Diesel-Electric Locomotive Engines & How They Work

This article describes the locomotive engine, Diesel-Electric and discusses the history and features of these locomotives in North America.

By Pat Lawless

The Diesel Electric Locomotive is the dominant type of locomotive in the world today. But what does the term "Diesel-Electric" really mean? There have been five major types of locomotives used in the history of railroads; The Steam Locomotive, The Electric Locomotive, The Diesel (or gas) Torque-Converter Locomotive, The Turbine Electric Locomotive, and finally, the Diesel Electric. A steam locomotive burns coal or oil, converting water into steam, and then uses the steam to drive pistons, which are connected by drive rods to the wheels. A straight electric locomotive, on the other hand, uses electricity provided by an overhead wire or "3rd rail" next to the tracks, to power electric motors (known as "traction motors") that are geared directly to its wheels. Straight electric locomotives are usually very powerful, fast, and long-lived machines (The Pennsylvania RR's famous GG1 is a classic example of a straight electric). Our third type, the diesel or gas torque-converter locomotive uses some kind of internal combustion engine which is geared directly to the drive wheels using a "torque converter", more commonly known as a "clutch". The disadvantages of this arrangement are many, as burning out a clutch 200 miles from your maintenance base would present obvious problems. The fourth type listed, the turbine-electric, is also one of the rarest types. The basic idea was to burn some kind of fuel to produce either steam or hot combustion gases, which were then passed through a turbine, which would spin at high speed. The turbine would drive an electric generator, which would provide electricity to traction motors on the wheels of the locomotive. Some turbines burned coal, others burned oil, and most were experimental in nature. The Union Pacific Railroad had a whole series of turbine-electrics that burned bunker C fuel. The last of their series were the most powerful locomotives ever built, at 10,000 h.p. each. Although successful, they had high maintenance costs, and used almost as much fuel at idle as they did at full throttle.

Finally we come the subject of this article, the diesel-electric locomotive. As you can probably guess by now, the diesel-electric uses a diesel engine to drive an electric generator, which then supplies the current to traction motors, which are geared directly to the locomotive's wheels. One of the main advantages of this arrangement is that, since the engine is not directly attached to the wheels, starting a heavy train cannot "stall" the engine, as in the case of the torque-converter locomotive. The motors simply heat up until they start the train moving, at which point the current level drops. Another advantage is that, unlike the straight electric locomotive, expensive and hard to maintain overhead wires (called "catenary") or third rails are not necessary. This is less of a factor in Europe, where distances are smaller, but since some North American railroads have tens of thousands of miles of track, it's a major consideration. And compared to a steam locomotive, Diesels require very little maintenance, and can be started up and shut down instantly. Steam locomotives would take hours to build up a head of steam, and required frequent boiler rebuilds and costly maintenance by skilled shop forces.

Diesel-electrics came into prominence in North America after the Second World War, when railroads, anxious to replace their war-worn fleets of locomotives, started looking carefully at the economics involved. Diesels, although of lower horsepower than modern steam engines, could be combined into multiple sets at will, all run by one crew. Thus a group of three or four engines could be combined to run a large freight, and then broken up to run a number of local trains with one engine each. This offered more flexibility than steam, which required one complete crew for each engine, making running multiple engines very expensive. The much lower maintenance costs of diesels were also a deciding factor in railroads switching over to them. A much smaller list of skills was required to maintain diesels than were required to maintain steam engines. This meant lower employment numbers, and big savings in salaries.



Diesel-electrics started out in the 600-hp range, and the early ones were primarily switchers. The earliest examples were built in the late 1920's, and really didn't start to catch on until the late 1930's when railroads turned to diesel switchers to solve their problems with smoke in railroad yards located in major cities. At this time many cities had started fining the railroads for excessive smoke production. All the smoke from steam engines really made life difficult for inner city dwellers and workers. After they had run the diesel switchers for a while, they started to notice the economics of these engines, but before they could experiment with them further, WWII broke out, and all further experimentation ceased. In the U.S., Diesel manufacturers were ordered by the war production board to produce whatever products that they had already developed, which meant that some companies which had successful diesel switchers were stuck producing only switchers for the whole war. Others, which had concentrated on diesel road locomotives, enjoyed a head start on their competition, as they had the whole war to further refine their products.

After the war, the diesel-electric really took off. In the U.S. and Canada, General Motors rapidly became the dominant diesel locomotive builder, eventually putting most of its competition out of business. It's landmark FT locomotive was embraced wholeheartedly by North American railroads, and by the end of the 1950's steam was all but dead. Railroads, once they decided to switch to diesel-electric, bought virtually anything that was available, including some fairly poorly designed products. Diesels by GM, Fairbanks Morse, American Locomotive Company, Lima, and General Electric were all over the continent. Eventually, all but GM and GE were eliminated from the market in the U.S. and Canada.

Today's diesel-electrics are impressive machines indeed. From the early days where a diesel road locomotive would be 1500-1700 h.p., we now see single diesels which have 6000 h.p. Modern diesels are high tech wonders, employing such features as ground radar to determine speed, feeding this information to computers that prevent the locomotive's wheels from slipping under heavy loads. Other diesels are equipped to control additional "mid-train" helper locomotives by means of radio control, allowing one crew to run as many as three separate sets of locomotives at the same time. Nowadays, General Electric in Erie, PA is the number one locomotive builder in North America, followed by General Motors Diesel Division in London, Ontario. Both builders have seen a boom in recent years, as railroads have expanded their markets for bulk commodities, truck trailers, and shipping containers. So it looks like the diesel-electric locomotive is here to stay! Go down to the tracks and check some out the next time you have the chance.

© High Speed Ventures 2011