Several testings were executed in Aprovecho (research lab in Eugene, OR) using briquettes made of sawdust and paper (app. 70%sawdust, 30% paper). Primary goal was to test different stoves and see where briquettes perform best; overall 6 different stoves were tested, but 3 basic forms distinguished: 3-stone fire (open fire), top-feed burning (like they’re usually burnt using stoves) and side-fed briquette with the new ‘Rocket’ prototype.
With Portable Emission Measuring Sytstem (PEMS), it was possible to read the levels of CO2, Carbon Monoxide (CO) and Smoke/Particulate Matter (PM) on the computer screen during the testing process and examine specific patterns of burning. CO was very important since represents one of the most dangerous emissions and cannot be tested without lab equipment.
With all stoves 1 liter of water was boiled as soon as possible and simmered as long as possible using app. 3 briquettes (3x100g-130g). Here are some general patterns that were recognized after 30 briquettes were burned in different settings:
Whats recognizable for all stoves?
1. In the phase of the burn when briquettes are loosing power (when there is no more fresh material left in the briquette) the CO levels get higher making a dangerous burn, especially with open fires. When we stop with cooking, its much better to intentionally stop the fire or close the stove door to limit the excess air than leaving the fire unattended! We can use the remaining ashes and unburned briquette material as a great fertilizer – biochar.
2. With all stoves we were able to boil one liter of water in 10-11 minutes in just few tests. That proves all forms of burning the briquette are powerful enough.
3. The best time (for less CO emissions) is to insert a new briquette when the previous one in burning throughout its mass (no fresh mass left; this can be seen by the porous texture)
1. Briquettes burn fast and powerful (through their own holes) and when they get on fire, there is not a lot of smoke any more, but CO level is always high – the gas doesn’t burn out without the extra combustion chamber.
2. Bigger holed briquettes (2 inch hole) burned much faster, while the small holed briquette (1 inch hole) lasts for long, with a steadier fire. if people would like faster burning briquettes with 3-stones or if a slow burning material is being used (like the water hyacinth for example), it might be suggested to try to enlarge the hole.
3. 3 briquettes were used just to boil the water, then the power went down. Comparing to other stoves, it makes it a fast, but very fuel-consuming ‘stove’.
1. When we insert a new (cold) briquette on the fire from top, the CO level rises very quickly, also smoke if we have no combustion chamber (Jiko stove). It also makes it impossible to control.
2. We don’t have the visual control over the fire (in a closed combustion chamber, like the China Stove) and have to lift the pot to insert a new briquette.
3. Its good since we can use wood sticks, even logs with this type of burning, but this surprisingly also rises CO levels. More tests should be made to figure out efficient hybrid fuel usage (wood + briquettes).
Side Feed Stove
The testing with side-feeding of briquettes showed very promising results, especially in low CO emissions. Like in 3-stone fire, some of the gases are burned already in the briquette’s own ‘combustion chamber’, but with the stove, the burn then continues through the insulated liner of the stove, making it very clean.
1. Start is very non-smoky since the briquette is burned gradually just from one side – not all of the cold mass is bumped on the fire at once. Chilling the fire makes smoke and CO.
2. We can additionally control the volume of the fire by partially closing the side feed with the door, but the door need to be tightly fitted to the inlet hole.
3. To minimize the CO emissions in the last phase, we completely shut the door, enabling the combustion chamber to retain the heat and slowly burn out the briquette.
4. When a new briquette is inserted, the CO went down, which was a surprise (happens just the opposite in other stoves). This needs to be tested more, but could work acc. to prolonging the combustion chamber (in front) that gases burn out better.
These are all still hypothetical results based on observation, although with scientific measurement system. There were not enough tests made to officially represent the results with numbers. Strong patterns were being recognized instead that can suggest more appropriate ways of burning this alternative fuel that has lots of potential still to be discovered. Feedbacks from the field are most appreciated; if there are some info that you not agree with, or would like to know more about, please respond to this article or write to the author on email: firstname.lastname@example.org
Aprovecho Research Lab, Eugene, OR