Congrats go to Tillerman again. I know, I know… I sound like a broken record with all his wins, but he loves these quizzes and he’s tenacious.
Yes, it’s a 1938 Heisler Fireless locomotive, which is now on display at the Baltimore and Ohio Railroad Museum in Baltimore, Maryland. Basically it’s a giant thermos that’s charged with superheated water, which it then uses for several hours until the temperature and/or pressure drops too low, then it returns for another charge. According to online sources, these particular locomotives had a specific purpose:
A fireless locomotive is a type of locomotive designed for use under conditions restricted by either the presence of flammable material (such as in mines and chemical factories) or the need for cleanliness (such as at a food factory). Thus a traditional steam locomotive is ruled out because of its open fire and the possibility of hot embers ejected from its chimney.
There are two types of fireless locomotive – fireless steam locomotives and compressed air locomotives. Diesel and battery electric locomotives fitted with equal protection are described as Flame-proof. — Wikipedia
This specific locomotive was used by Pepco at two local coal-fired electrical plants in the Washington, DC area — the Buzzard Point Power Station in DC proper and the Potomac River Power Station in Alexandria, Virginia.