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turbo basic design 

 

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 Post subject: turbo basic design
Posted: Thu May 25, 2006 6:29 am 
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i remember reading some post a while ago of an american mustang with the turbo mounted far in the exhaust. it was actually mounted near the boot i think(i cant really remember) but u get the point. so that got me thinking this week about turbo design and problems.
i went and read an article about how turbos work(i already know how they do from long time ago) and it got me thinking. the biggest problem in the system is heat. heat from the exhaust housing causes the compressed ait to heat up which basically is not good for the engine.
so how does the turbo work. the exhaust rushes through exhaust housing and thus turns the turbine shaft which turns the compressor wheel and compresses the air.

well here is my question. it could be stupid but im no expert and couldnt find an answer anywhere to it.
could the turbine shaft be made longer(not by me, just as theory in designing a turbo by a turbo company)? basically this will seperate the two housings. the exhaust housing will be on the manifold will the compressor housing will be say 30cm or more in front. this would probably take more space and the shaft would have to be made stronger, but otherwise is there something from preventing this from happening? imagine this on a turbo i6, where u would have the compressor housing right behind the right handside light with an air intake and heat sheildin between. will elliminate the use or intercooler.
just thoughts and ideas, all theory and nothing to be implemented.
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Posted: Thu May 25, 2006 6:43 am 
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the main thing than is room in the engine bay
most turbo's are compacted to keep heat away from other enigen parts in the bay
IMO

 

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 Post subject: Re: turbo basic design
Posted: Thu May 25, 2006 6:51 pm 
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rawan05 wrote:
i remember reading some post a while ago of an american mustang with the turbo mounted far in the exhaust. it was actually mounted near the boot i think(i cant really remember) but u get the point. so that got me thinking this week about turbo design and problems.
i went and read an article about how turbos work(i already know how they do from long time ago) and it got me thinking. the biggest problem in the system is heat. heat from the exhaust housing causes the compressed ait to heat up which basically is not good for the engine.
so how does the turbo work. the exhaust rushes through exhaust housing and thus turns the turbine shaft which turns the compressor wheel and compresses the air.

well here is my question. it could be stupid but im no expert and couldnt find an answer anywhere to it.
could the turbine shaft be made longer(not by me, just as theory in designing a turbo by a turbo company)? basically this will seperate the two housings. the exhaust housing will be on the manifold will the compressor housing will be say 30cm or more in front. this would probably take more space and the shaft would have to be made stronger, but otherwise is there something from preventing this from happening? imagine this on a turbo i6, where u would have the compressor housing right behind the right handside light with an air intake and heat sheildin between. will elliminate the use or intercooler.
just thoughts and ideas, all theory and nothing to be implemented.


yeah i think that is a really good idea mate. but i think the speed of the wheel spinning adds to the heat too... would be interesting to see if it could work. i dont think it is that big of an issue or turbo companies would work on better cooling. they could definately plumb more cooling lines through/around turbo if it posed such a big problem.
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Posted: Thu May 25, 2006 7:00 pm 
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most of the heat present in the intake charge comes from the basic problem of compressing a gas, it causes the air particles to bunch tighter causing them to vibrate faster, which creates extra heat.... i imagine the amount of time the air spends in the compressor housing is so small it wouldnt have much affect on its temp, as far as heat transfer from housing to air is concerned

 

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Posted: Thu May 25, 2006 7:25 pm 
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ebs_4l wrote:
most of the heat present in the intake charge comes from the basic problem of compressing a gas, it causes the air particles to bunch tighter causing them to vibrate faster, which creates extra heat.... i imagine the amount of time the air spends in the compressor housing is so small it wouldnt have much affect on its temp, as far as heat transfer from housing to air is concerned


I agree, most of the heat comes from compressing the air, think how fast the air would be travelling through the housing, there would be minimal heat transfer.

 

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Posted: Thu May 25, 2006 8:23 pm 
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As the air is compressed it is heated. The engry to spin the compresor turbine wheel (exhaust side) is taken not only from the exhaust gas flow but from the tempture of the gas as well. Temp is energy as well. The heat transfer from the turbine to compressor is not all that great. Also the reason why turbo cars are quite is that sound is also energy and is taken out of the flow hence quiter exhaust niose. The compresor wheel and the turbine wheel are airfoils and if you look very closely you will notice that the areas on the wheel are atually are ventruis same as what is in you carboretor. The simplest way to see how heat is transfered to air when it is compressed is to get a bike pump and pump up a tyre. You will feel the heat in the pump and the line. The reverse wil happen when you let the air out of the tyre on a cold day, you will notice ice appears on the valve stem as it now is the ventrui, as the gas expands it losses all its heat energy and cools to such and extent it forms ice. Hopes this clears it up for you,
Steve

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Posted: Fri May 26, 2006 2:12 am 
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thanks
makes more sense now. cheers for the info.
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Posted: Thu Jun 01, 2006 9:05 am 
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What stevegt is refering to is adiabatic efficiency...or the ability of the turbo to compress air without heating it up.

Anyhow, I thought I might put my 10 cents worth in too.

By extending the length of the turbine shaft you would be adding huge amounts to the rotating assembly weight. You would have so much lag trying to turn the extra weight it would negate the benefit of a few degrees cooler intake charge. You would also need a lot of support bearings to stop shaft whip at 120,000 plus RPM, thus more frictional drag on the shaft and more lag in trying to spool it up. A long shaft would also have greater expansion and would possibly lengthen sufficiently to drive the compressor wheel blades into the compressor housing. The shaft may also suffer from warpage and droop which is typical of turbine shafts when they stop in a state of sufficient heat to allow them to deform under their own weight.

Quite frankly I can't see any benefit. A very good thought though. What you have to remember is that the compressor housing is air cooling itself and huge amounts of air go through it and keep it relatively cool. A spray of water or an intercooler do more than enough to offset any heating of the intake charge by either adiabatic heating or conduction from the turbine.

Hope this sheds some light on it all.

Chris
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