Simple Filters for Simple Fire Systems

Too many household projects to get the MGB out. When I get some time, I’m going to install an O2 sensor and A/F gauge. I’ll report on start up times when I get her back on the road.

Thanks for the thumbs up. For my Africa rig, I’m keeping your maintenance advice in mind: full clean out of reactor and filter every day.


For the Africa gasifier I will need to add something that gets occasional mention in the old literature, but has been largely overlooked by those of us who drive on paved roads. The dirt roads will require a filter on the primary nozzle inlet. It has been reported that the dust entering the gasifier can make its way into the gas stream and cause significant engine wear. Perhaps a safety filter at the engine will do, but an ounce of prevention is worth a pound of cure. What are your thoughts on this filtering issue?

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I agree with your proverb but l think a gasifier produces a lot more dust thain the air holds. Til sugests chargas is as such wery rough on the engine if not cleaned properly (opposite to woodgas-the moisture participates out together with most ash). And l agree. I think a sack filter or a paper filter is a must with chargas. I was wery pleased with the arrangement on my Seat, first a towel filter then a air mixer, then the gas/air mix passed the original paper airfilter.


Hi Bruce,

What engine you’r going to run in Africa, hence what’s the size of the gasifier ?

I also use ( sometimes) an original sportsfilter in line with the engine to filter out the unwanted particles. But mostly not needed if the foam filter is been maintained daily.

Thinking of: what about the oiled filters they use in motorcrossing ? clean the large hole’s sponge, then soak with sticky oil, squese out the residu ond of you go…


250cc engine. 10 inch diameter gasifier. Height is 30 inches of charcoal above nozzle. How long will this run under load before refill?

I too had oiled foam motocross filter in mind for gasifier air inlet. That is what I use for my mixing air filter on the MGB.

I intend to use a cyclone followed by two vertical 4 inch X 30 inch PVC cylinders in series for the main gas filter. First one filled with stainless steel scouring pads and a piece of oiled open cell foam at the top exit. The second filled with polyester batting or wool sock. I may add a final safety filter just in case someone isn’t careful with these main filters.


Hi Bruce,
I’m in accordance with Kristijan. I suggest a fabric filter for the gas (felt, fine woven filter cloth or similar) which is the best for dry charcoal gas but I think no filter is needed for the generator air inlet. The gas should be filteres anyway, so some road dust passing the generator is caught here.
Maybe extend the air inlet to a higher level where there is less dust (similar to a snorkel on some 4WDs).
Regards, Til


Thanks, Til. Makes sense.

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So, it quickly became evident that my filter was too open and let char dust pass. I cut a couple discs of old towel to go between furnace filter material. I think that should catch the fine stuff.


Looks good. How’s it so far?


Have not run it sincee then.

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Stuff tends to follow the wall of the filter vessel and may slip by your discs. Many have followed Gary G. who uses a block of foam rubber that he cuts round, and slightly oversize, on a bandsaw.


Of course the flow will follow the path of least resistance. My original course filter has no discernable resistance to flow, so the dust settled right in line with the center pipe and started to spread out from there. The towel discs are a bit oversized so im thinking the other disks will hold them tight to the wall.


Due to a very hot and dry summer here in Australia , i have not had much need to run my charcoal generator that often the past few months , well that was up until a few weeks ago when i noticed the lack of sunshine on my panels due to the smoke from the bushfires and then 4 days ago clouds covering us for about 4 days , i live half way up a mountain and so we often have our heads in the clouds up here and its at least 4 degs cooler .
I have limited amount of charcoal left to see me through the fire ban period , so no burning off out side and far too hot to light my wood burning stove indoors , that’s where most my daily engine running charcoal comes from , and so the other day i ran my generator a lot longer than normal , well till the engine stopped if i am honest , and to show you what i found the next day when i went out to refill my system .
First i have to let you know that i have changed my typical 55 gal updraft Gasifer slightly i have a 30 gal barrel within the 55 gal drum while experimenting and not got round to changing it just yet ,and anyway this is what greeted me when opening up and cleaning my system .

notice the white ash covering everything !
this is the lid

from the outlet fitting on the lid the 1 inch pipe goes off to a cyclone with a condensation trap on the bottom ( forgot to take a photo of that as there was nothing showing in the jar at the bottom , so strange will open that up in a while and maybe the cyclone is gummed up with damp charcoal dust )
from the cyclone it feeds into a 8 inch x 32 inch tall thick walled tube that was once my small gasifier , this tube i fill with open cell foam and lambs wool , this tube i have now found out was once part of a sausage meat stuffing machine

this is the open cell foam and lambs wool

Again you can see that the white dust has managed to get past the filter material and carry on up stream towards the engine where i have the last line of defense , and that’s a inline water filter with a fine mesh basket , and i have wrapped a small piece of micro cleaning cloth around it this is what it looked like before and after i gave it a wash out out

So the next photo is the inlet barb into the gas/air mix valve

And as you can see no white dust what so ever managed to get past that micro cloth and into the engine .

Ok so now what do you think that white dust could be ? , i have always had a little on the outer walls of all my gasifers builds when i have run low , but never this amount before maybe its a mineral or something along those lines
I have decided to pull my finger out and do what i said i would do a year or so back and try building a simple downdraft charcoal gasifier i have 1 maybe 2 idea’s i want to try and wondered does anyone else have thoughts on what they they would try ? i know Kristijan’s multi nozzle downdraft looked real good and had plenty of gas .


On another note Dave, how far are the fires from you? Seems if you went to where the fires were you could probably scrounge up a couple years worth of charcoal. :smiley:


Could it be high levels of particulate matter carried by intake air? (i.e. airborne ash from the fires?)

Hi Dave,
Not so much things that it could be … :grin:
I think your gasifier is well tuned, so that your ashes actual travel with your gas stream and not form to much of a clinker… ( fine dust particles travel far downstream… )

For Charcoal gasifiers , as i build and use, a combination from coarse cell sponge , or stainless scrubs, with sticky oil, does the best trick, balancing the little pressure drop with sufficient stick on dust to the filter…

Next in line comes the good old oilbath filter…

I have to mention that any lower pressure drop equals a huge gain in engine power… But then again, i also run those engines without carb restrictions…


I am really looking forward to seeing what you come up with. I had high hopes of building a larger charcoal reactor to run a generator, but it has been pushed way off into the “someday” category.

I had thought about also trying a downdraft, but had not gotten as far as putting together a design. Keep us posted!


Dave, I’ve been thinking about you lately.
On latest news yesterday, they said the fires cover an area eq to 1/3 of my country. Made me realise the fires we had 1 1/2 years ago were small bonfires in comparence.
In the back of my mind I remember you live in the very south, close to Melbourne, right? How close are you to the NSW fires?
I wish you all well and I’ll do some rain dancing for you.


Hi All , Don you really really don’t think that i had thought of that :grin: There are 2 or rather there used to be 2 Large fire fronts 1 in NSW and one in Victoria where i live , now the 2 larger fires have met up on the border and is now 1 huge fire , trust me there is no way you can even get close to area’s that the fires have been through , police and residents are only just being allowed back to check and even then its not a pretty site , i am about a 2 hour drive from where the fires started i think , and i guess it was just the way the winds were blowing that took the fire front away from us here , there are still a few towns that are still cut off from the outside world and getting air drops of fresh water and food , there are still dozens of smaller but still life threatening fires going on all around Victoria and New South Wales , the last few days we have had a drop in temps and also some rain so that’s helping a lot its just the winds that cause worry .
On another note i just came in from running the generator again this morning and again i have run it right down till the engine stopped , at the moment its too hot to open up , but looking at the micro filter down stream that’s clean but for some reason today the micro cloth is soaking wet , of course living in the clouds my charcoal can absorb a fair mount of water even when stored in air tight metal drums , i guess condensation is to blame as well maybe .
Tomorrow i will be gathering the pipe fittings to convert the 55 gallon drum into a simple downdraft and try at least to get my 4 and 5 hour run times back that i was used too with my propane tank gasifier , i shall post some pics of what i have thrown together as this will be a real simple converstion ! fingers crossed and if i can get 6 or more hour runs i will be over the moon .
O by the way , the Thick-Wall-HEXOLOY-Silicon-Carbide nozzle i got from ebay thanks to Steve [smaresca] is still going brilliantly no wear at all and has been in since oct 2018 and has had many hundreds of hours on it , i have been waiting for it to need changing for so long now as i really want to test out the Tungsten carbide nozzles Bruce kindly posted to me from the USA so next week i shall be putting at least 1 of those tungsten nozzles into the downdraft .
Koen, you just might be correct in your thinking because i have never ever had to empty out ash from below the nozzle , only ever a molten slag mountain around the nozzle tip
Steve there is only smoke haze here and no particles as such floating around , just flying insects :laughing:


Hi Dave, I have been thinking about the white deposit you found in your gasifier and want to propose a possible scenario. There is always some ash in the charcoal and that ash content and amount is dependent on the source material. Grass, bamboo tend to have high ash while wood, especially if there is very little bark, has less. The grasses tend to have high silicone ash while the wood ashes are potassium and calcium based. When you ran your gasifier, the ash typically accumulated in front of, around and underneath the nozzle. I have found this easy to remove, seldom making a vitrified clinker but usually rather soft and crumbly ash. This material is made up of potassium and calcium oxides and probably some silicone. By the way, take some of this ash, wet your hands and rub some of it on them. It really cuts the grease and leaves your hands soft. In your case, the charcoal level kept dropping and all the ash in that charcoal collected near the nozzle. The intense heat vaporized this ash which coated the gas outlet and the filter. I’ll bet the material deposited is either an oxide or a carbonate of potassium or calcium. If it is a carbonate, it should fizz in vinegar. If an oxide it should make your hands slippery when wet. (be sure to rinse your hands real well because oxides turn into hydroxides that dissolve fat, Think LYE) Glad you did not ruin your engine in this rundown. I’ll have to get some of those microtowels and give them a try. Looks like a neat solution.
Take care and thanks for sharing.
Gary in Pa