Nozzles in the Firetube and sizing

How about a discussion on this, hole size in the nozzles or tuyeres. How many nozzles do you need. Odd or even numbers of Nozzles. The velocity of air coming out of the nozzles according to number and hole size of the nozzles or tuyeres with engine cylinder displacement.
Firetube sizing and length and Thickness with high and lower velocities of air.
Why are simple drawings of air flow coming out of the nozzles or tuyeres in a fire tube down draft misleading?
First of all the firetube is full of charcoal and blocking the straight flow out of the nozzles. The air has to go around the charcoal pieces to get to the center or down into the firetube.
Higher velocity air pushes the charcoal away from the nozzles or tuyeres opening a lot more then lower velocities of air out of the nozzles or tuyeres.
So where is this white hot lobe of charcoal we are talking about in the gasifer firetube? Is it where the most oxygen is located?
Where the charcoal has lost most of its moisture content in It?
Where the velocity is stronger or weaker?
Lots of variables, one thing is all the air is subject to the vacuum pull out of the nozzles and turning into gases in the firetube full of hot charcoal and going through the restiction opening finishing the prosses as it makes way to the grate or grateless charcoal pile.
Any ones input on this is welcome and appreciated.

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That is exactly how I would have explained it. Have you ever experienced how absolutely short a time you need to hold a torch to the lighting tube? Only about 3 seconds here gets a bright orange glow that quickly turns white hot and like Wayne says reduces in size while farting gas. That size reduction makes room for the next char in line and so on. Amazing really.


As you say Bob, there’s so many obstructions in the burn area that air flow is certainly not linear,probably each jet flattens, dissipates and rounds out pretty short travel. So my 2 cents is that odd or even number of nozzles is irrelevant, superstition really. Even if there was nothing in the burn area the air jets would be off enough due to random imperfections that they will not meet or vortex in the center.


When I was building my simple fire char gasser. I wanted to see what the air collum coming out of my virtical nozzle looked like. So, before I loaded the charcoal I injected some smoke through the air intake with a bilge blower held next to some smoky embers I had put in a metal pan held close to the blower. It looked pretty cool.
My blower was a tired 130 cfm bilge blower, but it still made good gas.
I got a nice cone of smoke, coming out of the nozzle. Looked just like the pictures I had seen, when I was researching wood, or char gas. I tested my metal buckets for air leaks by injecting smoke through the air intake, and pressurizing the the bucket while the gas outlet was closed almost completely. By using a bucket vac. with a dimmer switch in the power cord. I was able to change the air speed. Faster, or slower.
By increasing the air speed I noticed the cone form a bit farther from the nozzle. Too much air speed and the cone does not form.
My dimmer switch only allowed me to slow down to a certain point then the vacuum wold shut off. That was where my char gasser made the best gas. On an empty wood gasser you could see what the air is doing when it comes out of the nozzle s.
You should be able to see your air spray circle inside your gasifier while looking down inside with the top open. Hope this helps

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Another factor overlooked that throws off simple visualizations is that the hot char chunks will be surface and ~1/4" (4-5mm) below the char chunks surface outgassing converting.

At low forced flow past; and static conditions; you can see this as surface pulsing.
Outgassing. Then flow stripped away. Heat conversion outgassing building again. Repeat. Repeat. Repeat. So long as the flow is not changed.
At higher induced flows. this pulsating does not take place. With rapid surface stripping away.
AND that in my opinion is when you are making carbons soots.

Not enough hot enough makes sticky tarry soots.
Too high of forced flows makes dry soots.

Just what I’ve observed.
There is a fairly wide sweet spot of best conversion range. Find this. Operate there.