Electro-diesel locomotive

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). For the most part, these locomotives are built to serve regional, niche markets with a very specific purpose.
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 autonomous and electric mode, although with different power. 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).
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. For example, The Southern Railway types were of 1,600 horsepower (1,200 kW) or 'Type 3' rating as electrics, but only 600 horsepower (450 kW) as diesels. Later classes had as much as 2,500 horsepower (1,900 kW) on electric power, but still the same diesel engines. Despite this large difference, their comparable tractive efforts were much closer (around three-quarters as diesels) and so they could start and work equally heavy trains as diesels, but not to the same speeds.
These locomotives are usually operated on electrified railway lines that have non-electrified sections in the short final part of the route, the so-called "last mile". That can be a small branch lines, stations with non-electrified siding tracks or tracks with another type of electrification, lines at cargo terminals, industrial facilities, construction sites, wharves, factories, mines, quarries at loading points where overhead lines cannot be used due to the need to load cargo. That eliminates the need to change a mainline locomotive to a shunter locomotive. Also in case of a third rail electrification, these locomotives can be used to cross non-electrified gaps (e.g. level crossings) or tracks with unpowered third rail (e.g. at freight yards during shunting operations or on metro lines at night, where the power supply is temporarily switched off for the safety of the working personnel).
The Southern Region of British Railways used mainly-electric dual-mode locomotives from 1960-s to cross non-electrified gaps and to haul boat trains that used tramways at the ports of Southampton and Weymouth, and also at freight yards. Some of these locomotives were originally built as electro-diesel locomotives at the factory (e.g. British Rail Class 73), others were converted from electric locomotives (such as the British Rail Class 74).
Since the 2010s, in continental Europe, several locomotive manufacturers have started to produce electric locomotives with an optional small "last mile diesel", and this name was getting popular. These are electric locomotives with a small diesel engine of truck type (usually with 180–300 kW (240–400 hp) power output), used in low speed, low gear, for operation at small flat freight yards or with short freight trains at branch lines, eliminating the need for a shunter locomotive.
At the same time, locomotives with more powerful diesel engines, which are also capable of self-powered operations when hauling a normal freight train at low speeds, were also produced (e.g., British Rail Class 88 with 710 kW (950 hp) diesel engine). Locomotives of this class are very close to fully dual-mode locomotives, though they are mostly limited to last mile operations.
This is effectively a diesel locomotive with auxiliary electric capacity for power supply from electric network (or auxiliary electric motors in case of diesel-hydraulic transmission), usually operating from a low-voltage catenary (e.g. 750 V DC third rail in the USA or 1000 V DC overhead lines in Switzerland), where non-electric traction is banned. These locomotives are generally based on conventional diesel-electric locomotives and can be converted relatively easily by adding current collectors (pantographs or contact shoes), contactors and voltage regulation equipment when powered from an electric supply. Due to the low input voltage and current limitations in electric mode, the power output on the traction motors and the maximum speed of such a locomotive are lower than when powered by a diesel engine.
The primary function for these models is to provide a "one-seat ride" (a rail trip that does not require a transfer to a different train) between the electrified and non-electrified sections of a rail system or to allow trains to run through tunnels or other segments of track where diesel locomotives are generally prohibited due to their production of exhaust.
In the United States, such locomotives (e.g. EMD FL9, GE Genesis P32AC-DM, EMD DM30AC, SC-42DM) are used for certain trains servicing the New York City terminals of Grand Central Terminal and Penn Station, as the various rail tunnels into Manhattan have exhaust restrictions. Once out of the tunnels, the engines are started and operation is as a normal diesel locomotive.
This type of dual-mode locomotives has a high power and traction force at home running at high speeds both "under the wires" and under diesel power. These locomotives normally operate under pure electric traction where possible, and use the diesel engines to extend the journeys along non-electrified sections which would not be cost effective to electrify. They may also be used on long cross-country routes to take advantage of shorter sections of electrified main lines.
Historically, most mainline dual-mode locomotives have had mainly electric or mainly diesel designs, as it was difficult to fit a powerful diesel engine and powerful electric capacity into a single unit while maintaining the permissible axle load. Mostly, full-fledged dual-mode electric-diesel locomotives were either small shunting and narrow-gauge locomotives with a low-powered diesel engine, which had a comparable power outputs in electric and diesel modes, or two-section industrial freight locomotives with separate electric and diesel sections, united by a common control system and power supply for traction electric motors (for example, Soviet quarry electric diesel locomotives OPE1 with two A-units or electric diesel locomotives OPE1A/OPE1B with the main electric A-unit and diesel B-unit).
Since the 2010s, thanks to the development of technologies and the emergence of sufficiently powerful and compact high-speed turbocharged diesel engines, as well as compact power electronics, it has become possible to create single full-fledged dual-mode and even tri-mode (with battery-electro-diesel) locomotives with an acceptable axle load (e.g. Stadler Euro Dual, Bombardier ALP-45DP). With modern electronics, it is much easier to construct (or adapt) such locomotives.
The electrical equipment and the diesel generator usually occupy more or less equal space in the engine room, depending on the power and size of the diesel. Although the power output of the diesel generator and traction electric motors of such locomotives is usually significantly lower than when powered from overhead lines in pure electric mode (especially on lines with high-voltage AC electrification, and can be several times less), it is still sufficient to maintain normal speed with a train. For example, in Stadler Euro Dual locomotives, the diesel engine power can vary from 1–2.8 MW (1,300–3,800 hp) in diesel mode and up to 7 MW (9,400 hp) in electric mode.
In Russia, a number of electro-diesels were built which had both pantographs and diesel prime movers. These included:
Narrow-gauge dual-mode locomotives:
Industrial freight locomotives:
Mainline freight locomotives:
Electro-diesel subway locomotives for London Underground include:
Electro-diesel locomotives whose electricity source is 650 — 750V DC third rail include:
Electro-diesel locomotives whose electricity source is 25 kV 50 Hz AC overhead line include:
Several, primarily diesel locomotive types and a multiple-unit have been built to operate off a 750 V DC third rail into the New York City terminals of Grand Central Terminal and Penn Station (with the third rail system being rarely used on open-air tracks).
The following are in service:
The following were retired from New York City service:
The Indian Railways WDAP-5 is a class of Electro-diesel locomotive that was developed in 2019 by Banaras Locomotive Works (BLW), Varanasi for Indian Railways. The model name stands for broad gauge (W), Diesel (D), AC Current (A), Passenger (P) and 5000 Horsepower(5). The locomotive can deliver 5000HP in electric mode and 4500HP in diesel mode. It was made to reduce the travel time of passenger trains which needed to change the electric locomotive with a diesel locomotive. However as of 2024, this locomotive does not have much practical use as 97% of Indian Railways has been electified. Only one of these were ever constructed and what happened to that locomotive remains unknown.
A specialized type of electro-diesel locomotive is the hybrid locomotive. Here, the electricity comes from a battery charged by the diesel engine rather than from an external supply. An example is the Green Goat switcher GG20B by Railpower Technologies, a subsidiary of R.J. Corman Railroad Group since 2009.