I learned a while back, way back when I painted models that you don't paint acrylic over enamel, it cracks up. The enamel dries slower than the acrylic on top and you can see the color underneath.
So, I used that same technique here in the center, Yellow is underneath the flat black and it is started to crack and pull away, it looks like an ember, and the fire is being expelled all around. It did come out quite nice.
I took it to work today and got the wow's and Ooooooh's.
Came out better than I ever thought it would.
Merlin