Just to give a better reason: Diesel-electric locomotives were introduced because of the massive torque the electric motor can give. The same reason for which we can enjoy e-MTBs today Funny thing though is nobody managed to make regenerative braking of diesel-electric locomotives and all energy generated during braking with motors/generators is dissipated in huge resistors of the locomotive.Diesel / electric locomotives have been using this principle for many years. The reason here is, an electric motor is easier to control than the massive mechanical clutch and transmission that would be required to handle the immense load of a freight train.
Regarding the idea of the OP: I can see a viable way to generate electricity from fuel in quiet and clean way: the fuel cell. I only cannot tell how big and expensive such generator could be. (Fuel cells typically run on hydrogen and oxygen, which is ecologically sound).