US3251394A - Brush type high velocity air-fuel burner - Google Patents

Description

May 17, 1966 M. L. THORPE ETAL 3,251,394

BRUSH TYPE HIGH VELOCITY AIR-FUEL BURNER Filed Dec. 10, 1963 2 Sheets-Sheet 1 III OOOOOOOOOOOQOOOOOOOOOOOOOOOOO May 17, 1966 M. L. THORPE ETAL 3,251,394

BRUSH TYPE HIGH VELOCITY AIR-FUEL BURNER 2 Sheets-Sheet 2 Filed Dec. 10, 1965 burner, particularly of the brush or ribbon type.

United States Patent 3,251,394 BRUSH TYPE HIGH VELOCITY AIR-FUEL BURNER Merle L. Thorpe, R.F.D. 1, and Kent W. Harrington, Dear-born Road, both of Suncook, NH. Filed Dec. 10, 1963, Sell. No. 329,483 9 Claims. (Cl. 15827.4)

This invention relates to brush or ribbon type burners and more particularly to air-fuel burners which, due to high velocity, have very high heat transfer rates, heretofore available only from expensive oxygen flames or electric arcs.

Burners of this invention are to be distinguished from post or ditfusionburners, whose flames have restricted velocity ranges, often not exceeding 150 feet per second with air or 600 feet per second with oxygen, due to the necessity of maintaining the velocity low enough to stabilize the post-burning flame.

Burners in accordance with this invention operate with rocket-type jets, being deliberately operated under conditions of flash back to a pressure chamber. As a result, the upper range of exit velocity is in no way limited by flame extinguishment considerations, since maintenance of a post-burning flame is not essential to continued operation, and little diffusion burning occurs.

When exit velocities can thus be raised, greater opportunity is afforded for utilizing air (21% 0 as distinguished from more concentrated oxygen, as the combustion sustaining material, without decreasing heat transfer performance. Air-fuel combustion products, at flame temperature, if given high enough velocity (upwards of 2000 feet per second) have heat transfer characteristics which substantially equal the heat transfer produced in a conventional post-burning oxygen flame. The cost per B.-t.u. transferred to the work is, however, so much less for air that substantial savings result with no loss in speed or efiiciency, so far as the work is concerned, as when the burner is used for stippling, thermally texturing, or spalling rock surfaces. Additionally, the high velocity jets have a scrubbing effect which is highly beneficial in 3,251,394 Patented May 17, 1966 FIG. 6 is a fragmentary cross-sectional view taken along the line 66 of FIG. 2;

FIG. 7- is a perspective view of part of one of the elements shown in the previous figures; and

. FIG. 8 is a diagrammatic view of a water jet accessory for use with the burner. v The burner comprises a cylindrical tube 14 of a high temperature alloy (such as standard 310 stainless steel pipe). Around the ends of the pipe are bolted rings 16 and 17 which provide seats for end caps 18 and 20, respectively, which are bolted to the rings with the intervention 7 of gaskets (not shown).

such operations as rock stippling or descaling steel plate. 7

The attainment and maintenance of these high velocities, while impossible in fuel-air post burning apparatus because of flame extinguishment at such velocities, are not readily achieved either in a miniature rocket-type These high velocities cause flame blowouts within the chamber, uneven gas distribution along the exit orifices, and excessive oscillation and resonance.

It is a primary object of this invention to provide a miniature air-fuel rocket-type brush or ribbon type burner which has stability without resonance at high through: puts producing a ribbon-like row of gaseous jets having heat transfer rates comparable to those of oxygen flames.

I have discovered that by utilizing a combination of features as hereinafter described, reliable and satisfactory operation of such miniature air-fuel type rocket burners can be achieved with high jet velocities and good stability.

A burner embodying the combination of this invention is illustrated in the accompanying drawings, wherein:

FIG. Us a side elevational view, partly in cross-section, of a burner in accordance with the invention, broken away to indicate extent;

FIG. 2 is an end elevational view of the lower part of the burner shown in FIG. 1';

FIG. 3 is a bottom view of the burner shown in FIG. 1;

FIG. 4 is a cross-sectional view of portions of the burner;

FIG. 5 is a cross-sectional view taken along the line 5-5 of FIG. 4;

Each of the caps 18 and 20 has a tap ed bore, 26, 27, respectively, communicating with ports 32 and 34 leading to off-center inlets leading into the interior of the chamber formed by the capped tube 14.

Each end cap is also drilled and countersunk to accommodate a bolt 36 and 38, respectively, which supports a flame stabilizer 40, one at each end of the chamber.

Lefthand stabilizer 40 has a hub portion 41 which is offset so that its outer end can be inserted into an axial bore in the end cap with its oifset seated against the internal wall 42 of the end cap. The hub terminates at its inner end in a thin disc which fits into the internal bore of cylinder 14. The disc is drilled to provide a series of apertures 46 equally spaced about the disc with the bores being at an angle to the axis of the tube, for example, 45, inwardly of the disc. Preferably each disc has 7 apertures 46 on 45 centers omitting any aperture at the bottom of the disc as shown in FIG. 5; Additionally, the stabilizer 40 has a pair of smaller axial apertures 48 spaced radially outwardly from and between each adjacent pair of inclined apertures 46. A row of 30 aligned apertures forming exhaust nozzles 50 are provided between the inner ends of the stabilizers 40.

Screw threaded couplings 52 extend from the threaded bores 26' and 27 for attachment of metal tubes 60 and 62 which lead upwardly into the interior of a handle 64 for communication with a common source 66 of a fuel-air mixture.

Soldered to the outside of the cylindrical tube 14, as .by a high temperature silver solder 'having a melting point of at least 1100 F., is a long length of copper tubing 70 having the configuration shown in FIG. 7. An inlet end 71 of the tube proceeds downwardly around one side of the burner and then longitudinally of the burner close and in parallel relation to the row of aper-- tures 50 to the other end of the burner; then upwardly on the same side of the burner and longitudinally back across the top of the burner; then around the other side of the end of the burner; back again longitudinally of the burner in parallel relation to the apertures 50 on the other side; then upwardly around the other side of the burner and to an outlet end 72. As shown in FIG. 1, the inlet 71 and outlet 72 may continue up through the interior of the handle 64 for connection to a source'of water or other cooling fluid and man exhaust so that the cooling fluid may be circulated through the tubing during operation of the burner.

The symmetrical arrangement of the cooling tube about the axis of the housing is an important feature of the invention. If cooling tubing is located only adjacent the exhaust orifices, the stresses set up in the rest of the housing when heated to the temperatures contemplated for proper operation in accordance with this invention, namely, upwardsof 1000 F., soon cause a warping or bending of the tube which severely limits its life. By cooling the housing along its length diametrically opposite to the row of orifices as well as in the area of the orifices, such buckling of the housing is overcome. Normally, with the walls operating at a temperature of 1400l500 F., the cooling medium can hold the bottom and top sections of the tube at 500 F. or less, without causing more than percent heat loss and usually only about 3.5 percent heat loss to the cooling fluid, which is perfectly feasible in a burner which generates, as does the embodiment shown in the drawing, upwards of 10,000 B.t.u.s per minute.

Also, to aid ignition, the bolt 38 has an axial bore 80 which communicates with an axial bore 81 through the righthand stabilizer 40 and with an annular recess 82 surrounding the bolt 38 near its head, the recess registering with an outwardly extending passageway 83 leading to a tapped bore 84 in cap for reception of a tube 85 which also leads upwardly through the handle 64 for connection to a source of oxygen.

In the particular construction shown the nozzles 50 comprise 30 inch holes on inch centers. The stabilizer apertures 46 are inch in diameter, and apertures 48 are each inch in diameter. All other parts are shown to approximate scale with respect to a tube of approximately 2.375 inches OD. and 2.067 ID. The ratio of about 3.14 sq. in. internal cross-sectional area of the tube to the 0.264 cross-sectional area of the inlets at one end of the tube is thus about 12:1; or about 6:1 with respect to the total cross-sectional area of the inlets at both ends of the tube. The ratio of exit to total injection cross-sectional area is approximately 1.29:0.528 or 2.45. If this ratio is decreased, operation becomes less and less satisfactory. As the ratio is increased, the chamber pressure decreases at a constant through-put with resulting reduction in exit velocity and reduced heat transfer so that the ratio should be maintained at not more than 8:1. Given a proper exit to injection cross-sectional area ratio, such as the above, chamber pressure may run up to 50 pounds per square inch or higher, depending upon the intended use and permissible jet velocity.

The cooling system is operated to maintain the burner walls at between 1000 and 2200 F., preferably 1400 to 2000 F. It has been found that at 2000 F. throughput can be raised to 250 cubic feet per minute as contrasted with only 20-40 c.f.m. with a 200 F. wall, but operation at 1400 F. is readily achievable with 125 c.f.m. through-put and jet velocities of 5001500 feet per second.

The cross-sectional area of the housing controls the through-put for optimum operation. This is because complete combustion is essential to successful operation, and too great input will result in incomplete combustion with the walls then operating too cool. The approximate 2 inch diameter housing shown has a cross-sectional area of about 3.14 square inches. This cross-sectional area is more than is needed for a cubic feet per end per minute input, being a .0628 ratio and is better adapted for a 50 cubic feet per end per minute input with a ratio of .0314 and is probably not enough for an input of 100 cubic feet per end per minute or a ratio of .0157. The lower limit of the ratio of tube cross-sectional area to cubic feet of air per minute should therefore not be less than about .02. Or, to put it in another way, the crosssectional area of the tube should preferably not be less than 1 square inch for each 25 cubic feet input of combustible fuel-air mixture per end per minute.

While the diameter of the combustion chamber may vary, anything less than /4, inch LD. would not be considered satisfactory.

This burner has been found extremely eflicacious and efiicient in stippling rock, specifically granite. For this purpose, the burner is mounted on an indexing carriage which traverses back and forth in progressively parallel paths over a prepared granite surface, for example, lengthwise of an oversize 4-foot-by-8-foot slab. The jets impinge perpendicularly downwardly onto the surface regardless of the direction of relative travel, thus aiding in securing uniform stippling on all traverses. The orifices should be kept as close as possible to the granite surface, not more than A2 inch, which means that the cooling tubing has to be less than /2 inch in diameter. Preferably,

they are outside diameter so there is about inch clearance during operation. With a chamber pressure of about 3 pounds p.s.i., the jets, if unopposed, are about 2 inches long when the burner is operated from a 40- pound source of combustible air and natural gas mixture producing a jet velocity of above 600 feet per second. The closer the stand-01f, the less the heat loss. Operating under these conditions, the burner may traverse a hardto-spall block granite surface at about 7 feet a minute can be increased up to 8.8 feet per minute at the 5-p0und pressure.

Also, because of the abrading effect encountered during stippling, the copper tubing on each side of the orifices should be on about inch centers to prevent the space between the tubes from becoming clogged with melted slag. Making the bottoms of the tubing wall as thick as possible is helpful in prolonging life due to abrasion; or thin strips of metal may be added to the bottoms of the cooling tubes to offer great thickness to prolong life against sand blast abrasion losses.

Since some granite slabs are only 1 or 2 inches thick and can crack when subjected dry to the heat transfers contemplated in the operation of the burner, it is desirable to wet the surface of the granite as by a water spray directed downwardly onto the surface of the granite at an angle in front of and behind the jets. This preand post-wetting of the surface in no way affects the stability of the burner operation, since the jet blast quickly clears the area beneath the jets. This is in contrast to post burner stippling devices, where the flame velocities are so low that they are badly affected by water sprays which can cause flame extinguishment. Moreover, a water spray traveling in front of the burner washes away all chips to insure that the jets impinge on cleaned stone. Thus, in FIG. 8 there is shown a water pipe surrounding the burner on supports 92 and having orifices which direct water jets as shown at an angle down onto the slab 91 being treated in advance of and rearwardly of the burner.

While the embodiment shown in the drawing has a straight single row of uniformly spaced exhaust orifices having parallel axes, it is contemplated that their spacing, axis orientation, and individual size may be varied, and that more than one row may be utilized, all depending upon the type of operation and end results desired.

As can be seen, one of the great advantages of burners which operate with an air-fuel mixture is that the jets, where a flame temperature of 3000 F. is developed, contain 78 percent nitrogen and therefore have much more mass than is present in a jet which constitutes the reaction products of oxygen-fuel-rnixtures at the same 3000" F. temperature. The additional mass is of course useful in displacing surface material, for example, in stippling spallable rock surfaces.

What is claimed is:

1. An internal combustion burner comprising a hollow cylinder of maximum wall thickness less than the maximum internal cross-dimension of said cylinder, cap means plugging both ends of said cylinder, :1 row of spaced exhaust orifices extending along one side of said cylinder, a plurality of inlets leading into said cylinder for injecting an air-fluid fuel combustible material continuously into said cylinder for combustion within said cylinder with discharge of the products of combustion through said exhaust orifices, and the total cross-sectional exit area of said exhaust orifices exceeding the total cross-sectional inlet area of said inlets, and a pair of flame stabilizers, one at each end of said tube, said stabilizers comprising apertured discs extending transversely of said tube in spaced relation to the inside walls of said cap means.

2. A burner as claimed in claim 1, wherein the stabilizers include apertures whose axes are inclined relative to the axis of said cylinder.

3. A burner as claimed in claim 1, wherein the stabilizers are located beyond the ends of the row of exhaust orifices.

4. The method of stippling a spallable rock surface comprising wetting said surface with water, traversing said Wet surface transversely with a row of impinging, closely spaced, concentrated high temperature gaseous jets directed perpendicularly downwardly onto said wet surface, said jets comprising the substantially complete prodnets of combustion reaction of an air-fluid fuel mixture, discharged continuously from a common internal combustion chamber at substantially uniform velocities exceeding 500 feet per second, wherein said surface is Wetted with water by directing a series of jets onto said surface at an angle thereto just prior to traversing said surface with said gaseous jets.

5. An internal combustion burner comprising a hollow tube of maximum wall thickness less than the maximum internal cross-dimension of said tube, cap means plugging both ends of said tube, exhaust orifice means extending along one side of said tube, an inlet leading into said tube at each end thereof for injecting an air-fluid fuel combustible mixture continuously into said tube from opposite ends thereof for combustion within said tube with discharge of the products of combustion through said exhaust orifices, and the total cross-sectional exit area of said exhaust orifices exceeding the total cross- 1 sectional inlet area of said inlets, and a pair of flame stabilizers disposed in said tube, one at each end thereof.

6. An internal combustion burner as claimed in claim 5, wherein each of said exhaust orifices has a width equal to at least a major fraction of the wall thickness defining said orifices.

7. An internal combustion burner as claimed in claim 5, wherein the cross-sectional area of said tube is about 6 times the total cross-sectional area of said inlets.

8. An internal combustion burner comprising a tube of maximum wall thickness less than the maximum internal cross-dimension of said tube, cap means plugging both ends of said tube, a row of spaced exhaust orifices extending along one side of said tube, each of said exhaust orifices having a width equal to at least a major fraction of the maximum thickness of said wall, each said cap means having an inlet passage extending therethrough and communicating with the interior of said tube for injecting an air-fluid fuel combustible material continuously into said tube from opposite ends thereof for combustion within said tube with discharge of the products of combustion through said exhaust orifices and the ratio of the total cross-sectional exit area of said exhaust orifices to the total cross-sectional inlet area of said inlets being from about 2:1 to 8:1, and a pair of flame stabilizers disposed in said tube, one at each end thereof.

9. An internal combustion burner comprising a tubular housing forming a combustion chamber, a row of uniformly spaced orifices extending'longitudinally along one side of said housing, and cooling means for portions of said housing comprising a pair of cooling channels extending longitudinally of said housing on each side of and in parallel relation to said row of orifices, a compensating cooling channel extending along said housing in diametrically opposed relation to said row of orifices, and means for connecting said cooling channels to a source of cooling fluid.

References Cited by the Examiner UNITED STATES PATENTS 971,105 9/1910 Bausher 126271.3 1,138,549 5/ 1915 Frederickson 158-27.4 1,514,815 11/1924 Anderson 15 8--27.4 1,660,018 2/ 1928 Steffen 1581 14 X 2,385,107 9/ 1945 Scherl 15827.4 2,781,754 2/1957 Aitchison et al l 2,826,248 3/1958 Angel 158-99 2,878,644 3/1959 Fenn l584 3,118,489 1/ 1964 Anthes 1587 FREDERICK L. MATTESON, JR., Primary Examiner.

MEYER PERLIN, Examiner.

V. M. PERUZZI, E. G. FAVORS, Assistant Examiners.

Claims (1)

1. AN INTERNAL COMBUSTION BURNER COMPRISING A HOLLOW CYLINDER OF MAXIMUM WALL THICKNESS LESS THAN THE MAXIMUM INTERNAL CROSS-DIMENSIONAL OF SAID CYLINDER, CAP MEANS PLUGGING BOTH ENDS OF SAID CYLINDER, A ROW OF SPACED EXHAUST ORIFICES EXTENDING ALONG ONE SIDE OF SAID CYLINDER, A PLURALITY OF INLETS LEADING INTO SAID CYLINDER FOR INJECTING AN AIR-FLUID FUEL COMBUSTIBLE MATERIAL CONTINUOUSLY INTO SAID CYLINDER FOR COMBUSTION WITHIN SAID CYLINDER WITH DISCHARGE OF THE PRODUCTS OF COMBUSTION THROUGH SAID EXHAUST ORIFICES, AND THE TOTAL CROSS-SECTIONAL EXIT AREA OF

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