>Displacement has been
> defined since the beginning of the internal combustion engine as
> the amount of air the engine pumps at a VE of 100% in one revolution
> of the output shaft. It is arbitrary. It is not good nor bad or here
> nor there... it is the LAW!

<snip>
> Paul Lamar
>
I've removed everything else, because this is the crux of the issue.  A
4 cycle piston engine requires TWO revolutions of the output shaft to
displace it's displacement.  A two cycle piston engine requires ONE
revolution, but the rotary requires THREE revolutions of the output
shaft.

As I've said before, the issue is confused by trying to define
_EQUILIVENT_ displacements.  Displacement is just displacement, and the
rotary engine is the only one I've seen where the proponents of smaller
displacement numbers don't want to run the engine thru a complete cycle
to define displacement.  (I define a complete cycle as all of the parts
being back in their original positions.)

Since your LAW as stated above is incorrect, are you willing to concede
the point?

Bob W.

http://www.bob-white.com
N93BD - Rotary Powered BD-4 (real soon)
Prewired EC2 Cables - http://www.roblinphoto.com/shop/



You are missing something here Bob. One rev and one rev only
for a four cycle determines the displacement.

This I totally disagree with.  It's easy to calculate the displacement
for a piston engine.  pi * (bore/2)squared * stroke * number of pistons.
But, it takes two complete revolutions to get all pistons to pump that
displacement.

Does a four
cylinder four cycle 2.6 liter engine fire twice per revolution or not?

Yes.  That's my point exactly.

A 4 cylinder 4 cycle 2.6 L engine fires twice in one revolution and has
displaced 1.3 L.  On the next revolution, it fires two more times and
displaces another 1.3 L.  We surely can't use all 4 cylinders and only
have two ignition events.  How many intake valves have opened in one
revolution?  Two!  This is shown clearly in your two cylinder diagram.
In the first revolution from drawing 1 to drawing 3, only piston 2 has
pumped.  In the next revolution, piston 1 pumps.

The 2.6 liter four cylinder four cycle fires twice per rev just like
a 2 rotor rotary and it pumps 2.6 litters of displacement in the
process. For a 2.6 liter one rotor it would have to be twice
as large and it would fire once per rev. A four rotor 2.6 liter
engine would have rotor housings half as large and fire
four times per rev. A 2.6 liter 8 cylinder engine
would have individual cylinder volumes half the size of the
four cylinder four cycle engine and fire four times per rev.
Therefore the number of firings per rev has nothing to do
with the displacement of four cycle engines.

Well, except for the fact that no matter how many pistons you have, it
only fires 1/2 of them per rev, only 1/2 the intake valves open per rev,
and it takes two revs to complete a 4 stroke cycle.

You are wrong about the rotary. It does not have to rotate
three times to pump 2.6 liters of air. It rotates once
and the rotors are repositioned 120 degrees in the process.

I'm not saying the rotary rotates 3 times to pump 2.6 liters.  It pumps
3.9 liters.

In a 2 cylinder 4 cycle piston engine both of the pistons are
repositioned 180 degrees.

After one revolution in a piston engine, the pistons are in exaclty the
same position. The cam shaft has rotated 180 degrees.

In a 4 cylinder engine four pistons
are involved in the process of firing twice per one rev. There
are three rotor faces that are involved in this process of pumping
air and burning it on any given cycle.  Each has done their
fractional share when  it comes time to fire the plug. They all
work together to complete the four cycles just as both piston
do in a equivalent piston engine.

It is as simple as that.

Therein lies the real genius of Felix Wankel's extremely simple
design.

Yes it is!

Looking at just one chamber at a time or as a single entity is
misleading. Yes it takes more than one rev to have that one chamber
pump it its max volume and fire it but in the mean time other things are
happening.

I don't see what's misleading.  It takes three turns of the output
shaft or one of the rotor for each face to go thru the 4 cycles.  While
that face is going thru it's 4 cycles, the other two faces are doing the
same.

It is the ultimate multitasking engine if you will.

Yes it is!

I know the rotary is hard to understand. There are zillions
of people out there that don't understand it including
my old friend Don Sherman who set records in rotary powered
cars and built the first 13B powered 1st gen RX7. I have seen
stuff published by Mazda themselves that got it wrong.
It it certainly is challenging to explain in words.

At the moment, we are disagreeing on the 4 cycle piston engine. :)

I think one of the problems is the formula required
to calculate the rotary chamber volume is not as simple
as pie r squared times the stroke.

I don't think I would even attempt to calculate the displacement of the
rotary, even with the graph.  :)  However, for the 13B it seems fairly
well established that the displacement of one face is about 650 cc.

Ansdale's book The Wankel RC Engine got it right. Unfortunately
the book is rare. Here are a few illustrations along with
one of mine.

Paul Lamar

There is a simple disagreement of fact here.  How many revolutions does
a 4 cycle engine have to make to pump it's displacement.  I believe
that with a little reflection on the diagram you provided, it is clear
that it takes two.

Paul, I think you've spent so much time comparing the rotary to piston
engines that you're overlooking the basics.  Displacement is only
defined by the bore, stroke, and number of pistons of a piston engine.

A two cycle piston engine can't be compared to a 4 cycle piston engine
with the same displacement.  This leads to statemenst like "A 1.3L 2
cycle engine is equilivent to a 4 cycle 2.6L engine".  If I want to
compare the rotary to a 4 cycle engine I would say a Mazda 13B 3.9L
engine is similar to a 2.6L 4 cycle piston engine.  (That's based on
your analysis and explanations.)  A 1.3L 2 cycle engine isn't a 2.6L
engine just because it compares to that size 4 cycle engine.

Bob W.