First introduced in the 1930s, diesel locomotives are the standard form of motive power for railroads worldwide. Indeed, the diesel locomotive was the ultimate “steam killer” (but they lacked the appeal of steam locomotives). Almost every railroad, from the large Class 1s to the tiny heritage railroads, has at least one diesel locomotive.
Despite how widespread they are, the inner workings of a diesel locomotive remain a mystery to most of us. In this article, we are going discuss the main parts of a diesel-electric locomotive (the most common type) and how they connect to the rest of the motive process. Afterward, we will discuss some of the cab controls and the brakes. Ready to power up? Let’s light the fires.
- The Diesel Engine
- The Alternator or Generator
- The Traction Motors
- The Cab Controls and Brakes
The Diesel Engine
The primary source of power for the diesel locomotive is the diesel engine. Invented by Rudolf Diesel, the diesel engine is an internal combustion engine that uses compression to ignite the fuel and air mixture, which in turn spins a crankshaft using pistons. One of the advantages of a diesel engine over a steam engine is that a lot less heat is wasted, particularly on slower-speed diesel engines, which are used in locomotives.
Diesel engines can use either two-stroke or four-stroke combustion cycles. The primary difference between the two cycles is that in a two-stroke engine, the cycle of the piston is completed in two movements (or “strokes”), one up and one down, whereas the movement in a four-stroke engine takes movements of the piston (one up, one down, one up, one down). Most older diesel locomotives use two-stroke, whereas many modern diesel locomotives use four-stroke engines.
The diesel engine is what provides power to the main alternator or generator, which is what in turn drives the traction motors which propel the locomotive. Without the diesel engine, the locomotive would need to receive power from an external power source, which is how electric locomotives operate. The diesel engine allows each locomotive to be a self-propelling unit.
The Main Alternator or Generator
Next in the power cycle is the main alternator or generator. The locomotive will be equipped with one or the other depending on whether the traction motors use DC or AC power. A generator will be used for DC, and an alternator will be used for AC power.
A DC generator works by converting the motion-based power of the diesel engine’s crankshaft into electrical current, which is then supplied directly to the traction motors that turn the wheels. In the case of an alternator, the electrical current is produced by converting the mechanical energy of the diesel engine into alternating current. This current is in turn provided to the traction motors, which we will discuss next.
The Traction Motors
As stated before, the traction motors are what propel the locomotive. The motors are connected to the axles on which the wheels are mounted. The traction motors work by using either the DC or AC power provided to them by the alternator or generator to turn gears which turn the axles, allowing the locomotive to move.
In early model diesel locomotives, the traction motors were DC-powered and were often connected to multiple wheels using connecting rods very similar to steam locomotives. In modern designs, however, the traction motors are AC-powered, and instead of driving the wheels, drive the axles instead. This allows for more direct control over the wheels and eliminates the need for connecting rods.
The Cab Controls and Brakes
The locomotive engineer has several controls available in the cab, all of which facilitate the safe operation of the locomotive. Those cab controls include the reverser, which allows the engineer to shift the locomotive into forward, neutral, or reverse. The reverser handle is removable, thereby preventing any unauthorized person from operating the locomotive.
The throttle controls the locomotive’s speed. The throttle is notched, from levels 1 to 8 (1 is slowest, 8 is fastest), allowing the engineer to leave the throttle in position without needing to adjust it frequently. This is in stark contrast to the throttle on a steam locomotive, which does not notch in place and must be frequently adjusted.
The braking system on the locomotive is also controlled directly from the cab. The brakes include the independent air brake system, which is for the locomotive exclusively, and the train brake system, which affects the entire train. Modern diesel locomotives use dynamic braking, which is the principle of using a traction motor as a generator to slow the locomotive down. Dynamic braking is used primarily on the locomotive, and the train brake system uses air brakes.
With air brakes, the air is generated by the locomotive’s air compressor and is sent to the railcars through an air hose line connecting the cars. When the air is applied, the brakes release, and when the air is removed, the brakes apply. To stop the train in an emergency, the engineer can “dump” the train, which means that all the air in the braking system is allowed to escape, stopping the train.
Conclusion
I hope that this article has provided you with a general overview of how a diesel-electric locomotive works. My upcoming courses will go into more detail about how these locomotives run, and how to operate them. Please subscribe if you wish to be contacted when those courses are launched. They will be as informative as possible. Happy railroading, my friends.
As always, thanks for reading!