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
Monty.
I understand your points well. Thanks for bringing them up for everyone. It
has occurred to me (and Paul is way ahead of me on this) that we would need
to compromise performance on the turbo compound side even with a special
oversized turbine and some sort of gearing. Logically two turbines as
described above would be a good way to test the turbo compound concept
limits. It would give us an idea of much power can be recovered from the
13B. without choking the engine. I believe a moderately boosted turbo
charged Renesis engine should put out about 300Hp near 7900 rpm. 55%
cruise power means 165hp. and 4345 e-shaft rpm. with a lot of exhaust energy
still available. If our power turbine can pick up even a paltry 10 ft./lbs
of torque at this low end range and transfer it at 90% efficiency, that
would mean we'd have an additional 10.8 hp. I would be happy.
If we can pick up 35 ft./lbs like Paul L. suggested at 90% transfer
efficiency we would have about 38 Hp increase in power. Paul would be so
happy he wouldn't sleep at night:) The heavy Renesis engine would suddenly
be a possible choice for pilots desiring a 300hp engine that would have a
better BSFC than the Lycoming IO540. We aren't re engineering the engine
per se. I would like to think we are just mining the waste.
I would be ecstatic to find a small power axial turbine designed to work
well in the 40 to 50K rpm range or even 10K faster. Monty if you could
point me to a source for turbines in this range I would be grateful. We
could get easily get a 10:1 reduction (300mmų down to 30mmų) with belts
and a large pulley, or a motorcycle chain and sprocket mounted where the
flywheel is now. I agree with you that we would have to match rpms and that
can be done using a rather new but seemingly simple technology and very
basic electronics.
Go here for details. http://www.magnadrive.com/
The units as shown are to heavy. We would have to redesign the clutch and
perhaps arrange the magnets in a different polar configuration for more
attraction but less slippage. Simply explained; the mag./clutch is designed
to slip from 100% down to about 3% by varying the gap between the magnets
and the copper conductor. The input power rpms are always larger than the
output rpms. in its intended design applications. However this might get us
into trouble or be a benefit in our application. Have to test it. Torque
stays the same though.
The micro toroid CVT. is our other option for matching rpms as well as
being a disconnect clutch, affording wider range of turbo speed ratios
rpms., and perhaps a few other goodies. I am now designing a few variations
of this device on paper.
This work is approaching a bench test on certain parts. Paul is busy
spinning gears and planning Hollywood stunt work while I am playing with
colored pencils and magnets:)
Doug in Japan
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