There was a program on Monday nights Channel 4 that had experts recreating machines ( cathedral cranes, balista, GREEK FIRE) and they used pictures from history to recreate the machines that produced greek fire, and they said that it was actually used on ships. It basically consisted of a boiler type vessell with a fire underneath (heating the oil) then a vacuum type system with a two man pump (similar to a seesaw) this pumped the oil type substance through to the pipe which jetted it out across a lit flame which ignited the oil. historuical pictures and accounts said that the flame burst out from a lions head.