Prime mover (locomotive) in the context of "Powertrain"

A diesel locomotive is a type of railway locomotive in which the power source is a diesel engine. Several types of diesel locomotives have been developed, differing mainly in the means by which mechanical power is conveyed to the driving wheels. The most common are diesel–electric locomotives and diesel–hydraulic.

Early internal combustion locomotives and railcars used kerosene and gasoline as their fuel. Rudolf Diesel patented his first compression-ignition engine in 1898, and steady improvements to the design of diesel engines reduced their physical size and improved their power-to-weight ratios to a point where one could be mounted in a locomotive. Internal combustion engines only operate efficiently within a limited power band, and while low-power gasoline engines could be coupled to mechanical transmissions, the more powerful diesel engines required the development of new forms of transmission. This is because clutches would need to be very large at these power levels and would not fit in a standard 2.5 m (8 ft 2 in)-wide locomotive frame, or would wear too quickly to be useful.

An electric locomotive is a locomotive powered by electricity from overhead lines, a third rail or on-board energy storage such as a battery or a supercapacitor. Locomotives with on-board fuelled prime movers, such as diesel engines or gas turbines, are classed as diesel–electric or gas turbine–electric and not as electric locomotives, because the electric generator/motor combination serves only as a power transmission system.

Electric locomotives benefit from the high efficiency of electric motors, often above 90% (not including the inefficiency of generating the electricity). Additional efficiency can be gained from regenerative braking, which allows kinetic energy to be recovered during braking to put power back on the line. Newer electric locomotives use AC motor-inverter drive systems that provide for regenerative braking. Electric locomotives are quiet compared to diesel locomotives since there is no engine and exhaust noise and less mechanical noise. The lack of reciprocating parts means electric locomotives are easier on the track, reducing track maintenance. Power plant capacity is far greater than any individual locomotive uses, so electric locomotives can have a higher power output than diesel locomotives and they can produce even higher short-term surge power for fast acceleration. Electric locomotives are ideal for commuter rail service with frequent stops. Electric locomotives are used on freight routes with consistently high traffic volumes, or in areas with advanced rail networks. Power plants, even if they burn fossil fuels, are far cleaner than mobile sources such as locomotive engines. The power can also come from low-carbon or renewable sources, including geothermal power, hydroelectric power, biomass, solar power, nuclear power and wind turbines. Electric locomotives usually cost 20% less than diesel locomotives, their maintenance costs are 25–35% lower, and cost up to 50% less to run.

An engine–generator is the combination of an electrical generator and an engine (prime mover) mounted together to form a single piece of equipment. This combination is also called an engine–generator set or a gen-set. In many contexts, the engine is taken for granted and the combined unit is simply called a generator. An engine–generator may be a fixed installation, part of a vehicle, or made small enough to be portable.

In a motor vehicle, the powertrain comprises the main components that generate power and deliver that power to the road surface, water, or air. This includes the engine, transmission, drive shafts, differentials, and the final drive (drive wheels, continuous track as in military tanks or caterpillar tractors, propeller, etc.). Hybrid powertrains also include one or more electric traction motors that operate to drive the vehicle wheels. All-electric vehicles ("electric cars") eliminate the engine altogether, relying solely on electric motors for propulsion. Occasionally the term powerplant is casually used to refer to the engine or, less often, the entire powertrain.

A motor vehicle's driveline or drivetrain consists of the parts of the powertrain excluding the engine. It is the portion of a vehicle, after the prime mover, that changes depending on whether a vehicle is front-wheel, rear-wheel, or four-wheel drive, or less-common six-wheel or eight-wheel drive.