The sun. [volume] (New York [N.Y.]) 1916-1920, 1919-07-20
SOME THINGS WE HAVE
LEARNED ABOUT MOTORS
Recent Experiments Force Several Interesting Changes
in Accepted Theories Concerning Spark
and Carbon Knocks
ny II. A. TARANToUs.

Ever since we have been using gallo
lene engines we have explained certain
actions such as the spark knock and the
parbon knock as being caused by pre-
ignition and that all that happened was
slapping of the pistons against the
cylinder walls Recent laboratory ex-
periments have shown almost conclut
hvely that the supposed actions do not
lake place at all and that the causes
rs we understood them are wrong. The
earbon knock in an engine instead Of
place after ignition. Both the carbon
knock and the spark knock are the re-
suit OF detonations or we might say
terrific explosions Of certain parts of
ME gasolene
These explosions accompanied by high
pressures and temperatures cause a
tremendous strain on the connecting
rods and bearings and are more damag-
ing In their results than we imagined.
The carbon knock theory as we have
been explaining 1t for years was to the
pffect that the incandescent particles Of
carbon fgnited the incoming charge Just
rs the inlet valve opened. thus causing
preignition, which In turn forced the
piston against the cylinder wall and
gave us the familiar metallic sound.
To understand the new theory, which
by the way is backed up by enough
proof to entitle II 20 consideration as a
tact. one must know that gasolene is
composed not of one single compound
but of n number of different compounds
All OF these compounds do not explode
1T once, that is each one has a different
signition point from every other one
Some Of these compounds do not explode
ht all In the automobile engine. result
IN In rrrht Nd ft,al
-fhe exhaust pipe and muller. Under
Pertain conditions of pressure and tenn
'perature the ones that do not ordinarily
explode burn with an accompanying high
pressure This pressure Is as high as
5000 pounds, so you can imagine the
terrific strain on the connecting rod and
rrankshaft bearings additional to the
,ther pressures on these parts Ordi-
aarily the explosion pressure Is around
tOO pounds; SO that when the excep-
honally high. pressure occurs It stuns
Everything in its path. It is thought
mat the specific compound or gas which
sxplodes with such pressure Is acetyiene.
but there has been no verification for
his.
the knocking occurs only with com
mercial fuels as tests have shown, be-
cause when specially compounded fuels
we're used eliminating those compounds
likely to cause detonations none ac-
tually occurred. This might explain why
owners are heard to complain about
trouble with fuel bought in a certain
district. whereas there is a total absence
H troublesome symptoms when fuel OF
another trade name is bought
When there is carbon on the piston
Top 1t practically insulates the combus-
Hon chamber from the wall of the CYL
hders. This causes the much higher
temperature to exist in the cylinder and
In fact is the reason that the engine
overheats. This higher heat further
raises the pressure and the combination
sf the heat and pressure causes the high
Explosive content Of the fuel to become
lgnited.
The spark knock now is explained as
caused by identically the same condi-
lions. When you are driving up a hill
and the engine is overloaded the yolu-
metric efficiency Is high. That Is. you
open the throttle wide and as you do
20 the engine knocks because you admit
more mixture. which causes an increase
In pressure and heat When you retard
the spark you simply ignite the mixture
when the pressure is lower. hence under