imagine its 1946 and for whatever macguffin’ the war is still on/the mustache man hasn’t ventilated his own skull yet, and you’re a B-17 ball gunner over Germany and last thing you see some gunless pacifist, aka ‘The Desperation Dorito’, flying right through your ass.
You actually can run just about anything that takes gas or vapour fuel on coal/charcoal, by burning a bit of it in very air-poor conditions so it forms carbon monoxide. Carbon monoxide is flammable.
The problem being that since the coal is half burned by the time it’s actually in the ramjet, it doesn’t have great energy density. For a car or generator that’s fine, but for powered flight…