Twig Stoves Part 1 Rob Jung

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1 Twig Stoves Part 1 It is surprising what we overlook. Personally, I nd it surprising that I have only recently seen the value of using a camping stove powered by small pieces of wood such as twigs. It is an obvious enough concept, but one I hadn t considered before I read Hester s ar cle in the November 2011, about Bas s stove. I have since learned that these stoves are not completely unknown here: some Australians have been using them for decades, although they are more commonly used in Europe and North America. Twig stoves are just a more elegant, portable adap on of a pit re, or even a camp re with its ring of stones, or a re created in an old fuel drum. And they are in essence what a large percentage of the world s popula on cook on. Why use twig stoves? There are good reasons why more Australian walkers should be using them. Their fuel is a renewable resource, which is greenhouse gas neutral. The wood they consume, small twigs and similar, is usually available and not a habitat for small animals, which larger logs (used in camp res) represent. They are also a much more e cient in their use of wood for cooking than a camp re, and as well, more convenient to cook on. Much of our bush burns naturally and regularly, so the ecological impact in using these stoves is negligible. Unlike a camp re, they leave no obvious trace, as the ny amount of powdery ash they generate is easily dispersed. The burning chamber of the stove contains the re very well, so they are safer than an open re - more like a replace. There are weight advantages in using such a stove, where the fuel is gathered rather than carried. There are also strategic advantages, as planes carrying walkers are not permi ed to carry the fuel used in conven onal stoves. Figure 1. Take a wood stove on a bushwalk? Why not just have a camp re? Camp res are good places to socialise and philosophise, but not e cient users of wood, not friendly for cooking and they scar the ground and leave a mesh of ash (Hatchers Hollow weekend with a full moon, October 2014). When we might not use twigs stoves? Twig stoves will not always be suitable. Time-poor walkers will not favour them, as they require more me and e ort to set and re up, and sustain the re. However with prac ce, skill can be acquired,and using them is actually quite easy. People who are used to managing camp res already have most of these skills. When star ng the re, smoke will be generated, and so ideally they would not be used in con ned spaces such as huts. Above the treeline, s cks are scarce, so again, liquid and gas-fueled stoves could be preferred. They don t, however, use much fuel, so some twigs could be gathered enroute, which could be used later in the stove at camp. Like non-pressurised alcohol stoves (Trangias), they are simple to operate, and robust, and importantly, cannot be stopped by blockages or malfunc oning parts. The same cannot be said for petrol stoves, or to a lesser extent, gas stoves. In sandy or dusty environments, such as coastal or arid areas, robust stoves should be the preferred norm. Requirements for a twig stove In considering a stove, the whole system: the stove, what you cook and the containers, need to be considered. I don t cook steaks or fry eggs etc. on walks, so my stove doesn t need to accommodate a wide frypan or griller. I do use a billy, and for me that needs to be able to cater for at least one or two people. I have used a number of billies, but I the found the 3½ pint size suitable (found in disposal stores). These billies are light and made of aluminium. 19

2 The Coast and Mountain Walkers of NSW Inc August 2015 No. 259 They are 12 cm diameter at the base and 12.5 cm high and their volume is 1.5L. I haven t found an equivalent tanium billy with a small lid. Ini ally I set out to buy a twig stove which would accommodate my billy, with the stove s burning chamber also providing a suitable windshield for my methylated spirits stove (a Brasslite Turbo 2D). A windshield that is too con ned causes over-hea ng with my stove, and sudden are-ups with the Trangia burner. My ini al searches using the Internet revealed no commercial designs suited to my needs. I was thus lead down a path of making my own, but I was encouraged to research how these stoves worked, while I was doing this. Later, I found quite a lot of informa on about these stoves, which included some mee ng my needs. I thought this informa on was worth sharing and so this ar cle followed. In it I will outline how these stoves work and brie y review some of the designs. It is my inten on to discuss my prac cal inves ga ons and give more details about the stove I built, in a future ar cle. Figure 2. Rob s stove (a type C) in use at camp near Mt Razorback, NT. Its re control was good enough to use the stove quite close to his ammable Silnylon tent, something he would not contemplate with a camp re. Types of twig stoves Simple twig stoves used for bushwalking tend to fall into varia ons of the four categories given in Figure 3. The notes in this Figure outline some advantages and disadvantages of the di erent designs. The most sophis cated design is the so-called wood-gas stove, shown as D in the gure. While the most e cient, this design is also more easily disturbed by wind. A sheltered loca on or good windshield are required if one of these is deployed in windy condi ons. Conversely, a breeze assists the func oning of the other types of stove, in par cular type C. I will not discuss more complex commercial varia ons of the wood-gas stove. These use small ba ery powered fans to control air ow. Figure 3. Types of wood burning stoves suitable for bushwalking. 20

3 I have made a summary of readily available twig stoves suitable for bushwalking in Table 1. My selec on is biased towards the lighter or more e cient designs. As it happens, the commercial stoves mee ng these criteria are all of type C or D. There are other commercial small stoves, which are of the simple single chamber type, but these are rela vely heavy. Most of the commercial stoves seat the billy on top of the stove, exposing it fully to the air, rather than using the upper stove walls as a par al windshield (as shown for types B and C in Figure 3). In windy condi ons, greater heat loss is likely from such exposure. Enclosed and well-made wood gas stoves (e.g. Bushbuddy) should be compared more to methylated spirits stoves, such as the Trangia, rather than camp res. The re is well enclosed. Although in use the base is too hot to comfortably hold, the dirt and wooden surfaces it sits on is not scorched. Table 1. Readily available twig stoves Name and descrip on Vargo. Ti, 115gm. Shape: truncated hexagonal cone, 12.5cm across at the base and 10cm across at the top, 10cm high. Folds at for travel. US$60. Available from REI or MEC. Emberlite-UL. Ti version 135g, SS version 315g. Stove is 4- sided 10 x 14cm at the base and 15cm high. Top is 9 x 9cm. US$85. Disassembled and folded at for travel. Honey Stove. Ti model weighs 160gm, the SS version 360gm. This stove is modular, disassembles and packs at. The design is very exible and can be used with a square or hexagonal base arrangement. It can also be used as windshield for another stove. It can accommodate a wide range of billies and the billy does not have to sit on top, unlike most of the other commercial designs. Hexagonal version is 12.5 x12.5cm diam. at the base while square version is 7 x 7cm at base. It is 12cm high Caldera Cone Classic Ti-Tri. Ti, This wood stove is designed as a system to t your billy, and burn other fuels. It comes packaged to protect the stove components in your pack. Weight varies depending on billy size: gm. US$80. They sell an accessory ( Inferno ) which converts the stove into a wood gas stove. US$45. Fire y UL, Ti. 80gm. All except the hearth grate is Ti and that is SS mesh. Very similar size to the Pocket stove. Disassembles and packs at. US$66. Some suppliers have useful accessories for this stove. The Pocket stove, all Ti, 56g, although its storage n weighs another 54g. 35. SS model is 140g. 7.5 x 7.5 cm at base and 10 cm high. Disassembles and packs at Comments Type C stove, although with not much ven la on at the base compared to other models. Wood addi on requires hinged door to be opened. Some users have found it a suitable windshield for another stove, but I thought it was too small. Type C stove, with good ven la on and wood addi on. Appears to be a be er design than Vargo, although also seems too small to use as windshield. Type C stove with good ven la on. Very exible design, with a windshield suitable for other stoves. Reviews: -a-wood-stove The standard version is a type C stove. Has good ven la on, and is mul -fueled. If you want exibility with the fuel and how it operates, this stove system is worth considering. Type C stove with good ven la on. Has a hinged door to add fuel. A rac vely light, although rather cramped to use as a windshield for other stoves. Suitable for one person cooking. Review: Type C stove with good ven la on. Similar in size to the Fire y UL, but has an open hole to add fuel. In my opinion, it is restricted in its use as a windshield, although it can t Esbit tablets or a Trangia burner. It is suitable for one person cooking.

4 The Coast and Mountain Walkers of NSW Inc August 2015 No. 259 Table 1. Readily available twig stoves (Con nued) Name and descrip on Chamber pot stove. For one design weighing 90g see: Single chamber with a re feeding hole stove. This appears to be the most common home manufactured type of wood stove. This design was used by Ian Armstrong, Bas Slade and others. Wild wood-gas stove MkIIt. SS, 270gm. A modular woodgas stove, i.e. where the stove components quickly pack away into a neat cylindrical package, 13cm diam. x 7cm high Bushbuddy. SS with Inconel hearth wires. 11cm diam. x 9.6cm high packed and 14.7cm high assembled. Comes in 3 versions, Trekker (180gm), Ultra006 (155gm) and Ultra004 (145gm). Its walls are of SS shim and in the lighter, Ultra versions the shim is thinner (i.e. 006 = ). The la er are durable, but need to be protected inside a billy, while being transported. CAN$ This stove is also made and sold by Nomadic Stove Co. US$ The Bush Cooker, very similar to the Bushbuddy Made of SS and 190gm, by Quist in Holland. Solo Stove, SS with nichrome wire grate, 250g., 11cm diam. x 9.5cm high nested and 14.5cm high assembled. Bushwhacker, SS, 190gm. Similar size to above. US$29, but only shipped to US addresses. The maker Jim Falk has a useful training video: Comments Type A wood stove, not a wood gas stove. Easily manufactured at home from available ns. Type B wood stove. Easily manufactured at home from available ns, or a billy. Type D (wood gas) stove. Appears to be well made. Its modular nature means it is also well adapted for use as a windshield for other types of stove. Type D (wood gas) stove, which packs away inside a billy. Well engineered and made of heat durable materials. Primarily a small wood stove, to cook for one or two people. For a compara ve review see: Type D (wood gas) stove, with comments as for the Bushbuddy. For a video see: Type D (wood gas) stove. Very similar looking and with the same comments as for the Bushbuddy. Type D (wood gas) stove. Has a similar func on to the above stoves, but looks more rus c and is cheaper. Notes on the Table: Ti = tanium and SS = stainless steel. Typically it seems 304 stainless steel is what is used. MEC = Mountain Equipment Co-op. (Canada) Materials used in the construc on of twig stoves It is worth considering the durability of the materials used in the stoves. Stoves made of plain steel, (or n plated) such as those made from food ns, are suitable, as the iron in them so ens and melts well above ame temperatures. They will eventually rust out, although they will be serviceable for some me. Steel stoves will corrode faster in salty environments. Then you just make a new one. 22

5 Aluminium readily oxidises, but the oxide forms a strong passive coa ng, protec ng the aluminium metal underneath from further corrosion. However at the higher temperatures in a stove, further oxida on is promoted and it will eventually disintegrate. Aluminium melts at 660 C, and it is not suitable as a billy support wire it melts in the ame which Hester and Bas noted. Bas and Hester also use an Aluminum billy as their burn chamber. This will work for a while, since these walls are exposed to the air outside, cooling them. However it would be expected that it will disintegrate eventually (from the inside of the stove). Titanium is another reac ve metal, which like aluminium forms a very strong passive coa ng that protects the metal. It is so reac ve, that it will react with nitrogen in the air, as well as oxygen (even at low temperature). At room temperature tanium is the strongest / unit weight of any metal, which is why it is widely used in the aerospace industry. However it weakens signi cantly when heated and starts to oxidise rapidly in air at above 1000ºC. In air it will burn well below its mel ng point (1660 C). It is used in many of these lightweight stoves, which means that strictly, their life me should not be expected to be forever, as is commonly suggested. What saves tanium in a stove applica on, is that in the single shelled stove designs (type A, B and C), the tanium walls are kept much cooler than the ame temperature by the outside air, so it will last longer. Expect a higher failure rate for tanium in the ho er part of the stove: the grate area, or the billy support wires. Titanium hearth grates distort with use, but so do those made of stainless steel. I agree with the manufacturers when they say, this does not a ect the performance of the stoves. Titanium would not be a suitable wall material for the inner chamber of a wood gas stove, which is probably why stainless steel is used. Your tanium billy is ne, as it will be kept to 100 C or below, so long as it contains water. By adding chromium and nickel to iron, the alloy stainless steel is produced and this also forms passive coa ngs, which protect it from oxida on. These alloys are more tolerant of heat than aluminum or tanium, although their heat tolerance varies depending on the composi on of the stainless steel. According to one source, the heat tolerance of the commonly used types of stainless steel (304 and 316) is similar to tanium. Refer to Bear in mind that this table was prepared with gaskets in mind rather than stove chambers. More heat resistant stainless steel formula ons exist, as do other alloys such nichrome and Inconel. A number of the wood gas stoves use Inconel for their hearth grates.