Prototyping a spinning cup oil burner

Perhaps that's the purpose of the tertiary and/or secondary air shown in other designs. You may have sufficient air overall, but the needed cumbustion air may be being blocked off.

Pete

 

There is that design factor, I was hoping to dodge that issue and did temporarily have a secondary air bypass 4mm wide round the rim of the restrictor but opted for trying to bend the fuel spray pattern forward as much as possible, something the commercial units don't do as much. I can still get a decent lean fuel mix with the current arrangement, if anything the fuel delivery tube/valve is oversized for the blower.

 

I've rigged up a water manometer this afternoon and tested the pressure of the blower system: 0.28456 PSI or 1.992 KPa

The manometer has an 8 inch height difference under blower pressure or 20 cm, so my math is:

Pressure = height x fluid density x gravity
or:
P = 0.2 metres x 1000Kg/M^3 x 9.81 M/second^2
P = 1962 Pascals or 1.962 KiloPascals or 0.28456 PSI

Not much pressure at all!!

 

.28 PSI? YUP, I fart harder than that. Amazing when you think about the size of these two blowers. They aren't doing squat after the pipe fills with air. The blades are just free wheeling beating the same old air it sucked in.

 

Maybe I don't understand this properly but the spinning cup replaces the usual spray nozzle and a blower provides combustion air so would a conventional blower in the form of leaf blower or similar not work in a furnace the average size?

 

Yes, the cup replaces a standard nozzle, the blower provides the combustion air as normal but is also used to deflect the fuel droplet spray from a flat plane shape at 90 degrees to the cup axis and tries to blow it forward as much as possible. At present that's blown forward roughly 45 degrees to give a 90 degree cone forward, which is the best I can currently get after playing around with cone speed and air restriction to boost velocity. So I'm trying to do two things with the blower air and higher pressures would give higher velocity round the cone to blast the droplets forward.

A leaf blower would probably work fine, I just haven't tried one yet.

Running those two units in series is not quite going to get the sum of their individual pressures. Restricting the exit pipe would get higher pressures, at the moment the three inch opening of the blowers is necked down to two inches. It would be great to get hold of a flow rate meter to get some idea of volume pumped too.

 

I really really think you should. For “industrial strength” air, try a gas powered backpack. I suspect it will be too much. More likely to be adequate and considerably better than the current arrangement is a corded blower. In my furnace, running a.75 gph Hago siphon, a 20v battery-powered unit jury-rigged to run on 12v with a blast gate 2/3 CLOSED is plenty.

 

I'll keep an eye out for a leaf blower at the recycle shop and try one soon, it's makes sense to try as much variation as I can before settling on a final design, there may be some nice sweet spot in operation. This current arrangement seems to work ok but two jumping castle blowers in series is a desperate move. It'll do for the waste sump oil test runs and I'll have to start on the other tools now like a crucible lifter and pouring handle. What I have now is hot enough to easily melt aluminium if the glowing red colour of the crucible was any indication, I had about a kilo in liquid form in six minutes before I ran out of the small amount of diesel I had.

Edit: I have a couple of identical vacuum cleaners with generic single stage blowers in them I can try tomorrow now that I can measure air pressure.

 

I did some digging for a central vac blower but couldn't find anything cheaper than ~$65 +shipping. Which I guess isn't bad, but more than my cheap ass would prefer to pay out.

Now, not to be the dick of the group, but I've got to think that a test using diesel, really isn't much of test. I think we all kind of expected it to burn an easy to burn fuel such as diesel. ...and if it didn't there be more of WTF? reaction. When to you plan to cold start with waste oil....?

 

Just thought I'd toss this in.

It's probably the clearest animation I've seen.

Pete

 

Yeah.....yeah..nah nah nah no! that's got to be one of the most highly optimised implementations for best economy and lean burn that I've seen with those multiple air circuits. I'd been looking at this US Navy training film at the 7:08 minute mark for guidance and watching it again I can see it's influences on my implementation.

Thanks for the encouragement Kelly, ideally I'd have a multi fuelled furnace that doesn't require a high level of filtering and processing of the fuel. I'm hoping to have:

• A low maintenance furnace
• Reliable atomisation across wide variety of fuels.
• Tolerant of very fine dirt particles and water from waste oil.
• Free from compressed air.
  
• Easy lighting, preferably free from preheating.
• Reasonably simple construction: If I have to make something like that Saacke burner video to get it to work, I'll walk away from the concept.

My first choice for fuel would be liquid petroleum gas which in Australia has gone up in price to about $5 per kilogram (2 litres) even though it's exported for $0.50 per kilogram overseas. I live next to a large airport and can get drums of Jet A1 for $1.20 per kilogram (1.2 litres) or AUD$100 per drum (USD$80). A restaurant nearby has 60 litres of cooking oil each week free for the taking as well.

The air fuel mix doesn't seem to be an issue at this point, I have no trouble at all with getting a clean burn without complex secondary and tertiary air circuits as the volume of air past the cup is excessive if anything. I do wonder what the fuel spray is doing inside the furnace if I'm getting white fuel vapours leaking out the rusty bottom of the furnace: is the bottom part of the fuel spray soaking into the sand of the jury rigged furnace.....does it even matter in a properly built furnace, once things get hot and there's excess air to burn it?.

 

Your quick to find $45 option has a few key words in the listing that you failed to apply to a search I may have done.



$65 with 15secs of searching or an hour, doesn't change the asking price of $65.

I was in talks with a vacuum repair shop that was closing down and liquidating their stock. They quoted me $150 for a plastic body 3 stage blower. Don't know the manufacturer because I ended the conversation once I saw that price....lol

 

This is the one advantage I see with the cup over the nozzle in the grand scheme of things imho. Sure you don't have a compressor to content with, but then there's the considerable complication of the burner design, so everything to a bad cup motor to one of the handful bearings in the current design can stop you from melting anything on a given day.

The downside to a drip burner is the required preheat. ...and although it is a minor thorn in the side of drip burner guys, the cold ignition the spinning cup would provide would be nice. However not at the cost of losing the devil may care fuel prep efforts we don't need to follow. I pour my waste veg oil through a rag and into my storage tank. That's it... A spinning cup isn't going to care about even "large" particles, and that's what I like about the idea. Now if it can cold start on veg oil..., I's consider making one.

 

Is blowtorch ignition allowed?

 

Cold start on straight oil? Yup. Sign me up. Blowtorch ignition allowed, but a lit rag soaked in gas would be better. The air compressor is still a non event for me. Mine runs for 30 seconds once every 5 or 6 minutes. I may be at 15psi, but I have a feeling my volume of used air is super low and that explains why it hardly runs. 60gallons helps too.

 

I can report back that it cold starts on a burning rag, it took a few tries until I shut off the forced air entirely, and then slowly cracked open the oil valve until oil sprayed at the cup. Ambient temps here are 35 deg C or 95 Fahrenheit so the oil is pretty warm in the sun. Even so, the oil flow over such a distance of 1/4" copper tube seemed to slow the flow down so much, that I had to rest the sump oil drum on top of 5x20 litre drums to get enough head of pressure. The furnace ran, but not too well: the air had to be shut off 3/4 and the oil valve just cracked open enough to get a smooth flow to the cup. There is a point where the oil flows, but drips in the cup causing surging in the spray so I had open it past that point. I was able to melt a couple of kilos of aluminium in 20 minutes of very rich burning and use about 3 litres of sump oil.

The dodgy furnace seems to have reached it's limits in it's current configuration and I'll have to seal up the base of it and make a lid to aid combustion: I could turn up the air flow but the white oil smoke was pouring out of the base which is resting on a 1/2" steel disc and covered with broken fire bricks. I may try using a clay sand mix as a temporary patch.

0:07 Seconds the oil valve is opened and the oil mist comes out the top of the furnace.
0:36 Seconds the air blowers are turned on with the slide valve wide open and it blows out the flame once up to speed.
1:05 Minutes the blower is turned off and the furnace relit.
1:34 The blower is turned on again with valve 3/4 shut.
1:45 Air slide valve is opened too much, blowing out the furnace.



I finally got the scrap aluminium slug cooled down enough and machined 1/4" off the bottom of it to see if there was any visible defects: seems ok.

 

Straight motor oil... Now we're almost cooking...lol "Cooking" status being reserved for veg oil...

Veg oil may not be on your list of fuels you care to bother with, but that's what is going to entice me to venture away from my brute. I may have to give it a go if you don't attempt it.

So your fuel feed design must be the culprit when it comes to pulsing. I'm willing to wager a coffee that one of the back feed concepts wouldn't suffer the same issue. ..or at least to a much lesser extent.

 

This is becoming a series of ever increasing challenges probably including a cold start with coal dust and finally ending in an attempt to burn "daylight" with this technique . I should have some vegetable oil lying around from an experiment and I guess the fuel testing's not really complete without giving that a try too . Fuel feed should improve if I change over to 1/2" copper tube as much as possible on the outside to reduce the flow friction and once the head height was 8 feet or so it flowed pretty well. The difference in flow rate between kerosene and sump oil was very pronounced but not surprising.

Considering it's all a quick proof of concept, it's worked well but the furnace needs improvement: better sealing for the vapours and a lid to confine the burnt fuel a bit longer. If I can increase the rate of burn without blowing out the flames and melt some bronze, I'll be really happy and move on to the next phase of an all stainless hollow shaft and cup with a belt drive motor in a 2 or 3" bore tube for the forced air.