05/15/2004

Two Stroke Diesels

Going back to piston port 2 cycle diesels.

All such piston ports are essentially symmetrical - they both open and
close at about the same time.

"Supercharge" valves force unsymmetrical into the piston timing.

Consider a rotating, properly phased butterfly valve in series with the
exhaust port.  This is an exhaust supercharge valve.

The rotating butterfly valve opens well before the piston port is
exposed, so that there is a sudden and sharp blow down of exhaust
gasses.

Near bdc and just after, the rotating butterfly valve closes,
effectively sealing the exhaust piston port.  

The intake port remains open, and fresh charge continues to enter the
cylinder until the intake port closes.  This "supercharges" the cylinder
in that there is more charge in the cylinder than what would be there
with symmetrical porting.

An intake would do similar things to the intake side.  Bellows are
sometimes used as intake superchargers.  What they do is keep the port
sealed until the cylinder pressure drops enough ( by by exhaust ) and
then opens up the port.

If you were to adopt the mechanism, you could change the phase angle
between the rotating butterfly and the poppet valve, and thus, control
the effective duration of the camshaft.

The two cycle variants where used extensively thru my latest data on
diesel, and the four cycle were used only on large stationary engines.