A diesel locomotive is a type of railway locomotive
in which the prime mover is a diesel engine.
Several types of diesel locomotive have been
developed, differing mainly in the means by
which mechanical power is conveyed to the
driving wheels.
Early internal combusition locomotives and
railcars used kerosene and gasoline as their
fuel.
Dr. Rudolf Diesel patented his first compression
ignition engine in 1898, and steady improvements
in the design of diesel engines reduced their
physical size and improved their power-to-weight
ratio to a point where one could be mounted
in a locomotive.
Internal combustion engines only operate efficiently
within a limited torque range, and while low
power gasoline engines can be coupled to a
mechanical transmission, the more powerful
diesel engines required the development of
new forms of transmission.
The first successful diesel engines used diesel–electric
transmissions, and by 1925 a small number
of diesel locomotives of 600 hp (450 kW) were
in service in the United States.
In 1930, Armstrong Whitworth of the United
Kingdom delivered two 1,200 hp (890 kW) locomotives
using Sulzer-designed engines to Buenos Aires
Great Southern Railway of Argentina.
In 1933, diesel-electric technology developed
by Maybach was used propel the DRG Class SVT
877, a high speed intercity two-car set, and
went into series production with other streamlined
car sets in Germany starting in 1935.
In the USA, diesel-electric propulsion was
brought to high speed mainline passenger service
in late 1934, largely through the research
and development efforts of General Motors
from 1930–34 and advances in lightweight
carbody design by the Budd Company.
The economic recovery from the Second World
War saw the widespread adoption of diesel
locomotives in many countries.
They offered greater flexibility and performance
than steam locomotives, as well as substantially
lower operating and maintenance costs.
Diesel–hydraulic transmissions were intrdouced
in the 1950s, but from the 1970s onwards diesel–electric
transmission has dominated.
== History ==
=== Adaptation of the diesel engine for rail
use ===
The earliest recorded example of the use of
an internal combustion engine in a railway
locomotive is the prototype designed by William
Dent Priestman, which was examined by Sir
William Thomson in 1888 who described it as
a "[Priestman oil engine] mounted upon a truck
which is worked on a temporary line of rails
to show the adaptation of a petroleum engine
for locomotive purposes.".
In 1894, a 20 hp (15 kW) two axle machine
built by Priestman Brothers was used on the
Hull Docks.
In 1896 an oil-engined railway locomotive
was built for the Royal Arsenal, Woolwich,
England, in 1896, using an engine designed
by Herbert Akroyd Stuart.
It was not, strictly, a diesel because it
used a hot bulb engine (also known as a semi-diesel)
but it was the precursor of the diesel.
Following the expiration of Dr. Rudolf Diesel's
patent in 1912, his engine design was successfully
applied to marine propulsion and stationary
applications.
However, the massiveness and poor power-to-weight
ratio of these early engines made them unsuitable
for propelling land-based vehicles.
Therefore, the engine's potential as a railroad
prime mover was not initially recognized.
This changed as development reduced the size
and weight of the engine.
In 1906, Rudolf Diesel, Adolf Klose and the
steam and diesel engine manufacturer Gebrüder
Sulzer founded Diesel-Sulzer-Klose GmbH to
manufacture diesel-powered locomotives.
Sulzer had been manufacturing Diesel engines
since 1898.
The Prussian State Railways ordered a diesel
locomotive from the company in 1909, and after
test runs between Winterthur and Romanshorn
the diesel–mechanical locomotive was delivered
in Berlin in September 1912.
The world's first diesel-powered locomotive
was operated in the summer of 1912 on the
Winterthur–Romanshorn railroad in Switzerland,
but was not a commercial success.
During further test runs in 1913 several problems
were found.
After the First World War broke out in 1914,
all further trials were stopped.
The locomotive weight was 95 tonnes and the
power was 883 kW with a maximum speed of 100
km/h.
Small numbers of prototype diesel locomotives
were produced in a number of countries through
the mid-1920s.
=== Early diesel locomotives and railcars
in US ===
==== Early American developments ====
Adolphus Busch purchased the American manufacturing
rights for the diesel engine in 1898 but never
applied this new form of power to transportation.
He founded the Busch-Sulzer company in 1911.
Only limited success was achieved in the early
twentieth century with internal combustion
engined railcars, owing in part to difficulties
with mechanical drive systems.General Electric
(GE) entered the railcar market in the early
twentieth century, as Thomas Edison possessed
a patent on the electric locomotive, his design
actually being a type of electrically propelled
railcar.
GE built its first electric locomotive prototype
in 1895.
However, high electrification costs caused
GE to turn its attention to internal combustion
power to provide electricity for electric
railcars.
Problems related to co-coordinating the prime
mover and electric motor were immediately
encountered, primarily due to limitations
of the Ward Leonard current control system
that had been chosen.A significant breakthrough
occurred in 1914, when Hermann Lemp, a GE
electrical engineer, developed and patented
a reliable direct current electrical control
system (subsequent improvements were also
patented by Lemp).
Lemp's design used a single lever to control
both engine and generator in a coordinated
fashion, and was the prototype for all internal
combustion–electric drive control systems.
In 1917–18, GE produced three experimental
diesel–electric locomotives using Lemp's
control design, the first known to be built
in the United States.
Following this development, the 1923 Kaufman
Act banned steam locomotives from New York
City because of severe pollution problems.
The response to this law was to electrify
high-traffic rail lines.
However, electrification was uneconomical
to apply to lower-traffic areas.
The first regular use of diesel–electric
locomotives was in switching (shunter) applications,
which were more forgiving than mainline applications
of the limitations of contemporary diesel
technology and where the idling economy of
diesel relative to steam would be most beneficial.
GE entered a collaboration with the American
Locomotive Company (ALCO) and Ingersoll-Rand
(the "AGEIR" consortium) in 1924 to produce
a prototype 300 hp (220 kW) "boxcab" locomotive
delivered in July 1925.
This locomotive demonstrated that the diesel–electric
power unit could provide many of the benefits
of an electric locomotive without the railroad
having to bear the sizeable expense of electrification.
The unit successfully demonstrated, in switching
and local freight and passenger service, on
ten railroads and three industrial lines.
Westinghouse Electric and Baldwin collaborated
to build switching locomotives starting in
1929.
However, the Great Depression curtailed demand
for Westinghouse's electrical equipment, and
they stopped building locomotives internally,
opting to supply electrical parts instead.In
June 1925, Baldwin Locomotive Works outshopped
a prototype diesel–electric locomotive for
"special uses" (such as for runs where water
for steam locomotives was scarce) using electrical
equipment from Westinghouse Electric Company.
Its twin-engine design was not successful,
and the unit was scrapped after a short testing
and demonstration period.
Industry sources were beginning to suggest
“the outstanding advantages of this new
form of motive power”.
In 1929, the Canadian National Railways became
the first North American railway to use diesels
in mainline service with two units, 9000 and
9001, from Westinghouse.
However, these early diesels proved expensive
and unreliable, with their high cost of acquisition
relative to steam unable to be realized in
operating cost savings as they were frequently
out of service.
It would be another five years before diesel-electric
propulsion would be successfully used in mainline
service, and nearly ten years before it would
show real potential to fully replace steam.
Before diesel power could make inroads into
mainline service, the limitations of diesel
engines circa 1930 - low power-to-weight ratios
and narrow output range - had to be overcome.
A major effort to overcome those limitations
was launched by General Motors after they
moved into the diesel field with their acquisition
of the Winton Engine Company, a major manufacturer
of diesel engines for marine and stationary
applications, in 1930.
Supported by the General Motors Research Division,
GM's Winton Engine Corporation sought to develop
diesel engines suitable for high speed mobile
use.
The first milestone in that effort was delivery
in early 1934 of the Winton 201A, a two-stroke,
Roots-blown, uniflow-scavenged, unit-injected
diesel engine that could deliver the required
performance for a fast, lightweight passenger
train.
The second milestone, and the one that got
American railroads moving towards diesel,
was the 1938 delivery of GM's Model 567 engine
that was designed specifically for locomotive
use, bringing a fivefold increase in life
of some mechanical parts and showing its potential
for meeting the rigors of freight service.Diesel–electric
railroad locomotion entered mainline service
when the Burlington Railroad and Union Pacific
used custom-built diesel "streamliners" to
haul passengers, starting in late 1934.Burlington's
Zephyr trainsets evolved from articulated
three car sets with 600 hp power cars in 1934
and early 1935, to the Denver Zephyr semi-articulated
ten car trainsets pulled by cab-booster power
sets introduced in late 1936.
Union Pacific started diesel streamliner service
between Chicago and Portland Oregon in June
1935, and in the following year would add
Los Angeles and Oakland California, and Denver
Colorado to the destinations of diesel streamliners
out of Chicago.
The Burlington and Union Pacific streamliners
were built by the Budd Company and the Pullman-Standard
Company, respectively, using the new Winton
engines and power train systems designed by
GM's Electro-Motive Corporation.
EMC's experimental 1800 hp B-B locomotives
of 1935 demonstrated the multiple-unit control
systems used for the cab/booster sets and
the twin engine format used with the later
Zephyr power units.
Both of those features would be used in EMC's
later production model locomotives.
The lightweight diesel streamliners of the
mid-1930s demonstrated the advantages of diesel
for passenger service with breakthrough schedule
times, but diesel locomotive power would not
fully come of age until regular series production
of mainline diesel locomotives commenced and
it was shown suitable for full-size passenger
and freight service.
==== First American series production locomotives
====
Following their 1925 prototype, the AGEIR
consortium produced 25 more units of 300 hp
(220 kW) "60 ton" AGEIR boxcab switching locomotives
between 1925 and 1928 for several New York
City railroads, making them the first series-produced
diesel locomotives.
The consortium also produced seven twin-engine
"100 ton" boxcabs and one hybrid trolley/battery
unit with a diesel-driven charging circuit.
ALCO acquired the McIntosh & Seymour Engine
Company in 1929 and entered series production
of 300 hp (220 kW) and 600 hp (450 kW) single-cab
switcher units in 1931.
ALCO would be the pre-eminent builder of switch
engines through the mid-1930s and would adapt
the basic switcher design to produce versatile
and highly successful, albeit relatively low
powered, road locomotives.
GM, seeing the success of the custom streamliners,
sought to expand the market for diesel power
by producing standardized locomotives under
their Electro-Motive Corporation.
In 1936 EMC's new factory started production
of switch engines.
In 1937 the factory started producing their
new E series streamlined passenger locomotives,
which would be upgraded with more reliable
purpose-built engines in 1938.
Seeing the performance and reliability of
the new 567 model engine in passenger locomotives,
EMC was eager to demonstrate diesel's viability
in freight service.
Following the successful 1939 tour of EMC's
FT demonstrator freight locomotive set, the
stage was set for dieselization of American
railroads.
In 1941 ALCO-GE introduced the RS-1 road-switcher
that occupied its own market niche while EMD's
F series locomotives were sought for mainline
freight service.
The US entry into World War II slowed conversion
to diesel; the War Production Board put a
halt to building new passenger equipment and
gave naval uses priority for diesel engine
production.
During the petroleum crisis of 1942-43, coal-fired
steam had the advantage of not using fuel
that was in critically short supply.
EMD was later allowed to increase production
of its FT locomotives and ALCO-GE was allowed
to produce a limited number of DL-109 road
locomotives, but most in the locomotive business
were restricted to making switch engines and
steam locomotives.
In the early postwar era, EMD dominated the
market for mainline locomotives with their
E and F series locomotives.
ALCO-GE in the late 1940s produced switchers
and road-switchers that were successful in
the short-haul market.
However, EMD launched their GP series road-switcher
locomotives in 1949, which displaced all other
locomotives in the freight market including
their own F series locomotives.
GE subsequently dissolved its partnership
with ALCO and would emerge as EMD's main competitor
in the early 1960s, eventually taking the
top position in the locomotive market from
EMD.
Early diesel–electric locomotives in the
United States used direct current (DC) traction
motors, but alternating current (AC) motors
came into widespread use in the 1990s, starting
with the Electro-Motive SD70MAC in 1993 and
followed by the General Electric's AC4400CW
in 1994 and AC6000CW in 1995.
=== Early diesel locomotives and railcars
in Europe ===
==== First functional diesel vehicles ====
In 1914, world's first functional diesel–electric
railcars were produced for the Königlich-Sächsische
Staatseisenbahnen (Royal Saxon State Railways)
by Waggonfabrik Rastatt with electric equipment
from Brown, Boveri & Cie and diesel engines
from Swiss Sulzer AG.
They were classified as DET 1 and DET 2 (de.wiki).
Due to shortage of petrol products during
World War I, they remained unused for regular
service in Germany.
In 1922, they were sold to Swiss Compagnie
du Chemin de fer Régional du Val-de-Travers
(fr.wiki), where they were used in regular
service up to the electrification of the line
in 1944.
Afterwards, the company kept them in service
as boosters till 1965.
Fiat claims a first Italian diesel–electric
locomotive built in 1922, but little detail
is available.
A Fiat-TIBB diesel–locomotive "A", of 440CV,
is reported to have entered service on the
Ferrovie Calabro Lucane in southern Italy
in 1926, following trials in 1924-5.In 1924,
two diesel–electric locomotives were taken
in service by the Soviet railways, almost
at one time:
The engine Ээл2 (Eel2 original number Юэ
001/Yu-e 001) started on October 22.
It had been designed by a team led by Yuri
Lomonosov and built 1923–1924 by Maschinenfabrik
Esslingen in Germany.
It had 5 driving axles (1'E1').
After several test rides, it hauled trains
for almost three decades from 1925 to 1954.
Though proved to be world's first functional
diesel locomotive, it did not become a series,
but it became a model for several classes
of Soviet diesel locomotives.
The engine Щэл1 (Shch-el 1, original number
Юэ2/Yu-e 2), started on November 9.
It had been developed by Yakov Modestovich
Gakkel (ru.wiki) and built by Baltic Shipyard
in Saint Petersburg.
It had ten driving axles in three bogies (1'
Co' Do' Co' 1').
From 1925 to 1927, it hauled trains between
Moscow and Kursk and in Caucasus region.
Due to technical problems, afterwards it was
out of service.
Since 1934, it was used as a stationary electric
generator.In 1935, Krauss-Maffei, MAN and
Voith built the first diesel–hydraulic locomotive,
called V 140, in Germany.
The German railways (DRG) being very pleased
with the performance of that engine, diesel–hydraulics
became the mainstream in diesel locomotives
in Germany.
Serial production of diesel locomotives in
Germany began after World War II.
==== Switchers ====
In many railway stations and industrial compounds,
steam shunters had to be kept hot during lots
of breaks between scattered short tasks.
Therefore, diesel traction became economical
for shunting before it became economical for
hauling trains.
The construction of diesel shunters began
in 1920 in France, in 1925 in Denmark, in
1926 in the Netherlands, and in 1927 in Germany.
After few years of testing, hundreds of units
were produced within a decade.
==== Diesel railcars for regional traffic
====
Diesel-powered or "oil-engined" railcars,
generally diesel–mechanical, were developed
by various European manufacturers in the 1930s,
e.g. by William Beardmore and Company for
the Canadian National Railways (the Beardmore
Tornado engine was subsequently used in the
R101 airship).
Some of those series for regional traffic
were begun with gasoline motors and then continued
with diesel motors, such as Hungarian BCmot
(The class code doesn't tell anything but
"railmotor with 2nd and 3rd class seats".),
128 cars built 1926 – 1937, or German Wismar
railbuses (57 cars 1932 – 1941).
In France, the first diesel railcar was Renault
VH, 115 units produced 1933/34.
In Italy, after 6 Gasoline cars since 1931,
Fiat and Breda built a lot of diesel railmotors,
more than 110 from 1933 to 1938 and 390 from
1940 to 1953, Class 772 known as Littorina,
and Class ALn 900.
==== High-speed railcars ====
In the 1930s, streamlined highspeed diesel
railcars were developed in several countries:
In Germany, the Flying Hamburger was built
in 1932.
After a test ride in December 1932, this two
coach diesel railcar (in English terminology
a DMU2) started service at Deutsche Reichsbahn
(DRG) in February 1933.
It became the prototype of DRG Class SVT 137
with 33 more highspeed DMUs, built for DRG
till 1938, 13 DMU 2 ("Hamburg" series), 18
DMU 3 ("Leipzig" and "Köln" series), and
2 DMU 4 ("Berlin" series).
French SNCF classes XF 1000 and XF 1100 comprised
11 high speed DMUs, also called TAR, built
1934–1939.
In Hungary, Ganz Works built Arpád railmotor
(see hu.wiki and de.wiki), a kind of a luxurious
railbus in a series of 7 items since 1934,
and started to build Hargita DMU amazingly
in 1944 (see hu.wiki)
==== Further developments ====
In 1945, a batch of 30 Baldwin diesel–electric
locomotives, Baldwin 0-6-6-0 1000, was delivered
from the United States to the railways of
the Soviet Union.
In 1947, the London Midland & Scottish Railway
introduced the first of a pair of 1,600 hp
(1,200 kW) Co-Co diesel–electric locomotives
(later British Rail Class D16/1) for regular
use in the United Kingdom, although British
manufacturers such as Armstrong Whitworth
had been exporting diesel locomotives since
1930.
Fleet deliveries to British Railways, of other
designs such as Class 20 and Class 31, began
in 1957.
Series production of diesel locomotives in
Italy began in the mid-1950s.
Generally, diesel traction in Italy was of
less importance than in other countries, as
it was amongst the most advanced countries
in electrification of the main lines and,
as a result of Italian geography, even on
many domestic connections freight transport
over sea is cheaper than rail transport.
=== Early diesel locomotives and railcars
in Asia ===
==== Japan ====
In Japan, starting in the 1920s, some petrol-electric
railcars were produced.
The first diesel–electric traction and the
first air-streamed vehicles on Japanese rails
were the two DMU3s of class Kiha 43000 (キハ43000系)
Japan's first series of diesel locomotives
was class DD50 (国鉄DD50形デ), twin locomotives,
developed since 1950 and in service since
1953.
==== China ====
One of the first home developed diesel vehicles
of China was the DMU Dongfeng (东风), produced
in 1958 by CSR Sifang.
Series production of China's first diesel
locomotive class, the DFH 1, began in 1964
following construction of a prototype in 1959.
=== Early diesel locomotives and railcars
in Australia ===
The Trans-Australian Railway built 1912 to
1917 by Commonwealth Railways (CR) passes
through 2000 km of waterless (or salt watered)
desert terrain unsuitable for steam locomotives.
The original engineer Henry Deane envisaged
diesel operation to overcome such problems.
Some have suggested that the CR worked with
the South Australian Railways to trial diesel
traction.
However, the technology was not developed
enough to be reliable.
As in Europe, the usage of internal combustion
engines advanced more readily in self-propelled
railcars than in locomotives.
Some Australian railway companies bought McKeen
railcars.
In the 1920s and 1930s, more reliable Gasoline
railmotors were built by Australian industries.
Australia's first diesel railcars were the
NSWGR 100 Class (PH later DP) Silver City
Comet cars in 1937.
High speed vehicles for those days' possibilities
on 3 ft 6 in (1,067 mm) were the 10 Vulcan
railcars of 1940 for New Zealand.
== Transmission types ==
Unlike steam engines, internal combustion
engines require a transmission to power the
wheels.
The engine must be allowed to continue to
run when the locomotive is stopped.
=== Diesel–mechanical ===
A diesel–mechanical locomotive uses a mechanical
transmission in a fashion similar to that
employed in most road vehicles.
This type of transmission is generally limited
to low-powered, low speed shunting (switching)
locomotives, lightweight multiple units and
self-propelled railcars.
The mechanical transmissions used for railroad
propulsion are generally more complex and
much more robust than standard-road versions.
There is usually a fluid coupling interposed
between the engine and gearbox, and the gearbox
is often of the epicyclic (planetary) type
to permit shifting while under load.
Various systems have been devised to minimise
the break in transmission during gear changing;
e.g., the S.S.S. (synchro-self-shifting) gearbox
used by Hudswell Clarke.
Diesel–mechanical propulsion is limited
by the difficulty of building a reasonably
sized transmission capable of coping with
the power and torque required to move a heavy
train.
A number of attempts to use diesel–mechanical
propulsion in high power applications have
been made (e.g., the 1,500 kW (2,000 hp) British
Rail 10100 locomotive), although none have
proved successful in the end.
=== Diesel–electric ===
In a diesel–electric locomotive, the diesel
engine drives either an electrical DC generator
(generally, less than 3,000 horsepower (2,200
kW) net for traction), or an electrical AC
alternator-rectifier (generally 3,000 horsepower
(2,200 kW) net or more for traction), the
output of which provides power to the traction
motors that drive the locomotive.
There is no mechanical connection between
the diesel engine and the wheels.
The important components of diesel–electric
propulsion are the diesel engine (also known
as the prime mover), the main generator/alternator-rectifier,
traction motors (usually with four or six
axles), and a control system consisting of
the engine governor and electrical or electronic
components, including switchgear, rectifiers
and other components, which control or modify
the electrical supply to the traction motors.
In the most elementary case, the generator
may be directly connected to the motors with
only very simple switchgear.
Originally, the traction motors and generator
were DC machines.
Following the development of high-capacity
silicon rectifiers in the 1960s, the DC generator
was replaced by an alternator using a diode
bridge to convert its output to DC.
This advance greatly improved locomotive reliability
and decreased generator maintenance costs
by elimination of the commutator and brushes
in the generator.
Elimination of the brushes and commutator,
in turn, disposed of the possibility of a
particularly destructive type of event referred
to as a flashover, which could result in immediate
generator failure and, in some cases, start
an engine room fire.
Current North American practice is for four
axles for high-speed passenger or "time" freight,
or for six axles for lower-speed or "manifest"
freight.
The most modern units on "time" freight service
tend to have six axles underneath the frame.
Unlike those in "manifest" service, "time"
freight units will have only four of the axles
connected to traction motors, with the other
two as idler axles for weight distribution.
In the late 1980s, the development of high-power
variable-voltage/variable-frequency (VVVF)
drives, or "traction inverters," has allowed
the use of polyphase AC traction motors, thus
also eliminating the motor commutator and
brushes.
The result is a more efficient and reliable
drive that requires relatively little maintenance
and is better able to cope with overload conditions
that often destroyed the older types of motors.
==== Diesel–electric control ====
A diesel–electric locomotive's power output
is independent of road speed, as long as the
unit's generator current and voltage limits
are not exceeded.
Therefore, the unit's ability to develop tractive
effort (also referred to as drawbar pull or
tractive force, which is what actually propels
the train) will tend to inversely vary with
speed within these limits.
(See power curve below).
Maintaining acceptable operating parameters
was one of the principal design considerations
that had to be solved in early diesel–electric
locomotive development and, ultimately, led
to the complex control systems in place on
modern units.
==== Throttle operation ====
The prime mover's power output is primarily
determined by its rotational speed (RPM) and
fuel rate, which are regulated by a governor
or similar mechanism.
The governor is designed to react to both
the throttle setting, as determined by the
engine driver and the speed at which the prime
mover is running.Locomotive power output,
and thus speed, is typically controlled by
the engine driver using a stepped or "notched"
throttle that produces binary-like electrical
signals corresponding to throttle position.
This basic design lends itself well to multiple
unit (MU) operation by producing discrete
conditions that assure that all units in a
consist respond in the same way to throttle
position.
Binary encoding also helps to minimize the
number of trainlines (electrical connections)
that are required to pass signals from unit
to unit.
For example, only four trainlines are required
to encode all possible throttle positions.
North American locomotives, such as those
built by EMD or General Electric, have nine
throttle positions, one idle and eight power
(as well as an emergency stop position that
shuts down the prime mover).
Many UK-built locomotives have a ten-position
throttle.
The power positions are often referred to
by locomotive crews as "run 3" or "notch 3",
depending upon the throttle setting.
In older locomotives, the throttle mechanism
was ratcheted so that it was not possible
to advance more than one power position at
a time.
The engine driver could not, for example,
pull the throttle from notch 2 to notch 4
without stopping at notch 3.
This feature was intended to prevent rough
train handling due to abrupt power increases
caused by rapid throttle motion ("throttle
stripping," an operating rules violation on
many railroads).
Modern locomotives no longer have this restriction,
as their control systems are able to smoothly
modulate power and avoid sudden changes in
train loading regardless of how the engine
driver operates the controls.
When the throttle is in the idle position,
the prime mover will be receiving minimal
fuel, causing it to idle at low RPM.
In addition, the traction motors will not
be connected to the main generator and the
generator's field windings will not be excited
(energized) — the generator will not produce
electricity with no excitation.
Therefore, the locomotive will be in "neutral".
Conceptually, this is the same as placing
an automobile's transmission into neutral
while the engine is running.
To set the locomotive in motion, the reverser
control handle is placed into the correct
position (forward or reverse), the brake is
released and the throttle is moved to the
run 1 position (the first power notch).
An experienced engine driver can accomplish
these steps in a coordinated fashion that
will result in a nearly imperceptible start.
The positioning of the reverser and movement
of the throttle together is conceptually like
shifting an automobile's automatic transmission
into gear while the engine is idling
Placing the throttle into the first power
position will cause the traction motors to
be connected to the main generator and the
latter's field coils to be excited.
With excitation applied, the main generator
will deliver electricity to the traction motors,
resulting in motion.
If the locomotive is running "light" (that
is, not coupled to the rest of a train) and
is not on an ascending grade, it will easily
accelerate.
On the other hand, if a long train is being
started, the locomotive may stall as soon
as some of the slack has been taken up, as
the drag imposed by the train will exceed
the tractive force being developed.
An experienced engine driver will be able
to recognize an incipient stall and will gradually
advance the throttle as required to maintain
the pace of acceleration.
As the throttle is moved to higher power notches,
the fuel rate to the prime mover will increase,
resulting in a corresponding increase in RPM
and horsepower output.
At the same time, main generator field excitation
will be proportionally increased to absorb
the higher power.
This will translate into increased electrical
output to the traction motors, with a corresponding
increase in tractive force.
Eventually, depending on the requirements
of the train's schedule, the engine driver
will have moved the throttle to the position
of maximum power and will maintain it there
until the train has accelerated to the desired
speed.
As will be seen in the following discussion,
the propulsion system is designed to produce
maximum traction motor torque at start-up,
which explains why modern locomotives are
capable of starting trains weighing in excess
of 15,000 tons, even on ascending grades.
Current technology allows a locomotive to
develop as much as 30 percent of its loaded
driver weight in tractive force, amounting
to some 120,000 pounds-force (530 kN) of drawbar
pull for a large, six-axle freight (goods)
unit.
In fact, a consist of such units can produce
more than enough drawbar pull at start-up
to damage or derail cars (if on a curve) or
break couplers (the latter being referred
to in North American railroad slang as "jerking
a lung").
Therefore, it is incumbent upon the engine
driver to carefully monitor the amount of
power being applied at start-up to avoid damage.
In particular, "jerking a lung" could be a
calamitous matter if it were to occur on an
ascending grade, except that the safety inherent
in the correct operation of automatic train
brakes installed in wagons today, prevents
runaway trains by automatically applying the
wagon brakes when train line air pressure
drops.
==== Propulsion system operation ====
A locomotive's control system is designed
so that the main generator electrical power
output is matched to any given engine speed.
Given the innate characteristics of traction
motors, as well as the way in which the motors
are connected to the main generator, the generator
will produce high current and low voltage
at low locomotive speeds, gradually changing
to low current and high voltage as the locomotive
accelerates.
Therefore, the net power produced by the locomotive
will remain constant for any given throttle
setting (see power curve graph for notch 8).
In older designs, the prime mover's governor
and a companion device, the load regulator,
play a central role in the control system.
The governor has two external inputs: requested
engine speed, determined by the engine driver's
throttle setting, and actual engine speed
(feedback).
The governor has two external control outputs:
fuel injector setting, which determines the
engine fuel rate, and load regulator position,
which affects main generator excitation.
The governor also incorporates a separate
overspeed protective mechanism that will immediately
cut off the fuel supply to the injectors and
sound an alarm in the cab in the event the
prime mover exceeds a defined RPM.
Not all of these inputs and outputs are necessarily
electrical.
The load regulator is essentially a large
potentiometer that controls the main generator
power output by varying its field excitation
and hence the degree of loading applied to
the engine.
The load regulator's job is relatively complex,
because although the prime mover's power output
is proportional to RPM and fuel rate, the
main generator's output is not (which characteristic
was not correctly handled by the Ward Leonard
elevator- and hoist-type drive system that
was initially tried in early locomotives).
Instead, a quite complex electro-hydraulic
Woodward governor was employed.
Today, this important function would be performed
by the Engine control unit, itself being a
part of the Locomotive control unit.
As the load on the engine changes, its rotational
speed will also change.
This is detected by the governor through a
change in the engine speed feedback signal.
The net effect is to adjust both the fuel
rate and the load regulator position so that
engine RPM and torque (and thus power output)
will remain constant for any given throttle
setting, regardless of actual road speed.
In newer designs controlled by a “traction
computer,” each engine speed step is allotted
an appropriate power output, or “kW reference”,
in software.
The computer compares this value with actual
main generator power output, or “kW feedback”,
calculated from traction motor current and
main generator voltage feedback values.
The computer adjusts the feedback value to
match the reference value by controlling the
excitation of the main generator, as described
above.
The governor still has control of engine speed,
but the load regulator no longer plays a central
role in this type of control system.
However, the load regulator is retained as
a “back-up” in case of engine overload.
Modern locomotives fitted with electronic
fuel injection (EFI) may have no mechanical
governor; however a “virtual” load regulator
and governor are retained with computer modules.
Traction motor performance is controlled either
by varying the DC voltage output of the main
generator, for DC motors, or by varying the
frequency and voltage output of the VVVF for
AC motors.
With DC motors, various connection combinations
are utilized to adapt the drive to varying
operating conditions.
At standstill, main generator output is initially
low voltage/high current, often in excess
of 1000 amperes per motor at full power.
When the locomotive is at or near standstill,
current flow will be limited only by the DC
resistance of the motor windings and interconnecting
circuitry, as well as the capacity of the
main generator itself.
Torque in a series-wound motor is approximately
proportional to the square of the current.
Hence, the traction motors will produce their
highest torque, causing the locomotive to
develop maximum tractive effort, enabling
it to overcome the inertia of the train.
This effect is analogous to what happens in
an automobile automatic transmission at start-up,
where it is in first gear and thus producing
maximum torque multiplication.
As the locomotive accelerates, the now-rotating
motor armatures will start to generate a counter-electromotive
force (back EMF, meaning the motors are also
trying to act as generators), which will oppose
the output of the main generator and cause
traction motor current to decrease.
Main generator voltage will correspondingly
increase in an attempt to maintain motor power,
but will eventually reach a plateau.
At this point, the locomotive will essentially
cease to accelerate, unless on a downgrade.
Since this plateau will usually be reached
at a speed substantially less than the maximum
that may be desired, something must be done
to change the drive characteristics to allow
continued acceleration.
This change is referred to as "transition,"
a process that is analogous to shifting gears
in an automobile.
Transition methods include:
Series / Parallel or "motor transition".
Initially, pairs of motors are connected in
series across the main generator.
At higher speed, motors are reconnected in
parallel across the main generator.
"Field shunting", "field diverting", or "weak
fielding".
Resistance is connected in parallel with the
motor field.
This has the effect of increasing the armature
current, producing a corresponding increase
in motor torque and speed.Both methods may
also be combined, to increase the operating
speed range.
Generator / rectifier transition
Reconnecting the two separate internal main
generator stator windings of two rectifiers
from parallel to series to increase the output
voltage.In older locomotives, it was necessary
for the engine driver to manually execute
transition by use of a separate control.
As an aid to performing transition at the
right time, the load meter (an indicator that
shows the engine driver how much current is
being drawn by the traction motors) was calibrated
to indicate at which points forward or backward
transition should take place.
Automatic transition was subsequently developed
to produce better operating efficiency and
to protect the main generator and traction
motors from overloading from improper transition.
Modern locomotives incorporate traction inverters,
AC to DC, with the capability to deliver 1,200
volts (earlier traction generators, DC to
DC, had the capability to deliver only 600
volts).
This improvement was accomplished largely
through improvements in silicon diode technology.
With the capability to deliver 1,200 volts
to the traction motors, the necessity for
"transition" was eliminated.
==== Dynamic braking ====
A common option on diesel–electric locomotives
is dynamic (rheostatic) braking.
Dynamic braking takes advantage of the fact
that the traction motor armatures are always
rotating when the locomotive is in motion
and that a motor can be made to act as a generator
by separately exciting the field winding.
When dynamic braking is utilized, the traction
control circuits are configured as follows:
The field winding of each traction motor is
connected across the main generator.
The armature of each traction motor is connected
across a forced-air-cooled resistance grid
(the dynamic braking grid) in the roof of
the locomotive's hood.
The prime mover RPM is increased and the main
generator field is excited, causing a corresponding
excitation of the traction motor fields.The
aggregate effect of the above is to cause
each traction motor to generate electric power
and dissipate it as heat in the dynamic braking
grid.
A fan connected across the grid provides forced-air
cooling.
Consequently, the fan is powered by the output
of the traction motors and will tend to run
faster and produce more airflow as more energy
is applied to the grid.
Ultimately, the source of the energy dissipated
in the dynamic braking grid is the motion
of the locomotive as imparted to the traction
motor armatures.
Therefore, the traction motors impose drag
and the locomotive acts as a brake.
As speed decreases, the braking effect decays
and usually becomes ineffective below approximately
16 km/h (10 mph), depending on the gear ratio
between the traction motors and axles.
Dynamic braking is particularly beneficial
when operating in mountainous regions; where
there is always the danger of a runaway due
to overheated friction brakes during descent.
In such cases, dynamic brakes are usually
applied in conjunction with the air brakes,
the combined effect being referred to as blended
braking.
The use of blended braking can also assist
in keeping the slack in a long train stretched
as it crests a grade, helping to prevent a
"run-in", an abrupt bunching of train slack
that can cause a derailment.
Blended braking is also commonly used with
commuter trains to reduce wear and tear on
the mechanical brakes that is a natural result
of the numerous stops such trains typically
make during a run.
==== Electro-diesel ====
These special locomotives can operate as an
electric locomotive or as a diesel locomotive.
The Long Island Rail Road, Metro-North Railroad
and New Jersey Transit Rail Operations operate
dual-mode diesel–electric/third-rail (catenary
on NJTransit) locomotives between non-electrified
territory and New York City because of a local
law banning diesel-powered locomotives in
Manhattan tunnels.
For the same reason, Amtrak operates a fleet
of dual-mode locomotives in the New York area.
British Rail operated dual diesel–electric/electric
locomotives designed to run primarily as electric
locomotives with reduced power available when
running on diesel power.
This allowed railway yards to remain un-electrified,
as the third rail power system is extremely
hazardous in a yard area.
=== Diesel–hydraulic ===
Diesel–hydraulic locomotives use one or
more torque converters, in combination with
gears, with a mechanical final drive to convey
the power from the diesel engine to the wheels.
==== Hydrostatic transmission ====
Hydraulic drive systems using a hydrostatic
hydraulic drive system have been applied to
rail use.
Modern examples included 350 to 750 hp (260
to 560 kW) shunting locomotives by CMI Group
(Belgium), 4 to 12 tonne 35 to 58 kW (47 to
78 hp) narrow gauge industrial locomotives
by Atlas Copco subsidiary GIA.
Hydrostatic drives are also utilised in railway
maintenance machines (tampers, rail grinders).Application
of hydrostatic transmissions is generally
limited to small shunting locomotives and
rail maintenance equipment, as well as being
used for non-tractive applications in diesel
engines such as drives for traction motor
fans.
==== Hydrokinetic transmission ====
Hydrokinetic transmission (also called hydrodynamic
transmission) uses a torque converter.
A torque converter consists of three main
parts, two of which rotate, and one (the stator)
that has a lock preventing backwards rotation
and adding output torque by redirecting the
oil flow at low output RPM.
All three main parts are sealed in an oil-filled
housing.
To match engine speed to load speed over the
entire speed range of a locomotive some additional
method is required to give sufficient range.
One method is to follow the torque converter
with a mechanical gearbox which switches ratios
automatically, similar to an automatic transmission
on a car.
Another method is to provide several torque
converters each with a range of variability
covering part of the total required; all the
torque converters are mechanically connected
all the time, and the appropriate one for
the speed range required is selected by filling
it with oil and draining the others.
The filling and draining is carried out with
the transmission under load, and results in
very smooth range changes with no break in
the transmitted power.
===== Locomotives =====
Diesel–hydraulic locomotives are less efficient
than diesel–electrics.
The first-generation BR diesel hydraulics
were significantly less efficient (c. 65%)
than diesel electrics (c. 80%) — moreover
initial versions were found in many countries
to be mechanically more complicated and more
likely to break down.
Hydraulic transmission for locomotives was
developed in Germany.
There is still debate over the relative merits
of hydraulic vs. electrical transmission systems:
advantages claimed for hydraulic systems include
lower weight, high reliability, and lower
capital cost.By the 21st century, for diesel
locomotive traction worldwide the majority
of countries used diesel–electric designs,
with diesel hydraulic designs not found in
use outside Germany and Japan, and some neighbouring
states, where it is used in designs for freight
work.
In Germany and Finland, diesel–hydraulic
systems have achieved high reliability in
operation.
In the UK the diesel–hydraulic principle
gained a poor reputation due to the poor durability
and reliability of the Maybach Mekydro hydraulic
transmission.
Argument continues over the relative reliability
of hydraulic systems, with questions over
whether data has been manipulated to favour
local suppliers over non-German ones.
===== Multiple units =====
Diesel–hydraulic drive is common in multiple
units, with various transmission designs used
including Voith torque converters, and fluid
couplings in combination with mechanical gearing.
The majority of British Rail's second generation
passenger DMU stock used hydraulic transmission.
In the 21st century designs using hydraulic
transmission include Bombardier's Turbostar,
Talent, RegioSwinger families; diesel engined
versions of Siemens's Desiro platform, and
the Stadler Regio-Shuttle.
====== Examples ======
Diesel–hydraulic locomotives have a smaller
market share than those with diesel electric
transmission - the main worldwide user of
main-line hydraulic transmissions was the
Federal Republic of Germany, with designs
including the 1950s DB class V 200, and the
1960 and 1970s DB Class V 160 family.
British Rail introduced a number of diesel
hydraulic designs during it 1955 Modernisation
Plan, initially license built versions of
German designs (see Category:Diesel–hydraulic
locomotives of Great Britain).
In Spain RENFE used high power to weight ratio
twin engined German designs to haul high speed
trains from the 1960s to 1990s.
(see RENFE Classes 340, 350, 352, 353, 354)
Other main-line locomotives of the post war
period included the 1950s GMD GMDH-1 experimental
locomotives; the Henschel & Son built South
African Class 61-000; in the 1960s Southern
Pacific bought 18 Krauss-Maffei KM ML-4000
diesel–hydraulic locomotives.
The Denver & Rio Grande Western also bought
three, all of which were later sold to SP.In
Finland, over 200 Finnish-built VR class Dv12
and Dr14 diesel–hydraulics with Voith transmissions
have been continuously used since the early
1960s.
All units of Dr14 class and most units of
Dv12 class are still in service.
VR has abandoned some weak-conditioned units
of 2700 series Dv12s.In the 21st century series
production standard gauge diesel–hydraulic
designs include the Voith Gravita, ordered
by Deutsche Bahn, and the Vossloh G2000, G1206
and G1700 designs, all manufactured in Germany
for freight use.
=== Diesel–steam ===
Steam-diesel hybrid locomotives can use steam
generated from a boiler or diesel to power
a piston engine.
The Cristiani Compressed Steam System used
a diesel engine to power a compressor to drive
and recirculate steam produced by a boiler;
effectively using steam as the power transmission
medium, with the diesel engine being the prime
mover
=== Diesel–pneumatic ===
The diesel-pneumatic locomotive was of interest
in the 1930s because it offered the possibility
of converting existing steam locomotives to
diesel operation.
The frame and cylinders of the steam locomotive
would be retained and the boiler would be
replaced by a diesel engine driving an air
compressor.
The problem was low thermal efficiency because
of the large amount of energy wasted as heat
in the air compressor.
Attempts were made to compensate for this
by using the diesel exhaust to re-heat the
compressed air but these had limited success.
A German proposal of 1929 did result in a
prototype but a similar British proposal of
1932, to use an LNER Class R1 locomotive,
never got beyond the design stage.
== Multiple-unit operation ==
Most diesel locomotives are capable of multiple
unit operation (MU) as a means of increasing
horsepower and tractive effort when hauling
heavy trains.
All North American locomotives, including
export models, use a standardized AAR electrical
control system interconnected by a 27-pin
jumper cable between the units.
For UK-built locomotives, a number of incompatible
control systems are used, but the most common
is the Blue Star system, which is electro-pneumatic
and fitted to most early diesel classes.
A small number of types, typically higher-powered
locomotives intended for passenger only work,
do not have multiple control systems.
In all cases, the electrical control connections
made common to all units in a consist are
referred to as trainlines.
The result is that all locomotives in a consist
behave as one in response to the engine driver's
control movements.
The ability to couple diesel–electric locomotives
in an MU fashion was first introduced in the
EMD FT four-unit demonstrator that toured
the United States in 1939.
At the time, American railroad work rules
required that each operating locomotive in
a train had to have on board a full crew.
EMD circumvented that requirement by coupling
the individual units of the demonstrator with
drawbars instead of conventional knuckle couplers
and declaring the combination to be a single
locomotive.
Electrical interconnections were made so one
engine driver could operate the entire consist
from the head-end unit.
Later on, work rules were amended and the
semi-permanent coupling of units with drawbars
was eliminated in favour of couplers, as servicing
had proved to be somewhat cumbersome owing
to the total length of the consist (about
200 feet or nearly 61 meters).
In mountainous regions, it is common to interpose
helper locomotives in the middle of the train,
both to provide the extra power needed to
ascend a grade and to limit the amount of
stress applied to the draft gear of the car
coupled to the head-end power.
The helper units in such distributed power
configurations are controlled from the lead
unit's cab through coded radio signals.
Although this is technically not an MU configuration,
the behaviour is the same as with physically
interconnected units.
=== Cab arrangements ===
Cab arrangements vary by builder and operator.
Practice in the U.S. has traditionally been
for a cab at one end of the locomotive with
limited visibility if the locomotive is not
operated cab forward.
This is not usually a problem as U.S. locomotives
are usually operated in pairs, or threes,
and arranged so that a cab is at each end
of each set.
European practice is usually for a cab at
each end of the locomotive as trains are usually
light enough to operate with one locomotive.
Early U.S. practice was to add power units
without cabs (booster or B units) and the
arrangement was often A-B, A-A, A-B-A, A-B-B,
or A-B-B-A where A was a unit with a cab.
Center cabs were sometimes used for switch
locomotives.
=== Cow-calf ===
In North American railroading, a cow-calf
set is a pair of switcher-type locomotives:
one (the cow) equipped with a driving cab,
the other (the calf) without a cab, and controlled
from the cow through cables.
Cow-calf sets are used in heavy switching
and hump yard service.
Some are radio controlled without an operating
engineer present in the cab.
This arrangement is also known as master-slave.
Where two connected units were present, EMD
called these TR-2s (approximately 2,000 hp
or 1,500 kW); where three units, TR-3s (approximately
3,000 hp or 2,200 kW).
Cow-calves have largely disappeared as these
engine combinations exceeded their economic
lifetimes many years ago.
Present North American practice is to pair
two 3,000 hp (2,200 kW) GP40-2 or SD40-2 road
switchers, often nearly worn-out and very
soon ready for rebuilding or scrapping, and
to utilize these for so-called "transfer"
uses, for which the TR-2, TR-3 and TR-4 engines
were originally intended, hence the designation
TR, for "transfer".
Occasionally, the second unit may have its
prime-mover and traction alternator removed
and replaced by concrete or steel ballast
and the power for traction obtained from the
master unit.
As a 16-cylinder prime-mover generally weighs
in the 36,000-pound (16,000 kg) range, and
a 3,000 hp (2,200 kW) traction alternator
generally weighs in the 18,000-pound (8,200
kg) range, this would mean that 54,000 lb
(24,000 kg) would be needed for ballast.
A pair of fully capable "Dash 2" units would
be rated 6,000 hp (4,500 kW).
A "Dash 2" pair where only one had a prime-mover/alternator
would be rated 3,000 hp (2,200 kW), with all
power provided by master, but the combination
benefits from the tractive effort provided
by the slave as engines in transfer service
are seldom called upon to provide 3,000 hp
(2,200 kW) much less 6,000 hp (4,500 kW) on
a continuous basis.
== Fittings and appliances ==
=== 
Flameproofing ===
A standard diesel locomotive presents a very
low fire risk but “flame proofing” can
reduce the risk even further.
This involves fitting a water-filled box to
the exhaust pipe to quench any red-hot carbon
particles that may be emitted.
Other precautions may include a fully insulated
electrical system (neither side earthed to
the frame) and all electric wiring enclosed
in conduit.
The flameproof diesel locomotive has replaced
the fireless steam locomotive in areas of
high fire risk such as oil refineries and
ammunition dumps.
Preserved examples of flameproof diesel locomotives
include:
Francis Baily of Thatcham (ex-RAF Welford)
at Southall Railway Centre
Naworth (ex-National Coal Board) at the South
Tynedale RailwayLatest development of the
"Flameproof Diesel Vehicle Applied New Exhaust
Gas Dry Type Treatment System” does not
need the water supply.
=== Lights ===
The lights fitted to diesel locomotives vary
from country to country.
North American locomotives are fitted with
two headlights (for safety in case one malfunctions)
and a pair of ditch lights.
The latter are fitted low down at the front
and are designed to make the locomotive easily
visible as it approaches a grade crossing.
Older locomotives may be fitted with a Gyralite
or Mars Light instead of the ditch lights.
== Environmental impact ==
Although diesel locomotives generally emit
less sulphur dioxide, a major pollutant to
the environment, and greenhouse gases than
steam locomotives, they are not completely
clean in that respect.
Furthermore, like other diesel powered vehicles,
they emit nitrogen oxides and fine particles,
which are a risk to public health.
In fact, in this last respect diesel locomotives
may perform worse than steam locomotives.
For years, it was thought by American government
scientists who measure air pollution that
diesel locomotive engines were relatively
clean and emitted far less health-threatening
emissions than those of diesel trucks or other
vehicles; however, the scientists discovered
that because they used faulty estimates of
the amount of fuel consumed by diesel locomotives,
they grossly understated the amount of pollution
generated annually (In Europe, where most
major railways have been electrified, there
is less concern).
After revising their calculations, they concluded
that the annual emissions of nitrogen oxide,
a major ingredient in smog and acid rain,
and soot would be by 2030 nearly twice what
they originally assumed.This would mean that
diesel locomotives would be releasing more
than 800,000 tons of nitrogen oxide and 25,000
tons of soot every year within a quarter of
a century, in contrast to the EPA's previous
projections of 480,000 tons of nitrogen dioxide
and 12,000 tons of soot.
Since this was discovered, to reduce the effects
of the diesel locomotive on humans (who are
breathing the noxious emissions) and on plants
and animals, it is considered practical to
install traps in the diesel engines to reduce
pollution levels and other forms (e.g., use
of biodiesel).
Diesel locomotive pollution has been of particular
concern in the city of Chicago.
The Chicago Tribune reported levels of diesel
soot inside locomotives leaving Chicago at
levels hundreds of times above what is normally
found on streets outside.
Residents of several neighborhoods are most
likely exposed to diesel emissions at levels
several times higher than the national average
for urban areas.
=== Mitigation ===
In 2008, the United States Environmental Protection
Agency (EPA) mandated regulations requiring
all new or refurbished diesel locomotives
to meet Tier II pollution standards that slash
the amount of allowable soot by 90% and require
an 80% reduction in nitrogen oxide emissions.
See List of low emissions locomotives.
Other technologies that are being deployed
to reduce locomotive emissions and fuel consumption
include "Genset" switching locomotives and
hybrid Green Goat designs.
Genset locomotives use multiple smaller high-speed
diesel engines and generators (generator sets),
rather than a single medium-speed diesel engine
and a single generator.
Because of the cost of developing clean engines,
these smaller high-speed engines are based
on already developed truck engines.
Green Goats are a type of hybrid switching
locomotive utilizing a small diesel engine
and a large bank of rechargeable batteries.
Switching locomotives are of particular concern
as they typically operate in a limited area,
often in or near urban centers, and spend
much of their time idling.
Both designs reduce pollution below EPA Tier
II standards and cut or eliminate emissions
during idle.
== Diesel's advantages over steam ==
As diesel locomotives advanced, the cost of
manufacturing and operating them dropped,
and they became cheaper to own and operate
than steam locomotives.
In North America, steam locomotives were custom-made
for specific railway routes, so economies
of scale were difficult to achieve.
Though more complex to produce with exacting
manufacturing tolerances (1⁄10000-inch or
0.0025-millimetre for diesel, compared with
1⁄100-inch (0.25 mm) for steam), diesel
locomotive parts were easier to mass produce.
Baldwin Locomotive Works offered almost five
hundred steam models in its heyday, while
EMD offered fewer than ten diesel varieties..
In the United Kingdom, British Railways built
steam locomotives to standard designs from
1951 onwards.
These included standard, interchangeable parts,
and were cheaper to produce than the diesel
locomotives then available.
The capital cost per drawbar horse power was
£13 6s (steam), £65 (diesel), £69 7s (turbine)
and £17 13s (electric).Diesel locomotives
offer significant operating advantages over
steam locomotives.
They can safely be operated by one person,
making them ideal for switching/shunting duties
in yards (although for safety reasons many
main-line diesel locomotives continue to have
2-man crews: an engineer and a conductor/switchman)
and the operating environment is much more
attractive, being quieter, fully weatherproof
and without the dirt and heat that is an inevitable
part of operating a steam locomotive.
Diesel locomotives can be worked in multiple
with a single crew controlling multiple locomotives
in a single train — something not practical
with steam locomotives.
This brought greater efficiencies to the operator,
as individual locomotives could be relatively
low-powered for use as a single unit on light
duties but marshaled together to provide the
power needed on a heavy train.
With steam traction a single very powerful
and expensive locomotive was required for
the heaviest trains or the operator resorted
to double heading with multiple locomotives
and crews, a method which was also expensive
and brought with it its own operating difficulties.
Diesel engines can be started and stopped
almost instantly, meaning that a diesel locomotive
has the potential to incur no fuel costs when
not being used.
However, it is still the practice of large
North American railroads to use straight water
as a coolant in diesel engines instead of
coolants that incorporate anti-freezing properties;
this results in diesel locomotives being left
idling when parked in cold climates instead
of being completely shut down.
A diesel engine can be left idling unattended
for hours or even days, especially since practically
every diesel engine used in locomotives has
systems that automatically shut the engine
down if problems such as a loss of oil pressure
or coolant loss occur.
Automatic start/stop systems are available
which monitor coolant and engine temperatures.
When the unit is close to having its coolant
freeze, the system restarts the diesel engine
to warm the coolant and other systems.Steam
locomotives require intensive maintenance,
lubrication, and cleaning before, during,
and after use.
Preparing and firing a steam locomotive for
use from cold can take many hours.
They can be kept in readiness between uses
with a low fire, but this requires regular
stoking and frequent attention to maintain
the level of water in the boiler.
This may be necessary to prevent the water
in the boiler freezing in cold climates, so
long as the water supply itself is not frozen.
The maintenance and operational costs of steam
locomotives were much higher than diesels.
Annual maintenance costs for steam locomotives
accounted for 25% of the initial purchase
price.
Spare parts were cast from wooden masters
for specific locomotives.
The sheer number of unique steam locomotives
meant that there was no feasible way for spare-part
inventories to be maintained.
With diesel locomotives spare parts could
be mass-produced and held in stock ready for
use and many parts and sub-assemblies could
be standardized across an operator's fleet
using different models of locomotive from
the same builder.
Modern diesel locomotives are designed to
allow the power assemblies to be replaced,
which greatly reduces the time that a locomotive
is out of revenue-generating service when
it requires maintenance.Steam engines required
large quantities of coal and water, which
were expensive variable operating costs.
Further, the thermal efficiency of steam was
considerably less than that of diesel engines.
Diesel's theoretical studies demonstrated
potential thermal efficiencies for a compression
ignition engine of 36% (compared with 6–10%
for steam), and an 1897 one-cylinder prototype
operated at a remarkable 26% efficiency.However,
one study published in 1959 suggested that
many of the comparisons between diesel and
steam locomotives were made unfairly mostly
because diesels were newer.
After painstaking analysis of financial records
and technological progress, the author found
that if research had continued on steam technology
instead of diesel, there would be negligible
financial benefit in converting to diesel
locomotion.By the mid-1960s, diesel locomotives
had effectively replaced steam locomotives
where electric traction was not in use.
Attempts to develop advanced steam technology
continue in the 21st century but have not
made a significant impact.
== See also
