined with the low revs that one would use in a FE driving application, may make the combustion diluted with exhaust gas, therefore lowering power output of the engine.

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Old 05-28-2008, 10:42 PM   #2 (permalink)
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Seeing as a turbo is powered by your engines waste, rather than off the crank itself, I dont think they draw any power from the engine. The power band depends on the turbo. A smaller turbo will spool quicker, if not off idle, and will make power right away, but will choke out in the upper rpms where the turbo cant flow enough air to keep up with the engines needs. Or you have have a big turbo that takes its time to spool up and pulls as far as your engine will take it.

I *dont* really see a turbo being "strong" enough to turn the accessories. Theyre made to move something "light" like air. Plus the tension from the belt would probably wipe out the bearings or bend the shaft right away.
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Old 05-28-2008, 11:10 PM   #3 (permalink)
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Good point with the bearing load being a definite fallback. I think one would have to be designed strictly for this purpose. But then again you're probably right about not being strong enough. I think that it would strong enough at its peak RPM, but at the low RPM's the engine would be turning, I don't think the exhaust velocity would be great enough to make much happen.... Meh, if someone can come up with idea that isn't already integrated into a car these days, there's usually a good reason the car manufacturers haven't already done it. Although OTOH, the cost vs. FE table is starting to swing in favor of FE more and more everyday so maybe some of these ideas aren't so bad.
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Old 05-28-2008, 11:59 PM   #4 (permalink)
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Turbos spin at over 100,000 rpm's. You would have to reduce it with a gear box. I don't think it will work but its a good thought!
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Old 05-29-2008, 10:33 AM   #5 (permalink)
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You could definitly do this and it has been worked on before. I forget which company was doing research into this, but there was a company. I suggest googling if you are interested. Using a gearbox to reduce rpms you could easily run an alternator.
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Old 05-29-2008, 10:57 AM   #6 (permalink)
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I heard about a company developing a turbo alternator. I'm not sure if they brought it to market yet.

The idea of driving the entire accessory chain with a turbo has some merit. If you use gears, the only the shaft with the big gear has a lot of bearing load from the belt. A planetary gear set could be used to neutralize bearing load on the turbo shaft. That way the forces on the gear translate into pure torque instead of a lateral force against the bearing. Also, you could use the waste gate to keep the accessory chain spinning at a constant speed, or reduced if you wish.
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Old 05-29-2008, 02:22 PM   #7 (permalink)
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Part of this already exists, as an APU
You would want to graft piping from the exaust thru the hot side of the turbine, and remove/seal up the cold side compressor componets. The problems might be the size of existing, inexpensive surplus units. You would also want to thermally insulate all the exhaust piping till you get to the APU, becuase you are acutally using the heat energy of the exhaust gas, not just its velocity.

http://www.users.zetnet.co.uk/gas/gtp30.htm
http://www.users.zetnet.co.uk/gas/lucas.htm
http://www.gasturbine.pwp.blueyonder.co.uk/newpage.htm
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Old 05-29-2008, 07:32 PM   #8 (permalink)
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Effort would be better invested in removing the accessory train than shifting its power source.

A turbo-driven accessory belt is going to be a pain to design and build. I don't mean to be a naysayer, but that time will see bigger returns by losing the alternator, A/C, water pump, and oil pump and going electric.

If you want to drive something with the turbo, send the energy back into the engine. You'll need a slip clutch, sprag clutch, and reduction gears. It has been done since WWII to great effect. Improving the efficiency at the top of the chain will yield more results than improving efficiency somewhere along the middle.

It feels like this forum is starting to cycle. I remember talking about these ideas months ago, and reading them half a year ago on GS. There needs to be a booklet or something...

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Old 05-29-2008, 08:42 PM   #9 (permalink)
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What about using a Stirling heat cycle engine instead? You could take the waste heat from the exhaust to power the engine.

I've also seen something about thermal electric generators being able to do this as well, just not as efficient.
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Old 05-29-2008, 09:10 PM   #10 (permalink)
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Quote:
Originally Posted by Daox View Post
You could definitly do this and it has been worked on before. I forget which company was doing research into this, but there was a company. I suggest googling if you are interested. Using a gearbox to reduce rpms you could easily run an alternator.

I probably should have searched google first. There is actually a company that makes them already it seems. I never would've thought to search "turbo alternator" and actually see results. They say they are for diesels, but I'm going to contact them anyway and see what they say. All I was thinking of running was my alternator anyway because I've seen the results of others who have went alternatorless and have seen pretty substantial gains.

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