US3023623A - Apparatus and method for selecting oil burner spray nozzle tips - Google Patents

Description

March 6, 1962 R. J. LANG ETAL 3,023,623

APPARATUS AND METHOD FOR SELECTING OIL BURNER SPRAY NOZZLE TIPS 5 Sheets-Sheet 1 Filed May '7, 1959 M fi w .mm m m m o .8 L kl s re ec dh wec i. RFM

By 4 r 20.0 M Patent Attorney March 6, 1962 R. J. LANG ETAL 3,023,623

APPARATUS AND METHOD FOR SELECTING OIL BURNER SPRAY NOZZLE TIPS 5 Sheets-Sheet 2 Filed May 7, 1959 Rober Long Frede L. M e Inventors Michael R. Sc menfi WWW Patent Attorney March 6, 1962 R. J. LANG ETAL APPARATUS AND M 3,023,623 ETHOD FOR SELECTING OIL BURNER SPRAY NOZZLE TIPS Filed May 7, 1959 5 Sheets-Sheet 3 Robert J. Long Frederick L. Menke Inventors Michael R. Schimmenti By W (2/0 7 Patent Attorney March 6, 1962 R. J. LANG ETAL 3,023,623

APPARATUS AND METHOD FOR SELECTING 0IL BURNER SPRAY NOZZLE TIPS 5 Sheets-Sheet 4 Filed May 7, 1959 FIG-5 Robert J. Long Frederick L. Menke Inventors Michael R. Schimmenti 7/0 7 Patent Attorney March 6, 1962 R. J. LANG ETAL 3,023,623

APPARATUS AND METHOD FOR SELECTING OIL BURNER SPRAY NOZZLE TIPS 5 Sheets-Sheet 5 Filed May 7, 1959 OIL SPRAY CONE INCLUDED ANGLE-DEGREES 5 4 3 2 wmIoZTzmwhbE m0 m35 m mu -DO FIG-6 Robert J. Lung Frederick L. Menke Inventors Michael R, Schimmenfl By r 7 Woi'en? Atto y United rates 3,023,623 Patented Mar. 6, 1962 Free I 3,923,623 APPARATUS AND METHOD FOR SELECTWG OIL BURNER SPRAY NOZZLE THPS Robert J. Long, Metuchen, and Michael R. Schimmenti, Palisades Park, NJ, and Frederick L. Monks, Havana, Cuba, assignors to Esso Research and Engineering Company, a corporation of Delaware Filed May 7, 19533, Ser. No. 811,741 13 Claims. (Cl. 73-432) This invention relates to an apparatus and method for selecting fuel spray nozzle tips for combustion devices to achieve the optimum fuel spray pattern with respect to the air discharge flow pattern of a given combustion device. It relates particularly to an apparatus and method for such selection of fuel spray nozzle tips to be used in a combustion device burning a liquid fuel, and it relates more particularly to an apparatus and method for such selection of fuel spray nozzle tips to be used in an oil-burning, furnace-ope combustion device of a size suitable for home heating purposes.

The majority of furnace-type combustion devices in home heating systems using oil as a fuel at rates up to about two gallons per hour are of the gun variety comprising an oil spray feed line and nozzle apparatus surrounded by an air barrel or blast tube, the spray nozzle being located closely adjacent the outlet opening of the tube. This blast tube may be fitted internally near its discharge end with vanes whereby swirl is imparted to the air of combustion for greater turbulence of mixing thereof with oil spraying from the nozzle tip.

Home heating combustion devices of the variety described may be classified further as low pressure or high pressure with reference to the oil supply. In low pressure units the oil is supplied to the spray nozzle at pressures in the range of 2 to 15 pounds per square inch. A small amount of air, perhaps 1 to 5 percent of that theoretically required to burn the fuel, is mixed with the oil ahead of or within the nozzle apparatus. The principal function of this air is to help break up the oil stream into fine droplets upon leaving the nozzle tip, the oil being thereafter mixed with air from the blast tube to achieve a combustible mixture. The air supplied by the blast tube will be at a pressure only slightly above atmospheric. In high pressure units oil is supplied to the spray nozzle at a pressure of about 100 pounds per square inch, and is not mixed with any air ahead of the nozzle. As in the low pressure unit, the blast tube supplies air for combustion at only a very slight positive pressure.

Each combustion device of the kind described, whether high or low pressure, will have its own particular air discharge flow pattern. In general, the fiow pattern of air of combustion leaving the outlet openin of a blast tube will be that of a hollow, diverging cone which is substantially coaxial with the blast tube and the oil spray nozzle. The hollow region will tend to close in some distance from the outlet of the blast tube, and from that distance onward the air flow pattern will be a solid cone. Whether the hollow region will in fact close in, and if so at what distance from the outlet of the blast tube will depend upon, among other things, the presence or absence of the afore-mentioned vanes in the blast tube for imparting swirl to the air. If air discharged from the blast tube has a swirl or tangential component of velocity, the hollow region of the air flow pattern will tend to be maintained farther out from the blast tube.

Whatever the pattern be of the air discharge flow, however, there will be a problem of obtaining good mixing of oil and air to achieve substantially smokeless combustion with a minimum percentage of excess air. The particular oil spray nozzle tip used will have a discharge flow pattern of its own, and for good results there must be compatibility of the flow patterns of, the oil and the air.

The spray pattern of the oil flowing from the nozzle will, like that of air flowing from the blast tube, be a diverging cone. The apex of this cone, being at the nozzle tip itself, will of course be within the flow pattern of the air. The function of the oil spray nozzle apparatus, particularly in a high pressure unit, is to break up or atomize liquid oil fed to it under pressure so that what flows away from the nozzle is an oil mist.

This oil mist will not necessarily be of continuous density on a plane taken transversely to the oil spray axis within the spray cone. Rather, it is possible for this cone to be characterized like the air flow pattern by a hollow region. An oil spray nozzle tip may, accordingly, be specified by the enclosed angle of its spray cone and the spray density or oil particle concentration distribution on a plane taken normally to the cone axis. For an example of such specifications of spray nozzle tips for high pressure oil burner units, reference may be had to pages 4 and 5 of Catalog 0, Monarch Oil Burner Accessories, dated February 10, 1955, published by the Monarch Manufacturing Works, Inc, 2501 E. Ontario Street, Fhiladelphia 34, Pennsylvania.

For oil burner units of the size indicated, those having oil rates up to about two gallons per hour, best conditions of combustion will be obtained if the oil spray and the air discharge flow patterns substantially coincide somewhere in the range of 3 to 7 inches out from the nozzle, preferably at about 6 inches. If they coincide unduly close to the nozzle, the oil having a comparatively high velocity may break out through the air stream without being mixed therewith, while if the coincidence take place unduly far out from the nozzle relative velocities between the oil and the air may be too low for good mixing. Of these two possibilities, however, it is generally preferable to have coincidence of oil and air patterns rather unusually far out from the spray nozzle instead of somewhat too near to it.

While the spray patterns of oil burner nozzle tips may be determined readily on the basis of catalog information, at least in the cases of nozzle tips for high pressure units, the air discharge flow patterns from combustion device blast tubes will not be known with any degree of certainty. In the past, oil burner servicemen have spent considerable periods of time changing spray nozzle tips on a given combustion device to find, by matching oil spray and air flow patterns through trial and error, that nozzle tip which would provide optimum conditions of combustion.

According to the present invention, an apparatus and method are provided whereby and wherein the air ,dis-. charge pattern of a fuel burning device characterized by a blast tube may be determined directly, and selection made of a fuel spray nozzle tip having such a spray pattern as is well compatible with the air discharge pattern for conditions of good combustion. By this apparatus and in this method a graphic record is made of the air discharge pattern by reacting one chemical, ammonia for example, in the air stream leaving the blast tube with another chemical, copper sulfate for the case of ammonia in the air stream, on an air-permeable screen disposed in way of air flowing from this tube to form a visible product on the screen. This product will be an ammonia complex in the case of the particular chemicals just named.

The nature and substance of this invention may be more clearly perceived and fully understood by referring to the following description and claims taken in connection with the accompanying drawings in which:

FIG. 1 represents a view in sectional elevation through a heating furnace showing part of the combustion chamber and a gun variety, high pressure oil burner unit, and particularly illustrating representative patterns of air and oil spray discharge from this unit;

FIG. 2 represents a detailed view, partly in section of the oil spray nozzle apparatus of the oil burner unit of FIG. 1;

FIG. 3 represents a view in side elevation, partly broken away, of a screen and screen supporting apparatus designed to be attached to the oil burner unit of FIG. 1 for determining the air discharge pattern thereof accord ing to this invention;

FIG. 4 represents an enlarged view in sectional elevation of part of the oil burner unit of FIG. 1 showing the screen and screen supporting apparatus of FIG. 3 attached thereto according to this invention;

FIG. 5 represents a view in sectional elevation through the apparatus assembly of "FIG. 4 taken along line 5-5 therein, and particularly illustrating the graphic record made on the screen member of that apparatus of the air discharge pattern from the oil burner unit thereof according to this invention, and

FIG. 6 represents a family of air discharge pattern curves whereby an oil spray nozzle tip of proper spray cone angle may be selected according to this invention.

Referring now to FIG. 1, the combustion chamber space of a heating furnace is designated 16. A centrifugal blower comprising a casing 12, a rotor element M, an air suction pipe 16, and an air suction filter 18 supplies air to the combustion chamber through a blast tube 2%. Within this blast tube is a bafile element 2.2, between which and the inner wall of the tube an annular air passage is formed. At the outlet of this passage is a ring of turbulator vanes 24 whereby swirl is imparted to the combustion air. A pump 26 supplies oil fuel under pressure. This pump discharges through line 28 which penetrates the blower casing and extends therethrough and also through the blast tube and the bafiie up to a spray nozzle apparatus 30. The oil pump may in fact be located within or without casing 12 of the centrifugal blower, and may further, like the blower, be driven by any suitable means such as an electric motor.

The flow pattern of air for combustion discharged through the outlet opening of blast tube 2% is a hollow, diverging cone having an inner boundary 32 and an outer boundary 34, both shown in dashed lines. This cone is substantially coaxial with the blast tube and the oil spray nozzle. Its hollow region is illustrated as closing into a point and terminating at some distance from the outlet of the blast tube. The flow pattern of oil spray from the nozzle apparatus is indicated likewise as a hollow, diverging cone, the inner and outer boundaries of which are shown in dotted lines, and are designated 36 and 38 respectively. The oil spray cone is more widely diverging than that of the air discharge, and will pass outwardly through the air cone at some distance from the blast tube outlet.

It should be understood that both the air and oil spray discharge cones shown in FIG. 1 represent undisturbed flow patterns; that is, the air cone is depicted as it might be in the absence of an oil spray and vice versa. With both materials being supplied to combustion chamber simultaneously, and particularly with combustion taking place, it is obvious and indeed intended that there will be substantial interaction of the flow patterns of oil and air.

Referring next to FIG. 2, fuel line 28 which extends from the discharge outlet of fuel pump 26 is terminated in a male compression fitting 40. The joint between fuel line 28 and fitting 40 may be made more or less permanent as by soldering or brazing. Compression fitting 40 is screwed into adaptor fitting 42 which has straight internal threads to engage those of the compression fitting, and is pipe threaded externally to screw into nozzle body member 44. This body member is threaded internally at 4 both ends. The threads at its left end are straight, and screwed thereinto is the nozzle tip member 46 which shoulders against the body'member. Attached to nozzle tip 46 as by screw threads, and extending within body member 44 is a filter or strainer element 48 which may be of porous bronze construction, for example. Any commercial spray nozzle tip 46 such as those listed in the aforementioned catalog of the Monarch Manufacturing Works, Inc. will be stamped or otherwise marked to indicate the fiow rate, cone angle, and oil particle concentration distribution (hollow or solid cone) of the oil spray which it generates for a given oil supply pressure.

Referring next to FIG. 3 which shows a screen and screen supporting apparatus designed to be attached to the oil burner apparatus of FIG. 1, 50 designates a screw plug which is cut with the same thread as spray nozzle tip 46, the threaded region of this plug being at least no longer than the straight threaded region at the left end of nozzle body 44. For reasons to be disclosed presently, the length or thickness of the hexagonal head of this plug should be made substantially equal to the combined length or thickness of the hexagonal and bulbous parts of nozzle tip 46. Fixedly attached to plug 50 and disposed substantially coaxially therewith is a rod 52. With respect to the cantilevered load which will be shown to be imposed upon it, this rod should be sufliciently stifi that it undergoes no practically perceptible deflection. Slidably mounted on rod 52 is a hub element 54 having a thumb screw 56 whereby it may be located definitely on the rod at any desired position therealong. Extending outwardly from hub 54 are spoke elements such as 58 which are connected at their outer ends with a shouldered rim member 60.

Stretched across rim 60 is a screen 62. This screen is made of an air-permeable material such as a loosely woven cloth, for example, cheese cloth. It is centrally perforated to allow its passage over rod 52. This feature of its design is illustrated further in FIG. 5. Screen 62 is of greater expanse than the area enclosed by the lower stepped boundary of rim member 60; for example, assuming that the rim is circular, screen 62 has an outside diameter which is larger than that of the lower stepped boundary of the rim. This being so, screen 62 may be stretched tautly across rim 60; its peripheral region formed over the lower stepped boundary of the rim, and finally secured in place on the rim by means such as a frame or hoop 64 which is configured to fit tightly but slidably over the formed periphery of the screen on rim 60, and to be stopped against the rim shoulder. With this construction, screens may be changed easily on rim 60 by first sliding off the frame or hoop 64, and finally sliding it back onto the rim. While element 60 is properly denoted a rim member with respect to hub 54 and spokes 58, it may also be considered a frame member with respect to screen 62.

Finally in FIG. 3 notice should be taken of the distance graduations 66 marked on rod 52 against which the inner edge of screen 62 may be set. Conveniently, these graduations will be laid off to indicate the distance along rod 52 from screen 62 to the left hand end of the hexagonal part of screw plug 50.

Referring next to FIG. 4, the tip element 46 and filter member 48 have been removed from nozzle assembly 30 of FIGS. 1 and 2, and the screen and screen supporting apparatus of FIG. 3 substituted for them. This substitution may be made simply by screwing plug element 56 into the threads at the left end of nozzle body 44. If the blower mechanism of the oil burner unit be energized to generate a stream of air leaving blast tube 20 and having inner and outer boundaries 32 and 34, this stream will pass through the air-permeable screen 62 wherever it strikes it Within the inner boundary of rim or frame member 60. To use this apparatus according to the pres-- ent invention, the screen should be shifted along rod 52 to bring it close enough to the blast tube that substantially all of the air leaving this tube will impinge upon and pass through the screen; that is, that outer boundary 34 of the air cone will intersect screen 62 within the inner boundary of frame 60. The screen should be far enough out along its supporting rod, however, that air leaving the blast tube will be flowing according to a more or less definite pattern by the time it reaches the screen.

Referring next to FIG. 5, the annular region of screen 62 which is shown shaded with inner boundary 68 and outer boundary 70 is that portion of the screen through which air from blast tube 20 has been or is being passed according to the arrangement of FIG. 4. The shading represents the graphic record made of the air discharge pattern and might be the visible ammonia complex mentioned previously, resulting from a reaction between ammonia in the air stream and copper sulfate on screen 62. The particular technique of using ammonia and copper sulfate to provide this record will be discussed presently as will the use of other graphic recording materals.

Referring finally to FIG. 6, the ordinate designation Outer Radius of Pattern-Inches, refers to the radius of outer boundary 70 of the, shaded area shown in FIG. 5. The abscissa designation Oil Spray Cone Included Angle-Degrees, represents the spray angle of a nozzle tip such as 46. The individual parameters of the several Curves, :L 3u nL 4,n :rL 5,u :L 6,n and rrL 7n refer to distances of screen 62 from the left end of screw plug 50 according to scale 66. With plug 50 having a thickness dimension corresponding to that of nozzle tip 46 in a manner indicated already, the distances read off of scale 66 will be, in effect, distances along rod 52 from screen 62 to the location of the outlet opening of the nozzle tip when installed, that is, distances from screen 62 to the apex of the oil spray cone.

Any point on any curve in FIG. 6 represents a condition in which, for an oil burner unit having a nozzle tip providing a spray cone of that particular included angle, the outer boundary 38 of the oil spray cone will break through the outer boundary 34 of the air stream as shown in FIG. 1 at a distance of six inches from the apex of the spray cone, that is, six inches from the left end of nozzle tip 46. Intersection of air and oil discharge patterns at this location has been stated earlier to be desirable for units of home heating size.

To illustrate the use of the curves of FIG. 6, suppose, for example, that the radius of shaded area outer boundary '70 in FIG. 5 obtained in the test of a given oil burner is two inches, and that the offset distance of screen 62 as indicated by scale 66 at the time of generating the pattern of FIG. 5 was five inches. Going to FIG. 6 with these data, the corresponding spray cone included angle is about 43. This is a direct and very important indicator of the nozzle tip which should be used with the oil burner unit in question. Another indicator would be whether the pattern on the screen is hollow or solid. The existence of an inner boundary 68 of the air pattern would be checked preferably with screen 62 ofiset six inches along rod 52 even though at this offset the outer boundary 76 of the air pattern might not be definable on the screen in the case of a wide-angle air cone. With knowledge of both the desired oil spray cone included angle and the preferred oil spray density distribution (hollow cone or solid cone), selection of an oil spray nozzle tip which is correct in all important respects for a given burner unit may be made promptly.

Consideration will now be given to several particular methods of taking a graphic record of the air discharge pattern of an oil burner unit according to this invention. Broadly, these methods may be classified according to the state of recording material injected into the air stream; that is, according to whether this material be gaseous, liquid, or solid.

An example of the use of a gaseous injected material is that of ammonia. In the ammonia method, considering that an apparatus arrangement exists according to FIG.

6 4, the screen 62 is initially moistened with an aqueous solution of copper sulfate. The blower apparatus is started to provide an air stream impinging on and passing through the screen. An ammonia source, for example a rag soaked in ammonium hydroxide from which ammonia will dissociate, is held closely adjacent blower intake filter 18. Ammonia gas is thus drawn through the filter and the inlet line 16 along with air, and is thoroughly mixed with the air in its subsequent passage through the blower wheel 14, scroll casing 12, blast tube 2%, and the turbulator vanes 24.

When the mixture of air and ammonia impinges upon the moist screen 62, at least part of the ammonia will dissolve in the liquid on the screen while the greater part of the air will pass through the screen fibres with no particular disturbance of its flow. Upon dissolution, the first, ammonia to reach the screen will react with the copper sulfate to form copper hydroxide which is of light blue color. As more and more ammonia is supplied and dissolved, the copper hydroxide will be converted to the complex cupric tetramine sulfate of dark blue color, and substantially stable nature. Operations should be continued sufficiently long and with ammonia injected into the air stream at sufficient rate that the complex product is obtained on the screen. More than one test may have to be made to bring the outer boundary of the air cone onto the screen and to determine whether this cone is hollow or solid six inches out from the spray nozzle.

Only a very few tests should have to be made in any case, however, and with note having been taken of the offset of screen 62 along rod 52 and subsequent measurement made of the radius of pattern boundary 70, the curves of FIG. 6 may be used to determine the proper included angle for the spray nozzle tip according to the example given above. In the course of preparing for and carrying out the foregoing operations, certain reason.- able steps and precautions should be taken which will apply generally to all process variations of this invention. These include cleaning the air passages of the oil burner unit, disconnecting the power supply for the burner ignition means, and making sure that no concentrations of fumes of a kind that are actually or potentially painful or dangerous to human beings are allowed to develop.

Another example of the use of a gaseous or at least a vaporous injected material is that of water. In the water method the screen 62 is initially coated with a solution of cobaltous chloride and then dried. In its hydrated form cobaltous chloride is pink while in its anhydrous form, the form in which it will exist on the screen after the drying step, it is blue. After so treating the screen to give it a blue color, filter 18 is removed from air suction line 16; a rag soaked in water is held across the open end of this line, and the blower is started. Air drawn into the blower through the moist rag will be at least substantially moistened if not actually saturated, and where it impinges on the screen it will reeonvert the cobaltous chloride to the hydrated form to give a pink pattern. This pattern will be of a transient nature, and measurement of its diameter or radius will have to be taken fairly rapidly. If desirable or necessary in any particular case, of course, water may be injected into the blower suction line 16 as a liquid spray of fine droplets from an atornizing device.

An example of the use of a liquid injected material in addition to that of a water spray just mentioned is that of an aerosol of ferric chloride. In the ferric chloride method the screen 62 is initially moistened with an aqueous solution of potassium ferrocyanide. This will leave the screen essentially colorless, assuming in this and other cases that the screen is initially white. While the screen is maintained moist, the oil burner blower is started, and an aerosol of ferric chloride is injected into its suction line 16. Where this latter chemical strikes the screen, it will react with the potassium ferrocyanide thereon to form a species of Prussian blue, KFe (CN) an extremely stable compound. In this way a long lasting, essentially permanent graphic record of the blast tube air discharge pattern will be made on the screen.

In the particular methods of forming a pattern on screen 62 described so far, a chemical or quasi-chemical reaction between at least two different substances has been required. Pattern forming methods may be employed, however, which do not call for any such reactions. An example of this, and a further example of a liquid material injected into the air stream, would be the use of any dye solution, either permanent or washable, which could be made into an aerosol or else simply sprayed into the blower inlet line from an atomizing device to impinge upon an untreated screen 62 and dye this screen in a pattern representative of the flow of air discharged from blast tube 20. Still another non-reactive method, and an example of a solid material injected into the air stream, would be the use of any colored substance in finely divided, solid form. A particular example of this kind would be the use of powdered carbon black. In the carbon black or solid pigment method, the screen 62 is initially moistened but only for retentive and not for reactive purposes. The oil burner blower is then started and the powdered carbon black or other finely divided solid pigment is injected into the blower suction line. Where this pigment powder is blown against the screen it will be largely retained thereon by the moist fibres, and so will provide the desired graphic record of the flow pattern of air discharged from the oil burner blast tube.

The utility of the above-described apparatus and method have been demonstrated by a series of experiments using a high pressure oil burner unit built by the Gilbert and Barker Manufacturing Company, and being of a size suitable for home heating purposes. This unit was provided with various end cones or end fittings for its blast tube whereby the diameter of the outlet opening of this tube for air flowing therefrom was regulated. These end cones were made either by the Monarch Manufacturing Works, Inc., or the ABC Manufacturing Company. Nozzle tip oil spray angle determinations were made on the basis of air pattern measurements according to this invention, The unit was fired at various oil rates using nozzle tips with various spray angles, and the minimum percentage of excess air for smokeless combustion was determined. The conditions and results of these experiments are summarized in the following table:

Gilbert and Barker high Minimum percent excess air for pressure burner blast Nozzle tip smokeless combustion with tube end cone spray cone nozzle tips having various angle despray cone angles termined g Maker Outlet by air patdia.,in. tern, deg. 45 60 70 80 The foregoing data show clearly that the minimum excess air requirement obtains when the nozzle tip used in practice generates an oil spray cone having an included angle which is the same as that determined on the basis of the air pattern of the oil burner unit with the apparatus and method of the present invention.

Although this invention has been described with a certain degree of particularity, it is to be understood that the foregoing disclosure has been made only by way of example, and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of this invention as hereinafter claimed.

What is claimed is:

1. An apparatus for determining the air discharge pattern of a fuel burning device having an air blast tube which is characterized by an outlet opening wherefrom air for the support of combustion is discharged and which is adapted to impose a mean axis of flow external to said device upon air discharged from said outlet opening, and further having a fuel spray nozzle retaining and feeding means located substantially centrally of said blast tube in the region of said outlet opening, said apparatus comprising a screen member of air-permeable material and mounting means therefor adapted to dispose said screen member in such spaced relation to said blast tube that said screen member will be impinged upon by substantially all of said air subsequent to the discharge thereof from said outlet opening, said mounting means comprising a rod member adapted to extend from and be supported by said fuel spray nozzle retaining and feeding means and a screen retaining member mounted on said rod member, said screen retaining member being adapted to retain in a substantially plane attitude substantially transversely to said mean axis of flow at least that region of said screen member intended to be impinged upon by air discharged from said outlet opening.

2. -An apparatus according to claim 1 in which said screen retaining member is adjustably mounted on said rod member in a fashion to allow variation of said spaced relation wherein said screen member is disposed to said blast tube.

3. An apparatus according to claim 1 in which said screen member is perforated to allow passage therethrough of said rod member.

4. A method for determining the air discharge pattern of a fuel burning device having an air inlet opening and having further an air blast tube which is characterized by an outlet opening wherefrom air for the support of combustion is discharged and which is adapted to impose a mean axis of flow external to said device upon said air discharged from said outlet opening, said method comprising the steps of treating an air-permeable screen member with a first chemical substance; disposing said screen member substantially transversely to said mean axis of fiow and in such spaced relation to said blast tube that said screen will be impinged upon by substantially all of said air subsequent to the discharge thereof from said outlet opening; operating said fuel burning device without any discharge of fuel to provide a flow of air from said outlet opening to impinge upon and pass through said screen member; injecting a second chemical substance into air flowing to said air inlet opening whereby said air flowing from said outlet opening achieves a content of said second chemical substance, said first and second chemical substances being reactable to form a visible product, and maintaining said screen member in said spaced relation to said blast tube wherein it is impinged upon by said air and said second chemical substance flowing from said outlet opening for sufiicient time to allow reaction between said first and second chemical substances to form a visible product on said screen member representative of the pattern wherein air from said outlet opening impinges thereupon.

5. A method according to claim 4 in which the step of treating said air-permeable screen member with a first chemical substance comprises moistening said screen member with an aqueous solution of copper sulfate, and in which said second chemical substance comprises ammonia.

6. A method according to claim 4 in which the step of treating said air-permeable screen member with a first chemical substance comprises moisten-mg said screen with an aqueous solution of cobaltous chloride and thereafter drying said screen to leave cobaltous chloride in anhydrous form deposited thereon, and in which said second chemical substance comprises water.

7. A method according to claim 4 in which the step of treating said air-permeable screen member with a first chemical substance comprises moistening said screen with an aqueous solution of potassium ferrocyanide, and in which said second chemical substance comprises ferric chloride.

8. A method for determining the air discharge pattern of a fuel burning device having an air inlet opening and having further an air blast tube which is characterized by an outlet opening wherefrom air for the support of combustion is discharged and which is adapted to impose a mean axis of flow external to said device upon said air discharged from said outlet opening, said method comprising the steps of disposing said screen member substantially transversely to said mean axis of flow and in such spaced relation to said blast tube that said screen will be impinged upon by substantially all of said air subsequent to the discharge thereof from said outlet opening; operating said fuel burning device without any discharge of fuel to provide a flow of air from said outlet opening to impinge upon and pass through said screen member; injecting a chemical substance into air flowin-g to said air inlet opening whereby air flowing from said outlet opening achieves a content of said chemical substance, said chemical substance being adapted to visibly color said screen by contact therewith, and maintaining said screen member in said spaced relation to said blast tube wherein it is impinged upon by said air and said chemical substance flowing from said outlet opening for suificient time to allow enough of said chemical substance to come into contact with said screen member to visibly color said screen member in a pattern representative of the flow of air from said outlet opening impinging on said screen.

9. A method according to claim 8 in which said chemical substance comprises a dye solution.

10. A method according to claim 8 in which said chemical substance comprises a finely divided solid pigment, and which includes the step of moistening said screen member.

11. A method according to claim 10 in which said solid pigment comprises carbon black.

12. A method for selecting a fuel spray nozzle tip for a fuel burning device having an air blast tube characterized by an outlet opening wherefrom air for the support of combustion is discharged and which is adapted to impose a mean axis of flow external to said device upon said air discharged from said outlet opening and further having a fuel spray nozzle tip retaining and feeding means located substantially centrally of said blast tube in the region of said outlet opening, said method comprising the steps of determining the outer boundary of the flow pattern of air discharged from said blast tube by discharging foreign matter from said blast tube along with said air and impinging said foreign matter upon a screen member to visibly color said screen member, and selecting a fuel spray nozzle tip adapted to generate a :fuel spray pattern having an outer boundary which will coincide with said outer boundary of said air flow pattern at a predetermined distance from said spray nozzle tip along said mean axis of flow.

13. A method according to claim 12 in which said predetermined distance is about six inches.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Adams: Lab Checks Technical Points, Fueloil and Oilheat, January 1957, pp. 78-81. (Copy in Patent Office Scientific Library.)

Schulz: Shell Oilburner Laboratory, Fueloil and Oilheat, December 1956, pp. 37-40. (Copy in Patent Office Scientific Library.)

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