How soon can an internal combustion engine be built, assuming a POD of no earlier than 1000 AD? Was metallurgy of the Renaissance up to the task? Could petroleum be refined, or ethanol processed significantly before it was IOTL, and preferably before 1700? Or can we go with a gunpowder-burning engine, as was proposed by Huygens in the 17th century for Versailles? Would any of these be feasible?