How to build a Babington Oil Burner
last update 2007-09-15

So you want to make a Babington burner?


(click for high-resolution image)

Image is of a dual .0135" Babington atomizer burning kerosene.  Liquid fuel is delivered through the 1/4" copper pipe at right, atomized by the two holes blowing 30 PSI compressed air, and a flame is sustained on the left side as long as the fuel flows.  The excess fuel that pours over the knob is caught by a steel funnel (in background) that guides it into a sump.


Index

Overview
History
Fuels burned
Making a Babington Burner
    Babington Atomizer (the "nozzle")
    Drilling the Itty Bitty Hole
    Compressed Air/Pressurized Gas
     Fuel Supply
    Burner Tube
    Fuel Sump
Starting your Babington
    Pre-heating the Oil
    Adjust the Compressed Air/Gas Flow
    Constant Fuel Flow
    Constant Air Flow
Additional Information
Acknowledgements

The (currently anemic) Babington Oil Burner FAQ is available here.

Overview

A Babington burner works like a whale's blow hole.  Fuel flowing over a curved creates a thin film due to surface tension.  When this film is pierce by a jet of air from a very small hole (typically .010 inch), the fuel is not only atomized quite well, but also, enough air is entrained by the atomized fuel to complete the combustion, so there's no need for additional forced air for combustion.

The huge advantage of Babington burners is that there's no nozzle to clog: the fuel flows over the small air hole, rather than through it, making this a very popular waste oil burner.  So long as the fuel pump can handle whatever is in the liquid, be it metal shavings, french fry bits, or dirt, the burner will continue working without fail.  The tradeoff for this lack of clogging is that you need to have a fuel sump that's located below the atomizer nozzle. 

Here's a picture of my very first Babington - not very elegant, but it worked!


The parts as seen are:
1) a Babington atomizer (the doorknob, in this case).  Normally, this is actually inside the burner tube, but I pulled it out for demostration purposes.
2) source of compressed air or gas (the 20lb propane container)
3) liquid fuel pump (typically a gear oil pump) (not visible, but hooked to the copper tubing)
4) burner tube (the old 100lb propane tank with the end cut off).  I mounted this on four legs to made a hand-height hand warmer for an outdoor work area, and it worked great!
5) fuel sump of some sort to catch the unburned fuel that runs over the atomizer (the cut-off end of the old 100 lb propane tank)
6) splash guard - part played by that chunk of H-beam, otherwise fuel splashes everywhere.

Here's an end view of the Babington while running (looking up cut-out propane tank):


(click for higher resolution image)

That's a cinderblock just downstream of the burner that greatly assisted in keeping the flame running.  Also, note that there's no smoke!  When everything is running properly, there's just wavy hot air as exhaust. 

You can also kind of see the gear oil pump floating in midair beneath the burner tube  It's drawing fuel from the upper left hand corner of the sump, pumping it around the propane tank twice (to preheat the fuel), and then pouring it over the doorknob where the fuel gets atomized.

Things odd about this setup include:
1) there's no propane regulator, and the propane flow was difficult to control just using the tank knob
2) I was making a dual-fuel burner (kerosene/glycerol), hence the "T" in the galvanized propane tubing and one capped end.  Someday...
3) since this was a test setup, there's no fuel tank - I just filled up the sump and ran off that fuel

History

Patent # 3,425,058 was granted to Robert S. Babington in 1969.  It has expired, and the burner design is now in the public domain.

Patent # 4,155,700 was granted to Robert S. Babington in 1979.  It details a dual-atomizer Babington burner that uses forced air for combustion.  It looks exactly like Babington Technology's Airtronics(r) burner (fancy that), which was primarily marketed for military food preparation and runs off of diesel fuel.  This patent has also expired.

John Archibald has really picked up where Mr. Babington left off, and is the father of the home-built Babington.  He has written at length about the Babington in the Wastewatts group over the past few years, so if you're going to read the archives from just one person, he's the one.

Fuels

Due to the excellent atomization, Babington burners will burn many heavy and waste oils such as:
(all the BTU values seem to change +/- 5% based on source and quality - take these numbers for comparison purposes only)

The only difference is that the preheat temperature, and compressed gas PSI, will change for optimum burning of different fuels.

I estimate that a single .010" hole consumes about 1/3 gallon of liquid fuel per hour.  This works out to about an 40,000 BTU heater with WVO.  To increase the output of the burner, drill another hole 1/4" from the original hole and you will double your fuel usage & heat output.  (If the hole is closer than 1/4", the streams will overlap and it won't burn quite as well)

Warning: do not attempt to burn gasoline, methanol, or an other volatile fuel with a Babington burner!  The whole sump as well as the atomizer can catch fire explosively, and while that can be exciting, that's not not the goal here. :)  I once burned some biodiesel that still had some methanol left in it, and yes, it was quite exciting, so I'm speaking from experience here.


Making a Babington Burner


Making a Babington Burner is faily simple, but there are a number of pieces that have to work together in order to do so.

Also, please note that I'm not a mechanical engineer (I'm a software engineer, actually), and playing with combustible fuels, while fun, can be rather dangerous.  I highly recommend keeping a fire extinguisher close to your Babington burner at all times, especially while you're tinkering with it.


Babington Atomizer (the "nozzle")

The fuel needs to flow over a curved surface in order to work properly.

The professional-looking way of doing this is to just buy a hollow steel ball.  Any size ball, made of any common metal, in any reasonable diameter is available from

J. G. Braun Co. • 8145 River Drive • Morton Grove, IL 60053053-2645
800-323-4072 • 847-663-9300 • Fax: 847-663-0667 • info@jgbraun.com

A 3" hollow steel ball is about $10.50 (but with $75 minimum order) from RB Wagner

However, some (most?) people use keyless interior doorknobs.  Cut off the shaft of a knob with a sabre saw, then braze or JB Weld a copper SLIP  x FPT adapter onto the shaft, and screw into your compressed gas source.  Make sure you clean both surfaces with a solvent first, and rough up the surfaces with a wire brush/wheel or sandpaper.  I have had some luck in this department, but a couple of failed attempts, too:


(click for larger picture)

I tried to braze both of them, but the doorknob on the left just wouldn't seal (it was actually a pro I asked to help me that blew a hole through it!).  The knob on the right was purchased new, but I couldn't get anything to adhere to, even after thoroughly roughing up the surface with a wire brush wheel.  A very old doorknob from a salvage yard, probably made pure brass, worked just fine, though.

Alternately, several folks have successfully used brass end caps with a groove cut into them.

What size atomizer is right for you?  Dave Brown says:

"I have tried both large and small balls.  The large balls were door knobs (interior, keyless, lockless) drilled with 0.010" holes (one hole and two holes).  The small balls were brass end caps (flare fittings) with 0.0135" hole (one only), with and without the groove.

I don't think it's as simple as comparing ball sizes, as other factors such as dirt in the fuel and delivery system play as big a roll.

The overriding goal or principle, regardless of size, is that optimum atomization of the oil requires a thin film of oil over the ball at the point where the pressurized air exits the ball.  So, given that basic premise, my observations are as follows:

BIG BALLS:  If your method of delivering the oil to the ball isn't precise, then the large ball has a decided advantage in that it will accommodate a higher flow rate and still deliver a thin film of oil to the air stream.  Excess oil runs off and is simply drained to the sump/oil tank and recirculated.  Since this oil has been pre-heated, it warms and lowers the viscosity of the oil in the sump. There is more latitude in fuel flow rates while continuing to deliver the desired thin film of oil to the air stream.  Seeing as consistent fuel delivery seems to be a constant headache, at least according to the history of posts to this list, the large ball is more forgiving.  It seems to me that it tolerates fluctuations in fuel flow rather well.  Last, but not least, is that the larger openings in the fuel flow controls will tolerate dirtier oil and larger particle size  of contaminates.  In other words the fuel lines and valves won't clog as easy.  The need to have fairly well filtered waste oil or drawing well away from sediment is moot.

LITTLE BALLS:  They sure do work just fine and deliver the oil to the air stream as required.  But they are different from the big balls.  I used brass end caps (3/4" and 5/8" size).  They come with a flat end which makes locating the center and drilling easier (to an extent).  I then chucked mine into a drill press and while they spun I used an angle grinder then some fine sand paper to round off the flat area.  I found out that you must
be careful because the caps aren't as thick as you think they are.  It's easy to take too much metal off and ruin the ball.  Now, given the size of the ball I found that you have to control your fuel delivery much more.  It is easy to flood and overpower the air stream.  Even a little bit of excess flooding can result in a deterioration of droplet size in the fuel fog, which in turn affects combustion.  I found that you really have to control the fuel delivery to the point of very little runoff or no runoff at all.  This has it's own set of plusses and minuses.  If you can get manage to achieve zero runoff then the plumbing for the runoff return line is taken away.  But, you should probably have it plumbed for runoff anyway so you don't create a puddle of overflow in the burner.  Since you are targeting such narrow control over the fuel delivery (i.e. needle valves or
similar) you have to be concerned with particulates in the fuel that could easily build up in the valve and create a blockage.  So, here again I've concluded that the fuel delivery method and level of filtration is the primary determining factor as to which size ball you really need."

Drilling the Itty Bitty Hole

For the atomizer to work properly, the hole for the compressed gas flow needs to be very, very small.  .010" is recommended, though you can use .0135" or even up to .0200".  Any bigger than that, and the droplet size gets too big, and results in poor atomization.

Q: where do I get .010 drill bits?
A: What you want are re-sharpened drill bits that are out of spec (too short) from the drilling of circuit boards. They are solid carbide with 1/8" shanks.

A source for small quantities of resharpened bits is Drill Bit City
5 packs of .0135" bits: $5.75
5 pack of .0100" bits: $7.15

These bits are so small that if you look at them sideways, they'll break.  Ever break a 1/16" drill bit?  These bits are less than 3% the size of a 1/16" bit.  Using a high speed micro drill (like a Dremel tool) is highly recommended.  Also, Dremel drill presses are inexpensive (about $40), and make it easy to drill the hole.   Just make sure you clamp your piece down tightly, and drill very, very slowly.  I've heard that it's possible to drill the hole freehand if you're going through a very thin-wall doorknob, but I broke several bits trying this, and don't recommend it.

To double the heat output, just drill two holes about 1/4" apart.  Note that in my image above of the dual .0135 hole Babington atomizer, the holes are too closely placed - they should be about 1/4" apart instead of the 1/16" apart as shown.  The two fuel sprays collide and form larger droplets, which isn't ideal, but still works.

Compressed Air/Pressurized Gas

Using compressed air for atomization is cheap, and works great.  Highly recommended.  From this chart, we can estimate that a single .010 hole Babington should use approximately 4 cubic feet/hour at 30 PSI (a .010 hole should about 40% the air that a 1/64 hole uses).

Since the air needed is quite low, someone on Wastewatts recommended "some  refrigeration compressors, even possibly an aquarium air pump."

Possible sources for suplus (read: cheap) air compressors:

www.surpluscenter.com
www.usamfg.net

If you don't have an air compressor handy, propane works fine, too.  Expect to use about 0.1 gallons of propane/hour of runtime for each .0135 hole that you drill.   Since 0.1 gallons of propane = 4000 BTU, and a one hole Babington uses about 2/3 gallon of fuel per hour (~80k BTU), the propane component of the heating is less than 5% of the total heating mixture.

Propane pressure seems to make the mixture a little rich, and you have to care about propane leaks, which is annoying.

Fuel Supply

Fuel Pump: A gear oil pump is highly recommended.  Again, try the following places for cheap surplus oil and fuel pumps:

www.surpluscenter.com
www.usamfg.net

I got a 12V gear oil pump that worked great for $20 from Surplus Center.

Dave Brown made a nice diagram of how the fuel supply pump is hooked up in the system:

Fuel Supply Diagram

(click for larger image)

Gravity Feed: Generally, this is a bit more difficult because as the liquid level in the source container drops, the fuel pressure drops, and hence the fuel flow over the atomizer changes.  Some people have gotten it to work just fine, but using a fuel pump is easier.

Constant Head System: Whether you're having problems with an oil pump that pumps at too high of a pressure, or a inconsistent fuel pressure due to gravity feed, one option to guarantee constant fuel flow is to use a constant head system like this one designed by John Archibald:

Constant Head Diagram


I think this is one of the most elegant plumbing systems.  So long as the volume of fuel delivered by the pump is sufficient for the burner, it doesn't matter what kind of pump you have, how much fuel it's delivering, or the delivered fuel pressure.  This will convert it into a low volume, low pressure delivery system, which is what you want in this case (high pressure will splatter fuel off the atomizing ball).

Regardless of how you achieve it, a constant fuel flow is necessary.  If the flow varies at all, the flame can start oscillating and put itself out.

Burner Tube
John Archibald recommends a 6" x 3' tube.  Personally, I've had pretty good luck with a 3" ID by 3' long  pipe so long as it is a single hole.010" atomizer.  Heavy wall pipe is better, as it holds more heat in, making for better combustion.

I've also managed to get a dual hole atomizer working with an old 12" diameter propane tank (see above pictures).  However, when you use a larger diameter pipe, the flame tends to be unstable once the burner tube heats up.  After watching it go out a few dozen times, my theory is that the fuel & air mixture expands so much that it creates a pressurized section in the pipe that is strong enough to overcome the air jet coming out of the Babington nozzle, and this leads to a burner oscillation that will put the flame out.  It's a distictive sound that you'll get to know well until you get it fixed.  How I overcame this problem with the large diameter pipe was to install an inner combustion pipe, 3" x 12", to channel the flame and assist in air entrainment.

You should also block off most of the back of the burner tube, ideally with an adjustable flue of some sort.  I just stuck a cinderblock downstream in the pipe (visible in the pictures above)  Iit retards the airflow away from the atomizer, reducing the chance of it blowing out, as well as helping it to stay hot.  It  was also quite necessary when running in a windy location.

Also, drilling four holes in the burner tube can be quite helpful.  Dave Brown says:
"These holes need to be placed in opposing  pairs.  One pair left and right on the pipe and just slightly (i.e. about 1" plus or minus) forward of the front tip of the nozzle/ball.  The next set should be top and bottom on the pipe and just slightly (i.e. about 1" plus or minus) forward of the first set of holes.  This does more than simply admit combustion air.  It disturbs  the shape of the fuel cone and improves the air/fuel mix in the process, thus improving combustion efficiency and propagation.  More holes may help, but if there are too many or admit too much air at low velocity then it does little to help combustion.  Also, too much air means that you have to also heat that air and send it up the chimney rather than into the walls of the pipe and hence into the space to be heated ... your "shop", as it were.  I do not know if there is any information available regarding how much air or hole area is best.  In my case, using a 6" diameter pipe, I drilled 3/8" (9.5mm) diameter holes and they seem to do the job just fine."

Fuel Sump
This catches the fuel that runs over the atomizer, but is not atomized.  I used the bottom part of an old 20 lb propane cannister as my sump, and used a piece of sheet metal rolled into a cone to keep the fuel from splashing into the sump (this was an improvement from the small H-beam in the photo above).  I should have made the sump deeper than the 3 inches it is: the next version will be an old 20 lb propane tank with the top cut off, which should hold about 12" deep and hold 3 gallons.  This will be my primary fuel source, and when burning 1 gallon per hour, will act as a 3-hour timer on the burner - just about right for my purposes (YMMV).

Starting Your Babington Burner (and how to keep the flame from going out)

Turn on the gear oil pump, turn on the air compressor, and then light the atomized liquid fuel with a small propane torch or butane jet lighter.  Watch it burn for a second or two and then, most likely, go out.  This begs the question: how do you keep it lit?

Pre-heating the Oil
Pre-heating the oil before it pours over the atomizer is pretty much required to keep your Babington lit.  The simplest way to do this is just make a couple of wraps around your burner tube with 1/4" copper tubing before delivering the fuel to the gear oil pump.  Adjust the number of wraps until the fuel is preheated to an adequate temperature.  About 140 degrees F seems to be about right for kerosene or diesel, and 160-180 F for any heavier oils.  If you get any hotter, you may start causing in-line gasification, and you then risk building up crud in the line and plugging it up.

Warning: if you coil your supply fuel line around your combustion tube for preheating, then if your fuel supply runs out or the pump stops, the fuel in your fuel line will heat up to the temperature of the burner (about 1200 degrees F), which is above the flashpoint for most fuels.  If your fuel flow stops for more than a few seconds, is it safest to wait 10-15 minutes until everything cools, then try restart the burner. I once didn't wait, and had superheated oil flow into my sump and start it on fire - not good!

However, using fuel line wraps around the burner only helps preheat the fuel _after_ the burner is running: it doesn't help when you first start up your burner.  Possible solutions include:

Adjust the Compressed Air/Gas Flow
20-30 PSI seems to be about the right range for good combustion, 30 PSI for startup, 20-odd PSI for running.

If the flame is blown down the tube before igniting, lower the gas pressure.  If it's already too low, you may be using too small of a tube (a 3" tube is too small for a dual hole atomizer).  Also, did you remember to put a flue or otherwise restrict the flow out the end of the burner tube? 

If the flame is yellow and sooty, increase the gas pressure.  The mixture is too rich, and needs more air.

For feedback and comparison purposes, it helps to have an air pressure gauge in the system.  These can be found as most any big box hardware store in the air tools section.  They should cost about $10 each.

Constant Fuel Flow - oscillations in the flame front can be caused by inconsistent fuel flow over the atomizer.  See the "Fuel Supply" section for more information on avoiding this problem.

Constant Air Flow
If, after burning for a few minutes, the Babington goes out when the flame "runs away" down the burner tube, you may need to install a flue to control the airflow.  This usually happens if you have a vertical exhaust vent.  What's probably happening is that the vent is heating up, increasing the flow of air through the tube, and eventually blowing out the burner with too much air.

Still having problems?
Are you using a .010" hole?  Larger holes create a larger droplet size, which are harder to light and sustain.


Additional Information

Hundreds of photos of working Babington burners can be found in the Wastewatts photo gallery:
http://photos.groups.yahoo.com/group/wastewatts/lst

Here's a nice Babington made from 1.5" pipe:
http://dragoneagle.50megs.com/metalworking/babington.html

The (currently quite anemic) Babington Oil Burner FAQ is available here.

There is a Babington Burner-specific email list:, altfuelbabington, that is an offshoot of the altfuelfurnace group.
http://dir.groups.yahoo.com/group/altfuelbabington/

To ask questions of knowledgeable people, join the Wastewatts discussion group on Yahoo Groups.  Search the message archives for answers to most any Babington-related question (and I mean most any question - they've all been asked before).

The original page where I learned how to make a Babington burner can be found here:
http://www.green-trust.org/2000/biofuel/babington/default.htm

Finally, here's a page about Babington burners from the folks that know best:
http://www.babingtontechnology.com/how_does_the_babington_burner_work.htm

Acknowledgements
Robert Babington
John Archibald - most of this document is taken from information he's collected and written about in the Wastewatts group
Dave Brown - some passages were lifted verbatim from his posts to Wastewatts
Steve Spence - for hosting the green-trust site where I first learned about the Babington
Nick Fankhauser and HC for providing good feedback
All the rest of the folks on Wastewatts for their insights and encouragement.

(c) 2004-2007 Tom McCarty (email tom at the domain aipengineering.com)
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