> ICE engines were miniature engines that also ran off of a fuel source (eventually settling upon oil, but many different fuel sources were considered

Fun fact - Rudolf Diesel's first engines were running on cooking oil. In fact, many diesel engines can operate on vegetable oils without modifications (not long term though). That sounds odd, but from the perspective of "burn hydrocarbons to generate heat", petrol, diesel, oil, body fat, coal or kerosene are all very similar to each other.