Sometimes, a while after a piece of firewood is throw in the fire, you can hear or see what is almost like a little blowtorch coming out of it. Don’t know how else to explain what I mean. It lasts 5-10 seconds and is like a butane torch flame coming out of the wood if you can see it. I’m trying to think if it happens in a particular species of wood more that others, but don’t think so. It just happened (I only heard it) in the stove at camp with ash. My only thought is there is a little pocket of air in the wood that gets super heated and under pressure, then when the fire finally hits it escapes quickly causing the torch like flame and noise. Any ideas what really causes this? And sorry no pictures.
I recall seeing what you are referring to in my dads open fireplace years back. My theory was the same as yours.
It's just smoke gassing off and burning. There may be some water in there adding some extra propulsion.