In engineering, a prime mover is an engine that converts
fuel
A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy b ...
to useful
work.
In
locomotive
A locomotive or engine is a rail transport vehicle that provides the motive power for a train. If a locomotive is capable of carrying a payload, it is usually rather referred to as a multiple unit, motor coach, railcar or power car; the ...
s, the prime mover is thus the source of power for its
propulsion
Propulsion is the generation of force by any combination of pushing or pulling to modify the translational motion of an object, which is typically a rigid body (or an articulated rigid body) but may also concern a fluid. The term is derived f ...
.
In an
engine-generator set, the engine is the prime mover, as distinct from the generator.
Definition
In a
diesel-mechanical locomotive, the prime mover is the
diesel engine
The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is a so-cal ...
that is mechanically coupled to the driving wheels (drivers). In a
diesel-electric locomotive, the prime mover is the diesel engine that rotates the
main generator responsible for producing electricity to power the
traction motor
A traction motor is an electric motor used for propulsion of a vehicle, such as locomotives, electric or hydrogen vehicles, elevators or electric multiple unit.
Traction motors are used in electrically powered rail vehicles ( electric multip ...
s that are geared to the drivers. The prime mover can also be a
gas turbine instead of a diesel engine. In either case, the generator, traction motors and interconnecting apparatus are considered to be the
power transmission system and not part of the prime mover. A
wired-electric or
battery-electric
A battery electric vehicle (BEV), pure electric vehicle, only-electric vehicle, fully electric vehicle or all-electric vehicle is a type of electric vehicle (EV) that exclusively uses chemical energy stored in rechargeable battery packs, wi ...
locomotive has no on-board prime mover, instead relying on an external
power station
A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation of electric power. Power stations are generally connected to an electrical grid.
Many ...
.
Weight distribution
The power unit represents the main weight in a locomotive design, other than the chassis or body. Its position back and forth is at the designer's choice and may be used to control overall weight distribution. In most locomotives designs, the power unit is placed centrally. In some locomotives, it is offset to one end, or the heavier engine is outboard of the generator. In extreme cases, such as
C-B wheel arrangements, the weight on each
bogie
A bogie ( ) (in some senses called a truck in North American English) is a chassis or framework that carries a wheelset, attached to a vehicle—a modular subassembly of wheels and axles. Bogies take various forms in various modes of transp ...
may differ so much that the engine-end bogie is given an extra carrying axle, to keep individual
axle loads more consistent.
See also
*
Engine
An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy.
Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ...
*
Powerpack (drivetrain)
References
{{reflist
Locomotive engines