Morgans wrote:

"Steve" wrote


As already stated, 2-stroke diesels really don't have a power-to-weight
advantage over 4-strokes. They still have to have a camshaft and
exhaust valves (they aren't like weed whacker engines, you know), so
they don't save that weight. Plus they have to have a blower for
scavenge air. The only area where they save weight is in that the
connecting rod and crank can be lighter, and that only helps offset the
added weight of the blower.


How about the fact that they have power pulses in each revolution? They
could possibly have half the displacement, and still get the same power, (or
close to it) with less weight than the double displacement 4 cycle. Yes,
the blower weight is added, but it is nice to make good power, way up there.


The blower also takes away a significant chunk of crankshaft power. The
blower has to do the same net work as those "non power" strokes in a
4-cycle diesel because its doing the same job- expelling burnt mixture
and bringing in fresh air. You can't get something for nothing.

This is all old-hat. 2-stroke diesels have been in widespread use since
Winton developed the basic foundation for what became both the EMD and
Detroit Diesel 2-stroke engine architecture back in the 1920s. 2-strokes
became very simple to service and reliable, but they rarely won on
either fuel efficiency or total power output per unit weight. That's why
you find 2-strokes in locomotives and ships where weight doesn't matter
(or is a benefit), but they all but disappeared from on-road
applications by the end of the 1970s and DID completely disappear by the
turn of the century.