The stormy weather had calmed today and so we were presented with an opportunity to give the wood gasifier stove a test run. Plans for this can be found simply by performing a search for "midge stove". We used a 20 litre vegetable oil can picked up from a restaurant for the outer container and a 1 kilogramme coffee can for the inner combustion chamber.
The top cowling is the bottom off another 20 litre oil can. These cans are very plentiful and we hope to use another one for the construction of an aluminium foundry. The hole at the top is a little narrow and will be widened for the next firing so that is corresponds with the diameter of the combustion chamber.
The fuel used was rhododendron "pellets". Whips of willow, birch and rhododendron are coppiced on the land here and cut into 25 mm lengths and range in width from 8 to 12 mm.
For this test run, 500 g of pellets were used.
The top layer of pellets were doused with paraffin oil and on top of that was placed a piece of cotton cloth, also doused in oil. The cotton was then lit.
After 10 minutes, the flame died down and a pyrolysis layer could be seen quite clearly beneath a layer of charcoal.
By using an infra-red thermometer we noted that the sides of the combustion chamber were at almost 600 C. The pyrolysis layer was much higher and was off the scale. The outer chamber temperature was over 100 C.
There was a period when a large amount of smoke was generated. Some stirring of the fuel with a metal rod stopped this and combustion continued as before. It is believed that a "bridge" had formed and prevented air from reaching the pyrolysis zone.
The total burn time was approximately 1 hour. The remaining ash was weighed and found to be 7 g or 1.4% of the initial mass of fuel. This means that 98.6% of the fuel was combusted.
With the outer can reaching over 100 C we wonder if a water jacket could be used to gather this heat for heating a hot water cylinder. This would be in addition to a coil in the much hotter combustion chamber.
Would the removal of heat affect the combustion? Further experiments will be needed to check this.
The next firing will be carried out after the cowling hole has been widened and the outer container air holes have been widened too.
A different fuel will also be tried in a later test, namely fine wood chips from a garden shredding machine.