How to tune a foundry oil burner

[MRA]

I think he just drips the fuel into the combustion air stream, and his fuel line stops at the end of the burner tube, about at the inside face of the furnace.
I have seen some flatten the end of the fuel pipe, but generally I don't think that is done with a drip-style burner.

That's how the two I have made, work. The oil is gravity fed into a narrow-bore copper radiator pipe which eventually runs down the middle-ish of a 2" bit of stainless pipe through which I blow air - this is my 'burner'. Both pipes stop at the end, entering tangential-ish to the inside of the furnace - the outer stainless pipe is slotted at the end to enable a kind of partially-folded vegetable steamer idea (I suspect this is not very clear!) to reduce the diameter and speed up the air stream a bit. I was told this was important by the guy who had already done it who advised me - I have not tried without.

Like this, but not as folded up!

KitchenCraft Stainless Steel Steaming Basket - 23cm

I start it on sticks and then adjust oil feed with a simple plug cock and air with a cheapo SCR controller on the noisy vacuum-cleaner blower. It all works well enough in a violent 'mouth of hell' kind of way. The one I used most often is located a long way from any neighbours, though it is not too smoky once it is warmed up.

 

[Toymaker]

GreenTwin, if you ever decide to return to using siphon nozzles, and you don't mind doing a little machining project, this is the solution I came up with to supply portable airflow to a 2mm siphon fuel nozzle.

Video: DIY Wobble Plate Air Compressor

The air compressor is turned by a fractional HP DC motor; the motor I'm using is 24 VDC, but you could just as easily use a 12 VDC motor and power it with your car's 12 Volt battery. The compressor is spinning at 700 rpm in the video and feeding 14 psi into the nozzle.

 

[GreenTwin]

Here is a test I ran with my siphon nozzle burner running on diesel.

Between the background noise and my southern accent, it is hard to tell what I am tring to say, but the jist of it is that I wanted to find out how low I could go with the atomizing compressed air pressure and still get good fuel atomization without dripping and puddling of the fuel inside the furnace.

I initially thought (was told by others) that up to 100 psi compressed air could/should be used with a siphon nozzle burner, but I have since learned that the compressed air pressure can be reduced to perhaps 30 psi (+ - ) without causing dripping/puddling.
The lower air pressure allows the air compressor to do a lot less work, and you can still get good combusion from the nozzle.

Diesel is not very volatile, and it is rather reluctant to burn outside the furnace, as you can see in this video.
Kerosene is far more volatile, and will flash into a rather big flame right in front of you, so use caution with more volatile fuels if you run burner tests like this.

I had to break the video up into smaller ones.

As the compressed air is reduced on a siphon nozzle, you go from a high velocity stream of air and diesel, with a flame that is extended away from the end of the burner tube, to a low velocity stream of air and fuel, with a lazy and richer very yellow flame that burns much closer to the end of the burner tube.
The lower compressed air pressure is definitely a better way to operate a siphon nozzle burner.
I turn my compressed air down as low as possible without getting so low as to cause dripping or puddling.

 

[creast]

Here is a test I ran with my siphon nozzle burner running on diesel.

Between the background noise and my southern accent, it is hard to tell what I am tring to say, but the jist of it is that I wanted to find out how low I could go with the atomizing compressed air pressure and still get good fuel atomization without dripping and puddling of the fuel inside the furnace.

I initially thought (was told by others) that up to 100 psi compressed air could/should be used with a siphon nozzle burner, but I have since learned that the compressed air pressure can be reduced to perhaps 30 psi (+ - ) without causing dripping/puddling.
The lower air pressure allows the air compressor to do a lot less work, and you can still get good combusion from the nozzle.

Diesel is not very volatile, and it is rather reluctant to burn outside the furnace, as you can see in this video.
Kerosene is far more volatile, and will flash into a rather big flame right in front of you, so use caution with more volatile fuels if you run burner tests like this.

I had to break the video up into smaller ones.

As the compressed air is reduced on a siphon nozzle, you go from a high velocity stream of air and diesel, with a flame that is extended away from the end of the burner tube, to a low velocity stream of air and fuel, with a lazy and richer very yellow flame that burns much closer to the end of the burner tube.
The lower compressed air pressure is definitely a better way to operate a siphon nozzle burner.
I turn my compressed air down as low as possible without getting so low as to cause dripping or puddling.

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Pat,
I ran mine at around 30 psi but it was a homemade nozzle so I can't quote the flow rate etc but it was quite frugal on waste oil heated to 40 deg C .
It would not ignite easily and needed a hot furnace to maintain stable burn.
Rich

 

[GreenTwin]

My first siphon-nozzle burner was made from a cutting torch tip, with oil in the center hole, and air in the surrounding ring of holes.
It worked well, but seemed to use an excessive amount of compressed air, or perhaps I just assumed that it needed a lot more compressed air than it really did.

I did not have any burner knowledge when I started building burners in 2012, and so everything has been trial and error.

I have a much better understanding of burner and combustion dynamics now than I did in 2012, thanks to folks like Art Bouvier.

I have built drip-style, siphon-nozzle, and Ursutz-style burners, and tested all of those designs.
I have tested siphon nozzle burners in multiple configurations, including multiple nozzles in a common burner tube.

I don't completely understand combustion dynamics, and there is much left to learn, but I think I have learned enough to be able to predict generally if a given burner design will work in a furnace application.


.

 

[creast]

Just did a quick and dirty video of my pumped nozzle setup.
Please excuse the rough mobile phone coverage.
A rough and ready calculation of the airflow was 300 litre per minute and the nozzle is 0.35 US gal /hour. I need to do some performance tests but also need to sort the back pressure leak which is causing unburnt diesel to weep from the tuyere joint which is not too serious but annoying (see smoking around the inlet).
The nozzle has a 60 deg cone with solid profile spray pattern.
The two things I am unsure of is how far to protrude the burner tube into the furnace and how far back to place the nozzle within the tube.
Common sense tells me to ensure the spray pattern doesn't hit the tube but any advice is most welcome.

 

[GreenTwin]

That is a nice burner/pump/furnace combination, and from the looks of it, it is working quite well.

My experience with nozzle placement in the burner tube is that any location other than having the nozzle at or very near the end of the burner tube causes impingement of the spray onto the burner tube, and dripping/puddling.

The burner tube should not protrude into the furnace at all, but rather be completely contained in the tuyere area.
Some folks extend the tuyere out a bit to give a good seal on the burner tube, and to support the burner tube a bit more without it having to protrude into the furnace.

If the burner tube protrudes into the furnace, it will run red hot, deteriorate quickly, and the heat will coke up the siphon nozzle.

Some folks inject fuel into the burner tube away from the furnace, and the ones that get this to work end up with a red hot burner tube, because there is flame in the burner tube.
In spite of what you read on youtube about the benefits of running a red hot burner tube (there are none), the burner tube should run cool to the touch at all times, and ditto for the nozzle.

The nozzle is cooled by the fuel flow and combustion air flow.
For siphon nozzles that contain an o-ring (or perhaps even if they don't), it is best to leave the combustion air blower going after you turn off the fuel (when you have removed the crucible at the end of the melt), so you don't coke up the nozzle and melt the o-ring.

.

 

[creast]

That is a nice burner/pump/furnace combination, and from the looks of it, it is working quite well.

My experience with nozzle placement in the burner tube is that any location other than having the nozzle at or very near the end of the burner tube causes impingement of the spray onto the burner tube, and dripping/puddling.

The burner tube should not protrude into the furnace at all, but rather be completely contained in the tuyere area.
Some folks extend the tuyere out a bit to give a good seal on the burner tube, and to support the burner tube a bit more without it having to protrude into the furnace.

If the burner tube protrudes into the furnace, it will run red hot, deteriorate quickly, and the heat will coke up the siphon nozzle.

Some folks inject fuel into the burner tube away from the furnace, and the ones that get this to work end up with a red hot burner tube, because there is flame in the burner tube.
In spite of what you read on youtube about the benefits of running a red hot burner tube (there are none), the burner tube should run cool to the touch at all times, and ditto for the nozzle.

The nozzle is cooled by the fuel flow and combustion air flow.
For siphon nozzles that contain an o-ring (or perhaps even if they don't), it is best to leave the combustion air blower going after you turn off the fuel (when you have removed the crucible at the end of the melt), so you don't coke up the nozzle and melt the o-ring.

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Pat,
Pretty much my thinking.
So far I have put the nozzle back from the burner tube by about 1/2" and the burner tube about 1.1/2" back from furnace interior wall and run for about an hour.
The burner tube has discoloured slightly at the end but the nozzle is as clean as when new.
Yes, the forced air is the key and I always run way after shutting off the furnace and pulling out the burner tube.
I have tonight created a seal collar to solve the tuyere blow back and control position of the burner tube for consistency.

 

[master53yoda]

When I was researching DIY burners for my forced air burner for boiler use, I came across a few YouTube posts that looked like they might work as foundry burners, so I'll post them here and see what the experts think I like the blue flame, indicating complete combustion.

Waste oil burner

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The problem with any burner that is red hot is that it is acting as a firebox, the reason for the blue flame is that the oil has been completely vaporized and has substantial amounts of excess primary air.

A burner by definition is a device that atomizes the fuel, mixes it with sufficient primary air to reach ignition conditions, supplies a source of secondary combustion air. And either supplies an ignition source or provides a sufficient heat source to maintain ignition.

On liquid fuels such as diesel or waste oil, the heat source must contain enough heat to vaporize the atomized fuel. With our furnaces the firebox provides that heat once it gets above the ignition temp. Most commercial oil burners have a constant spark ignition that provides that heat. or as in my furnace a propane pilot burner that maintains stable ignition temperatures until the furnace itself gets to the required temperature to provide the vaporization and ignition heat.

Flame out happens when the vaporized fuel becomes to rich or lean for ignition, losses a sufficient heat source or as in the case of gases fuels a velocity higher then the flame spread rate. The flame spread rate has to do with how long it takes to raise the fuel mixture to ignition temp with heat from the flame itself. Flame out happens actually when the heat is insufficient for the fuel mixture to reach the ignition temp. The flame triangle is Fuel, oxygen (air), and heat. If any one gets out of range you will have flame out or ignition failure. The size of a pilot has to do with how much fuel mixture has to be heated. I have worked on burners that require pilots as large or larger than our furnace burners. Power plant boilers can require pilots in the million + Btuh range to light from a cold start. A 2 gallon diesel per hour burner provides about 300,000 Btuh. My process furnace fires at 5 to 6 gal/hour when melting, that is a fireball about 4 ft long by 2 ft in diameter.

Art B

 

[awake]

I am using a gear pump and the relief valve is located in the reservoir itself. This valve is set to 120psi . Running pressure is 100 psi and achieved by adjusting pump speed to match the nozzle requirements.

Rich, did you make the relief valve, or purchase one?

 

[awake]

Just did a quick and dirty video of my pumped nozzle setup.
Please excuse the rough mobile phone coverage.
A rough and ready calculation of the airflow was 300 litre per minute and the nozzle is 0.35 US gal /hour. I need to do some performance tests but also need to sort the back pressure leak which is causing unburnt diesel to weep from the tuyere joint which is not too serious but annoying (see smoking around the inlet).
The nozzle has a 60 deg cone with solid profile spray pattern.
The two things I am unsure of is how far to protrude the burner tube into the furnace and how far back to place the nozzle within the tube.
Common sense tells me to ensure the spray pattern doesn't hit the tube but any advice is most welcome.

Very impressive! I think you are onto something with your home-built gear pump.

As you adjust the speed of the motor driving the gear pump, do you get more pressure, more flow, or both? Or to ask this another way, is the goal to turn up the gear pump to the point that it is driving the nozzle at the rated 100psi, and it is up to the nozzle to determine the fuel flow?

 

[master53yoda]

fuel flow is a product of pressure across an orifice, increasing the pump speed puts more oil in a small space increasing the pressure. The flow rate through the nozzle is a pressure difference. the answer above is more oil volume which increases the pressure untill the new volume from the pump can get out through the nozzle. The reason for a pressure releaf valve is to releve the excess volume that is being produced by the pump back to the suction side of the pump, most systems do this internally in the pump but can also be piped back to the storage tank as returning it internall generats heat and a loss of viscosity in the pump. The max pressure that a pump can produce has to do with the side clearance on the gears, a worn out pump is alowing oil to flow past the gears from the discharge side to the suction side.

Art B

 

[creast]

fuel flow is a product of pressure across an orifice, increasing the pump speed puts more oil in a small space increasing the pressure. The flow rate through the nozzle is a pressure difference. the answer above is more oil volume which increases the pressure untill the new volume from the pump can get out through the nozzle. The reason for a pressure releaf valve is to releve the excess volume that is being produced by the pump back to the suction side of the pump, most systems do this internally in the pump but can also be piped back to the storage tank as returning it internall generats heat and a loss of viscosity in the pump. The max pressure that a pump can produce has to do with the side clearance on the gears, a worn out pump is alowing oil to flow past the gears from the discharge side to the suction side.

Art B

Exactly, well explained.
In my case the pump is matching the flow requirement of the nozzle to achieve 100psi and is not being regulated by the relief valve (max safety setting) but is just giving enough for the nozzle and some combined leakages.
Since diesel has a very low viscosity there is significant internal leakage called 'slip' and also the shafts have no seals and leakage past these aids lubrication and merely drips back into the reservoir.
I have not tested the pump on oil to see how well it would act as a hydraulic pump or just how high it could go as that is not what it is intended for and meets my needs perfectly. In time the clearances will undoubtedly increase needing higher speeds or refurbishment but by the feel of it that's some time away.

 

[creast]

Rich, did you make the relief valve, or purchase one?

Fortunately I had some redundant stock thrown out by my employers before I retired.