Although the four-stroke cycle type of motor is used by most of the
automobile manufacturers, yet there is another type which has given
such good results that it is destined to become one of the important
forms to be used in gas engine vehicle manufacture.
[Illustration: Fig. 39.]
It therefore merits a brief description. It has the advantage of
being very simple in construction and operation, and for this reason
it has become very popular among the marine engine builders, although
with a few exceptions it has not as yet been accepted by motor car
engineers. It is called a Two-stroke Cycle Motor, so named because it
combines in _two strokes_ the series of changes ordinarily accomplished
in _four_ in the four-stroke cycle type. Its operation may be seen by
referring to the accompanying diagrams. It is first assumed that the
engine is being turned over by hand in the direction indicated by the
arrow. You will note that as the piston moves up it will uncover a port
(H), allowing the gasoline vapor from the mixing chamber to enter the
crank case. As soon as the piston moves down again, a port (J) will be
opened, allowing the mixture which has just been compressed to rush
through a “by-pass” (F), into the “combustion chamber,” or upper part
of the cylinder. Now, as the piston moves up again on the next stroke,
this charge is compressed still more, then as the piston reaches its
uppermost position the charge is ignited and the engine begins to work
under its own power. The gases continue to act on the piston until
nearly the end of the stroke is reached, when you will notice, by
referring to the drawing, the exhaust port (G) is passed. At this point
the burned gases rush out into the air. You will also notice that in
order to aid the discharge and fill the cylinder again, as the piston
travels a little farther down, the inlet port will be again uncovered,
and the next charge, which has meanwhile been taken into the crank case
and compressed, will enter the cylinder, forcing the exhaust gases out.
[Illustration: Fig. 40.]
In order to prevent the vapor which has just entered the cylinder
from traveling straight across and out through the exhaust port, thus
wasting a portion of the fuel, a “baffle plate” (K) is cast on top of
the piston which deflects the gases toward the top of the combustion
chamber, producing a sort of whirling action which tends to scavenge
the cylinder most thoroughly. In order to prevent the burning gases
from traveling back into the crank case and igniting the gas there,
thus producing a “back explosion,” a wire gauze (S) is placed in the
“_by-pass_.” You will note that this type of motor has no valves,
no cams and no cam shaft, in fact, its simplicity is such that it
practically cannot get out of adjustment. It therefore is a form of gas
engine which as soon as engineers are able to educate the public to
its peculiarities bids fair to become as popular and practical as the
four-stroke cycle.