Ian: Your input is very much appreciated and valued and I agree that there may be a potential problem with the current combustion chamber design. This whole project is being built in modules that can be changed. The combustion chamber walls will consist of four segments, like your unit. During the first part of testing, the feed tube will not be used and a removable lid will be in its place. Multiple sizes of fuel, from wood chips to split wood will be tried. If this works, then the feed tube will be constructed and installed. If it fails to perform satisfactorily as a rocket, two of these combustion chamber segments can be changed to Prof. Hill's or maybe your design.
The burn tube, riser, and inside part of the heat exchanger are pretty much by the book but could be a problem. The tests will first be without the heat exchanger, then with it in place without the water jacket, then with the water jacket. Smoke, temperature, and wood consumption observations will be recorded.
I don't expect this to reach completion for some time and have the patience to work with it. Fortunately, my old furnace still works and when this new project gets its water jacket, it will be connected to the main hot water storage tank. Will be able to play with it all winter if necessary. Any and all comments appreciated.