So, how much compressed (atomization) air can you run on a Hago Siphon Nozzle?

I think this is an interesting question that I intend to try to figure out. Since, for logistical reasons, I cannot run my furnace for a couple weeks, I will not be able to test this out for 10 days or so.

Background: I run my .75gph Hago siphon nozzle with supplied diesel at 9 pounds of pressure and 20 to 35 pounds atomization air. With such a setup, the max fuel flow I have averaged over 2 hours is about 3 gals per hour. Initially, I naively thought that a person could just keep on increasing compressed air and the nozzle would siphon more and more strongly. But this is clearly not true. On my last few melts I have tried different compressed air pressures and found that there is an upper limit to compressed air beyond which fuel flow actually decreases. This upper limit exists since the system reaches a state of "Choked Flow" (I think). https://en.wikipedia.org/wiki/Venturi_effect Another possible limiting factor could be the construction of the outflow chamber of the the nozzle where high atomization flow causes back pressure that may reduce fuel flow. Whatever the cause I observed slowed fuel flow measured over a couple hours when atomization pressure was slightly over 30 pounds and significantly higher flow in the low 20's. Another observation was that there was actual backflow of fuel with 50 pounds of compresssed air and the fuel line not connected to the fuel tank---the compressed air was forcing fuel back up the supply line.

So, I intend to try to set up a test to determine the sweet spot for atomization pressure. I am thinking of using my my usual setup with a standard line from a 5 gallon jerry can to a filter followed by an electric fuel pump which bumps the pressure of fuel to 9 pounds before it enters the nozzle. Since such a setup allows only for weighing the can every half hour to hour and calculating consumption, I intend to introduce a side "y' connector on the up side of the filter and pump that will allow me to switch to that line and suck fuel from a graduated cylinder holding, say, 250ml of fuel. That way I can measure flow over much shorter interval and with more precision and play with compressed air settings to determine the sweet spot for compressed air.
Perhaps Pat (or someone else) will beat me to this test as I know he has been interested in optimizing burn rates.

The other question is what is the maximum practical fuel pressure to use? Will increased fuel pressure allow more flow and that result in faster melts or is 3 gph all the furnace can handle anyway? It certainly sped things up for me to go from zero pressure to 3 pounds fuel pressure and even more to go from 3 to 9 pounds. If anyone has already done this testing, I'd love to hear about it.

Denis

 

The best spot for compressed air pressure for complete atomization seems to be 30 psi for a delavan siphon nozzle burner (1 gal/hr nozzle) when I tested it, and I did tests with the burner both outside the furnace and inside the furnace.
It is not an exact thing, but just judging the relative heat of the flame or furnace, whether or not the spray was breaking up into very large droplets or burning cleanly in small droplets, the radiant energy coming off the furnace hot face, etc.
Too low a pressure and you can get smoking and perhaps a sooty burn.

Above 30 psi seemed to make more noise, but did not seem to make anything operate hotter, and I suspect the flame temperature may have actually dropped at the higher pressures.
I know scavenger ran his siphon nozzle at a higher compressed air pressure, but he did not have the best of melt times/fuel usage compared to someone like ironsides.

But bottom line is that if 30 psi works very well (it does) then any more pressure is just overworking the air compressor.
I think myford runs less than 30 psi, but I an not sure of his exact stetup. As I recall he was preheating his oil, and that probably mean he could get away with less atomization since the fuel would vaporize faster.

The fuel flow out a siphon nozzle is proportional to the pressure on the fuel tank, or the elevation of the tank if a non-pressurized system is used.
I noted the exact fuel tank pressure I use, and as I recall, it was perhaps 15 psi (I will have to check my photos of my fuel pressure gauge, but I think my gauge is 0-18 psi, and the needle is slighly less than full travel).
I use a 30 psi safety relief valve to prevent overpressuring the fuel tanks if the regulator fails, and I use one air line with at tee to pressurized both fuel tanks.
I don't know if the fuel flow vs fuel tank pressure is linear, but it seems somewhat proportional, and increasing the fuel tank pressure definitely increases fuel flow.

So once I figured out the combustion air setting for approximately 2.5 gal/hr, now I can just turn on the leaf blower to the lowest setting, close the combustion air dump valve, and tweek the fuel flow to get a little flame out the lid of the furnace. I generally eyeball the fine tuning of the fuel needle valve to produce just the amount of flame out the lid that produces maximum heat. Too much flame out the lid is just wasting fuel, and too little flame out the lid produces a heat that is not at its maximum.

I have started using two Cornelius kegs for fuel tanks, since they have a very large opening which allows for easy filling from a 5 gallon can, are stainless so there is no danger of them ever rusting out, and will withstand some pressure (not sure how much, but certainly far more than we would require).
And I can refill one Cornelius keg while the other is being used, by using a 3-way fuel valve.
The Cornelius keg also allows me to use a hanging scale so I can accurately measure fuel usage and verify that my calibration (over a 1 minute time period) is accurate.

When I was setting up my multi-valve fuel test station, I calibrated the first valve flow setting at 2 gal/hr, but by the time I got to the 5th valve, I could not get 6 gal/hr to flow even with the needle valve fully open, so I just turned up the fuel tank pressure a bit, and easily got 6 gal/hr fuel flow out of a 1 gal/hr rated nozzle.
But I have found that a range between 2.5 and 3.0 gal/hr seems to burn hotter than any other fuel flow rate for my furnace size, and I tried between 2.5 gal/hr up to 6 gal/hr.

I can only speculate that for a given X amount of surface area in a furnace, there is an optimum Y value of fuel and an optimum Z value of combustion air that produces the hottest flame.
I tried increasing fuel flow with the associated increase in combustion air, and that seemed to actually cool the furnace, so that tells me that the interior hot surface of the furnace can only vaporize and burn a fixed optimum amount of fuel/combustion air flow, and anything else either more or less operates cooler (just my guessing, but it seems to hold up under experimentation).
I did not expect this result at all, but I did notice that at the Soule show last year, porositymaster's fuel flow was quite low, perhaps 2-3 gal/hr, and he was getting very hot iron melts, so that reinforces the idea, and ironsides data also reinforces the idea.

The way I roughly calibrate my nozzle is to open the fuel ball valve, and adjust the needle valve to get the desired fuel flow by sprayed (without compressed atomization air) the nozzle into a calibrated cup, with a stopwatch, and measuring for a 1 minute interval.
There are 128 oz/gallon, so 2 gal/hr is 256 oz/hr, or 4.27 oz/minute.
3 gal/hr is 6.4 oz/minute. (multiply the gal/hr by 128/60 to get oz/min).

If the needle valve is all the way open, and the fuel flow is still too low, then increase the fuel tank pressure perhaps 5 psi and repeat the calibration.
For me, 15 psi on the fuel tank easily produced over 6 gal/hr fuel flow, not that you need that much flow.

For my furnace size (interior dimensions are 13" dia, 14" tall), less seems to be more (hotter) as far as fuel and combustion air flow, and I think that is one of the tricks to melting iron is that you really need to find that optimum temperature spot to get iron up to pour temperatures.

With other metals you can perhaps not have optimum burner settings and still reach pour temperatures, especially with aluminum; not so much with brass/bronze.

Edit:
You could go up to a 1.0 gal/hr nozzle, but I really don't see that being necessary.
I think a siphon nozzle will go 4:1 as far as a range of flows, and I have pushed quite a bit more through one than recommended, perhaps up to 8:1.

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