What does Kernel size indicate?

I have been reading an article on the auto-ignition for my thesis, and wonder about the bubble(spark) that produced in auto-ignition process.

First question is

What does this Kernel(bubble) indicates?
I understand it as just an evidence of auto-ignition during combustion process
but does it indicate more than that?? flame stability and so on?
(propagate-increase Kernel size-affect the flame to wrinkle more)

What does it mean by large or small number of Kernel show on one shot of flame image?
(just strong and weak evidence of auto-ignition?)


ps. I am going to test the turbulent, non-premixed combustion with co-flow jet burner.