Visit: http://www.vuthisa.com or see this blog post: http://vuthisa.com/2011/08/02/charcoal-gas-stove/
Some of the Bioenergylist stove discussion list members aka Richard Stanley, Kobus Venter and John Davies got together and constructed this gasifier stove, with the flame forming outside the combustion chamber. John effectively replicated a coal gasifier, having had hands on experience with industrial processes. He can be heard talking in the background. The 'through-burner' with the flames protruding out from was a simple metal cup with perforations and was ignited externally.
John explained the process as follows, and note this can only be achieved with packed fuel bed containing red hot glowing embers: All oxygen present in the combustion chamber will react with carbon (above approximately 400 °C) to form CO2 (exothermic reaction - heat evolved). When CO2 without oxygen comes in contact with carbon at approximately 800 °C it will react and form CO (endothermic reaction- heat absorbed). If any oxygen comes into contact with the CO at high temperature it will react to form CO2 (exothermic reaction) - heat evolved. It is therefore possible to operate the stove with the 'through-burner' for an extended period of time (provided entire fuel bed is glowing red) and small amounts of primary air is allowed to be drawn up through the bed.