Revi wrote:I agree that a hybrid electric engine seems to be the best way to move a train. We went on a run from Brunswick, Maine to Rockland a couple of week..
Keep in mind that a "hybrid electric engine" is not at all like a hybrid car, and should more correctly be called a "diesel-electric" engine, since power transmitted to the axles is not
a combination of chemical and electrical power, as it is with hybrid cars.
From a workshop I took when I was a consultant to PTT Switzerland (who run the trains there), my understanding is that the diesel-electric engine design is primarily because electric speed control at high power is easier to achieve than mechanical speed control.
The diesel runs continuously at optimum RPM, driving a generator, which then goes to a switch box that controls speed by a combination of putting huge resistors into the circuit between the generator and the trucks, and switching the trucks into different winding and series/parallel configurations. (The large, flat, finned boxes with fans on the tops of locomotives are the resistor packs.)
When decelerating, the trucks do use regeneration for dynamic braking, but send their energy into the resistor packs to be dissipated, rather than into a battery.
Except when operating at full speed, this design is not particularly efficient -- at half-speed, for example, fully half the power could be dissipated in the resistor packs -- but it is cheaper to manufacture than building an automatic transmission capable of handling the peak torque of a 2,000 horsepower diesel engine. And diesels travel at full speed most of the time, anyway. (It's much more complicated than this simplistic example. You could travel at half or quarter speed at full efficiency by switching the trucks into different series/parallel combinations, but my point is that some dissipation of energy via resistor packs happens from time to time.)
Switzerland has a nation-wide electric rail system, so their trains are almost completely electric-only. They do
save energy with regenerative braking, by boosting the EMF in the field winding to the point that the energy from braking is fed back into the track. But without huge, expensive, heavy batteries
diesel-electric trains cannot possibly store braking energy without a mechanical "battery" using a flywheel. I'm not aware of any that do such a thing.