Reading Turbine Maps
Turbo Mini Forums

OK, we seem to have got compressor maps well and truly sorted.

But what about the turbine performance?

Garrett provide nice little graphs of flow against pressure ratio but do not explain how to use them.

For example a typical Turbine Map:
http://www.turbobygarrett.com/turbobygarre...27264turb_e.jpg

So my questions are:
1. Is the gas flow corrected to inlet conditions? or do you need to take account of combustion?

2. Is the pressure ratio across the turbine or the compressor.

3. How do you relate the curve to the turbine speed or the compressor power demand.

I feel that it is important to understand this because in order to get a high volumetic efficiency of the engine, you need turbine inlet pressures lower than the boost pressure. I'm sure that these "Turbine Maps" give the information we need but I'm not sure how to interpret them.

Edited by Paul S on 11th Oct, 2007.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

30 views and no replies!

I've found this:


It shows how you can relate turbine speed and mass flow to pressure ratio efficiency.

Obviously Garrett only publish half the information you need.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

1 view was me, but i'm thick as shit and had no idea, so didnt post.

Another view was me and I am still thinking about it.
Would it not be easier to make a best guess, see what the results are and then change in light of what you found?
It seems we are a bit in the dark regarding the 5 port A series and trial and error on top of an educated guess might be what is needed.
What do you think?
Regards
Dave

Well, I went off to find a link i found, and still haven't found it. Grrrrrrrr.....

So, did you find this picture in a single place, or is there some background reading? I don't know that i've got enough input to make any real assumptions despite the picture.

All I've been doing is comparing how folks with the bigger turbos (the ones who get a choice of three turbines) do with their turbine choice as regards power and drivability for the CC of engine they used.
To be honest, it doesn't answer a whole lot, as folks use GT30's on vtecs and v8's... :(

according to this http://www.owendevelopments.co.uk/turbos/garrett-turbos.asp

1. the gas flow is corrected to temperature and exhaust manifold pressure
2. the pressure ratio is across the turbine
3. not the foggyist!

Thanks for your replies.

The picture came from here:
http://www.turbodriven.com/en/turbofacts/designTurbine.aspx

I've been thinking about this a bit this afternoon.

The power required to drive the compressor is a function of the mass flow, pressure differential and adiabatic efficiency.

This power has to be provided by the turbine with a mass flow, pressure differential and adiabatic efficiency.

Given that the efficiencies are similar, 70% ish, unless the mass flow changes through combustion, then the pressure ratio has to be higher - which is not good for high VE.

So I need to know about combustion! Good job that my youngest is doing A Level Chemistry. If I can get him off the playstation, I'll try to get him to explain.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Well, he says that there is no mass change though combustion.

What I've missed above is temperature - of course :$

The turbine is driven by flow through a nozzle. This converts pressure and heat energy into kinetic energy that drives the turbine wheel.

The expansion through the nozzle, from high to low pressure follows the same laws as compression, but in reverse. So instead of a temperature rise you get a temperature drop.

If you start off with a high temperature, you get a higher temperature drop and this then contibutes to a higher energy conversion.

So it is highly likley that the pressure drop is less than boost unless the nozzle is too small.

How I can convert the above into anything useful is still puzzling me.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Hi,
I was going to say it's not rocket science, but having read this post it's not that far off
Cheers,
Gavin :)

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Just been looking in to this and found a good thread about the subject here:

http://www.dieseltruckresource.com/dev/sho...ad.php?t=168543

Thanks.

That looks useful. I'll study it later.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

http://www.owendevelopments.co.uk/turbos/garrett-turbos.asp

This has some useful formulae for correcting turbine flow as well.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Yes probably, but yours will be correct lol

Actually, I reckon that guy on the diesel truck forum has got it wrong.

That's why I was struggling because I could not get the same answers as him.

He's not using the Ideal Gas Law correctly - I think.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I don't think he is allowing for pressure? he states

"let's say that there's no backpressure in the manifold or that it's negligible."

I think thats where the difference lies, although I could be talking crap because there are so many numbers and scribbles in front of me right now

I've come to the same conclusion.

His numbers are correct if you do not correct for the pressure ratio.

But he is dealing with very low boost pressures and presumably low back pressures.

If you start to increase the pressure ratio, to anything like we are running then it makes a significant difference in the corrected gas flow.

I still don't know what I'm going to do with this information, but I don't like unknowns.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Sooo, how wrong would i be to say that running too rich under boost, has the effect of not creating as much pressure at the turbine due to lower exaust temp, thus increasing lag to an extent??

and would that create a less steep curve on a diagram?
basic i know, sorry!
regards
colin

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

yes indeed,
im very slow at typing and had further refined my last response, but not beforew you got back, as in my last two posts went together, and didnt get timt to respond to you.sorry
so to your previous post i would agree indeed, and my thoughts on the rich mix v temp was before your chart, which i would also agree with. to the theory anyway, the adjustment of the figures is what im trying to get around at the monent.
regards
coln

But surely running rich would increase the initial flow figure due to the fuel content? Maybe enough to ofset the cooling effect?

A rich mix could increase that 10.1 by almost another 1lb/min surely...?

First let me say I know nothing about turbine maps. But if I look at the curve shown and using Paul's numbers, does that mean that the turbine becomes a significant restriction at 4000RPM and that either the wastegate has to start opening or the backpressure will increase?

Does it also mean that the wastegate should be opened above 4000RPM if backpressure increases regardless of the intake pressure because the turbine won't flow more anyways? If so, then would it make sense to control the wastegate from both the intake and exhaust pressure?

I'm sorry if I'm completely off track but I'm just trying to make sense of this.

Jean

http://www.jbperf.com/