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