Prototyping a spinning cup oil burner

Gentlemen.......it works!, not only that but it works well, really really well: the new Mk2 cup creates a low pressure zone probably like a venturi that actually sucks all the drips from the copper tube back into the cone for re-atomisation. As a result there's no drips at all now, I have a 2&1/4" opening made from 20mm (4/5") thick mild steel and the spray is pretty close to a 90 degree cone out the nozzle. I made a new fuel tube with a tighter bend and a crimped end necked down to 1/8" to minimise the dripping, it's held in place firmly with four hose clamps to keep the tube opening right up inside the cone where the fuel can distribute evenly. To begin with I had a roughly A20 sized crucible in the furnace resting on some broken kiln bricks and sand. A rag soaked in kerosene was lit and placed in the furnace opening and the spinning cup and blowers were powered up, once the fuel valve was cracked open slightly it all should have run but the crucible is a tight fit so the spinning cup fuel didn't ignite until I poked the rag down past the crucible. The fuel can be seen running on minimal setting at first and then I play with opening and closing the fuel valve, at one point it's shut off entirely but reignites easily once cracked open again. The video is not full length, it ran for about 8 minutes burn time before running out of kerosene but I've edited out the dull bits.

 

ROCK and ROLL! Congrats. Looks nice and stable

 

That furnace is an old perlite-fireclay-cement experiment I had lying around, the steel bottom has mostly rusted out, so I had it resting on the two concrete blocks, then some kiln bricks and sand packing. The sand almost completely blew away leaving the crucible resting on the bricks, at that point you can see the white smoke vapour coming out the bottom and burning at one point with flames round the back of the base. So that escape of flammable vapour should be cured with a properly made furnace. I should have a steel disc to go under the bricks as a temporary repair. All in all I'm very happy with it's function and now need to move on to extended testing with waste oil and diesel.

 

I think it's going to work just as well with diesel and probably the same with used motor oil.

 

Fingers crossed, I hope so!!!

 

Looks to me like it will generate a huge amount of heat. Any idea what ball-park fuel burn rate? Way to go!

 

It ran for about 8 minutes with three litres of fuel, with rate of burn going up to full throttle a lot of that time, so 22.5 litres per hour or 5.28 US gallons per hour, probably less at a normal setting.

 

That would probably be enough heat for a couple hundred pound iron melt! Good to know. Glad you went ahead and “Lit Em Up!”

 

That's good to get a ballpark figure, I'd like it to be fast to melt an A20 of bronze, ideally around 20 minutes is my target figure. A future furnace would have a lid with a smaller opening to retain some of the heat for a bit longer and let me throttle it back.

The furnace lining had absorbed a lot of water over the years sitting outside and it was all driven off fairly quickly with clouds of vapour. It's cooled down enough to take a good look inside: The lining has three cracks vertically right where the three inside PVC formwork pieces were joined and was slightly thinner ( a rounded triangle a bit like a Wankel rotor in cross section) . There is no signs of soot, in fact the old soot from the propane gas burner experiments and from the coal residue has been burnt off the lining surface. Some of the high temp kiln bricks are partially melted and glassy on one face, it may be from the beach sand melting too.

edit: Rewatched the video, the bricks had melt marks to begin with, before firing the furnace.

 

Looks like it works like a champ, and the atomization appears to be very consistent across various fuel flows.

 

It seems the slight gamble on this style of burner has paid off pretty well, there may be some issues but no real deal breakers yet.

The current setup is nothing too complex and would be relatively easy to make. I've just finished a short run using diesel as the fuel from a cold start, You can get an idea of the richness of the mixture as opening the valve makes yellow-orange flames come out the furnace opening and reducing the air also makes the mixture rich and flames come out the top. When the mix seems right, very little flame is visible out the top.

 

You appear to have excellent control over the mixture. In the piston engine world, we always look for a little bit rich of peak EGT. Known as best power. Example, I lean a piston engine to peak exhaust gas temp... Then typically enrichen it (cooler) by 75 degrees C. It's ironic if you think about it... but this is basically what we all do when we adjust for 3-5" flames just licking outside the exhaust hole. Physics is non negotiable that's for sure. No deal breakers that I can see. Now that you know this is feasible, the fun part can begin with experimenting slower rotation speeds and simplify that blower setup. Twin bouncy blowers is not something that I want to deal with. For some reason, I can't even be bothered to make a proper shroud for my twin fan microwave blower setup. I'm still running a ketchup bottle and only utilizing one fan.

 

Hey Mark..... If you measure air pressure about 3 feet from the furnace, have you got any idea what it is yet?
I'm going to guess.............. 2psi A cheapo vacuum gauge could tell us...

 

Air pressure from the blowers or in the combustion chamber?. I should rig up a water manometer and take some measurements with enough copper pipe length to lose any heat. The furnace really is a throw away unit, I'll have to buy some real furnace cement and make a permanent furnace complete with lid before I get any real world pressure readings.

What the video doesn't show is that the crucible fills the furnace with less than an inch gap around the rim of the crucible to the furnace wall as the furnace was made well before I bought the oddball shape crucible. The crucible clearance forms a narrow exit for the combustion gasses and allows chamber pressure to build. In this photo it's resting on a kiln brick stood on end to raise the height of the crucible.

 

Excellent results Mark. How do think a scaled down one would work in a 2" tube?

 

I have thought about scaling down the unit, I think the current unit size fitted to a 2" tube with no restrictor with a suitable high pressure blower and you should be good to go. My unit has a 2" restrictor hole that the cup fits into anyway. Two inch air plumbing will have a higher resistance to airflow than my 4" pipe so higher pressures would likely be needed, but all other factors would be identical like cone size and RPM. Lowered cup RPM will need less airflow to deflect the fuel spray droplets but droplet size gets bigger.

Hmm, maybe a similar sized or smaller cup, lowered RPM and a restrictor to speed airflow near the cup to boost droplet deflection forward to compensate for less airflow of a smaller blower unit. It'll need some experimentation again to get a good result but should be possible.

The unit I built was able to be throttled right down, both fuel and airflow so worst case scenario is the angle of the spray cone widens at lower air volumes

 

A 2" version would be very useful, Are you saying a standard leaf blower type blower would not be suitable though?
Where is the "reply with quote button"!

 

Just hit the “reply” button on the message of interest. It will open a reply box with the message of interest quoted. Most other forums seem to use a different convention with either a with or without quote button option. That is how I quoted you in this reply.

 

air pressure from the blowers mark.

 

I really have no idea, I have to take some pressure measurements. A leaf blower might work, but again I've never used one before.

Ok, I'll see what I can do and get some data on this thing.

Judging by the richness of the orange flames coming out the top, the cup can put far more fuel into the furnace than the current blower arrangement can supply air to burn.