Vaporizing oil spray experiment.

So after much theorizing about what goes on in my furnace, I noticed that drawing the fuel spray nozzle back a few inches into the tuyere improves furnace performance and seems to make the furnace run noticeably hotter, if the colour of the refractory is anything to go by. There is a point where drawing the nozzle in a little further makes the furnace run worse (very noisy, sputtering combustion) than not drawing the nozzle out of the furnace chamber. So I suspect the best performance is when the fuel spray hits the hot refractory around the tuyere hole. Today I fabricated a 20 cm (8") long by 10cm (4") diameter stainless steel pipe and lined it with 15mm (9/16") thick castable refractory. This gives a 65mm bore that matches the diameter of my existing cone air nozzle. I should have identical airflow speeds as before but be able to withdraw the spray nozzle back into the tuyere so the fuel spray hits glowing hot refractory. I think OldIronFarmer does something similar with the fuel squirt hitting preheated refractory liner.

Ideally it should make fuel oil spray hitting the tuyere walls a desirable thing. It may even make a spinning cup burner practical.

 

Maybe Mark. I know there is a point where too much up the tube is no good either, My kwiky screwed me pretty good for the first 3months and I almost gave up. I was hosing the walls of my pipe down. Kinda like the split fork piss at 4am when ya soak the toilet paper and the bath tub at the same time

 

It'll need a preheated furnace to work so start the furnace with the spray into the chamber and once it's all nice and toasty, draw it back just enough to hit the hot refractory. I should test it outside the furnace first and see if it works as theorized. It may even fix a leak out the bottom of the furnace where the fuel gets between the keg and the refractory lining because of how I made it in the first place.

 

Will the blower air cool that to much to be effective or will it partially protrude into the furnace, or am I mis-understanding things (probably, you know your furnace better than I)

"split fork piss at 4am when ya soak the toilet paper and the bath tub at the same time" try explaining to the wife how that happens, mine just accuses me of being too drunk to aim!

 

It'll be flush with the furnace chamber so plenty of radiant heat and the doughnut chamber under the plinth disc directs the flames back at the tuyere too. An open air test would confirm combustion is possible in the tuyere too.

 

I'd forgotten about the flame trainer/disc. I can see how that would work now.

 

Mark,

I suspect you are onto a good idea. It is worth noting that Mifco seems to encourage combustion within the tuyere. See image below (whickh is a "printscreen image I hopes shows up OK)



Denis

 

Denis, that does look interesting: the ignition spark gap is right before the refractory material.

 

Yup.

Denis

 

It seems the devil is in the detail: looking at Laurie Hall's old furnace which he mostly ran off gas, he had a short refractory lined tuyere, something I neglected to have in my copy of the furnace...at least I did size the tuyere diameter so it could be possible later on.

 

It is interesting and generally contrary to widely held opinion (including mine) that he evidently had flame impinging on his crucible. Where did fuel mix with air with respect to the tuyere external opening occur? Was his furnace especially successful? Does your furnace have flame directed against the crucible? I tried to answer my own questions by searching on that name but found nothing.

Denis

 

Hi Denis, that furnace is now on it's second owner and dates from 1958, yes the flame impinges on the crucible but I've been told it wasn't an issue in 1977 when a Morgan AC20 silicon carbide crucible cost AUD $30 or so. The fuel nozzle is a 1/2" copper pipe about 8-12" back from the furnace, I should have a photo somewhere of it. Laurie was a friend of mine and made a range of equipment from reference optics to telescopes to gemstone faceting machines, he passed away in 2017 aged 93. His legacy website is here: http://www.turbofast.com.au/astrotel/faceting.html and the furnace details are here: http://www.turbofast.com.au/astrotel/furnace1.html

My furnace has the crucible sitting on a 9.5" diameter by 2" thick refractory disc with the tuyere opening below the disc level so the bottom 1/3 of the crucible may not have any flame on it at all.

So the 1/2" copper gas pipe feeds into a steel tube welded into a steel elbow and can be slid in and out the tuyere. It's mostly been fueled with gas but has run oil in the past.

 

Part of my trials are because Laurie is no longer around to ask foundry questions to. I know that he helped a guy build an oil fired furnace back around 1983 and that it melted the refractory at full throttle: the Foseco guys thought the sample provided was a prank and accused them of using an electric arc furnace to melt it. He also worked on World War Two projects such as high speed small diesel engines and also experimental turbojet engines.

 

My dad's furnace had a tuyere directly centre, the burner jet (propane) was completely external and drew air and the flame through a steel/refractory tube. All of which was home built around 40 years ago. The flame front split around the plinth if I remember correctly (It was a long time ago) I was fascinated the jet could be that far out of the furnance but pull enough air without blowing us up!

 

So he had a venturi effect from the gas draw in naturally aspirated air and was able to have combustion start in the tuyere?.


The fuel nozzle sits well in the refractory liner, I'll just have to fabricate some vanes to keep it on centre but allow sliding up and down the liner.



This is my current nozzle assembly which can slide up and down the tuyere pipe.

 

Well put Kelly. In many respects the computer has inhibited thinking things through.

I still wonder how the ancients melted and handled large volumes of bronze, much less creating the marvelous statues.

 

Lots of charcoal and big bellows I'll bet!

 

Double post

 

I agree and disagree at the same time. Smaller engines have been developed with way more horsepower. At one point manufactures struggled (and are still struggling a little bit) with 100 hp per litre of displacement. I believe the first to do this was the Honda Civic Del Sol. Developments with double overhead cams and duel injectors per cylinder were game changers. but, this did come on the backs of computerized injection systems.

Even household furnaces moved away from one torch to four or five torches with better efficiency in a smaller package.