Diesel multiple unit
From Wikipedia, the free encyclopedia
A Diesel Multiple Unit or DMU is a multiple unit train powered by one or more on-board diesel engines.
Contents |
[edit] Types
DMU's can be classified based on their form of appling motive power to their wheels.
[edit] Diesel Electric
In a Diesel-electric Multiple Unit (DEMU) a diesel engine drives a generator which produces (usually) AC current. This current can then be fed to traction motors in the wheels or bogies. Power is controlled by the engine, the more fuel supplied to the engine, the faster the engine and generator spin and so the more current is generated for the motors.
In most modern DEMUs, each car is entirely self-contained and has its own engine, generator and electric motors. In older designs some cars within the consist may be entirely unpowered or only feature electric motors, obtaining electrical current from other cars in the consist which have a generator and engine.
Some DEMUs have the ability to use external electrical power sources where available, usually in areas where the pollution caused by internal combustion is not acceptable or simply as it is more economical.
Rheostatic braking (sometimes called dynamic, electric or regenerative braking) is also available on some DEMUs. By attaching the motors to an electrical load they act as generators and slow the train down. The load is usually resistors which dissipate electrical energy as heat to the atmosphere, though it is sometimes used to heat the interiors. In some cases it is stored for later use or passed back into external power supplies. The advantage for this method of breaking is reduced wear and tear on the main service brakes.
[edit] Diesel Mechanical
In a Diesel Mechanical Multiple Unit the rotating energy of the engine is transmitted via a gearbox and driveshaft directly to the wheels of the train.
See also Transmission (mechanics)
[edit] Diesel Hydraulic
In a Diesel Hydralic Multiple Unit, a hydraulic Torque converter acts as the transmission medium for the motive power of the diesel engine to turn the wheels.
[edit] Basics
The diesel engine may be above the frame (e.g. British Rail Class 205) or underslung. When underslung, it is also referred to as Railcar or, in North America, a Rail Diesel Car (RDC). The RDC was a single passenger car with two diesel engines and two sets of controls. Any number of cars could be connected together and all the propulsion systems controlled from a single operator's station or cab. The other design places two or three cars together in a set. There are control systems at each end of the set and multiple sets can be connected together.
A regional rail train composed of DMU cars "scales" well (i.e. adding additional car sets automatically adds power). Distribution of the propulsion among the cars also results in a system that is less vulnerable to single-point-of-failure outages. Because they operate on diesel, there is no need to run overhead electric lines or electrified track, which can result in lower system construction costs.
More rugged than units strictly designed for operation on light rail, DMU systems can be safely operated within freight rail corridors, though safety regulations necessitated by the use of heavier trains in North America generally prevent this, requiring that they be operated on separate tracks in North America.
[edit] Situation in North America
The US Federal Railway Administration effectively prohibits the use of lightweight DMUs on main line railways in the United States (the situation is much the same in the rest of North America) with higher buff strength requirements than European regulators. Several manufacturers, notably Colorado Railcar, are currently marketing DMUs suitable for mainline use in North America.
The South Florida Regional Transportation Authority received a grant from the Department of Transportation for a DMU feasibility study in 2003. In October 2006, a Colorado Railcar bi-Level DMU and Coach consist entered regular, daily revenue service with South Florida's Tri-Rail commuter rail line as a technology demonstrator. Tri-Rail currently operates a heavy commuter rail service along an 87-mile corridor between Miami and West Palm Beach, Florida.
The Los Angeles County Metropolitan Transit Authority approved an allocation of $250,000 for a feasibility study of DMUs for "future transportation options for the region" on July 5, 2006 (Ara Najarian, Metro Board Member).
Chicago's commuter rail line, Metra, is studying the use of DMUs on its newly proposed lines. They claim these DMUs will have better acceleration, be more fuel efficient, and seat more customers than the current diesel engine cab and double decker rail cars that are currently in use.
Amtrak is reportedly encouraging the state of Vermont to buy DMUs for Amtrak's state-subsidized Vermonter service, in order to save money over the current locomotive-pulled arrangement. [1]
The Massachusetts Bay Transportation Authority is reportedly considering options to utilize DMUs on the Fairmount Line, currently run by locomotive-pulled carriages, in order to improve service and headways on the line. This plan has become known as the Indigo Line.
In North America the term is also used in conjunction with individual diesel locomotives. In these cases the connections typically consist of seven air hoses and one electrical cable. The largest hose, located next to the coupler is the main air brake line or "train line". Outboard of this are two smaller hoses which link the air compressors on the locomotives. Further out are two hoses which control the brakes on the locomotives independently of the rest of the train. The two outermost hoses control the application of sand to the rails. An electrical cable above the coupler transmits throttle information from one locomotive to the next. Locomotives set up to use slugs have extra connections for transmitting electricity from the diesel electric generator on the "mother" unit to the traction motors on the slug.
[edit] Australia
DMU's are extensively used across Australia for medium distance intercity routes.
Western Australia's Transwa operates the Prospector, Avonlink and Australind
In Victoria V/Line operate VLocity DMU's
NSW CountryLink uses Xplorer DMU's
A DMU variant of Queensland's QR Tilt Train is in use between Brisbane and Cairns.
TransAdelaide In South Australia uses DMU's on their commuter rail lines.
See Rail transport in Australia.
[edit] Germany
The Flying Hamburger of Germany, introduced 1933, established the then-time fastest regular railway connection of the world. Top speed was 160 km/h, the average speed being 124 km/h on the tracks between Berlin and Hamburg.
Also from Germany is the CargoSprinter concept. With two motorized units and three flatbed wagons between them, this DMU container train tried to compete with container road trucks by profiting from existing railway access to factories and businesses, but eliminating the need for inflexible locomotive-pulled cargo trains. The payload was 160 tons. Suffering from technical problems and failing political support for short-haul cargo railway connections, the prototypes were sold to Austria.
[edit] United Kingdom
[edit] History (in the UK)
DMUs were widely used in the United Kingdom after their introduction in the 1960s by British Rail. At that time there was an urgent need to move away from steam which led to many experimental designs using Diesel-electric traction and multiple units.
A type of DEMU nick-named "Thumpers" (after their characteristic sound) was widely used in south-eastern England. They were intended as a stop-gap to cover lines that were shortly to be electrified. However it was about 40 years before they were withdrawn in 2004 to be replaced by more modern DMUs.
Similar to the "Thumpers" were the Class 201 "Hastings" DEMUs, introduced in 1957 for the London – Hastings service via Tunbridge Wells - see the Hastings Line.
Northern Ireland Railways used DMUs extensively throughout its system, notably the NIR 80 Class introduced in the early 1970s and currently being replaced (as of 2007).
The British Rail High Speed Train (HST) was a much more powerful version, branded as "InterCity 125" (because their top speed was 125 miles per hour). These trains have always run with 2 power cars and between 5 and 9 intermediate coaches. Although originally classified as DEMUs, the power cars later became Class 43 (the second use of the designation, the first being the "Warship" class) to allow flexibility in the event of failures, instead of being confined to the semi-permanent formations. Essentially the power cars are just special Diesel-Electric locomotives and the coaches modified from loco-hauled stock.
[edit] DMUs in Britain today
DEMUs are now making a reappearance on British railways in the form of Class 220 Voyager, 221 Super-Voyager and 222 Meridian/Pioneer units, running many services previously provided by the High Speed Train and some faster DMUs (such as the Class 158, 166 168 and 170 series). These units are a sharp contrast to the "Thumpers" and "Hastings" of old, they are air-conditioned through out, with powered doors and a top speed of 125 mph.
Acceleration is regarded as fast in comparison to the High Speed Train and DMUs they replace. They can reach 60mph in less than 60 seconds under good conditions. It is for this reason that Midland Mainline chose the type to replace their Class 170 Turbostars and Virgin Trains chose them to replace their HSTs. The Class 221 Super-Voyager even has the ability to tilt where infrastructure permits, allowing it achieve higher speeds on bends. The noise and vibration levels from the 750 bhp engines under the floors have made them unpopular with some passengers, especially as they operate on long express routes (including the longest train journey in the UK, from Penzance to Aberdeen).
[edit] Preservation
A number of older DEMU types (Thumper and Hasting units) have been preserved and are in use on private railways and for occasional main-line excursions. Notable examples are:
- Class 205 "one end Hampshire and one end Berkshire" DEMU 1118 located at pontypool and blaenavon railway
- Class 201 "Hastings" DEMU 1001 owned by Hasting Diesels Limited
- Class 205 "Hampshire" DEMU 1125 on the Watercress Line
- Class 207 "Oxted" DEMU 1317 on the Spa Valley Railway
[edit] South Korea
Korail operates many DMUs. The DHC (Diesel Hydraulic Car), which made its debut for the 1988 Seoul Olympics, can reach speeds up to 150 km/h and serves Saemaul-ho trains. The NDC (New Diesel Car) serves Mugunghwa-ho trains and the CDC (Commute Diesel Car) serves Tonggeun trains. The NDC and CDC can reach speeds up to 100 km/h and are not used for mountainous lines such as the Taebaek Line.
[edit] Manufacturers
DMU manufacturers include:
- Bombardier Transportation of Montreal, Canada
- Colorado Railcar
- Niigata Transys of tokyo, Japan
- Rotem of Seoul, South Korea
- Siemens Desiro DMU
- Integral Coach Factory of Chennai, India
