Turbo Map Interpretation

[TurboTom]

Hi all

I'm currently researching a turbo based design and I'm having trouble interpreting the standard turbo maps. Before you all rip into me, I've done a lot of reading up and I'm just reaching out to the greater community.

On a typical turbine map there is usually mass flow vs pressure ratio and efficiency somewhere on the map as well. What I'd like to know is that at a given flow rate is the pressure before the turbine (p1, given that p2 is atmosphere I assume) caused by the back pressure of the turbine, and therefore you can approximate an exhaust pressure (before the turbine) at a given mass flow rate? Or have I got this completely wrong?

Tom

[TurboTom]

Hi all

I'm currently researching a turbo based design and I'm having trouble interpreting the standard turbo maps. Before you all rip into me, I've done a lot of reading up and I'm just reaching out to the greater community.

On a typical turbine map there is usually mass flow vs pressure ratio and efficiency somewhere on the map as well. What I'd like to know is that at a given flow rate is the pressure before the turbine (p1, given that p2 is atmosphere I assume) caused by the back pressure of the turbine, and therefore you can approximate an exhaust pressure (before the turbine) at a given mass flow rate? Or have I got this completely wrong?

Tom

[Rex Chan]

So, RMIT are thinking of doing a turbo, eh? I think Monash were thinking of going forced induction for 2013 or later. And maybe E85 too.

To answer your question: Sorry, I know nothing about turbos, so will keep my mouth shut. But we do have a Garrett GT12 sitting in the office. Brand new...

[Jon Burford]

There is a lot of info available on the Garrett website regarding the maps. Also try Googling 'selecting a turbocharger'. All the relevant maths shouldn't be there.

Good luck with it.
@Rex. Why do you have a 12?

[Rex Chan]

I think it's from the days of the Wattard engine. We've never run a turbo apart from that engine.

[Jon Burford]

Of course.

[TurboTom]

Rex

Well, I'll leave you to make your own conclusions, but if you come in one morning to your workshop trashed, and the GT12 missing, at least you'll know who it was.

Tom

[Mbirt]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by TurboTom:
What I'd like to know is that at a given flow rate is the pressure before the turbine (p1, given that p2 is atmosphere I assume) caused by the back pressure of the turbine, and therefore you can approximate an exhaust pressure (before the turbine) at a given mass flow rate? </div></BLOCKQUOTE>Yes. As basic as it is, I feel that Corky Bell's "Maximum Boost" does a pretty good job of explaining this.

[Jon Burford]

Agree with Mbrit,
Bell is a good place to start

[bharath supra]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by TurboTom:
On a typical turbine map there is usually mass flow vs pressure ratio and efficiency somewhere on the map as well. What I'd like to know is that at a given flow rate is the pressure before the turbine (p1, given that p2 is atmosphere I assume) caused by the back pressure of the turbine, and therefore you can approximate an exhaust pressure (before the turbine) at a given mass flow rate? Or have I got this completely wrong?

Tom </div></BLOCKQUOTE>
i didn't understand your question fully, may be i don't know much about turbos or you have got it completely wrong.

the pressure ratio of a turbine is the ratio of total pressure at the turbine inlet and static pressure at the turbine outlet.The static pressure at the inlet of the turbine may be equated to the exhaust back pressure in the manifold due to the turbine. And the static pressure after the turbine is not equal to atmosphere as there is some back pressure in the muffler/silencer.
In most of the turbine maps there is no single curve of mass flow vs pressure ratio, instead there are several curves which represent the different speeds of the turbine(60,000 - 2,00,000 rpm). so how can you approximate the exhaust pressure by mass flow rate when you don't know the turbine speed. a smaller turbine spins faster and bigger one spins slower for same mass flow rate.

[Warpspeed]

One big complicating factor with the exhaust turbine is that the flow is going to be nothing like steady state.

The fewer cylinders there are, the worse the pulsing gets, and there is no simple way to predict exactly how a given exhaust turbine and housing is going to perform on a given engine type.

Your best bet may be to just trust Garrett's recommendations for sizing as a starting point, and do some dyno testing yourself.

Sizing the compressor should be pretty straightforward, as there will be almost constant flow. Whatever turbine wheel comes with that compressor should be very close.

The flow side of things should be fairly well sorted out by the initial matching of compressor wheel and turbine wheel by Garrett.

The pressure ratios on the other hand (on both sides) can vary widely, and that is where choosing the optimum exhaust housing area ratio comes into it.

Having to go up or down maybe one size on the turbine housing is not at all unusual and is to be expected. Don't assume that what you have is optimum, until you know for sure the next size definitely is not as good.

[TurboTom]

Thanks all for your help!

bharath supra - What I've understood anyway, is that as a turbine is free to rotate, it should only rotate at approximately one speed at a given mass flow, providing a certain back pressure (hence pressure ratio) and efficiency.

Whilst the static pressure at the turbine outlet will not be exactly equal to atmosphere, for the time being for rough calculations I will assume so until I can get more accurate data, and hence get a rough figure of the static exhaust outlet valve pressure.

As for the problem of pulsing, well for the time being I will assume an infinite plenum (constant pressure & flow) and add an efficiency drop somewhere along the line. Compressor sizing should be reasonably straight forward, but for the time being I'm concentrating on the exhaust turbine and I'll cross that bridge when I get to it

Thanks again
Tom

[Kirk Feldkamp]

Not a lot of time to type out the long answer about turbine calcs at this point, but I may this weekend. Do notice, however, that there are multiple, overlapping speed lines on the turbine map. You will NOT find RPM's on 99% of publicly available turbine maps... but they're absolutely necessary to do a turbine match calculation. The GT12 and GT15V maps provided by Garrett have RPMs, which is awesome. Also important to note is that in reality the turbine efficiency on the lower PR end of the curve is much higher than indicated - mostly because of exhaust pulse effects. People will like to tell you that turbo manifold design doesn't matter... but this is where it does. Also, as RPM's increase, the closer the exhaust flow will approximate steady state. As a side note, compressor and turbine maps are generated on steady state gas stands. The turbine map for the GT15V has the same curves generated for various vane positions.

IIRC, Bell's book doesn't cover turbine sizing in any really formal or technical way. Hell, it does a barely passable job at explaining the compressor side. There are better resources out there...

Warpspeed: Unfortunately, because of the displacement and power limitations of FSAE engines, you really only have a few realistic choices of turbos to start with. Within those choices, there are no available turbine housing alternatives. In other words, these guys have to work with what's available.

[Drew Price]

Awesome reply Kirk (as always), I did not know that the maps were developed from the steady state.

[Warpspeed]

Thanks Kirk, I had forgotten that the very small sized turbos don't offer alternate turbine housings. That makes it far more difficult.

Just to toss a smoke grenade into the discussion, has anyone thought of using a positive displacement supercharger ?

It would seem to offer fewer problems than matching a turbo. It should be far simpler to adjust the drive belt ratio on the dyno for optimum results with the infamous restrictor.

[Jay Lawrence]

Warpspeed, Auckland were supercharged whilst running the 600 a few years back. Was a very fast car. They are inherently simpler (I believe) but are also generally less efficient, which is a sizable consideration these days.

[TurboTom]

Kirk

I'm currently looking at the GT12 turbine map, and it appears as if there is no data for flow rates between 2.5-4.8 lb/min. Is this right? I'm also assuming that the different data points (eg 109423 for example) are the rpm of the turbo at that point

[Mbirt]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mbirt:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Warpspeed:
Just to toss a smoke grenade into the discussion, has anyone thought of using a positive displacement supercharger ? </div></BLOCKQUOTE>University of Washington apparently has. This is from their 2012 build album:http://bfree32.smugmug.com/UWFSAE/Manufacturing/i-ZPmzMCt/0/D/MG8303-D.jpg </div></BLOCKQUOTE>

[Mbirt]

Bump in effort to ignite UW 2012 billet supercharger discussion!

[acedeuce802]

http://www.fmvperformance.com/forum_items/Smileys/default/icon_eek.gif

[Warpspeed]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mbirt:
Bump in effort to ignite UW 2012 billet supercharger discussion! </div></BLOCKQUOTE>
That would be hijacking the turbo thread LOL !!!

Much better to begin a separate supercharger thread for those of us that are really interested. It will also make it a lot easier for anyone in future doing a search.

[Mbirt]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Warpspeed:
That would be hijacking the turbo thread LOL !!! </div></BLOCKQUOTE>This is what happens when you throw a smoke grenade, Tony! Haha.

[turbosupercharger]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">does anyone have a link to University of Washington 2012 build album supercharger?any specs on the blower? </div></BLOCKQUOTE>

[Mbirt]

Mr. TSC,

The UW FSAE albums with the 2012 pictures can be found here: http://bfree32.smugmug.com/UWFSAE

The pictures from their unveiling, assembly, and testing indicate that the car will most likely not be sporting a blower in Nebraska.

http://bfree32.smugmug.com/UWFSAE/Assembly/i-crFF9dV/0/L/IMG9647-L.jpg