Just a quick note... I apologize for my hands being present in some of the photos. I used photos pulled from the video footage. It certainly doesn't take anything away for this, but I thought it was worth mentioning. Moving on!

Gasifiers work on some very simple processes, so there is quite a bit of flexibility in the construction. The main parts can be labeled and explained in general terms while still conveying the ideas pretty easily. I'll start explaining from the beginning of the process to the end.

First stop? Fuel storage! A simple feeding hopper with sides that are steeper than the angle of repose for the highest friction coefficient fuel you could possibly use is ideal. But it's a just a metal bin. Anything that somewhat guides anything into the fire tube would be fine haha. Build it as big as you'd like! In my research, the general rule of thumb is that 20 pounds of wood is the approximate equivalent energy of 1 gallon of gasoline. So that'll be the determining factor in how long you'll be able to go in between refueling.

The fire tube is the next step. This is where the fuel is preparing to be burned in the shaker grate. The type of gasifier I'm showing you today is what is called a "stratified downdraft gasifier." This name is because of the operation of the fire tube. The air is pulled uniformly downward through the fuel in the fire tube, and, according to the informational that FEMA published on the use of gasifiers in 1989 for emergency use, there are four stages of reactions that occur in the fuel inside of it. I'll link the FEMA paper in the end of this Instructable. It's basically the Bible on simple gasifiers haha.

The stages work from the top down (downdraft.)

Zone 1. The upper-most zone is fairly uninvolved. This stage simply contains the unspent and unreacted fuel in preparation for the next.

Zone 2. This is the where the fuel starts undergoing the pyrolysis process. In simple terms, pyrolysis is the reaction of something being broken down into its elements through heat. The volatile components of the fuel react with oxygen here and are burned to produce heat for future pyrolysis reactions. All of the available oxygen should be spent upon exiting the bottom of this zone.

Zone 3. In this zone, hot combustion gases from the pyrolysis stage react with the charcoal to convert the carbon dioxide and water vapor into carbon monoxide and hydrogen.

Zone 4. Here is where your spent ash and carbon come to rest. However, they still play an important role in the process. The act as a buffer in two ways. It absorbs excess heat and oxygen, and it acts as a charcoal storage region. The action of it being a heat absorbing layer before the shaker grate can help to protect it from excessive temperatures and premature deterioration.

So, that's where most of the magic happens!! As you can imagine, the size of the fire tube is an important factor in determining the size of the engine that we can safely run. The more space in the tube, the more fuel that can react, the more heat and gas you can produce. There is a table with these numbers in the FEMA paper that I'll include down below.

Inside fire tube diameter (inches) Minimum length (inches) Engine power (hp)

2" - 16" - 5hp

4" - 16" - 15hp

6" - 16" - 30hp

7" - 18" - 40hp

8" - 20" - 50hp

9" - 22" - 65hp

10" - 24" - 80hp

11" - 26" - 100"

12" - 28" - 120hp

13" - 30" - 140hp

14" - 32" - 160hp

I know that's a lot of information for some welded metal tubes, but I think that you having a thorough understanding of what you're seeing can be pretty helpful.

After the fuel makes it's way down the tube it meets a suspended metal container with venting holes called a "shaker grate." This acts as a filter to deal with the used up fuel. The reason for the name and the need for it to be suspended is because it should be able to be externally agitated to sift down the excess built up ash. The straight forward way of constructing the grate suggested in the FEMA paper is to hang a stainless steel bowl with holes drilled in it from chains. It's simple, but effective. It's the way I built mine and it's held up quite well. I overlooked the shaker assembly in mine in the interest of simplicity. Running a moving part through the side of the reactor and keeping it sealed up was a pain in the butt in my first gasifier. I just drilled ample holes in the shaker grate to compensate for this and haven't had any problems. There really isn't a right or wrong way to drill holes in the thing either. I just got busy with a hand drill and a 5/16" drill bit.

Okay. now you're almost producing gas! Now, you just have to stick all of that into a sealed enclosure and run a pipe out of the side! I was quite pleased with the method of ash clean-out that I used in mine. It requires no tools to remove and it's just a simple remove it, dump it, replace it, and keep going. It also allows for easy maintenance of the parts inside. I show it in the video and it'll be easier for you to see than it is for you to try and imagine through my written description.

So that's the reactor! Unfortunately we can't use the gas from it quite yet though. It's too dirty and full of tar and other junk that we need to remove before piping it into our engine. That's where the need for filters exists.

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