I have created a better video of the MIDGE stove in operation. I'm no Orson Welles but I do come in on budget.
The stove is a particular type of gasifier known as an 'inverted downdraught gasifier'. Essentially, that makes it an upside-down downdraught gasifier. The difference being that the wood gas is immediately burnt in the inverted gasifier but in the normal configuration it is tapped off for running an internal combustion engine.
The inverted downdraught gasifier in its most basic form consists of one can suspended inside another. The outer can acts as a cowling permitting air to enter its primary air holes where it can pass into the inner can. The inner can has holes at the bottom, in the form a grating which aids combustion of the fuel, and a ring of secondary air holes at the top which create an air/fuel mixture with the wood gas.
Fuel consists of wood chips. This permits easy fuel collection from broken tree boughs and the sort of waste that owners of log burning fires reject. The chips are packed down into inner combustion can and a small amount of some flammable liquid (spirit or paraffin) is dripped on top so as to get the fuel to sustain a hot flame long enough for char formation.
A fire is lit on top of the fuel, which results in a char layer forming. Beneath this layer is the pyrolysis layer where wood is converted into hot wood gas. Combustion continues down through the wood chips, converting the chips into charcoal which is then reduced to wood gas. The wood gas rises up, meets hot air at the secondary air holes and ignites.
You can think of a MIDGE stove as a device for making charcoal, which is then reduced to various volatile gases and a small amount of ash. The operation is very efficient, is virtually smokeless and yields little ash.
YouTube - Wood Gas Stove