When using a reduction tube, it seems most designs use something like 1.5 times bigger diameter then the restriction.
What will happen if I use a reduction tube of same diameter as the restriction, will it get to hot or will the charbed be to small?
I want to make a grate that I can remove from above through the restriction…
I generally go much bigger than this. I generally match the largest diameter of the hearth. What will happen is your char ash will pack against the walls creating its own natural regenerating insulation. This is why my machines generally on video when new make more smoke as this insulation has not been established yet. The user will find the gas will get better as the machine is used as this insulation is built up. Eventually it will hit a threshold of thickness and the core diameter will be what it is.
The reduction process is the heart of the gasification process. You want this as big you can possibly make it with out it clogging up. This is the what makes your produced gases not the hearth. The hearth is where we oxidize the fuel and create the Tary Pryrolyisis gases. The restriction bellow this process cracks those chains (ideally to the simplest possible form before entering the reduction process) . The reduction process is basically ripping out the oxygen and recombine with the carbon in the carbon bed. This process produces CO. What is left behind is H2 plus additional CO and CH4.