- Current Ideas: The “J” Stove Design
Description – the J stove has a shape like the letter J and is made of soil-cement bricks with a solid soil-cement base (90% soil, 10% cement). It offers four advantages: (i) it is smokeless, (ii) it allows standing up will cooking (instead of squatting over an open fire), (iii) it uses much less fuel, and (iv) its cost is very cheap (about $15 in materials). Link to video
Notes (25 March 2010)
Field Test, Lafutialau, Ambae - I took with me a small demonstration stove made of sheet metal. It could be dismantled and packed into a suitcase. The stove was demonstrated in seven villages on Ambae and Ambrym. The villagers, especially the women, were very interested once the stove began to work.
The villagers made suggestions for improvements; lengthening the chimney to be able to heat two pots at once, making the fuel chamber larger to make lighting and cleanout easier, and extending the chimney horizontally to provide a flat surface to dry shredded coconut.
The design of the soil-cement stove was modified before going on to make it out of bricks. The burn tunnel was shortened and the base was formed as one piece.
The mix of 90% local soil and 10% cement held together well, and dried to a strong brick. The same mix was used for the base of the stove.
The villagers showed much enthusiasm for the work and
actually did the mixing and stove making. The soil-cement
stove was not completely finished before I had to leave (the interisland ship that brought the materials was 3 weeks delayed and arrived 3 days before the end of my visit).
The stove works best with sticks of firewood stacked vertically in the fuel chamber. It will burn twigs, leaves, and coconut husks, but space must be left for air to flow easily through the J shape. Currently when cooking on an open fire, villagers find they use less fuel when they have very little flame and more hot embers. The J stove will produce the same or more heat using less firewood but the fire must flame in order for the air to be drawn up the chimney – the embers approach does not work.
Notes (January 2010)
I redesigned the J stove to be made from bricks made from 90% soil and 10% cement. I used soil from my backyard (it was winter and the ground was frozen but I managed to break out enough to do some test bricks). I devised a tool to hand make the bricks. The soil in Calgary appeared to be similar to the soil I had seen in Vanuatu. The bricks held together well when wet, and dried strong enough to lay with a sand-cement mortar. I tested some bricks in a fire – building a large fire around and over them – and they came out glowing, lighter in weight but did not break or crack.
I built a J stove using the bricks, with a stove top and fuel chamber cover made from sheet metal. The stove was large and I had some difficulty keeping the flame moving across and up the chimney – especially as the wood burned down to embers.
Notes (November 2009)
I redesigned the sheet metal stove with a small space at the bottom of the fuel chamber, which had an opening to the outside and a grate for ashes to fall through. The idea was to be able to light the fire from below like a rocket stove) and also to be able to clean out the ashes through the opening.
I found it difficult to seal the opening in a simple fashion. When air entered from the bottom, the flames rose upward out of the fuel chamber instead of being drawn sideways and up the chimney.
After using the stove about 8 times, I found that the sheet metal was breaking down from the intense heat and holes were beginning to appear. Another material was needed.
Notes (September 2009)
Researching stove types on the internet, I came across a design used for biomass mass heaters – the ‘J’ stove (the stove is shaped like a letter J),is a close relative of the rocket stove. The main advantage that attracted my interest was the feeding tube that allows loading enough fuel to burn for long periods. I modified the mass heater design to become a stove with a place for a pot on the top of the chimney.
I built a J stove using sheet metal and insulated it inside with ceramic fibre insulation to understand the mechanism
– would fire really burn sideways instead of upwards
through the fuel chamber? It did.
The chimney draws air so strongly that air is drawn downward through the fuel chamber and the fire is blown sideways. When it is operating well, the stove makes a rushing wind sound – hence its other name ‘Jet Stove’.
The J stove produced a lot of heat with very little fuel. I tried small twigs and leaves and they burned well as long as air was able to pass through them to feed the burning edge. It did require a flame, however. If the fuel burned down to embers, the flow of air could change direction – drawing down the chimney and up the fuel chamber.
The stove was awkward to light and required
reaching down the fuel tube to light the wood at
the entrance to the burn tunnel. And it was difficult to clean the ashes out.
Notes (August 2008)
Field Test, Lafutialau, Ambae - the stove was used to boil down a potassium hydroxide solution leached from ashes to make soap from coconut oil. It performed well and the coconut husks burned well. The husks still contained the coconut
shells – the waste byproduct of copra making.
The chief difficulty was in adjusting the lower air inflow so that the husks had enough air to burn, but the airflow was not so fast as to allow the pyrolytic gases to escape before being burned.
Villager interest remained high, especially among the women.
Notes (June 2008)
To go further with the use of coconut husks as a fuel, I changed the rocket stove design to accept the husks (generally 6”x6”x4”) from the top. Air was introduced from the bottom and sides. The stove was made of sheet metal (24G) and insulated with ceramic fibre insulation. It could accommodate two cooking pots which rested on a grill laying on top of the stove.
The burning chamber is large and retains the heat well.
Very little air enters through the lower air inlet. The gases burst into flame as they mix with the air entering through the upper air inlets.
Notes (October 2007)
Field Test - the Rocket Stove was demonstrated in Lafutialau village, northwest Ambae. There villagers showed a lot of interest in the stove. The smokeless burning was a surprise to them, as well as the stove’s ability to make strong heat with just twigs and leaves. An impromptu request to try coconut husk as a fuel led to the discovery that it too would burn without smoke. Coconut husk is a waste byproduct of the copra-making process. It is sometimes used as a fire starter, but seldom used as a main fuel because it tends to smolder and smoke in an open fire. To be able to use it as an alternate fuel to firewood in a rocket stove would significantly lessen the fuel gathering time for women.
The chief disadvantage in using the stove, compared to an open fire, was the need to constantly feed material into the combustion chamber. The small openings (5”x2”) meant the fuel had to be reduced in size before being fed into the stove.
Video of Samuel Bani and rocket stove
Notes (April 2007)
The key quality that determines whether a burning fuel will smoke is whether the fuel is fully combusted. To do this, wood and other biomass fuels need sufficient heat, and oxygen. An open fire generally provides poor heat concentration and only passable oxygen flow. To improve combustion, a technology must allow good air flow, and heat retention in the combustion area.
The Rocket Stove is one design that brings these three
elements together (fuel, heat and oxygen) in a very simple way. Providing a ‘second skin’ of sheet metal with the inter-space filled with insulation improved the heat retention in the burn area.
When biomass is burned it released pyrolytic gases. The flame that rises high above the burning match shown here, is the result of these gases being released from the wood, rising and catching fire.
Open fires burn only a portion of these gases. By
insulating the stove to retain heat in the burning chamber, and allowing sufficient oxygen to mix with these gases, they can be fully burned increasing the heat available for cooking. The proto-type stove was made from sheet metal and insulated with ceramic fibre insulation. I found that by introducing air above the point of combustion (via a tube connecting outside to inside), I was able to burn all of the pyrolytic gases produced and greatly enhance the burning. At times, the flames shot 12”-18” above the stove.