Prototyping a spinning cup oil burner

Full steam ahead! (see what I did there?? ) oh nvr mind..

 

And damn the torpedoes/annoying things like physics/proper design principles . I wonder if I need a workshop steam plant for stuff.....I suppose I could do baked resin sand moulds

 

Some crazy complication in some of the suggestions thus far.

I still think the drive belt version is the easiest for the diy guy to bang out. Not sure if the integral blower running off the cup spinner shaft is a great idea though. If you make the cup small enough you can probably get away without balancing efforts, but running a blower fan at 20,000rpm as well would undoubtedly cause some serious structural failures.

 

The fuel tube could be quite small.
I have always used 1/4" copper tubing (some use steel brake line) just because it is easy to find 1/4" copper tubing and fittings to connect it to the nozzle adapter, but a much smaller tube could be used for the fuel.
Copper tubing can be sources in sizes smaller than 1/4".

Even with an oil burner running flat out, it does not have very much fuel flow.

 

I am watching this develop with great interest and love the original thinking behind the design.
For my suggestion how about those brushless motors used for RC drones as the power source?
I have no experience with these but a quick look shows they can run at speeds in excess of 20.000 rpm easily controlled and with no brushes there is less to wear.

 

I really like this approach. I had something similar swimming around in my head early on, but wasn't sure how the intricate machining of the cup would be received. Makes the overall build much simpler even though the cup is more complex. Although I think the reality is the fuel lines will vibrate and wear out against the spinning objects surrounding them.

Depending on the fuel rate, you may not even need the 'half wall' on the back of the cup where the fuel tubes end. I think someone made the comment on this particular approach, but I don't know how much I'd count on a low pressure zone pulling fuel into the cup. This burner screams for positive pressure on the fuel source.

 

That Japanese manufacturer Sunflame mentions in their brochure that they went away from integral shaft blowers as having separate speeds on the cup and on the blower gave better control. It would have made sense on a ship when the whole unit was steam driven.

I have all the components mocked up in place now, just have to drill some exit holes for the power and fuel lines. It won't be happening today as I'll be helping do a whole lot of bronze and aluminium pours. We are making salt water heat exchanger end caps in LG2 leaded gunmetal for marine refrigeration units today in three sizes. This is with the gas fired furnace that can melt an A20 of bronze in 15 minutes when hot and sacrifices efficiency for speed as gas is cheaper than labour.

I hadn't even thought of those motors, very small, quite cheap and like you say, no brushes to wear out. The mains power supply shouldn't need to be too heavy duty either as you won't be running it at full load. They do need forced air cooling but in an air blower tube that's not an issue.

 

I was able to run my prototype unit in some 4" stainless tube fed by the 4" PVC pipe from the blower which is intended for a kids jumping castle. The airflow is too slow to sweep all of the water droplets out the tube opening: about half the droplets hit the tube wall and then dribbled out the tube mouth in a steady stream. I cut the speed back from '5' on the multi tool dial to '2' with no discernible difference except the droplets were noticeably larger in size. The copper fuel tube also intercepted some of the spray and had a bit of a dribble too. The water supply was a bucket high enough for a siphon effect and I could be wrong but there appeared to be a suction effect from the fuel tube mouth being less than 1/8" from the middle of the spinning cup. The siphon was ridiculously easy to prime with the throttle valve wide open. The 2 gallon bucket emptied in about 15 minutes with the valve wide open but that would vary with the head of pressure from the siphon. Next step will be to machine an airflow restrictor and see if that gets all the droplets out of the tube opening.

 

I'm not surprised that the centrifugal force the droplets are under overcame the combustion air.

Neat problem though... You can reduce their mass (the droplets) by increasing the cup rpm, but then you introduce more inertia into them... catch 22 if you will. Looks like increasing the air flow is the only solution. Unless you want to place the mouth of the cup right at the end of the burner tube.

 

I can certainly see the advantage of a trial run of the cup with water as opposed to diesel fuel.

On the other hand, since the surface tension of diesel is between 1/2 and 1/3 that of water at room temperature (and decreases dramatically with elevated temperatures) and is also significantly less dense, I’d be curious to see how your current setup would behave if tried with diesel. Maybe it would not be appreciably better. But then again.....

 

It's a classic set of conflicting issues to solve if this thing is going to work well, should be a good challenge. Next step is to machine a 1/2" thick plastic ring to restrict the tube bore past the cup and boost the air velocity. The blower has a 3" exhaust port so it has a surface area of 7 square inches, the 4" pipe I'm using has a cross sectional area of 12.6 inches or about 70% more area: that's got to be a serious slow down. So I'll machine a 2" opening in the ring and see how it performs, then 2.5" then 3" openings and see how they affect the droplets. I have a second similar blower I could attach with a PVC 'Y' fitting and get an instant doubling of airflow if all else fails.

That was something I hadn't even considered in my plans..... physics strikes again!. I guess if I test with water then it has to work with the lower surface tension/ lower density of the fuels and gives a safety margin.

 

Just for a quick experiment, I ran the unit with two 450W-500W blowers (not 600W mentioned earlier) for a total of 900W or 1.2 Hp. The unit on the left functions as a fairly strong venturi if turned on first, creating decent suck through the right hand side blower intake. The roughly doubling of airspeed resulted in about two thirds to three quarters of the droplets going out the opening but still having a steady stream of droplets now coming from all round the rim of the tube instead of being able to run out the bottom of the tube before exiting. Will try to fit a an airflow restrictor later today to boost the velocity even further. The stainless tube has that 15 degree bend simply because it's less than 1/3rd the cost of a straight joiner (store must sell more pipe that way).

 

I assume you haven't gone to diesel and are using gravity fed water. Adding 20% or so isopropyl alcohol will lower the surface tension significantly and may give you a better idea of how diesel will work although I have no idea how accurately. It will definitely make your water wetter though. Dish soap will do it too. That can have other side effects as well but would be less expensive than alcohol.

Pete

 

Did somebody mention DEFLOCCULANTS?


MOST COMMON DEFLOCCULANTS
Sodium carbonate
This compound is commonly called "soda" and has the formula Na2CO3 or Na2CO3.10H2O depending, respectively, on whether it is anhydrous or hydrous. The deflocculating action is carried out by an increase in pH, but the carbonate ion, before hydrolysis, can react with calcium ions that may be present in the solution, thereby forming CaCO3 which is insoluble and therefore a flocculating element is removed from the suspension. This carbonate is often used in combination with a silicate, and the resulting mixture, whose exact proportions have to be arrived at via experimentation, is the traditional fluidifier for fine tableware, porcelain and sanitary fixtures.

Sodium silicate
This is the main deflocculant used for the preparation of pastes for casting or for refractory plastics. The ratio of SiO2 to Na2O can vary from 3.75:1 to 1:1 and is available in liquid or solid form. Sodium silicate increases the pH of the suspension, due to hydrolysis, whereas the silicon separates out in the form of colloidal silica which also performs a role as protective colloid, according to the following reaction:

Na2O.nSiO2 + H2O => nSiO2 + 2Na+ + 2OH

When used alone, the percentage in pastes varies between 0,3 and 0,7%.

Alkaline lignosulfonates
These compounds are water-soluble by-products from the manufacture of cellulose using the bisulphite method. Their molecular mass varies between 200 and 100,000, but the most common types have a molecular mass around 4000 and contain monomers on which 8 - SO3 functional groups can be found, associated with benzene rings. They can also act as binding agents for flocculant cations, but their deflocculant action is carried out by the functional groups already mentioned.

They are anionic polyelectrolytes which are strongly hydrolysed even at pH's below 5 and can be absorbed by argillaceous particles up to a pH of 10. Sure enough, dissociation in sulfonate groups - SO3Na- is considerably stronger than in carboxylic or phenolic groups associated with other polymers of natural origin or resulting from synthesis, such as humates.

Polyphosphates
Alkaline polyphosphates (normally from sodium or ammonium) are dissociated in solution and the anions are absorbed onto the clay particles, generating a strongly negative potential. Moreover they are able to capture polyvalent flocculant cations, such as calcium and magnesium, associated with water and soluble salts.

Polyphosphates evolve slowly, by hydrolysis, and are transformed into orthophosphates, thus reducing their deflocculant power with the aging of suspensions.

The main sodium salts used as deflocculants are listed on the following table.

Polyphosphates
Name Formula Solubility
Tripolyphosphate Na5P3O10 12% - 140 g/l per 25 C
Pyrophosphate Na4P2O7 5%
Tetraphosphate Na6P4O10 High
Esametaphosphate (NaPO3)6 Unlimited
Tripolyphosphate
This is a sodium phosphate triple-polymerised so as to form a single molecule with a chain structure.

Its deflocculant power is shown by an increase in negative charge on the surface of the clay particles, via adsorption of the phosphoric anion, and therefore by an increase of zeta potential which causes repulsion between the particles.

It also forms insoluble compounds with flocculant anions, removing them from the dispersive vehicle and preventing their action. In particular, the tripolyphosphate anion forms complex and highly stable anions with calcium, of type (CaP6O18)4- and (Ca2P6O18)2-.

It hydrolyses in water, increasing pH up to 9-10 depending on its concentration. Products on the market are often a mixture of different salts, mainly anhydrous and hydrous tripolyphosphates with pyrophosphate, metaphosphate and orthophosphate; in some cases there may be residues of reactants used in preparation of the product, such as monosodic phosphate (NaH2PO4) and bisodium phosphate (Na2HPO4). The content of phosphates other than tripolyphosphate must be minimum as these reduce the deflocculant capability of the product.

Tripolyphosphate also exists in two crystalline forms with different speeds of dissolution in water.

Esametaphosphate
As for tripolyphosphate, its deflocculant power is shown by an increase in negative charge on the surface of the clay particles, via adsorption of the phosphoric anion, and therefore by an increase of zeta potential which causes repulsion between the particles. It also forms insoluble compounds with flocculant anions, removing them from the dispersive vehicle and preventing their action. In particular, the tripolyphosphate anion forms complex and highly stable anions with calcium, of type (CaP6O18)4- and (Ca2P6O18)2-.

Alkaline polyacrylates (Na-NH4)
These are polymers of the following type:

- CH2 - CH -
|
COO.Na+ n

Molecular mass varies between 1000 and 20,000.

They are effective deflocculants above pH 5 for the dissociation of carboylic groups and for the absorption of polymeric anions on clay particles.

They are highly stable polymers over time and also under variation of temperature.

They do not interact with plaster moulds and can also be used for hot casting.

They have been used in the traditional ceramics sector since the 1970's.

Polyacrylic acid is obtained from polymerisation of acrylic acid, and after neutralisation with soda or ammonium, sodium and ammonium polyacrylates are obtained. The process allows for adjustment of chain length and it is therefore possible to obtain a broad range of molecular weights, whose value depends on the properties of the product.

Polyacrylates with a molecular weight between 1000 and 10,000 are energetic fluidifiers, whereas those with a weight higher than 10,000 increase viscosity in suspensions. Chains are less rigid and complex than those of CMC and thus products with low molecular weight cause little water retention.

Polyacrylates reduce interactive forces between particles, attaching themselves to those areas of the particles whose charge is responsible for the formation of three-dimensional structures.

Polyacrylates act more strongly than polyphosphates in reducing tixotropy and yield point, and, like them, are strong sequestrators of polyvalent ions.

In case of excessive dosage, yield point can be reduced to zero, in which case sedimentation may occur.

 

I may resort to some additive to lower the surface tension down the track, I'll persist with plain water for now and exhaust all possibilities with that first. If I can get water to work then fuel liquids should have a good margin of performance if the blower gets throttled back to lower settings.

Surfactant maybe??.

 

That works too.

 

I'm going to throw this out there, so everyone just take it for what you think it's worth...

I'm going out on a limb and will say that in working furnace all this concern about surface tension may be moot.

 

I really have nothing against deflocculation, just so long as it's done in moderation by consenting adults.

 

The latest results with a 2" restrictor were that it's reaching the point of stalling two blowers and requires careful starting of the blowers by starting them both, working out which one is not really pumping air and temporarily choking the intake of the stronger one to give the weaker unit a chance to pump air. Once in operation there is a combined fine mist and heavier droplets from the water mist hitting the restrictor bore and then getting blown off that surface again. I need to rig a water manometer to get some relative idea of air pressures and then try supercharging one blower with the other to get higher air pressures. It seems these blowers are high volume but not very high pressure and running two in series should give a pressure boost.

So next up is to try a 2&1/2" bore and a 3" bore and then the same again with two blowers in series. The few furnace blowers I've seen are relatively narrow 2" but large 24" diameter blowers to get higher air pressures from around a 1Hp drive.