Surface Machinery and Methods for Oil-Well Pumping

36 SURFACE MACHINERY AND METHODS FOR OIL-WELL PUMPING.
Before the engine is started the chamber or bulb c must be heated with a
torch to a dark-red color, after which the successive explosions of the fuel oil
will keep it hot. Inserted into this chamber in some engines is a thin-walled
copper pipe against which the oil is sprayed. This small pipe can be heated
quickly and readily absorbs heat from the chamber. It therefore tends to
reduce the time required for starting the engine, which can thus start before
the entire bulb is heated, and it also reduces missed ignitions after the engine
is operating. Heating of the bulb sufficiently to permit starting the engine
requires 10 to 20 minutes. Compressed air, usually furnished by a small inde-
pendent air compressor operated by a gasoline engine, is used to start the
engine.
ENGINES WITH TWO-STROKE CYCLE.
Figure 7 illustrates the working of an explosion oil engine having a two-stroke
cycle. Engines of this type have a closed crank case, provided on one side
with large disk valves opening inwardly to the crank case and serving as air
intakes. A large conduit connects the crank case with the cylinder, the conduit
ports being so placed in the lower
part of the cylinder that they are
closed by the piston during the
greater part of its travel; they
Fe ( - I are uncovered only a few degrees
1/' \before it reaches its lower dead
center.
6 I tFigure 7, A, shows the engine
-c with a crank case full of air
compressed by the previous
downward travel of the piston,
< this internal pressure having
\ closed the disk valve a leading
to the atmosphere. The piston
has traveled to its outer (lower)
dead center and uncovered the
exhaust port b and the air port c.
The pressure in the cylinder is
A B higher than that of the atmos-
FIGURE 7.-Explosion oil engine, two-stroke cycle. phere, so that the burned gases
are swept out of the exhaust-gas
port. The air port c admits fresh compressed air into the cylinder, sweeping it
free of the products of combustion and refilling it with air needed for burning the
next fuel charge. On its upward travel the piston covers the exhaust and air
ports, compressing the air thus imprisoned in the cylinder. The air still in the
crank case expands and its pressure falls below that of the atmosphere. Con-
sequently the disk valve opens automatically and lets in a fresh supply of air
(Fig. 7, B). Just before the piston reaches its inner (upper) dead point a fuel
charge is sprayed against the heated surface of the hot ball; the vaporized fuel
is ignited and burned with a great increase of temperature and pressure by the
time the piston has passed its inner dead point. The resulting impulse drives
the piston downward, the 2-stroke cycle being then repeated.
In explosion oil engines, the air is compressed in the cylinder to a pressure
of 145 to 220 pounds per square inch and in the crank case to a pressure of
1 to 7 pounds per square inch. The explosion pressure varies from 270 to 470
pounds per square inch. The cylinder and the cylinder head are water-cooled,
with the exception of the hot ball, which is kept at a dull-red heat. The con-

George, H. C. Surface Machinery and Methods for Oil-Well Pumping. Washington D.C.. UNT Digital Library. http://digital.library.unt.edu/ark:/67531/metadc12407/. Accessed April 18, 2014.