How to tune a foundry oil burner

One of the biggest obstacles I had with learning to melt gray iron was figuring out how to tune my oil burner so that I had close to the highest temperature that could be achieved using my burner and furnace combination.

I experimented with all sorts of oil burner configurations, including siphon nozzles, drip-style burners, Ursutz burners, etc.

I always found the siphon nozzle to be by far the easiest to fine tune and control, and so I have stuck with that burner type.

I never tried the pressure nozzle burner, but am building a burner that uses that style, and I plan on using it in the future instead of a siphon nozzle.

The difference between a siphon nozzle and a pressure nozzle is that the sipon nozzle uses a stream of compressed air to atomize the fuel stream, almost exactly like a paint sprayer, and the pressure nozzle uses pressurized fuel at about 100 psi (in lieu of compressed air) to atomize the fuel stream.

At a glance, the siphon nozzle and pressure nozzle burners look and I think operate almost identically.

I don't like maintaining and running an air compressor, since they require a good bit of power, are not cheap to purchase, and will wear out with long term foundry use.

The pressure nozzle burner that I am building uses a fractional horsepower motor and a gear pump from a commercial oil heating unit.

My first attemp to melt and cast gray iron was a success, but it was somewhat of an accidental success, since I really had no idea how much combusion air I needed, and didn't know how much fuel flow to use either.

Later attempts to cast gray iron were plagued with problems when I tried to guess at what the best combustion air and fuel flow combination was.
I mistakenly assumed that more was better as far as fuel flow and combustion air, and it took me a few years to figure out that to achieve the maximum furnace temperature, less air and fuel would actually produce the highest temperature.

I finally figured out what produced the hottest temperature by using a fuel valve tree to quickly switch between various fuel flows (each ball valve had its own calibrated needle valve), and using a 2" ball valve on my combustion air blower.

At the time, I was using the output from a shop vacuum for combustion air.

I ran into a guy named Clarke Easterling (Windy Hill Foundry) at the Soule museum, and he had built a furnace not too long after I did, and he figured out exactly how to tune his oil burner.
He was using a Toro variable speed leaf blower, operating on the lowest speed, with great success, and so I copied that air flow (whatever that may be), and used the same leaf blower on the same speed setting, with my valve tree.

I operated my furnace at night, in total darkness, and observed how radiant the interior of the furnace became when using various diesel fuel flows.

It turns out that the hottest temperature for my sized furnace was between 2.6 and 2.7 gallons per hour, with a Toro leaf blower running on its lowest speed.

Once I figured out hot to get the hottest flame temperature, then my iron melts became almost routine, and very predictable (about 1 hour to reach pour temperature).

I was really exasperated with trying to figure out how to operate an oil burner, and folks like ironman (luckygen) kept encouraging me and offering advice; otherwise I would have given up on casting gray iron.

In later years, comparing notes with others who have mastered casting gray iron with a furnace that is similar in size to mine, the number 2.6-2.7 gallons per hour keeps popping up, and so that sort of reinforced what I had discovered.

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I calibrate my oil burner by discharging it into a measuring cup for 1 minute, using a stopwatch, and no combustion air, and measuring the output.
I adjust the fuel needle valve until I get 2.7 gal/hr.

I use 10 psi (with a 30 psi safety valve) on my diesel fuel tank, to give a consistent fuel flow regardless of tank level, or any other variable.

I use I think 30 psi compressed air on the siphon nozzle.
Using too little compressed air will cause incomplete fuel atomization, and the burner will drip and puddle inside the furnace.
Using more than about 30 psi just causes excessive wear on the air compressor, and does not give a hotter burn (as far as I can tell).

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I was told a better method of determining optimum fuel flow and maximum temperature for a furnace by a guy named Art Bouvier, who also sells excellent aluminum ingots.

Art knows more about combustion engineering than anyone I know, and has worked on those systems for years.

According to Art, to find out the maximum amount of fuel that any given furnace size can completely combust inside the furnace, and thus the maximum temperature that can be achieved, is as follows:

1. Turn on the burner and combustion air blower.
2. Increase the oil flow until yellow flames protrude about 5 inches out the top of the furnace lid.
3. Increase the combustion air until the flames receed into the furnace.
4. Increase the oil flow again, to get the yellow flames protruding from the lid.
5. Increase the combustion air until the flames receed into the furnace.

At some point after increasing the fuel flow, when the combustion air is increased, the flames coming out the furnace lid will get larger, and not receed into the furnace.
This is the point where you have exceeded the amount of fuel that can be completely combusted inside of your particularly sized furnace.

Your optimum fuel/air flow and maximum temperature will be a little below this maximum point.

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Another thing to remember is that you can tune your burner for either an oxidizing (lean) or a reducing (rich) burn.

I have found that using a lean burner seems to produce too much slag on the top of the molten iron.

The folks that I know that melt gray iron generally have about 4-5 inches of yellow flames coming out the lid opening.

Some folks use fuel flow meters, but those are entirely unnecessary, and just another thing to fail in my opinion.
I know pretty much exactly how much fuel flow I have, and I have never used a fuel meter.

Once you know the correct flow rate, it never changes.
I never change my fuel needle valve, and I never need to change the setting of my fuel needle valve.

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Furnace sizes vary quite a bit.

My latest furnace is 12.5" diameter inside, and 14" tall.

Many folks use a beer keg as a furnace outer shell, and thus their interior is smaller than mine.

Your furnace size all depends on how large of a casting you want to pour.

The smallest crucible I have used so far with melting gray iron is a #10 (hand lift and pour), and the largest is a #30 (with a crane and pouring cart).

Commercial "small" furnaces can hold pehaps up to a #200 crucible (check me on that), generally using more than one burner for the larger furnace sizes.

The largest crucible I have seen in a backyard setting I think was maybe a #70, shown in the video below.
Justin used a single siphon nozzle oil burner for all of his pours.
I am not sure what his fuel flow rate was.

You can calculate the approximate crucible size by dividing the brim-full capacity of the crucible by three, for iron.
His crucible was not completely full, but 75 lbs divided by 3 is 25, so perhaps not a #70 crucible.
Another one of his videos mentions a #A40 crucible, so perhaps that is what size he is using.

It should also be noted that a correctly tuned oil burner will not produce any visible smoke.

This is my furnace running at iron temperatures.

Shaded welding glasses need to be worn when melting iron, since the infrared coming off the furnace and crucible will quickly sunburn your eyes.

I use an old refrigerator shelf as a shield, in addition to a face shield, when looking into the operating furnace.
Without the refrigerator shelf, your face shield will melt in a few seconds.
Without a face shield, you should not lean over the furnace to look into it, since the heat is extreme and intense coming out of the lid (like looking into a 2,800 F leaf blower).

An iron furnace will melt anything plastic that is near an open furnace, including clothing, shoes, camera, etc., sometimes up to 8 feet away.

You can actually see the fuel valve tree that I temporarily used in this video (above the keg top on the right side) (to determine optimum fuel flow for this furnace).

Dual compressed air pressure regulators, one for the fuel tank pressurization (10 psi), and one for the siphon nozzle for fuel atomization (about 30 psi).

The PVC valve above the leaf blower is for dumping the combustion air when starting the burner, so you don't blow the initial flame out.
Once the burner is running on compressed air and oil only, then you close the PLC combustion air valve fully, putting the total output (on the lowest speed) of the leaf blower into the furnace.

Edit:
A better lid lifter configuration is to move the pivot point down to about the center of the lid, eliminate the vertical chain, and use a bearing at the top of the suport tube, also about the center of the lid.
This lid lifter works well, but my new design is much more simple, and works even better (just a wrist joint that pivots and rotates), with the same U-shaped yoke seen below around half the lid.

A daytime pour of some plaques, in gray iron.

And a rather dramatic night demonstration pour, in the rain (I was under a shed roof).

I don't recommend pouring iron in the rain, but there was a herd of folks watching and waiting for the pour, so it was damn the torpedoes.

I got nervous and forgot to unlatch my lifting tongs, and so that is why I strugged to release the crucible from the lifting tongs at 0:10.
I had never poured in front of that many people before (a large art-iron group at the FIRE 2019 Exhibition).
This was an A10 crucible.

The sheet metal sheild on the pouring shank is a must with iron, else you will burn your hand through any glove.

I use the clock to give me an idea of when to expect reaching pour temperature, which is generally about 1 hour for a #10 crucible.
Some can achieve a slightly faster melt with a #10, such as 45 minutes, but I have not achieved that yet.

Thank you, Pat - a wealth of information here that I will work through carefully later today.

GreenTwin said:

It should also be noted that a correctly tuned oil burner will not produce any visible smoke.

This is my furnace running at iron temperatures.

Shaded welding glasses need to be worn when melting iron, since the infrared coming off the furnace and crucible will quickly sunburn your eyes.

I use an old refrigerator shelf as a shield, in addition to a face shield, when looking into the operating furnace.
Without the refrigerator shelf, your face shield will melt in a few seconds.
Without a face shield, you should not lean over the furnace to look into it, since the heat is extreme and intense coming out of the lid (like looking into a 2,800 F leaf blower).

An iron furnace will melt anything plastic that is near an open furnace, including clothing, shoes, camera, etc., sometimes up to 8 feet away.

You can actually see the fuel valve tree that I temporarily used in this video (above the keg top on the right side) (to determine optimum fuel flow for this furnace).

Dual compressed air pressure regulators, one for the fuel tank pressurization (10 psi), and one for the siphon nozzle for fuel atomization (about 30 psi).

The PVC valve above the leaf blower is for dumping the combustion air when starting the burner, so you don't blow the initial flame out.
Once the burner is running on compressed air and oil only, then you close the PLC combustion air valve fully, putting the total output (on the lowest speed) of the leaf blower into the furnace.

Edit:
A better lid lifter configuration is to move the pivot point down to about the center of the lid, eliminate the vertical chain, and use a bearing at the top of the suport tube, also about the center of the lid.
This lid lifter works well, but my new design is much more simple, and works even better (just a wrist joint that pivots and rotates), with the same U-shaped yoke seen below around half the lid.



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Pat, thinking about the information you have provided above, and watching this video, I was wondering about the air hose and fuel hose. Do they run a danger of melting? Or is the danger of melting only or primarily above the lid?

Very useful info there Pat. Cheers!

awake said:

Pat, thinking about the information you have provided above, and watching this video, I was wondering about the air hose and fuel hose. Do they run a danger of melting? Or is the danger of melting only or primarily above the lid?

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The fuel line and air hoses are at risk of being damaged, and/or melted, however the radiant heat seems to roughly be limited somewhat to a sphere above the top of the furnace, and starting at the top of the furnace.

My furnace is well insulated with a layer of insulating fire bricks, and then two layers of 1" ceramic blanket, and so most of the exterior metal shell on my furnace remains cool to the touch when the furnace is operating.

The furnace shell does get a bit hot at the lid/furnace junction, and I have never found a way to make a reliable and complete furnace/lid seal at iron temperatures. Basically you make the furnace/lid mating surfaces perhaps 2"-3" wide, and as flat as possible, but there will always be leakage at this joint I think.

And if the burner tube is not fitted tight to the tuyere (the tuyere being the opening in the side of the furnace for the burner), then you will blow hot gasses back onto the burner tube, and overheat it and melt the combustion air hose and possibly the fuel line.

My plan for my air and fuel lines is to either cover them with a welding blanket (in the future), or put them in a piece of flexible metal conduit.

I have heard of one person melting his fuel line, and having a large puddle of burning oil appear under his furnace.
This is one good reason to use diesel as opposed to kerosene.
Diesel is much more reluctant to light if spilled on the ground than kerosene.

I use a ball valve for the fuel at the burner, and another one at the fuel tank, for quick turn-off of the fuel if required.

The inside of the furnace lid is very hot, and you can see that my lid swings away from the burner when the furnace is opened.
If my lid swung over my burner, it would melt the fuel line and combustion air line.

Some folks use a lid that opens up, so that you are directly exposed to the lid hot face.
For a small furnace, I guess this is ok, but I don't need exposure to that much heat with an iron furnace.

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I have seen some backyard folks (more than one) build siphon nozzle burners, and then use them without learning the fundamentals of how an oil burner works.
These folks get super frustrated, and then go online and often post online about how bad the siphon nozzle burner design is.

It is sort of like someone driving a car for the first time, and they never shift out of first gear, and then exclaim how badly the car drives.
Or they push the brake and accelerator at the same time, and then complain "the car won't go".

Unfortunatly there is not a lot of good information about how to start, operate, or optimally tune a siphon nozzle oil burner online, and in fact there is a lot of bad information out there that should be ignored, so I do understand where these folks are coming from.

One backyard guy built a siphon nozzle oil burner, and never learned how to operate it correctly, and he launched his furnace lid over the top of his house when he had a flame-out and then re-ignition. He ranted on and on about how terrible siphon nozzle burners were, but never took the time to learn how to operate his. He would jerk the fuel and air valves around wildly, and he is a poster child for someone who should never attempt to operate a backyard foundry.

A siphon nozzle oil burner is a very powerful tool, and perhaps operates in the 200 kW range, which is a lot of energy flying around.
An oil burner has to be treated with great respect and a complete understanding of its operation.

I had some flame-outs in the beginning, before I learned how to operate an oil burner, and now I know exactly how to handle those.
I will post a video that shows a flame-out during startup of my furnace.
The flame-out was due to using too large a piece of cardboard under the crucible (between the crucible and the plinth that the crucible sits on), and the cardboard obstructed the burner flames at startup.

The key is to have a fuel ball valve within easy reach, and use that ball valve to turn off the fuel immediately if you get a flame-out.

There is really no reason to get a flame out with a siphon nozzle burner, but I did let the fuel tank run out of fuel one time, and that caused a flame-out.
Now I always check my fuel tank level before I start a melt.

Operating an oil burner is not a casual affair, especially at iron melting temperatures, and so one really needs to do their homework before operating an oil burner, or before operating a backyard foundry in general.

Sort of like a non-pilot should never just walk up to an airplane and attempt to fly it without the proper training; you will crash and burn.


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Here is an example of a flame-out with an oil burner using diesel.

No big deal if you just turn off the compressed air and fuel ball valves immediately.

I use a paper towel with a little diesel on it as a starter, and it eventually burns and parachutes out in several pieces, as you can see at 1:03, and a good reason to cover the fuel line with something non-flamable.

And I have gotten complacent with not wearing a face mask when starting the burner, since I am so familiar with its operation, and know what it will do.
I would recommend always wearing a full face mask though, regardless.

The smoke coming out at the tuyere is from water that got into the ceramic blanket (I keep this furnace outside, and the cover sometimes does not cover as well as it should).

Once the furnace is operating, and assuming the moisture in the ceramic blaket has dried out, there is no smoke at all, and this is the way an oil burner should operate, ie: no visible smoke at all.

I put on full leathers and leather boots before I pour.

The starting proceedure is to open the compressed air and fuel ball valves at the same time, but without starting the leaf blower.
Once the burner is lit, then the leaf blower is started, but the dump valve is open, and so no combustion air is going into the furnace.
Then the dump valve is slowly closed, and 100% of the combustion air is going into the furnace.

At this point the burner is running at approximately 2.6 gal/hr, and the melt begins.
I don't ramp up the burner over time, but instead start it at full output, and never vary from full output during the melt.

Another word to the wise: Never walk off and leave a furnace running unattended.
You should stay in the vicinity of the ball valves during the entire melt.

GreenTwin said:

I don't like maintaining and running an air compressor, since they require a good bit of power, are not cheap to purchase, and will wear out with long term foundry use.

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I have used the same air compressor to pressurize my propane cylinder oil tank for 27 years and still works fine. Using a mechanical pump to pressurize oil for a foundry type burner is gross overkill when one hose is needed for my set up and three hoses are needed for a mechanical pump.

100model said:

I have used the same air compressor to pressurize my propane cylinder oil tank for 27 years and still works fine. Using a mechanical pump to pressurize oil for a foundry type burner is gross overkill when one hose is needed for my set up and three hoses are needed for a mechanical pump.

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I'm not quite following - why would 3 hoses be needed for a mechanical pump?

GreenTwin said:

Here is an example of a flame-out with an oil burner using diesel.

No big deal if you just turn off the compressed air and fuel ball valves immediately.

I use a paper towel with a little diesel on it as a starter, and it eventually burns and parachutes out in several pieces, as you can see at 1:03, and a good reason to cover the fuel line with something non-flamable.

And I have gotten complacent with not wearing a face mask when starting the burner, since I am so familiar with its operation, and know what it will do.
I would recommend always wearing a full face mask though, regardless.

The smoke coming out at the tuyere is from water that got into the ceramic blanket (I keep this furnace outside, and the cover sometimes does not cover as well as it should).

Once the furnace is operating, and assuming the moisture in the ceramic blaket has dried out, there is no smoke at all, and this is the way an oil burner should operate, ie: no visible smoke at all.

I put on full leathers and leather boots before I pour.

The starting proceedure is to open the compressed air and fuel ball valves at the same time, but without starting the leaf blower.
Once the burner is lit, then the leaf blower is started, but the dump valve is open, and so no combustion air is going into the furnace.
Then the dump valve is slowly closed, and 100% of the combustion air is going into the furnace.

At this point the burner is running at approximately 2.6 gal/hr, and the melt begins.
I don't ramp up the burner over time, but instead start it at full output, and never vary from full output during the melt.

Another word to the wise: Never walk off and leave a furnace running unattended.
You should stay in the vicinity of the ball valves during the entire melt.



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Is there (I'm assuming there is) something that keeps the blower air from blowing out the bottom tube of your burner? I.e., the pipe supplying the diesel and air is thin (12-15mm?), but it goes into a 50-60mm or so pipe. (I may be wildly off on my estimates of the dimensions ...)

Here is a video of me trying various compressed air pressures with my siphon nozzle burner operating on diesel.

Kerosene is considerably more volatile than diesel, and it will flash much easier, so be careful if you attempt this test with kerosene instead of diesel.

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100model said:

I have used the same air compressor to pressurize my propane cylinder oil tank for 27 years and still works fine. Using a mechanical pump to pressurize oil for a foundry type burner is gross overkill when one hose is needed for my set up and three hoses are needed for a mechanical pump.

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It should be clarified that 100model (luckygen/ironman) is using a drip-style burner, not a siphon burner, and has great success with it.
I tried to duplicate 100model's drip burner exactly, down to the last detail, and I could never get any sort of consistent control over it.

After many attempts to make my drip-style oil burner operate like 100model's, I gave up and decided I liked my siphon nozzle burner a lot, especially the very fine and instant control it gives.

If anyone else can get their drip style burner to work as well as 100models, then more power to you; you have figured out how to operate a very simple burner style. I can't make one work no matter what I try; perhaps it is just me.

With a drip-style burner, you literally just drip the fuel into the furnace, and let the combustion air carry the droplets over to the hot furnace interior wall, where it is vaporized.

One of the major dislikes I have about drip style burners is that you have to preheat the furnace interior to a red hot condition using propane, before you start your oil drip.
I don't use any propane to start or run my siphon burner (on diesel), and a gear-pump diesel burner (using diesel) also does not need propane to start or run.
So basically a drip-style burner forces you to have two fuel sources instead of just one, and that requires more fuel lines (one for oil, and one for propane).

There is really no free lunch in the foundry burner world.

The beauty of the gear pump pressure nozzle burner is that it does not require compressed air (atomization is achieved by the 100 psi fuel pressure expanding through the nozzle tip, just like a perfume atomizer/sprayer).
The pressure nozzle burner also does not require a pressurized fuel tank.
And a gear pump only requires a tiny amount of 120V power.

There is much to be said for the gear pump pressure nozzle burner, and I will be using it exclusively as soon as I complete my build.
The advantages of the pressure nozzle burner are:
1. No compressed air required.
2. No propane start if using diesel.
3. Instant 100% power at startup.
4. Very fine and instant burner control.
5. Very consistent and even burn, with no surging.
6. A motor and gearpump combination is a small, lightweight, portable package compared to many air compressors, and requires perhaps 2.0 amps at 120 volts. This is important for a remote demonstration pour, such as in the middle of a field where the only power is a small generator.







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