It all started with a couple of soup cans. I had seen some videos online with various ways to experiment with wood gasification. This led me to building a simple stove to experiment with the concept myself which impressed me. That let me to looking at various turbo stoves, then to trying to design one myself. Pictured is the initial sketch for the idea I had, originally depicting (and building a prototype of) a round stove, eventually culminating in a stainless/aluminum square version.
Step 1: Building the Prototype
To test the concepts I had in mind, I used my initial 110v welder and some galvanized (yeah, I know - don't weld galvanized! I kept the welding on that material to a bare minimum doing it in a well ventilated area, and left most of my practice welding to sheet metal - non-galvanized - that I used for the inner burn chamber and the air and fuel intakes)
I knew that plain old duct sheet wouldn't work long term, but wanted to see if I understood the basic concepts of the gasifying and the air flow well enough before spending considerably more money on a final version of the stove. The original took some testing, but I eventually got it burning so well, it burnt all the galvanize coating off the top lid on the best burn in a rather short period of time!
I eventually donated this version to another tinkerer in town who was also interested in the gasification processes, but was satisfied enough to chase down parts to build a better version.
Step 2: Assembling and Starting the Parts for the Real Mccoy
A few trips to Alro metals in town and I had a nice sheet of stainless to work with and some aluminum for the corners, a large 4" square, 1/4" wall piece for the burn chamber and a small 4"x1.5" piece for the fuel intake. I started on the intake, making a catch on the front of it that would allow me to remove the piece as needed to make it easier to check problems or take the entire thing apart again.
Since the original design involved a 2 walled structure, I cut the pieces for the maximum width I could get with a 1" distance between the inner and outer walls. This also allowed a 1" distance between the inner and the burn chamber. Once I had all the pieces cut, I made aluminum pieces to hold the outer corners (I didn't need the inner piece to be as pretty so welding it was the best way to finish it off once I was satisfied with the shape and hole cuts)
I fashioned a stand for the base of the inner piece which also serves to block off the air flow from the bottom, and fashioned a small sheet-metal drawer for the bottom to catch what little ash falls out of one of these things (which isn't much - they burn almost all the fuel!)
The original test piece used a single wall chimney, but ultimately I mounted a fitting in the back for a double walled chimney pipe. This allowed me to still use the single wall pipe during testing so that is what is shown here.
I then cut the holes in the front of each front piece for the fuel pipe to go into.
I fitted the burn chamber with a small sheet cut to fit it's top with four screws in the corners to hold it in place, then drilled holes evenly spaces around the outer edge to facilitate the gas to escape.
I cut a hole in the back and found a small pipe for a sink drain to hold a tubular PC cooling fan I had found online that ran on a few hundred milliwatts at 12v.
One thing I learned quickly was that before full gasification, smoke would escape out the fuel tube, so I made a small metal cap to go on it until it was burning well.
Once I was satisfied with all those pieces, I started drilling the holes to suspend the burn chamber through both walls of the stove, spot welded the chimney pipe on the back and drilled the holes around the edges for the aluminum frame.
Step 3: Two Ways to Light
One of the things I had a hard time with the other stove was getting it lit. I hadn't really built that one to be easily lit - I was more interested in the burn. I tried a few experiments on 'accelerants' with the round stove, included one that ultimately singed my eyebrows and sent the metal lid about 50 feet in the air. (apparently white gas still goes 'POOF' even if you let it breath out of the wood for more than an hour in the cold-dead of winter - don't try this at home! Wood alcohol worked best if you are in a hurry. But even then, let it air out before even putting the soaked wood chips into the stove)
This time around, I decided instead to build a small burner to go under neath and eventually rigged up a barbeque grill piezo spark igniter and propane/butane screw on fuel line to it. (see the video for the design) The burner is nothing more than a piece of 1/4" copper tube with jeweler drill micro holes around the top shaped into a square with the end crimped off. I picked up some plumbers fittings and adapters to fit a barbed flange down below that I could attach the propane hose to. (picked up a hose at home depot)
The other method was to get a small 1" piece of stainless tubing and drill a hole below the burn chamber through both faces and fit the outside with a small removeable metal cap that allows me to insert a small barbeque lighter if I use fuel soaked wood.
Step 4: Slight Modification
One of the things I learned right away on this one vs. the prototype was that by using the larger burn chamber, it was harder to get an even coal going inside for the gasification and was also harder to get a consistent airflow. The end result was that I got more of a burn at first around the bottom of the burn chamber itself rather than through the holes out the top. This would eventually warm up the burn chamber to increase the internal gasification and result in more gas out the top but the bottom burn never fully stopped.
To get around this, I removed the expanded grating on the bottom of the burn chamber, cut it to fit the inner diameter rather than the outer diameter and moved the grate up inside the burn chamber about 1/2". Then I made a small tube to go up through the heart of the chamber including more of the expanded sheet curved into a tube at the top to help more air flow go through the wood at the top of the chamber, thus encouraging more air flow to push the gas out the top. This fixed the problem with the bottom burning considerably. There was a small amount on start-up, but again, this would heat the chamber and then stop which was ultimately a good behavior.
Step 5: It Almost Burns Too Hot!
The ultimate fuel mixture for this stove turned out to be plain-ole wood chips, which it turns out our city gives away for free. While they are giving them away for landscaping purposes, they don't fret too much when I show up just wanting a bucket full for tests with the stove.
It took some testing to figure out this was the best fuel, but once I got that narrowed down, there were only a few minor problems left that I'll work out in future modification. The biggest one at the moment is a small fuel hopper that clogs up sometimes. (you have to manually poke the fuel down. My ultimate hope would be to have one that fed itself from a hopper - see my sketches - but I have to try moving the fuel input to a corner of the chamber first to see if I can stop the clogging inside due to the lower feed angle)
Once burning, there is barely any white smoke at all, and I can burn a small bucket full of chips for hours and have very little residue in the drawer at the bottom. Note the picture which was taken at night. The entire stove 'glows' and I commented on the original posting of the pic that I will have to install a cage around it so nothing comes in contact with it when in use! It works better than I could have imagined!
At some point, I want to try playing with using peltier elements lower down to see if I can use the heat to power the fan.