Turbo Compressor/Turbine Map Requirements

[brophyb]

With Turbo Mapping, I know that standard turbo maps for the compressor are readily available for a given turbo unit i.e. from the manufactures. I know that these maps show the relationships between the mass flow of the gas (air) to the pressure ratio of inlet to outlet for at a given shaft speed and compressor isotropic efficiency.
My question is this: Has anyone ever seen the matching turbine maps for a given turbo unit, with the same set of parameters, i.e. mass flow pressure ratio for a given shaft speed and turbine isotropic efficiency.
If so, where can I get this information for a specific turbo?

I have seen the Garrett catalogue but the turbine maps don’t refer to the shaft speed or efficiency.

Can anyone help me with this or point me in the right direction?

Cheers
Barry

 

[Warpspeed]

I doubt if it can be done. Compressor maps are only made possible because standard inlet conditions are assumed.

With an exhaust turbine there is no such thing as standard inlet pressure and temperature, or even steady flow. So under what inlet conditions would you specify your turbine map ?

 

[gtsim]

Hi Warpspeed,

This can be done, and in gas turbines we normally plot compressor and turbine maps on a non-dimensional basis (i.e Mach numbers). A good text for such maps, are Gas Turbine Theory and Gas Turbine Performance, where turbine and compressor maps are described in detail.

Best wishes,
gtsim

 

[Warpspeed]

I am surprised, because changing the engine air/fuel ratio or ignition timing can have a fairly dramatic effect on exhaust gas temperature when running under full load.

Even though mass flow may be known, enthalpy certainly will not. Down stream conditions from the turbine (exhaust back pressure) can significantly influence the whole deal as well. Some fairly extreme exhaust pulsing from the engine can result where there are very few cylinders feeding the turbine, and the turbine is close to the cylinder head.

I would be surprised if one simple turbine map could cover all possible operating conditions for a particular turbine.

 

[gtsim]

Yes indeed, one map can describe the performance of a turbine. We plot the non-dimensional flow (W*(RT/Gamma)^.5)/P vs Pressure ratio for a series of turbine non-dimensional speeds (N/(RTGamma).

W=mass flow rate
T=Temperature
R = is the gas constant
Gamma=cp/cv
N=Speed

When we do this the map is unique (for high Reynolds numbers – turbulent flow).
We need the fuel-air ratio to determine R and Gamma. Give a fuel-air ratio the enthalpy can be calculated. We do this all the time in gas turbine calculations and simulations. In turbines and in particularly axial types, the non-dimensional mass flow becomes constant after a pressure ratio of about 2 on 3 (depending on the number of stages) and the speed lines generally collapse into a single line (choked nozzle guide vane). You can check out the references I gave in my previous response, which discusses the performance of both compressors and turbines in details including the maps.

I don’t understand the point about he pulses. As long as we have the pressure ratio we can use the type of map discussed. I thought there is some type of air box to dampen out these pulses (particularly in large engines)?

Best wishes,
gtsim

 

[Warpspeed]

While an industrial or aeronautical gas turbine may be an almost steady state device, a turbocharger most certainly is not. The whole purpose of a turbo in a vehicle is usually to improve acceleration.

That is probably the most significant difference. A turbo has to rapidly accelerate during the transition from almost closed throttle to wide open throttle. How quickly it can do that has a more profound effect on the vehicle than just steady state thermodynamic efficiency.

One of the factors is how much pipe volume there is between the engine exhaust valves and the turbine. Exhaust pulsing is a very important factor. Split pulse exhaust housings and special manifolding can make a very significant difference to practical turbine performance. And it is the actual performance under rapid acceleration that is vitally important, particularly in the lower gears.

An optimum design that runs successfully at full constant load on an engine dynamometer, may be an absolute disaster under transient load conditions on the road. Such factors as rotational inertia and pipe volumes become extremely important.

 

[gtsim]

All gas turbines, both aero and industrial, have to accelerate and decelerate quite rapidly, especially fighter aircrafts (including the affects of afterburners). We again use these characteristics (maps) for compressors and turbines to simulate the transient performance (dynamic simulation) include the affects of volumes, which is of paramount importance in predicting the transient performance of these engines.

Please note there is noise and therefore pulses in a gas turbine, but they are somewhat difference to that of reciprocating engine or compressor.

Best wishes,
gtsim

 

[Tmoose]

I think the design guideline for factory turbo exhaust manifolds is thick walls and short runners and mount the turbo RIGHT THERE.

Porsche did it this way on the early 911s. The box surrounding the individual pipes is to capture warm air for the heater.

http://www.pelicanparts.com/911/911_Parts/1978-83/2-2.JPG

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Volvo 4 cyl turbo exhaust manifold here.

http://wwwrsphysse.anu.edu.au/~amh110/all_gifs/Turbo page gifs/Garrett_fr.jpg

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Some Volvo ex manifold here

http://wwwrsphysse.anu.edu.au/~amh110/all_gifs/Turbo page gifs/Mitsub_man.jpg

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Porsche Cayenne turbo engine here. Items 10 and 11 are the ex manifold and turbo.

http://www.panix.com/~clay/cayenne/engine.html

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saab turbo manifold here

http://www.petestacticalknives.com/Image Expert Images/Vito/Exhaust-man.jpg

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Another Volvo turbo on exhaust manifold

http://sp3ak.tunkeymicket.com/cars/volvo/volvo_turbo2.jpg

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2 shots of older Saab turbo manifold here

http://www.thesaabsite.com/900new/20050423f.Turbo_studs.jpg

http://www.thesaabsite.com/900new/20050423m.Manifold.jpg

 

[turbomotor]

Garrett and Borg Warner typically use a hot gas stand to develop and map the turbine (expander) stage. The IC engine, do to the pulsating nature of the exhaust flow, drives the expander differently. (See Watson et al "Turbocharging the Internal Combustion Engine".)

For the above reasons, the turbine (expander) map is not as useful in matching the stage to the IC engine requirements, unless one applies experientially derived adjustments to the steady-state gas stand map.