Fuel cut-out to conserve fuel

[Jeremy Edmondson]

Jody Shapiro wrote:
> 
> > You'll still have air entering the cylinder that will have to be
> > compressed and that will take some energy.  How much energy is the
> > question.  The other cylinders will have to compensate for the "dead
> > wood" in the cycle by increased fuel consumption, I think.
> 
> True, I hadn't really considered that to be a major energy loss.  If
> nothing else, the air will be heated by the compression;  makes we wonder
> how much cooling Cadillac actually gets out of running some cylinders
> with just air (and no fuel).
> 
> However, wouldn't most of the energy lost to compression be regained
> on the power stroke as the compressed air now has the opportunity to
> expand and push slightly on the piston as it heads downward?
> 
> -Jody
> --
> http://www.token.net/~jshapiro/z28/

Adiabatic compression is reversable, look at a compression ignition engine, very low 
pumping losses.  Cutting out cylinders is effective if it is not throttled, 
typically if cyliners are cut out by not injecting fuel the gains in efficency are 
small as this situation occurs at very small throttle openings and hence pumping 
losses are still significant.  Ideally one wants to shut the valves completly which 
will cause pistion ring 'suck by' and oil will be consumed or the clyinder in 
question be unthrottled.  Better still run engine extremly lean with stratified 
charge techniques such as Mitsubishi is doing.

Jeremy