I just love mucking around with building clay ovens, trying different methods of making them, using unusual materials, creating different sizes and shapes.
"Dusty" is one of my test ovens, built from sawdust, clay and Portland cement and was working well but was rather weak having used a 4,2,1 mix. So I thought I might see if I could strengthen it by "Sintering" (melting together the clay particles to form pottery), which starts at around 900oC.
With dry wood I was getting around 750oC and I knew I wasn't losing much heat through the walls, for after 40 minutes the outside was only about body temperature (the sawdust was doing it's job nicely). So I tried using home made charcoal, which seemed to make no difference to the final temperature.
What about preheating the air I wondered? That should help by the fire not having to heat the incoming gases. So I tried two ways.
They both used some stainless steel flue pipe held into the entrance of the oven by a mix of moist clay and sawdust.
The first was a simple stainless steel tray underneath the final 18 inches of the flue with a wood fire in it. With this I achieved over 930oC.
The second trial was at the suggestion of the ever helpful Aranya, a contained preheater.
I used an old aluminium tube I found at a local scrap yard. About now my 700oC rated thermocouple exploded and I had to replace it with another. This peaked at 860oC, lower than the first design...
Was the original thermocouple reading faulty due to being used over it's design limit? Did the now highly coiled tube reduce the airflow to the oven and hence the amount of power it could produce? Was the air intake for the preheating fire to close to the oven air intake and causing a partial vacuum that reduced the air flow to the oven itself?
Watch this space for more experiments that will try and answer these questions and see if an ordinary clay oven powered by wood can break the 1000oC barrier and perhaps become useful for the odd bit of pottery making or aluminium casting.