8 cycling 4 stroke?

[Clint Corbin]

At 03:43 PM 2/25/98 +0000, you wrote:
following intake stroke restores the correct mixture balance so the next
>comp stroke fires OK. Then the '8 cycling' starts again! Hence the lumpy
>idle of a big-cammed engine. I guess lean-burn engines are examples of
>how
>to make use of lean & partly burnt mixtures. The gains are in emmissions
>and
>economy but not really power, I think. Does anyone know the mechanics of
>how 
>the Mitsubishi GDI(gasoline direct injection)series engines combine
>incredible 
>economy and power? 
>Ross


Ross,

Off of the top of my head, I would have to say it was due to a thing called 
"Stratified Combustion".  Basically, you design the chamber/injector/spark
plug/etc so that it creates a rich mixture around the spark plug and a very 
lean mixture everywhere else, especially at part throttle.  This way, when 
the spark plug fires, it has a nice, easy to light rich mixture to fire
off.  The
flame front thus generated will ignite the lean mixture in the rest of the 
combustion chamber.  (In case anyone is wondering, an electrical spark is
really a crappy way to light a fire!  An open flame will light air/fuel
mixtures 
that are orders of magnitude leaner than anything that could be light by an
electrical spark)  With a properly tuned system, you could get rid of the
throttle valve (just like a diesel) and control the engine power with just the
amount of fuel injected.  This will get rid of you part-throttle "loop-loss",
which will help to increase you fuel economy.  

Clint Corbin

PS: "loop-loss" is the energy the engine uses to lower the piston in the
       bore against the vacuum generated at partial throttle.