Does anybody know if this stove is still available anywhere? The links in the thread all seem to be dead.
Thank you. I assume that people here are still happy with theirs? I have both made and bought many TLUD stoves of differing sizes over the years and experimented with things like the balance between primary and secondary air, forced mixing of wood gas and secondary air, and flues to help air throughput. I like the technology a lot. I am now looking for two improvements. (1) less soot/easier running with damp or non-ideal fuel and (2) better longevity of the burn chamber when used on a regular basis. I believe that forced-air will help with (1) and I am making my own test stove to experiment with this. The small and neat LOFI stove seems to demonstrate both of these benefits for example, but at a high price and with low fuel capacity. As regards (2), I have found that all my made and bought stoves where the burn chamber was made of stainless steel eventually rotted out - presumably from the combination of high temperatures and the acidic residue left by burning wood. Whether this is inevitable with S/S or partly due to thickness or alloy quality I don't know. I am also curious about the relative longevity of Titanium in the burn chamber. Most of the common Ti alloys have a higher melting temperature and better corrosion resistance than typical S/S, but there is also work showing that it can anneal and become brittle earlier than S/S. The people who experiment with and design big TLUDs with very low emissions for 3rd world countries tend to aim for ceramic burn chambers to get the best longevity.
With frequent use, year round, my original 8-year-old stove is still working well with no corrosion of the interior (burn chamber).
Consider too that Asian 'stainless' can vary massively in quality. You're on the right lines with ceramic materials- any design of stove which burns wood cleanly involves temperatures higher than metal can withstand in long service. Refractory materials are required, but these come with their own challenges. They tend to be brittle so require chunky cross sections unsuitable for small scale portable stoves, while the flexible sorts like ceramic fibre paper are in theory ideal but become as hazardous as asbestos after heating beyond 1260°C. Even the body soluble forms, which are only safe to handle until they have been fired.
Interesting. Would you say that Titanium will suffer in the same way that S/S tends to long-term? Again it probably depends upon the specific alloy.
Titanium is less durable in high temp/high oxidising environments that just about any stainless. Stainless varies massively, there are some aerospace grades which are nearly adequate and in reality will give a long service life, but they would be serious money even if you could find a source. Experience shows that to maintain a wood fire hot enough for optimum combustion, metal is ultimately doomed and refractory materials are the only current option. For a serious rabbit hole, and a tangent but directly relevant in terms of materials, try some reading about rocket mass heaters* and rocket cookstoves. *Hippy reinvention of the masonry stove, not gasifiers as such but some overlap. Caution, a lot of uninsulated, smoking contractions are given the title 'rocket cookstoves', but it's the insulation which cleans up emissions.
Extensive use as I say for eight years and it’s evident that there’s no degradation of the combustion chamber.
The forced air definitely helps, it provides a degree of air cooling to the materials although at the expense of sub-optimum combustion and increased NOx emissions etc. Even so it's likely with the kind of use @Hopster is hinting at (fires 1-3 times daily?) it would have degraded well before now. Metal may be long enough to get an adequate lifespan, if depends on frequency of use in the same way that a canvas tent may last half a century of regular camping, leave it up for two years and it's compost. And going bigger requires more robust materials. Aware we've gone somewhat off topic!
Yes that still looks like it's going strong. Perhaps a superior alloy or just thicker than average. Mine would always start to rot around either the primary or secondary air vents.
That would be oxidation, rather than acid erosion. The environment adjacent to the air holes is oxygen rich, combined with the high temperature it's very harsh on materials. Steel 'rusting' is of course just 'burning' very slowly due to the low temperatures involved. Crank up the heat and that oxidation/burning happens much more quickly, and will even happen to stainless which is corrosion resistant in normal environments.
So it seems that we can expect this eventually in all metal burn chambers whether S/S or Ti. I bought some refractive ceramic cloth a few years ago from an AliExpress supplier. This was in order to thoroughly insulate a short chimney on my home-made gasifier stove and thereby prevent heat loss whilst still promoting mixing to reduce soot emissions. It seemed to work pretty well but was itchy to work with and I had concerns about inhaling or accidentally ingesting particles. I am not sure whether it would have been physically tough enough to put in the burn chamber, so I may explore some refractory materials that could be formed like a thin layer of clay on the interior of the burn chamber and then fixed it place by heat. I wonder if that would be some kind of solution, albeit with a weight penalty.
Eventually, but 'eventually' may or may not be an issue depending on intensity of use. As @presscall reports, his example has had a lot of use over years and shows no signs of degradation around the inlet ports, so for many users the material is going to be perfectly adequate for a lifetime of use. Perhaps if the material specification is unusually high, combined with forced air keeping temperatures down, this design would last a lot longer than TLUDs you have tried? The only way to find out is through experiment! Another other option is to go with modular designs and regard the areas which burn as consumable parts. If you want to be certain of a very long lifespan, or want to scale up, you're onto refractories. Your concerns about ceramic fibre products are valid- look for 'body soluble' products* which are safer to work with as any ingested particles supposedly break down internally. But ALL ceramic fibre products become dangerous when fired above 1100ish C (Some reckon 800C), although it's unlikely you'd hit these temperatures in a small TLUD. The other issue as you say is the durability, they will wear quickly from abrasion of feeding fuel and the fuel moving as it burns. There are some stabilising agents (search 'waterglass rocket mass heater') which can be applied to form a harder skin. All this has been experimented with before, rocket mass heaters, small scale charcoal retorts and wood fired pottery kilns- plenty of material out there in the various online communities. We're sadly still some way off coatings which can effectively be applied to metals, or resilient thin and safe refractory materials which work on this small scale and in a DIY context. *Body soluble ceramic paper does exist is various thicknesses- like ceramic fibre blanket but more compressed and much thinner. I'm about to order some for another purpose. Durability is going to be poor when used in contact with the fuel, so it's back to the coatings question.
