PRIME MOVERS AND POWER PLANT MACHINERY.
increase in speed, and the governor prevents one or more explosions
by holding the exhaust valve open and the inlet valve closed. This
is done, by means of cams or eccentrics which are geared to the crank
shaft and in turn control the inlet and exhaust valves by rod
The throttle-control governor is designed to give an impulse to
the piston regularly, that is, regular firing on every cycle or two
cycles, the speed being held constant by regulating the quantity of ex-
plosive mixture admitted to the cylinder or by varying the richness
of the mixture. This type of governor acts directly on the throttle
valve. The governor proper is actuated by the centrifugal force of a
flywheel or flyball, and at no time is the connecting mechanism
disengaged from the driving cam. (See Plate VI at e.)
Two-cycle engines always have throttle-control governors because
the design usually precludes control of the ports as in the hit-and-
METHODS OF IGNITION.
A minute part of the mixture of gas and air in the engine cylinder
must be raised to the ignition temperature in order to produce
an explosion and work the piston. The higher the initial tem-
perature of this air and gas mixture, the less heat is required from
the ignition system. The initial temperature will be largely deter-
mined by the heat of the cylinder and the degree of compression.
The charge of air and gas in the cylinder is ignited by hot-tube
ignition or electrical ignition.
Hot-tube ignition is based upon the principle that a combustible
gas mixed with the proper amount of air may be ignited by bringing
it in contact with a surface heated above the ignition point. The
hot tube consists of a small metal tube closed at one end and
attached to the cylinder by the open end so as to communicate with
the charge in the cylinder. An asbestos-lined chimney is placed
around the tube. A gas burner in the space between the tube and
the chimney keeps the upper part of the tube at a temperature above
the ignition point.
Each compression forces the mixture of air and gas further and
further into the tube until at the highest point of compression
it reaches the part of the tube heated to the ignition temperature,
and explosion results. The length of the tube required varies with
different conditions. The point of maximum heat in the tube should
be so located that the explosion takes place at the highest com-
pression. Lowering the point of maximum heat advances the
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 December 19, 2014.