Good evening, Paul!
My name is Jacobo and I'm from Spain. I'd like to subscribe to your
newsletter because I'm very passionate about the Wankel engine. But in
my case, I'm more interested in the automotive uses of the rotary
engine. I believe that there are some innovations in aircraft Wankel
engines that can be successfully applied to automotive Wankel engines.
I'm looking forward to your newsletter. Best regards from the other side
of the pond!
Jacobo
Well if you want to build a really high performance car the Mazda Wankel
is for you.
If you can find an RX2 made in 1972 or later or 1974 RX3 and later.
All late Mazda engines will bolt right in including the RX8 engine .
The 1973 RX2 weighed only 2000 pounds.
With our all aluminum 200 pound Mazda TTC turbo 650 HP will give a
spectacularly performance
both in acceleration and top speed. The rear axle will not be needed to
be beefed up
as the torque required is more related to the width of the rear tires.
The tires will just
spin if you apply too much HP. A high mounted rear wing will, with some
work on the
nose down force, also result in an increase in cornering G's.
Check out
http://www.rotaryeng.net/who.html
<http://www.rotaryeng.net/who.html> There is a lot of car info
on that section
of the web site. I can help you with any changes you might want to make
on the car.
Here is a 800 HP drag racing turbo engine.
Paul Lamar
What I have in mind is building a four rotor engine suitable for both
street and endurance racing. I was originally considering going with a
naturally aspirated engine so as to not increase fuel consumption way
too much. But I've been reading about turbo-compound engines on your
website and I think it ought to be the best way to go.
I'd like to ask some questions before going ahead with the planning (and
to clarify doubts I might have). I hope you can answer them:
1. How much power can be recovered and brought back to the engine by a
turbo-compound system in terms of percentage? How much would fuel
consumption and range improve?
2. I read that you were building a turbo-compound system for rotary
engines. Did you manage to finish it and test it? If so, were the
results satisfactory?
3. How much boost can a rotary engine resist safely without breaking apart?
4. Would the use of a turbo-compound system increase heat and mechanical
stress on a wankel engine? If so, how can the engine be protected
against this heat and mechanical stress?
Looking forward to hearing from you, Paul. Best regards.
Jacobo Guimeráns
A turbo compound version is 20 to 30 percent more power with the same
fuel burn.
I finished it but I did not run it on the dyno. I gave a talk to the F1
engineers and
they adopted a hybrid version for F1. You can read my talk at
http://www.rotaryeng.net/Oxford-Race-Tech-art-Dec-08.pdf
<http://www.rotaryeng.net/Oxford-Race-Tech-art-Dec-08.pdf>
There are now four companies building turbo compound engines. Mercedes,
Ferrari
Renault and Honda.
Well we have had it up to 85 inches of Hg and it is still running fine.
I don't know what the max is. I'll bet it might be over 100 inches of Hg.
Turbo compound would not increase heat unless it was a hybrid version.
I don't recommend that as it increases weight and cost. It does nothing
for an airplane.
Paul Lamar
So, if we have (for example) a 400 hp engine with a fuel consumption of
25 mpg in its base form, with a turbo-compound system would be in the
range of 480-520 hp with the same 25 mpg fuel consumption. Is that correct?
I saw on your website pictures of the pieces you used for your
turbo-compound system and a render of a full turbo-compound system on a
rotary engine. Do you have pictures of the system fully assembled on the
engine? I would like to see it and see how it would look fully assembled
on an engine.
As for turbo boost, Formula One cars in the 80's managed to get boost
pressures of almost 120 inches of Hg. Pressure above that number would
be something insane on an engine, and I'm sure that insane boost would
make piston engines break apart.
There's one thing I don't understand. The power recovered by the
turbo-compound system is transmitted to the eccentric shaft, but how
does this power affect to the e-shaft? Would it spin faster or something
else? I need to clarify that.
Looking forward to your answers, Paul. Best regards.
Jacobo Guimeráns
Very difficult to convert MPG into aircraft fuel burn.
The way to do it is rate engines in terms of pounds of fuel burned per HP
generated. This has been a world wide standard since the early 1900's.
One gallon of gasoline weighs about 6.25 pounds.
The Mazda burns about .47 pounds per HP generated.
The Continental O-470 in my Cessna C182 burns about .53 pounds per HP.
Some latter air craft engines are .43.
Surprisingly this has not changed much since 1900. A small improvement
in this
number for a particular engine is a major achievement.
A turbo compound version of any of these engine might go below .40 or
even down to .33.
Here are some more turbo compound pictures.
The TC puts more torque in the prop shaft so a higher pitch can be used or
more blade area can be added. The RPM of an aircraft engine is limited
by the tips of the prop going supersonic.
Paul Lamar
Hi Paul, this mechanical setup for TC seems complicated compared to the
turbine
wheel attached the the eccentric shaft ! What am I
not seeing here?
Steve Carlisle
Well the flow speed over a blade in a turbine must be near the velocity
of the blade.
It works just like a wing. The exhaust flow speed in a Wankel is near
super sonic.
That means the blade must be really going fast. There are two ways to
get the
blade to speed up. One is use very high rpm with a small diameter turbine.
That is how turbo chargers work. On the order of 100,000 RPM.
The other way is use a much larger turbine diameter and run it at e-shaft
speed. 6,000 to 10,000. Just bolt it on the e-shaft. Super simple. The
down side
is the weight and cost of the turbine. If you use a small turbine
rotating at high
RPM you need a gear box to get that down to e-shaft RPM.
That is how you get the HP out. In the hybrid configurations they use
a DC motor operating at turbo charger RPM's of around 100,000.
For power recovery it becomes a generator. This is typical for DC
electric motors. You can then use it as a motor to speed up the turbo
charger and get max HP out of the engine faster. No turbo charger lag.
Not necessary in an aircraft engine.
In the CW R3350 TC engine the turbine was about
12 to 14 inches in diameter and it was way geared down to to the crank
shaft
speed of around 2000 RPM. My guess it was operating at 20 to 30
thousand RPM.
When the blade is going at half the gas velocity you get max HP.
When the blade is stopped you get max torque and no HP. When the blade is
going at the gas velocity you get zero torque and zero HP.
You need both torque and RPM to get HP.
The equation is torque times rpm divided by 5252 and that gives you
the HP.
------------------------------------------------------------------------------------------
The greatest engineering blunder in history was when Curtis Wright fired or
retired all their turbo compound engineers and then started developing
the Wankel.
Then they spent millions of dollars trying to improve the Wankel BSFC.
The solution
was staring them in the face. The TC guys had already told the CW
president and
the world that 20% of the recoverable energy in the exhaust was being
dissipated by the exhaust valves.
They spent millions trying to make them live in the R3350 TC. Four R3350
TC's could
not make if from San Francisco to London with out at least one exhaust
valve failing. Part of the exhaust valve would take out one turbine and
that engine would have to be shut down.
The Wankel has no exhaust valves and that is why the exhaust is near
super sonic. If Curtis Wright had applied their turbo compound knowledge
to the Wankel back then there would now be no piston engines.
Just turbo compound Wankels. I am sure Pratt & Whitney Canada knows
this.
Paul Lamar
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