[Wonder Warthog]

"There’s a larg enough gulf between the BTUs of diesel fuel and the BTUs of natural gas to make a significant dent in engine efficiency. With diesel, locomotives approach (and sometimes exceed) 40 percent heat efficiency; that’ll be cut a great deal (perhaps as much as half) with a switch to natural gas. Those big prime movers will now need spark plugs, too, making yet another dent in heat efficiency (more parts, more thermodynamic breakdown)."

Not necessarily. There is a dual-injection cycle in which both natgas and a SMALL amount of diesel are injected simultaneously. The diesel serves as the ignition source when compressed, igniting the natgas (thus no spark plugs), and the total efficiency is supposedly HIGHER than diesel alone.

[MCF]

Would it be practical for them to switch to a gas turbine engine to power the generators?

[Olog-hai]

So we have more complexity for not very much return. And how is this supposed higher efficiency calculated?