Yes, diesel engines are some of the most efficient internal combustion engines, the best of them are slightly better than 50% efficient from tank to crank. And

Yes, diesel engines are some of the most efficient internal combustion engines, the best of them are slightly better than 50% efficient from tank to crank. And then diesel-electrics have more losses converting that to electricity, and then more losses again to convert back to rotational power. It is more efficient to generate electricity at a power plant and electrify the tracks, because power plants can far exceed 50% efficiency. Also they can run on something less dirty.