How Diesel Locomotives Work

The Layout: Power, Fuel and Batteries

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Mouse over the part labels to see where each is located on the diesel engine.


Head-end Power Unit

The head-end power unit consists of another big diesel engine, this time a four-stroke, twin-turbocharged Caterpillar V-12. The engine itself is more powerful than the engine in almost any semi-truck. It drives a generator that provides 480-volt, 3-phase AC power for the rest of the train. This engine and generator provide over 560 kW of electrical power to the rest of the train, to be used by the electric air conditioners, lights and kitchen facilities. By using a completely separate engine and generator for these systems, the train can keep the passengers comfortable even if the main engine fails. It also decreases the load on the main engine.

Fuel Tank

This huge tank in the underbelly of the locomotive holds 2,200 gallons (8,328 L) of diesel fuel. The fuel tank is compartmentalized, so if any compartment is damaged or starts to leak, pumps can remove the fuel from that compartment.


The locomotive operates on a nominal 64-volt electrical system. The locomotive has eight 8-volt batteries, each weighing over 300 pounds (136 kg). These batteries provide the power needed to start the engine (it has a huge starter motor), as well as to run the electronics in the locomotive. Once the main engine is running, an alternator supplies power to the electronics and the batteries.

Let's take a more detailed look at some of the main systems on the locomotive.