Rotary Engine wrote:
Every few months or a year the subject of the exact rotary engine
displacement comes up yet again. Here are a few indisputable facts.
Anybody near a rotary engine that is running can verify
these facts.
1. The one rotor rotary engines fires once per revolution
of the E-shaft. Easy to check. Stick your finger in the spark
plug lead :)
2. The displacement volume of one chamber of the Mazda rotary is
40 cubic inches. One can verify this by filling the combustion
chamber with a measured amount of oil through the spark plug holes
when the rotor is at bottom dead center.
3. The rotor rotates at one third of the e-shaft RPM.
Just look at the rotor phasing gears.
How then is one 40 cubic inch rotor chamber full of fuel
and air able to fire once per revolution of the eccentric
shaft?
There will be a prize for the first correct answer.
Paul Lamar ...No rotor no motor.
-------------------------------------------------------
Because there are 3 rotor faces - thus 3 chambers to go through the "4 cycles" of ICE,
and the phasing gears make each of 3 chambers complete their cycles once per
revolution of the e-shaft.
-dave Arbogast
------------------------------------------------------------
1/3 * 3 = 1. Doc Custer
----------------------------------------------------------
The 4 phases of combustion, intake, compression, ignition, and exhaust
take place in one rotation of the rotor. Each face of the rotor is in a
different phase of combustion so as face 1 is in the intake phase, face
2 is in the compression phase (arbitrary designations). These
activities are happening simultaneously. In one revolution, each
face has a combustion event, three faces, three events, three
rotations of the e-shaft.
Bob White
----------------------------------------------------------
Paul,
The rotor forms 3 chambers, 1 of which will pass into firing position per
revolution of the e-shaft.
Bill Jepson (unless I'm missing something here)
-----------------------------------------------------------
Um.. 'cause the rotor has three sides/chambers to it??
Jarrett Johnson
-----------------------------------------------------------
The E-Shaft turns at 3 times the rotor rpm, Virgil Salisbury
------------------------------------------------------------
Bzzzt! The "rotor chamber"(*) is
*much* more than 40 cubic inches. I
think you meant the "portion of the rotor chamber partitioned off by the
apex seals." And there are 3 apex seals, so there are 3 partitions
phased 120 degrees apart. Since the rotor "rotates"(**) at a 1:3 ratio
with the eccentric shaft, then each partition fires once per eccentric
shaft rotation.
Russell Kent
(*) The rotor chamber is that void inside the housing where the rotor
moves about.
(**) Really the rotor follows an eccentric path while rotating about its
center. But we'll simply call this "rotating".
------------------------------------------------------------------
Paul,
Due to the 3 lobes on the rotor, you have all the required cycles required
to run occurring concurrently in a single rotation of the eccentric shaft. I
want to see you do that with a single piston engine!
Larry Childs
-------------------------------------------------------------------------
There are three chambers per rotor and since each of those fire once per
rotor revolution only one will fire per e-shaft revolution.
This doesn't answer the question of displacement, though. It's not
clear to me how it should be measured. Is it the volume of all the
chambers in the rotary engine (analogous to the volume of all the
cylinders in a reciprocating engine)? That would require three
revolutions of the e-shaft to get power out of all the chambers. Our
beloved 13B would have to be renamed 39B. Mazda chose not to do it that
way. I'm sure there is some fallacy in my understanding of the volume
calculation for the rotary. I'm looking forward to learning the facts.
Dave Detty
-----------------------------------------------------------------------
One third of the eccentric shaft revolution is what it takes for the rotor
face to complete intake, compression, combustion and exhaust.
Alfonso Lebron
---------------------------------------------------------------
Because there is three such chambers for each rotor!!??
Steve Izett
Perth WA
---------------------------------------------------------------
I probably am not the first however...The answer is : One 40 cubic inch
rotor chamber full of fuel and air is able to fire once per revolution of
the eccentric shaft because their are three faces on the rotor and they each
fire for each revolution of the eccentric shaft, even though the rotor is
turning at one third the rpm of the eccentric shaft.
Norm Deboer
------------------------------------------------------------------------
Each surface of the single rotor engine completes the sequence of intake
compression combustion and exhaust in three e-shaft revolutions.
Looking at the rotor that will turn clockwise you count the fireing order
of the rotor by counting the surfaces counter clockwise.
For every revolution of the E-shaft the previously counted
surfaces will systematically complete the power stroke.
Therefore you have one power stroke for every e-shaft revolution.
Kenneth McKenzie
-----------------------------------------------------
I'll let you the readers be the judge. You can vote on the winner if you wish. I'll tally
the votes when I get back.
The displacement of all internal combustion engines are calculated on
the amount of volume each cylinder displaces times the number
of cylinders.
Since the rotary has three 40 cubic inch chambers in the one rotor engine
is the displacement 120 cubic inches?
If not what then is the real equivalent displacement of the Mazda rotary engine and why?
The key is to study the operation of the two cylinder four stroke piston engine.
This is the closest analogy to a one rotor Wankel.
Hint: Note that in one revolution of the 2 cylinder 4 stroke piston engine only one of
the two cylinders fires. In the next revolution the other cylinder fires and so on.
BTW This is and the high RPM of the Wankel make piston engine ignition coils
unsuitable for the rotary.
Paul Lamar ...No rotor no motor.
OK Here are the responses from the people that sent me stuff after I uploaded the
previous message and after I went out of town for a week so they had the benefit of the hint :)
----------------------------------------------------------------------
It's not the same chamber firing once per e shaft revolution. 3 chambers
firing in sequence one per 1/3 rotor revolution or one per e shaft revolution.
John Prendergast
-------------------------------------------------------------------------------
Paul,
The one 40 cubic inch rotor chamber fires once per rev of the output shaft.
The chamber defined by the other faces of the rotor are doing their exhaust,
intake and compression thing staging for their turn of the shaft. I tend to
equate each rotor with an 80 cubic inch boxer twin.
Steve Brazil
---------------------------------------------------------------------------
If we're simply looking for the piston displacement equivalent, the rotary
has a pumping displacement of 40 CI per rotor (35 CI for the 12A/70 mm housings)
where as a 4 stroke piston motor has only 1/2 the pumping displacement they are
rated at. Wankel got it right, Otto was wrong...or vis vera if you're the sentimental type.
Tom Lee
------------------------------------------------------------
Paul,
From past discussion, I believe it was agreed that displacement of the 4-stroke
engine is determined by 720* of crankshaft rotation. As we know, the rotary
requires 3 complete rotations (1080*) of the eccentric before it starts over.
However, you only count two of the three chambers to find "equivalent displacement"
because that is how many chambers will fire in 720* of eccentric shaft rotation.
Therefore, the "equivalent displacement" for a one-rotor would by 40 x 2 = 80 cu in.,
or 40 x 2 x 2 = 160 cu in for a 2-rotor 13B.
It is my opinion that true total displacement should take into account the firing
of all faces without repeating any, or 1080* eccentric rotation.
But that wasn't the question.
Mark Steitle.
--------------------------------------------------------------------------------
On Wankel operation and its displacement
Paul and all,
It may be considered unfair for me to respond as well, after having read all the answers.
Nevertheless, here is my assessment.
We all agree that at one revolution of the eccentric shaft one of the faces of the rotor fires.
At the next rotation of the shaft the next face fires. Rotation 3, face three fires.
On rotation 4, face one fires again. For the sequence of operation, it is really
irrelevant which face fires and how many faces there are. After all, it is one rotor,
it only turns over and changes position.
_Two-stroke RPE__:_
Comparing this with the reciprocating piston engine it is the same as a one-cylinder
two-stroke engine. It too fires once at per revolution of the crank shaft, however
always the same piston. (It does not turn over, so to speak.)
Say the displacement is also 40 cu-in, both, the RX7 and the 40 cu-in single cylinder
two-stroke are making the same hp, considering all else being equal. At least the
same amount of air is displaced in case the VE is equal on both. The shaft rpm has
to be equal as well, naturally.
_Four-stroke RPE: _
To match that sequence, two cylinders re required since it takes two revolutions
for the four-cycle operation to be completed for each cylinder and piston.
To achieve the same air throughput as the above two engines, the four-stroke RPE
will have 2 * 40 or 80 cu-in displacement. Again assuming all else being equal,
all three engine are now the same.
That is a Wankel with 40 cu-in per chamber, a two-stroke of 40 cu-in, and a four-stroke
of 80 cu-in are all the same as far as displacement per shaft revolution in concerned.
We can see, even the RPE’s are named differently; two- and four-strokes are
_not_ equal.
No wonder we have confusion.
It should be noted that it is of no consequence how many cylinders are used in the
two-stroke and four-stroke engines, as long as their total displacement is 40 cu-in
in the two-stroke, and 80 cu-in in the four-stroke. It is the way two and four-stroke
engines are being designated. More cylinders only means a higher number of power stroke
per shaft revolution, more overlap, better smoothness, and usually higher speed capacity
as the piston stroke is reduced. With speed hp goes up.
_The Wankel engine:_
Now comes the hard part. Since the Wankel engine works per the four-stroke principle,
should it be compared to the four-stroke RPE and be called an 80 cu-in engine?
Or should it be designated like a two-stroke of 40 cu-in? You be the judge.
For my taste, I would consider it to be an 80 cu-in engine to be easily comparable
the one other four-stroke engine, namely the RPE that is in existence.
Regards
Rolf Pfeiffer
--------------------------------------------------------------------------
I've heard of people being two-faced. But an engine that is three-
faced? Get real. The right answer to this question is that it's all
done with smoke and mirrors. That's the best answer and I deserve
the prize.
John Dinkel
-----------------------------------------------------------------
Paul
Not displacement discussions again. Remember this time you started it:)
Ok ....having stuck my finger in the rotary engine coil wire I notice that
every time the I heard a 'chug' and air escaped from the leading plug hole
I got a little excited. Doing the same thing with the 2 cylinder piston
engine I had to turn the engine over two revolutions before the whoopee.
Therefore if we want to have a comparative displacement number, comparing
apple and oranges so to speak, we have to measure the rotary at twice the
number of combustion events. The one rotor, or one half 13B, will have a
displacement of 655.48cc X 2 or 1.31096 liters of milk.
Doug in Japan.
------------------------------------------------------------------------
OK I want some votes. Who wrote the best explanation?
Send me you votes and I will tally them up in a few days.
Anybody sending the explanation before I went away gets two votes.
Paul Lamar ...No rotor no motor.
The Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site.
http://www.rotaryeng.net
Copyright 1998-2007 All world wide rights reserved.