Ace's are regular fire and they burn like that. He can turn into red and orange flames and generate huge quantities of fire pretty much endlessly or until he gets tired.

Mine are similar, but still very different.

In my world there are three types of devil fruits. Logia, Paramecia, and zoan. Logia are like Ace or the admirals and can turn into an element. Fire, sand, magma, light, things like that. Paramecia are like Luffy or my father and sort of encompass a lot of different abilities. Earthquakes, rubber, whatever. Zoans have an additional animal species they turn into. I'm not a logia, but Ace is.