The ignition of diesel fuel pushes pistons connected to an electric generator. The resulting electricity powers motors connected to the wheels of the locomotive. A “diesel” internal combustion engine uses the heat generated from the compression of air during the upward cycles of the stroke to ignite the fuel.

Train engines primarily get power through one of two systems: Diesel-Electric or Electric. In a diesel-electric locomotive, a large diesel engine acts as a "prime mover" that turns an internal alternator to generate electricity. This electricity is then sent to traction motors located on the axles, which turn the wheels; the diesel engine never actually "drives" the wheels directly. Purely electric trains, common in Europe and the Northeast US, draw power from external sources via overhead catenary wires or a "third rail" on the ground. This electricity is collected by a pantograph or contact shoe and fed into the train's motors. In 2026, we are also seeing the rise of Battery-Electric and Hydrogen Fuel Cell trains for shorter routes, which store energy on board to eliminate the need for expensive infrastructure. Regardless of the fuel source, the final stage of power is almost always an electric motor, as they provide the high torque necessary to move thousands of tons from a standstill.