Wood-gas stove for the BPL Trapper Mug, Part 3

Today, instead of cleaning all day like I should have been doing... I decided to go test some hypothesizes I had on my wood burning stove. The main hypothesis I had was that it was starving for oxygen as the stove burned for longer periods of time. The reason for this thought was that initially the stove would burn fine, than after five minutes or so it would slowly die down and smolder. In the earlier stages say 5 to 10 minutes you could add some thin tinder and blow a little on the coals and it would flare back up. The longer that the stove burned for the harder it would become to "relight" the stove. This equated out to the complication of never getting my water to a boil. I also noticed that every so often the updraft would flare flames between the lid and the burn box. So I epoxied the 2 parts together hoping that it would permanently seal the 2 parts together.

Yesterday, I placed 4 small holes semi-equidistant from each other, approximately half way up the burn box. I also took a look at the outer can and decided to slightly boost the available air intake by removing the sections between the holes to make 4 semi-equidistant large intake holes with a regular sized hole in between each large hole.(think of it as forming a + sign of large holes, one large hole at the point of each plus sign.) The burn was a lot better after these modifications, but as the fire burned longer it would still become difficult to revive the flame if the fire died down to a smolder. After the burn I JB Welded the lid and the burn box together to help seal and eliminate the leak between the parts.

Today, I cut 2 grooves in between each of the 4 mid height burn holes at the base of the burn box. Hoping that this would help increase the flow of air to the base of the fire and ultimately increase the ability to revive the fire after I threw too much wood in the burn box, or after it just smoldered down to coals. After a trial run it proved to greatly help the fire rehabilitation after it died down. The fire barely took a breeze from my breath and the fire would self revive and flare back up. The fire was a lot more consistent and became a lot easier to keep a good flame going strong. Initially in order to keep the flame going I would have to be using paper thin sticks only. With the lower and midway holes I was able to start using pencil thick sticks to fuel the stove, which reduced the frequency of which I had to feed the stove, but it still needs a constant tending due to the small burn box. The JB weld was a waste though, since the fire exceeds the temperature rating of the JB weld and it started to bubble and eventually failed.

Don't mind my the dyslexia, I initially did not plan on making a video out of this... So I was supervising the cats, tending a fire, videoing and trying to think while talking with no preparation...


The mid height burn holes and the first slots for the lower vent holes.

Here you can see the elongated holes in the base of the stove, I have sticks abound broken and ready for starting the stove.

The stove loaded and you can see the fire starter on top of the wood stack and the little bridge above. Which will be ignited by the fire starter and drop down and ignite the rest of the wood. The twin wall design stoves operate with an updraft in the outer wall creating convection currents sucking the air into the outer wall, through the holes to fuel the fire. After much research and lots of trial runs this method has been the most effective at quickly starting and preheating the inner wall to start the convection currents on these small stoves.
Prepared for the burn.
Here is the final lower venting setup. If I were to make another one I would drill the vent holes in before I removed the can's base, since there is not enough structure to push against in order to drill the holes without the base of the can I just used the cut off wheel on my dremel to turn the slots into triangles.


After the video test run, I enlarged the holes near the base of the burn can and ran a burn without the pot. With the larger holes I was able to start using pinky width sticks after the fire was good and hot. Granted you still need to be mixing in a lot of small wiry sticks and pencil sized sticks with the larger sticks to keep the flame burning hot. Using the larger sticks though helped lower the amount of constant feeding that was required in the earlier prototypes, but it still needs constant tending and watching. I'm pretty happy with where this model has gone and I'm very glad that I kept with it and didn't give up. The only thing left to tinker with is the height of the pot stand and take the final weight measurements. The next major step is an actual field test along the trail at a cozy campsite after I'm tired from walking... Only then will I be able to tell if I want to keep this as a potential stove for fair weather to moderate weather trips where wood will be plentiful. We'll see how the field testing goes...

The present weight of the stove without a windscreen or pot support is 2.6 oz. So figure the final weight will be between 3.0 to 3.5 oz with a windscreen and pot support.

Warning! Playing with fire and tools can be dangerous! This post is for informational purposes only. Using any of these methods, or using a fire, a stove or tools can cause health hazards, injury or death!!! Use this information at your own risk.

Wood-gas Stove for the BPL Trapper mug Part 2

The other week I got a few more minutes to play with the stove designs in an attempt to get them to work a little more efficiently. I'll be getting less time over the next few months since Fall quarter of college starts on the 28th of September.

I took Prototype 1 and shortened the outer can by 1" to get the bottom of the burn box a little closer to the base of the stove and to see how it performs with getting the hot coals closer to the actual fire. Since they fall through the grate as they become ash. I also revised the mesh on the bottom of the burn box as I had previously intended. I used a 1/2" wire fence mesh from Home Depot, which was also used to make the pot support. I was tempted to get the 1/4" mesh... but I went with the standard 1/2" mesh for weight and the fact that is what it appears most stove builders use for pot stands as well. After cutting the bottom of the outer can, without my hydraulic press was fairly hard to get the base of the can to press neatly onto the can. I dented the outer can and partially crushed it... I straightened it back out with a pair of pliers and turned the lid inside out and worked it back onto the bottom of the out can. With some help of the pliers I managed to get everything to fit fairly snug back together.

The next model revision (prototype 2.0) I made was to use the same standard sized peach/soup can and use a Campbell Tomato Soup can for the inner fire box. Figuring it would allow me to use the full depth of the peaches can, by giving me an extra 1/2" of length and a 1/2" wider for the fire box. I took a different approach to the holes on this stove. Instead of marking to drill every 1" and using a 1/2" drill bit, which was than augured out to be ~ a 3/4" hole as I used on the original can... I marked ever half inch and drilled a 3/8" hole which I augured out to ~ a 1/2" hole. I figured I'd try more holes at a smaller size... I used a similar procedure as part 1 to make the burn box and installed the wire mesh and put the stove together.

The 1" cut mark for the the first prototype.
The start of prototype 2.0
The soup can nested into the peach can.
The old burn box next to the new burn box.
The cheesy wire grate before replacement in ver. 1.0, and the wire grate in ver. 2.0
The stoves side by side.
Testing... The new design smoldered a lot and I could barely get it to even get a couple minutes of good burn time... Which has been a fairly consistent problem with both designs, yet it was definitely amplified with this model. Some of it might be my choice of wood, but I think these stoves are slightly suffocating due to the small amount of ventilation and their small burn box size. Which gets full and I can see where O2 movement could be a problem. I need to play with the oxygen delivery systems on the inner can first, I think I'll add a couple holes lower on the burn box to help fuel the fire mid can. Prototype 1.1 burned a lot better, but I still had trouble getting a consistent burn, granted it was a little better.

Trapper mug, stove 1.1, stove 2.0
Stove 2.0 with the new pot stand.

The next plan is to do a little more research, and play with the O2 delivery (add a few holes to the inner can at a little lower level, and maybe some mods to the outer can holes as well). I might also cut down the tomato can to fit into the shorter can as well. I'm not going to give up quite yet, but I might reroute my design to a larger stove if I can't figure out a way to get this stove to burn better. There might just not be enough distance between the walls on the second stove... But only tinkering and testing will tell... Nothing like smelling like a camp fire at the end of the day!

Warning! Playing with fire and tools can be dangerous! This post is for informational purposes only. Using any of these methods, or using a fire, a stove or tools can cause health hazards, injury or death!!! Use this information at your own risk.