system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why are diesel locomotive engine more of diesel-electric, rather than direct drive?
gpt
Internal combustion engines operate at their maximum efficiency only within a narrow range of torque and RPMs. Electric motors on the other hand are essentially equally efficient at any operating speed and torque. When you have massive locomotive hauling a massive train and vehicle weight/size really isn’t a concern, it’s actually more fuel efficient to have the combustion engine always running in its maximally efficient zone running a generator, and then use the electricity to run traction motors to drive the wheels.

This historically wasn’t feasible to put in a small car, but now some hybrid vehicles can operate similarly. Part of a hybrids improved fuel efficiency comes from the fact that you can run the engine closer to its efficiency zone all the time, and charge up the battery some when the vehicle needs less power than the engine is providing, and vice versa when the vehicle needs more power than the engine can efficiently provide.