The NRE 3GS21B is a low-emissions diesel

Diesel locomotive

A diesel locomotive is a type of railroad locomotive in which the prime mover is a diesel engine, a reciprocating engine operating on the Diesel cycle as invented by Dr. Rudolf Diesel...

 road switcher

Road switcher

A road switcher is a type of railroad locomotive used for delivering or picking up cars outside of a railroad yard. Since the road switcher must work some distance away from a yard, it needs to be able to operate at road speeds, it must also have high-visibility while it is switching, and it must...

 locomotive

Locomotive

A locomotive is a railway vehicle that provides the motive power for a train. The word originates from the Latin loco – "from a place", ablative of locus, "place" + Medieval Latin motivus, "causing motion", and is a shortened form of the term locomotive engine, first used in the early 19th...

 built by National Railway Equipment

National Railway Equipment Company

National Railway Equipment Company is a railroad equipment rebuilding and leasing company, headquartered in Mt. Vernon, Illinois. NREC sells rebuilt locomotives to railroad companies worldwide, with an emphasis on the North American market....

. It is powered by three Cummins

Cummins

Cummins Inc. is a Fortune 500 corporation that designs, manufactures, distributes and services engines and related technologies, including fuel systems, controls, air handling, filtration, emission control and electrical power generation systems...

 QSK19C I6 engines with each one developing 700 hp and creating a total power output of 2100 hp. At least 16 3GS21C genset locomotives have been produced to date at NREC's Mount Vernon

Mount Vernon, Illinois

Mount Vernon is a city located near the center of Jefferson County, Illinois, in the United States. In the 2010 census, the city's reported population was 15,277 people....

 shops in Southern Illinois.

Flexibility

Because the engines are modular, flexibility is obtained:

• If one engine fails, the others can keep on going at reduced power.
• If a lower axle load is needed, one engine can be left off.
• When reduced power is needed, one or more of the engines can be turned off, saving fuel and wear and tear.
• The QSK19C engine is common to the four variants of the NRE 3GS21C engine.
• The QSK19C engines from Cummins
  Cummins
  Cummins Inc. is a Fortune 500 corporation that designs, manufactures, distributes and services engines and related technologies, including fuel systems, controls, air handling, filtration, emission control and electrical power generation systems...
  
  is widely used for non-railway applications, and spare parts are readily available.