02/07/2004

Gas Lubricated Pistons

If you were truly insane, you may want to consider gas lubricated
pistons.  Basically ring less design's.  Steel or iron, with steel or
iron cylinders.  A moderately long very close ring less skirt with
clearances very very thin.

SWRI and the Army, among many others, did a lot of research on this, in
particular with regard to adiabatic engines and the elimination of oil.

The gases center the piston and "blow by" the skirts.  The tighter the
clearance, the less blow by.  About 1-2% for steel steel piston cylinder
tolerances.

So what happens is the piston is riding on trapped gasses between skirt
and wall and is essentially frictionless.  A moderate length skirt is
better than no skirt for containing the trapped gasses and making a
friction free design.

Most such designs use a cross head piston and use the bottom of the
piston as a compressor.  Great design - but not practical for adaption
to most engine design.

Note that the gas completely fills the crevice and the piston floats on
the gas.  Blow by is not essential for the operation.

SWRI took a 3 inch piston by 2 inch stroke and ran it at approaching
20,000 rpm. 

The blow bye could be controlled by a single ring at the bottom of the
skirt, because the piston would allows be centered by the gasses.

A full circumference full length skirt could be employed with two small
cutouts for the pin which will be riding on a welded pin bosses.

Just a sketch for a near frictionless piston.  Probably would not work -
but when the money arrives, I might try it on a Brayton (Joule) cycle
engine.