I guess that a big turbo is also needed for a 4 rotor turbo-compound
engine.
I'm considering adding a supercharger (a Roots type is the main
option) at the intake manifold, but I fear for an increase in fuel
consumption when I'm looking for the opposite. Would you recommend
adding a Roots supercharger at the intake in a turbo-compound
system? What are the benefits and the drawbacks?
Jacobo 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 Guimer�ns
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 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 Guimer�ns
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 Guimer�ns
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
The question is: if we are using the traditional turbo-compound
system of having a big turbo feeding the engine and a smaller one
being fed from the exhaust gasses and connected to the e-shaft via
gears, we would need to find out how many gears we should use, the
RPM of both the small turbo and the e-shaft, the horsepower of the
engine and the gear ratio of the gears. That data should give us a
clue on how the turbo-compound system should be built.
Jacobo Guimer�ns
I suspect you mean big super charger feeding the engine? That work
of course as that is the way the CW did it on the R3350.
The calculation on the power recovery turbine are rather simple.
First you make an assumption on the exhaust velocity. Then the power
recovery turbine RPM (blade speed) can be calculated on half of the
exhaust gas velocity. The exhaust gas velocity can be adjusted over
a limited range either by a converging nozzle or a diverging nozzle.
Paul Lamar
I was thinking of something like Detroit Diesel, Scania and Volvo do
on their trucks. Here's a video of Volvo's turbo-compound system.
https://youtu.be/9PbxmRA9vbs
Jacobo Guimer�ns
They are not as efficient as they could be. Every time you pass the
exhaust gases through a device you lose energy in the form of heat.
It is better to use this configuration. Just one turbine.
Paul Lamar
Is one turbo enough for a turbo-compound system? In that case, I
guess the size and boost pressure of the turbo depend on how much
power you want to get for the engine.
Jacobo Guimer�ns
Correct. You will need a big turbo for a 3 rotor.
Paul Lamar
I guess that a big turbo is also needed for a 4 rotor turbo-compound
engine.
I'm considering adding a supercharger (a Roots type is the main
option) at the intake manifold, but I fear for an increase in fuel
consumption when I'm looking for the opposite. Would you recommend
adding a Roots supercharger at the intake in a turbo-compound
system? What are the benefits and the drawbacks?
Jacobo Guimer�ns
Mechanical blowers suck HP and fuel from the engine. Turbo Chargers
use the otherwise waste energy in the exhaust.
Paul Lamar
Paul,
I have always wondered, how is the turbo compound rpm mated to the
crankshaft
output rpm so that the turbo is always �helping� the crankshaft, and not
hindering?
If it is a clutch, is it a sprag clutch or something similar?
Gene Kahn
In the R3350 TC it was done with a fluid coupling. One way shaft
clutches are really low cost.
In an aircraft engine it is not much of a problem as everything runs at
a constant RPM. I'll draw a 10:1 gear box for you.
Paul Lamar
The Rotary Engine free News Letter. Powered by Linux. If you want off
the list PLEASE let me know and I will remove you. ACRE NL web
site.
http://www.rotaryeng.net You Tube
http://tinyurl.com/beqqxas
Copyright 1998-2017 All world wide rights reserved.