Ashland tidings. [volume] (Ashland, Or.) 1876-1919, 1915-08-19
EXPERT EXPLAINS CAUSES
OF CARBON DEPOSITS

Lieut.. G. s. Bryan, government ex-
pert, in an article in the February
issue of the Journal of the American
Society of Naval Engineers says:
Carbon may exist in a motor oil
in two forms; First, as free carbon
held in suspension, and, second, in
combination with hydrogen, forming
the numerous hydrocarbon COM
pounds which go to make up the oil.
The amount of free carbon in we'll
refined oil is very small, and the OBJ
jectionable carbon deposit is gener-
ally due to some other factor.
"The conditions attained in the
cylinder of internal combustion en-
gines that result in the formation of
carbon are: First, high temperature,
and, second, limited supply of oxy-
gen (air). References have been
made to oil burning. This term has
been used rather Ioosely, as, strictly
speaking, burning means the com
bining of the vapors from the oil
with the oxygen of the air, and does
not include simple vaporization of
the oil. Unless air is present in ex-
cess of that required for the combus
tion Of the gasoline or fuel oil, and
usually it is not, the oil can not real
ly burn. Under the intense heat,
however, the inner surface of the oil
film will be vigorously affected, and,
in the absence of the air necessary
for burning, three things may hap
pen:
Cease 1. The compounds may vol
atize with decomposition.
Case 2. The compounds may de-
compose with the formation of free
carbon and hydrogen.
Case 3. The compounds may de-
compose with the formation of other
hydrocarbon compounds OF differ
ent nature.
"The products formed in case l
give no trouble, as being gaseous,
hey are carried out with the ex-
laust, whether burned or not OF
he products formed under case 2,
he hydrogen would pass out of the
whether burned or not. The
arbon may be blown out with the
,ases, or may remain in the cylinder.
Whether or not it remained in the
ylinder would depend greatly on the
ondition Of the oil film on the cylin-
Ter walls. Some oils form a thick,
iscous, gummy deposit, which re-
aims the carbon formed on its sur
ace and prevents it from being
lown out through the exhaust. This
ummy deposit gradually gets thicker ,
nd harder, eventually forming the
ard carbon deposit so we'll known
n cylinders. s.
This gummy deposit is due to the $
ction Of the compounds mentioned
n case 3. The free carbon liberated I
n case is light and fluffy, and of
tself would not form the hard de- I
osit Where the compounds break
p into new compounds, however,
ONE of the new compounds are vol
tile, while others are heavier and
lore viscous than the original COM
ound. Continued action of the kind
lentionel in case 3 will, therefore,
esult in the gradual thickening of
he film, and the retention and alb
orption by the film of the carbon
hat is liberated will increase this
fleet until, finally, hard, brittle
eposit results.
"1n the absence of any gummy de- !
o9it of this kind to cement the free
irbon together, the latter will gen.
ally be blown out through the ex-
aust The oil that will give the best
,sults, then, is not necessarily the
ne that will form the least carbon,
ut the one that will form the least .
lrbon in the cylinders.
coils made from asphalt-base
'udes have shown themselves to be
uch better adapted to motor cylin-
ers, as far as their carbon-forming
roclivities are concerned, than are
le paraffine-base Pennsylvania
ls."