I have just finished a new forge burner for a vertical welding forge I will build soon

it is a 1" burner main burner tube is 30cm long 1" stainless steel pipe the mixing chamber is 1 1/4" pipe 18cm long with 3 milled 25mm wide 7,5cm long slots the choke sleeve is 1 1/2" pipe flared at the end for smoother air flow
the 1" pipe was also flared for a smooth inside where it meets the 1 1/4" mixing chamber so there's no hindrance to the venturi effect.

sprayed a bit of Ford blue on it just for kicks

the flame holder is just black pipe and just for testing the forge i will build will have the shape for a flame holder cast in it.

here is a few pics









here is a few vids testing it

it is running with a 0,8mm MIG welding tip for the gas injector


whatya think?
will it be big enough for a 30cm tall by 20cm round vertical chamber ?

I have been thinking would it have made a difference (improvement maybe) with the burning and gas/air mixing if i had made say 6 slimmer slots for air intake??

and is the step down in size from the 1 1/4" to 1" "mixing chamber to burner tube" enough or will more, say 1 1/2 mixing chamber for a 1" burner be even more efficient??

all thoughts and input much appreciated

cheers.

Based on the video, I don't think you're getting enough air mixed with the propane initially, which is why the flame is predominantly yellow (propane mixing/burning with the air later.) In my experiance, moving the tip much further into the slots helps a lot with this. Somewhere between 1/4" and 1/2" shy of the slot's end. Basically, you'll get better vaccume, which pulls more air into the tube, letting it burn a bit hotter.


In my opinion, the "mixing chamber" is primarily just an air inlet. Mixing happens in the tube proper. As long as you have a surface area of the slots as big as the cross sectional area of the pipe you've got plenty of capacity. A larger diameter mixing chamber, just allows you to grow the slot area, really. I think you're fine as far as that goes.


Push the tip forward 2-3" and see what happens. I think you'll be surprised at the difference. At least, it helped my design signifigantly.

Kcrucible is right. You want maximum velocity at the choke-point in the venturi. I think you're losing too much velocity with the gas so far away. It's no longer a jet, it has fanned out by the time it gets to the choke-point.

AHA! so thats the problem will have to make a new longer injector
thanks you Kcrucible and Grant will report back when I get it done

The venturi principle is hard to visualize. We're no trying to use the gas to push air through the pipe, That only works to a limited extent. In a venturi the high velocity jet crates a partial vacuum which pulls* the air in. The higher the velocity at the choke-point in the venturi, the better the vacuum. With your air control open, you should be able to get a lean blue flame.

*I know, (technically) it's actually atmospheric pressure that "pushes" the air in.