Robert S. BABINGTON
Nebulizer
N. Metzger: "Clog-Proof Superspray Oil Burner" ~ Popular Science (January 1976)
R. Babington: US Patent # 4,573,904 ~ Liquid Delivery Apparatus & Method for Liquid Fuel Burners
R. Babington: US Patent # 4,155,700 ~ Liquid Fuel Burners
R. Babington: US Patent # 3,425,058 ~ Fuel Burner
R. Babington: US Patent # 3,4228,795 ~ Apparatus for Producing Finely Divided Liquid Spray
R. Babington: US Patent # 3,864,326 ~ Spraying Devices, in Particular Nebulizing Devices
R. Babington: US Patent # 3,790,080 ~ Method of Spraying
R. Babington: US Patent # 3,425,059 ~ Power Humidification Apparatus
R. Babington: US Patent #3,421,692 ~ Method of Atomizing Liquids...
Popular Science (January 1976) ~
"Clog-Proof Superspray Oil
Burner"
by Norman Metzger
A new type of nozzle promises fuel savings of up to 15%
"We’re in the midst of an energy crisis", inventor Robert Babington reminded me at his home in this Washington suburb. "And if you ask what the advantage of this device is, it’s a 15% saving in fuel oil."
The device Babington was describing is an oil-burner head with a revolutionary new spray nozzle (PS, May 1973). In addition to its remarkable fuel-saving potential, Babington claims oil furnaces using his invention won’t soot up, will never clog, and can even run on crankcase oil and diesel-fuel mixture.
Experts I’ve talked to back up the claims for the oil burner, which could one day shave your fuel costs two ways:
(1) Fuel can be burned more evenly and completely, because it is converted into a superfine, uniform spray.
(2) Heavier, less-costly oil can be used; the burner’s operating principle makes it independent of fuel viscosity.
The secret behind the new oil burner is in the unique properties of the burner head. Most nebulizing sprayers (misting sprays used for everything from medical tents to insecticides) use compressed air to spray liquids through a nozzle.
Babington, a former NASA engineer, reversed that principle. He forces only air through one or more tiny slots in a bulb. The air breaks up any liquid flowing over the slot into minute particles. Since no liquid goes through the slot, there’s no clogging problem. And, unlike conventional sprays, the viscosity or thickness of the liquid isn’t critical. Babington gave me a dramatic illustration: one by one, he poured motor oil, turpentine, and paint thinner over a flaming oil-burner head. The flame kept going in spite of the liquid used.
Burning Crankcase Oil
What’s important is surface tension. Almost any liquid fuel will burn, since most have similar surface tensions. Babington explained what this implies: "With this burner, a gas stateion could take compressed air, mix its crankcase oil with diesel fuel or kerosene, burn it, and see no real difference in performance compared to what they’re getting today from straight diesel fuel [See "Adventures in Alternate Energy", PS June 1975]."
There’s solid support for the oil burner from people who have taken a hard look at it. "We field-tested about 50 of them", says Rix Beals, technical consultant to the National Fuel Oil Institute (NOFI), the trade association for home-heating oil dealers. "Even though we had teething problems in these field tests", Beal said, "most of the men who tested these burners are still bugging us, asking when they’re going to get to market, because they want them". NOFI has backed the Babington burner with cash -- about $250,000 in direct and indirect funds -- in the effort, as yet unsuccessful, to market the new burner.
NOFI, a subsidiary of the National Oil Jobbers council, has also looked at costs for the Babington burner. "There was a range of values", Beals told me, "and at every point we felt it could be produced at no more -- and apparently in many cases a good deal less -- than conventional burners."
"I don’t see what’s wrong with it", adds Gerald Leighton, who at the time was Chief of Energy and Utilities Applications for the US Dept. of Housing and Urban Development (HUD). "It’s low cost. It’s efficient. The potential for life-cycle costs looks excellent. And I haven’t seen a comparable device."
Despite the enthusiasm, however, there’s still no manufacturer for the burner. Babington made his first working model of the burner in 1967, using part of an aquarium pump and a sewing machine motor. He then licensed the burner to an aerospace company trying to diversify into consumer products.
Eventually another company was set up to market the burner, but it was run by people who "didn’t understand the basic principles of the device", according to Babington. He saw their product for the first time at a 1972 Washington trade show. To his horror, it had a host of problems: sooting, poor ignition, and too long a flame; ultimately, the burner was rejected by Underwriters Laboratories. "If you give the wheel to the wrong team, they won’t be able to roll", is the way Babington sums up that episode.
Babington has since recovered the license to his burner and has made basic changes that, according to Beals, "solve some of the problems we ran into in the field tests".
Two Heads Are Better...
Babington stopped the sooting by moving the igniters out of the spray zone. He added a second atomizing head or bulb; two sprays and thus two flames are contined in one burner head. The two sprays meet to produce what Babington calls a "really beautiful fire".
NOFI’s Beals agrees: "The double atomizing head is definitely an improvement. By using two flames firing at each other", he explains, "you create a fixation or stabilizing point for the flames out in space. The electrodes now have a point at which to create ignition. So, the burner will start better than any previous model; it will start almost instantly without any pop or puff.
"The fixation point", Beals adds, "makes the flame more stable, less bothered by drafts, and more reliable. That burner should ignite literally thousands of times in sequence without misfiring."
The savings, Beals explained, come largely from the very fine oil mist produced in the Babington burner. A homeowner could save some $60 a year, based on the national average annual consumption of 1200 gallons for each home at 25 cents/gallon.
"We knew", says Beals, recalling NOFI’s long search for a better burner head, "that the touchstone to improvement was atomization, the quality of the drops produced. Not only how fine they are, but also how uniformly fine. If you have a fog of fine droplets, it ignites easier and you should be able to use less power in your ignition system.
"There were other atomization techniques, but for the most part they were not reliable, And they added cost, weight and power draw. They had a lot of negatives, and besides did very little to eliminate the clogging problem."
When Beals and his NOFI team tested the Babington burner, they found that at practical flow rates (one-half to one gallon/hour), it achieved a finer droplet size than any other atomization technique they had found.
The finer droplet size means easier ignition. It also means less air is needed for complete ignition and a more manageable flame. All this adds up to a better burning fuel. As evidence for this, Babington cites two things: a 14.5% carbon dioxide level instead of the average 9% for conventional burners, and a lack of smoke.
The new burner, Babington and Beals say, can replace existing heads in almost any oil furnace. Most of these are "gun burners", named after the shape of a high-pressure oil pump and pressure nozzle. Those nozzles do a heck of a good job, Beals says, but they do clog and do not atomize fuel the way a Babington burner will.
What’s next? "It’s at the point", Beals told me, "where -- possibly with some alternate control and ignition systems -- you can make some manufacturing decisions, and then sit down and design a final manufactured form".
Meanwhile, Babington is working on other things, including a vaporizing burner, one that atomizes the fuel completely, not just into small droplets. The fuel is then burned as a gas would be.
He showed me a model of this vaporizing burner; its secret is that the liquid fuel is kept vaporized until it reaches the ignition point. Once again, Babington did it by installing two atomizing heads in his burner, but his time he made one smaller than the other. The spray from the smaller head is ignited instantly as it comes out of the bulb. It intersects the second larger -- and unlit -- spray. The latter, however, does not ignite because it doesn’t have enough air. Heat from the smaller flame keeps the second spray vaporized, and it ignites when it finally "sees" enough air, or when a second set of igniters turns it on.
Vaporizing burners already developed sometimes use heated plates to vaporize fuel poured over them. This creates problems, including soot and smoke. Babington claims his "free-stream vaporizing burner" doesn’t have these problems. He acknowledges the burner needs more work before it’s ready to try commercial waters.
Medical Nebulizers
The engineer has already shown he can take his invention along the treacherous seas from a good idea to a commercial product. The Babington principle is the heart of several commercial nebulizers marketed by American Hospital Supply Corporation’s McGaw Laboratories. The devices have captured about 10% of a $5- to $6-million-a-year market.
Babington is also working on additional medical and health applications of his nebulizing spray. He’s created a "medicant" nebulizer. With each breath, a patient inhales mist and medication through a disposable mouthpiece. And a working mode of his "home-therapy console" is in his workshop, too. Switches convert it to either a nebulizer or humidifier, and change the amount, intensity, and temperature of the mist.
For now, Babington’s hopes -- and those of quite a few others -- are riding with the new oil burner he created some 8 years ago. "It’s been a long, slow struggle with this thing", recalls Beals. "And it’s been mainly a matter of finding the right company. But we’ve never given up hope we can get to market because it’s one of the things we need. And we need it more now than we did 5 years ago."
The 170 gallons average that would be saved annually by each home oil burner outfitted with a superspray nozzle could make a significant contribution to our national fuel reserves. The question now is whether we can afford to neglect it for even another season.
How Superspray Works
Liquid washing over the outside surface of a small glass or plastic bulb forms a thin surface film. Air forced through one or more slots in the bulb breaks the liquid into a fine spray (right) that can shoot out 6 feet or more. Key advantages of sprayer principle: Uniformity of particle size and the elimination of clogging. A second atomizing bulb has been added to improve efficiency.
Liquid Delivery Apparatus & Method for Liquid Fuel Burners and Liquid Atomizers
Abstract
An improved apparatus and method for delivering liquid are disclosed for use in fuel burners or atomizers of the type which comprise a hollow atomizer bulb having a convex exterior surface which tapers toward a small aperture through which high pressure gas if forced to atomize liquid as it flows in a thin film over the bulb. To provide thinner films when lower atomization rates are desired and thicker films when higher atomization rates are desired, a feed tube is positioned above the atomizer bulb with its discharge opening oriented so that the vertical distance from its front edge to the surface of the bulb is from 1.5 to 2.0 times the vertical distance of its rear edge to the surface of the bulb. In another embodiment the discharge opening of the feed tube is elongated and has a major axis oriented transversely to the axis of the spray leaving the aperture.
References Cited
U.S. Patent Documents:
3425058 ~ Jan., 1969 ~ Babington ~ 431/117
4155700 ~ May, 1979 ~ Babington ~ 431/117
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is related to three other applications filed concurrently and entitled Flow Control Module and Method for Liquid Fuel Burners and Liquid Atomizers (two applications) Ser. No. 476,292 and Ser. No. 476,455 and Improved Atomization Apparatus and Method for Liquid Fuel Burners and Liquid Atomizers Ser. No. 476,454, now U.S. Pat. # 4,507,074; # 4,516,928; and # 4,507,076 respectively.
TECHNICAL FIELD
The present invention concerns liquid fuel burners and liquid atomizers and methods of operating such burners and atomizers. The apparatus and method of the invention are particularly related to liquid feed systems for burners and atomizers of the type which incorporate an atomizer bulb having a smooth, convex exterior surface tapering toward an aperture. A flow of air or other gas is directed through the aperture to atomize fuel or other liquid as it flows in a thin film over the exterior surface of the atomizer bulb.
BACKGROUND ART
In January 1969, U.S. Pat. # 3,421,692; # 3,421,699 and # 3,425,058 issued to Robert S. Babington, the present applicant, and his co-inventors. These patents disclose a type of liquid atomization apparatus which is particularly useful in liquid fuel burners. The principle involved in the apparatus, now frequently referred to as the "Babington principle," is that of preparing a liquid for atomization by causing it to spread out in a free-flowing thin film over the exterior surface of a plenum having an exterior wall which defines the atomizer bulb and contains at least one aperture. When gas is introduced into the plenum, it escapes through the aperture and thereby creates a very uniform spray of small liquid particles. By varying the number of apertures, the configuration of the apertures, the shape and spray characteristics of the surface, the velocity and amount of liquid supplied to the surface, and by controlling the gas pressure within the plenum, the quantity and quality of the resultant spray can be adjusted as desired to suit a particular burner application. Various arrangements of such atomization apparatus have been disclosed in other U.S. patents issued to the present applicant, namely U.S. Pat. # 3,751,210; # 3,864,326; # 4,155,700; and # 4,298,338. The disclosures of the patents mentioned in this paragraph are specifically incorporated by reference into this application.
So that liquid fuel burners and liquid atomizers constructed in accordance with the Babington principle will have the widest possible range of applications, it has been found desirable to provide the maximum possible variation in the volumetric flow rate of the atomized fuel or other liquid between the lowest and the highest flow rates required. For example, flow rates as low as 0.3785 liter (0.1 gallon) per hour may be required for some applications and as high as 3.785 liters (1.0 gallon) per hour may be required for others.
Once the particular geometry for a given atomization apparatus has been selected, however, changes in the flow rate of the atomized liquid must be made primarily by adjusting the flow rate of liquid onto the atomizer bulb. For the lowest flow rates desired, the liquid film thickness at the aperture preferably would be the thinnest achievable while still maintaining a continuous film over the exterior surface of the atomizer bulb. On the other hand, to provide higher flow rates of the atomized liquid, it is necessary to increase the thickness of the film at the aperture without increasing it so much that undesirably large liquid particles are formed. In the prior art apparatuses, a single liquid feed tube has been positioned above each atomizer bulb a distance of approximately 3.175 to 9.53 mm (0.125 to 0.375 inch) so that a variable flow rate of atomized liquid from about 0.757 to 2.27 liters (0.2 to 0.6 gallons) per hour has been achievable. Various applications have remained, however, in which flow rates above and below this range have been desired but have not been reliably achievable.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide an improved apparatus and method for delivering liquid fuel to an atomizer bulb which operates in accordance with the Babington principle so that both higher and lower flow rates can be achieved than have been found possible with prior art atomizer bulbs.
Another object of the invention is to provide such an apparatus and method in which the high intermediate and low flow rates produce essentially stable films at the aperture of the atomizer bulb.
A further object of the invention is to provide such an apparatus and method in which entrained gases or bubbles in the liquid are shed immediately from the feed tube delivering the liquid to the atomizer bulb and also from the surface of the atomizer bulb, to eliminate undesirable fluctuations in the liquid film flowing over the atomizers and, hence, fluctuations in the firing rate, which the presence of such bubbles would otherwise tend to cause.
Yet another object of the invention is to provide such an apparatus and method for feeding liquid fuel which can be used with atomizer bulbs made in accordance with the Babington principle but which have a variety of convex surfaces which taper toward the atomizing aperture.
These objects of the invention are given only by way of example; therefore, other desirable objectives and advantages inherently achieved by the disclosed apparatus may occur or become apparent to those skilled in the art. Nonetheless, the scope of the invention is to be limited only by the appended claims.
The apparatus and method according to the invention are particularly adapted for delivering liquid fuel or other liquid to an atomizing means of the type which includes a plenum having an exterior wall with a small aperture therethrough, the exterior surface of this wall being smooth and convex and tapering toward the aperture. A feed tube is provided through which liquid is to be flowed over the exterior surface and across the aperture, the tube having a downwardly directed, essentially straight portion with a center line. The straight portion terminates above the plenum with a discharge opening which is positioned with its front edge closer to the aperture than its rear edge and with the extended center line of the tube reaching a convex portion of the exterior surface of the plenum.
In one embodiment, the vertical distance from the front edge of the discharge opening to the convex portion preferably is about 1.5 to 2.0 times the vertical distance from the rear edge to the exterior surface. As a result of this configuration, when liquid flows through the feed tube at flow rates sufficient just to cover the exterior surface of the plenum with a thin film suitable for low atomization rates, a bulbous-shaped stream is established between the discharge opening and the surface of the atomizer bulb. The bulbous-shaped stream preferentially directs itself more away from the aperture than would a stream flowing parallel to the discharge leg of the feed tube. On the other hand, when liquid flows through the tube at relatively high flow rates sufficient to smoothly cover the exterior surface of the plenum with a thicker film suitable for higher atomization rates, the stream between the discharge opening and exterior surface preferentially directs itself toward the aperture. At liquid flow rates in between these minimum and maximum conditions, the path of liquid leaving the feed tube is parallel to the axis of the discharge leg of the feed tube, as one might expect. Thus, a thinner film is formed over the aperture at lower flow rates through the feed tube due to the bulbous effect and a thicker film is formed over the aperture at higher flow rates through the feed tube because of a forward deflection of the liquid, so that respectively lower and higher flow rates of atomized liquid can be achieved.
In this embodiment of the invention, the plane of the discharge opening of the feed tube is horizontal; however, it is also within the scope of the invention to position the rear edge of the discharge opening below the front edge. In such a case, the vertical distance from the front edge of the tube preferably is at least equal to the inside diameter of the feed tube. In order to ensure smooth flow from the discharge opening of the feed tube, its downwardly directed, essentially straight portion preferably has length about 10 to 15 times the inside diameter of the tube.
In another, preferred embodiment of the invention, the discharge end of the otherwise cylindrical feed tube is flattened into a somewhat "duckbill" configuration having a flow area shaped as an elongated oval with major and minor axes. The plane of this oval discharge opening preferably is essentially parallel to a plane tangent to the upper surface of the atomizer bulb with the major axis of the oval discharge opening preferably essentially perpendicular to the spray axis of the atomizer bulb. In this preferred embodiment, the stable minimum film thickness at the aperture is less than can be reliably achieved with the previously described embodiment, for the same minimum flow rate through the feed tube. Also, a greater, stable maximum film thickness can be achieved at the aperture with a smaller maximum flow rate through the feed tube, than can be reliably achieved with the previously described embodiment. In the latter case, less fuel must be recirculated at the maximum atomization rate, so that reduced pump capacity is needed. In addition, the reduced liquid flow over the atomizer bulb provides better film stability and causes the drain-off liquid stream to be more or less laminar, thereby facilitating its removal and return to the sump. This preferred embodiment is also very effective in shedding bubbles that might otherwise hang up in the space between the atomizer bulb and the discharge end of the feed tube.
In the preferred embodiment, the sensitivity of the film thickness at the aperture of the atomizer bulb to changes in the flow rate in the feed tube decreases dramatically as the major axis of the oval discharge opening is rotated from a position perpendicular to the spray axis to a position parallel to the spray axis. In the latter, limiting case, the film thickness at the orifice remains essentially stable regardless of changes in the flow rate in the feed tube. However, when the major axis of the oval discharge opening is parallel to the spray axis, the feed system continues to resist formation of bubbles between the feed tube and the atomizer bulb.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a fragmentary elevation view of an atomizer bulb which operates in accordance with the Babington principle, a feed tube for liquid fuel positioned above the atomizer bulb in accordance with one embodiment of the present invention and the associated air and fuel sources and ignition device necessary to comprise a complete fuel burner.
FIG. 2 shows a fragmentary elevation view of a liquid fuel atomizer according to one embodiment of the present invention and particularly illustrates the direction of flow of fuel away from the atomizing aperture at low fuel flow rates.
FIG. 3 shows a fragmentary elevation view of a liquid fuel atomizer according to one embodiment of the present invention and particularly illustrates the flow of the fuel toward the atomizing aperture at high fuel flow rates.
FIG. 4 shows an elevation view of a tubular blank used to make a feed tube for use in the preferred embodiment of the invention.
FIG. 5 shows an elevation view of a feed tube according to the preferred embodiment of the invention, in the preferred position above the automizer bulb.
FIG. 6 shows a section view taken on line 6--6 of FIG. 5.
FIG. 7 shows an elevation view of an alternative configuration of a feed tube according to the preferred embodiment of the invention, as positioned above the atomizer bulb.
BEST MODE FOR CARRYING OUT THE INVENTION
The following is a detailed description of several embodiments of the present invention, reference being made to the drawing in which like reference numerals identify like elements of structure in each of the several Figures.
FIG. 1 shows a system for atomizing liquid fuel or other liquid, which operates in accordance with the Babington principle. An atomizer bulb 10 comprises an enveloping, convex exterior wall 12 which defines an internal plenum (not illustrated) and includes a frontal aperture 14, typically a narrow horizontal slit passing completely through the exterior wall. A source 16 of high pressure air or other gas is connected to the plenum defined by exterior wall 12 by means of a conduit 18 so that in operation a flow of air is caused to pass through aperture 14. Positioned above atomizer bulb 10 is a liquid feed tube 20 which preferably has a circular cross-section but may also have other cross-sections without departing from the scope of the present invention. Liquid drawn from a sump 22 through a conduit 23 by a pump 24 is caused to flow through a further conduit 25 into feed tube 20 from which it flows over atomizer bulb 10 and forms a film of liquid which completely covers the surface of bulb 10. As air flows through aperture 14, the film of liquid continuously forming at the aperture is continuously broken into tiny droplets of liquid which move away in the form of a fine, conical spray 26 of atomized liquid. Liquid not atomized to form spray 26 flows from the lower side of bulb 10 as a stream 28 which is directed back to sump 22, as illustrated. To complete the schematic illustration of a fuel burner, FIG. 1 also shows an igniter 30 which extends to spray 26 at a downstream location in order to ignite the fuel in the manner described more completely in the previously-mentioned patents.
In prior art liquid fuel burners and liquid atomizers which operate in accordance with the Babington principle, the firing rate of the burner, or the atomizing rate, is varied by changing the volumetric flow rate of liquid in spray 26. In a typical prior art application, a flow of approximately 7.6 to 45.4 liters (2 to 12 gallons) per hour through feed tube 20 results in a spray flow rate or firing rate of approximately 0.76 to 2.27 liters (0.2 to 0.6 gallons) per hour. The change in flow rate through feed tube 20 causes a corresponding change in the thickness of the film reaching aperture 14 so that a change in firing or atomizing rate is achieved.
In accordance with the embodiment of the present invention shown in FIGS. 1 to 3, the position of feed tube 20 is selected so that at the lower flow rates through feed tube 20, the stream of liquid leaving the feed tube is preferentially directed away from aperture 14 so that a thinner film is produced at aperture 14 than has heretofore been achievable. Conversely, at the higher flow rates through feed tube 20, the stream of liquid leaving the feed tube is preferentially directed toward aperture 14 so that a thicker film is achieved.
As shown in FIG. 1, feed tube 20 has an essentially straight portion 32 which extends downwardly toward atomizer bulb 10 and includes a centerline, as illustrated. The length L of portion 32 preferably is ten to fifteen times the internal diameter D of feed tube 20 that any irregularities in flow through the feed tube 20 will have dissipated, for the most part, by the time the liquid issues from discharge opening 34. In accordance with this embodiment of the invention, the front edge 36 of discharge opening 34 is positioned further away from the surface of bulb 10 than is the rear edge 38 of discharge opening 34; and the center line of portion 32 is positioned so that it passes through a convex area of exterior wall 12 as illustrated. Wall 12 preferably has an exterior surface which is smooth, convex and tapered toward aperture 14. As used in this application, "convex" means that geometric normals will diverge when constructed at neighboring points on the "convex" portion of bulb 10. Thus, at the tip of atomizer bulb 10, the exterior wall 12 may be spherical having a radius R, ellipsoidal, hyperbolic, parabolic, and so forth. The portion of bulb 10 to the rear of the center line of feed tube 20 may be a right circular cylinder, a frustrum of a cone whose sides diverge at an angle .beta. or the other half of a sphere, ellipsoid, paraboloid or the like.
In accordance with the invention, the vertical distance V.sub.f from front edge 36 to exterior wall 12 and the vertical distance V.sub.r from rear edge 34 to the surface of wall 12 are chosen so that V.sub.f is approximately 1.5 to 2.0 times larger than V.sub.r. In this embodiment, front and rear edges 36 and 38 are in a common horizontal plane; however, it is also within the scope of the invention to position point 38 below point 36, or vice versa, as indicated by angle .alpha. in FIG. 1. Whether .alpha. is positive (i.e., edge 38 below edge 36) or negative as would be the case if edge 36 was below edge 38, depends upon the flow rate through tube 32, and the amount and size of air or gas bubbles contained in the liquid stream. If the burner is to be operated at generally lower firing rates a positive .alpha. is preferred, whereas at higher firing rates a negative .alpha. is preferred. In general it is easier to shed large air bubbles when .alpha. is positive, but the corresponding film is not as stable at high flow rates. Because of these tradeoffs, and the desirability of a burner to handle a variety of fuels over a wide firing rate range, an .alpha. of 0.degree. is often selected as a happy medium and for ease of manufacturing.
When feed tube 20 is configured and positioned in the manner just described, the flow of liquid through discharge opening 34 displays unexpected and important characteristics. FIG. 2 illustrates the position assumed by the stream of liquid leaving discharge opening 34 when the flow through feed tube 20 is at the lowest possible flow which still achieves a complete film on the exterior surface of bulb 10. As shown in FIG. 2, the stream takes on a rearwardly directed bulbous shape which preferentially directs fuel away from aperture 14 because the bulbous stream touches the atomizing surface closer to edge 38 than to edge 36. This occurs because the axis of leg 32 intersects the convex surface of atomizer bulb 10. As a result, the film of liquid fuel formed at aperture 14 is quite thin and the firing or atomizing rate is proportionately smaller. As the flow of liquid through feed tube 20 is increased, the stream leaving discharge opening 34 gradually assumes a more vertical position as illustrated in FIG. 1 and the amount of liquid leaving in spray 26 increases accordingly. Finally, as illustrated in FIG. 3, when the flow through feed tube 20 is increased to the maximum consistent with maintaining a smooth film of liquid on the exterior surface of bulb 10, the stream of liquid leaving discharge aperture 14 preferentially shifts itself toward the front of atomizer bulb 10. This causes a relatively thicker film to form at aperture 14 which results in a correspondingly higher flow of liquid in spray 26.
The following dimensions represent some typical values for a liquid fuel atomizer, according to the embodiment of FIGS. 1 to 3, which will produce a variable atomization rate from about 1.1 to about 3 liters (0.29 to about 0.79 gallons) per hour based on fuel feed rates of about 7.5 to 45 liters (1.98 to 11.89 gallons) per hour through feed tube 20. A typical atomizer bulb 10 has an essentially spherical convex portion having an outside diameter of about 10.2 to 1.5 mm (0.4 to 0.6 inches) The cross-sectional area of discharge aperture 14 typically is about 10.97.times.10.sup.-4 to 12.26.times.10.sup.-4 cm.sup.2 (1.7.times.10.sup.-4 to 1.9.times.10.sup.-4 square inches) and the pressure applied to the interior of atomizer bulb 10 typically is in the range of 1.02 to 1.6 bar (15 to 23.5 psi). The spacing between the lower end of feed tube 20 at rear edge 38 and the surface of atomizer bulb 10 preferably is from about 1.78 to 2.54 mm (0.070 to 0.100 inch). The spacing between the forward edge 36 of the feed tube and a vertical line through aperture 14 is normally between 1.02 to 1.65 mm (0.040 to 0.065 inch) while the internal diameter of tube 32 is between about 2.16 to 2.54 mm (0.085 to 0.100 inch). Liquid fuel atomizers thus configured and operated have been found to exhibit the desired flow switching characteristics when operated with liquid fuels having a viscosity range of 2.0 to 10.0 centistokes.
FIGS. 4 to 7 show the preferred embodiment of a liquid fuel delivery apparatus according to the invention. Here, feed tube 20 is formed from a blank 20', shown in FIG. 4, for example made from about 3.18 mm (0.125 inch) outside diameter, about 2.36 mm (0.093 inch) inside diameter stainless steel tubing. Blank 20' has a horizontal upper portion 40 and a downwardly extending, forwardly angled portion 42. The angle .gamma. between portions 40 and 42 preferably is about 100.degree., but may be in the range of 90.degree. to 110.degree. without departing from the scope of the invention. So that the plane of the discharge opening of the feed tube ultimately will be essentially parallel to a plane tangent to the upper surface of an atomizer bulb of the type previously described, the discharge end 44 of blank 20' preferably slopes upwardly and rearwardly at an angle .delta. of about 20.degree., but may slope at an angle in the range 10.degree. to 30.degree. without departing from the scope of the invention.
In the preferred embodiment of the invention, discharge end 44 of blank 20' is flattened transversely to the plane of the center lines of portions 40 and 42, as shown in FIGS. 5 and 6, to provide a short flow passage 46 and discharge opening 48 having a flow area shaped as an elongated oval with a major axis 50 and a minor axis 52. For a blank 20' of the size and material previously described, the tube is squeezed until the minor axis 52 is approximately 1.4 mm (0.055 inch) and the major axis is 3.30 mm (0.130 inch). The axial length of flow passage 46, the "duckbill" portion of the feed tube, preferably is in the range of 6 to 9 mm (0.250 to 0.350 inch) to ensure that any flow irregularities induced by the change in cross-section will be adequately damped by the time the fuel discharges from opening 48.
A feed tube configured as shown in FIGS. 4-6 preferably is positioned directly above atomizer bulb 10 so that the plane of the discharge opening 48 is 0.51 to 0.76 mm (0.020 to 0.030 inch) above the surface of the atomizer bulb; the leading edge of opening 48 is 5.1 to 6.4 mm (0.200 to 0.250 inch) behind aperture 14; and major axis 50 is essentially perpendicular to the spray axis 54 of the atomizer bulb. In this configuration, the thickness of the film at aperture 14 varies smoothly from a minimum at a flow rate through feed tube 20 of about 7.6 liters (2.0 gallons) per hour corresponding to an automization rate of about 0.56 liters (0.15 gallons) per hour, to a maximum at a flow rate through feed tube 20 of about 30 liters (8.0 gallons) per hour corresponding to an atomization rate of about 3.8 liters (1.0 gallons) per hour. Bubbles in the fuel do not tend to adhere between discharge opening 48 and the upper surface of atomizer bulb 10, primarily because of the close spacing between end 48 and the surface of atomizer 10.
As major axis 50 is rotated relative to spray axis 54, while maintaining essential parallelism between the plane of discharge opening 48 and a plane tangent to the upper surface of the atomizer bulb, the thickness of the film at aperture 14 and the corresponding atomization rate vary less and less with changes in the flow rate through feed tube 20. When duckbill portion 46 is positioned so that major axis 50 is essentially parallel to spray axis 54 as shown in FIG. 7, virtually no change in atomization rate is experienced due to changes in the flow rate through feed tube 20. Thus, the configuration of FIG. 7 may be preferable where substantial fluctuations in flow are anticipated in conduit 25 and where the burner is to be operated at an essentially constant fuel rate. However, the atomization rate remains essentially stable in this limiting case and bubbles in the fuel do not tend to adhere between discharge opening 48 and the upper surface of atomizer bulb 10, for the same reasons as previously mentioned.
Industrial Applicability
While the present invention has been disclosed as particularly suited for use in liquid fuel burners, those skilled in the art will recognize that its teachings also may be followed for other applications of the Babington principle where it is desired to obtain a maximum variation in the flow rate of the vaporized liquid.
US Patent 4,155,700
Liquid Fuel Burners
Abstract --- An improved fuel burner particularly adapted for domestic use and capable of burning fuels such as fuel oil and the like with extremely high efficiency and low pollutant output is comprised of a pair of identical spray heads, each including a spherical plenum onto which the fuel is flowed for atomization, the spray heads being disposed at the end of a flame tube which in turn is located within a blast tube, said spray heads further being disposed symmetrically with respect to the axis of both the flame tube and the blast tube and angularly disposed relative to each other whereby the spray output from the spray heads creates a turbulence within the flame tube such that the propagation of the flame front within the tube can be readily controlled and whereby the fuel may be readily ignited by a spark type of ignitor which is disposed centrally between the spray heads. The plenum is provided with one or more apertures through which atomizing gas is passed to generate the spray, and air access ports are so located in the flame tube such that substantially complete combustion of the fuel is effected.
References Cited
U.S. Patent Documents:
1577114 ~ Mar., 1926 ~ De Walt ~ 239/543
1910615 ~ May., 1933 ~ Laney ~ 239/543
3067582 ~ Dec., 1962 ~ Schirmer ~ 431/117
3425058 ~ Jan., 1969 ~ Babington ~ 431/117
3539102 ~ Nov., 1970 ~ Lang ~ 239/434
3595482 ~ Jul., 1971 ~ Loveday ~ 239/434
3923251 ~ Dec., 1975 ~ Flournoy ~ 431/351
4035137 ~ Jul., 1977 ~ Avand ~ 431/351
4036582 ~ Jul., 1977 ~ Fehler et al. ~ 431/352
Primary Examiner: Yuen; Henry C. ~ Attorney, Agent or Firm: Pollock, Vande Sande & Priddy
Description
PRIOR ART AND BACKGROUND
As is well recognized in the industry, there has long been a need to develop and to provide a fuel burning system which is capable of burning a liquid fuel in a very efficient manner and without the side effects of inadequate combustion which lead to the omission of pollutants into the atmosphere.
In the case of residential oil burners, the burner must operate with low smoke emissions to prevent sooting of the heat exchanger and objectionably high smoke levels in residential neighborhoods. The result is that large amounts of excess air must be introduced in the residential combustion process to assure that the burner operates at acceptable smoke levels.
It is well known that conventional oil burners burn very differently when they are placed in different type furnaces. This is because of the poor fuel atomization of current high pressure oil burners, which when installed in a furnace, cause some of the oil particles that discharge from the nozzle to be very large. These large particles take time to vaporize and burn and may therefore, fall to the bottom of the combustion chamber without burning. When the combustion chamber is cold, these large particles form a puddle in the bottom of the combustion chamber. When the combustion chamber is heated, these large droplets or, in some cases, puddles of fuel, eventually vaporize and burn.
There will be more or less puddling or spattering of large particles on the walls of the combustion chamber, depending upon the particular combustion chamber design and the temperature within the firebox. As a result, the combustion chamber or firebox, in a normal home furnace, acts as an afterburner to burn large particles of fuel because the atomization system in a conventional gun burner cannot by itself adequately atomize the fuel.
An oil burner may be 2-3 times larger than is necessary to provide adequate space heating when it is intended that the same burner shall be used to provide hot water in addition to space heating. When outside temperatures are low and hot water demands are high, the burner must be able to satisfy both of these requirements when the demands are at a peak. However, when the demand for heat is low, as in the spring and fall months, and hot water demands are at a minimum, as would be the case at night, the burner still operates at the same firing rate as it does when heating and hot water demands are high. The only difference is that when the requirements are low, the burner may only stay on for quite short period. This is an inefficient mode of operation since, under these conditions the burner cycles on and off many times so that fuel economy is very low. During this short on cycle with such a burner, the burner cannot achieve smokeless operation, and reasonable efficiency, before the thermostat cuts it off. During "off" cycle, much of the residual heat in the furnace is dissipated to the atmosphere and contributes to increased fuel costs.
An innovative approach to fuel burners is illustrated in U.S. Pat. # 3,425,058, issued Jan. 28, 1969, to Robert S. Babington. The burner therein disclosed represents an adaptation of the liquid atomization principles disclosed in U.S. Pat. # 3,421,699 and # 3,421,692 issued Jan. 14, 1969, to the same named inventor and his co-inventors in developing the apparatus and method shown in these patents.
In brief, the principle involved in the aforementioned patents is that of causing a liquid to be atomized to flow over a surface in a highly stressed state, either due to surface tension or due to the particular configuration given to the surface upon which the liquid is discharged.
The surface upon which the liquid is flowed is generally the outside of a plenum chamber having one or more very small apertures over which the liquid flows in a continuous film. Air is introduced into the plenum and passes through the aperture and thereby causes a phenomena in the film whereby very fine micro-sized particles of the liquid are caused to separate from the film in substantial numbers.
By such variations as increasing the number of apertures, the configuration given the apertures, the characteristics of the surface, the regulation of the liquid flow, and/or the regulation of the air pressure, it has been found that not only can great numbers of micro-sized particles be generated but they can be generated in such density that it is impossible to penetrate the resulting spray with light.
It is this basic principle, described above, that was utilized in the development of the very burner disclosed in said U.S. Pat. # 3,425,058.
In the above-mentioned patent, the developmental burner comprised of simply a cylindrical chamber having a cover thereover, the cover being provided with an aperture adapted to discharge spray generally vertically from the chamber. Disposed within the chamber is a spherical plenum having a lower cone-shaped appendage, the chamber being in communication with a source of air. Liquid is introduced into the chamber so as to flow over the surface of the sphere and drain downwardly along the appendage to a funnel disposed beneath the appendage. The fluid not expended in the combustion process is then discharged back to a sump for recirculation into the liquid system. The plenum is provided with a small aperture centrally located beneath the opening in the cover and the air exiting therefrom creates a fine mist which is discharged upwardly and out of the container for mingling with the atmosphere and combustion occurs at that point.
Means comprising a series of regulatable apertures are also provided in the container below the sphere such that aspirated air can be drawn into the chamber and mingled with the spray as it discharges from the top opening.
From this very simple version of a fuel burner was derived more sophisticated equipment, such as that shown and discussed in an article in the January 1976 issue of Popular Science; entitled "Clog-Proof Super Spray Oil Burner". As noted in the article, one development that evolved was the use of two atomizing heads arranged to discharge the atomized liquids toward one another to create a very high concentration of atomized liquid at a fixed point at which is disposed an ignitor to initiate the combustion process.
A similar arrangement of opposed spray heads is also suggested in U.S. Pat. #3,864,326, dated Feb. 2, 1975.
All of the above noted developmental work based on the utilization of the "Babington" principle proved conclusively that the system was perfectly capable of use in a fuel burning system and that, if properly designed, such a system has the potential of evolving into a commercial, practical, highly efficient fuel burner which can be used for domestic heating furnaces. This invention, then, deals with a novel fuel burner, particularly adapted for use in practically every type of domestic heating furnace and in particular, as a retrofit burner for existing heating systems. Grade or fuel oil can be burned with 95% efficiency and at a zero smoke factor within thirty seconds or less from the time of ignition.
SUMMARY OF THE INVENTION
The present invention, the inefficiencies associated with many on-off burner cycles are eliminated. By simply controlling the liquid film thicknesses over the atomizing surfaces as will be described, the firing rate of the burner can be modulated over a typical range of 5-1. This means that the same burner, without changing atomizers, can be modulated either manually or automatically to match the heating and/or hot water loads. For example, during modestly cool spring and summer evenings, the burner can be set to operate at a firing rate of 0.3 gal/hr. and during cold winter days when hot water is required, the same burner can be adjusted to consume fuel at a rate of 1.5 gal/hr. These adjustments can be made manually by simply adjusting the fuel flow rate over the atomizing spheres by means of a simple valve in the liquid feed line, and by making a corresponding adjustment to the combustion air delivered to the flame tube. In the most sophisticated version of the novel burner disclosed herein, these adjustments can be made automatically with suitable control techniques readily available on the market.
Another object of the present invention is to produce an oil burner whose firing rate can be simply modulated either manually or automatically to suit the heating demand.
Another object of the invention is to produce a burner that performs with high efficiency regardless of the combustion chamber that it is placed into and therefore is ideally suited as a retrofit or replacement burner for existing furnaces.
Still another object of this invention is to produce a oil burner that will permit substantial reductions in energy costs when retrofitted into existing furnaces.
Still another object of this invention is to produce an oil burner with exceptionally stable flame front.
Another object of the invention is to produce a burner that is capable of operating at low firing rates, as for example less than 0.5 gal/hr. without clogging problems.
The burner of this invention comprises a cylindrical blast tube housing concentrically therein a flame tube to define an annular air passage therebetween said passage being closed at one end by an annular plate; the opposite end of said passage being closed by a second annular plate having apertures therein, said flame tube being open at said first mentioned end and being provided with a perforated closure having a large central aperture at the second mentioned end; atomizing heads being provided to discharge through said perforated closure, said flame tube having apertures therein located at relative angular positions to stage air into the flame tube to control the shape of the emitted flame.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference is now made to the appended drawings and the detailed description which follows, showing one preferred mode of practicing the invention;
FIGS. 1A and 1B are a schematic view of a typical heating furnace or firebox and showing the utility of the present invention as compared to the usual prior art apparatus;
FIG. 2 is a front end view of a fuel burner assembly as utilized in the firebox referred to in FIG. 1;
FIG. 3 is a vertical section view taken along the line 3--3 of FIG. 2 and showing details of one of the spray heads, and
FIG. 4 is a sectional plan view taken approximately along the line 4--4 of FIG. 2 and showing details of the flame tube assembly.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Deferring descriptions of FIGS. 1A and 1B momentarily, consideration will first be given to FIGS. 2 and 4 which show the improved fuel burning assembly. As shown in FIG. 4, a conventional blast tube 1, which is essentially an elongated open ended pipe disposed in the firebox of the furnace, supports concentrically therein a flame tube 3 supported on a plurality of annular rings 5 and 7 such that the flame tube 3 is located concentrically with respect to the blast tube to define an annular air passage therebetween. The flame tube 3 is open at both ends, one end 9 facing 1 toward the firebox of the furnace or the like, the other end facing toward the exterior of the firebox and upon which the spray heads are mounted and, as is also the oil and air supply motors and compressors carried in a suitable housing.
The open end 9 of the flame tube 3 is provided with a pair of cutouts 13, 13', the function of which will become apparent subsequently. Similarly the flame tube is provided with a further pair of apertures 12, 12' located approximately midway of its length. These apertures are disposed at 90.degree. relative to the cutouts 13, 13'.
The cylindrical flame tube 3 is provided at its opposite end 11 with a pair of spray heads 30 and 30' which are defined by cuplike atomizing chambers 15, 15', respectively.
The atomizing heads are supported upon a foraminous fire wall 14, which is shown as being generally cone shaped, said wall being provided with a relatively large central aperture 16 passing through the wall 14 at its center.
Projecting through the central opening 16 in wall 14 and disposed midway between the atomizing heads 30, 30' is a conventional spark igniter 18 which includes a pair of discharge electrodes 19 and 21. The igniter may be supported by a suitable bracket and, of course, is energized from a source of high voltage electricity.
As shown in FIGS. 3 and 4, the chambers 15, and 15' respectively, may be provided with discharge cones 17 and 17' which discharge atomized fuel inwardly into the flame tube 3.
FIG. 3 shows that each atomizing chamber 11 is provided with a pair of conduits 23' and 25' which are, in essence, elbows having one end projecting into the chamber along a generally vertical plane passing immediately through the walls thereof. The uppermost conduit 23' defines a fuel supply conduit while the lower conduit 25' defines a drain-off conduit, the functions of both of which will be apparent subsequently.
Disposed directly below each fuel supply conduit 23' and supported on the rear wall 31' of the chamber 15' is a spherical plenum chamber 26' which is supplied with air under pressure through conduit 27', which also extends through the rear wall 31' of the cup-shaped vaporizing chamber 15'. The plenum chambers 26, 26' is provided with at least one being small aperture 29', only one shown in FIG. 3, which is located so as to discharge air directly toward the discharge horn 17'.
As clearly shown in FIG. 3, the rear wall 31' of the vaporizing chamber 15' is provided with an aperture 33' whose function will be described in detail hereinafter.
Though not shown, it is to be understood that each inlet conduit 23' are connected to a source of liquid fuel by means of a pump, whereby the fuel may be pumped through these conduits and deposited on the spherical surfaces of the plenum chamber 26'. Similarly, the drain or discharge conduit 25' is connected to the fuel supply system so that liquid which is not atomized within these chambers can be returned to the fuel system not shown and recirculated therein.
The description given above with specific reference to spray head 30' of FIG. 3 applies in identical fashion to spray head 30 shown in FIG. 4.
MODE OF OPERATION AND COMPARATIVE DATA
Directing attention now particularly to FIGS. 3 and 4, the operation of the improvement in fuel burning heads is as follows.
Liquid fuel is introduced into the system by the conduits 23, 23'. The liquid fuel flows over the plenum chambers 26, 26' and a portion thereof is atomized by air under pressure which is introduced into the plenum through the conduit 27. Liquid which is not atomized flows to the bottom of the chambers 15, 15' and is withdrawn therefrom by conduits 25, 25' for recirculation in the fuel supply system.
As described above, the atomizing heads utilize the basic "Babington" liquid atomization system disclosed in prior mentioned U.S. Pat. # 3,421,699 and # 3,421,692.
Due to the discharge of air from the plenum chambers through apertures 29, there is created a venturi effect as the air fuel mixture projects outwardly and is discharged through discharge horns 17 and 17' where such horns are provided. In order to enhance this effect, air enters the ports 33, 33' and is drawn along with the atomized fuel into the flame tube 3. Combustion air is supplied through the aperture 16 in the foraminous fire wall 14 and provides combustion air so that the turbulent mixture that results when the two sprays from atomizers impinge beyond the horns will readily ignite when the igniter 18 is energized to cause a spark between electrodes 19 and 21.
Additional combustion air passes along the annular passage between flame tube 3 and blast tube 1 and is staged into the interior of the flame tube 3 through the staging ports 12 and the cutouts 13, 13'.
The unique configuration of the flame tube within a blast tube provides a unique heat exchanger in which combustion air for staging purposes passes through the annular area between the flame tube and the blast tube. In traversing this route, the combustion air picks up heat from the inner hot walls of the flame tube. This hot air, as it is delivered to the interior of the flame tube at the two aforementioned staging locations, helps to promote rapid vaporization of the atomized fuel to complete the combustion process downstream in the flame tube. The staging of combustion air in this manner allows the temperature within the flame tube to be maintained at the desired level to keep nitrous oxide emissions to a minimum.
Still another advantage of the manner in which the combustion air is staged is to produce a flame which, when emitted from the burner, is short and bushy. This is achieved by introducing said staged air in a non-symmetrical manner which is contrary to the fuel/air mixing technique used in conventional residential type oil burners. For example, at the first combustion air staging location, downstream from the spray impingement site, two air blast may be introduced perpendicular to the long axis of the blast tube, at 3 o'clock and 9 o'clock location. By subjecting the flame within the flame tube to a non-symmetrical air blast of this type, the flame is caused to squirt out and fill the flame tube at the 6 o'clock and 12 o'clock position. Furthermore, the low static pressure within the air blasts at the 3 and 9 o'clock positions causes the flame to wrap around the air blasts and thus produce a shorter and more compact flame which fills the entire flame tube. In the second combustion air staging location, two air blasts are introduced at the lip of the blast tube but this time the air blasts are introduced at the 12 o'clock and 6 o'clock positions. This causes the flame to spread out in the 3 o'clock and 9 o'clock position as it leaves the burner blast tube and enters the combustion chamber. A short bushy flame of this type is ideal for a retrofit or replacement burner, because it is suited for use in any type of combustion chamber. This is in contrast to a long thin flame which would impinge upon the back side of many combustion chambers and cause erosion of the combustion liner. At the same time, the combustion air passing between the flame tube and the blast tube serves to keep the outer blast tube cool, thereby preventing heat erosion of the blast tube. In the case of the present invention, the atomization system is so efficient, and the subsequent fuel/air mixing and vaporization is likewise carried out in such a highly efficient manner, that the burner does not require a hot combustion chamber to achieve high combustion performance. The present burner design has been utilized in a wide variety of different combustion chambers and has always been able to achieve smokeless operation, and flue-gas CO2 levels between 14-141/2%, when operating at a firing rate which is close to that of the furnace rating. Even when the present burner is set to operate at firing rates well below the furnace rating (e.g. burner operating at 0.5 gal/hr. in a 1.0 gal/hr. furnace) CO2 levels with smokeless operation will normally never fall below 13%.
This is in contrast to the average conventional home oil burner that operates at CO2 levels of 8% even when the burner firing rate is matched to the furnace capacity. These characteristics of total independence of furnace design and furnace temperature makes the present invention ideal as a replacement or retrofit burner. This non-dependence on furnace temperature also means that the present burner will achieve smokeless operation the instant ignition occurs and before the combustion chamber becomes hot. The typical conventional high pressure burner takes several minutes for the smoke level to drop to acceptable levels after ignition has occurred.
Another fact to be noted is that conventional high pressure nozzles have difficulty operating at firing rates below approximately 0.7 gal/hr. without encountering a high incidence of clogging. In the present burner, there is essentially no minimum firing rate that can be attained; a prototype burner has been operated at a firing rate of 0.5 gal/hr. This means that each individual atomizer is operating at approximately one-half that firing rate. Further, it is not necessary, in the present burner, that both atomizers be generating the same amount of fuel spray for the burner to operate efficiently. For example, one atomizer may have a firing rate of 0.3 gal/hr. while the other has a firing rate of 0.2 gal/hr. A burner of this type will operate just as efficiently as one in which each atomizer is delivering a spray rate of 0.25 gal/hr. This low firing rate capability of the present invention is very important in light of the present energy crisis because homes in the future will be built with better insulation and the trend is towards low firing burners that can provide highly efficient operation.
It should be noted that the perforations in the fire wall 14 are so numbered and sized that a very soft flow of air passes through this wall. This soft air flow tends to keep products of combustion from filtering or rolling back toward the spray heads and the igniter, thus inhibiting sooting of these elements.
The included angle between the atomizing heads 30, 30' is shown in FIG. 4 as being approximately 90.degree.. This angle can be varied, however, and may be between 45° and 150°.
Turning now to FIGS. 1 and 1A, it will be noted that in the prior art the atomizing nozzles are located close to the interior of the firebox. Consequently, the nozzles are subjected to high temperatures. Due to this fact, the nozzles are subject to varnish depositions and clogging are continually subject to soot and dirt and varnishing caused by decomposition of the fuel due to its exposure to the heated parts which results in a varnish deposit being laid down on the atomizing nozzles and those parts which are disposed within the firebox.
In contrast, utilizing applicant's improved fuel burning head, the atomizing heads are located well inwardly of the end of the blast tube and are thus not subjected to the radiant and convective heat of the firebox. Since the parts then remain virtually cool, there is little decomposition of the carbons in the fuel and hence there is little or substantially no varnishing to interfere with proper atomization of the fuel or operation of the atomizing parts.
Fuel Burner
Abstract --- The disclosure relates to liquid fuel burners wherein the fuel to be consumed is supplied to and dispersed from a film forming surface in spherical shaped droplets of spray, the excess fuel supplied to the surface being recirculated.
Disclosure
The invention is concerned with a fuel burner of the atomizing type and in particular with a liquid fuel burner which is universally adopted to cause efficient combustion of any liquid fuel.
An object of the invention, then is to produce a liquid fuel burner with a high combustion efficiency that will not deteriorate with the operation of the burner.
Another object of the invention is to produce a liquid fuel burner capable of burning almost any fuel in liquid form, without changing the burner configuration or spray head.
Still another object of the invention is to produce a simple reliable liquid fuel burner
A further object of the invention is to provide a novel recirculating type of fuel burner.
Still an additional object of the invention is to produce a liquid fuel burner of extreme simplicity wherein the fuel does not pass through any nozzle and therefore is not susceptible to clogging with dirty fuel.
An additional object of the invention is to produce a fuel burner for liquids in which the rate of combustion can be easily and quickly regulated.
Another object of the invention is to produce a liquid fuel burner capable of burning large amounts of fuel and releasing a large amount of heat energy in small compact combustion chambers.
Still a further object of the invention is to produce a simply gravity or pressure fed, low air pressure liquid fuel burner.
These and other objects of the invention not specifically set forth, but inherent therein will become readily apparent from a consideration of the subject matter which is directed to a liquid fuel burner comprising a plenum chamber having a source of pressurized air connected therewith; a liquid fuel source, means for admitting fuel from said source onto the outer surface of said plenum chamber, the point of application of said liquid being spaced from the aperture a distance sufficient to permit the fuel to form as a film on said surface before and after encountering said aperture, a housing surrounding said plenum chamber, said housing comprising an apertured chamber and a closure, said closure being provided with at least one dispensing opening aligned with said aperture whereby the liquid may be discharged from said housing and burned externally thereof and means for collecting excess fuel draining from said plenum surface for recirculation thereover.
Having thus described the invention in broad aspects, the operation and details thereof will become apparent from the following detailed description, wherein reference is made to the drawings in which,
Figure 1 is a side elevational view in section, showing the fuel burner, the fuel and air pressure sources being illustrated schematically,
Figure 2 is a plan sectional view taken along the line 2-2 of Figure 1,
Figure 3 is an elevational view of a modified diffuser in assembly,
Figures 4a-c are top views showing various diffuser assemblies,
Figure 5 is a top plan view of a modified cover or shroud assembly, and
Figure 6 is a sectional view taken along the line 6-6 of Figure 5.
Considering, now, Figure 1 in detail, it may be seen that the burner is comprised of a chamber 1, of generally cylindrical form and having a closed bottom 3. Chamber 1 is also provided with a top 5 having a central opening 7 provided, as shown with an upwardly flared peripheral wall 19. While the chamber is illustrated as cylindrical and the top as generally dome shaped, it should be noted that the invention is not so restricted since any convenient wall and top configuration is possible. A cylindrical form, however, is most easily fabricated as is the domed top 5.
Top 5 is provided with a downwardly depending cylindrical skirt 11 adapted to frictionally engage the interior of the chamber wall to retain same in place.
Disposed within chamber 1 is a funnel-like fuel collector 13. This collector is positioned concentrically in the chamber and may be held in place by any suitable support means. In the embodiment of the invention shown, the collector 13 is supported on an elbow like drain tube 15 which is simply a hollow tube having one branch connected to the collector 13 and disposed vertically and the other branch fixed to the chamber 1 and extending therethrough to define a fuel return outlet 17.
Also disposed within chamber 1 and preferable concentric therewith and with respect to collector 13, is a fuel diffuser assembly 20.
The fuel diffuser assembly is formed by an uppermost and spherical chamber 21 having at least one aperture 23, provided in its surface. In the embodiment disclosed this aperture is disposed at the uppermost point in the spherical surface and as will be explained later may take a variety of forms. In addition as will be discussed, more than one aperture may be provided.
The spherical chamber 21 is open at its bottom and this opening communicated with a generally tube shaped chamber 25 having a closed bottom in the shape of a downturned cone or point 27. This cone or point is disposed generally over the center of the fuel collector 13.
Extending radially outwardly from chamber 25 is a tubular conduit 29 which is fixed to the wall of chamber 1 and terminated outwardly thereof, whereby the hollow sphere 21 and tubular chamber 25 are placed in communication with a source of gas pressure, outside of chamber 1. The diffuser assembly 20, then, comprises a closed plenum supported within chamber 1.
Also extending through the wall of chamber 1 radially thereof is a further tubular conduit 31 having an inward terminal end 33 disposed adjacent but spaced from the spherical surface of chamber 21. It should be noted that conduit 31 is positioned so as to lie on a diameter extending through the center of the sphere.
Surrounding chamber 1 is an annular or hoop-like collar 35. This collar may be positioned on the outside of the chamber by any suitable means, friction detents such as 27, so that while same is prevented from sliding down the cylindrical chamber, it may be readily rotated with respect thereto. The collar 35 is further provided with at least one, preferably more --- two being shown --- apertures 39, 39’ in the form of windows which may be displaced at a variety of angular positions around cylinder 1.
It will also be seen that the cylindrical wall of chamber 1 is provided with windows 41, 41’ located so as to be disposed within the vertical dimension of the collar 35 but having an opening area commensurate with that of the windows 39 in the collar. Thus as the collar is rotated the window or as shown windows 39, 39’ and 41, 41’ can be brought into and out of registry to any desired degree, the collar 35 serving as a damper as it is rotated and registry between the windows is reduced or obviated completely. As shown in Figure 2, the collar 35 is positioned so that about half of the window areas 39, 39’ and 41, 41’ are registered.
As illustrated schematically in Figure 1, the conduit 31 is supplied by fuel under pressure from reservoir S, via pump P1. In some cases the liquid fuel may be passed directly from reservoir S to conduit 31 provided a suitable gravity flow head is established between reservoir S and conduit 31.
As is also shown, conduit 29 is supplied with gas from a pressure source shown simply as pump P2, tough this may be a charged gas container or any suitable means capable of supplying gas under pressure at about 3 to 20 psig over sustained periods of time.
Conduit 17 which defines the fuel return conduit also enters into pump P1 and is returned to reservoir S through, again depending on the location of the reservoir S with respect to the burner, this pump P1 may be dispensed with. In other words, while a workable system is disclosed the burner is not inflexible tied in with any particular system of supply and return so long as the requisite mediums fuel and a gas under pressure are supplied to conduits 31, 29 respectively and unburned fuel is removed from collector 13 via conduit 17.
As illustrated in the drawings, the burner may be made of glass. However, any suitable material may be used to fabricate these structural parts. For example, the chamber 1 may be stainless steel while the fuel collector is made of similar materials; the diffuser being glass or vice versa. Similarly the diffuser can be made of stainless or other metallic or even plastic material. Moreover, as will be seen the material may be governed by the type of fuel being burned so that whatever the fuel the burner construction is resistant to solvent action or corrosion by the fuel. Thus, because glass is relatively inert and almost totally unaffected by any fuel and because the burner is adaptable to the combustion of practically every known fuel from gasoline through bunker C oil, it has been illustrated as formed of glass components.
In Figure 3, however, a modified version is shown wherein the diffuser assembly is comprised partly of metal, partly of nonmetallic material to further illustrate the versatility of the structure.
As shown in Figure 3 there are various means by which the basic structure may be adapted to accommodate various fuels, combustion rates, etc. Figure 3 illustrates one such means, it being understood that same is merely exemplary of one mode effecting this result. In this figure a diffuser, assembly 20’ is shown in partial elevation and the spherical upper portion thereof, 21’ is affixed to the lower member 25’ by means of a threaded connection. As seen in Figure 1, the diffuser sphere is provided with an opening 23’ shown as a round hole having an outwardly divergent circumferential wall. The wall would of course be straight, i.e., define a cylinder concentric with the central axis of the assembly 21’, however for reasons of greater efficiency it is generally preferred that the aperture be defined by an outwardly opening conical or divergent wall.
By connecting the spherical portion 21’ of diffuser assembly 20’ to the lower portion 25’, by means of a threaded or push-pull type connection, it is possible to change the sphere quite easily. Thus, if as will be explained, it is desired to change the material of the sphere 21’ this can be readily accomplished by substituting one sphere for another. Also where it is desired to produce a greater burner capacity and/or modify the flame configuration, sphere 21 may be modified to include more than one aperture 23 the apertures themselves being varied from round holes to elongated slots disposed in various locations in the uppermost portion of the spherical surface. Examples of various modifications are shown in Figures 4a, b and c, showing a plurality of diffusers 40, 50 and 60 provided with apertures 43, 53, and 63 respectively. It will be noted that in Figure 4a the apertures are in the form of slots disposed at equally spaced locations around the surface of the sphere. Four such slots are shown in this embodiment. In Figure 4b the apertures 53 are in the form of round apertures 53 at diametrically spaced points on the surface of the sphere 51. Figure 4c sows the opening 63 as a slot disposed parallel to the direction of fuel flow. In this connection it should be noted that fuel flow in these figures is illustrated by the arrows.
From the foregoing descriptive matter, it is believed apparent that while a simple structural embodiment and several variations thereof have been shown, the burner is capable of various modification and changes as will be readily understood as the mode of operation is described.
In respect of the burner operation, the fundamental concepts involved in producing a spray characterized by the spheroid shape of the miniscule drops is described in great detail in copending applications Ser. No. 605,777 and 605,779, both filed Dec. 29, 1966. Basically the process involves the introduction of the fluid to be sprayed on an apertured surface with sufficient kinetic energy to cause the liquid to film out or be stressed during its flow over the surface. At the point where the dynamic film is stressed to a high degree -- as evidenced by its smooth almost invisible flow pattern -- air at very modest pressures is emitted from an opening and small almost perfectly shaped spheroid particles of the liquid are caused to emerge from the film. Experimentation has shown that these particles of liquid are on the order of 50 microns in size where, for example, water is caused to flow in a thin film over a glass surface and air at a pressure of 8 psig is caused to flow through a small orifice in said glass surface. In the operation of the disclosed apparatus it generally requires less energy or gas pressure to atomize a liquid fuel than it does to atomize water. This is because virtually all liquid hydrocarbon fuels have a low surface tension and excellent wetting characteristics. Good wetting is helpful in the forming of a highly stressed film and a low surface tension allows the liquid particles to be easily dispersed from the thin film. For example, because of these favorable physical properties, gasoline can be atomized better at a gas pressure of 3 psig than water can be atomized at a gas pressure of 8 psig.
Surprisingly enough, it has been found that if the liquid is introduced onto a film forming surface with sufficient kinetic energy, not only will the liquid flow and spread downwardly as where it is introduced at a point above the surface, but if, as shown, the liquid is ejected against a properly curved surface such as the spherical portion of the diffuser assembly 20, from fuel inlet pipe or conduit 33, the fluid can be caused and will flow upwardly to completely envelop the upper portion of the spherical surface and is highly stressed into a thin dynamic film which passes over the apertures or aperture 23. If, then, air at very low pressures above the ambient pressure in the chamber is cause dto flow through the aperture 23 or apertures 23’, 45, 53 and 63, there occurs a separation of miniscule drops of liquid from the highly stressed dynamic liquid film. As stated, evidence indicated the drops of droplets are almost uniformly dispersed as to size and shape, being spheroids on the order of 50 microns or less.
While the entire phenomenon is not clearly understood, it has been found that if the spray thus produced is caused to be ejected upwardly through a shroud or cover 5, as shown in figure 1 and air is introduced into the chamber 1 through ports 41 as secondary or combustion air, the diffused liquid will be exited in great volume through the aperture 7 in shroud 5 and if ignited the liquid fuel burns with a highly intense combustion rate about one-half to three-quarters of an inch above the aperture 7 and will not propagate itself back into chamber 1. This phenomenon has manifested itself with a variety of liquids including highly volatile fuels such as gasoline. One explanation is that the quantity of atomizing air is so small by comparison to the quantity of fuel atomized, that the fuel/air mixture within chamber 1 is "fuel rich" that is the fuel/air ratio is so unbalanced by the presence of excess fuel, that combustion is impossible. Once the fuel is ejected from the chamber, however, due to the fineness with which it is dispersed, the attainment of a favorable combustion ration is quite rapid with the consequence that burning occurs quite close to the point of exit of the spray and throughout the entire spray area.
Because of the above described phenomenon, it is possible to regulate the spray pattern and volume by means of the cover or shroud 5 by the simple expedient of providing multiple, selectively usable covers in which the dimensions of the spray exit aperture 7 is varied from one cover to another. Thus, by a matching of a selected opening 7 with the fuel being burned not only can the combustion rate be readily and easily varied by not only the cover change but by coupling this feature with a selection of anyone of the diffuser designs as exemplified in Figure 4. It has been found that the spray, hence combustion pattern can be varied from an almost vertical column to a an shaped pattern.
The quantity of fuel spray and the shape of the spray cloud can also be controlled by rotating collar 35 to allow more or less secondary air to enter chamber 1 through windows 41 and 41’. Air is induced to flow into these windows by the ejector or pumping action of the total spray cloud leaving the fuel burner. The small amount of atomizing air by itself provides very little pumping action. However, when combined with the mass flow of the atomized liquid, a significant amount of secondary air is induced to flow into chamber 1, when windows 41 and 41’ are in the open position. By restricting the flow through windows 41 and 41 by the rotation of collar 35, the degree of vacuum in chamber 1 can be controlled. The vacuum control in chamber 1 can be in turn used to regulate the quantity and shape of the spray cloud leaving the fuel burner. For example, rotating collar 35 to restrict the secondary flow into chamber 1 through windows 41 and 41’ has the effect of increasing the degree of vacuum inside chamber 1 which in turn reduces the quantity of fuel spray and suppresses the height of the spray plume. It should be noted that while significant secondary air flows into chamber 1 during operation of the burner with side windows 41 and 41’ wide open, this amount of air-flow is not sufficient to generate a combustible fuel/air mixture inside chamber 1.
In order to further simplify the structure, a modified shroud or cover 73, such as that shown in Figures 5 and 6 may be used. Again the mode of carrying out the structural manifestation of the inventive concept is exemplary only and not limiting. Other and equivalent means will readily occur to those skilled in the art. However, turning to Figures 5 and 6 it will be seen that cover 73 is plane surfaced and provided with a central opening 77 of rather large diameter. Disposed above the opening and retained on the top surface of the shroud or cover 73 by means of simple L-shaped lugs 79 are a plurality of segment-shaped slidable restrictors 81, 83, 95 and 87. Each restrictor may be provided with an adjustment knob noted generally by the numeral 89. It will be noted that the edges of restrictors 83 and 87 underlie the edges of restrictors 81 and 85, whereby while each restrictor may be moved inwardly and outwardly with respect to the center of aperture 77 the restrictors acting as a whole form a solid shield or mask which rests on top of cover 73. As will now be obvious movement of the restrictors inwardly has the effect of reducing the overall diameter of the exit aperture through the cover 73 and vice versa. In other words, restrictors 81, 83, 85 and 87 define an iris-like shield whereby the effective area of the aperture may be readily reduced to meet a desired set of conditions.
Having thus described the invention and various aspects thereof, it is believed obvious that a variety of modifications thereof can be made, such being within the spirit and scope of the inventive concepts involved; these being limited only as defined in the appended claims.
[Claims not included here]
Apparatus for Producing Finely Divided Liquid Spray
Abstract --- Apparatus for producing finely divided liquid particles which includes two chambers having means for conveying liquid from one chamber to the other and back again to the first chamber in response to a means for producing a pressure differential between the chambers. A hollow apertured plenum chamber having a smooth outer surface is positioned so that the liquid impinges on its exterior surface as it traverses its flow path. Gas is supplied under pressure to the interior of the plenum and ruptures the thin film of liquid at the aperture to produce the finely divided liquid particles.
Spraying Devices, in Particular Nebulizing Devices
Robert S. Babington
Method of Spraying
Power Humidification Apparatus
Method of Atomizing Liquids...
