Electro-diesel locomotive
railway locomotive capable of running either under electrical or diesel power
An electro-diesel locomotive (also referred to as a dual-mode or bi-mode locomotive) is a type of locomotive that can be powered either from an electricity supply (like an electric locomotive) or by using the onboard diesel engine (like a diesel-electric locomotive).
Overview
Electro-diesel locomotives are used to provide continuous journeys along routes that are only partly electrified without a change of locomotive, avoid extensive running of diesel under overhead electrical wires and giving a solution where diesel engines are banned. They may be designed or adapted mainly for electric use, mainly for diesel use or to work well as either electric or diesel.
In most cases, electro-diesel locomotives use diesel–electric transmission and the same traction electric motors when moving in both diesel and electric mode, although with different power source. However, locomotives with diesel-mechanical or diesel-hydraulic transmission and separate electric motors were also created.
Note that, as well as the electric multiple unit (EMU) and diesel multiple unit (DMU), where no discrete locomotive is present, an electro-diesel (bi-mode) multiple unit train is called electro-diesel multiple unit (EDMU) or bi-mode multiple unit (BMU).
Types
Primarily electric
This is effectively an electric locomotive with a relatively small auxiliary diesel prime mover intended only for low-speed or short-distance operation. For economy, the diesel engine and its generator are considerably smaller than the electric capacity, which occupies most of the interior space of a locomotive. Unlike typical diesel locomotives, where the diesel engine is located in the center of the frame, in mainly electric dual-mode locomotives the auxiliary diesel engine and generator can be located at the side of the engine room.
The output power of a diesel-generator in mainline locomotives of this type is similar to the power of engines of small shunting locomotives (usually no more than 800 kW) and is significantly smaller than the nominal power of electric motors when they are powered from the electric supply.
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