Trystan Casey
A diesel electric multiple unit (DEMU) is a type of train that does not require a separate locomotive as it is powered by onboard diesel engines. DEMUs are self-propelled train sets that use diesel engines to generate electricity, which then powers electric traction motors to move the train. They are used on non-electrified routes for suburban and regional services, in rural and remote areas, and as backup or auxiliary services on electrified routes. DEMUs are also bi-mode, meaning they can be powered by electric power picked up from overhead lines or third-rail systems.
Diesel Electric Multiple Unit Characteristics
| Characteristics | Values |
|---|---|
| Definition | A diesel-powered train of semi-permanently connected powered cars. |
| Types | Diesel-mechanical DMMU, diesel-hydraulic DHMU, or diesel-electric DEMU |
| Engine Placement | Above the frame in an engine bay or under the floor |
| Driving Controls | At both ends, on one end, or in a separate car |
| Transmission | Diesel-electric transmission |
| Power Source | On-board diesel generators |
| Speed | 110 km/h |
| Power | 1600 hp |
| Acceleration | 0.3 m/s2 |
| Country | Nepal |
| Usage | Non-electrified routes, suburban and regional services, backup or auxiliary services on electrified routes |
| Manufacturers | Stadler, Bombardier, CAF, CRRC Zhuzhou Locomotive, CRRC Dalian, Newag, Renfe, Hitachi, British Rail, Stadler, Medha |
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What You'll Learn
- Diesel multiple units (DMUs) are trains powered by on-board diesel engines
- DMUs are classified by their transmission type: diesel-mechanical, diesel-hydraulic, or diesel-electric
- DMUs are commonly used on shorter or less-travelled routes in remote areas
- DMUs have been used in countries including the UK, Ireland, Croatia, and the Czech Republic
- Electro-diesel multiple units (EDMUs) are bi-mode trains that can be powered by electricity or diesel engines
Diesel multiple units (DMUs) are trains powered by on-board diesel engines
A diesel multiple unit or DMU is a multiple-unit train powered by on-board diesel engines. DMUs do not require a separate locomotive as the engines are incorporated into one or more of the carriages. Diesel-powered single-unit railcars are also generally classed as DMUs. DMUs are usually classified by the method of transmitting motive power to their wheels.
In a diesel–mechanical multiple unit (DMMU), the rotating energy of the engine is transmitted via a gearbox and driveshaft directly to the wheels of the train, like a car. The transmissions can be shifted manually by the driver, as in the great majority of first-generation British Rail DMUs. However, in most applications, gears are changed automatically.
In a diesel–hydraulic multiple unit (DHMU), a hydraulic torque converter acts as the transmission medium for the motive power of the diesel engine to turn the wheels. Some units feature a hybrid mix of hydraulic and mechanical transmissions, usually reverting to the latter at higher operating speeds as this decreases engine RPM and noise.
In a diesel–electric multiple unit (DEMU), a diesel engine drives an electrical generator or an alternator, which produces electrical energy. The generated current is then fed to electric traction motors on the wheels or bogies in the same way as a conventional diesel–electric locomotive. On some DEMUs, such as the Bombardier Voyager, each car is entirely self-contained and has its own engine, generator and electric motors. In other designs, such as the British Rail Class 207, some cars within the consist may be entirely unpowered or only feature electric motors, obtaining electric current from other cars.
DMUs are used mostly on shorter or less frequently travelled routes in remote areas. They are also used as a backup or auxiliary service on electrified routes, providing additional capacity or serving routes during maintenance or emergencies on the main electrified lines.
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DMUs are classified by their transmission type: diesel-mechanical, diesel-hydraulic, or diesel-electric
A diesel multiple unit or DMU is a multiple-unit train powered by on-board diesel engines. DMUs are classified by their transmission type: diesel–mechanical, diesel–hydraulic, or diesel–electric.
Diesel-mechanical
In a diesel-mechanical multiple unit (DMMU), the rotating energy of the engine is transmitted via a gearbox and driveshaft directly to the wheels of the train, like a car. The transmissions can be shifted manually by the driver, as in the great majority of first-generation British Rail DMUs, but in most applications, gears are changed automatically.
Diesel-hydraulic
In a diesel-hydraulic multiple unit (DHMU), a hydraulic torque converter, a type of fluid coupling, acts as the transmission medium for the motive power of the diesel engine to turn the wheels. Some units feature a hybrid mix of hydraulic and mechanical transmissions, usually reverting to the latter at higher operating speeds as this decreases engine RPM and noise.
Diesel-electric
In a diesel-electric multiple unit (DEMU), a diesel engine drives an electrical generator or alternator, which produces electrical energy. The generated current is then fed to electric traction motors on the wheels or bogies in the same way as a conventional diesel–electric locomotive. On some DEMUs, such as the Bombardier Voyager, each car is entirely self-contained and has its own engine, generator, and electric motors. In other designs, such as the British Rail Class 207 or the Stadler GTW and Stadler FLIRT DMU, some cars within the consist may be entirely unpowered or only feature electric motors, obtaining electric current from other cars.
DMUs are used mostly on shorter or less frequently travelled routes in remote areas. They are also used as a backup or auxiliary service on electrified routes, providing additional capacity or serving routes during maintenance or emergencies on the main electrified lines.
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DMUs are commonly used on shorter or less-travelled routes in remote areas
DMUs, or Diesel Multiple Units, are multiple-unit trains powered by on-board diesel engines. They are commonly used on shorter or less-travelled routes in remote areas. This is because they are a more efficient and cost-effective option for these types of routes, as they do not require a separate locomotive. The engines are built into one or more of the carriages, and the driving controls can be at both ends, on one end, or in a separate car.
DMUs are well-suited for shorter or less-travelled routes because they are often used on non-electrified or partially electrified lines, which are typically found in rural or remote areas. They are also used as backup or auxiliary services on electrified routes, providing additional capacity or serving routes during maintenance or emergencies. This makes them a versatile option for shorter or less-travelled routes, as they can fill in gaps in service or provide extra capacity when needed.
In addition, DMUs are often used on regional and local services, which tend to have shorter distances and fewer passengers than longer, more heavily travelled routes. For example, in the Republic of Ireland, DMUs were introduced in the mid-1950s and were the first diesel trains on many main lines. Today, the main DMU in use in Ireland is the Class 96 Siemens Desiro, also known as the Săgeata Albastră or "The Blue Arrow".
DMUs are also used on shorter or less-travelled routes in other countries, such as Croatia, the Czech Republic, and Slovakia. In Croatia, DMUs cover local, regional, and distant lines across the country, including on unelectrified or partially electrified tracks. Similarly, in the Czech Republic, DMUs play an important role in covering local, regional, and distant lines, especially in areas with lower passenger numbers. In Slovakia, DMUs are commonly used for hauling passenger trains on non-electrified regional lines, and these trains often excel at low travel speeds.
Overall, DMUs are well-suited for shorter or less-travelled routes in remote areas due to their efficiency, versatility, and ability to operate on non-electrified lines. They provide a cost-effective and reliable option for rail services in these areas, ensuring that passengers in rural or remote communities have access to transportation.
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DMUs have been used in countries including the UK, Ireland, Croatia, and the Czech Republic
DMUs, or diesel multiple units, are multiple-unit trains powered by on-board diesel engines. They require no separate locomotive, as the engines are incorporated into one or more of the carriages.
DMUs have been used in several countries, including the UK, Ireland, Croatia, and the Czech Republic.
In the UK, British Railways introduced first-generation DMUs in the 1950s. These included 4-wheel diesel railbuses, ACV/BUT railcars, the Battery Multiple Unit (BMU), and Blue Pullmans. Images and booklets from this era can be found on the Railcar website.
In Ireland, the Córas Iompair Éireann (CIÉ) introduced DMUs in the mid-1950s, and they were the first diesel trains on many main lines. DMUs are now used mostly on shorter or less frequently travelled routes in remote areas. The main DMU in use is the Class 96 Siemens Desiro, also known as the Săgeata Albastră or The Blue Arrow.
In Croatia, DMUs play an important role in the national passenger service, covering local, regional, and distant lines across the country. Croatian Railways (HŽ Putnički prijevoz) operates DMUs on both electrified and non-electrified lines, with the average age of their DMUs being 23 years as of 2009.
In the Czech Republic, DMUs are also operated by the national operator, České dráhy. They cover local, regional, and distant lines, and are manufactured for foreign carriers as well. Leo Express, for example, operates DMUs on selected routes and plans to employ more units in the future.
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Electro-diesel multiple units (EDMUs) are bi-mode trains that can be powered by electricity or diesel engines
A diesel multiple unit or DMU is a multiple-unit train powered by on-board diesel engines. Diesel-powered single-unit railcars are also generally classed as DMUs. DMUs are used mostly on shorter or less frequently travelled routes in remote areas. They are also used on local, regional and distant lines across the world, from the Czech Republic to Croatia.
EDMUs have their own independent traction motor systems, and can be operated from the cabs of either the electric or diesel power cars. They can also be designed with more powerful diesel engines, which are capable of self-powered operations when hauling a normal freight train at low speeds.
In 2018, the first bi and tri-mode EDMUs were introduced, including Class 800/802s built by Hitachi for Great Western Railway, Hull Trains, London North Eastern Railway and TransPennine Express. EDMUs are also in service in Norway, the Netherlands, Russia, China, and the US.
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Frequently asked questions
A diesel multiple unit or DMU is a multiple-unit train that is powered by on-board diesel engines. They are used mostly on shorter or less frequently travelled routes in remote areas.
A DMU requires no separate locomotive as the engines are incorporated into one or more of the carriages. Diesel-powered units may be further classified by their transmission type: diesel–mechanical DMMU, diesel–hydraulic DHMU, or diesel–electric DEMU.
A diesel-electric multiple unit (DEMU) is a type of DMU where a diesel engine drives an electrical generator or an alternator that produces electrical energy. The generated current is then fed to electric traction motors on the wheels or bogies in the same way as a conventional diesel–electric locomotive.
Some examples of diesel multiple units include the Class 77 and 78 DMUs in the Republic of Ireland, the Class 812 ZSSK in Slovakia, and the Series 7021, 7022, and 7023 in Croatia.
