You don’t necessarily have to pull the gasses back through char. Tar and smoke are very combustible, just not clean enough to combust in an internal combustion engine (for very long). Remember tar is essentially a hydrocarbon, and smoke is just visable carbon particles. Both of which will burn just fine outright. What causes the secondary burn is the sheer heat of the product gas. The product gas(smoke/ tar) is very very very hot. Hot enough to combust if you just combine it with the right amount of oxygen. That’s why we get the cutting torch effect with air leaks in the gasifier system where HOT product gas and fresh (oxygen containing) air mix.
That’s an interesting Idea you’ve got though. Basically that should work. I think the hotter you can get the secondary air the more likely it will allow this secondary burn to take place. Still toying with where I will put my secondary air inlet on my 2 drum style wood stove.
I have a perforated grate under which primary combustion air is introduced. After the burn is going good and hot (lots of wood off gassing) Then open the secondary air located farther up (exactly where to be determined) and get the secondary burn going.
Wayne Keith has talked somewhere about how on a badly designed (or improperly dampened) wood stove you can almost light off the flue gases.