Help troubleshooting a Venturi burner

[Jaja]

I  based the design off of  online research and some observations using another forge at a makerspace (not in my country). It was difficult to stick to a single design for several reasons, mainly sourcing the exact parts (took 6 months to order stuff online). So I tried to improvise.

First I couldn't get the burner to light at all, so I dug around for a bit and learned the air-gas ratio could be wrong. I played around with the intake size until I eventually got it to light. The problem is the very first time it lit the flame burned way too close to the jet and there was lots of sputtering and popping. The flame was nice and straight and the burner roared however.

Learning how to properly light the burner I finally got the flame to where it was supposed to be. But I can only seem to get one of two results:

1. A very, very quiet burner with a huge, "soft" flame. Achieved by almost completely covering the intake. Flame readily adjusts with increasing gas pressure.

2. A roaring burner with a rather small flame that often extinguishes itself. Intake was 1/4 way open. Flame extinguishes immediately with the slightest variation in gas pressure.

Anything more than 1/4 way open for the intake would result in a flame that burns beautifully, but will not stay lit without a starting flame held against it.

I used tape to adjust the size of the intake since I did not add a choke. Most designs I observed did not need it to operate. 

I experimented both in open air (including trying to shield the intake from the wind with the burner placed parallel to the wind) and in the forge itself. The results are almost the same however, its much easier to prevent the flame from being extinguished when its inside the forge. I also varied the height of the burner in the forge...same results.

The intake is a 3/4" x 2" reducer.

Jet is a 0.035" MIG tapered tip.

Mixing shaft is 3/4" x 8".

The end of the burner consists of a 3/4" x 1" reducer and a 1" x 4" nipple. I also considered replacing the end of the burner with a 1-1/2" x 3/4" reducer. I am unable to do so until I can get someone with a vise because its screwed in too tight to loosen by hand (trust me I've tried). That reducer was actually the original intake until I read that a 2" opening would be better. I had the opportunity to get both so I did. Again, replacing the current intake with the smaller reducer requires me to go to a workshop to drill and tap for the jet's clamp. 

Would it be possible to fix the problem with a modification to the current set up at home?

[Buzzkill]

The video shows an extremely rich unstable flame.  However, since you have most of the air choked off with the tape I have no idea what the flame looks like under "normal" conditions.  Your burner is unlike any that I have personally used, but I have never seen a flare with as much overhang past the end of the mixing tube as you have, and I don't really know how that affects the performance of your burner. You would probably have better results without the 4 inch nipple on the end.  I have used burners in the past that would only stay lit at fairly low pressure (under 5 psi) in the forge when first fired.  For one of those burners I would leave it running at low pressure for a few minutes to allow the forge to heat up.  Once the forge interior started to glow I could increase the pressure without the flame blowing out.

That may or may not work for you, but if you can keep the flame at the end of the burner inside the forge at any pressure without restricting the air flow it's worth a try.  Have you checked to see how well your jet is aligned inside the tube? A misaligned jet can produce some of the symptoms you seem to have.

Hopefully someone with more experience with that general style of burner can chime in and help a little more.

[stevomiller]

Some more questions (sorry video doesn’t play for me) so they might be answered in it.

What pressures are you running? The orifice size you listed tells us the volume of gas supplied only when in conjunction with pressures.

Is the regulator rated for high flow as well as high pressure? For example regulators used with say a BBQ won’t supply sufficient gas for a forge burner.

Agreed the burner nozzle seems too big, it increases the overall length of your burner to quite a bit longer than most 3/4 burners, that and the increased diameter I believe will slow the velocity of the charge significantly.

Hopefully Mike and Frosty will chime in since they both have built Reil type burners and can give good advice to help you get running. It’s unfortunate you live in an area that is secluded and difficult to obtain more typical plumbing fittings.

 

[Jaja]

Well here are two more videos (sorry for uploading them multiple times...I'm having a hard time getting them to sit neatly in the post). Both videos are attempts to light the burner with the intake completely open, in open air. I have also attempted it in the forge and the result is the same. The second video (11.wmv) is attempting to light the flame in open air at high pressure. Lowering the pressure eventually results in the backfire and stuttering seen in the first video (1.wmv). Higher pressure doesn't seem to help in lighting the burner properly at fully open intake. Eventually I start smelling gas and I take that as a sign nothing is going to be burned and I'm approaching a possible explosion hazard. 

I will love to get more advice about the end of the burner...because I had some suspicions about it. I will definitely try to get that thing unscrewed so I can test different sized nozzles.

Also, the regulator is rated for 0-40 psi. I don't have a pressure gauge so I can't say exactly what I'm running at. But to compensate for that I've tried all sorts of combinations.

One of the videos I referred to used this regulator and it worked just fine (I can't post it here). I've seen this regulator in a lot of other setups as well.

Here are more details on the regulator: https://www.amazon.com/gp/product/B0033JF0GE/ref=oh_aui_detailpage_o00_s01?ie=UTF8&psc=1

I have also noticed the jet is slightly pointed down relative to the mixing shaft. The misalignment is very slight. Its difficult to adjust it to be perfectly centered, but I will try to see if I can fix that during the next test...at least to eliminate or minimize any problems from that. My gut however (as much as that means here) is telling me that is not the problem however.

[Mikey98118]

There is a permanent thread called Burners 101 on this forum; you desperately need to read it. Your most obvious problem is your flame retention nozzle, but until you found out the why and how of burner design, there is no telling how much is wrong inside your burner.