Aprovecho just put out a video about the state of their research into ceramic rocket stoves. They are finding that 6 inch wide systems work better than the 4 inch systems they used to build. The 4 inch systems encourage laminar flames that licked the pot. This caused incomplete combustion and smoke. By widening the combustion chamber they get more mixing which breaks up the laminar flow and the flames end before they can touch the pot.
Paul no longer builds RMHs that are less than 6 inches. A big reason is that he can't reach his hands in a smaller system to clean it out. That constraint doesn't exist for a small cooking rocket stove. When I want to clean mine I just turn it on it's side and tap out the ashes. It's interesting that Aprovecho came to a similar solution under a different set of constraints.
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