-A 20mm insulation air gap that should increase fuel efficiency while at the same time radiating some heat off the middle cylinder to the outer cylinder. The outer cylinder should be safe to touch while the stove is in operation. The theory is using a 3 cylinder stove creates a sweet spot for metal lifespan, fuel efficiency and safety. Need to compare water boiling times and outer metal surface temperatures with and without the middle cylinder
-The handles are double so 1.5mm goes to 3mm which is hopefully thick and robust enough. The double welded tabs should provide strong attachment of the handle to the outer cylinder - maybe orientate North-South so they don't act as hinges when the stove is tipped over!
-An independent pot stand that is suspended above a 1.25kg Milo tin riser and 'Permastove'. The legs are made from bamboo (any variety) and the metal cross should be able to support flat-based pans as well as round-based pans/woks. If the fuel runs out, the 'Permastove' can be easily removed and replaced with another 'Permastove' (with fuel) without any need for moving the pan/pot/wok during cooking.
-The lid tabs could be screwed into the outer cylinder with 3.2mm x 20mm galv screws which would help anchor the cylinders, increase pressure in the secondary air gap by reducing air leakage at the top
-For USB fan control I found this: https://www.coolerguys.com/products/coolerguys-manual-speed-controller-for-usb-fans It means now you can adjust the (5V USB centrifugal computer) fan speed which will adjust the flame size for better cooking control - just like a deluxe gas stove ring!
-2 spare grates per stove. The inner cylinder will eventually wear out from exposure to fire and need replacement at some stage but probably not before the grate will burn out in the middle. Replacing the grate will extend the life of the inner cylinder. For convenience the central grate should be able to be snipped out with good tin snips and replaced with a spare one that can be screwed in with 3.2mm x 20mm galv screws (can be purchased from Bunnings).
-The power bank could be the 'Zendure X6' or 'Ultron'
-The power bank could be powered from a 60W Megasolar PV panel which has USB C PD output, DC and USB A
-Why not a TLUD dehydrator? There's always the ol' solar bed frame...
-Why not a solar oven when the sun's shining and a TLUD when the sun's not shining?
Where's the CAD for 'The Permastove V3'?
I'm still saving up dollar to prototype 'The Permastove V3'. Information will be provided during the prototyping stage as there may need to be final adjustments to the CAD - which might be posted if I think the stove is worth mass producing!
The 'Permastove V4' is a '4 in 1' stove for
(1) multiday trekking/hiking/backpacking, solo or group. Day/overnighter trekking/hiking would be better served with the 'Ohuhu' TLUD stove which can also take solid fuel tablets eg.Hexamine as a backup. Note that biomass stoves probably shouldn't be used during the fire season (unless indoors)
(2) car camping
(3) backup stove for the household (if you already have a stove connected to the grid)
(4) primary stove for the household (if you're off grid)
-lightweight: made from 0.9mm 304 stainless steel - very durable too
-multi-fuel: can use plant waste (biomass) from the environment while trekking or use fuel pellets if you're alpining eg. sawdust, rice husk, coffee bean pulp etc The base/grate has many small air holes so all types of fuel won't fall through
-light ecological footprint (offsetting Carbon released by unsustainable sources and technologies eg. fossil fuel based transportation, energy production, agriculture et al like deforestation/land clearing...)
*fuel efficient with clean emissions (smokeless) via passive/non-pressurised micro-gasification (uses primary and secondary air supply)
*produces biochar (as a by-product of pyrolysis via water boiling/cooking). This can be left in the environment and will lock up Carbon for hundreds to thousands of years (eg.35,000+ years) reducing the impact of climate change/chaos
*no non-recyclable fuel (gas) canisters to deal with (that usually get turfed into the environment)
-no moving parts eg.no fan or any electronics
- to reduce volume in bag: fits in all sizes of billies eg.1.4 litre, 2 litre, 3 litre; Sigma 2.7/3.7 litre pots; Pathfinder GEN3 bottle/cup nests inside the inner cylinder
-replaceable inner cylinder
-works well with a heat shield that is elevated above the air holes on the outside of the outer cylinder
-creates local 'Green collar' jobs along the supply chains eg. fabrication, biochar collection and application
Prototyping will be done over the next few months.
Note that the 3D model is for illustrative purposes only. Unfortunately, a software bug prevented lining up the base perfectly central with the inner cylinder - it's not a design fault :)
Managed to get a burn for 2 hours 40 minutes using wood pellets. The fire took about 15 minutes to stabilise. I used a ss bowl with ss pollen mesh lid, filled with water, on the stove and it was able to get up to boiling no problem. I had to top it up every half an hour to replace evaporated water lost during water boiling. I used a hexagonal heat shield around the stove/bowl which protected the flame nicely as it was a little gusty. The wood pellet biochar produced from the burns looks like good quality which I will need to test in a lab for confirmation. The air jets worked ok during the burn but only worked very effectively when the pyrolysis front was near the bottom of the reactor/inner cylinder. Presumably, this was because there was more airflow available to the fire and more wood gas was getting sucked up to the air jets. I'm going to try sealing the stove lid with high temperature silicone which I think will increase the secondary air pressure in the air gap and through the jets which will add more oxygen for cleaner and hotter secondary air combustion. I'm also going to try adding a fan when it arrives and close off the outer cylinder air holes at the base. I hypothesize that the forced air/fan assisted burn will produce faster pyrolysis, shorter burn time, higher temperature fire and improved secondary air combustion.
Run time was 1h40m. Shorter compared to the first run due to better secondary combustion now that the lid is sealed properly with high temperature silicone on the top/outside edge. The silicone shows no loss of structure after the burn which may have even helped bed in the silicone. The wood pellets with kerosene shaken in a small container worked great as a firestarter. These charged pellets were placed as a thin top layer on top of the rest of the wood pellets up to the level of the first air jets. The heat shield worked perfectly. The Pathfinder boiled in 5 minutes but I allowed it to boil over which almost put the fire out. So. needs to be removed with leather gloves before boiling over. When the fire began to smoke, that signalled the end of the burn. At this point, I poured the pellets into a bucket with water. I never pour water directly on to the stove as it will deform it while it is hot. The resultant biochar looks clean and crumbles cleanly which is a good sign.
This rapid prototyping is addictive and expensive. So, the prototype of the 'Permastove' V4 was 2D laser cut, rolled and welded. It turns out that my laser cutter has a 3D laser cutter for tube. A couple of wise men recommended I used preformed tube for the cylinders to save cost and I think they are right in terms of what's appropriate and available. The Permastove V4 is primed now for workshops with only a 2D flatbed laser cutter available and local fabricators that can do TIG welding and cylinder rolling that don't charge $100/hr for labour. As I've mentioned before, a good design should take into account locally available tools, materials and labour. So, it is appropriate that I redesign V4 to take advantage of 3d laser cutting and available stainless tube in Oz. It turns out that the tube is imported but I'm trying to establish whether or not it's Australian iron ore used.
I've already modified V4 to V5 based on these new constraints and opportunities of 3d and 2d manufacturing.
So what's in V5?
*Suitable for multi-day solo/group trekking/hiking/backpacking, car camping or primary/backup household stove. Day/overnight trekking/hiking use is well covered by Silverfire 'Scout' and knock offs such as the 'Ohuhu' stove on amazon.com.au. You could argue that for longer treks you need to go more lightweight but from the perspective of wanting to glamp a little, it's good to have a stove that runs longer so you can have your 2 or 3 course meal and tea/coffee/Milo. A longer run time is also good for group cooking!
*No additional welding (the ss tube is from Taiwan and welded - I tried local suppliers but no one had Australian-made 304 ss tube).
*Assembled for use each time as it doesn't pack down like the 'Ohuhu'
*V5 will probably won't be fan assisted and remain a Natural Draft (ND) TLUD
*There will be less air jets for secondary combustion on the inner cylinder. All these jets are not needed and less of them will save money/less time needed on the 2D laser cutter
*Perforated tabs will be used throughout the design.
*The lid will still be screwed on to the outer cylinder and should fit perfectly with no air leaks if the modelling is good. No high temperature silicone required.
*The pot stand could be made into a square, with four pieces, that sits centrally above the inner cylinder and lid. This would be more stable than the cross, especially when using a wok.
*The tab guides for the inner cylinder will be be more wide than the inner cylinder, longer and more stable.
*To reduce its volume in a bag: fits in 1.4, 2 and 3 litre Zebra billies; Sea to Summit Sigma 2.7/3.7 litre pots; Pathfinder GEN3 bottle/cup nests inside the inner cylinder (note that Pathfinder offers it's own very lightweight stand for the bottle/cup in a regular campfire but is not as efficient as a TLUD and doesn't produce biochar or clean emissions).
*Could invert the 'Pathfinder' cup and use the 'Ohuhu' bowl to place in the bottom of the reactor/inner cylinder and burn fuel tablets eg. hexamine, on top of the inverted cup. This could be used as backup/last resort to the environmental/pellet biomass
*A small tubular heat shield (same diameter as the outer cylinder) for the 'Pathfinder' bottle/cup could be added resting on top of the lid.
**That's probably enough changes for a new version...
The stove will hopefully be available for sale by mid 2020!
NORI's lightning sale has just been joined by the Schwarzenegger Institute, offsetting the footprint of their operations. So what I am thinking is if I can work out the supply chains for the Permastove V5, I could embed the purchase of NORI CRCs into the cost of buying the stove in order to offset Carbon emissions of manufacturing/production. Then, if a village or co-op down the track wanted to buy stoves (or even produce their own stove on the coop level with 2D and/or 3D laser cutter purchases via public/private philanthropy), biochar produced could be reimbursed with CRC purchases providing NORI tokens proportional to how much biochar they produce.
The 'Permastove' is more complicated to build compared with the 'Carbon' V3 (See the Flat-Tiki 'Carbon' page). There are more parts and more things need to be done to the metal. I've been told that the double fold on the 'Carbon' V3 is tricky but doable for a skilled press brake operator. The 'Permastove' V2, V3, V4 however requires rolling, bending (with the exception of V4) and welding in addition to 2D laser cutting (which is a skill in itself). The 'Permastove' V5 requires 3d tube laser cutting and 2d flatbed laser cutting. I'm thinking that 500W fiber optic 2D laser cutters and 3d tube laser cutters could be purchased in a given region (maybe with Nori tokens) and located at a centralised workshop for both the kilns and stoves. The 'Permastove' V2, V3, V4 could be distributed as a flatpacked kit to local workshops that can do rolling, bending (with the exception of V4) and welding. The 'Permastove' V5 doesn't need any additional fabrication after laser cutting so should be made at a centralised workshop. These workshops could then act as stove and fuel distrubution hubs. For stoves, I prefer this model over a centralised workshop that does everything but only creates distant jobs through the biochar related supply chains but in some cases centralisation may be the only option (eg. 'Permastove' V5). It makes more sense to do the cutting and folding of the 'Carbon' V3 at a centralised workshop then distribute it from there. For both stoves and kilns it depends on local preferences too eg. What's the most appropriate way of doing business? Where is the unemployment? What transportation links are available? Most importantly, where is the market?