Graham guardian., 1915-08-20
LUBRICATING OILS
Interesting Points on the
Science of Lubrication by
Lieut.. Bryan, u. S. N.

Few motorists know what lubrica
ton really means, or can tell just
what happens when the oil strikes
the hot cylinder walls, and how it is
affected. An article by Lieutenant
G. S. Bryan, U. S N, published in
the February Journal of the Amerl-
can Society of Naval Engineers,
throws considerable light on the
subject. He says in part;
The lubricating value of an oil
is due to the fact that when the
surfaces of the cylinder and piston
are separated by film of oil the
friction of these two metal surfaces
is eliminated and the friction that
remains is only that occasioned by
the sliding action of the molecules
of oil past each other. In other
words, it is the same as if two lav-
ers Of oil are sliding past each other,
and the friction that occurs takes
place inside the oil film and not on
the surface between the film and
the metal. In other words, we have
a dual film-oil working against oil
Under the conditions of high
rubbing speed and small piston ring
pressure that are generally found
in motor cylinders, light oils, such
as are used in turbines, would prob
ably give the NEST efficient results
if it were not for the high temper
atures encountered in the cylinders
Before discussing the effect of
these high temperatures, it will be
we'll to determine just what they
are. Recent experiments abroad
have shown that the maximum tenn
perature attained in an internal
combustion engine is about 2,7O0
degrees F. This is the maximum
and is obtained only at the top of
the explosion stroke.
"A recording thermometer used
in the above investigation showed
that the maximum temperature was
about 2,7O0 degrees F., the mini
mum about $50 degrees F., and the
average during a complete cycle
about $50 degrees F. These tenn
peratures are those of gases in the
cylinders and are not those of the
cylinder walls. There is greater
difference between the temperatures
of these two. AS long as the water
is not boiling we know that the
temperature of the wall is little, if
any, higher than 267 degrees F.
1T naturally follows that the
inner and outer surfaces of the oil
film will be exposed to quite differ
ent conditions. The inner surface
is exposed to the high temperature
of combustion, and without doubt
is very greatly damaged thereby.
The outer surface is exposed only
to the comparatively low tempera-
ture of the cylinder walls, and with
a film of any appreciable thickness
would be protected from the heat
due to low conductivity of this film.
We can consider the film as con-
sisting of two layers, the function
of one of these being to furnish the
fabrication, and of the other being
to withstand the destructive action
of heat and to protect this lubrica
ting layer. 1t is well known that
an exceedingly thin layer will fur
nish fabrication, and it is probable
that the greater part of the thick
ness of the film is used up in giving
the requisite protective action from
the heat. At any rate the part that
we must look to for fabrication is
that part having the lowest temper
ature, which is the very thin layer
next the cylinder walls.
Lubricating oil does not burn
very easily or very fast, however,
and time given for it to burn in a
motor cylinder is very short. Under
the intense heat, however, the inner
surface of the oil film will be vigOr-
ously affected.
Some oils form a thick, viscous,
gummy deposit, which retains the
carbon formed on its surface and
prevents it from being blown out
through the exhaust. This gunImy
deposit gradually gets thicker and