Forced Air Diesel Fuel Burner

[Toymaker]

Thanks for both posts GreenTwin. Nozzle designs have made huge advances over the years.

Delavan is the first manufacturer I've seen that includes the CFM numbers for air flow of their nozzles,...too bad for me, they don't offer nozzles in the 3 to 4 gal/Hr size range,...if they did, I could at least get a ball park guess-tament for how much air is used to drive the 14 L/Hr nozzle I'm using.

 

[GreenTwin]

The folks I am aware of who use a Delavan siphon nozzle for backyard foundry work with a furnace generally use the #30609-11 and operated it between 2.0 and 3.0 gal/hr, typically (for melting iron).

The range of compressed air that I see used with a Delavan nozzle is usually between 5 and 20 psi.

The cfm of compressed air used by a siphon nozzle remains the same regardless of whether you operate the nozzle at 1 gal/hr or 3 gal/hr (that is my understanding of it).

I use a pressurized fuel tank (at 10 psi), and a needle valve to control fuel flow, so as to get my 2.7 gal/hr fuel flow rate.
Some use an automotive fuel pump with either variable speed, needle valve, or return line needle valve, to get their desired fuel flow.

I provide a constant 20 psi (+ -) compressed air to the nozzle for atomization, regardless of the fuel flow.
I could probably operated my compressed air a bit lower than 20 psi, and I will probably try 10 psi.

Too little compressed air causes incomplete atomization, and so the burner starts to dribble liquid out its tip, and this liquid will puddle in the bottom of the furnace. Many have said "Fuel can never puddle in the bottom of a red hot foundry furnace", and they would be wrong.
Fuel can easily puddle in the bottom of a red hot foundry furnace, and if you have ever operated a furnace, you could easily prove that.

Beware the armchair backyard foundry folks who have never actually operated a furnace or cast any metal; they can easily mislead you.
Some of the folks who have worked in a foundry have great general knowledge of the overall foundry process, but sometimes they have no idea about how to apply that knowledge effectively to a small scale backyard foundry/burner/furnace.

The compressed air is not provided to the nozzle for combustion, but rather it is used for atomizing the liquid fuel.

A Delavan pressure nozzle uses 100 psi pressure to atomize the fuel, and does not use compressed air at all.
If you don't want to operate an air compressor for a siphon nozzle burner, you can use a gear pump, and a pressure nozzle.
The siphon nozzle burner and pressure nozzle burner will operate basically identically.

I have seen some operate their Delavan siphon nozzles at higher compressed air pressure, such as up to 100 psi, and I have tried that myself.
The higher compressed air pressure does not help the burner, and can actually make it run cooler, since the velocity of the compressed air at 100 psi causes the flame to climb up the back of the furnace at a 45 degree angle, instead of swirling around the crucible for maximum heat transfer.
A higher compressed air pressure not only serves no purpose, but it also causes the air compressor to work much harder, and requires a much larger air compressor capacity.

You pick the fuel flow rate that you want, and use a compressed air pressure between about 5 and 20 psi, and then adjust the combustion air flow to get a complete burn.
Combustion air is provided by a blower, and should not be confused with compressed air, which is used only to atomize the fuel.

.

 

[Steamchick]

Thanks Green Twin, you have explained from an experienced viewpoint how the furnace burner works. I admit to being the model of the armchair non-expert person you mention. So I am glad to learn from your experience. In my limited experience, I have only ever operated gas burners (or vaporised petrol, diesel or paraffin burners), where all the combustion air is mixed at the jet, and within a mixer chamber prior to combustion, and, when correct, a clean blue flame is achieved with no CO in the exhaust. All the installations I have experienced where some external air is required to complete combustion have high CO, so do not effect full and clean combustion. (E.g. using diesel fuel in a paraffin blowlamp style burner, where liquid droplets are expelled from the jet with vapour, so the flames roar but are luminous yellow! A smaller jet cured that by restricting the fuel flow to a suitable level for the length of vaporiser tube. Thus only vapour was released at the jet and the fuel-air balance was restored.). Even when I use my blowlamps around a crucible inside a firebrick furnace, I never see yellow or white flames, as per Toymaker's combustion.
Do you see yellow or white flames? Your diesel burners are 10 times bigger than my blow-lamp style burners that pre-heat the fuel to vapour from the jet.
K2

 

[Steamchick]

I had a slightly weird experience today. Testing someone else's boiler, I connected the propane cylinder to the regulator for the gas supply, but when I turned the burner on full, the CO alarm sounded after just a couple of minutes. I restricted the burn by shutting the valve after the regulator (non-adjustable) and the ceramic burner glowed a brighter red, and the CO alarm was happy. So the jet is too large and the fuel-air is too rich and cooler than a correct mixture. The burner is limited by the total gas flow, and this is made of the fuel gas and the residual capacity is air. So in my case, a smaller jet permits more air and restores the ideal mix of gas and air. NO secondary air post ignition is permitted in this boiler. All the air is entrained at the jet. The total system is defined by the exhaust gas that the burner can push up the flue.... Back-pressure from excessive exhaust gas just means less air, more CO, and headaches! So design burners, boilers and flues as an integrated system for gas flow, to avoid the limitations on a burner - hence imiting boiler performance.
Staying alive...
K2

 

[GreenTwin]

Thanks Green Twin, you have explained from an experienced viewpoint how the furnace burner works. I admit to being the model of the armchair non-expert person you mention.

Nope, not true, this comes from a large number of comments I have seen on youtube, and other various forums, websites, etc.
I highly value your knowledge on all sorts of things, and I read everything you post.

.

 

[Toymaker]

GreenTwin,...Thanks again for sharing your knowledge,...it's always good to hear from the "voice of experience". I very much appreciate knowing that I can feed the siphon nozzles slightly pressurized fuel and the only impact will be greater fuel burn for any given air pressure. The "Siphon Nozzle Capacity Chart" you posted alludes to this characteristic by showing that fuel burn increases as the lift distance decreases, while the air CFM remains constant. The chart shows two ways to increase fuel flow through the nozzle: 1) Increasing the fuel pressure while keeping air pressure constant, & 2) Increasing air pressure (which increases CFM) while keeping fuel pressure constant. I suppose you could consider increasing both fuel pressure and air pressure a third method.
Again, many thanks Always nice to know I'm on the right path.

 

[Steamchick]

Nope, not true, this comes from a large number of comments I have seen on youtube, and other various forums, websites, etc.
I highly value your knowledge on all sorts of things, and I read everything you post.

.

Thanks Green Twin. Well, Maybe true in this case, as I have not got a "proper" furnace, and have never experienced this type of burner relying mostly on external air mixing with the flame and fuel supply in such an engineered turbulent way...
Thanks for your kind words. - And please verify my "knowledge" with other sources, and question anything you feel is "imperfect" as that way we both get more information and improve...
K2

 

[Steamchick]

GreenTwin,...Thanks again for sharing your knowledge,...it's always good to hear from the "voice of experience".
Always nice to know I'm on the right path.

Hi Toymaker, I am glad Green Twin has joined the discussion - I was feeling I was in too deep for my experience (Only with Blue Flame burners). GT has the knowledge /experience I am lacking, so I hope I didn't meddle too much and drift off track...
K2

 

[Toymaker]

Hi Toymaker, I am glad Green Twin has joined the discussion - I was feeling I was in too deep for my experience (Only with Blue Flame burners). GT has the knowledge /experience I am lacking, so I hope I didn't meddle too much and drift off track...
K2

As I mentioned in an earlier post, you can meddle all you want,...I always know you're trying your best to help.

Still on the subject of boilers and burners, (just not mine) did you read Basil's post on "Flash steam powerplant"? The flash boiler for the boat is a rather nice design; uses vaporizing tubes inside the boiler to vaporize the fuel before its fed into the burner nozzles.

Also, if you're not already familiar the SES Steam car and the boiler-burner it used, it's worth a look; the design has the fuel injector shooting the fuel into the on-coming air flow as both fuel and air are sucked into a centrifugal blower, which further mixes the fuel-air, and then finally igniting as it exits the blower. It's truly a masterful piece of engineering.

 

[GreenTwin]

Art B has talked a lot about flame propagation speed, and how to keep propane from combusting in the burner tube.
My large propane burner will occasionally get flame inside the burner tube, and it starts acting like a pulse-jet engine, and overheats quickly.

For foundry burners, you should not have flame inside the burner tube, since that will degrade the tube rather quickly, even if the tube is made from stainless steel.

Some of the white gas camp stoves loop the fuel line through the flame, for vaporization, but a siphon nozzle is providing the atomization of the fuel, and so no preheating is required for atomization.

The Cretors popcorn wagons had a vaporizer, which is a block of bronze, and a pilot flame was directed on the block to vaporize the white gas within.
Once vaporized, the air/fuel mixture traveled down pipes to the popcorn and peanut burners, where it exited multiple small holes in the pipe, and then burned.

The Stanley steam car had a gasoline burner, but I forget the specifics about exactly how it was configured, but I seem to recall it was configured basically like a Coleman white gas stove burner (check me on that).

I have seen a few foundry oil burners that used a small copper fuel line wrapped around a hot burner tube, to heat the oil, but as I recall, these tubes always clogged/gummed up in a short period of time.
I don't know of any reason to heat oil prior to introducting it to the nozzle, other than the case of Art B where he is using waste oil in very cold weather.

Art B heats his oil to keep its viscosity at a workable level, but it is a rather mild amount of heat, and the oil is not overheated.
You want to avoid overheating oil, since it begins to gum up if overheated.
Sometimes the Coleman-style burners have to be cleaned to remove the built up gum.

I do recall a fellow called "myfordboy" heating his oil using a cooktop stove, but one must be very careful doing that, so as to not overheat the oil, and start an inferno.
I think myford heats his oil for the same reason Art B heats his oil.
If I were to heat my oil, I would put the heater and the oil well away from the house and anything combustible, since heater thermostats can go bad, and you can overheat oil.

I use diesel, and with diesel or kerosene you don't need any preheating, even down to freezing temperatures.
Diesel lights easily by itself, and kerosene lights even better than diesel, since it is a lighter fuel.

The beauty of the Delavan siphon or pressure nozzle is that there is no way for it to backfire and start burning inside the burner tube.
Introducing a mixture of air and fuel into piping/blowers, etc does open you to the possibility that a backfire will explode the blower.

As Art B has described elsewhere, it is about the speed of the flame front (correct me if I am wrong Art), and that is important to keep the flames from traveling back to where it is not suppose to be, such as a propane tank.

.

 

[GreenTwin]

There is a video of Jay Leno starting one of his steam cars (perhaps a Stanley), and the burner backfired and singed his eyebrows.
Once you get a gas burner going, they seem to work fine.

Another interesting study is the design used for heavy crude oil that was burned to fire ship boilers.
They used steam injection to heat the oil and vaporized it.

 

[GreenTwin]

The aggregate dryer burners are huge, but still seem to work the same way as our smaller burners.
I think the blower motor on this burner is 200 hp.

.

 

[GreenTwin]

Here is another burner design from an old book.

Generally the large oil burners had multiple air paths, and were very adjustable.

 

[GreenTwin]

Here is a ship burner, with adjustable vanes.
You will always see a swirl disc somewhere on the nozzle, as can be seen in these photos.

There is a video associated with these screencaptures on youtube.



.

 

[GreenTwin]

Here is the video I was looking for.

See 22:00 for a good explanation of the burner lighting and operation.

 

[GreenTwin]

It took me a while to figure out how to light an oil burner.
I could not find any instructions for this.

Here is a video of me lighting my siphon-nozzle burner, running on diesel, and this is the burner I use to melt gray iron.
I put a paper towel with a little diesel on it inside the furnace, light the paper towel, and then turn on the compressed air and fuel simultaneously using ball valves.

I always put two layers of cardboard under the crucible to prevent it from sticking to the plinth, and in this video, I used cardboard that was too large, and it blocked the airflow to the point where the burner flamed out when I started it.

A flameout is not a big deal, but you should immediately turn off the compressed air and fuel ball valves, as I did, and then start over again.

I use a Toro variable speed leaf blower, which operates at its lowest speed for 2.6 gal/hr diesel.

I have a PVC dump valve in my combustion air line, so that I can start the burner, and then slowly ramp up the combustion air, so as to no blow out the burner.

I have a needle valve upstream of the fuel ball valve, and the needle valve is preset to the 2.6 gal/hr fuel flow rate.
I never change the needle valve setting after I calibrate it to 2.6 gal/hr.

Once the burner has started, the dump valve is fully closed, delivering all of the air that the Toro leaf blower produces on its lowest speed into the furnace.

This burner uses the Delvan nominal 1 gal/hr nozzle, operating at 2.6 gal/hr via a fuel tank pressurized at 10 psi.
I use a compressed air pressure somewhere between 15 and 25 psi.

If you are new to burners, you should wear a full face mask when starting a burner.
In the video below, after years of operating oil burners, I am comfortable enough with starting this burner with safety glasses only, since I know exactly what it will do, and exactly how it operates.

When in doubt, wear a full face shield (better safe than sorry).

.

 

[GreenTwin]

And this is what the furnace looks like during an iron melt.

Nice clean burn with no smoke, and a reducing atmosphere inside the furnace (some excess yellow flames out the lid opening), to minimize oxidation of the iron.

Shaded welding glasses are needed for iron melts, due to the high level of infrared coming off the radiant surfaces.

The two gauges are for fuel tank pressure (10 psi), and compressed air pressure (between 15-25 psi).
The valve tree in front of the blower was for testing purposes, and it not needed to operate the burner.

The combustion air dump valve is the PVC valve sticking up in the air above the leaf blower.

.

 

[master53yoda]

I'll chime in here in a couple areas,
The compressed air's only purpose is atomization, fuel flow is based on the pressure between the fuel line and the area right in front of the nozzle the siphon effect is a by-product of the atomization process. I run my burners with 6 to 8 psi on the oil tank and 15 psi on the atomization. the 2 burners high fire at up to about 3.5 GPM ea any higher and the volume of the furnace is to small to get complete combustion. My burners are variable firing down to about .75 GPM using the microprocessor to control the needle valves based on the melted metal pool temp

Heating fuel oil prior to the burner is used to lower the viscosity. my oil heater is based on a electric water heater element controlled by microprocessor The heater is a 1000 watt element but ON time is 1 or 2 seconds with an OFF cycle of 15 to 30 seconds it uses an electronic relay for control. it also has a manual reset high limit at 180. on crude oil burners they use steam for both atomization and preheat for viscosity control.

Back flow into the fuel source can only happen if the combustion air has a higher pressure then the fuel pressure, even with low pressure natural Gas as a fuel is 5" water column and very few fans can reach that kind of pressure. You need a check valve in the acetylene line on Oxy acetylene torches because of the higher Oxy pressure.

Any vapor fuel like propane has a flame propagation rate, propane's is about 79 ft/minute Natural gas is a little slower. The flame front on a burner is where the fuel air mix velocity slows to the propagation rate. I use a velocity plate in my burners about 3/8 to 1/2 " from the end of the burner the plate has a number of holes about 1/8th in to 1/4". the velocity through the holes is higher then the propagation rate but goes below the rate as soon has it passes through the plate. The # and size of the holes will set the flame front about 1/16" in front of the plate. By using the plate it makes no difference if the burner is to big or to long as it prevents the flame from moving up into the burner tube. The purpose of a flare on small bore burners when firing outside the furnace is to slow down the velocity, inside the furnace the back pressure slows it down. if the velocity is to high the burner will blow out.

Art B

 

[Steamchick]

Excellent. GT, What would you adjust to get a clean flame (not a reducing flame as you need to eliminate oxygen from the melt)? I am familiar with Pottery kilns using reducing gas fired flames for the same reason as in your furnace. (It creates brighter colours in the glaze than an "oxidising" atmosphere).
A steam boiler (IMHO) needs a balanced air-fuel ratio at (close to) stoichiometric ratio to be clean of CO without excess air that simply reduces boiler efficiency? (Power stations have monitors for CO and O2, just like the car exhaust systems, and feed-back to the air blowers to regulate the mixture - or they did back in the 1970s!).
The significant differences between a boiler and furnace I think are as below:
Furnace - uses refractory insulation so any direct flame impinging on the surface heats above CO combustion temperature, so maintains the combustion to completion of all the O2 or fuel.
But: The boiler firebox surfaces are below CO combustion temperature (and water-cooled to steam temperature by the boiler water) therefore any flame impinging on boiler firebox walls is immediately quenched to stop the CO combustion. This can be tested by taking a CO meter into the exhaust, or extracting a sample of exhaust and igniting it in air at the end of the sample tube. (CO burns with a near invisible dark blue flame).
The furnace is so hot, the surplus heat and exhaust is vented rapidly. The main aim is adequate power from combustion and insulation so all the combustion heat is concentrated - and lower temperature gases post combustion would cool the melt, not helping the melt.
In a boiler, all the heat should be captured - down to steam temperature by boiler-tubes, etc. - or below steam temperature by the addition of feed water economisers. "Efficient" boilers start with high temperatures of combustion - for high heat flow into the water - and long passages - to extract as much heat as possible to the water - before the exhaust leaves the boiler. Furnaces use "just the hottest bit from combustion" and exhaust cooler gases where there is no further combustion.
Boilers that have superheaters in "post-boiler" exhaust that can raise the steam temperature above boiling temp. are actually passing HOT (wasted) exhaust up the chimney. And boilers are all about efficiency...
I'm sure there are other differences, but that is just my view on the significant points for Toymaker to consider?
Hope this "meddle" helps a bit... just my ideas...
K2

 

[master53yoda]

Steam chick.

Your boiler explanation is good. our melting furnaces are actually combustion chambers as we tend to fire the furnace completely full of flame.

Co ignition temp is about 1100F, most boiler combustion chambers are refractory lined and will maintain a temp above Co's ignition point.
When doing boiler setup we normally have 15 to 20 % excess air before we get complete combustion or 0% Co

Art B