Re: Hmm

[telljb@ozemail.com.au (Tell)]

Rob Kearey <r.kearey@prentice.uq.edu.au> wrote:
>EMD diesels use the supercharger to scavenge the cylinders after a power
>stroke - being two stroke engines, they don't have an exhaust stroke to
>do that. I far as I'm aware, the supercharger on these engines doesn't
>significantly compress the intake charge air - they're simply roots
>scavenged, naturally aspirated engines. I'm really not sure about your
>last point, either. Diesels being compression ignition, the compression
>and stochiometric qualities of the intake charge are, AFAIA, what's
>important for effective combustion. [1]

The term supercharger is not only wrong but completely
misleading.  EMD and Detroit diesels use Roots BLOWERS
which give these two cycle diesels "natural aspiration"

Do not confuse two stroke diesels with two stroke
petrol engines.  Petrol engines draw their air/fuel
charge through the crankcase which is then compressed
by the downward motion of the piston and transferred
through a transfer port to the combustion chamber.

EMD and Detroit engines DO NOT, they simply expose
ports on the cylinder liner during the downward motion
of the piston.  The blower forces air through the ports
into the combustion space at normal air pressure which
assists in scavenging the burnt exhaust gases from the
previous cycle via an exhaust valve in the cylinder
head, (two stroke petrol motors do not have valves) and
the incoming air on EMD and Detroit engines refreshes
the cylinder for the next compression and combustion
stroke.

In other words, EMD and Detroit diesels without turbo
charging are classified as naturally aspirated diesels
there is NO boost as with turbo charging.
     
Four stroke petrol engines with supercharging, such as
used on the Holden Commodore actually boost the
incoming air at pressures way above atmosphere as is
the case for turbo charging.

----Tell