> >> You got me George :) Perhaps it got mixed up in the translation
> >> from Japanese to English. The only thing I can think of is they did
> >> it that way so the new engine would fit in the RX8 with a minimum of
> >> changes in the engine compartment. I do understand the need for more
> >> torque but they could have achieved the same result with a dual clutch
> >> Formula One type transmission. The car would be more fun to drive.
> >>
> >> Aspect ratio means length divided by width.
> >>
> >> --
> >> Paul Lamar ...No rotor no motor.
> >>
> >> George, you are talking about optimum theory, not practical
application.
> >>
> >> First, most spark plugs are offset in the cylinder head, especially in
> >> dual-ignition engines. The Rotax 2-strokes are notable exceptions.
> >>
> >> Second, the shape of the standard spark plug "shadows" a very large
> >> area, which is blocked by the negative electrode (the metal bar
that you
> >> bend to adjust gap). This means that the flame radiates in an "ace of
> >> spades" pattern, with initiation taking place later behind the
electrode
> >> than in the rest of the chamber.
> >>
> >> Third, the theory also assumes a stationary, uniformly stoichiometric
> >> mixture, while in an operating engine, the mixture is a
highly-turbulent
> >> non-uniform mixture, drawn in at high speed through a variable
opening a
> >> few millimeters across at the widest. This problem is actually worse
> >> with fuel injection, as the fuel is only partially vaporized as it
> >> enters the cylinder (with a carb, the fuel vaporizes more
completely in
> >> the intake).
> >>
> >> Fourth, a large percentage of the gases in the cylinder are residual
> >> waste from the previous cycle (in a 1:10 compression, less than 90% of
> >> the waste is expelled during the exhaust stroke, and in most 4-stroke
> >> engines, some is drawn back in as the piston begins the intake stroke
> >> (while the exhaust valve is still closing). Turbulence at the valve
> >> opening keeps some of the waste from being exhausted, which is why
it's
> >> necessary to make the exhaust system as wide open as possible to
> >> increase power. To make matters worse, this waste, being several times
> >> the temperature of the intake fuel-air mixture, will rise to the
top of
> >> the cylinder -- which is where the spark plugs are usually found. Fuel
> >> only burns once, and the mixture is more lean at the top due to the
> >> waste which mixes with it.
> >>
> >> As you see, the piston engine is actually working against itself
when it
> >> comes to combustion.
> >>
> >> Now, look at the fluid dynamics inside the Wankel.
> >>
> >> First, the combustion chamber actually travels past the spark plugs,
> >> giving a greater "illumination" to the spark while carrying the
> >> fuel-laden mixture past them. The optimum for the piston engine is an
> >> "expanding hot spot" centered on the electrodes, while the Wankel
> >> distributes the spark as a "streak" relative to the combustion. The
> >> greater the contact between the fuel and the spark, the more
uniform the
> >> combustion.
> >>
> >> Second, this movement of fuel is ACROSS the plug, rather than randomly
> >> swirling around it, thus the movement of the flash front is more
stable.
> >>
> >> Third, the fuel-air mixture is more stable, because the intake port is
> >> larger and not blocked by the stem of a valve.
> >>
> >> Fourth, a far greater percentage of waste gases are exhausted, because
> >> the port is wide open during the exhaust portion of the cycle (less
> >> turbulence), because there is less "leftover" space between
trochoid and
> >> wall, and because there is less "drawback" from the exhaust. What
waste
> >> remains is not concentrated where the spark plugs are.
> >>
> >> Now, as to the narrower chamber being even more efficient, my guess
> >> would be that it provides an even more stable flow of intake
mixture and
> >> allows the flash front to move in a more controlled way.
> >>
> >> Keith W
> >
> > Keith,
> >
> > Very illuminating, I'm always ready to learn and I hope you don't,
me using
> > these arguments, although I think they may be more relative to the
renesis
> > engine than to the PP in regard to overlap and retention of
contaminated
> > gases. I guess with a narrower rotor the unburned squish areas are
less as
> > well.
> >
> > Never the less I've learned something (a few things) today about
the piston
> > engine idiosyncrasies and it does indeed make the rotary look even
better.
> >
> > BTW you forgot to mention the rotary's tendency to throw the
heavier fuel
> > molecules toward the spark plugs, making for better burn of leaner
mixtures
> > ( the term escapes me at the moment).
> >
> > I appreciate your effort in this regard.
> > George ( down under)
>
> We're here to swap knowledge, so I'm glad it helps.
>
> As far as the heavier molecules, I consider this a very minor factor,
> compared to the typhoon of fuel-laden air flowing past the plugs --
> that's where the efficiency comes from. The more fuel molecules you
> ignite with the spark, the better your burn will be.
>
> Keith W
>
> Perhaps some one should try small walls in the rotor combustion chamber
> depressions to promote turbulence.
>
> Paul Lamar
>
> Paul and group,
>
> StarApex web site may give clues for better power from rotaries. The
> 13b has an e-shaft "throw" of less than .6" which is where torque comes
> from, (as compared to 3 to 4" for a typical V8 engine). Also, the
> trailing end of the rotor continues to product pressure (torque) on the
> e-shaft, much more so than the leading end.
>
> Mazda, or any rotary manufacturer, can make more torque by lengthen the
> rotor leverage to the e-shaft by increasing the "throw". Of course this
> requires all new housings. My understanding of the Taiki design is that
> is what Mazda did, in part.
>
> When I first saw the pics of the Aixro engine it is understandable how
> Paul W. gets so much power in that small package. ie. the rotors are
> VERY wide, creating a larger surface area ratio to "push" on the
> e-shaft. An interesting study would be to make an engine with a larger
> rotor while still keeping 300cc chambers and compare torque, hp, and
> fuel consumption. Do we know enough about the operation of rotaries to
> do a computer simulation? Would a chamber offset toward the trailing
> edge produce more torque? Is anyone going to lose sleep wondering about
> this?? :D
>
> Dan
>

Dan:

If I had mongo computing power and the requisite engineering background,
I would lose sleep to do it.  To slay the Evil Count Otto and his
Reciprosaur, which has terrorized and laid waste the automotive
landscape for a century?  It would be worth it.

Les Nordman

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