Due to him being half dragon has the ability to create and store a flammable liquid in his belly so he can breathe fire, But if he wants to breathe any amount of fire, he needs to store a lot of that liquid like, a lot a lot to the point he becomes immobile because his belly gets too big.

If he needs fire fast he can down canisters of gasoline and sometimes crude oil to refill his reserves being completely immune to those chemicals that are normally toxic.