Quick and dirty burner help.

[acrosteve]

I built a basic burner using Ron Reil's design.  Sort of like this, but without the nozzle on the end.

 

Now, at this time I am not using it in a forge, nor do I intend to yet.  Just in free air.  But there is a problem with it I would like to work out without a whole lot of fuss.

I am running on natural gas with pressure of a few psi. My problem is that I can "blow" the flame out quite easily.  By this, I mean that as I open the valve, the flame gets pushed away from the end of the nipple.  Up to nearly 5" or so before it "blows" out.  I don't really need more heat, just a stable dependable flame using the line pressure I have on hand.

I used a 3/4 x 1-1/2 bell and have a 6" long 3/4 nipple in it.  I am thinking that the nozzle pictured on the end of the nipple is not needed in my application.  Where I differed from the original design is that I used 1/4" nipple for the gas, rather than the 1/8 recommended.  I started with an orifice hole of 1/16" but increased it to around 3/16 and improved things a little but not much.

 

Is the 1/4" pipe obstructing the airflow that much?  I am thinking that is the 1st thing that I am going to try is going to the 1/8" pipe.

 

I have also seen that perhaps my 3/4 nipple is not long enough - something about cross sectional area to length ratio.  Perhaps using a 1/2 x 6" nipple in the same bell assembly?

 

We have some other similar burners, not using pipe fittings and the gas orifice opens into a much larger diameter pipe - perhaps 2".  And an orifice size of around 3/16 - 1/4".

I would like to keep the nipple type design, as it allows me some flexibility in mounting or holding it.

 

Thanks

[Mikey98118]

Ron Reil's design employs a 1-1/2" X 3/4" reducer; that's not what you have. Reil was quite used to building his own tapered flame nozzles, which are quite different from yours. You can buy the correctly tapered nozzles (in the needed stainless steel) from Larry Zoeller Forge online.

 

but your biggest problem is a gas jet with an orifice size of around 3/16 - 1/4"; that would be proper on a fan-blown burner, with very low input gas pressure; it's no good on a naturally aspirated burner.

[acrosteve]

Thanks.

 

I did use the 3/4 x 1-1/2 bell reducer.  The photo above is not mine.

[Buzzkill]

11 hours ago, acrosteve said:

I am running on natural gas with pressure of a few psi.

This is probably your biggest hurdle.  We're used to trouble shooting propane burners with a significantly higher gas supply pressure.   The fuel to air ratio for natural gas is different than propane, and you do need a certain amount of pressure for the gas stream to induce air.  I have no experience with NA burners using low pressure natural gas so I can't be of much help there.  However, it appears that you are trying to use a propane design and hoping or expecting it to function well for natural gas.  That's not likely to happen.

[Latticino]

How are you measuring your natural gas pressure?  Typical residential pressure is around 7-14" WG (.25 to .5 psi).  Unless you have a natural gas pressure booster (expensive) or are running a commercial line (which often cap at 2 psi, which wouldn't be enough either) you most likely don't have enough  pressure to operate a NA burner.  Get a blower.

Cross-posted with @Buzzkill who I agree with.

Also, the terminal flare IS typically required to help with flame stability in a burner that runs outside the forge.  The ones serving a forge directly don't always need them.

[ThomasPowers]

Ditto, Ditto, Ditto  You are using a system designed for propane pressures  and propane BTU content with much lower pressure and BTU content Natural Gas

Basically you are trying to run your gasoline engine car on diesel and wondering why it's not working... (not an exact analogy...)

Natural Gas can be used for a forge burner; but you have to use a burner designed for it.  They can be simple; when I took a casting course the instructor used a simple homebuilt burner; blown with a large orifice for NG to melt brass that pretty much just dumped large quantities of low pressure NG into the air stream.

[timgunn1962]

A Naturally Aspirated burner uses the speed of the gas emerging from the jet to entrain the combustion air.

The gas speed through the jet is dependent on the diameter of the jet, the shape of the jet (they are almost always round holes, but the shape of the lead-in affects the "discharge coefficient"), various technical characteristics of the gas (we can usually ignore these since they remain constant once we've fixed the gas we are going to use) and the pressure difference across the jet (we don't usually vary the downstream pressure significantly, so this is normally the gas pressure supplied to the jet).

If I am understanding the OP, the picture of the burner is not the one in use?

The description seems to be of a straight nipple without a "flare".

I'd be strongly inclined to fit a flame retention cup.

http://amalcarb.co.uk/downloadfiles/amal/amal_gas_injectors.pdf

The flame retention cup shown in the Amal leaflet works very well with the Amal low-pressure burners and has worked equally well for me on homebuilt burners. The "burner port nozzle with chamfered end" is not usually necessary IME. Without it, the "burner port nozzle diameter" will be the inside diameter of the nipple. The retention cup ID will need to be "about" twice the nipple ID: if you are using a 1" nipple, the retention cup should be 2" pipe, but the diameter ratio is not critical to the point where you need to worry about the pipe schedule. The transition from nipple to cup needs to be a step change. A perfectly-machined transition is not needed but just screwing on a 2" x 1" reducer with a tapered transition does not work nearly as well as the step. It may work well enough for your purposes though: possibly worth a try if you cannot easily make a square-edged cup?

The air:fuel ratio (and therefore the flame temperature and Oxidizing/Neutral/Reducing characteristic) is a function of the burner design (effectively a constant once you have stopped fiddling with it), and the jet diameter. 

To tune the burner, you will need to be able to change the jet diameter. This looks like a fair amount of work with a drilled hole in the gas tube, but it is possible: start too small and open out the hole in very small steps until it works as you want it to. I'd keep going until it is obviously too big, then make a second tube and drill it to the size that worked best.

If you have a jet that is "too small" and fit a choke, the burner will run lean with the choke fully open and you can adjust the choke to richen the mixture until it is optimum for the task in hand. This is the way I tend to build high-pressure Propane burners. It may not be so good for a low-pressure burner because using the smaller gas jet will mean less gas and therefore less heat input (heat is not the same as temperature) and you will not have the option of increasing the gas pressure to get the heat input back up. You mention that you don't need more heat, so this may be an easier option than faffing about with drilling all those holes.

[acrosteve]

Thanks for the discussion.  It will likely help when i do build a forge which will be propane for sure.  However, for this discussion, the purpose of this flame is just heat, and not a roaring jet type flame meant to heat metal.  This is for where I work - a grey iron foundry.  I forget what the gas pressure is, but it is plant supply, not regulated like it would be for a device.

 

Let me describe what I did today.  It may or may not relate to some of the discussion, which are naturally geared to forge use.

To be clear - the picture I posted was NOT my actual burner.  Only the style I built.  Differences are - My orifice nipple is steel, not brass and 1/4", not 1/8. No flame stabilization nozzle flare. 

1st thing I did was to replace the 1/4" nipple with one made from 1/8" pipe.  I tapped my hole and installed a .030 welding tip.  Well, actually 1/2 of the tip, as it was too long to install and rotate, so I cut it in half.  I also used a 1/8" valve, rather than the 1/4".

This resulted in a smooth, stable flame, but I would like it to be a little more powerful giving me the option of more heat. The valve is wide open.

 

I was building two of these.  So with the 1st one burning and in use - I turned my attention to the other.  Wondering if the smaller nipple really made the difference, i kept the 1/4" nipple and valve, but tapped that hole for a mig tip also.  This one I used a .045 tip - hoping to get more flame.  I did not have another 3/4 x 6" nipple, so I used a 3/4" x 5".

Well, this one would not even light at all.  I could hear more gas coming through the bigger tip, but the 1/4" pipe must block too much of the air.  Strange, I thought, as previously I had a very strong flame from a .0625 hole and slightly longer nipple.

 

 

 

I had other stuff to do, so that is where I left it.  Next, I will change it to the 1/8" pipe with the .045 nozzle and see how it performs with the shorter "nozzle".