One of the improved portable cooking stoves is the Rocket Stove developed by Aprovecho11. The special advantage of transportable stoves over other “improved cooking stoves” is that they can be ignited outside the house (the short period when smoke is produced) and brought inside to use. Most of the mud-based improved cooking stoves are in fixed position (in the kitchen) and still produce smoke when lighted. When the stove is burned out, the transportable stove can be taken outside the house for cleaning.
The small transportable stoves required small pieces of wood (an disadvantage for the person who needs to chop the wood), having a cross section of about 1-1½" and not longer than one foot. These small wood sections burn much better than thick wood. The person tending the fire is required to constantly feed the burner to maintain adequate heat during the entire cooking process.
The shield around the cooking pot traps a substantial amount of heat from the flames and the hot gasses escaping upwards along the outside of the cooking vessel. This shield design is highly effective in windy areas and should be made applicable for all outside stoves in high altitudes. The FoST stove has a loose shield that is more than often not used.
The special advantage of the charcoal briquette stove is that inside the house the smoke emission is minimal12 and comfort is maximal, as compared to the woodstove, because the cook does not have to tend the fire all the time.
11 Aprovecho, with Dr. Larry Winiarsky has realised the Rocket Stove. This is a stove with an elbow-shaped fire chamber from which the burning chamber is insulated and includes a skirt around the cooking pot. The better the insulation of the burning chamber and the skirt around the pot, the more fuel efficient is the stove. This model has been adopted by Foundation for Sustainable Technologies (FoST) in Nepal.
12 Most of the smoke which the biomass produces has been already expelled during the manufacturing process. This means that the overall production is not smokeless. However, burning the charcoal produces a minimal amount of smoke.
Research can be made for the development of a Rocket-type stove in which charcoal briquettes can also be used. The following adjustments are suggested:
• An elbow or Rocket-type stove with a vertical component of 5" diameter and with an internal height of two briquettes or minimal 7" (13 cm round x 18 cm high). The two briquettes will provide a fire of longer duration, whereas the firewood opening allows the fire to be supplemented for some time without the need for a complete new briquette lasting for an hour. A grip-tool needs to be supplied to place one briquette exactly over the other.
• The air intake of the firewood opening simple to must regulate. This is not the case with the current FoST stove.
• The shield is to be fixed to the stove body and should be adjustable, according to the height of the cooking pot. In the skirt an opening must be available for a pot with a long handle.
• To assure a good fit between the cooking pot and the shield, an accompanying cooking pot, which is only ¾" (2 cm) smaller than the shield and having a lid, can be supplied along with the stove for optimum efficiency.
• The stove needs to have a long carrying handle, like the Tibetan briquette stoves. This way the entire stove with cooking pot can easily be carried around and placed in another location.
• The inner chamber should be lightweight to minimise heat loss. Because a thin sheet metal chamber will burn through fast, the FoST stove has a rather thick plate. An alternative would be a thin stainless steel inner chamber, which better resists the fire and looks very neat.
• The space between the stainless steel inner chamber and the outer chamber functions like an insulator and can be about one-inch thick, giving the stove an overall width of 7".
• The new model should have interlocking components and can be changed, if necessary. Welding should be minimal and damaged components should be replaceable without the need for replacing entire stove.
• Because the main feature of the stove would be that it is movable around the house, the new two-briquette elbow stove can be called a “Satellite Stove”.
In Myanmar, a biomass Paru gasifier stove has been developed13 in which biomass can be stuffed in the outside cavity wall of the stove. When the biomass gasifies, it creates a clean flame in the interior burning chamber. With the Aprovecho or Satellite Stove, a wider cavity wall can be made. In addition, the top section can be modified in such a way as to enable easy assembling/disassembling. With this construction biomass or agricultural residues can be added into the cavity space. If holes are made in the bottom of the stainless steel inner lining, the gas emitted from this biomass will burn inside the central chamber, thus adding to the heat with clean fire. Such a design can be developed as a further option.