higher expansion and thermal efficiency of the diesel. Its constant torque
throughout the speed range provides good pulling power at low speeds. Also,
it performs well and is reliable in all kinds of weather. In addition, a
diesel engine is much safer because its fuel is not as volatile as gasoline.
And, too, the exhaust gases are not as dangerous as those of automobile
engines because they are directed upward and dissipated into the atmosphere.
b. Function. The diesel engine changes heat energy into mechanical
energy for turning a generator, to produce the electrical energy needed to
operate the traction motors supplying motive power. Some of the mechanical
the air compressor that supplies the air pressure for the airbrake system of
the entire train.
All dieselelectric locomotives have at least two generators, its main
and auxiliary ones, and sometimes a third, a steam generator. Their
functions are described in the subparagraphs following.
a. The main generator, such as the one shown in figure 2.3, converts
the power output of the diesel engine into electrical power for operating
the traction motors, discussed later in this subparagraph. Note the main
generator's location on the locomotive, just forward of the engineman's
controls, in figure 2.1 at the part numbered 12 and its blower, at the part
The main generator is directly connected to the diesel engine which
turns the armature within the main field. With the generator directly
connected to the diesel engine, the armature's speed varies with engine
speed between approximately 350 and 1,800 rpm for small engines and 300 to
1,000 rpm for large engines. Even though the speed of rotation varies, the
main fields are designed to produce up to 1,200 volts of direct current with
a constant kilowatt output. The armature is built and balanced to withstand
highspeed rotation and all the vibrations incurred in operating with a
The traction motors receive electrical energy from the generator and
are geared to the locomotive axles, and, by driving the axles and turning
the wheels, they supply the locomotive's tractive effort. The motors are
mounted on the axles in the trucks of the locomotive.