So after very little time with the the simple fire… I couldn’t help myself and started messing around with a single flute down draft. It’s not a great design and it’s too small to be useful. I was hoping to be able to get a flare and get some practice running it before spending too much time on something bigger. Below is a quick sketch of what I’ve got. The flute is 6 inches above the grate with 4 1/8" holes. I formed an ash cone around the grate. The grate itself is 3"x2" with 1/4" slots cut into it.
So far, I haven’t had any luck getting a flare. I’ve heard it can be hard getting a flare with out a water drip. I don’t have a great setup for a water drip yet, but was hoping I could get by squirting tiny bits of water into the flute. It’s been a nice learning experience, but now I’m a little stuck. In a previous attempt I think I had the flute way to close to the grate, not having a large enough combustion zone to consume all the oxygen. Now that I’ve moved it farther away from the grate, the output gas is way hotter. I’m assuming because of the larger lobe of glowing charcoal? Even with an aluminum gas cooler it ended up killing the blower eventually. Whoops! I’m going to pressure test everything again. But before I ran it everything looked good.
The weird thing is, I was able to get some puffs by running the blower on high for a while then dropping it down to 75% and giving it tiny sprays of water. I’m trying to figure out what this is telling me but can’t tell for sure. You can see what I mean in the video below. It almost seems like I need it hotter, but with a slower air flow? Perhaps I need to smaller air inlet holes and the air focused on a smaller area? Also if I’m getting gas that hot, does it mean I’m not getting the endothermic effects of reduction?
Really? Wow! I was thinking I would need to go the other direction. That’s an easy change I can try.
I pressure tested at 10 PSI. The only thing that seems a little sketchy was the lid. I had some leaks there on an off but thought I got it under control. The leak would have to be right around/after the combustion zone in order to ignite right?
Yeah you would see a hot leak somewhere at the bottom. If you’re not seeing any bubbles from a soapy water test then it isn’t leaks. I’m a little surprised your gas is that hot. With that much charcoal between the jets and the grate it should be pretty cool.
Have you considered dropping the grate to the bottom of that cube shaped reduction? Would give you more char bed distance.
With direct downwards facing jets they tend to bore out a void since it’s path of least resistance is directly below, and it’s hard for the charcoal to fill in the void since the pipe is blocking the way.
If you’re able to either change out the nozzle pipe or rotate it without too much work you could experiment with holes pointing downwards but outwards at a 45° angle on either side. They’ll meet back down but it will elongate the combustion zone, and if you add water drip it will give the water a chance to properly evaporate and add more efficient hydrogen.
I’ve bounced this around in my cranium a few times and still don’t understand where there is any advantage to downdraft charcoal. Could someone please explain it to me?
Tom, what Cody sayd. Also, you can dampen your fuel with about 15% water wich eliminates dust when handling fuel and eliminates the need of a water drip. The gas is also dryer because in an updraft any moisture from the char gets in the gas and dilutes it. I once calculated that even if the gas gets cooled and condensed, it still contains up to 10%vol of water vapor. Not a neglible amount.
Also, updrafts require frequent dumping out because ash buildup. Makes long runing machines a pain. Downdraft basicly never needs to be emptyed and most of the times you can even refuel with the motor runing.
That makes sense. Especially the ash build up. I have one charcoal gasifier I built with a grate that could be reworked to run down draft pretty easily. I’ll work on that after the harvesting and processing of the garden is done.
Thanks a bunch Cody! I’m getting ready to tear it apart so I can move the grate to the bottom of the reduction zone and change the flute like you suggested. I was also considering replacing the ash cone with ceramic insulation. I saw you had that in one of your builds. Did that work out alright?
It is a good idea but don’t use ceramic wool without getting the rigidizer, and when handling the wool please wear gloves and a dust mask. It’s as dangerous as asbestos. The rigidizer helps keep the wool from falling apart and making dust that’s dangerous to breathe.
I think you can do fine without it, ceramic wool is just a bonus.
Thanks for sharing your design trials, I want to build a down draft for a 4 cyl, pickup truck, I wish there was a true and tested book for a complete set of plans like the have wood will travel book,only four charcoal powering a 4 cyl vehicle. I will be watching your designs.
hello dan and kevin, i am actually working on a 4 cylinder engine for charcoal - look at my topic historic woodgas tractors - we have had recently the first test run , sucessfull, for a half hour…than we stopped because there is to do with the engine…oil circuit, water circuit ecc.
there is nothing easier as charcoal gasifiers, you need only good charred and sized coal, relatively dry…
in this build i have made updraft, but gas exit not on top but approx half hopper hight. and this can be regulated by pipe lenght, more down or more high…
i look in my gasifiers to have always enough protection coal around the hot area to avoid metal damaging…
it must not be stainless, also steel barrels or propane tanks work well…
look also at eddy ramos page, he has described his system for his truck
The gas is still pretty hot but I think that’s just because the vacuum motor I’m using is way over powered for this little guy and the fan controller I had didn’t go low enough.
I’m planning on adding a cyclone to hopefully cool the gas a little more and remove the embers shooting out of the flare and also slowing the blower down. But, when sizing the blower or the cyclone, are you cutting the CFM draw from the engine in half? With a 1:1 air-fuel ratio and the air being pulled in after the gasifier and cyclone would that be correct?
Dan since that’s a universal motor you could just run it off of a battery. I have a Lamb motor as well and tested it with a 12v car battery. Still felt strong but I bet at 120v it’s intense.
Also you don’t necessarily need a cyclone but since you’re using it for cooling, you could build an oversized cyclone that won’t have as bad of a pressure drop. I go by Steve A’s simple guide. There’s many ways to figure your cyclone size.
Basically just take the diameter of your outlet pipe, and the cyclone body will be 3 times that.
Edit: if you are planning to use this in an engine that’ll be at a mostly fixed RPM then a cyclone will work great. Their efficiency is best in a certain zone that is defined by its dimensions.
Ha! I just assumed the blower wouldn’t run on DC. Wish I would’ve known this the other day
I was planning on running an open frame generator, but if I ran an inverter generator I wonder if two different sized cyclones would help account for the fluctuation in RPMs
You dont need to build a cyclone. They are way more work than they are worth,. Just build a media filter out a small drum. They will cool the gas much better as well.
I personally don’t use cyclones, but I wouldn’t run them in series. I’ve heard of them being ran in parallel but only identical sized ones.
If you use a small barrel for a filter body you’ll cool the gas down well enough. I would consider adding more cooling tubes though, or extending the tubes you do have. If your gas is running hot out of the cooler then that vacuum motor is running the gasifier on the razor’s edge.
For your filter if you’re worried about embers, you could use two drums with one bigger than the other or a drum and a metal bucket with a lid. Weld the bucket/smaller drum into the lid so the smaller drum acts as a baffle and a place to put your filter media. You’d cut out the bottom of the inner drum and maybe weld or bolt/rivet on some expanded mesh to hold the media in place. This setup would double as a drop-box and filter in one spot. Maybe aim for drums that would have an inch or so of space between each other, so a 2" diameter difference if you can find it. If you wanna get real fancy, have the dirty gas enter on a tangent to make the gas go around for a cyclone effect instead of running right into the side of the inner part.
You could also roll up some barrel material or whatever and weld it to the inside of the lid of a drum, instead of blowing out a hole for a bucket just weld in a gas outlet in the center. Lots of ways to skin this cat. You wouldn’t need a very big outer drum either.
Thank you Cody. That’s way simpler. I’m glad you guys talked me out of the cyclone.
I was going off of old posts, and it’s cool to see peoples recommendations change with all their experience. I would have thought you were all about the cyclone Matt. Im saving tons of time thanks to the hours you guys have already put in. So thanks again!
