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From: The Marchands (no email)
Date: Sat Nov 02 2002 - 08:18:21 EST
Eric:
GM two stroke diesels are very different from the familiar two stroke
gasoline engine.
In the two stroke gasoline engine, fuel/air mixture is sucked into the
crankcase on the piston up stroke, and then pushed into the combustion
chamber on the down stroke. Since there is no crankcase that can act as an
oil sump, the oil must be mixed with the fuel.
But the GM diesel two stroke is a very different animal. It has an oil
filled crankcase just like a four stroke engine. The combustion air (no fuel
at this point) is pushed into the combustion chamber with a mechanical,
Roots type blower (similar to a supercharger on a gasoline fueled dragster).
Then fuel is injected near the top of the piston stroke, just like a four
cycle diesel. But whereas a four stroke diesel goes through another
complete cycle to exhaust the combustion gasses, the two stroke diesel uses
the next shot of combustion air to push out the gasses at the bottom of each
stroke, just like a two stroke gasoline engine. But it is the blower that
provides the pressure to do this, not the pumping action of the crankcase as
in a gasoline two stroke.
Two stroke diesels are inherently less efficient than four stroke diesels.
But, back to the question of synthetic oil. Synthetics are not necessarily
more slippery than natural lube oils. But they are more stable. That is why
they can go for longer periods without changing.
David
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