Something like this, but the lizard is optional.
How do you like your goanna?
The reason I'm interested is I've been designing a "rocket stove" for use in the DR and I want to know if I should use rim for the burner or something else. I cast my first prototype yesterday and did a small burn today. Think of a cone made out of two stacked terra cotta flower pots(an 8" diameter and a 6" diameter) cast inside of a five gallon bucket using an insulated refractory cement. Set it up on some cinder blocks over a fire and then have a burner with about a 4" opening. There's a gap between the two layers to suck air into a secondary burn chamber. The flower pots are removed after casting. The cone acts as a venturi and the masonry insulates and focuses the heat back into the hot gases. It burns with a clear flame.
I used perlite and mortar for this cast, but I'm hoping to do a higher temp blend for the next batch. After burning brush for two hours, the outside of the burn chamber was still only about 130 degrees and the high inner temp and air flow made for better burn efficiency and very little smoke. Perlite was $20 for 30 gallons(4cu ft) so it's costing about $5 per cast for stoves that weigh about 20 pounds each.
Lots of Youtubes out there on rocket stoves. Most are L shaped burn tubes using 4" PVC.