the Bundle of Joy wood gas stove

Andrew Ma, March 11, 2010

Minimalist, most accessible and, lightest wood gas stove I've seen or built so far. (But got a few more ideas). Credit goes to WorldStove and its Everything Nice Stove design.

Instructions

Fuel Preparation:
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Take a stick. Mine was a maple branch found on the sidewalk when I was walking my dogs - 28mm diameter and 1.9m tall - barkless and bone dry. Break it into small 20 to 40 cm segments by wedging it in the "V" between two tree trunks and pushing the stick sideways.

Take 3 of the broken segments - preferably with one of the ends not splinted into a point. Tie a piece of rubber strip (e.g. from bicycle tire inner tube) or strong elastic band and wrap around the thicker end. Place this end on a rock or something solid. Split the stick vertically by placing a hunting knife across the top and hitting the
knife with another stick. You should be able to split each segment
into 8 or 10 pieces length-wise. The rubber band holds the chopped splints together until you are done. (Thanks goes to the author of the Youtube video where I saw this technique).

Gather all the splints into a bundle. Remove all pieces which have horizontal branches.

Stove Construction:
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Rip a piece of aluminum foil twice time the circumference of the bundle of wood and place it horizontally in front of you. Place the bundle of wood on the foil so that the top edge of the bundle is 20mm below the top edge of the foil. This will be the top edge of the stove. Wrap the aluminum foil lightly around the bundle and then squeeze it to remove excess space without puncturing the foil.

Add small charcoal pieces before closing off the bottom of the inner cylinder for (A) Protection of inner cylinder from excess heat at the air holes, (B) Reduce the amount of smoke when the fire is out, and (C ) To diffuse the primary air to allow it to reach the centre of the fuel.

Gather and squeeze the foil at the bottom end of the stove then tap it lightly on a flat surface to flatten the aluminum. Make sure the stove can stand and is stable.

Take a small sharp splinter of wood and puncture 3mm holes around the bottom of the stove with holes spaced 10mm apart. These will be the primary air holes.

Corrugate the top edge very slightly using you fingers. This keeps the foil together and slightly reduce the diameter to allow the outside cylinder to slip on more easily.

Take another sheet of foil that is the same length as the first. Fold to reduce the width to = (height of the inside tin + 20 mm + 1/4
diameter of the inside tin). Place the foil horizontally in front of
you. Measure a strip of width = (1/4 diameter of the inside tin +
10mm) along the top edge. This will be the top end of the outside
tin. Fold the strip 90 degrees up. The strip will become the flame
concentrator ring. Corrugate the edge of the strip (but without
corrugating any part of the 90 degree fold) until you form the concentrator ring and the foil becomes a cylinder.

Shape the cylinder (the outside tin) until its diameter is 20mm
greater than the inner tin. Verify that there is a 10mm gap on all
sides when you place the cylinder over the inside tin. Verify that
the opening in the flame concentrator is about half the diameter of the inside tin.

Place the cylinder upside down on a flat surface and use a wood segment to shape and flatten the flame concentrator ring.

Take two small pieces of sticky tape (any type of tape will do, even transparent office tape). Stick one piece on the inside of the cylinder to over the overlapping fold so that the inside diameter can be maintained. The second piece is used to secure the outside fold to
prevent it from unfurling. The two pieces of tape should be mounted
near the bottom of the cylinder where the temperature will be lower.
(I believe in a crunch you can fold up the bottom edge slightly to achieve comparable results).

Place the cylinder over the inner tin. Place both tins on a grate to allow air to enter from the bottom. (Alternatively place two sticks under the outside tin to elevate it by 10mm . ) Verify that there is a 10mm gap between the top edge of the inner tin and the concentrator.
Trim the lower edge of the outside cylinder if required.

Measurements of the Above Stove

Stove Material - 12 inch (304mm) heavy duty recycled aluminum foil.
Stove weight - 12 g for inside tin and 10 g for outside tin.
Height - 180mm inside tin, 190mm outside tin.
Diameter - 90mm inside tin, 110mm outside tin Flame concentrator ring opening - 50mm Fuel - 190g maple wood sticks 50mm to 120mm long and 5mm to 12mm diameter Fire starter - 1ml alcohol on top of 5 g toothpick size twigs Burn time - 25 minutes (had to re-light once 12 minutes into the burn when the wind blew out the flame)
Characteristics of the flame - Smokeless during the burn. Strong
flame averaging 150mm high (when the wind was not blowing), but up to 200 mm high at times. Didn't smell any smoke even when I was right on top of the flame, but the wind was pretty strong.
Placed remaining char in a snuffer 5 minutes after flame out.
Char remaining - 30g - no smell. Very little ash visible on some pieces of char.

Condition of the stove at the end of the burn:
Outside tin - 14mm along one edge of the concentrator melted slightly, width=6mm, but no other damage to the outside tin, including the sticky tape. Reusable.
Inside tin - 60mm gash formed at the bottom of the inner tin (6 holes
lost). Not reusable. I think if I put the amber into the snuffer at
flame out, I could have saved it. But I was looking for my gloves.
Some soot on the inside of the inner tin and some soot on a small part of the concentrator ring. No smell on either.

Alternative fuel - I constructed several aluminum foil stoves for burning wood pellets with very good success, and posted one video on youtube.

Measurements of the stove in the video
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- Material - (A) Two sheets of heavy duty recycled aluminum foil, 12
inch width. Length = 460mm and 540mm. (B) Two small pieces of sticky
tape.
- Inside cylinder - weight 9g. Height 250mm. Diameter 70mm. 25
holes (2.5mm diameter) located 9mm off bottom.
- Outside cylinder - weight 14g. Height 260mm. Diameter 90mm. Flame concentrator ring opening diameter 40mm. No bottom. No holes.
- Fuel is 191g of maple sticks (including 10g of toothpick sized sticks as fire starter) plus 22g of charcoal
- Fire starter - 1.2ml of alcohol as accelerant delivered via a syringe and the 10g of toothpick sized sticks
- To light the stove, just throw in one lighted match
- Total time to flame out - 32 minutes
- Weight of remaining charcoal immediately after flame out - 75g (including the original 22g of charcoal which was not consumed)

Observations:
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- No smoke visible during the burn except for the final 2 minutes.
- Very light smoke odour throughout the burn, even with the exhaust fan running.
- Top section of the outer cylinder was hot to the touch but not unbearable.
- Bottom of the outside cylinder was cool even near the end of the burn.
- The outside cylinder and the concentrator ring provides good wind protection.
- Flame extended from the edge of the inner cylinder to the concentrator opening without touching any part of the outer cylinder and the concentrator ring -- there was a 6mm clear airflow visible on the underside and extending to edge of the concentrator ring preventing the flame from touching the concentrator ring. This airflow should be of temperature much less than the flame and responsible for keeping the outside cylinder cool and preventing the concentrator ring from melting.
- After flame out, unroll the aluminum, all holes at the bottom of the inside cylinder were found to be intact.
- 2 small holes (1mm wide and 4mm high) in middle of inner cylinder visible after the burn. Likely caused by wood puncture since the metal at the hole did not melt and it looked like a rip.
- Inside of inner cylinder blackened from the top of the charcoal layer to the top. Most were shinny black but top 40mm are powdery carbon. Inner cylinder has no smell after the burn. Reusable..
- Outer cylinder very slightly blackened inside and outside of the concentrator ring. No other discolouration or damage, including the two pieces of transparent plastic tape. No smell. Reusable.

Recommendations for future development of Bundle of Joy stove:
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- Teach kids about wood gas, chemistry of combustion, carbon cycle, biochar and terra preta in science class.
- Could be useful for teaching boy/girl scouts about fire. The stove
design is safe and fun for children to build if sheets are pre-cut.
Adult supervision needed to use, obviously. Use popsicle sticks or
wooden coffee stirrers as fuel, wooden toothpicks as fire starter material. Will not burn picnic tables if you first load bottom with small stones.
- Cook something. Try using 2 or 3 stoves under a large pot if more heat is needed
- Find the maximum practical size
- Determine the lifespan of the aluminum foil, assuming after each use the stove is spread flat, rolled for storage in a backpack, and then unrolled for reconstruction.
- Try other fuel - small twigs, annual plants, bamboo, braided grass.
(Already tried wood pellets and that works great - up to 55 minutes on one load)
- Change in direction for product design. Suggest using Aluminum Venetian blinds as material for a light weight collapsable stove.

Notes:
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- If there is no grate, then put three small objects under the outside cylinder to allow air to enter from below
- If no alcohol, then place a little very fine flammable material (e.g. pine needle) on top of fuel. Light it. Then quickly place three 5mm diameter sticks across the top of the stove opening, place finer sticks on top of that. The small sticks will weaken when burned
and fall into the stove and ignite the wood. First saw this on J.
Falk's video (trailgear555)
- Saw the technique on how to break a stick into small splints using a rubber band on YouTube, but I was not successful to find it again.
Thanks goes to this author.
- Unrolling the inside cylinder and the reconstructing it will likely misalign the primary air holes between the two wrappings for the inner cylinder and new holes will need to be made. This weakens the metal.

My hope is that the Bundle of Joy wood gas stove can be used by others for emergency purposes and for the ultralight hikers. I have video of the construction and the burn and will post this weekend, if I get a chance, on YouTube under the jw934 id.

Andrew Ma
March 11, 2010