Paul Carey wrote:
Hi Douglas and Paul
In my discussions with Theo, the Neptune owner who sold me the Power
Turbine, he could talk endlessly about the PT blade design and
material
specs, and from memory he called it a "bucket" design - the blade
can absorb
most of the exhaust gas energy under load (as in - connected to the
engine).
You can see the attached photos of the blades, the angle of attack
and
double wall. The wheel is driven clockwise in these photos.
I wonder how a turbocharger, designed to free rev with no load, will
handle
being direct driven. Will the turbine be able to absorb enough
energy, and
what will the gas path be doing?
Regards PC
Paul Carey LAME, MC
Aero Group Pty Ltd ACN 109 854 015
Aero Management - aviation consultants.
www.aeromanagement.com.au
(08) 9371 5205 0418 959 892
Hello Paul Carey,
Interesting picture. I was just wondering today if anyone had a design
that
could capture most of the rotary exhaust energy. Power Turbine is that
the
company name or product name? Actually I was wondering where to get
some
specs. on how much exhaust gas flow is coming from the Mazda rotary
engine.
We know the area of the ports so if we could measure the hot exhaust
gas
speed then we could calculate the cubic meter/sec at different rpms.
Temp.
would give us density.
How would you use this turbine shown to compound your race engine?
Initially I mentioned to Paul L. that a fool proof way to test the
turbo
compound system would be to have one exhaust manifold with two turbos
connected to it. One to drive the compressor and one to drive the
eshaft
through a power reduction unit if needed or just a magnetic slip
clutch if
the turbo speeds and torque where in the right range. Each turbo
would be
designed and sized for its application and have a throttle valve on
its
intake. Weight and cost were considered to be drawbacks. But then
again
CVT and gear boxes are also heavy and expensive.
This double turbo concept is still on my agenda to test and would
give us
an idea of how far we could push the turbo merits.
This turbo you are showing looks to have some high lift blades and I
would
assume it turns fairly slow. Can you point me toward some
specifications?
I'm curious on why you would mention driving the turbocharger.
Wouldn't that
be the same as a supercharger?
Doug in Japan
What you are looking at here Doug is on of three 300 HP blow down
turbines
normally installed on the CW R3350TC 3800 HP aircraft engine.
Paul Carey, I would try mounting just the turbine wheel direct drive
on the end of the E-shaft nose of the 3 rotor and fabricating some
exhaust
nozzles out of light weight Inconel.
Paul Lamar
On immediate second thought you might get into torsional resonant problems
on the
3 rotor e-shaft due to the weight and rotational inertia of the turbine
wheel.
Probably better to replace the flywheel and mount the clutch on the back
side
of the turbine wheel. Figure out some other way of starting the engine
such
as an electric starter motor and belt reduction drive to the front
of the engine. GM will be doing that soon in the US. Just a few ideas to
kick around.
Paul Lamar
Monty Roberts wrote:
Gentlemen,
Some things to consider:
1) Radial inflow turbines as used for Turbochargers do not have good
characteristics for use as a power turbine. This has to do with the stalled
torque values.
2.) Axial flow turbines are good for power turbines because they have a high
stalled torque and operate like a torque converter.
3.) Turbines (both types) are typically designed to operate with choked flow
through the nozzle.
4.) Turbines (both types) are designed to operate at a given wheel speed
relative to gas flow. The solidity, inlet and exit angles, and airfoil type
are all based on wheel speed and throughput at a given temperature ratio.
5.) All things equal higher wheel speed results in increased performance and
decreased size.
Trying to slow this specific turbine down to the e-shaft speed for direct
drive will not produce satisfactory results. You will have to use a gearbox
to utilize this specific turbine. You will have to match the wheel speed
from the original installation and also the corrected mass flow. If there is
not enough gas flow to result in a positive net torque for transient
operation through a gear box, then the engine will be spinning the turbine
up to speed through the power train. For the turbine to work properly over a
wide range, the nozzle will have to be choked and this may or may not
produce too much back pressure for a race car. It all boils down to testing.
Transient operation involves multiple variables and is probably too complex
to allow a simple mechanical solution to meet all needs. For an aircraft
variable gearboxes will probably prove to be overly complex and heavy. The
power turbine and nozzle guide vane should be sized for cruise conditions at
altitude. Performance at other points will suffer. In a race car, transient
operation is more important, the best compromise will win in each case.
Also keep in mind that inconel is typically limited to about 1850degF
continuous operation. Not sure what materials were available when the
original Wright engine was made. You will have to keep your EGT reasonable
for this thing to last under continuous operation in an aircraft. My guess
is you will have to go to a cooled turbine or one of the newer materials
like MAR-M-$$$$ for aircraft use.
An ambitious project.
Monty
This particular application is a 1/4 mile dragster. The blades ARE air cooled.
This turbine normally runs at 8000 RPM on the Wright so I am a bit worried the
the three rotor will over speed it.
Paul Lamar
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