Hello all- My first post here. Found this forum while researching gassifiers & how to improve after buying one of the small Chinese camping stoves and being disatisfied with the dirty burn, sooty cookware and smoke. This is an identical but differently branded stove to the first generation Lixada shown in several posts here. This is unmodified, gas combustion is mosrly above the stove. Primary air inlets (bottom) are WAY too big, draft is insufficient to draw in enough air at secondary (top) inlets. Some back of the envelope calculations were in order... Then a tin can end disk from the recycle bin, a quick visit to the hardware store and out to the shop A HVAC 3" to 4" adapter was jurry rigged as a stack to increase draft- And here we go, 300 grams of softwood (pine) pellets, sold as bedding for horse stalls, $5.00 US $ per cubic foot bag. That's better!!!
Cool. Would a wrap-around adjustable damper work in an adjustable way to reduce the size of the 'bottom' holes? I do that with my cat food can alcohol stove. AND ..... Welcome to CCS.
Thanks! I drilled out TWO can ends in a stack, with the intent to put a rivet in the center hole and be able to twist them in and out of registry to damp the primary air inlet. Maybe tonight. I didn't know that editing was cut off at 10 minutes, if a moderator could clean up the post by putting the last two photos into the spaces as I intended...
Tonight I tried several things in hopes of increased fuel efficiency and a cleaner burn First, adding a circular set of vanes in front of the secondary air inlets, hoped to get the combustion "swirling" for better fuel/air mixing and a cleaner burn. Second was to insulate the outer wall of the stove from the open air around the secondary air inlets, I hoped hotter air entering the stove at the upper inlets would increase efficiency. I made the vanes out of a section from the end of a 29 oz. size tin can. For insulation I sacrificed a woven heat shield I used to use as a flame guard while sweating pipes near flammable walls, cutting it into strips and wrapping the double walled section. My attempt at producing better mixing with the vanes did not work, the obstruction to air flow by these vanes in front of the air holes cut down on secondary air, lots of gas was emerging and burning above the "stack". When I removed the vanes, the area where the gas burned moved back down towards the seondary air inlets and proceeded much more smoothly. The insulation seems to be useful, the burn after I insulated had the least flame visible in or above the upper stack so far, it also started to gasify a miute or two sooner. The flame pattern was more "stable" than the burns without insulation as well. I would need to try timing boiling a liter of water with and without tge insulation to be sure- Maybe Sunday. Got to work Saturday night.
Hi @Robert Rowe, welcome to the Land of the Free (wood) and the forum. Yep first step is reducing the primary air to approx 5% or slightly less. My next plan when time permits is to add a recuperator in a similar manner to your excellent effort. I will return to your results at a later time when I come to make one.Interesting your vanes caused too much interuption to the flow` although I was thinking of fewer larger vanes. With the original grate it.s really just a chicken feed open fire rand not a gassifier in the intended sens, and the wood pellets seem to offer the optimum fuel source. You can achieve a good 30-40 mins burn time with a couple of handfulls of the stuff. Going to have to do an OMC and rush off, but thanks again for experiments in gassifier terratory.
Nice work and excellent photography @Robert Rowe Welcome to CCS. Great to have a fellow enthusiast on board. John
What the members who are tweaking the gassifier hardware here probably are looking for in these cheap, cute little naturally aspiratated, no moving parts, no electricity required burners is the most complete burn possible to fix the "sooty everything" issues. Which may also provide lower CO emmision and better fuel use efficiency. Plus, we get to photograph really cool looking flame patterns! Biomass may be cheap where we live, but using it poorly is messy (tar, soot, CO) and, since I'm kind of OCD about efficiency, personally unsatisfying. Getting the fuel to smoulder, char and offgas, then (mostly) burning the gas at the secondary air inlets before it reaches the cookpot/open air was pretty easily accomplished (thanks to other members previous work- I appreciate the information I got here, thanks!), Adjusting the ratio of primary to secondary airflow while providing enough "draw" gets much better efficiency than the "as supplied" stove. Pitty the original and knock off manufacturers don't design for well tuned burners, but hey, their stove designs were already good enough that people buy them. Youtube is full of videos by people with flames shooting several feet out the top of their stove who think this is awesome... They can't see CO, may not think much about % efficiency as long as water boils reasonably quickly- but would appreciate not having soot on their pots. As mentioned earlier, bad case of OCD about efficiency here. And just enough engineering knowledge to be dangerous. I am reading some research papers on topics that seems to be related to igniting the residual fuel gasses that didn't combust fully near the secondary air inlets and are wasted as fuel, plus depositing soot. Low oxygen dilution/high-temperature air combustion is the term I'm seeing engineers use. Getting a small ammount of fuel in a hot, mostly Oxygen depleted gas mixture to burn as completely as possible. Engineers have been here, there is information related to devices such as high efficiency internal combustion engines and industrial heating burners. The philanthropic and educational groups trying to help improve women's health plus lower greenhouse gasses with better stove designs have some testing facilities working too. Several have stated that one needs forcred air to accomplish soot free burns. For me, adding a blower runs counter to the simplicty and low cost that made the gassifier stove attractive. How far can you go with a burner aspirated purely by convection, just tweaking draw, stack gas and air flows? How complete CAN combustion at the secondary air inlets get? After getting what burning you can done at the secondary inlets, adjust gas flow pattern/dwell time in the stack above to favor a lean burn, mix in some more pre heated air and have a 3rd burn zone? Put a ceramic mesh or other surface in the flue to trap and burn the soot at, similar to what my truck's diesel engine has? Anyone got ideas?
Checking on the industrial side, lots of papers on the how and why of soot being formed in the first place (we can't stop soot from being formed completely, it is intrinsic to the way biomass pyrolizes. We CAN lower the quantity). The physical requirements to burn off soot before it escapes the flame. To prevent soot being emitted? Thorough air mixing, proper air/fuel ballance, ensure high temperature flames, don't run burners at low output, keep partially burned mixtures of gasses from being cooled (as in, touching a relatively cold piece of metal filled with water!), prevent low oxygen areas from forming in flames. HAVE SUFFICIENT OXYGEN AT THE TOP OF THE FLAME ENVELOPE TO BURN ANY SOOT WHICH HAS FORMED. So, the 3rd set of air inlets might be good, as long as they don't cool the flame- You want pre heated air, same as at the secondary inlets. Just punching some holes further up the stack may be counterproductive. Also, methods for turning hot soot into flammable Carbon species (CO) so the Carbon can be burned to CO2. The most promising one looks like injecting STEAM into the flame, just a few % of the weight of your fuel, not too much. Don't think it would be workable for this application, but for a home heating furnace? Yes, with flue gas monitoring and automatic controls. It's done industrially, places that "flare off" hydrocarbons in particular do this. Adding a second air heating jacket feeding hot air to a 3rd set of air inlets in the stack a bit above the secondary inlets is where I would start. Insulating the outside surfaces of the stack too, keep the gasses hot and well mixed with sufficient preheated air at all zones above the fuel gassifying zone. Let's science the F*** out of this soot.
Been reading the ARC PDF "Clean Burning Biomass Cookstoves". Would upload it here, but it's too large a file. Link here: http://aprovecho.org/?paybox_id=139 I have been re-inventing the wheel. I was proceeding more or less in line with some of what ARC had designed, at least- Now, with the parameters from ARC, it should go more quickly. Trying to design and jury rig modifications onto the cheap Chinese TLUD stove, it might have ended up functionally equivalent to the "Kirk Harris Natural Draft Top-Lit Up Draft (TLUD) Stove", the second high efficiency/low soot & CO design shown in the PDF. Going forward: Make a small fan blade shaped "swirl inducer" to mount centrally just above the secondary inlets, regardless of how the 3rd inlet is accomplished. Mounted far enough away from the secondary inlets to not reduce the airflow in, as my first attempt using peripherally mounted vanes did. Possible embelishment? Use a vertical, centered TUBE running up from the bottom of the fuel pan, mounted over the center one of the primary air inlets to support the swirl blades instead of a plain rod or bolt as the Harris design did, carrying the top of said hollow blade support up well above the blades, discharging the hot (and normally oxygenated) air rising through this tube as the 3rd air inlet. The top of tube would be closed, drill a number of radial holes near top and discharge this "afterburner" air horizontally. Would want to be able to adjust draft on that inlet tube/blade support on the fly, also the draft on the primary air inlet (which Harris does). Leave the secondary inlets as they are, tune the gas generation below and afterburn air supply above around the existing second stage air.
That was a bit of resume of what we in Vestaland are currently working on. DrTLUD has been my source currently amongst others. Sadly TLUD trials this end have been suspended for a while but your detailed investigation is certainly in the area I'm hoping to explore further decorating permitting.
Thanks for the reference to DrTLUD! More time spent reading- I have attached, lots of design information on just a couple of pages TLUD Basic Design Parameters http://www.drtlud.com/?resource=prt15740
I have been trying a few more experiments. Added a central air feed of a 1/2" ID Copper pipe, emmited as 3rd air feed about 2.5" above the secondary air vents. The apparent quantity and radianceof the "flames" leaving the stack went down quite a bit- As much of the visible light from a wood flame is black body radiation from hot particles (soot, largely), I suspect that more C is being burned in the area between secondary air and top of stack. Burn time per weight of fuel used did NOT increase, it went down a couple of minutes. Soot deposited on pot during a test on heating water was markedly less than the unmodified stove, see picture. This was a 29 oz. can with 500 ml of water, left on fire from beginning of gassification to end of visible flames above the remaining charcoal (about 18 minutes). Covered, the water boiled in less than 8 minutes. No wind shield or sleeve around the can, open air with light & variable winds, about 40 F. I would need to remove modifications (and set up a wind shield to remove weather as a factor) to test changes in real world performance (heat transfered to water, Carbon deposited on pots). Maybe later. Right now, I'm building a fan blade to "swirl" the gasses above the secondary air vents, and perhaps a damper for the 3rd set of air inlets.
