I need help with tuning a propane burner.

[S. Heslop]

Some of you might have seen my other thread. I'm building a gas forge which needs a burner.



I've been trying to use this burner I pulled out of an old oven. The original orifice was pretty big at about 1.1 mm so today I made a slightly smaller one at about 0.8mm, which seems to be the size most people go for in most home made forge burners (it was also the smallest microdrill I had).


It's running here at a pretty low pressure, maybe below 1 bar.


And here's about as far as I can open the choke before it blows itself out. The flame is still pretty yellow.

Is this just a case of the orifice still being too large or is there some other problem? I'm pretty hopeless with burners and i've not had much luck finding any real information about them online, so I can only guess as to what the problem might be.

[Swarfing]

It could be you need some more air forced in? To get higher temps on my furnace i use a hairdryer for the job. Another way of messing with jets is to use mig welding tips if you want to play with sizes there. What adapter are you using for the gas bottle?

[S. Heslop]

It could be you need some more air forced in? To get higher temps on my furnace i use a hairdryer for the job. Another way of messing with jets is to use mig welding tips if you want to play with sizes there. What adapter are you using for the gas bottle?

I was kinda hoping to avoid forced air with the venturi. I'm a little short on sockets.

I'd also been keeping away from mig tips because I'd have to machine them to fit and I think they're made from beryllium copper.


Not sure what you mean by gas bottle adapter but the bottle goes to a 0-4bar regulator, through an 8mm hose, and then onto what's left of the burner. I flared out the steel pipe a bit to hopefully keep the hose from slipping off. It's maybe not the best arrangement and I was going to machine a proper hose barb for the burner if I could get it to work.

[Bluechip]

Polly Engineering at Long Eaton stock jets for burners, ie. the ceramic plaques, but maybe they would be too small for you.
No idea what the hole size is, they just have numbers.

http://www.pollymodelengineering.co.uk/sections/bruce-engineering/docs/Catalogue-October-2012.pdf
 
Other than that, if you need titchy drills I get my PCB bits from Gloster Tooling, he has an EBAY shop.

http://www.glostertooling.co.uk/


All manner of diameters < 1mm.
 
 Dave BC
 
 
 
 
 

[stevehuckss396]

http://www.backyardmetalcasting.com/oliverburner1.html

Take a peek at this burner. It is made from a couple pipe nipples. I have had one for a few years now and have no trouble melting aluminum and brass with it.

[sparky961]

The burner will function very differently with a "flare" on it, or inside of a smaller chamber.  You may want to try putting it inside a pipe about twice the diameter of the end, and maybe about 1-2 times the D inside it.

[vtsteam]

Pure guesswork , but looks to me like your square air opening is too far back to benefit from the gas jet, so the jet isn't pulling much air in.

Is it possible to put in a good size spacer to move the jet orifice back without making a whole new tube?

You could also make a split ring of a short bit of tube to slide over the main tube and adjust the air orifice size and position with it after you move the gas jet back.

ps. If you haven't already, flare the end of your small gas inlet pipe, where the tubing and hose clamp (jubilee clip?) attach -- a hose clamp can't really hold fast onto a smooth pipe. Wouldn't want that hose to come off. 

[andyf]

I don't know if you are trying it out in an unheated environment, but the vapour pressure of propane at 0°C is only about 2/3 of its vapour pressure at 30°C, and as you draw propane off from the bottle at 0°C, the bottle will slowly cool down to below 0C. Thus, the ambient temperature will affect on the propane pressure at your nozzle. Not a very big effect, of course; we don't see 30°C very often in the UK.

I've never seen this book, except in recommendations: "Gas burners for forges, furnaces and kilns" by Michael Porter, but maybe it would help if you can locate a copy.

Andy

[Pete49]

I've never seen this book, except in recommendations: "Gas burners for forges, furnaces and kilns" by Michael Porter, but maybe it would help if you can locate a copy.
Andy

The book is available via amazon and is a handy reference book for $20. The link is http://www.amazon.com/Gas-Burners-Forges-Furnaces-Kilns/dp/1879535203
Pete

[S. Heslop]

Pure guesswork , but looks to me like your square air opening is too far back to benefit from the gas jet, so the jet isn't pulling much air in.

I don't understand why opening the choke would blow the flame out in this instance.

Maybe I could try rolling a flare.

[vtsteam]

Pure guesswork , but looks to me like your square air opening is too far back to benefit from the gas jet, so the jet isn't pulling much air in.

I don't understand why opening the choke would blow the flame out in this instance.

Maybe I could try rolling a flare.

My guess was that you don't have enough oxygen mixing in. The flame is yellow and moves out away from the burner nozzle as you increase pressure because it is trying to mix with air beyond the burner before it can combust. Opening still further blows it out.

My guess is also that the gas orifice you built is located too far forward to draw in much air from your air ports. That's why it's so rich.

If you move the orifice back or move the ports forward you will draw in more air (I believe) and should have a leaner flame and one that stays more attached as you open the gas tap further.

Look at Lionel Oliver's burner referenced by Steve Huckss above. Notice that the orifice (a tiny drilled hole) Is located considerably aft of the air port holes. Now look at your topmost photograph of your own burner. Where is the air port in relation to your jet orifice?

I believe that the higher the gas pressure, the further forward a port needs to be to draw well. As you increase your gas, your ports are (in my estimate) reducing the amount of incoming air, rather than increasing it.

Again, all guesswork on my part.

[S. Heslop]

Pure guesswork , but looks to me like your square air opening is too far back to benefit from the gas jet, so the jet isn't pulling much air in.

I don't understand why opening the choke would blow the flame out in this instance.

Maybe I could try rolling a flare.

My guess was that you don't have enough oxygen mixing in. The flame is yellow and moves out away from the burner nozzle as you increase pressure because it is trying to mix with air beyond the burner before it can combust. Opening still further blows it out.

My guess is also that the gas orifice you built is located too far forward to draw in much air from your air ports. That's why it's so rich.

If you move the orifice back or move the ports forward you will draw in more air (I believe) and should have a leaner flame and one that stays more attached as you open the gas tap further.

Look at Lionel Oliver's burner referenced by Steve Huckss above. Notice that the orifice (a tiny drilled hole) Is located considerably aft of the air port holes. Now look at your topmost photograph of your own burner. Where is the air port in relation to your jet orifice?

I believe that the higher the gas pressure, the further forward a port needs to be to draw well. As you increase your gas, your ports are (in my estimate) reducing the amount of incoming air, rather than increasing it.

Again, all guesswork on my part.

Ah that makes sense.

I just tried out making a flare out of a bit of scrap pipe and it made a fair bit difference, but still not ideal. I'm letting the garage air out for a bit then i'll try moving the orifice back. The brass bit is loose in the steel tube and can slide back a bit, although i'd need to hold it aligned by hand myself. If it works out I could figure out a more permanent solution.

Come to think of it, I could make a whole new part to hold mig tips as orifices.

[S. Heslop]

I think I finally got it working. Had to order a new pin chuck for smaller microdrills. Got it online for a few reasons. I'd heard that Eclipse brand were still the best around but the one I got is far from that. It was out of concentricity by at least 2 millimeters, and i'm lucky I had a 4 jaw chuck to get it better aligned.

Drilled out a 0.6mm gas orificie and here it's running at about half a bar pressure.


Thanks for the help though everyone. I think I better understand how these things work now.

[DaveH]

It isn't quite so easy designing burners for natural gas as it was for coal gas.
A good place to start maybe to have a look at a Natural gas Bunsen burner with a flame retainer.
 
DaveH