This one is interesting. It has only been a few
years that these
papers have been declassified and placed on the
internet.
420.Turner, L Richard Desmon, Leland G Performance
of blowdown turbine driven by
exhaust gas of nine-cylinder radial engine
naca-report-786 1944
Engine power at sea level was only decreased by 1%
while the power out
of the turbine was an additional 9% of engine power.
The altitude performance is stunning! At an ambient
pressure of
10" Mg the turbine is generating about 115 free HP
with no increase
in fuel burn. The basic engine has lost no HP. This
is a 22% gain
in HP with no increase in fuel burn. That means the
BSFC of a
current Mazda rotary engine would go down to about
.37 from
about .47. Even better on the RX8 engine.
The total HP of a current Mazda 250HP RX8 rotary
with this feature
would be about 305 HP with an unprecedented low
BSFC.
As a light plane engine this combination would have
no equal
in the world today. Range would increase by by
about 22% for
the same fuel load. Best of all, without the worst
failure mode of
all the early turbo compound engines. Namely exhaust
valve failure.
This with a turbine RPM of 75% of its redline or 56%
of max blade stress.
Obviously not yet optimized at this very early stage
of development.
Paul Lamar
Jim Mederer wrote:
Hi Paul,
Yes, this is quite interesting. However, a couple of
points...... The RX-8 engine probably couldn't run
continuously at peak power due to the high RPM -
probably around 8000 ~ 8500 - and I have been told
that egt is near recip engines, limiting exhaust
energy. For compounding, peripheral exhaust might be
better - if the turbine materials will take the
temperature.
Jim Mederer
Good to hear from you Jim.
It is also good to hear that the RX8 exhaust temp is now down near recip
levels as we are having a hell of a time getting the 1700 F exhaust
to live at aircraft power levels. The lower temps will help
the turbine live in a tubo compound configuration.
This particular failure resulted in damage to this very expensive
and nicely made aircraft when the broken exhaust overheated the
fuel system and the aircraft made an off airport landing.
I don't think anybody is considering using the RX8 engine at
8500 RPM in an aircraft. Even for take off. That would require
a gear reduction ratio even greater than the 2.85:1 we are now
considering switching too from the current 2.17:1. Probably
7500 RPM will be the top RPM used for the foreseeable future in
aircraft applications.
BTW I got to drive the RX8 on Friday at the Automobile test day with
Don Sherman in Fontana. Got it up to 100 MPH in the parking lot :)
Real sweet. Picks them up and lays them down :) I am shopping
for a good deal.
It needs a slightly bigger rear sway bar. A cockpit
adjustable one would be a first on a street car. Also the rear
rubber suspension bushings need tuning as you get a bit of chatter
when you drop the clutch at 5000 RPM. IMHO it also needs a super
charger to get a bit more squirt off the line. I am hoping you are
working on this kind of stuff already :)
Paul Lamar
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