Ok so what you are saying is that steel simply cant handle the head of the interior of the combustion chamber. I'm not against using other materials, I just don't have much space. Can I encase the bricks used for the j tube in steel? And are you saying that the thin sheet these guys (see video) used to encased the perlite clay in will all burn away?
Does the steel in the mini rocket cookers hold up because it doesn't reach as high of temps?
would a design like this work for some sort of a low mass heater? And what would be the durability of something like this? I want maximum portability. Can I drop it on its side? If not that's ok, just want to know what I'm working with here.