Fireless locomotive

Locomotive powered by a reservoir of superheated steam or compressed air.

A fireless locomotive is a type of locomotive which uses reciprocating engines powered from a reservoir of compressed air or steam, which is filled at intervals from an external source. They offer advantages over conventional steam locomotives of lower cost per unit, cleanliness, and decreased risk from fire or boiler explosion; these are counterbalanced by the need for a source to refill the locomotive, and by the limited range afforded by the reservoir.

This keyword could refer to multiple things. Here are some suggestions: