Paul wrote>
I wonder when the IC engine manufacturing world is going to wake up to
the
potential
of the turbo compound? Ideal for the rotary has it has no exhaust
valves
to fail and take out the turbine. That was the achilles heel of the
R3350TC.
Paul Lamar
Mark Wrathall wrote:
Paul, I thought we worked through this. The low mass flow is the show
stopper for compounding a 200HP engine. Small flow means small turbine
which
needs very high rpm to get efficiency, which then leads to a very
differcult
gearbox problem. How do you build a gearbox to convert 15hp from an
overslung turbine at 100,000+ rpm to 6000 rpm with a clutching or
damping
mechanism. Likely not unsolvable, but not a feasible path for producing
a
"free" 15HP, or 10% SFC. Technical interesting, and we would all love to
see
someone do it, but a huge challenge.
What do you mean "we" white man? :)
There is an old joke where the Lone Ranger and Tonto ride up over
a ridge. In the distance there is huge war party of Indians.
The Lone Ranger says "Holy shit Tonto, look at all those
Indians! We need to get the hell out of here!" Tonto replies:
"What do you mean "we" white man?"
I just agreed that a large diameter
slow turbine was not the way to go. The 15 HP recovery figure is too low.
3800HP/2800HP is 135% more
or 70 HP at a 200 HP level.
At a turbo 300 HP level it would be about 107 HP or 407 HP
net.
BTW no increase in cooling system requirements over the base
300 HP turbo engine. In other words turbo compounding
does not add to the waste cooling heat.
I would now use a oversize turbo charger turbine and
remove the power from the turbocharger shaft out through the
compressor inlet. Same as the Caterpillar TC diesel engine does it.
Yes it will need a gear reduction but only to 8000 RPM from 100,000
or 12.5 to one which can be done in two very small planetary stages.
Yes we will also need some sort of small friction clutch or fluid
coupling to decouple the turbine from the output shaft.
I think the BSFC improvement can be more like 20% and considering
current world wide hysteria over fuel consumption can be
economically viable. Certain cheaper than a silly hybrid car
not to mention way less weight.
Compounding an R-3350 was much simpler from an aero perspective because
of
the resonable (in turbine terms) mass air flow; from the mechanical
perspective due to the resulting lower turbine RPM; and from a business
perspective because it was was pretty easy to sell any technical idea to
the
US government in the forties and fifties :)
Mark Wrathall
The main use of the R3350TC was not military. The main use was
in the Connie and the Douglas DC7 Seven Seas. It was not until the
R3350TC that routine transatlantic non-stop NY to London and Paris
flight became possible. In fact there was a 24 hour TWA Connie
polar flight from San Francisco to London non stop. It took years
for jets to equal that range. I think the B747 was the first. The R3350TC
was used by the Navy in Lockheed P2Vs. One of which flew non-stop
un-refueled from Australia to Ohio. That range record held until
the Rutan Voyager went around the world.
Paul Lamar
Mark wrote:
Didn't think you'd just roll over and quietly slip away on this one Paul.
The ~50% of your paid-for fuel energy sneaking off down the tail pipe sure
is an attractive engineering challenge. I guess detroit isn't interested
because, as you often point out, cars only need 35HP.
My number of 15hp comes from the shaft HP generated by a 66mm Garrett
turbine running at 100,000 rpm in a model engine. Much lower EGT. You are
right that the potential energy is greater.
I don't think that turbo compounding a 13B is imposible or even a bad idea,
I just don't think it is cost effective at 200HP. A bigger turbine means
either an aircraft turbo ($$) or a truck turbo (designed for a deisel, will
it stand the heat??) If anyone has a used turbo charger or a turbine map
with a good big wheel (like 100mm) it sure would be interesting to run the
numbers on this. At that sort of diameter you are already done to around
65,000 RPM.
Could you please resend the NACA report on the R3350TC which you posted
about two weeks ago, I'd like to use it against you :) I think you might be
comparing apples (The R3350-?? non TC at 2800HP) to oranges (the R3350TC at
3800HP). Is the 1000HP achieved at the same fuel flow. My memory of the NACA
report you posted was that the Turbines were driving compressors as well as
the power take off. The report stated there were certain conditions were
they were run in Turbo charger mode, and some where they were also coupled
in power take up mode. Oviously the the R3350TC still had the mechanical
supercharger as well. I would be curious whether a compunding turbo, with
it's increased back pressure would provide a net gain on a normally
aspriated engine. If not, you also have the added complexity of either a
mechanical supercharger, or trying to do power take off from a full turbo
charger running at high speed.
One bright spot in this tunnel is that there are guys running model gas
turbine power turboprops and helicopters so the gearbox thing must be
doable.
Funny you should point out the Connie and DC-7. I was going to use the
Connies range as my business case, but figured I'd add a light touch.
To the question of using the exhaust turbine to drive the accessories, this
doesn't make sese as it not a constant power source, so you would need a
clutching system to drive these systems at low power settings (like an idle
descent). Better to just feed the power into the e shaft.
Mark.
The NACA report I have is on a preliminary smaller test engine. Not the R3350TC.
There are some NACA reports on the R3350TC I have just not dug them
up yet.
Who would have thunk a hybrid car was cost effective? The wackos
out here in The Peoples Republic of CA are ordering them like
hot cakes. But then again most of the hypocrites among them drive SUV's.
If you paint it green the wackos will buy it.
Paul Lamar
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