Just a comment here on "compression ratio."  My take is that it is
not as important as "expansion ratio."  If you look at the PV diagram
of the Otto cycle, that is where the work is done and the more you
let those hot gasses expand against the working surface (piston crown
or rotor face) the more work you get out of them.  Normally in piston
engine design both ratios are the same.  But you can play
tricks.  That is the trick employed by current manifestations of
the  Atkinson cycle.  Build a piston engine with geometry that
permits 12  to 14 to one expansion ratio and you get more work out
of each  combustion event.  Then you trick the intake valve timing
so the  effective compression ratio is enough lower to prevent
detonation and  you are on the way to the efficiency of a diesel
with light fuel and  a spark plug.

SD

Look up Mazda Skyactive G. 13:1 CR. The variable valve timing
bleeds  off pressure at low RPM to control detonation. At high RPM
the  timing contains the intake for more power. Supposed to be
substantial power and economy gains.

Dale Davies

Sounds like WW I high altitude German fighter planes with two
throttle  levers :) Current race piston engines are running 14:1.

Same idea will work on the rotary. One just needs a valve
in the compression chamber that bleeds off pressure at
low RPM. That is also similar to the Atkinson cycle.
http://en.wikipedia.org/wiki/Atkinson_cycle

Clever marketing and PR :)

Mazda already built and sold some of those supercharged piston
engines in the Millenia S but sales did not meet expectations and
it  was discontinued.

http://townhall-talk.edmunds.com/direct/view/.ef21e99

Paul Lamar

The Skyactive engines are not forced induction. Bit of an article
in  the latest Zoom Zoom magazine. Getting away from turbos as untrained
owners have problems. They think they can drive them like a 350
Chevy; come screaming in off the freeway and shut it down without a
cooling off period.

Dale Davies

What I said was similar :)

As far as 3rd gen RX7 turbo charging is concerned what was
happening  was people were cranking up the boost without changing
the computer program.

Paul Lamar

Paul,

I think you mentioned on a previous post that what manufacturer's
call Atkinson cycle was invented by Bruce Crower. You effectively
let the intake think it is on a 300CID engine when in reality it is
on a 350 engine. You sort of get the 350 power out of the 300's air
and fuel.

The 13:1 CR gets back the lost power with the effective CR limiting
detonation. Once the RPM get up the detonation is not as big a
problem and the valve timing reverts to a normal event and the power
is increased.

Dale Davies

Not as I recall. I Think Bruce Crower invented the six stroke engine.
Half gasoline and half steam.
http://en.wikipedia.org/wiki/Crower_six_stroke

The Atkinson cycle was invented by Atkinson :)
http://en.wikipedia.org/wiki/Atkinson_cycle

Paul Lamar

The Mazda Millenia used a Miller cycle. My interpretation is it is like the
new rendition of the Atkinson cycle, but with a supercharger to keep the
charge density.

Atkinson used linkages to vary the effective stroke between the intake and
power strokes. Now it is done with late intake closing. The intake could be
closed very early so the "carburetor" saw a smaller intake than the
displacement actually is. The power stroke would remain the same. Only problem
there is it would be choked at anything over idle. The late closing allows the
ram effect to come into play as th RPM increases to maintain power.

Back in the early '70's, I think it was Crower but may have been Crane that
proposed the late intake closing. At that time carbureted engines saw a low
idle vacuum and the mechanical controls required major tuning to make it work.
Electronics makes this fairly simple to implement.

Dale Davies