Subject: Turbo charger HP data
From: ACRE
Date: 1/24/2005, 2:28 AM



This is not exactly what we are looking for but there are
some clues here.

This is from SAE paper 821149 "The Effects of Turbocharger Design
and Installation on Gasoline Vehicles Transient Response" I provided
some of the instrumentation on the R&D reported in this paper.
Note the 20 HP loss in the overall steady state engine net HP out going
from a .63 to a .38 A/R. This is a T3 turbo charger. R, the radius
of the turbine, is fixed and A, the area of the nozzles, is changing.
Basically what is going on here is more back pressure and net HP loss
is being being generated by the smaller nozzle.

Just like electric motors you can get the same HP from a
turbine if you make a small one running at high RPM or a large
one running at low RPM. In this case the weight penalty is less
severe in the over all scheme of things. The larger turbine
will have the same HP loss with the same nozzle area but the
RPM will be less and the turbine torque higher. Consequently turbine
power will be nearly the same. Turbine power is the bottom line
for turbo compounding.

Paul Lamar



BTW Doug I made contact with my old friend at Garret, David Elpern (He is
still
there. Now Honeywell). See SAE paper 821149 The "Effects of Turbocharger
Design
and Installation on Gasoline Vehicles Transient Response". He is working on
gathering
HP data on the turbo chargers but don't hold your breath as that is not what
they
are really interested in. You might have to build a turbo dyno. (Not as hard
as
it sounds.)
Paul Lamar



Here is a chart from Corky Bell's book "Maximum Boost".
For a turbo compound it looks like we need the largest  A/R available for
the  TO4. Checking the 1999 Turbonetics catalog for the 13B that is 1.52
Garrett
part number 407263-0039 Tang Divided (One pipe from each exhaust port).
P-trim with a 2.544 Exducer.

For the RX8 engine with the confused side exhaust system an undivided
A/R = 1.71 should work as well. Garrett part number 407264-0039. P-trim
with a 2.544 Exducer. Big shaft in both cases.

Here too is a clarification on the A/R number. As you move around the scroll
the A/R ratio remains the same.

BTW the A/R as near as I can calculate it for the 88 89 Turbo II 13B
appears to be about .82.


Paul



Thanks for clearing up a few points. Time to search ebay. I'll test the
concept with what I have presently at hand,  the 13B.

..... So if the RX8 doesn't have a better BSFC in mid range and high range
and only gets it's increase in power from higher revs and in the high
powered version larger area of intake ports,  what advantage does it have
for turbo compounding compared to a 13B?

Doug in Japan


I don't expect much from the RX8 engine except perhaps a few hundred degrees cooler
exhaust due to slightly later exhaust port opening and the fact the exhaust is
cooled somewhat better by the cooling system. Slightly more heat lost to the cooling
system and a little less coming out of the exhaust.

If the turbine would live the 13B peripheral exhaust is probably better
for a turbo compound or a turbo charged engine. I could be wrong. There
may be some minor advantages that will swing the balance the other way.

The main advantage of the side exhaust ports occurs down in the
idle and low power ranges of the engines. Mostly emissions.

Paul Lamar


I did a few more calculations on the stock Mazda turbo.
Looks like the turbine wheel is about 3 inches in diameter.
Lets use Francois's number for turbine RPM.
At 130,000 RPM or 2200 RPS the tips are going 21,000 inches per second.
1700 feet per second. Area of the scroll at a radius of 3.5 inches is
about 2.8 square inches. A/R = .8. Two, 2 inch exhaust pipes would have an area
of 6.28 square inches total. The gas velocity in the scroll would then
be about 2.2 times the exit velocity from the 2 inch exhaust port.

According to Scientific Design of Exhaust and Intake Systems exhaust gas velocity
is on the order of 200 to 300 feet per second from a typical four cycle piston engine.
So exhaust gas velocity in the turbo scroll would then be 450 to 670 feet per second.

Obviously the exhaust gas velocity in the rotary is two
or three times that number or one would get no torque out of the turbine.

Not in the ball park.

Another possibility is I am off on the diameter of the turbine wheel.
Lets see, a T3 wheel can be 2.319 or 2.559 inches in diameter. Using the 2.559
number that would bring the tip velocity down to 1470 feet per second.

Still not in the ball park.

Vance this is right down your alley. What say you? Where am I going wrong?
Is the exducer diameter the controlling factor?

How do I figure the exhaust gas velocity knowing the cubic feet of air
per minute going into the engine? (P1 x V1)/T1 = (P2 x V2)/T2 ?

Paul Lamar


If I do (P1 x V1)/T1 = (P2 x V2)/T2  and assume 300 CFM in and 100 F in 
with 1600 F out with two 2 inch pipes in and out I get 1800 feet per second 
out which is in the ball park. I can see how that could be 200 HP coming
out of the exhaust pipe.

Wow that exhaust gas is really moving in rotary engines. About
supersonic at those temps. No wonder it eats steel exhaust systems for lunch.

Check my arithmetic.

Paul Lamar
 
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