Some input from the heritic - Vance  - I DO admire the Wankel, but as in every
engineering approach there is no free lunch.

ACRE NL wrote:

This is elementary for most of you I am sure.
This was intended to be a side bar for a magazine article.
I will add this to the web site as well.

How the Wankel Works copyright by Paul Lamar

The wankel rotary consists of a three sided rotor moving in a  modified oval
chamber or rotor housing. There are at least two holes in the walls of one
side of the rotor housing. In the other side of the rotor housing there is
at least one spark plug. One hole is used as an intake port and the other as
an exhaust port. Just like a one cylinder two cycle piston engine. The rotor
rotates around the center of the eccentric on the output shaft while at the same
time rotating around its own axis.

To clarify -The axis of the rotor IS the center of the eccentric , where ever it may
be, and it rotates about that axis at 1/3 output shaft speed and is "whirled" about the
engine centerline at full output rpm..

This is very similar to the way the earth
rotates around the sun while rotating around its own axis. The rotor rotates
one third as fast about its own axis as it does around the center of the
output shaft. Actually what is happening is the center or CG of the rotor is
moving in a circle around the center of the output shaft while the output
shaft rotates. Very very clever on the part of Felix Wankel to invent and
engine that uses this motion.

As this motion is taking place the tips of the triangular shaped  rotor are
passing the ports in the housing. As one tip, call it tip 1, passes the
intake port in the rotor housing the face behind tip 1 starts to draw in the
fuel air mixture. Call it face or chamber A.  When the next tip call
it tip 2 passes the intake port the mixture is captured and starts to
compress. As the chamber continues around the housing it encounters the
spark plug and the mixture inside it is fully compressed.  The spark plug
fires and the chamber starts to expand imparting the pressure energy in the
burning mixture to the output shaft. As the rotor continues on around tip 1
passes the exhaust port and the burnt mixture starts to leave chamber A.
This completes the four cycles for chamber A. In the mean time chamber B
and chamber C are completing various cycles of this same sequence
simultaneously.

The rotor position at your zero shaft point is analogous to the bottom dead center
intake stroke position for a classic piston engine. After 270 degrees of shaft
rotation
and 90 degrees rotor rotation (1/3rd) the position is compression TDC. The face A
has moved relative to the engine center twice the offset of the eccentric, or as one

might say, over the clammer of naysayers, "full stroke" . The displacement of
chamber
volume during this event is the face area times this "stroke" plus a factor for the
chamber
shape during this event. It wou;ld appear that about 2/3 of the swept volume is
accomplished by the stroke Analogous to a reciprocating engine) and about 1/3
from the chamber shape (analogous to a true rotory displacement device, such
as a vane compressor) - Question ! - what is the eccentric offset on a 13B?)

This three chamber simultaneous action  is the reason the wankel  engine is
so light and compact for the power it is able to generate. Furthermore the
forces in each chamber due to the pressure in each chamber are completely
contained in the one piece cast iron rotor.

This is not true, tho it may appear so at first inspection. Compression and
expansion forces are primarily reacted on the eccentric "crank pin" with
the other instantaneous (moving) reference being the engagement of the
rotor gear to the stationary gear. If this were not true you would get no
useful work out of the engine. The forces on the other flanks of the
rotor provide some mitigation to these forces, just as the othe two
connecting rods of a 3 cylinder radial engine input to the common
crank pin. As in a typical piston engine, these forces are overshadowed
by the acceleration forces on the  pistons and rods at high speed. In
the Wankel case this is the centrifugal force of the  rotor (undoubtedly
much heavier than the equivalent rod and piston - tho a shorter stroke)

In a four cycle piston engine
this is not the case. The compression force must pass down a connecting rod,
into the crankshaft and up another connecting rod into another chamber that
is expanding and extracting power from the burning mixture. This makes
piston engine force paths and consequent stresses far far more complicated
than the wankel engine.

Although the wankle has similarities with a two cycle engine,  particularly
in regard with the way the porting mechanism works, it is in no way a two
cycle engine. All four cycles are continuously taking place simultaneously
and those are intake, compression expansion and exhaust.

Paul Lamar

The compact packaging for the effective displacement, and the elimination of
heat sensitive valving, are definate pluses for the Wankel. However, the
very non optimum combustion chamber, and the destructively hot exhaust
remain significant challanges. I am also sure that chamber leakage is also
a contibuter to some of the heat, efficiency, and emission woes. (Model
T owners could frequently leave a cylinder at compression, and come
back out of the store and start the engine by moving the spark adavance
lever - try that on a modern engine some time)

Running for cover - but adamantly defiant - Vance

You can run but you can't hide :-)

Paul Lamar
 
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