Greetings!
I'm new to the forums, but having been reading through them I'm impressed with the expertise available. A couple of years ago I made a
coffee can
rocket stove that seemed to work well
enough to heat a pot of soup to boiling. Having read how they burn
wood more efficiently at higher heat, I thought, "That's what I need for Asian stir fries in the WOK." So, I set out to make a larger version to use on my deck utilizing what I thought were most of the same principles that seemed to work in the coffee can
rocket stove.
CONSTRUCTION:
I've attached a few photos to help communicate the design. I used a galvanized steel garbage can for the shell. The riser pipe is 6" stove pipe, the bottom of which is capped off with the fitting for that purpose. The horizontal intake pipe (which actually inclines towards the center of the stove ever-so-slightly) is of steel. I don't know what kind of pipe it is but it came with an aluminum liner inside which I have removed in order to get more inner diameter. I fashioned a tray for holding the sticks in the upper chamber of the intake pipe from steel sheet metal which simply slides into the intake pipe.
I cut a hole in the stove pipe (riser) into which the horizontal intake pipe could be fit. The bottom - capped portion of the stove pipe riser is about 2/1/2 - 3" below the lower lip of the intake pipe. which creates an "ash catch basin."
I was concerned about the device tipping over either because of wind gusts or becoming top heavy with a WOK full of hot/sour soup sitting on it. Therefore, I sought to add some ballast which I accomplished by mixing some hypertufa (1:1 cement and pete-moss). I figured that since hypertufa is lighter than straight cement it is due to the pete-moss filler and so the hypertufa might have a better insulating effect than straight cement. I was trying to avoid a big heat sink. The base of the garbage can is filled with hypertufa which is about two inches thick. It comes up to just under where the horizontal intake pipe comes into the riser. I did use a small amount of the hypertufa to seal any gaps where the two pipes came together.
The remainder of the garbage can is completely filled with a mica-insulation (billed as vermiculite) and it must be effective because the outside of the garbage can doesn't even get warm no matter how much fire is in the hole.
At the exit of the riser I measured, cut, and bent two inch wide tabs every other one either bending inward or outward, the result being two concentric circles consisting of five tabs each which serve as grates on which to rest pots, pans, or WOK of different sizes.
PERFORMANCE:
I consider this device to be a failure overall, but providing good opportunities to learn. To ignite the stove I wrapped several smaller sticks about the diameter of my fingers, each in several sheets of news paper and shoved them down the barrel of the riser. The fire quickly builds into an audible roaring fire as air is pulled into the intake pipe and jet-like flames shoot out the top. However, as the fuel in the vertical riser is consumed and used up, the sticks protruding in horizontally from the intake tube are insufficient to keep the fire going. I end up with glowing embers. On a particularly windy day, facing the intake pipe into the prevailing wind, a few prolonged gusts did reignite the glowing sticks into flames, but they quickly went back to glowing embers when the wind died down.
What I seem to have is a good incinerator. A lot of fuel in the vertical riser can cause enough draft to get it going. However, the main fuel sticks are insufficient to maintain any drafting, therefore, I don't consider this to be a workable rocket stove. As an added note, the hypertufa does heat up and maintains significant warmth hours after the fire goes out as the bottom of the garbage can is quite warm to the touch.
I would appreciate any insights the experts can offer about what I might have done right and where I went wrong. Thanks.