Know the Diesel Locos

A diesel locomotive generates its own power using an on board diesel engine. The mechanical power is converted to electrical power using an alternator and is fed to traction motors attached to the wheels. Many diesel locomotives can be coupled together and run by a single crew. They can also be operated without physical coupling through the use of distributed power system. To save fuel even as they idle features like the Auxiliary power unit is fitted on these locos which cuts in automatically. These locomotives are based on various sheds and thus we see the different colour schemes.



Typical Layout of a diesel locomotive:


The driver’s cabin in a locomotive is near one end and this end is called the short hood while the other end is called the long hood. The controls of the locomotive are available to the driver at the control stand. The locomotives have a governor which controls the amount of fuel delivered depending on the load and the speed of the train. To make the engine more efficient the intake air is compressed through a turbo charger which is run using the exhaust gases.


  1. Classification of Locomotives

If we look at a locomotive we see certain numbers and four or five letter codes written on them in the front and rear end generally below the coupling area. Each of these has a specific meaning as below:


  • The first letter (Gauge)


  • W – Indian Broad Gauge (the “W” Stands for Wide Gauge – 5 ft 6 in or 1676 mm)
  • Y – Metre Gauge (the “Y” stands for Yard Gauge – 3 ft or 1000mm)
  • Z – Narrow Gauge (2 ft 6 in)
  • N – Toy Gauge (2 ft)


  • The second letter (Motive Power)


  • D – Diesel
  • C – DC electric (can run under DC overhead line only)
  • A – AC electric (can run under AC overhead line only)
  • CA – both DC and AC (can run under both AC and DC overhead line); ‘CA’ is considered a single letter
  • B – Battery electric locomotive (rare)
  • The third letter (Job Type)


  • G – Goods
  • P – Passenger
  • M – Mixed; both goods and passenger
  • S – Shunting (also known as switching engines or switchers in the USA and some other countries)
  • U – Electric Multiple Unit (used to carry commuters in city suburbs)
  • R – Railcars


For example, in “WDM 3A“:


  • “W” means broad gauge
  • “D” means diesel motive power
  • “M” means suitable for both goods and passenger service
  • “3A” means the loco’s power is 3100 HP (‘3’ stands for 3000 HP, ‘A’ denotes 100 HP more)


  1. Traction


 History of diesel locomotives


  • WDM 1 (First mainline diesel electric locomotives used in India. Introduced in 1957. Imported from ALCO. Out of service now. 1950 HP)
  • WDM 2 (Most widely used and first homemade mainline diesel-electric locomotives in India. Original prototypes were made by ALCO. Introduced in 1962. More than 2700 have been made. Rated at 2600 HP)


  • WDM 3A (Formerly WDM 2C. Another WDM 2 variant. It is not related to WDM 3. Max speed 120kmph. 30450 kgf of tractive effort. Built since 1994)
  • WDM 4 (Entered service along with WDM 2. Prototypes designed by General Motors. Though considered superior to WDM 2 in many ways, these locomotives weren’t chosen as General Motors did not agree to a technology transfer agreement. 2600 HP)

 Passenger locomotives


  • WDP 1 (Bo-Bo bogies, 80 tons weight, Rated speed of 140 kmph, 12 cylinder engine, 2300 HP. Built by DLW in 1970. Homed at Vijayawada and Tughlakabad sheds only.
  • WDP 2 (New class name WDP 3A. Dedicated passenger diesel loco. Entered service in 1998. Max speed 140kmph, Built by DLW, 29.25 tons of tractive effort. 3100 HP)
  • WDP 3 (These locomotives are actually prototypes of the class WDP 1 and never entered serial production. Designed in 1996 by DLW. 2300 HP. Co-Co bogies. )


  • WDP 4 EMD (former GM-EMD) GT46PAC, fundamentally a passenger version of the WDG 4 (GT46MAC). 4000 HP. Another variant is the WDP4B and D which is a 4500 HP locomotive and the latter has a dual cabin.


 Goods locomotives


  • WDG 2 New class name WDG 3A. This class is actually a technically upgraded form of WDM 2. Max speed 100kmph. Built by DLW
  • WDG 4 (Dedicated goods locomotives. These are General motors’ GT46MAC models. First units were imported in 1999. They are numbered from #12000 upward till #12999 and #70000 upwards. Local production started in 2002. 4000-4500 HP)
  • WDG 5 They are numbered from #50001 upward (Only one produced till date). Rated at 5500 HP. The locomotive series is named ‘BHEEM’, after the strong Pandav brother from epic of Mahabharat.

Shunting locomotives


  • WDS 4, WDS 4A,WDS 4B,WDS 4D (Designed by Chittaranjan Locomotive Works. 600-700 HP. C bogies. Built between 1968-97)
  • WDS 6 (Heavy-haul shunters made in large numbers for industrial concerns as well as for Indian Railways. Rated at 1200/1350 HP)

The Diesel Locomotive Works (DLW) in Varanasi, India, is a production unit owned by Indian Railways, which manufactures diesel locomotives and spare parts. Founded in 1961, the DLW rolled out its first locomotive three years later, on January 3, 1964. It manufactures locomotives which are variants based on the original ALCO( American locomotive Company) designs dating to 1960s and the General Motors Electro Motive Diesel designs of the 1990s. DLW has an annual production capacity of 300 locomotives. DLW locomotives have power outputs ranging from 2600 hp to 5500 hp. Currently DLW is producing EMD GT46MAC and EMD GT46PAC locomotives under license from Electro-Motive Diesels (formerly GM-EMD) for Indian Railways.


There are 56 loco sheds for maintenance of BG, MG & NG Diesel locos in different divisions of Indian Railways. The locomotives work trains based on loco links which indicate the trains the locomotive will run after it is turned out from the shed. The drivers for these trains and locomotives are booked based on crew links. The drivers are based in various headquarters within a division and work for three to four days before they return home. Normally there is an assistant driver in each locomotive.


The locomotives have many safety features like the headlight, marker light, flasher light, automatic braking system, sanding gear, hand brakes, speed recorders etc. The flasher light is a yellow light next to the headlight and gets automatically switched on in case of an accident. Most of the locomotives are microprocessor controlled for better fuel economy and can be remotely monitored by the base sheds by watching key parameters of maintenance and operation on the net. For ensuring fuel efficiency some locomotives are being equipped with auxiliary power units, low idle features, electronic fuel injection, roller suspension bearings etc. All these features have made the present generation of Alco locomotives very different from what had been inherited in the 1960’s.








4 Responses

  1. good information.

  2. I think so Dual Cab in Engine should not be modified, Visibility issues can be overcome through other Techniques too.

  3. Thanks for the info!

  4. good information sharing indogerman industries is manufacturing Locomotive spare parts

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