On a lighter note, what is your thoughts on coupling
 a exhaust turbine to the crankshaft, via cog belt or micro v belts? My
 thoughts are to stop the vibrations of the crankshafts getting thru to
 the turbine, while extracting the energy from the exhaust.
 I also have not been able to locate the suppliers of
 alloy end bits for the rotary engines.
 Thanks

 John Burey.


 Paul, we have an interest in a similar setup replacing the gearbox
with a
 starter/generator and deleting the compressor.

 milo

 Will the generator run at 100,000 RPM?

 Paul Lamar

 High speed microturbine electric generators are common state of
 the art in low power (50 to 200 kW) cogeneration sets.
 The 80,000+ RPM, 2 poles or homopolar generators are reliable
 industrial machines...  for still ground based installation,
 not for flying machines with angular velocity and accelerations.

 As a minimum requirement for aircraft use, I would place the
 turbogenerator axis parallel to the roll axis of the airplane,
 axis of maximum rotational speed, and, of course, avoid aerobatics.

 Philippe Dejean


 What is the efficiency of the generator alone Philippe?

 Paul Lamar
 -
 On high RPM and/or high frequency generators, the losses
 increase in the stator core material,
 Up to 1000 to 1500 Hz, laminated steel is still the best
 material as far as induction remains in the linear range
 (<1.6 or 1.7 Tesla anywhere).
 For much higher RPM/Frequency ferrite is to be used, but
 induction cannot be more than 0,4 Tesla.

 On a 30 to 60 kW 80,000+ RPM two poles permanent magnet
 generator, the overall power efficiency of the generator alone
 should be around 90%, including the 1,5 to 2% of losses in the
 power electronics to make industrial frequency (50 or 60 Hz)

 I think you could have more information by contacting CAPSTONE,
 the american leader on that market, based in California.

 Here is some data found on their site :
 (See attached file: c30electrical.pdf)(See attached file:
 capstone_specs.pdf)(See attached file: diesel.pdf)

 Applied to Wankel turbo compounding, the generator electronics
 should not produce 50 or 60 Hz, but the frequency
 required by the starter-generator placed on the Wankel shaft to
 work as a motor...

 Philippe dejean

 I have heard of them before and I am rather surprised the 25%
 overall efficiency is as high as it is. They are not saying what the
 turbine eff. or generator eff. is. Just the overall 25%.

 Not so hot. I think a turbo compound Wankel would do better.

 The problem with any gen set is prime mover eff X gen eff.
 For example if the turbine is 80% and the gen is 80% the combination
 eff. is 8 x 8 or 64%. This is giving it a huge  benefit of the doubt.

 Obviously the turbine eff is more like x times 80 = 25 or
 turbine eff = .31. That is a very high number for a small turbine.
 Most diesels are .35, Gasoline engines .3 and a turbocompound
 Wankel could be .35 or higher.

 A bottoming cycle full size power plant can be as high as 50% overall
 by using the waste heat from a turbo-shaft engine exhaust to make steam.
 Another form of turbo compounding.

 Paul Lamar



Philippe,
Bon jour.   Electric turbocompounding?  This is an idea that
just doesn't go away:) We see it every year. Sort of like
electric pumps and electric superchargers.   I stand guilty of
having an interest in them as well though. There is a tendency
to get wowed by the high efficiencies of the  Switched
Reluctance generators available now.  98% is possible and I have
personally witnessed the data from generators operating at even
higher efficiencies. However those high points  were just a
sweet spot on a relatively steep rpm bell curve.  74%  might be
a better number to pick from the data cloud of numbers.  And it
is a cloud as generator output is affected by rpm  as well as
the  voltage output and frequency selected.  Same for inverters
efficiencies.   85% is a commonly accepted number though they
can get into the mid nineties with a very light loads. In
general  lower voltage outputs have greater losses.  Low means
24vdc. in my thinking.

Now if you have the turbo powered gen.  connected to a large
electrical load, say a refrigeration compressor on a lorry, than
this line of reasoning  makes a lot of sense.   The turbo gen.
would probably output high DC voltage,  (270 - 300 vdc) to an
inverter, which in turn would supply 220 - 240 AC power to run
the compressors and refrigeration loop that could cool a fair
size house in Mexico.  Think ice. Compare this with the common
method of using an auxiliary engine to drive a dedicated APU for
the 'reefer.'

For airplanes I don't see the merit.  Sort of like making an
electric powered Delorean.  Will it work? Sure but it won't get
very far carrying around the double shell foam injected FRP body
and the cosmetic stainless panels.  Don't ask me how I know:)
Electric powered anything is very weight sensitive at this stage
of the game and I'm not speaking about batteries.  Controllers
and/ or inverters to handle the high electrical currents are in
the neighborhood of 10kg/per kilowatt output at nominal
operating efficiencies.

Now I know someone is going to say, but wait,  what about the
super efficient electric SR  superchargers?  Yes they are out
there and they may be a good alternative to moments where
critical power is needed but  they are amp hungry.  They rely on
stored energy from a  battery though and have nothing to do with
turbo-compounding.   The battery can recover slowly during
normal flight and solar panels on wings could be an ideal match
to assist charging.  The battery must expend a lot of energy
very quickly though.  The battery that can do this is not your
usual deep cycle battery. Hence a two battery system would be
called for.

Turbo compounding is a very mechanical idea in its best form.
To date the most amazing break through for turbo compounding
IMHO is the traction drive reduction unit.  This is a gear less,
roller, drive that combines the merits of both fluid dampening
and low rolling friction all in one package.  In operation,  oil
is momentarily compressed between a slightly flexible annulus
ring and the rollers  to achieve remarkable 98% energy transfer
efficiencies and up to 13:1 step down ratios.  The technology
depends on critical clearances and the proper selection of
compatible component metal alloys and their respective heat
treatments.

A traction drive coupled to a multi-V belt,  can match engine
speed  by adjusting pulley sizes.  As units handle more power
the step down ratio lowers.  I have found a 7:1 ratio is a good
match for transferring up to 100 hp.  Challenges remain in
designing the mid section between the hot turbine and the thin
drive shaft of the traction drive. The critical operating
parameter is traction oil temperature. It works best from 20 to
80 degreeC.   Because these traction drives lose little energy
to heat,  in an airplane at high altitude, the oil may need to
flow through insulated lines and have a thermostat and 30 watt
heater in the oil tank.

You don't see these traction drives on the big diesel TC engines
however and suspect it is a issue of material strength.  The
amounts of torque these diesels turbines can deliver are  much
higher than present traction drives, can handle.  It is an issue
with mass times velocity.  Said another way scaling a traction
drive up and keeping the turbine velocities the same would
result in a  hand grenade.


Installing a starter/ gens is one place I considered installing
new electrical technology  but in all honestly I found the
weight advantages minimal and the risk factor high. Why?  The
combined unit is much heavier and bigger than a starter motor.
The controller weight  and  reliability adds an undesirable risk
but only saves  overall a couple kgs. of weight.  This idea
needs a few more years of refinement and I never recommend
buying the first generation of any product.

What I would rather see is a technology that could start the
engine by firing off a particular rotor.   Mazda does this with
their piston engine cars now and turns the engine off when
stopped at traffic lights.  Saves fuel, kind to the environment,
good for company image.   Engine starts are within 0.3 seconds.
When the engine stops, a small motor moves the crank so that one
of the pistons is in a firing position, and is waiting for a
high pressure squirt of fuel and then ignition.  Would it work
on a rotary?   Possibly but a little differently.  I would bet
my lunch that Mazda is working on this right now.

A very small (fist size) geared starter motor is connected
through a sprague clutch and accessory V belt, or for us
aviation buffs, perhaps located where the oil injector pump used
to be.  Remember this motor's output is slowwww.   The starter
motors job is only to  position... lets say rotor #1.  The
sequence would be: First the rotor moves to inject position
angle, then it is primed either manually or  electronically as
it travels on through to the compressed location and fired with
the leading plugs.

 Seeing that injector on top of the 16X should give you ideas by
now.  Looking at the aluminum boss on the top of 13B housings
should also make you realize that Mazda has been thinking of
injecting here for a long time.  Injector speed has been one of
several limiting factors. No longer factor. This location is
perfect place for injecting a variety of fuels at the moment
when the inlet ports are shut but the pressure is still near
ambient. Injectors operating at  the ms speed are instantaneous
compared to the rotor  passing on its way to the compression
stage in a start up sequence.

The advantages of a 1.5 kg geared positioning motor?  Toss the
starter ring gear, or better yet replace it with a light weight
pulley and/or magneto.  Toss  the starter motor,  its' heavy
copper cabling and solenoid contactor.  And alternators?  Yes,
if no magneto is on the engine then install two alternators on
dedicated belts and if possible one on each end of the engine
ala Mistral.  The one near the prop will cool better, the other
needs a shroud and blast tube.  Orient the cooling blades in the
proper air flow direction


Doug in Japan

Caterpillar did a lot of work on electric turbo compound so far.
2011 will be the last year for the R&D.
Detroit Diesel wupped them good first with the 350 HP DD15
TC and now the 650 HP DD16 TC.

Caterpillar's goal (not yet reached) was a 10%
reduction in BSFC and I think DD demonstrated that in current
production TC engines.  They are years ahead.

I think the show stopper was/is the heat from the turbine
affecting the generator.

Paul Lamar


I think the stopped motors are started by alternator/starter flywheel
which are used as brushless motors and alternators, mostly as 48 volt
they start the engine instantly and without a sound of a starter.
            John Burey