I think you could benefit from visiting my site
“My first small engine run” in the small engines section
on this site. I have a stationary system where I had to address
the very items you will encounter. Some reading may give
you answers and insight to the entire stationary build
and the handling of gas,tars, filters etc. My site is an extremely
well documented build of a stationary unit for running a
woodgas driven gas generator. Many of your questions will
be answered there. If not feel free to pick my brain. Be
specific about your questions and reference my answers
if you have any questions.
Again some been-there tried-it-done-it feedback Mark Thompson on the using woodstoving logs to gasify with.
This CAN be done with efficiency on huge large scale systems. E.G. the Australian 1930’s to 1960’s experience of, “A Whole Town Powered By Wood” (for distributed out electricity).
Small scale I and others have fallen into this rabbit hole and spent years before climbing back out.
You really need to library read here on the DOW and under stand just how critical the TimeXTemperatureXTurbulance factors come into play turning raw wood into engine grade woodgas fuel.
Stick-wood/logs and you loose finite control of the Time-in-Residence; and the Turbulence factors. Have to go super wide area; super HOT to get gasification results. Your wood-in, to gas volume/quality out, efficiency sucks badly then. Like maybe only 15-20%. Good wood gasification consistently comes in at 70-75%.
Pre-chunking up the wood to the gasifier selected size/use gives you control over the in gasifier Time-in-Residence and Turbulence factors for the best thermal/chemical conversions.
Been there. Never waana’ go back. I’ll save the logs and trash/difficult woods portions like pitchwood, barks, and actual rot-wood for my eats-all wood heating stove.
A raw wood gasifier is souffle making. Not ham, eggs and potatoes cooking.
I honestly think you would use more energy in the 1300C stainless steel, then you could recover from the woodgas. It needs to be 1100C for .5 seconds which actually could be quite a long tube for a 22hp engine. It is cheaper and possibly easier to get the tars to crack on the charbed.
The same goes for the electrostatic filtering system, which will use less power but I am unsure of anyone that has DIY’d one either.
I wouldn’t use limewater. It would add moisture and you don’t really want that. NG’s combustion gases are mildly acidic as well and it used to be with those tri-fuel generators, they had different carbs and compression but also had slightly better corrosion resistant metals that resisted the pitting from acids.
Matt was talking about the rings which are wear parts and essentially saying it won’t matter whether you use NG, propane, woodgas, etc. it will all have the same problem. IF You are paranoid about tearing the engine down because of tar, you can try charcoal. Or you can use like seafoam or marvell mystery oil to clean out the engine.
Electrostatic filtration is a far better way to go. I have a friend that tested it, l think he used 2 TV transformers each about 100w on a filter that was hooked on a realy badly gasifier (tar machine) and run a Fiat 500 engine just fine. The filter was big and bulky but it extracted preety much everything. Tar, soot even water mist.
Here is an electrostatic precipitator. He is using a High voltage power supply, but doesn’t mention what voltages he is using. A tube tv, or a microwave would have HV transformer in it. Also the HF electronic flyswatter has a small hv boost converter in it.
You might be more interested in this. They are using a microwave, a catalyst (aluminum oxide/nickel) for a fluidized bed reactor. This may be more appropriate for the hemp thread because of the short fiber length.
So here is an idea. What IF; we take a wood gasifier and combine a charcoal unit in the lower. (bare with me here; this is different than my other like experimental, stuff.) Let say in the charcoal unit we isolate its produced gases and fully oxidize that gas before mixing with the produced wood gas before leaving the reactor / Ash bin. You would get more than enough heat for tar cracking. It would be direct heat to the gas as well and recover the char waste, most are just going to throw it away anyways.
Isn’t the major selling point of the downdraft gasifier is woodgas goes over the charbed to do the cracking and thus less tar to deal with?
If you are getting that much char in the ash bed, it seems like it would be easier to add a small secondary air inlet by the existing charbed, which in effect turns it into more like a Dasifier as that is a downdraft, then has the updraft that goes through the ash/char bed then you take the gas out in the middle which is in the middle of the char bed. (the char from the downdraft portion extends up from middle a bit)
Tar cracking is accomplished pre char bed / reduction. The char bed / reduction process is a stripping process of ripping the oxygen out of the molecule chains and re combining with the carbon. Im sure some tar cracking is happening here but this is not the main process or reactions that take place here. Tar cracking is the point of the restriction bellow the hearth oxidation zone.
Typically 15% of the fuel consumed in process is left char ash. This 15% is actually quite a bit and can indeed be put back into process. Especially if you add steam reforming to compound that 15% into much greater input back into the system.
Ive built a few machines with both processes combined. I had a machine at last year Argos event that could do this.
No there should not be any oxygen here. It should be fully consumed at the oxidation process in the hearth. That is sort of the point. to enter enough oxygen into the system to oxidize the fuel enough to where the chains are simplified enough for further tar cracking and then stripping down to simpler chains, (your H2, CO and CH4) There are some complexities here at the oxidation level of why the machine may produce tar. More complex chains maybe more difficult to crack. Cause for this could be many factors, insufficient flows, wet fuel etc. Thus resulting in less heat to deal with cracking compounding this issue further.
Physics first, chemistry second.
The reduction process is endothermic, this process is something that is fighting us the entire way. The higher your temp differential from pre reduction to post grate the better your process is.
This is why you go from 1600f and beyond at combustion level to just 400 or even below gas temps as the gas leaves the reactor. That is a huge drop in a very short distance and is not from radiant cooling.
Oxygen should be fully consumed as part of the oxidation process otherwise the oxidation process will continue to burn up the gases you want. However, you need heat from the oxidation process to drive the whole reaction which includes thermal cracking as well as partial oxidation so there is a delicate balance.
There isn’t enough heat from the oxidation process to sustain the cracking process in the char bed. So I believe what we are talking about is how to add heat to further assist the thermal cracking processes.