Burner: Anyone ever tried using a Brass Sprinkler Sprayer?

[DC712001]

I was out tinkering and scrounging to build a burner. Got the MIG welding tip and the 1/8-inch brass pipe, but while checking the drawers of my plastic, mini-storage bin, I saw some brass sprinkler-head sprayers; The kind that screw into a sprinkler head and can be changed-out for say 1/2-circle or spraying a strip.

Got me wondering.... Might a burner be enhanced by spraying the gas/propane more like a shower-head than from a simple orifice hole, like we do from a MIG weld tip???

Anyone ever try it or does it sound like an idea that might work to better mix the fuel-air prior to combustion?

[Frosty]

Now you're venturing into an area I've wondered about for some time though I've never had time to experiment. A water sprinkler won't do it of course but something scaled to the right size might indeed.

There are a couple commercial variants used in different induction devices. One is a "circumferential laminar flow jet." This is a descriptive phrase as I don't recall the proper name, it's been many years since I actually studied the things. Picture a tube with an internal slit going all the way around the circumference through which a gas or liquid is injected along the inner surface of the tube. This is the laminar flow and is a terrific induction technique.

Anyway, this type of inducer has a threshold of operation around 1:25. This means that it doesn't operate below that ratio which is considerably higher than a neutral propane:air ratio 1:17.5.

Another jet type calls for directing the stream from the primary, (Propane in our case) over a pointy target, something that looks like a bullet. As the high velocity jet of gas flows over the curved surface of the target (again, I don't recall the correct term) it creates a powerful vacuum and seriously increases induction in the tube. That's a good thing so long as the bottom end threshold isn't above the neutral burn ratio for propane and air. Which you can design and tune this particular gizmo to be within range and still do it's thing.

The particularly tasty thing about this type gizmo is what happens after it passes the target widget. There is usually severe turbulence, even cavitation directly behind the target. This can be designed out of course or it can be caused or enhanced.

What's so exciting about turbulence or cavitation you ask? Well, it has to do with one of propane's properties, it doesn't willingly mix with many other gasses air included. If fact, unless you introduce it into the impeller vanes in your blower, mount swirl strips, run the air:fuel mix around a couple 90* bends or install another mixer of some sort it isn't going to be thoroughly mixed when it enters the furnace chamber.

This is why Ron Reil didn't get the BTUs nor the furnace atmosphere he expected when he tested his burners with instruments. His fuel usage was saying his atmosphere SHOULD'VE been rich (carburizing) but it was in fact oxidizing. Then to add to the confoundment there was dragon's breath of burning fuel to account for.

What was happening was fuel and air were entering the furnace in packets of either rich or lean mixtures so at one point there's an oxidizing flame and the next one might be carburizing. Commercial burners, at a higher efficiency level than you see on commercial forges that is, have sophisticated mixers designed in.

So, we're back to the bullet shaped target gizmo and cavitation. Cavitation is something akin to little bubbles of vacuum that can occur behind an object either moving fast through a liquid or gas or a stationary object in a fast liquid/gas stream. (It's the same thing to the object and stream)

So, there's an area directly behind the target that consists of turbulence or even a cavitation zone. When a cavitation bubble collapses it yields something akin to a sonic boom that is VERY destructive. This is what causes 99% of the wear and tear on blue water propellers. Cavitation literally strips molecules off the trailing edges.

What this means besides slowly eroding the bullet shaped target gizmo is there are all these incredibly violent little events taking place right behind the point where a high velocity stream of propane is meeting a low pressure, high velocity stream of air. Mixing should be far more thorough than even feeding the propane into blower vanes.

One of these days, when I get my lathe set up in the new shop so I can spin proper burner tubes I plan on experimenting with various turbulence and cavitation inducing widgets. (called features if they're part of the tube or throat venturi)

However, please feel free to research and experiment yourself. I didn't invent any of this, hold no patents, intellectual (HAH!) or otherwise. Just let us know how it goes.

Frosty

[brucegodlesky]

How about turn the thinking around a bit. here's a burner Mike Sweany built me that has it's own built in mixer. This bugger really screams! Rathe rthan creating a vortex down in the tube, the turbulance is created when air enters the bell.
I suppose it could be downsized for a smaller forge.

[John B]

So? if you feed the propane into the fan intake rather than the air before the gas, and feed this into the chamber, this should break up the propane and burn more efficiently?

[DC712001]

I believe Frosty would say Yes to that, (feeding the air/fuel mixture through the blower would serve to better mix the mixture.) Of course, don't try that with an electric blow-dryer:o. Perhaps a vortex-generator?

Appreciate the thoughts and concepts. Lots to consider.

Hmmm... I wonder if a Spray-Nozzle off a pump-type Garden-Sprayer would be closer to the correct scale?

[Frosty]

Derek:

Yes, I'd say Yes. If you aren't using the heat coils and there's no reason you should, you could feed the propane through the impeller. I don't think a blow drier will supply enough air though but I've never tried.

Bruce:

That is an ejector type inducer and you are right, all the small holes induces turbulence and will help with mixing.

Mike Porter has been working more and more towards laminar air flow in his burners. He has (I believe) stopped trying to improve his and is now working on different uses for them. That's the subject of his next book anyway.

How this applies to my approach to making burners is this. I like a certain amount of turbulence to aid mixing. Mike has done his best to eliminate turbulence and his type 5 is about as good a home made naturally aspirated burner as you are going to find. For example, A "T Rex" is a type 3 Porter burner What Mike calls a "hybrid".

My point is I don't have the "RIGHT" answer to home made burners. I have a design that works, not as well as one of Mikey's or Rex's but I can make one of mine in about 15 mins. with up to another 15 mins to tune. Mike spends all day in his shop machining one of his and I don't know how long Rex spends machining one of his out.

It's about balance, the point of diminishing returns and what you need. Some folk just want to make a hot enough fire to deform metal, some have the money but no time so they buy commercial, some have time and little money and have to make everything, others just like tinkering and others have a drive to get it as perfect as Possible.

Ron Reil and Mike Porter are perfectionists, I like to tinker and make tools but mostly want it to do the job so I stop well short of perfection.

It's a matter of what you want, need and can do.

Frosty

[DC712001]

More good info.

Actually though, my point about not feeding the mixture through an "Electric" Blow (hair) dryer, is that the motor produces electric sparks that would likely ignite the mixture inside the unit.

Sort of like what happened to the gasoline thief that tried using a Shop-Vac to suck the fuel out of a victim's gas tank. The thief didn't realize that some of the air from the vacuum's blower, is blown over the electric motor to cool it.

Gasoline vapors quickly "surprised" the thief, permanently:o.

[Frosty]

Don't feed the gas through the motor!

SHEESH.

Frosty

[DC712001]

Can't be helped.

Similar to the vacuum-cleaner, some of the air from the impeller or fan in the Blow-Dryer, gets directed to the electric-motor in the blow-dryer, to keep it cool. The motor isn't completely sealed-off from the impeller.

Moving Air through a blow-dryer is fine, but moving Air+Fuel through a blow-dryer means a blow-dryer on fire.

[Frosty]

A vacuum cleaner, yes. The motor is typically imbedded in the impeller so the brushes, if it isn't a brushless motor, would indeed spark in the air fuel mix. Bad thing.

Blow drier, not unless you feed it into the back of the motor housing. The motor only uses the low pressure made by the impeller to draw air through it. So you could feed propane in the other side and not get it anywhere close to the motor. Non-event.

Still, a hair drier isn't likely to put out enough air for a decent forge. Then again I haven't given it a try so I most certainly could be wrong.

Frosty

[Justin Caradoc]

just a though..... could you "rifle" the pipe for the blower to create a vortex out of the incoming air? I don't know alot about propane blowers but it was a thought I had.

[John B]

I was not thinking of using a hair drier, I pictured using an angled approach into and across the open impeller end of a squirrel cage fan, the air flow should drag the gas into the fan and out through the exit port. Will try it first with smoke to establish an expected air flow.

[ThomasPowers]

Well a typical blowdryer puts out too much air for a coal forge in many cases.

[ChrisB]

If we are trying to get a better gas to air mix, I would try a form of annular booster arrangement. Or maybe force the mixture thru a screen.

[ptree]

I can offer that all of the large industrial forges that I have seen that burned natural gas or Propane injected the gas into the blower case. These were purpose built blowers and were often 2 to 4' in diameter.
One axle billet forge in particular I remember used a 4' od blower, feeding a manifold to the 6 burners. The gas was fed at 20 PSI (not inches, PSI) and the burners were refractory. Used about $20,000 a month in natural gas for 2 shifts in 2004.

[Frosty]

Okay, we weren't actually suggesting using a blow drier for a propane forge. And seeing as I've never tried it I could be entirely wrong, a blow drier may work just fine. If someone gives it a try please let me know how it works.

It's actually a discussion of safe ways to introduce propane or other flamable gas into the air stream. The impeller blades of a blower are an ideal location to introduce gas If. And this is a big IF it does NOT introduce the gas upstream of the motor's brushes.

If an air fuel mixture meets the sparks generated by a motor's brushes it WILL IGNITE. This is a BAD thing.

There are a lot of mixing strategies designed for propane and air. Usually the tube has a swirl strip rather than a version of rifling. Another is to induce a vortex with vanes in the air intake. There are cavitation and other less aggressive turbulence generators and so on. Usually though the more positive mixers require a gun burner to overcome the back pressure though not always.

In a home built and most commercial forges simply turning a corner will do the trick adequately. If you're turning a corner with a naturally aspirated burner you need to increase the diameter by 1/4" or so to reduce back pressure. OR make and tune it for the conditions.

A naturally aspirated burner has less need for added turbulence than a gun does. A gun tends to produce a more laminar air flow after leaving the blower, impellers cause pressure pulses in the tube but waves have little mixing power. Then the gas is introduced usually at low pressure through a large diameter pipe. (compared to the gas jet in a NA burner) So the propane and air tend to remain segregated in the tube. If you make it turn a 90* some pretty severe turbulence is created and the two mix adequately for a forge furnace.

A naturally aspirated burner on the other hand induces air intake by creating a partial vacuum as the high pressure (relatively speaking) gas is directed down the tube. The partial vacuum not only induces air but it helps vaporize the propane droplets further and there is an induced turbulence as the air meets it.

Propane is odd stuff. As it comes out of the tank, especially at high volume it acts more like a cloud of droplets rather than a true gas. Kind of like fog rather than simple humidity. Anyway, whether or not it's a true gas it ACTS like finely divided droplets. This is one reason it doesn't like mixing with air or oxy in a torch. It just needs a little extra violence to learn it's lesson and oxidize properly.

Frosty

[larrynjr]

Not sure if this is what you meant by a blow dryer for a gas forge but Jerry at Old Cedar Forge has most of his set up like this. Nothing special on the gas tube, just copper into the blow tube. gets to forge welding heat no problems.

[ChrisB]

If you wanted to get super fancy you could use a small turbo and run your fuel/air mix thru one side of the turbo while using a elec blower on the other side to run the turbine. You would get the mixing action and forced air you need. The catch is you'll need to build a oiling system for the turbo and drive a oil pump or the turbo will fry its bearings.

Would that much effort be worth it though? My guess is no. Would be uber cool...

[Glenn]

Why not put a mixer into the air/mix tube? The mixer could be as simple as a piece of thin-tin the size to match the ID of the tube with a twist or spiral for the first half of the length, and a reverse twist for the second half of the length.