I wonder if this reply I got from Wayne has any relevance to this problem?
This next comment is in the Premium section. I’ll try not to copy/paste too much from there but there is a lot of information in the post including a bit about the size of the fuel.
If we have a big and deep char bed and our driving habits are slow the reaction will be taking place high in the char bed and the ash or very fine carbon dust will begin to accumulate just below this area. After a while the char bed will begin to plug the gasifier.
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Also the the restriction plate can be moved closer to the nozzles and the restriction diameter decreased . This will let the oxygen plum get closer to the grate for better purging.
Hello. Building on what has been observed by you JanA.; ash at the restriction. What J.O. has said. What BrianM. has quoted.
Reverse think this way.
Accept that the natural cell walls of different wood species; and even cut portions of the same wood species varies 10 to 1 as a percentage of remaining cell walls mineral ash.
So you either have to specially design the gasifier hearth to handle a 10%+ ashing wood.
The WK does this much by a relatively large restriction and a larger above restriction active volume than below the restriction. Intentionally grate slipping-spilling a lot of char to move the ash downwards.
The so called Imbert does high ashing wood handing by keeping the gas speed flowing high. Why it falls down at low loadings. More than just a heat decline.
Instead for an already constructed gasifier find the wood species or wood portion it can internally ash handle. This operation change works. Conifer woods without bark are very low ashing. Used VERY DRY helps minimize their make-tars tendencies.
Me? Why now I will only use a command active grate system. Does wonders for variable ash handling. Not then not having to be so dependent on internal gasifier fixed dimensions and gasifier variable loadings.
Steve Unruh
Good point. If that’s the case, all you have to do is shrink the hight between restriction and nozzles. But it takes a while to establish such a tube/cone, and meanwhile…
Do you think something happens when restriction is right?
SMP has (almost) these dimensions as a recommendation, they changed from 265mm to 300mm on the last drawings of the fire tube, for the small engines.
How far do you have it between the nozzles and restriction on the Volvo?
I had 12 inches between nozzles and restriction for about a year. After that I put the restriction on top of a 5 inch tall cone and drove for another year. I couldn’t tell a difference. Maybe it ran a few degrees hotter for the same load - that’s all.
Yes Steve you have stated it correctly about the grate needing to slip char and ash through it.
If there is no grate it will slip out the side of the pile of Charcoal and fines of ash.
At low idling the Velocity of the air coming out the nozzles is lower. But as soon as you increase the idle to running speed the vaccum will increase and froce the char to slip through and off the grate by boring holes through the reserve charcoal bed below the restriction opening. You can actually feel this happening when driving. It is a slightly increase in power from a long time idling like a stop light or just sitting there idling the engine. If you stop at again right after the ash fines have cleared out and charcoal slippage has taken place, you can take off from a stop and you will not lose power. This is one thing the WK Gasifiers also have is the big turn down ratio. It holds the firetube heat in by introducing hot air in through the nozzles and not just warned air.
If at a idle the gasifier cools down to a point where tar is being not converted completely then at the point of increasing the air Velocity in the fire tube and a high vaccum demand tar might slip through.
So I always shutdown quickly from a high RPM or high velocities of the engine, when my gasisier is 1/4 full to almost empty in the hopper. I never let it just idle for a while and then shut it down if possible. I like to run the engine of gasoline for a little while coming home. Then drain my system of water in both tanks and then tar if needed.
Velik premer vroče cone lahko požira večje kose lesa , za manjši premer pa usrezajo manjši kosi , o tem piše tudi gospod Wayne. Če je omejitvena odprtina majhna , ne bo spodaj veliko oglja , saj bo ustavljeno zgoraj , dokler ne zgori in se spremeni v prah in pepel , naj povem še enkrat moj način za pretvorbo različnih velikosti lesa v plin , na vrhu je dovod zraka v premeru 350 mm , luknje so vrtane pod 45° (10) , tako da pokrivajo čim širše območje , nižje je vroča cona premera 230 mm , kjer se nahaja že pretežno oglje , nato se zoža na 180 mm in spodaj v sredini je šoba . Ta predel je vedno zasut z drobnim ogljem in pepelom , ki se spodaj dviga in umika v stran . Katranu je prehod popolnoma onemogočen , saj je spodnji del vedno razgret , ker tukaj skoraj vedno doteka sveži zrak , pomislite , dovod zraka je ločen od izhoda le z razdaljo 70 mm , ki mora biti zasuto z drobnim ogljem in pepelom.
Jaz se ne zanašam na pepelni stožec , ki bi tvoril vroče območje , pepel ohranjam le v predelih , kjer je potrebno tesnenje ali toplotna izolacija , vročo cono mora tvoriti oblika iz kovine ali iz šamota . Zelo me mika , da bi poskusno zgradil plinifikator z dvojnimi šobami , kot sem narisal v skici
Goranov Volvo
The large diameter of the hot zone can swallow larger pieces of wood, while with a smaller diameter, smaller pieces are cut, Mr. Wayne. If the opening of the restrictor is small, there will not be much coal below, because the above will be stopped until it burns and turns into dust and ashes, let me tell you again my method of converting different sizes of wood into gas, there is an air inlet at the top with a diameter of 350 mm, the holes are drilled at an angle of 45° (10) so that they cover as wide an area as possible, lower is the hot zone with a diameter of 230 mm, where most of the coal is already located, then it narrows to 180 mm and at the bottom in the middle is the nozzle. This area is always filled with fine coal and ash that rises below and moves sideways. The passage of tar is completely impossible, because the lower part is always heated, because fresh air almost always comes here, think about it, the air inlet is separated from the outlet by only 70 mm, which must be covered with fine coal and ash. I don’t rely on the cinder cone to form the hot zone, I only keep the ash in areas where sealing or thermal insulation is needed, the hot zone must be formed by a metal or fireclay form. I’m very tempted to try building a dual nozzle carburetor like I drew on the sketch Goran’s Volvo.
Tone, I read it with my translated text on my phone and it does make good sense to me. Because of not having the turn down ratio like the heavy WK gasifier firetube in the baffling air preheating part. your written method with Goran Volvo drawing firetube is another way of keeping it hot at lower velocities of air moving through the firetube. A different approach but the same results. Making good gases. The big plus here is a much lighter weight gasifier that still makes good gases with out letting tar to pass by.
You must lay awake at night thinking all about gasification stuff.
Jan, yes, ash/slag in any pure charcoal gasifier is something you have to live with. Its a tradeoff for the other benefits that charcoal brings, like simplicity and low weight. In a wood gasifier however, thats not a good sign.
Too often we take just the hearth dimensions as the actual “gasifier” but in truth, the gasifier is the whole unite. Air preheat, fuel preheat, monorator, hopper volume… they all play a important role. So its hard to give someone direct directions on what to do to make things better.
Will try anyways. What you describe all hints to the fact that your gasifier is too big for the engine. All the gases alredy react before they even reach the restriction. So, the restriction is actualy just a grate and the “reduction zone” is just a filter in your case, collecting dust.
If anything else works good for you perhaps l wuld first try drilling out the nozzles. That way there will be less turbolence in the hearthand oxigen will be sucked in deeper, towards the restriction where it can do its magic.
Ok, so that’s why it went so well last winter after I sealed it, because I ran on spruce and pine, this year I tried birch, and seems to get a much harder (tighter) reduction area?
It went well on conifers, I can feel the loose bed I get on the s10 when I drive conifers, much harder on birch, should be the same on ferret. Thank you, Kristian.
