The mechanism of a 'Chariot of fire' is somewhat that of a rocket. And if you take a rocket or one of recent machines 2000 years back in time, the people of that era would only describe it with the knowledge of what they see around them. And what they cannot understand becomes supernatural. God in his sophistication, cannot be riding on chariots and horses, while we mere mortals are flying planes and jets. It was God who took Enoch and Elijah into Heaven. But I think the instrument he used was so advanced observers were able to describe it as a 'chariot of fire' which modern men can relate to UFO.