the team organized their benchmarking by four main concept areas. for the most part, it is possible to mix and match from each category to make different stove systems.
· fuel type was limited to wood, which is commonly used and widely available in Guatemala and other developing areas.
· combustion chamber was by far the most complex area for consideration. five main types were investigated and will be discussed below.
the team narrowed down their main concepts to six stoves (combustion chambers): three stone open air (baseline), clay enclosed, rocket stove, TLUD stove, downdraft J chamber, and charcoal combustion chamber.
· a downdraft J chamber stove acts similarly to a rocket stove, but the fuel is loaded from the top and heat flows sideways before going up to the cooking surface.
· a charcoal combustion chamber stove is said to be similar to other stove designs, but uses a reflective surface inside to reflect heat back into the chamber.
the team used decision matrices to examine their options for combustion chambers, heat transfer methods, and flue designs. a decision matrix takes the original design specifications and weights relative to one another for importance. each concept is then evaluated as to how well it meets each criterion, and the score for each is determined by adding the weighted evaluations. using this method, the best two concepts for combustion chamber were the rocket stove and the TLUD. for heat transfer, a griddle stood out far and above the rest. for flue design, especially since cost and easy manufacturability are important, a straight flue beat out a balanced flue. the combustion chamber decision matrix is included here in case you are interested.
having thus figured out their best design options, the students went about building simple prototypes of a rocket and a TLUD stove. they used metal paint cans as the main component of their combustion chambers, and assembled other parts from easily available products (sheet metal, other cans, rocks, etc.) time and temperature were collected from a boil test with each stove. the rocket stove took 21 minutes to boil four cups of water while the TLUD took only 12, a 43% improvement. (though it should be noted that there were difficulties in keeping the rocket stove lit at the beginning, possibly biasing the data.) the second test determined the amount of time each stove could maintain a cooking temperature with a set amount of fuel. this test appeared to also favor the TLUD stove. the team also measured outside skin temperature of the stoves and found the same results from both stoves: too hot to be touched.
next up: the design solution!
|team's TLUD stove prototype|