Yet another keg furnace

Bought this mystery tank for $24 at the scrap yard. It's a stainless steel body with what looks like a plated steel lid and some sort of floating piston inside. Volume is 42.5 litres or 11.2 US gallons, I wasn't planning on a pressurised fuel tank but this is now possible to do. It has three cast aluminium feet and to my eye looks at least 30 years old, absolutely no idea what it's used for in the first place, has a stainless butterfly valve on the top and water pipe on the bottom. Anyone seen something similar that isn't used with toxic substances?

 

That's in line with what I'm seeing with my earlier furnace, and in other's oil fired furnaces on Youtube. There's many things I've done wrong that I'm hoping to address with a fairly airtight, crack free furnace chamber and now a decent tight fitting lid on top. I'll try a conventional spray nozzle and see how it goes from there. I hope to boost air pressure a bit to increase the burn rate and by having a smaller furnace volume increase temperatures. I've been advised by two people who have either seen or operated similar furnaces to increase the length of the tuyere if burning waste oil. If anything this should increase the dwell time that the hot gases are confined in the furnace.

I'm assuming that kerosene/diesel/waste oils have a slower flame speed than the propane that an identically sized furnace uses with no issues. It turns out that under identical conditions fuels burn at different flame speeds, with hydrogen being 7.7 metres per second and methane being 0.55 metres per second. I have no idea what the flame speeds for fuel oils like kerosene, diesel etc. are.

 

My simple drip burner just works great once the firebox is hot. I have too much heat at the bottom, if anything, but I have my burner angled down. End of my dirp tube is 1/8" past the end of the air tube: everything is burning in the furnace.



But my furnace burns clockwise so maybe the molecules are rubbing too much trying to go counterclockwise.

 

I'll shelve the spinning cup idea for now as it's too hard to direct/bend the spray forwards, so it's impractical unless I can make a breakthrough. The last few spinning cup tests will be with pointy bits for the oil to fling off, according to some online papers it matters more than cup speed or cup diameter to achieve fine droplet spray. As Oldironfarmer suggests, one way to boost the oil FPS is to preheat the oil as much as possible. It might follow Ahrrenius' law that every ten degree C increase doubles the speed of chemical reactions (FPS?). So if the oil is hot enough it'll burn fast enough to work fine.

 

Now that I think about it, it's not so much the fuel preheat but the temperature of the combustion area: according to the little reading I have done the temperature of the flame has an exponential effect on flame propagation speed. So a hot combustion area boosts the flame speed, in other words once that furnace gets hot, the FPS get much faster.

 

Just a quick update: the furnace plinth is now resized and resting on a bed of refractory cement, sifted refractory cement was used to grout the plinth-bore gaps.

 

Nice work Mark. Don't forget your cardboard under your crucible. You'll only stick one crucible to that sucker.
What did you wrap around that? Plastic sheet? 2:52

 

I've been wondering what to put under the crucible, fired clay dust made into a paste?, will cardboard be enough to work?. The plastic is some mystery sheet from a LCD TV backlight: it actually had a chemical reaction with the curing refractory and had several ruler straight width-ways splits. At least it had cured before the splits.

 

I have had good success with brass/bronze, and aluminum using two layers of cardboard under the crucible.

For my last cast iron melt, I did the same, and while two layers of cardboard usually work with cast iron, this time it did not since the slag bubbled over and ran down the side of the crucible, cementing it securely to the plinth.
My plinths are not fastened to the furnace, so the plinth came out with the crucible.
I guess if the plinth is cemented in, you may need to twist the crucible gently if it gets stuck to the plinth.

I have some graphite powder, and I may sprinkle a bit of that on the top layer of cardboard next time when melting iron.

Edit:
That foam cutter is niffty.

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Ya know I had some 56" old school rear projection tv. I pulled the fresnal lens outta of it and screwed with it out in the sun. I could have melted lead with that sucker with sunlight! I think the thing could be priceless in a survival situation so I slid it behind the couch. Don't tell my wife.

yup... 2 layers of cardboard has been working great for me. I put it in there when the furnace is cold, set the charged crucible on it and lite it. Pats technique of twist worked for me when I stuck the SOB to the plinth on my very first melt! I have a plinth outside the furnace and I even put 2 layers on it when it comes out of the furnace. Creates a nice fire effect for the viewers. After the pour is done, I shut the furnace off and drop in 2 more layers on the plinth inside, set the crucible on it and close the lid. I cover my exhaust hole and remove the burner. Can't get a much slower cool down than that. Sucker is still blazing hot 6hrs later. No cracks so far.

 

So is the cardboard necessary for all the melts or is is just the first time round?. Silica sand (quartz) melts at 1710 deg C, I could sprinkle some of that down on the plinth for the first few firings.

Pat: that wire cutter is pretty good for a quick lash up: it has a 20mm by 8mm compression spring to keep the wire taut when hot and I run it off a 6V 50 Amp DC power supply and variac.

 

New cardboard for every melt.

 

Doing that is better than a stuck down crucible any day!.

This is the result of playing around with an oil nozzle prototype last night and just jamming it into a 1/2" garden hose for testing. The idea is the steel pin will function as an adjustable needle valve for flow (temporarily held in place by grub screws). This worked fine with a conventional needle but showed no sign of spray, just a very long jet flow that was perfectly laminar for over a metre or so. I had the idea of the blunt needle shown in the photo: it could be adjustable and the expanded tip could break up the flow. It did give a narrow 10 degree spray but only at higher pressures ( I think the water mains is 100 PSI here). So now the plan is to have a 4mm (3/16") needle that tapers to 3mm (1/8") with a 3mm threaded end that allows various tips to be screwed on for testing. The brass T joint has copper olives to grip the test nozzle and provide a high temperature seal, though obviously the needle adjuster screw thread will need some teflon tape to seal.

So picture a brass needle adjuster screw on the left of the brass T that screws the needle in and out of the nozzle hole on the right of the brass T, while fuel flow in the bottom of the T via a 1/2" copper pipe.

 

I think of the cardboard as an evenly distributed layer of carbon. Carbon does not make a very good glue at 3,000F and doesn't melt until over 6,000F.

 

This week I was able to successfully machine a working brass spray nozzle, the main advantage is that it will be free of any rubber o rings and rely on a copper washer for sealing. In water tests it has a slow drip past the 1/2" thread every few seconds without any seals fitted. I've cleaned up and overhauled the oil pump, fitted some new pulleys and a new belt with soft soldered 1/4" copper plumbing. The GM car engine pump had the oil filter bypass removed and the gallery blocked and the spring loaded piston pressure valve has been left intact: no idea what pressure it pumps to. As I don't have an adjustable pressure regulator to use, I have a valve between pump intake and exhaust as well as a ball valve between the pump and nozzle. Hopefully this will be enough to crudely set the fuel flow for testing.

The nozzle is a garden sprayer type pressure driven nozzle and give a spray at very low pressures which becomes a fine mist at higher pressures with water. It's using a 1/2" UNF thread which was cut with a tap and the corresponding internal male part was threaded on the lathe. The outer section screws down on the thread until the tip bottoms out at the nozzle hole to give a good seal for the four hand filed swirl channels.
Using some felt pen blue shows that it does indeed bottom out and seal at the swirl area.



A 1/2" to 1/2" brass compression fitting is used to grip the nozzle and provide a good pressure tight seal.




Australian made GM-Holden 202 cubic inch, 6 cylinder "Red Motor" oil pump.

 

That is some nice machining.
It will be interesting to see how it works.

 

The nozzle gives a 60 degree hollow cone on the garden hose in still air, the air blower should bend it forward a bit too. I hope to have it tested tomorrow with cooking oil into a bucket as I don't want to run any water through the oil pump if I can avoid it. At low enough pressures it actually forms an inch long teardrop shaped bubble: I think the surface tension of the unbroken fluid curves it back into itself.