Glenn Herbert wrote:Good question. Ones I can recall had a metal liner/form only for the riser. All of those instances were J-tubes. I don't have specific posts at hand, aside from this one about a batch box:
"3. Chet style portal is starting to deform from heat but is functioning extremely well and certainly acts as intended
4. The riser is 1200mm 10mm wall hydraulic pipe, it has suffered spalling for 800mm of it's length, which hot spots from 100mm to 400mm particularly affected."
From my own experience, I have looked down into J-tube feeds and seen that the burn tunnel as far in as I can see is hotter than the junction of feed tube and burn tunnel, in cob-built cores which are not as well insulated as full refractory units would be.
Hi Glenn, Thanks for the info, as I suspected, it looks like the metal inserts you spoke of were just in the riser and thus do not give any indication of whether the burn tube was hotter or cooler.
As I've said before, batch boxes are "a horse of a different color"! Has anyone measured temps in their burn chamber and the heat riser? But I am talking about a J Tube.
Then you said you could "see" that the burn tunnel was hotter than the junction of the feed tube and burn tunnel. What did you see? More flame? That is what I see as well in mine but you don't see intense radiation heat from the combustion area of any fire, but the temps of that radiation are tremendous never the less! Such must be measured or observed by what they will melt or cause to glow. That is how I know that the hottest temps in my core are at that junction of feed tube and burn tube. IN an insulated system, those high temps would soon spread throughout the entire core by way of conduction and convection, but the initial hottest heat source location, I will maintain until I see evidence to the contrary is where the combustion is initiated as combustible gases meet the oxygen.
Thus this is the area on which I am concentrating my efforts to insure proper cooling
away of that radiation energy
which makes the steel glow in this area alone.
The other videos, (I've seen lots of them!) Show systems with insulated cores which can only spell disaster for anything made of steel as the material is forced to overheat on every firing! A waste oil burner will burn much hotter than a wood fired one ( I know from experience!) So one cannot expect such to stand up for long to such punishment. I am seeking to find out if a J-tube rocket can function well with a steel air-cooled core with no insulation around it. All my tests so far have indicated the only area I need to be concerned about in such a system is that at the junction of the feed and burn tubes. More info to be gathered as I fill the integral mass (around the barrel) with a rock and sand mass. Will keep you posted.