2 Stroke cycle explained

[TomC]

A point about the Bypass Valve on turbo Detroits. It is not designed to bypass all the boost from the turbo. Rather it is designed to equalize the pressure on each side of the blower to allow the blower to free wheel-and actually be powered a bit by the turbo boost.
Detroit experimented with a 3 wheel turbo that the 3rd wheel was powered by the engine oil pressure to keep boost up (around 5psi) at idle. But it turned out to be not effective enough.
On the big locomotive 2 stroke Diesels, they have a combination turbo with mechanical drive with an over run clutch. Think of your bicycle. When the turbo reduces in speed, the mechanical gearing takes over to keep boost. When the engine gets up to speed, the turbo speeds up and the mechanical part of the drive is over run. Many different ways. Good Luck, TomC

[Oonrahnjay]

The blower is blowing.  Air doesn't go through the center but around the around the outside between the lobes and the housing.

       Thanks for that Lee.  That explains and clarifies a lot -- they should have made the graphic plainer, though.

[daddysgirl]

..."In the diesel engine, air alone is compressed in the cylinder; then, after the air has been compressed, a charge of fuel is sprayed into the cylinder and ignition is caused by the heat of compression.

"In the two-cycle engine, intake and exhaust take place during part of the compression and power strokes, respectively. ...The blower is provided to force air into the cylinders, for expelling the exhaust gasses, and to supply the cylinders with fresh air for combustion. The row of ports on the on the cylinder wall admit the air as soon as the rim of the piston uncovers the ports. The undirectional flow of air toward the exhaust valves produces a scavaging effect, leaving the cylinders full of clean air when the piston again covers the inlet ports. As the piston continues on the upward stroke, the exhaust valves close and the charge of fresh air is subjected to compression...The fuel is sprayed into the combustion chamber and ignited by the heat generated during compression."

Loosely quoted from the Detroit Diesel Allison Service and/or Operators Manual, Page 4. August, 1980

Love the DD Books as much as the MC8 Manuals

[HB of CJ]

If memory serves, the exhaust valves, (either 2 or 4) open well before the ports open up.  The blower only provides 3-5 pounds of air pressure.

The cylinder pressure is still hundreds of PSI.  The remaining air in the cylinder blows out the exhaust valves.  It has too.  The blower pressure is too low.

THEN ... when timed correctly and when the cylinder pressure has dropped to about nothing, the piston uncovers the sleeve ports.  Just an observation.

[lostagain]

And when timed and tuned correctly, it runs so sweet! Music...

JC