Los Angeles herald., 1910-05-15
HEAR THAT POUND, Ell?
THE SPARKS TO BLAME
It's All Simple Enough When You
Know, and Here's the
Explanation
BIT DIR. CHARLES w. SNYDER
IncnI Agent Middleby Cars

To secure the best results, the maxi
mum pressure in gas engine should
occur just an instant after the piston
has passed over upper center, this Civ
ing the greatest mean efficient pressure
on the piston obtainable.
The charge in the combustion cham
ber is not all burned the instant it is
ignited by the spark on the plug, but
takes an appreciable time for complete
combustioin The speed of the flame
through u mixture of gasoline and air
is about thirty-two feet a second,
therefore if you have four-inch cylin-
der with the spark plug at one side,
IT will take about one-hundredth of a
second to completely consume your
charge.
If your engine is running at 1000 rev.
olutions a minute each stroke will re-
quire one and three-fourths seconds.
Now, as your maximum pressure is not
secured until the charge is completely
burned, and as it taxes one-hundredth
second for the charge to complete the
combustion, to secure this maximum
pressure Just as the piston passes
over the center and is going downward
on the power stroke, you must ignite
the CHARGE before the compression
stroke is completed, and at this speed
the ignition should occur at practically
two-thirds of the compression stroke.
The time that is required to consume
a given charge is always the same, and
assuming that it always takes one
hundredth second to burn it. it is read
ily seen that the proper point of igni-
tion varies with the speed of the en-
CINE This is the reason the timer is
not fixed to fire at one point, but may
be rotated to a certain extent, ad
vancing or retarding the time relative
to a point on the crank circle, that the
spark occurs.
This illustrates also the cause of the
knock" heard when the timer is adj
vanced too far the charge in this case
being ignited so early that it is all
burned, and the maximum pressure Sc
cured before the piston has passed over
center and is on its power stroke. In
other words complete combustion is
secured so early that the maximum
pressure occurs on the compression
stroke, and tries to reverse the engine,
but the inertia of the f1ywheel prevents
this if the engine is in rapid motion.
However, this same condition occurs
If the spark is not retarded before the
engine is cranked, and causes the
"kick back" often causing the engine
to actually turn over backward two
or three times.
In cranking an engine retard the
spark as much as possible, so that the
piston has passed over center.
Often in climbing a long grade. it Is
found that 1t is necessary to retard
the spark as the engine slows down,
or the power is greatly lessened. This
is due to the facts above mentioned.
The engine already having about its
maximum load, an ignition a trifie
early causes the combustion to be
completed before the power stroke has
actually commenced, and the little
excess in pressure on the compression
stroke, while it may not be enough
to cause an audible pound, interferes
very materially with the already over
loaded motor. Retarding the spark in
this case will make the motor pick up.
A good driver always runs his en-
gine on the spark" as much as pos
sible: that is, he always keeps his
spark advanced as far as it will go
without the engine pounding. By doing
this he secures a better efficiency and
causes the highest temperature to oc-
cur when the piston is nearly on GEN.
ter. which means that the cylinder
head only is in contact with this great
heat, and of course the smaller the
surface of contact the less the cylinder
tends to become overheated.