snips...
As far as USEFULLY expanding down to atmospheric temperature is concerned
I agree but I won't give up. We now go to plan B where we convert the
un recovered heat to steam and inject it into the turbine. We then condense
the steam in the exhaust back into water down stream. We might need to carry
a bit of make up water. Here is a diagram from Marks for such a scheme as
it is applied to a gas turbine. Gas turbines with this type of exhaust
heat recovery are called combined cycle engines and according to Marks
approach 60% over all efficiency. Here is a scan from Marks.
I am researching membrane technology as we speak to possibly further extract
water vapor from the exhaust.
I think it ridiculous of the engineering world to go on building 30% overall
efficient internal combustion engines without spending some R&D money on
making
them more efficient. Instead the car companies spend billions on electric
hybrids
using the same 30% efficiency ICE engines while adding 500 to 700 pounds
to the weight of cars.
A combined cycle turbo compound internal combustion engine is not going to
be more than 100 pounds heavier if that.
Paul Lamar
snips...
Since the HP numbers are so low in a car cruise situation you could use a
very small turbine and a small heat exchanger and a small condenser.
I think the heat exchanger can be as simple as a counter flow concentric
pipe inside the all ready long exhaust pipe. The condenser can take
the place of the aft muffler. If one is really clever the cooling
system could be in the loop for additional heat recovery. It just
takes money for R&D.
Paul Lamar
Hi Paul
I don't have the book about alcohol making. I'll pick it up though.
Thanks. So far I have been speaking to and hanging out with some to the
local saki breweries in town. Make a beery solution, add yeast and distill
the result. It seems ethanol came be made made from hundreds if not thousand
of varieties of plants. Interesting that those yeasty beasties give off
alcohol and C02 in equal amounts. Best to sequester the CO2 or we are just
exchanging NOX for another greenhouse gases huh?
As you noticed in the turbocharging book a lot of racers inject
alcohol/water mixtures to lower the detonation point so they can increase
manifold pressures. I wonder if I need to go to the low compression rotors
on the Renesis if running alcohol with a slight 4psi boost. One way to find
out huh? Boom boom. Of course if I want to get 300Hp out of the Renesis I
will probably have to wait for the low comp rotors, or modify the 13B
rotors. First lets see what the 13B can do. 110 octane ethanol will help.
OK so the best BSFC on the turbo compound engine was up around 25,000 feet.
That is starting to make sense.
Half Bakery is at this location...Mostly amateurs kicking around all sorts
of half baked ideas.
http://www.halfbakery.com/idea/Supercharger_20_2b_20Modified_20Turbo
Someone also mentioned injecting steam into an auxiliary turbine.
So if I understand you correctly the exhaust manifold super heats a working
fluid, turns it to steam, which is then injected in a small steam turbine
that is connected to compound mechanism right? A cooling condenser and
storage tank is also in the loop. Sounds like we have to cannibalize an old
refrigerator and high speed pump:)
Did I ever tell you I lived in Stead, Nevada in 1970 for a year? I use to
wander over to Bill Lear's shop and look at the steam turbine he developed
for the Monte Carlo demo car. He ran it on a closed loop freon system and
turbine.
IMHO this line of thinking for an add on to the 13B or RX-8 aircraft engine
will be way too complex and heavy to create with our limited research funds.
.... But... if integrated into an APU ground station it is a superb and
excellent concept. The building floor, water heating or air conditioning
loop will be the heat sink. The total efficiencies will be in the high 80s
I am sure. Of course on the ground in this application we compete with
diesel engines.
I might have missed something. Is the GT-28R a turbo compound possibility
as well. It seems small.
Doug in Japan
I'll send the book to you. I think it is long out of print. I just happen
to run across a used copy in the Op Amp book store.
The steam is injected back into the same turbine. No second turbine required.
Here is the diagram again. Perhaps you are not getting all your email.
I was not too clear on this point in my discussion of it above.
No additional weight except for a steam pipe in the exhaust pipe and a
condenser.
The condenser's job is to convert what is left of the steam in the exhaust
back into
water. The left over heat in the exhaust (900 F) after some of it has been
extracted
by the turbine will convert the water in the pipe into steam. I will do
a 3D pluming diagram.
Probably not necessary as the aircraft turbo compounding will be running
at much higher HP numbers so there is a lot more kinetic energy in the exhaust
to drive the turbine. There is no reasons to believe there was a higher
ratio of kinetic energy to plain heat energy in the exhaust of the R3350 TC
than
there is in the exhaust of a 13B rotary engine. (With the possible exception
of the occasional broken exhaust valve parts :)) If they got 20% more HP 60
years ago
with the same amount of fuel we can get 20% more HP now with the same amount
of fuel with hopefully better technology. If Caterpillar and Scania can get
10% more HP out of a diesel engine with a much cooler exhaust surely
we can get 20% more HP out of a hot blooded rotary engine.
I don't think the GT28R would make a good turbine for a turbo compound
engine. Stick to the TO4 for now. I am still gathering information on this
new line of Garrett turbos.
Here is that combined cycle diagram again. Let me know if you don't get
this attachment.
Paul Lamar
Paul
I got the diagram alright. It looked like an open system axial turbine
burning a fuel with steam added. To add steam into a radial turbine that is
optimized for a different density fluid would be counter productive. Besides
we would have to carry more weight in water and have a recovery system.
I think we are exalting the wrong model here. I am not so sure the Connie's
performance is a good comparison for to make for the rotary engine. It is
sort of pie in the sky:) Without a doubt the Connie had some great
performance figures. They did it with great complexity, at high altitudes,
low drag, specific rpm, low density pressures and blow down turbines etc..
Looking at the engine brings admiration, wonder and also shudders into any
homebuilder considering turbo-compounding. The other aircraft engines like
Allison and Napier are interesting but not practical. Cost/performance and
ability to work on the systems ourselves will be the a main sales point.
Perhaps a better comparison for our adventure is the latest Scania research.
I think your remark below means you would still like to capture more kinetic
energy.
Maybe I need one of those model turbojet engines and throw away the compressor
:) Wouldn't that be a hoot if that worked?
Monty and I talked about this in October. For an axial turbine with
planetary gearing to would work at over 80% efficiency we would need a high
volume of gas at a high velocity and pressure. Not likely the heat exchanger
needed to produce the quantity of steam would fit into our limited cowling
size. Still we are losing energy heating water to steam.
Hmmmm!
I have come to understand that this project ain't that easy. But that is OK
since I haven't cut any metal yet. I made piles of notes and drawings though
I am sure your drawing piles are huge by comparison. Ok sensei here is my
1/2 baked idea.
Though not needed in this concept if we want a boost then we could mount a
small rammed air combi supercharger on the engine cool side and incorporate
an intercooler near it. The supercharger is small enough to be only used
only for critical climb applications or providing some boost at very high
flight levels. Electric clutch disables it when not needed. If it only
needs to deliver about 5psi over ram effect at altitude then it could be
electric. Remember the bell housing large starter motor alternator. OK OK
... owch... if more than a turbine compressor.
Find out how many BTUs are coming out the exhaust at mid range 4,000 rpm.
5psi boosted, ported, tuned intake 110 octane ethanol running RX-8. My
estimate is 130 hp. Same amount of heat leaving the engine through the
exhaust right?
Turbocompounding is like co generation at power plants only at a micro scale
sooo.....
By going with a closed system and some of the more exotic working fluids
like freon that have a high vapor pressure and phase change in our operating
conditions, the heat exchanger can be downsized. Perhaps wrapped around
Jerry's log like spin muffler or inside a muffler after the tuned exhaust
like you suggested. Make the rings absorb heat and break up sound waves as
well. [Lots of design possibilities right there] If someone still wants a
turbo/compressor put it after the heat exchanger and tuned exhausts and let
it be the muffler.
I did some work 24 years ago as part of Japan's Sunshine Project with solar
water heaters and was impressed with the properties of freon. Perhaps there
are better fluids now.
What about choosing a vane motor that runs at 2.5 K and is pulley ratio up
to the eshaft speed and works on the high pressure freon fluid? Like a
hydraulic motor, great torque and simple operation. Lots of data from power
plant companies doing co-generation work out there. In some small APU the
total efficiency increases are over 20%. For the rotary, we may require
machining our own multiple stage pump ..I mean motor. Call it a staged
turbine. I think you have the idea. Basically a SUS 304 pipe shape with
aluminum manifolds on each end. Design the first one to deliver 20Hp net to
the eshaft. Graphite rotors in vane pumps are tough but a little oil has to
be included in the freon because it tends to dry out the seals. There are
lots of these working fluids to choose from and many have the advantage of
going from fluid to gas and back with minimum temperature changes.
Condensers can be conformal. Obviously it would be nice if the system was
gravity feed. Condensers high and heat exchanger low. If not possible the
required pump would be miniscule. The advantage of aircraft over ground
applications is that we can get up in the regions of cooler air and increase
our delta T so system works better at altitude where we are likely to use
it.
In summary, we have been trying to mine kinetic energy base on the Connie's
model, perhaps we should be mining the simpler heat energy from the engines'
water, oil and of course exhaust.
Doug in Japan
I am not advocating steam for an aircraft. You have enough kinetic energy in the
exhaust to build a conventional turbo compound for aircraft use based on the Connie model.
Seems like the R&D is simpler than the freon working fluid system.
For a car one has this long tail pipe that one could convert to a heat exchanger
and a large muffler just ahead of the rear bumper that could be replaced by a condenser.
the forward motion of the car would provide the cooling air for the condenser.
Just choose a turbine that works the best for both steam and exhaust gas.
All the steam does is increase the kinetic mass flow.
Paul Lamar
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