Locomotive
A
locomotive (from Latin
loco motivus) is a
railway vehicle that provides the motive power for a
train, and has no payload capacity of its own; its sole purpose is to move the train along the tracks. In contrast, many trains feature self-propelled payload-carrying vehicles; these are not normally considered locomotives, and may be referred to as
multiple units or
railcars; the use of these self-propelled vehicles is increasingly common for
passenger trains, but very rare for
freight (see however
CargoSprinter). Vehicles which provide the motive power to haul an unpowered train, but are not generally considered locomotives because they have payload space or are rarely detached from their trains, are known as
power cars.
Traditionally, locomotives haul (pull) their trains. Increasingly common these days in local passenger service is
push-pull operation, where a locomotive pulls the train in one direction and pushes it in the other, and is therefore optionally controlled from a control cab at the opposite end of the train. This is especially true of "
High Speed Rail lines", such as the
Japan's
Shinkansen and
France's
TGV trains.
The first successful locomotives were built by
Cornish inventor
Richard Trevithick. In 1804 his unnamed locomotive hauled a train along the
tramway of the
Penydarren ironworks, near
Merthyr Tydfil in
Wales. Although the locomotive hauled a train of 10 tons of iron and 70 passengers in five wagons over nine miles it was too heavy for the
cast iron rails used at the time. The locomotive only ran three journeys before it was abandoned.
In
1813,
George Stephenson persuaded the manager of the
Killingworth colliery where he worked to allow him to build a
steam-powered machine. He built the
Blucher, the first successful
flanged-wheel adhesion locomotive. The flanges enabled the trains to run on
top of the rails instead of in sunken tracks. This greatly simplified construction of
switches (called "points" in UK) and rails, and opened the way to the modern railroad.
There are many reasons why the motive power for trains has been traditionally isolated in a locomotive, rather than in self-propelled vehicles. These include:
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Ease of maintenance - it is easier to maintain one locomotive than many self-propelled cars.
*
Safety - it is often safer to locate the train's power systems away from passengers. This was particularly the case for steam locomotives, but still has some relevance for other power sources.
*
Easy replacement of motive power - should the locomotive break down, it is easy to replace it with a new one. Failure of the motive power unit does not require taking the whole train out of service.
*
Efficiency - idle trains do not waste expensive motive power resources. Separate locomotives mean that the costly motive power assets can be moved around as needed.
*
Flexibility - large locomotives can be substituted for small locomotives where the gradients of the route become steeper and more power is needed.
*
Obsolescence cycles - separating the motive power from the payload-hauling cars means that either can be replaced without affecting the other. At some times, locomotives have become obsolete when their cars are not, or vice versa.
Locomotives may generate
mechanical work from fuel, or they may take
power from an outside source. It is common to classify locomotives by their means of providing motive work - the common ones include:
Steam
Main article: steam locomotive
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Walschaerts valve gear in a steam locomotive. In this animation, the red color represents live steam entering the cylinder, while the blue represents expanded (spent) steam being exhausted from the cylinder. |
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A steam locomotive at the Gare du Nord, Paris, France, in 1930 |
The first railway locomotives (
19th century) were powered by
steam, first by burning
wood, later
coke and
coal or
petroleum. Because of the steam engine, some people took to calling the steam locomotives themselves "steam engines". The steam locomotive remained by far the most common type of locomotive until after
World War II. The age of steam correlates highly to the
coal era.
The first steam locomotive was built by
Richard Trevithick, and first ran on
21 February 1804, although it took some years before steam locomotive design became efficient and economically practical.
Fairy Queen, built in
1855; plying between
New Delhi and
Alwar in
India, is the longest-running steam locomotive in regular service in the world, but
John Bull, built in
1831, is currently the oldest operable steam locomotive.
John Bull is preserved in mostly static display at the
Smithsonian Institution in
Washington, DC.
The all-time speed record for steam trains is held by an
LNER Class A4 4-6-2 Pacific locomotive of the
LNER in the United Kingdom, number 4468
Mallard, which pulling six carriages (plus a dynamometer car) reached 126 mph (203 km/h) on a slight downhill gradient down Stoke Bank on
3 July 1938. Aerodynamic passenger locomotives from other countries such as Germany and the United States attained speeds very close to this, and this is generally believed to be close to the practicable upper limit for the direct-coupled steam locomotive.
Before the middle of the
20th century, electric and diesel-electric locomotives began replacing steam locomotives. Steam locomotives are less efficient than their more modern diesel and electric counterparts and require much greater manpower to operate and service.
British Rail figures showed the cost of crewing and fuelling a steam locomotive was some two and a half times that of diesel power, and the daily mileage achievable was far lower. As labour costs rose, particularly after the second world war, non-steam technologies became much more cost-efficient. By the end of the 1960s-
1970s, most western countries had completely replaced steam locomotives in passenger service. Freight locomotives generally were replaced later. Other designs, such as locomotives powered by gas turbines, have been experimented with, but have seen little use.
By the end of the
20th century, almost the only steam power still in regular use in
North America and Western
European countries was on
heritage railways specifically aimed at tourists and/or railroad enthusiasts, known as
railfans or
train spotters, although some
narrow gauge lines in Germany which form part of the public transport system, running to all-year-round timetables retain steam for all or part of their motive power. Steam locomotives remained in commercial use in parts of
Mexico into the late
1970s. Steam locomotives were in regular use until 2004 in
China, where
coal is a much more abundant resource than
petroleum for diesel fuel. India switched over from steam-powered trains to electric and diesel-powered trains in the 1980s. In some mountainous and high altitude rail lines, steam engines remain in use because they are less affected by reduced air pressure than diesel engines.
Diesel locomotives
Main article: diesel locomotive
Steam locomotives were eventually displaced by locomotives using
diesel engines. Diesel locomotives vary in the form of transmission used to convey the power from a
diesel engine (or engines) to the wheels, the primary types being mechanical, electric, and hydraulics.
Diesel locomotives require less maintenance than steam, and their exhaust, while still polluting, is less noxious than coal smoke. They require less personnel to operate and obviate the standpipes and towers required to replenish steam locomotives at intervals. The dynamic brakes of diesel electric locomotives have proven to be a major boon in mountainous areas.
On the other hand, diesels, unlike other locomotive types, are limited to a single fuel: petroleum. Demand for diesel fuel is high and subject to political and economic shocks. And the exhaust emissions make them unsuitable for underground application, where electric locomotives remain the motive power of choice.
Gas turbine-electric
A gas turbine-electric locomotive, or GTEL, is a locomotive that uses a
gas turbine to drive an electric
generator or
alternator. The electric current thus produced is used to power
traction motors. This type of locomotive was first experimented with in
1920 but reached its peak in the
1950s to
1960s. The turbine (similar to a
turboshaft engine) drives an output shaft, which drives the alternator via a system of
gears. Aside from the unusual
prime mover, a GTEL is very similar to a
diesel-electric. In fact, the turbines built by
GE used many of the same parts as their diesels.
A turbine offers some advantages over a
piston engine. The number of moving parts is much smaller, and the
power to weight ratio is much higher. A turbine of a given power output is also physically smaller than an equally powerful piston engine, allowing a locomotive to be very powerful without being inordinately large. However, a turbine's power output and efficiency both drop dramatically with
rotational speed, unlike a piston engine, which has a comparatively flat power curve.
Gas turbine locomotives are very powerful, but also tend to be very loud.
Union Pacific operated the largest fleet of such locomotives of any railroad in the world, and was the only railroad to use them for hauling freight. Most other GTELs have been built for small passenger trains, and only a few have seen any real success in that role. After the
oil crisis in the
1970s and the subsequent rise in fuel costs, gas turbine locomotives became uneconomic to operate, and many were taken out of service. This type of locomotive is now rare.
Electric
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Former Soviet electric locomotive VL60pk (Ð'Л60пк). |
The
electric locomotive is supplied externally with electric power, either through an
overhead pickup or through a
third rail. While the capital cost of electrifying track is high, electric trains and locomotives also cost slightly more to run than diesels .
The
world speed record for a wheeled train was set in 1990 by a French TGV which reached a speed of 515.3 km/h (320 mph).
Some electric locomotives can also operate off
battery power to enable short journeys or shunting on non-electrified lines or yards. Battery-powered locomotives are used in mines and other underground locations where diesel fumes or smoke would endanger crews, and where external electricity supplies cannot be used due to the danger of sparks igniting flammable gas. Battery locomotives are also used on many underground railways for maintenance operations, as they are required when operating in areas where the electricity supply has been temporarily disconnected. However the cost and weight of the batteries are prohibitive for using battery-powered locomotives on extended runs.
See also:
Railway electrification systemMagnetic levitation
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Transrapid maglev train on the test track at Emsland, Germany. |
The newest technology in trains is
magnetic levitation (maglev). These electrically powered trains have a special open motor which floats the train above the rail without the need for wheels. This greatly reduces friction. Very few systems are in service and the cost is very high. The experimental
Japanese magnetic levitation train
JR-Maglev MLX01 has reached 581 km/h (361 mph).
The
transrapid maglev train connects
Shanghai's airport with the city.
The first commercial maglev trains ran in the
1980s in
Birmingham,
United Kingdom, providing a low-speed shuttle service between the airport and its railway station. Despite the huge interest and excitement in the technology, the system was closed down due to a lack of spare parts and replaced by cablecars running on modified groundwheel chassis a few years later.
Experimental
There are other forms of motive power in experimental use.
The Parry PeopleMover is an experimental
light rail railcar that is powered by energy stored in a
flywheel. The flywheel is powered from an onboard battery-driven motor or internal combustion engine and is also recharged through
regenerative braking. A proposed alternative is to recharge the flywheel from external electric motors installed at station stops; although this would increase installation costs it would substantially reduce the weight of the vehicles. It would also still cost less than providing a continuous electrical supply.
Parry People Movers have been tested on several railways, including the
Ffestiniog Railway, the
Welsh Highland Railway and the
Welshpool and Llanfair Light Railway. The first mainstream timetable service for the flywheel railcar was launched in February
2006 providing the Sunday service on the short link between
Stourbridge junction and
Stourbridge Town in the
United Kingdom.
The three main categories of locomotives are often subdivided in their usage in
rail transport operations. There are passenger locomotives, freight locomotives and
switcher (or shunting) locomotives. These categories mainly depend on manoeuvrability, traction power and speed. Freight locomotives are normally designed to provide a high
torque and deliver high power levels to the rails, while passenger locomotives are designed to operate at high speeds, typically with lower loads. Mixed traffic locomotives (us: General purpose locomotives) are built to provide elements of both requirements, and trade efficiency for a given job with flexibility.
Most steam engines are direct drive (that is, they have no gearbox), and the effective transmission ratios were determined by the wheel sizes. Thus steam locomotives for freight purposes generally have many smaller wheels, while steam passenger locomotives have larger wheels. With diesel and electric locomotives, the gearing is more flexible, and it is easier to create good general-purpose locomotives.
Some locomotives are designed specifically to work
mountain railways, and feature extensive additional braking mechanisms and sometimes
rack and pinion. Steam locomotives built for steep rack and pinion railways frequently have the boiler tilted relative to the wheels, so that the boiler remains roughly level on steep climbs.
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Articulated locomotive*
Bank engine*
Diesel multiple unit*
Duplex locomotive*
Electric multiple unit*
Electric locomotive*
Famous Locomotives (category)*
Gas turbine-electric locomotive*
Geared steam locomotive *
Heritage railway*
High pressure steam locomotive*
List of heritage railways*
List of locomotive builders*
Live steam*
Locomotion No 1*
Royal Hudson*
Steam dummy*
Steam engine*
Steam locomotive nomenclature contains detailed explanatory diagrams
*
Steam locomotive production*
Steam turbine locomotive*
Stephenson's Rocket*
Whyte notation*
An engineer's guide from 1891*
Animated engines, Steam Locomotive*
Database of surviving steam locomotives in North America*
Information on North American steam railroads in operation*
List of railroad car manufacturers by country (in
French)
Books on steam locomotives
* C. E. Wolff,
Modern Locomotive Practice: A Treatise on the Design, Construction, and Working of Steam Locomotives (Manchester, England, 1903)
* Henry Greenly,
Model Locomotive (New York, 1905)
* G. R. Henderson,
Cost of Locomotive Operation (New York, 1906)
* W. E. Dalby,
Economical Working of Locomotives (London, 1906)
* A. I. Taylor,
Modern British Locomotives (New York, 1907)
* E. L. Ahrens,
The Development of British Locomotive Design (London, 1914)
* E. L. Ahrens,
Steam Engine Construction and Maintenance (London, 1921)
* J. F. Gairns,
Locomotive Compounding and Superheating (Philadelphia, 1907)
* Angus Sinclair,
Development of the Locomotive Engine (New York, 1907)
* Vaughn Pendred,
The Railway Locomotive, What it is and Why it is What it is (London, 1908)
* Brosius and Koch,
Die Schule des Lokomotivführers (thirteenth edition, three volumes, Wiesbaden, 1909-1914)
* G. L. Fowler,
Locomotive Breakdowns, Emergencies, and their Remedies (seventh edition, New York, 1911)
* Fisher and Williams,
Pocket Edition of Locomotive Engineering (Chicago, 1911)
* T. A. Annis,
Modern Locomotives (Adrian Michigan, 1912)
* C. E. Allen,
Modern Locomotive (Cambridge, England, 1912)
* W. G. Knight,
Practical Questions on Locomotive Operating (Boston, 1913)
* G. R. Henderson,
Recent Development of the Locomotive (Philadelphia, 1913)
* Wright and Swift (editors)
Locomotive Dictionary (third edition, Philadelphia, 1913)
* Roberts and Smith,
Practical Locomotive Operating (Philadelphia, 1913)
* E. Prothero,
Railways of the World (New York, 1914)
*
M. M. Kirkman,
The Locomotive (Chicago, 1914)
* C. L. Dickerson,
The Locomotive and Things You Should Know About it (Clinton, Illinois, 1914)
