It's a beautiful model, Kroolo.
Fireless locomotives sometimes ran on compressed air, but fireless
steam locomotives stored steam from an external boiler.
The Wiki article describes it this way: "A fireless steam locomotive is similar to a conventional
steam locomotive, but has a reservoir, known as a
steam accumulator, instead of a
boiler. This reservoir is charged with
superheated water under pressure from a stationary boiler. The engine works like a conventional
steam engine using the high pressure steam above the water in the accumulator. As the steam is used and pressure drops, the superheated water boils, replacing the used steam. The locomotive can work like this until the pressure has dropped to a minimum useful level or the water runs out, after which it must be recharged."
https://en.wikipedia.org/wiki/Fireless_locomotive#Steam
Here's an example, with images of the locomotive and the charging mechanism:
http://www.whippanyrailwaymuseum.net...0-4-0f-no-7240 "This type of engine is essentially a giant thermos bottle lying on its side, with wheels."
The Railroad Museum of Pennsylvania at Strasburg has a big eight-wheeled fireless steam locomotive on display:
https://commons.wikimedia.org/wiki/F...D_fireless.JPG
Don