This article details changes we made to the original MIDGE stove. When building a wood gasifier, care must always be taken to prevent air from entering from where it should. If air is permitted to enter from anywhere other than where it should then the gasifier will not operate properly and can even explode under certain circumstances.
When first built, the combustion chamber rested precariously on four bolts attached to the outer chamber.
The weight of the combustion chamber pushed down on the bolts and allowed a sizeable air gap to appear between the top of the combustion chamber and the top lid. This gap allowed cold air to get to the secondary air holes from the top rather than entering through the primary air holes at the bottom.
To remedy this problem the hole on cowling lid was widened by cutting small tabs around the circumference of the hole so that the hole the combustion chamber could just pass through. The tabs were then folded back onto combustion chamber to lock it in place.
The area around the tabs was then sealed with fire cement to ensure there were no air gaps, as can be seen in the following photo.
Not only did this reduce the air gap but also meant that the supporting bolts could be removed from under the combustion chamber as the cowling lid now supported the combustion chamber.
Another test firing was performed. The air throughput was much enhanced resulting in much higher temperatures being read.
In the following photo we see a burn with a stove pipe on top of the stove, which increases the air throughput.
The draught was such that red hot particles of ash were ejected from the combustion chamber. A draught control that changes the size of the primary air intake may be needed. The very bright colour of the combustion shows great heat being generated. Small jets of gas can be seen emanating at the perimeter where the secondary air holes meet the wood gas.