Implementation of a Rotary Engine (Wankel Engine) in a CFD Simulation
Tool with Special Emphasis on Combustion and Flow Phenomena
2015-01-0382 Published 04/14/2015
IMHO This is the best technical paper on the Wankel so far.
Frank Herfert found it. Thanks Frank.
"In summary, the loss analysis shows that the main losses of the
Wankel engine result from the protracted and retarded combustion.
Consequently, the wall heat losses are lower than expected. "
" The mechanical losses, as well as the gas exchange losses, are
lower than comparable conventional spark ignition reciprocating
engines. The comparison between the investigated Wankel engine and a
normally aspirated, throttle-controlled gasoline engine with port
fuel injection under full load and high revolutions, is illustrated
in Figure 37."
"The largest deficits of the Wankel engine can be found in the area
of combustion (implementation loss due to incomplete implementation
of the fuel and combustion loss ) and leakage loss. The lower wall
heat release loss , compared to the conventional gasoline engine,
results from the late and delayed combustion. The lower mechanical
losses and charge exchange losses arise from the port control and
consequently, absence of the valve train."
What they did not investigate was multiple sparks on the same spark
plugs or more spark plugs. In effect, unlike a piston engine, the
combustion travels past the spark plugs. In a piston engine the
combustion moves away from the spark plugs some what.
That is where my new high speed CD ignition system comes in to play.
It is capable of firing the plugs six times.....five degrees apart
at 8000 RPM. Patent is still pending.
It can be tested now, on a dyno, using multiple MSD capacitor
discharge ignition systems fired by a high speed computer 5 degrees
apart at 6 to 8K RPM.
I do not have a dyno to test this but I can supply the control
computer. Simon Saba has a rotary engine dyno in northern
California. Please Simon, see if you can get the money to try this.
Paul Lamar
Hi!: as discussed, I requested Kevin Landers, from
RotaryResurrection, to implement the Fujikawa, Kawasaki, combustion
promoting improvement plug hole triangular extension, pointing to the
trailing side of working chamber (Patent 3848574, of 1974), but it
took over one year for the tuned 1987 13B NA the engine to arrive
from NJ to Barcelona, and it's still pending to be installed in my
1976 AMC Pacer Sedan, along with a Mazda RX-7 four speed plus reverse
automatic transmission, if the project is concluded, I'll try making
a comparative test with an ordinary 6-L 4.2 liter AMC Pacer, and let
you know results.
Thanks, have a nice 2017, best regards, + Salut †
Jose Gros-Aymerich
Madrid, Spain
I don't think you will learn much Jose.
The best BSFC islands are in entirely different places for the Pacer
and the RX7. The Pacer has much more frontal area and the drag
coefficient is much higher than the RX7.
Paul Lamar
Hello Paul, I think of Austro Engine because at the end of the first
paragraph of the Introduction the Austro Engine Company is called
the research partner of the Technical University of Vienna ... If
you have a look at table 2, the Vc is 404 cc - exactly the volume,
Austro engine has given in the description of 2009 - please see the
enclosed screen shot. It must be an existing engine, because they
have it run on a test bed ... But the 407 cc engine from the Wankel
AG has a width of 6,5 cm, not 7,44 cm. So I've guessed, that it's
the AE75R prototype ;-) Perhaps there is yet another engine of this
size - of course I do not know all RE in the world today ;-)
But I think, that it's not very important, which engine they've
analysed in Vienna. Their work is rearly serious - without "pink
glasses".
It's a good base for further development ...
I have a "strange" idea related to the trailing section problem -
perhaps I will try to explain it with Paint, although I think, the
mechanics will not work / will not be feasible ... ;-)
Yours very truly - I wish you a perfect start into the new year
Franky / Frank Herfert
I was at the Austro engines factory in 2001. Here are some pictures.
Paul Lamar
On that graph with blue red colors I am not sure what is meant by
'Implementation loss'.
Item 3 does not sound to be right. The wall surfaces of the Wankel
are admittedly larger than on the RPE.
Hello Franky. If you can show your idea, then pass it by us, but
only if it is not confidential. Or, if you would like, get back to
me privately. Paul may pass on my email address.
Rolf Pfeiffer
"Efficiency Loss Due to Combustion Loss The real combustion in the
engine is not isochoric and does not take place at TDC. Thus, this
loss can be divided into two. Efficiency loss due to the center of
heat release According to. 42 it is assumed that the energy
conversion takes place isochorically, but not at the TDC, but based
on the real position of the MBF50 of combustion. Efficiency loss due
to real heat release In this step, the real duration and shape of
the heat release is considered. In Figure 32, areas that are
enclosed between isochoric and real combustion processes are marked.
These have to be accumulated and considered as loss."
Here is fig 32.
The reason the wall loses are lower is the energy loss in the
combustion results in less heat getting into the walls compared to a
piston engine. It would probably be higher if the combustion was
improved. We are very close. Ignition of all the mixture as soon as
possible is the key. Surface mount spark plugs well a head of TDC
would help greatly. The Mazda Lemans had 3 spark plugs the third
being head of the regular two.
I have suspected this for years. Here is a drawing I did in 1998.
Paul Lamar
Hello Paul,
it's after one o'clock in the night now - so I will only send "some
remarks" ... ;-)
Enclosed you will find the Screen shot, I've talked about - I've
simply forgotten it - sorry, sorry ... ;-)
To Rolf ... I have the book you've described - it's written in a
positive point of view + that's ok ... ;-)
Unfortunately there are only a few books available - e.g. by Ulrich
Knapp, 2006, Waxmann Verlag GmbH, ISBN 3-8309-1637-x, with
interesting details ... (German)
I don't think, that my "idea" is worth to be discussed seriously -
will more a kind of joke - well, on paper there's everything
possible, but in reality ... ;-) __________
To Jose in Madrid ... the figures in the patent US 3.848.574 are
showing a rather big opening - so the question is, how much blow
back there will be ...
Perhaps you get in trouble with hot residual burning gases, that
"find" their way into the following chamber - means danger of
preignition far before TC + "negative torque" ...
Or you will loose some fresh mixture out of the following chamber
into the leading exhausting one ...
Generally you can say, the smaller your "openings" for ignition or
injection, the "better" ...
But since you haven't tried it, you can't be sure ... ;-)
May be, that you can transfer some unburned rich mixture from the
"forerunner" to the following chamber - you can see an example in the
preview of the SAE paper 2007-32-0098 (small RE for unmanned
helicopter)... ___________
Combustion in general ... the "up+down" freaks are using turbulences
since may be 70 years. With some swirls / vortexes / eddys you can
speed up the combustion "dramatically", but you will also get more
heat losses to the walls - again "the dose is the decisive factor"
... ;-)
And: flow speed is not the same as turbulence. In the first case a
relatively thin flame front with only a little active surface "is
blown forward through the mixture", in the other case you have a big
/ wide active surface - a bit like chain reactions in many different
directions, even a very little bit against the flow direction ...
Of course, a strong ignition source will help, too. There are a lot
of ideas with + without active or passive "pre chambers" to study +
then there are the ideas by the "Plasma guild" ... ;-)
At the end the relationship between costs + the gain you may see is
the most important thing. So, perhaps it's better to wait until
Paul's new ignition system is available ... ;-)
But, I think, there are a lot of other people, that do know much,
much more about combustion kinematics + chemical reactions ... (Dale
Davies ?)
Btw: avoiding leaded AvGas for RE is a good idea for two reasons ...
- lead hinders the fast + proper "growing" of the oil film on the
trochoid surface (less important in Mazda engines since 1986) - lead
is a combustion retarder - it slows the burning speed (therefore it
was used as "anti knock solution" in the last century ...)
Now it's late enough here in "old europe" ;-)
With kindest regards
Franky / Frank Herfert
That patent is so old (1974) that over 2.5 million Mazda engines
have been sold since then. If it had worked it would be used by now.
Good point on the lead. In theory aviation fuel is now low lead but I
wonder what they use now to retard knock.
The choice of the Austro engine for research is a bad choice as they
use high pressure air to cool the rotor and rotor bearing instead of
oil cooling. That is a BSFC penalty of almost 10% due to the HP
consumed by the blower. That type of rotary is typically .53 BSFC
while a Mazda is .47 BSFC. lbs/HP per hour.
A another thing about that paper is the emphasis on "squish flow".
I quote.
"Due to the squish flow, the flame propagation is retarded [11]
against the direction of rotation of the rotor and intensifies the
wall heat flux. As proved, the remaining unburned mixture combusts
until it has escaped from the
trailing part of the combustion chamber. Figure 29 shows the process
described above with reference to the CFD simulation. The flame
spreads primarily in the same direction as the rotation of the
rotor. Similar results are shown in [31] and [32] based on test
bench measurements and in [16] with the help of CFD simulation. The
penetration in the opposite direction happens very late because of
the pronounced squish flow.
The reason is that the gas velocities of the squish flow in the
region of the flame formation move at about 70 to 180 m/s (see
Figure 30), while turbulent flame front speed as a function of
pressure, temperature and turbulence in the combustion chamber of a
conventional SI reciprocating engine has a one power lower value,
shown in [33], [34], [35], [36] and [37]."
Squish flow is easily over come by moving the bath tub to the
trailing side of the rotor. As I recall Mazda may have tried this
but without the aid of the CFD analysis.
Note the CFD's show two spark plugs side by side. The Austro engine
has a relatively wide rotor.
Paul Lamar
I failed to attach figure 27. Here they all are again. If what they
say about squish flow is correct in this SAE paper we are on the
cusp of a MAJOR breakthrough in the fuel burn on rotary engines.
It is as simple as moving the rotor depression back towards the
trailing apex seal.
Back in 1969 Kenichi Yamamoto wrote the book "Rotary Engine". On
page 104 here is what he had to say on the subject of chamber
position on the rotor.
"Effect of rotor combustion chamber The location and shape of the
hollow combustion chamber of the rotor are , interrelated with the
efficiency and quietness of combustion and the required octane
value, and they have a substantial influence on general engine
performance. Fig. 9. 20 shows an ,example of the effect of
compressing t~ generate turbulence, and the effect of forming a
quenching area to prevent abnormal combustion, calculated for their
influence on the speed of gas flow in different types of combustion
chambers.
In terms of the ratio of the combustion chamber surface area to the
volume of the combustion chamber at top dead center (s/v), the
rotary engine is intrinsically disadvaptageous compared to the
reciprocating engine with an equivalent displacement and compression
ratio. On the other hand, with a rotary engine, it is easy to
generate a turbulent flow, whose speed is far greater than the speed
of combustion, and the trailing side of the rotor forms ~quenching
area to reduce the temperature of end gas. These factors contribute
to a unique combustion mechanism for the rotary engine which is
relatively uncritical to the kind of fuel, and provides superior
anti-knocking characteristics."
It is not clear to me why he chose to put the chamber in the middle
of the rotor.
Hear are the diagrams.
Pual Lamar
Paul and Jose,
I have done a variation of the Kawasaki mod and it works well.
It is only done on the leading plug.
I used a NACA duct type lead-in to the base of the sparkplug. It was
tested using combustion testing and proved to increase the burn rate by
2 degrees... that is, in order to bring the peak pressure back to 45
degrees ATDC we had to remove two degrees of advance.
Sorry I don't have a jpg photo available right now because I am in
Houston with grandkids. But maybe you can access my photobucket account
below.
Barry Bordes
[URL=
http://s287.photobucket.com/user/bbordes/media/Engine%20pictures/porting%201_zpscgsbgjzs.jpg.html][IMG]
http://i287.photobucket.com/albums/ll129/bbordes/Engine%20pictures/porting%201_zpscgsbgjzs.jpg[/IMG][/URL]
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