Sport Pilot wrote:

Steve wrote:

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.


I would have agreed at the start of this thread, but the two stroke
desiel does not have to be the same as the old locomotive desiels. The
blower is not needed if the crankcase is used to pump fuel/air mixture.


You're describing a weed-whacker engine, not a 2-stroke Diesel. Good for
cheap manufacture and relatively light total weight, but at the expense
of a very narrow power band, terrible efficiency, terrible emissions,
and except at the peak of the power band, terrible power/weight ratio in
spite of being lightweight.