Pressure and Siphon-Nozzle Style Foundry Oil Burners

[GreenTwin]

I have a white paper somwhere, and they were trying to improved the efficiency of siphon nozzle oil burners, which are still used in a lot of smaller countries to run smaller founderies.

As I recall, the pulsed fuel produced an increase in efficiency of 20-30%.

I have read literature by the head of engineering at Delavan, and he discusses droplet sizes, and such, and the topic of creating the most efficient and hottest burn is not as clean cut as one would imagine.

You would think smaller droplets would provide more surface area, and higher efficiency, but this is not the case.

The most efficient and hottest burning oil burner is the one that produces the largest and hottest surface area on each droplet, regardless of the droplet size.

I played around with my siphon nozzle burner, out of the furnace, and observed the droplets for various fuel flows and compressed air pressures.

I started with 100 psi compressed air, and gradually reduced the pressure, and it seems like the burn is hotter with a lower air pressure, such as 20-30 psi, with a more coarse droplet.

If you reduce the compressed air pressure too much, then the droplets get so large that they do not completely burn before they settle to the ground, and so you get puddling of unburned oil on the ground as you drop below about 20 psi.

I was going to pulse my fuel, but have not had time to try that, and am not sure exactly how to pulse it.
I piston pump seems like it would work; perhaps just an eccentric that strikes a spring-loaded piston rod.

I would think between 30 and 60 Hz, but that is a blind guess.

A few pictures of experiments with various siphon nozzle burners.

I have tried all sorts of burner configurations, including single siphon nozzle burner, dual siphon nozzle dual burner tube, duel siphon nozzles in a single burner tube, etc.

In the end, the single siphon nozzle per burner, with dual burner tubes at 180 degrees I think is the best performer, especially for larger furnaces.
For my furnace, which has an interior of about 13" diameter, and 14" tall, a single siphon nozzle works very well, and it is hard to justify a second burner tube.

And as I have mentioned, I am transitioning to a gear pump burner, just so I can run the furnace at remote shows that don't have compressed air, and don't necessarily have electricity.
The gear pump can be run from a small generator, since it is fractional horsepower (less than 1/4 hp would work).

One thing I have found is that bigger is not better, and more fuel and air is not hotter, but often times cooler.

The trick no matter what burner you use is to create droplets that burn very hot, and introduce precisely the right amount of fuel and air into a give size furnace to get complete combustion inside the furnace.

2.7 gal/hr is about what produces the most heat and the fastest melt for my furnace size, and any more or less runs cooler.

Image 6114 shows the flame produced by the twin 180 degee burners, and the velocity is low, with the flame burning hot and pretty complete very low in the furnace.

.

 

[GreenTwin]

When the compressed air and combustion air velocity go up, you get what I call the "wall-climbing" effect, where the fuel/air mixture strikes the back wall of the furnace and climbs up at a 45 degree angle.

You are left with a large cold spot in the furnace.
As the furnace interior reaches operational temperatures, the effects of the wall climbing are reduces, but I have to guess that there are still differential temperature differences inside the furnace.

Some folks angle their burner tube down a few degrees to try and correct the wall climbing issue.

Using dual burners at 180 degrees allows you to reduce the combustion air velocity by 50%, which pretty much stops the wall climbing, and gives a very even burn low in the furnace.

You can see the wall climbing effect in this picture, and also see the cold spot above it.
.

 

[GreenTwin]

You can also see that there is a cold spot directly in front of the nozzle, where the fuel has been atomized and has left the nozzle, but has not started to combust yet.

The higher compressed air pressure and combustion air pressure, the farther out this cold spot extends from the front of the burner tube.

.

 

[Nerd1000]

At present I'm thinking

I have a white paper somwhere, and they were trying to improved the efficiency of siphon nozzle oil burners, which are still used in a lot of smaller countries to run smaller founderies.

As I recall, the pulsed fuel produced an increase in efficiency of 20-30%.

I have read literature by the head of engineering at Delavan, and he discusses droplet sizes, and such, and the topic of creating the most efficient and hottest burn is not as clean cut as one would imagine.

You would think smaller droplets would provide more surface area, and higher efficiency, but this is not the case.

The most efficient and hottest burning oil burner is the one that produces the largest and hottest surface area on each droplet, regardless of the droplet size.

I played around with my siphon nozzle burner, out of the furnace, and observed the droplets for various fuel flows and compressed air pressures.

I started with 100 psi compressed air, and gradually reduced the pressure, and it seems like the burn is hotter with a lower air pressure, such as 20-30 psi, with a more coarse droplet.

If you reduce the compressed air pressure too much, then the droplets get so large that they do not completely burn before they settle to the ground, and so you get puddling of unburned oil on the ground as you drop below about 20 psi.

I was going to pulse my fuel, but have not had time to try that, and am not sure exactly how to pulse it.
I piston pump seems like it would work; perhaps just an eccentric that strikes a spring-loaded piston rod.

I would think between 30 and 60 Hz, but that is a blind guess.

A few pictures of experiments with various siphon nozzle burners.

I have tried all sorts of burner configurations, including single siphon nozzle burner, dual siphon nozzle dual burner tube, duel siphon nozzles in a single burner tube, etc.

In the end, the single siphon nozzle per burner, with dual burner tubes at 180 degrees I think is the best performer, especially for larger furnaces.
For my furnace, which has an interior of about 13" diameter, and 14" tall, a single siphon nozzle works very well, and it is hard to justify a second burner tube.

And as I have mentioned, I am transitioning to a gear pump burner, just so I can run the furnace at remote shows that don't have compressed air, and don't necessarily have electricity.
The gear pump can be run from a small generator, since it is fractional horsepower (less than 1/4 hp would work).

One thing I have found is that bigger is not better, and more fuel and air is not hotter, but often times cooler.

The trick no matter what burner you use is to create droplets that burn very hot, and introduce precisely the right amount of fuel and air into a give size furnace to get complete combustion inside the furnace.

2.7 gal/hr is about what produces the most heat and the fastest melt for my furnace size, and any more or less runs cooler.

Image 6114 shows the flame produced by the twin 180 degee burners, and the velocity is low, with the flame burning hot and pretty complete very low in the furnace.

.

View attachment 149358View attachment 149359View attachment 149360View attachment 149361View attachment 149362View attachment 149363View attachment 149364View attachment 149365

Based on practical pump dimensions I'll probably be running at 1000-2000 rpm. The fuel flow and pressure my nozzle wants imply a pump power of about 40 watts, so my drive system (as intended for the gear pump) is just a brushed R/C car motor and speed controller, running on 12V.

A cam-follower arrangement should be a good option for driving the pump. Will be sure to post details if it works!

 

[GreenTwin]

A foundry burner appears to act somewhat like a V-2 rocket pulsa-jet engine, in that it produces a low frequency rumble/roar, so much so that I use rubber under my furnace wheels so that I don't transmit that sound energy into the ground, and disturb the neighbors.

I am aware of one individual who had to add an stack over his furnace lid opening, to reduce the sound level, and this was actually very effective, and eliminated the noise complaints he was getting from his neighbors.

I think what is happening very quickly is that the oil gets sprayed out, it combusts in a burst of flame, and then new oil and air come in behind it, and then that combusts. It all happens very fast.

It seems like pulsing the fuel pressure would give waves of fuel droplets, with space between them, perhaps maximizing the space between waves of droplets to help give some space and air for combustion.

The nozzle itself would seem to be pulsing the droplets, and I guess that occurs when the fluid surface tension is broken, and the fluid gets broken off into a droplet. This would create evenly spaced droplets for a give fuel viscosity.

Fuel viscosity is another discussion, and a higher fuel viscosity results in a higher fuel flow, which seems the opposite of what I would expect.

.

 

[GreenTwin]

At present I'm thinking

Based on practical pump dimensions I'll probably be running at 1000-2000 rpm. The fuel flow and pressure my nozzle wants imply a pump power of about 40 watts, so my drive system (as intended for the gear pump) is just a brushed R/C car motor and speed controller, running on 12V.

A cam-follower arrangement should be a good option for driving the pump. Will be sure to post details if it works!

In the foundry world, the true test of a burner is if you can reduce melt times while maintaining the same pour temperature.

I noticed a dramatic reduction in reaching pour temperature when I finally learned how to tune my oil burner, and used 2.6 gal/hr with the appropriate amount of combustion air.

I went from iron melt times of 2 hours or more to melts under 1 hour, using the same size crucible and iron charge.

Its nice when you can affect a measurable change in melt time.

Good luck with your design.

.

 

[Nerd1000]

Fuel viscosity is another discussion, and a higher fuel viscosity results in a higher fuel flow, which seems the opposite of what I would expect.

.

That would be normal for a gear pump. As I understand it they are more efficient (less leakage back past the gears) with thicker fluids, some manufacturers say their gear pumps can handle 'liquids' as thick as peanut butter. I'm not sure why it would be the case with an air driven nozzle however.

 

[Nikhil Bhale]

The downside is of course that a single cylinder piston pump will only deliver fuel 1/2 the time.

Hi,

You could think of incorporating an accumulator on the discharge side of the pump. The accumulator will smooth out/dampen the pressure pulse and will give almost continuous non pulsating flow.

Regards
Nikhil