The Washington herald., 1921-11-13
nv =. e. LoCkHAI-

we all know the symptoms Of an
excessive carbon formation Within
the cylinders of an automobile en-
gine. Each time we step on IL
too quickly, or each time we at
tempt 10 force the motor q trfne
over its usual amount Of work, as
for instance, when we encounter
hard pulling or steep gradient. we
encounter a characteristic, irregular
knock which we have come 70 know
a spark knock or carbon knock
some of the more obseryant of US.
who have driven cars for long
time. say from six to ten years,
have come 10 appreciate that our
present day cars are much more
likely 10 give trouble from this
particular maiady than the cars OF
yesteryear.
Time was, when We explained this
phenomenon as resulting from what
we. termed "preignition." II was
caused, so we explained, by too early
Ignition of the tael charge on the
compression stroke, which resulted
I'm a tendency for the piston TO be
forced back In the wrong direction,
setting up the banging sound which
was so annoying.
when the carbon deposit was not
particularly bad. we could generally
effect a correction of the condition
by retarding the spark slightly.
This had the effect OF counteracting
the early ignition Of the charge so
that there was no tendency for the
piston to be propelled in the wrong
direction.
But when the carbon deposit was
very bad. no amount Of spark re-
tard would effect a cure-the only
possible relief was to let up on the
throttle or accelerator slightly un-
TIL the banging stopped-and that
had the effect OF limiting the pow
er output of the engine to such an
extent that generally IL was neces-
sary 10 change down to a lower
gear In order for the car to pull up
the grade or through the bad
stretch.
Yes. there Is one alternative
method OF effecting q cure which Is
sometimes used to a great advan-
tage since II does not result in a
great falling of in power. That is
to enrich the mixture considerably
when knocking occurs, which IL has
been explained, makes II slower to
ignite so that the condition becomes
less acute. OF course. to enrich the
mixture II was simply necessary to
pull out the carburetor choker
slightly.
There are a couple OF little incon-
sistencies in this explanation of the
cause OF preignition or rather the
cause Of the spark knock" In the
first place, 1t usually is pointed out
that the carbon layer actually glows
and under this red hot heat the
COMPRISING fuel charge ignites.
Yet retarding the spark will have
no effect in reducing the red heat
OF the glowing mass OF carbon so
that IL this analysis Is admitted, the
act OF retarding the spark should
have no effect in remedying the
condition. But nevertheless. It
does, except in cases. as explained
above, where the deposit 10 Excess
sive.
In the second place. the knock is
self, while II has q metallic ring,
certainly is radically different from
any noise resulting from a piston
slap. Just how an early explosion
could move the piston to create any
noise whatsoever, Is not apparent.
When the piston is coming up on
the compression stroke. It is nat
urally held very firmly against the
cylinder wall away from the crank
pin due to the pressure on top of
the piston acting along the ang ular
line OF thrust created by the posi-
ton of the connecting rod. Any in
crease in pressure with the rod in
this same angular position. will
simply increase the pressure OF the
piston against the cylinder wall
without any tendency to cause
"canting" or slapping SO that II is
practically impossible for the pis-
ton to be responsible for the gener-
alton of the sound which the engine
emits under the conditions enumer-
ated
And. II the piston were respons-
ible for the noise, we should expect
very decided metallic beat, occur
ing rhythmically much like a pis-
ton slap. Instead we have a pc
culiar ringing sound, spasmodic
and most irregular.
Finally, we all know that to start
our engines in cold weather. we en-
rich the mixture to make It easier
to ignite. It seems very inconsist-
ent to enrich 1t when about to cor
rect spark knocks" with the op-
posite end in view-to make II
harder to ignite.
When we check what we have OBJ
served in the combustion of the
fuel in the glass tube by