Quote:
Originally posted by P.E.Haiges
Leathermang,
2 cycle Diesels do not introduce a mixture thru the ports. They only admit air thru the ports and the fuel is injected same as a 4 cycle Diesel.
The Detroit 2 cycle Diesel has overhead intake valves. The air is pushed thru the intake valves into the cylinders by the supercharger at the same time the exhaust is going out the ports at the bottom of the cylinder.
P E H
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Actually, it's the other way around. The overhead valves on 2 stroke Detroits are exhaust valves (there are 2 valve versions and 4 valve versions). The blower (yes, they're supercharged, but it's necessary for their operation, so most people consider non-turbo'ed Detroits to be naturally aspirated) blows air into the crankcase, and when the piston gets below the ports in the cylinder walls, the blower pushes the air into there, forcing the exhaust out of the exhaust valves and into the exhaust manifold.
Only problem is the positive crankcase pressure and the ports combined with oil control rings make for an engine that has a bit of an appetite for oil. As many people have put it, the only two-stroke Detroit that doesn't leak or use oil is the two-stroke Detroit that has been freshly rebuilt and has yet to be fired off.
As to the first question, at idle, theoretically, it should be after TDC. Given the higher pressures with a diesel and the fact that the fuel's introduced independently of the air, it's actually possible to start and run a diesel backwards. I read somewhere that a guy accidentally did this when he push-started his VW diesel with the gearshift in reverse instead of 1st. Engine ran, until he realized that he had 5 reverse gears and one forward gear. With the fuel firing before TDC at idle, I can imagine it firing the cylinder and pushing it back down the wrong way...and a healthy diesel may wind up being able to actually run based on that.
Just a thought.