One can screw around with injectors and intake heat until one is blue in
the face but one is wasting ones time. Unburned fuel is a very small part
of
the overall efficiency loss of the engine less than 10%. The rotary
combustion
chamber will never be as good as a cylinder let alone a sphere.
On the other hand if one focuses on the single largest potential part of
the lost heat equation, namely the 36% exhaust heat, the aircraft engine
world market will beat a path to ones door. The technology is 60 years old
for
*&^% sakes. Sheesss! TURBO COMPOUND IS THE ANSWER!
The downfall of the old turbo compound engine was the exhaust valve.
Pray tell me; where is the exhaust valve in a rotary?
This means Lycoming and Continental cannot copy you as their
exhaust valves are now at the absolute limits of their durability.
For an aircraft engine forget the the variable ratio part of this
friction drive gear box. Just optimize it for cruise RPM since you have
a constant speed prop.
This is the umpteenth zillion time I have mentioned turbo compound on this
newsletter.
Paul Lamar
I have put considerable thought and no little amount of R&D on the TC gear
box
problem. The friction drive and the gear drive have their pros and cons.
The limit with gears is the mesh line speed. The major problem with
friction drive is the thrust bearing requirements are severe.
A major insight has just occurred to me. The answer for the gear option is
to limit the turbo charger RPM to 65,000. How do we do that? Simple!
We use a small A/R turbine. In other words a large diameter turbine wheel.
The A/R ratio is the area of the turbine nozzle divided by the radius
of the turbine wheel. To get the HP out of a large turbine wheel we need
a small area nozzle. Hence a small A/R. In other words we are going for
the torque.
Any number of compressors will give us the required 25 pounds per hour
of air at 65,000 RPM.
Paul Lamar
Paul
Yes this is getting closer. I definitely agree with you on the TC concept
and in an attempt to make it simpler over the holidays I sketched a few
different scenarios. To limit the gear speeds to some manageable velocities
I think we need a turbine operating at from 30K (eshaft 45% 3465rpm)
to 50K (eshaft 75% 5625rpm) This is also in line with your max 60K thinking
In the simplest scenario connected between the turbine and compressor is a
thin (less than 50mm thick)inline (parallel shafts) gearbox. I explored two
possibilities. A two shaft version and a three shaft version. In both
scenarios imagine the turbine is nearer the front side of the plane although
the reverse is more suited to my plane.
Both have advantages and disadvantages. First the two shaft. The main drive
shaft between the Turbine and Compressor has a 30mm helical gear pressed on.
The secondary drive shaft gear must be sized large enough to allow the
output shaft enough room to clear the compressor housing and give a fair
reduction allowing the final pulley to the front housing to be sized near a
2:1 ratio. I choose a 120mm diameter size for this gear. At top operating
cruise range of 50K rpm, the primary gear will have line velocity of 78.66
M/s. The secondary gear line speed will be the limiting factor however as
its will be four times that. Looking at what Scandia designed for their
gear box it appears their gear line speeds may have been 20% greater.
The second scenario gives us more options. Three shafts
Bolt a thin gear box onto the exhaust turbine. The middle power shaft
contains a 40mm gear. On one side of this power shaft is a secondary shaft
with a 20 mm gear. Its' 1:2 step-up output goes to a very small compressor
or blower whose air intake can be controlled (vanned) and outlet overboost
protected. If this compressor has a rammed air inlet then so much the
better.
On the other side of the primary shaft is the third shaft containing the
120mm gear going out to the electric solenoid controlled clutch and pulley
with a 2.5:1 ratio. Gearbox output speeds will vary depending on how much
torque the compressor is pulling. The higher the plane goes the more boost
is needed and hence the more the turbine is loaded thus lowering the
compound output shaft speeds.
Solution: Design the output speed to be well in excess of the eshaft speed
and exchange unneeded compressor loads for electrical generating load by
sandwiching a generator between the gearbox and compressor. That is the
control as well. Even though the gear box will need oil lubricating and
cooling the generator and compressor may be able to be thermally isolated to
some extent. Any rpms 10 to 15% in excess of eshaft speed should not be a
problem. We are predominately adding more torque to the e-shaft and the
engine will adjust to a new equilibrium rpm. Engine loads always drag down
the engine speeds. The reverse is also true.
I think this design will make our life much, much easier. The clutch allows
us to engage the system in its most appropriate range. Wisdom dictates two
electrical generating sources should be used on a aircraft engine and the
higher compressor shaft speeds allows the back-up generator to be much
smaller and lighter.
These power shafts are still going to need some sort of thrust bearings
within an aluminum gear box and that is this months' homework. In my search
for an high speed gear box expert I found a good source for custom carbon
fiber parts. Who knows?? if I keep looking for gears maybe I'll eventually
find my car keys:)
Doug in Japan
I wish you did Rhino 3D :)
Paul Lamar
Paul,
Soon, soon, my Windows oriented laptop arrives next month and after that
Rhino.
Doug in Japan
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