iirc this was just an engine that could run on most combustible hydrocarbons, a small gas turbine and some elaborate digestion setup I seem to remember, and the press really stretched a badly worded explanation of how it worked into ‘it eats corpses’. Which is fair, humans are mostly made from tasty biomass, but still.

edit: here’s a couple sources about it, it sounds like it does indeed run on vegetable biomass.