Diesel locomotives (or "diesel engines") are locomotives that are propelled by a diesel engine(s). The name itself, derives from Rudolf Diesel, who invented the diesel combustion-engine, locomotive, and fuel to power the diesel engine.
The diesel type of combustion-engine was invented by Rudolf Diesel in 1893, and was first used for early refrigerators. But after several failed experiments, he decided to use his unique engine on locomotives. With several unsuccessful attempts, Rudolf Diesel developed a successful engine for locomotives. Hence, the birth of the diesel locomotive.
Diesel locomotives first began as modified railcars, until companies like ALCO, GE and EMC (Electro-Motive Corporation; now Electro-Motive Division) began building some of the very first official diesel locomotives, which weren't modified railcars or trainsets, and were also streamlined.
Diesel locomotives are the primary locomotives used for powering trains nowadays. Many have been built, and have replaced steam locomotives as being the primary use of locomotives, but diesel locomotives still carry-on their legacy, and both forms of locomotives still (of course) exist in high numbers.
They may not have as much history as steam locomotives, but are still in the process of developing history as being the primary form of locomotive power.
The diesel-fueled internal-combustion engine in a diesel locomotive, is powered by large cylinders and pistons that create power — usually converted to electricity via an electric generator — to move the locomotive.
Turbochargers are also used to help give the locomotive more horsepower, therefore giving greater pulling power or speed depending on application. As well as having two or more engines combined to form a unique, extraordinary, and revolutionary "double diesel" 'super-powered' diesel locomotive.
Having two or more diesel locomotives facing opposite ends from one another also helps with crews move locomotives from other trains easier, and having two or more locomotives combined adds more horsepower to an actual train.
Airhoses and electrical hoses (multiple-unit cables) are used to provide 'mating', which is having two or more diesel locomotives coupled together in a consist and working together at the same rate while being controlled by the lead unit. This is also referred to as 'slaving'. (Not the type of B-unit, but rather having multiple locomotives such as an SD40-2, SD70M, and SD60 coupled together and working all at once with the lead unit being the control unit.)
Dynamic braking also helps diesel locomotives come to a complete stop quicker and easier.
Modern North American diesel locomotives didn't have air conditioners or radios until around the 1970's.
Although in the 1990's microprocessors (computer-chips) made it possible to apply alternating current traction-motors; the majority of diesel locomotives that have been produced for the US and North American locomotive markets, are direct current powered.
There are three main types of diesel locomotive: diesel-mechanical, diesel-hydraulic and diesel-electric. The most basic form of diesel locomotive is the diesel-mechanical variant, and the most complicated is the diesel-electric.
Both diesel-mechanical and diesel-hydraulic locomotives are best suited to shorter distances. Such as shunting or moving between a port and rail-yard within a city. Diesel-electric locomotives have, for a long time, run long-distance hauling due to their better fuel economy and generally higher horsepower rating.
There are three types of final-drive mechanisms:
- In the direct-drive type the engine is connected to the wheels via drive-shafts, differentials and powered-axles on diesel-mechanical and -hydraulic types. This system becomes very complicated when dealing with multiple powered-axles. Diesel-electrics have a traction-motor driving each powered axle in this configuration.
- The coupling-rod drive type is usually only used on rigid locomotives that have no pivoting trucks (bogies). The engine is connected to a drive-shaft, a differential and a powered-axle on diesel-mechanical and -hydraulic types. To maintain efficient adhesion coupling-rods are attached to the ends (outer-side of the wheels) of all the powered axles; the powered axle pushes the rest around. Diesel-electrics have a direct-drive traction-motor placed on one, or at least a minority of, axle(s). The other axles are driven by coupling-rods like the mechanical and hydraulic types.
- With the geared type, usually diesel-electric, the "powered" axles are in pairs and have gears on them. The gears' cogs (teeth) interlock with cogs of another gear placed between, and slightly above, the two "powered" axles. The third gear is usually connected to a traction-motor.
Diesel-mechanical locomotives have a heavy-duty gearbox, much like that of a truck or a ship, through this, drive-shafts, differentials and powered-axles the engine drives the wheels. Direct-drive and coupling-rods are the normal final-drive systems for transferring power.
Diesel-hydraulic locomotives are much the same as their diesel-mechanical cousins, but they have a torque-converter instead of a gearbox. The converter has a viscous (thick) fluid inside that transfers the power based on how much speed, or how much power, the engine is producing. Direct-drive is the normal final-drive system for transferring power.
Diesel-electric locomotives use a diesel engine(s) to power an electric-generator, which produces direct current (DC) electricity for the axle mounted traction-motors. These are called DC-traction diesel locomotives. Some modern diesel-electric locomotives use microprocessors (computer-chips) to allow the use of alternating current (AC) electricity to be produced, by similar means, for AC traction-motors. They often give more horsepower, and are called AC-traction diesel locomotives. Direct-drive, coupling-rods and gears have all been used on diesel-electrics, though direct- and geared-drive are the most common final-drives.
- "Engine" often refers to an actual locomotive itself, particularly diesel and steam locomotives. Yet, this should not be confused with the actual "engine" officially referring to the combustion-engine that powers it.
- "Traction-motor" is a term used to describe an electric motor used to propel a locomotive.
- The largest and most-powerful diesel locomotive ever built, is the Union Pacific EMD DDA40X.
- The smallest diesel locomotive ever built (in perspective), would be Talyllyn Railway's Midlander.
- The fastest diesel locomotive ever built is the BR Class 43, which beat the records of the Union Pacific M-10000 and Burlington Route's Zeyphr.
- A number of AC-traction diesel locomotives exist on US and North American railroads.
- "Prime-mover" is a term used by most railfans, employees, and train enthusiasts referring to the motor/engine starter or generator that powers the actual engine for diesel-electric locomotives as well as the actual locomotives themselves.
- Because of how early types of North American diesel locomotives were originally built as "road switchers" (switching or shunting engines meant for yard service in and outside of a railyard) and didn't become as popular as steam locomotives until after World War 2 (though further ending and dominating over such during the "Post War" era; which marked the "End of the Steam Era"), the name "road switcher" is a designation now used for average types of diesel locomotives which stuck as a result of what they originally served for: "road switchers"; basically serving as a nickname to how they evolved.