1897

Diesel Locomotive

Rudolf Diesel (1858–1913)

Imagine that you are an engineer in the 1930s and you want to create a new locomotive based on a diesel engine, first operated successfully by Rudolf Diesel in 1897. Steam engines have been operating successfully for more than a century, but a diesel engine is a completely different animal. If it is going to pull a train that is one hundred cars long, then the load could weigh thousands of tons. Pulling that up a hill requires immense power from the engine. You also want it to be as efficient as possible.

Your first instinct might be to engineer the locomotive like a diesel truck. These trucks pull heavy loads. But the problem is the transmission. Where a car needs a four- or five-speed transmission, a truck might need nine, thirteen, even eighteen gears because of the much greater load. Therefore, if we were to go from truck to locomotive and needed to add even more gears, the size and complexity of the transmission starts to get ridiculous. To eliminate the transmission, locomotives therefore start with a two-stroke diesel engine. The engine is huge, with twelve to twenty cylinders, and a supercharger improving efficiency.

This engine then connects to an electric generator or alternator rather than a transmission. If the engine is rated at 4,000 horsepower, the alternator can produce up to three megawatts. In other words, a diesel locomotive is actually a small electrical power plant. The electricity then flows into electric motors. If the locomotive has six axles, there can be six motors.

The advantages of this engineering innovation are numerous. First, the use of electric motors eliminates the need for a large, complicated transmission. Second, it is much easier to drive the six axles with six electric motors than to connect them all together with drive shafts from the transmission. Third, if one electric motor fails, the train can still function. Fourth, the engine runs at discrete speeds, improving efficiency and making it possible to gang multiple locomotives together.

When miniaturized and combined with batteries, this same kind of approach makes hybrid cars possible. Engineers developed an important efficiency breakthrough.

SEE ALSO Supercharger and Turbocharger (1885), Two-Stroke Diesel Engine (1893), Prius Hybrid Car (1997).

Santa Fe’s Super Chief diesel streamliner rounding a curve on the Los Angeles to Chicago route.