Paul,
I don't understand what you are trying to say.
The actual physical displacement of the Wankel combustion
chamber --
that is, the volume of any of the three "flanks" of the rotor -- is
what it is. In the Ansdale illustration that is 500 cc.
In a 13B engine it is 1300 cc for the two rotors or 650 cc per
rotor. That is the actual physical volume and that is the amount of
air-fuel charge that is combusted in each power stroke. Is this
not so?
That is why the naming conventions of all Wankel engines that I
have
seen are based on actual displacement.
For each complete revolution of the three-sided rotor, there are
three power strokes. Since the engine shaft turns three times for
every turn of the rotor, that means one power stroke per turn of
engine shaft.
That means the "equivalent" or "effective displacement is twice
that
of a piston engine. But what actually happens is that each
combustion chamber of half the size has two power strokes, in the
same time frame as the piston engine has one power stroke of a
combustion chamber that is twice as big.
So how does it make it right to pretend that the Wankel combustion
chamber is twice as big? In order to do that we then also have to
pretend that a power stroke only occurs once every two turns of the
engine shaft.
To me that's like calling a 650 cc 2-stroke a 1300 cc engine.
What is wrong with this picture? I don't get it.
Regards,
Gordon.
Ah well you have touched on the solution.
The rotary is not a two stroke. It is a four stroke.
Lets turn it around. How much air would a 2.6 liter two cylinder
TWO STROKE engine pump in one revolution?
As far as HP is concerned the ONLY thing that matters is how much
air a four stroke engine pumps in ONE REVOLUTION at 100% VE.
Not the physical displacement of x number of chambers.
The definition of displacement, as far as engines are concerned,
is only valid in context with the type of stroke.
Here is what Ansdale has to say about that.
13B rotaries are raced in the 2.6 liter class world wide
for a good reason. The only reason they generate more power
than a 2.6 liter four cylinder engine is they turn faster
and breath better. Lately that is less true as the piston
engine RPM has been raised by detail development and the
use of high strength to weight ratio materials like titanium.
Also four valves per cylinder has improved the breathing.
It is very rare for any 2 valve cylinder to have a VE over one.
The RX8 engine is just over one and P-ports are typically
1.2.
Formula One (2.5 liter as I recall) V8 engines are now
turning 19,000 RPM. At least four valves per cylinder with
a very short stroke so larger valves can be used for a given
physical cylinder displacement. You will not find the details
of a competitive Formula One engine anywhere. Its a well
kept secret. However I would not be surprised if the VE's were
well over one. Applying the RPM difference to a 2.6L p-port rotary
making 340 HP at 10,000 RPM would make the Formula One engine
about 19,000/10,000 times 300 HP or 655 HP which is about
right for a Formula One engine.
Paul Lamar ...No rotor no motor.
I'm sorry I ever brought it up. I just wanted to know what turbo would
work best on my 20B.
Don
No need to be sorry Don. I certainly don't mind. Each time
I explain it I get better and better at it:) If you hadn't
somebody else would sooner or later. I need to add this
stuff to the web site.
Paul Lamar ...No rotor no motor.
Paul,
Not wanting to beat this silly topic to death (this is clearly a
potayto-potahto thing), but hp does not always depend just on amount
of air.
If you have oxygen in your fuel (ha ha)....
And yes, the 80 ci (actual discpament) Wankel does pump the same
amount of air as a 160 ci piston engine. But it does it by having
two intake strokes in the same time (measured in engine shaft
turns) a piston has one. (And two power strokes, etc.)
This economy of movement is the genius of the Wankel design. Half of
the piston's up and down motion is really wasted in a 4-stroke engine.
Regards,
Gordon.
" And yes, the 80 ci (actual displacement) Wankel does pump the same
amount of air as a 160 ci piston engine."
Not true. The 4 cycle 80 ci rotary pumps the half the air of a
160 ci 4 cycle piston engine. However a two cycle 80 ci piston engine
pumps the same air as a 160 ci 4 cycle piston engine. Nobody has
built a two cycle Wankel yet but it is possible.
"But it does it by having two intake strokes in the same time
(measured in engine shaft turns) a piston has one.
(And two power strokes, etc.)"
Half true. Yes the 80 ci one rotor does fire twice in 720 degrees and
a 160 ci one cylinder piston engine fire onces. The piston engine
in this case has twice the power.
Part of the confusion is there are three 80 ci active chambers working
in concert in the one rotor rotary and there are only two in the
2 cylinder piston engine.
BTW a simple two cycle, two cylinder piston engine would have four
active chambers. One above each piston and one below each piston.
Just in case we needed more confusion :)
As I said above: As far as HP is concerned the ONLY thing that matters
is how much air a four stroke engine pumps in ONE REVOLUTION at 100% VE.
The ONLY advantage the rotary has, HP wise, is a better VE and a
higher RPM capability. Nothing to do with a displacement advantage or
disadvantage or configuration.
Paul Lamar ...No rotor no motor.
Paul,
I give up.
Now you're saying that each rotor on a 13B takes in 80ci of air on
each intake stroke? And combusts 80 ci inches of air on each
combustion stroke?
Why is it called a 1300cc engine?
Let's forget about the revolutions for now and just concentrate on
the actual physical volume. And by that I mean the maximum volume
formed by the rotor and the housing when it takes in the intake
charge. I believe this is 650 cc per rotor, no?
I think this is confusin g a lot of people.
Regards,
Gordon.
"Now you're saying that each rotor on a 13B takes in 80ci of air on
each intake stroke? And combusts 80 ci inches of air on each
combustion stroke?"
Well not in so many words but yes that is it... more or less
like it is in a one rotor engine.
Lets call them chambers rather than a rotor. Each 80 ci chamber
moves around in the rotor housing performing all four cycles.
It sucks in 80 ci of air, compresses it, expands it and exhaust
it. It just takes longer than one rev of the e-shaft.
There are three 80 ci chambers doing this simultaneously.
The total amount of air pumped by all three 80 ci chambers
in one rev is 160 ci.
It just so happens the one rotor engine fires once per rev
of the e-shaft and the amount of air all three chambers pump
in one rev is the same as a 2 cyl four stroke 160 ci engine.
As Dave Leonard pointed out it is unfortunate the inventors
called it a 80 ci engine.
BTW I would say the word "displacement" has a specific
meaning in the context of an internal combustion engine.
People need to understand this. This is part of the reason
why the Wankel is so frequently dismissed or discriminated
against.
Paul Lamar ...No rotor no motor.
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