Oil Furnace swirl experiments

Discussion in 'Furnaces and their construction' started by Mark's castings, Sep 18, 2019.

  1. This is just a very quick post before heading off to work: I ran some experiments to increase the path of the flames in my furnace. I've noticed the flames normally travel about 15cm/6" away from the fuel nozzles before performing a right angle turn and going vertically up the side of the crucible and out the lid. I made a mild steel disc that's a neat fit to the furnace bore with a section cut out of the rim. This forces the flames to travel a longer path around the plinth before exiting and may set up a circulating flame around the plinth to preheat the fuel even further. The steel is badly eroded after an hours use with signs of iron oxide spray up the bore of the furnace, so I know I hit 1540 degrees C / 2800 deg F as that's the melting temperature of iron oxide (Correction: red iron III oxide melts at 1540 deg C, but black iron II oxide melts at 1377 deg C which is what I actually had). I'm including some "before" and "after" photos of the furnace, the "before" photo is well after an hours run time of a 2 hour run and the "after" photo with the swirl plate is about the 45 minute mark. I think the next step is to cast a refractory disc a few inches thick to sit on the plinth with a uniform gap around the rim to evenly distribute the flames as the hot spot caused the cheap clay graphite crucible to fail. The iron oxide seemed to eat into the outside of the crucible like acid until it cracked and leaked.

    The furnace does appear to run noticeably brighter/hotter with the steel plate fitted and at higher blower airflow you can see the flames swirling under the plate with no crucible, so hot flames and gasses are hitting the fuel spray and heating the fuel which should increase the flame propagation speed. By increasing the distance travelled in the furnace I should be able to make use of higher rates of burn for slower burning fuels like oil. The fuel consumption was 25 litres or about 6 US gallons for a short ten minute run and then 56 minutes continuous, the amount of iron was 14 Kgs or about 30 lbs.

    Steel disc on the plinth, the tuyere air opening is on the bottom left of the bore so it has to travel about 10" to reach the opening in the disc.
    swirl disc 1.jpg

    Furnace running at close to full throttle after 90 minutes with no steel disc:
    no swirl plate 1.jpg

    Furnace at close to full throttle at the 45 minute mark, with the steel disc, the crucible failed at the 55 minute mark:
    swirl plate 1.jpg

    The crucible leaked at the point just above the finger, while the side opposite is still fine where the iron oxides didn't hit it.
    crucible failure point.jpg
    Last edited: Oct 28, 2019
  2. Rasper

    Rasper Copper

    It would appear that you are running an extremely oxidizing flame, hence the rapid destruction of the steel. What is the purpose?

  3. Hi Richard, the photos are frame grabs from video and are timed to minimize the white hot flames from the rich mixture.

    Last edited: Sep 19, 2019
  4. oldironfarmer

    oldironfarmer Silver

    I angle my burner down 10 degrees or so and get a similar effect.
  5. PatJ

    PatJ Silver Banner Member

    Demolition derby.
  6. I have a 4.5" tuyere diameter so I'm wondering if a nozzle/restrictor will direct the flames into the furnace with more horizontal velocity. Right now the flame bends upwards after short distance without the steel plate to direct it. I think a refractory disc in place of the steel one with a narrow uniform gap round the rim will eliminate the hot spot, another option is to line the tuyere and start the combustion earlier.

    The poor crucible had a lot of things going against it: a cheap one intended for non ferrous use so no protective glaze, definitely not a Morgan Super Salamander. The inside had some damage from lime flux and iron oxides but what really killed it was the chemical attack of the iron oxide slag on the outside where the graphite is gone. It had exactly 20 melts on the clock and you can see how I've burnt the graphite out of the clay, maybe by running too lean over that time.

    dead crucible 1.jpg dead crucible 2.jpg
    Last edited: Sep 19, 2019
  7. OMM

    OMM Silver Banner Member

    Mark, I’m producing a lot of 3500°F IFB wedges. I bet A half dozen these will produce what you’re looking for. Do you want some??? I bet 2-3 of these stacked 2-3 tall just in front of your crucible directing the flame might be a fun test. If so send me a PM with your address.

    Moderators, I wish location was voluntary lightly published below call name...

    Last edited: Sep 19, 2019
  8. OMM that would have been great except for the postage cost. Those bricks are $11 AUD over here and the nearest seller over 1000 miles away from me. I was eyeing off some porcelain dinner plates at the supermarket today and wondering how they handle thermal shock, they even have a nice aerodynamic radius round the rim. I have a bag and a half of dense castable so I'll make a 1-2" thick disc with a rounded radiused rim. I also pulled the trigger and bought a Morgan A25 Salamander Super for about AUD$240 ($163) delivered, at least it will have some glaze and I understand some of the better clay graphites have silicon carbide too, for added chemical resistance.
    Last edited: Sep 19, 2019
  9. OMM

    OMM Silver Banner Member

    AUD, AUZZY? Fair. That would be a postage!
    Mark's castings likes this.
  10. Tobho Mott

    Tobho Mott Silver Banner Member

    Not a mod, but I can tell you that tapping on someone's username at the top of a post will bring up some of their profile info (without leaving the page), including location if they have provided it. Works on my phone at least.

    OMM likes this.
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Yes, what Jeff said.

    Zapins likes this.
  12. Today I cast a 50mm/2" thick dense castable refractory to replace the steel disc. This will give a 16mm gap all round the bore of the furnace to hopefully distribute a uniform flame round the crucible while still having some circular motion of the combustion gasses under the disc round the plinth. The surface area of the gap should be about 60% more surface area than the tuyere pipe intake to the furnace. I nearly didn't clamp the vibration motor to the MDF mould but I'm glad I did as the refractory was fluid enough to get a dense void free casting: even bubbles were coming to the surface in the fluidised refractory with only the recommended water content.

    I've been theorizing of how the swirling gases round the plinth benefit the combustion of the oil:
    • Higher temperatures near the fuel spray due to flames now hitting the spray to aid the vaporization and breakdown (pyrolysis) of the diesel into component hydrogen and carbon: this will boost flame propagation speeds.
    • Possibly higher pressures which would increase combustion speed and flame propagation speed.
    • The swirl will make the flames turbulent which also increases flame propagation speed relative to a smooth laminar flow.
    • Having precombustion inside the furnace chamber reduces heat loss compared to furnaces with external precombustion with their glowing red hot steel chambers, not to mention being hotter, durable refractory material than mild steel.
    • A longer path for the flames inside the furnace will improve combustion of slower burning fuels.
    At least that's what I think is happening, the reality may be completely different and it remains to be seen if it'll allow much higher rates of oil burn on a par with high volume propane furnace.

    refractory disc.jpg
    Last edited: Sep 24, 2019
    Tobho Mott likes this.
  13. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Ramming is for the birds. What vibe does to a seemingly dry refractory mix is almost magical. 2" thick is a bit of a chunk. Why so thick?

  14. I'm not sure how thin I can make the disc and not have it crack, so thicker seemed better and I needed a bit of extra height for the crucible as there's a fair gap between the top of the crucible and the lid. I can always tune the height of the bleach bottle plinth if it becomes an issue. Also I can use a diamond disc in the grinder to cut spiral grooves up the rim to try and swirl the flames and increase dwell time even further if needed. I'm also going to fit the mild steel tuyere nozzle from the spinning cup experiments to see if I can get swirl without the disc.

    I've reviewed a lot of my earlier photo and videos and this appears to be the hottest I've ever had the furnace with a bright yellow glow around the inside rim of the lid which has never happened before, only a bright orange at best.
    Last edited: Sep 24, 2019
  15. OMM

    OMM Silver Banner Member

    The Thicker is always better, unless dealing with the thermal shock. Hard/rapid changes in temperature

    Thinner: deals with thermal shock better as the change in thermal properties effect more uniform.

    There is in every property elastic Deformation and tensile strength.

    If you rapidly heat/cool something(too Fast) it gets a hard scale and bends causing micro fracturing. This is called surface/work hardening. This even happens with the ceramics.. Ceramics are some of the most heat resistant materials known to man. If you thermal shock them, they fracture and they are done!

    My ceramic lathe tooling works best with no coolant and a good feed rate. The chip comes off red hot red hot. I'm carving stuff 60-68 Rockwell.
    Last edited: Sep 24, 2019
  16. I'll be pushing the refractory to it's upper temperature limits I suspect, so hopefully there'll be enough material thickness to hold it together. I'll take off any sharp corners to reduce hot spots and maybe make it less noisy. The new clay graphite crucible should arrive next week, so the disc should have plenty of time to cure and dry out for use.
  17. Ran the furnace today: with the round refractory disc fitted to create a small chamber round the plinth as well as an air nozzle cone to boost the airflow speed, I was able to get a nice even flame around the A25 clay graphite crucible that took a spiral path round the furnace chamber before exiting. After 12 minutes of run time everything was looking good and the crucible was a bright orange colour so I put 9 Kgs of iron in the crucible and ran it close to full throttle. At the 32 minute mark (44 minutes total) I took a quick look and was surprised to see a pool of liquid iron under the slag so soon: I had to scramble to put on some proper casting clothes and protective gear and assemble a sand mould. At 52 minutes (since the iron went in) I was able to skim the slag, add a small portion of ferrosilicon and pour into the spindle mould with the rest going into a steel ingot mould. The casting finish looks good but I didn't line up the core properly when assembling it so the casting was faulty unfortunately. Fuel consumption was about 26 litres for 64 minutes run time and a total of 8 Kg iron yield. All in all I'm happy to be able to melt iron at last after a year of experimenting.

    first iron 3.jpg

    first iron 1.jpg

    first iron 2.jpg
    Last edited: Oct 6, 2019
  18. PatJ

    PatJ Silver Banner Member

    Hey congrats on the iron.
    The part looks great.

    It reminds me of the movies, where I borrow a similar phrase "I love the smell of iron pours in the morning", LOL.

    There is nothing quite like (in my mind anyway) that beautiful red/yellow metal running out of a crucible and into the mold.
    This is one of the joys of reading about other's accomplishments on this forum (successful iron pours).

    Note: You can tune your burner to to 11 liters/hr and get the same or hotter results.
    Less is more when using an oil burner for iron melts.

    And if the ferro level was good, then you will get a very nicely machinable part.
    Good job !

  19. It has been a while since I embarked on this journey, a bit over a year for this particular furnace. While it only had less than a third of a crucible of iron, I have no doubt that a lot more iron will fit into the A25 crucible for the same fuel consumption at which point the consumption should make more sense. I notched and broke a runner: there's a bubble and a black inclusion in there but no obvious chills and nothing but grey iron: I have high hopes for these castings.

    first iron 5.jpg
    joe yard likes this.
  20. PatJ

    PatJ Silver Banner Member

    Looks like some pretty clean iron.
    Maybe some aspirated air on the bubble.
    Did you make a video of the pour?

    From the experiments that I did, it appeared as if the higher fuel and air flow rates actually cooled the furnace.
    With higher air/fuel flow, the velocity of the air/fuel stream increases, and the dwell time of the burning mixture around the crucible is reduced.
    It is as if the droplets get pushed through the furnace and out the lid opening before they have time to fully combust and release their energy (when the fuel/air flow is too high).

    I think it is a safe assumption that any fuel flow over 11 liters/hr is just sending a lot of wasted fuel out the lid opening.
    It took me 6 years to figure that out, and when I compared that value to what others are using for iron melts, it seems to be a universally used value (11 liters/hr), pretty much regardless of the crucible size (at least up to perhaps a #30 or so).


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