US 2697910 A
Description (OCR text may contain errors)
Dec. 28, 1954 w. BRZOZOWSKI FLUID FUEL BURNER WITH SELF-CONTAINED FUEL VAPORIZING UNIT Flled July 29 1950 WATE an ww 5 m2 m m. M, 5 M
United States Patent FLUID FUEL BURNER WITH SELF-CONTAINED FUEL VAPORIZING UNIT Witold Brzozowski, Newtonville, Mass., assignor to Thermal Research and Engineering Corporation, Waltham, Mass., a corporation of Delaware Application July 29, 1950, Serial No. 176,670
2 Claims. (Cl. 60--39.55)
This invention relates to a fluid fuel burner, and more particularly, such a burner having a self-contained fuel vaporizing unit. The invention is especially useful in burning oil at high velocity while producing a short, high heat-release flame, to which use, however, the invention is not restricted.
It is necessary, in designing-certain types of combustion equipment, to provide for rapid release of the energy in the fuel. In apparatus for burning fluid fuel diffused in a column of air moving at high velocity through a chamber or tube, rapid vaporization of the fuel is exceedingly important. In the past, however, fuel vaporizing units for speedily vaporizing all but the most volatile fuels have usually been of a size which requires considerable space and will not permit them to be constructed as an integral part of a selfcontained burner.
I have now found that it is possible to construct a fluid fuel burner with a self-contained fuel vaporizing unit which is particularly adapted for burning fluid fuel diffused in a column of air moving at high velocity with a very short, high heat-release flame. Thus, it is possible to provide a fuel vaporizing or heating unit of minimum size, one which requires a minimum space, and one which may be formed as an integral part of the burner. Burners constructed according to the invention have an exceedingly high rate of heat release per unit of size and volumetric space requirement. They are of general utility as heating apparatus, particularly in installations which employ the products of substantially complete combustion for heating primarily by convection. The apparatus may also be used for special purposes, as in gas turbine power plants.
According to the invention, an auxiliary fuel supply. under pressure is burned and the products of its combustion are mixed with a portion of the air supplied to the burner which is heated by the products of combustion. Consequently when the main fuel supply is injected into the stream of pre-heated air the main fuel supply vaporizes rapidly and mixes with the main air supply to form a good combustible mixture. The velocity of the air stream is high enough to prevent combustion of any substantial part of the fuel during vaporization and initial diffusion into the air. However, subsequent ignition of the fully vaporized fuel completely diffused into the air column produces a short high heat release flame.
Three applications of the invention are illustrated .in the accompanying drawing, in which Fig. 1 shows, semi-diagrammatically, a broken longitudinal mid-section through a burner constructed and arranged according to the invention.
, Fig. 1A is an enlarged partial cross-section of the flame holder taken on the line 1A-1A of Fig. 1.
Fig. 2 is a similar view of a different type of burner according to the invention; and
Fig. 3 shows in like section another form of burner in accordance with the invention.
The burner shown in Fig. 1 comprises a chamber, in the form of a tube 10, through which a column of air moves from left to right in the position illustrated. The right hand or exit end of the tube is constricted, as at 11. Within the tube 10, in downstream sequence, each axially centered therein, are disposed a fuel vaporizing unit 12, a main fuel supply unit 13, and a flame holder 14.
The fuel vaporizing unit 12 comprises a cylindrical shell 15, disposed coaxially within the tube 10. The shell 15 has a conical end 16 pointed upstream and an opposite open end 17. The conicalend 16 of the shell 15 is pierced to form a number of orifices 18 therein, for a purpose which will later appear. A series of open-ended cylindrical members 19, 20, 21, of progressively increasing diameter are disposed downstream from the shell 15, the upstream end of each overlapping the downstream end of the next upstream member. The cylindrical shell 15 and the cylindrical members 19, 20 and 21 may be held within the tube 10 by any means which does not interfere unduly with the passage of the air therethrough, as by pins attached thereto and to the inside of the tube (not shown). Accordingly, the column of air passing through the tube 10 moves in contact with the cylindrical shell 15 and the cylindrical members 19, 20 and 21, and some of the air enters the fuel vaporizing unit 12 through the annular openings between the downstream ends of the shell 15 and the cylindrical members 19 and 20, and the upstream ends of the members 19, 20 and 21 respectively. A small quantity of air also enters the shell 15 through the orifices 18 in its conical upstream end.
An auxiliary fuel supply pipe 22 extends radially into the tube 10, and axially through the apex of the conical end 16 of the cylindrical shell 15 to terminate in a spray nozzle 23 within the shell. Furthermore igniting means is provided within the shell 15 for continuously maintaining ignition of the fuel supplied thereto through the spray nozzle 23. As here shown, this igniting means is a spark plug 24 projecting through the wall of the conical end 16 of the cylindrical shell adjacent one of the orifices 18 therein.
Accordingly, air moving at high velocity through the tube 10 enters the cylindrical shell 15 through the orifices 18 and mixes with the fluid fuel spread into the shell through the nozzle 23. The spark plug 24 ignites the resulting combustible mixture. As the burning mixture moves through the vaporizing unit, additional air passes through the annular openings between the downstream and upstream ends of the shell 15 and the cylindrical members 19, 20 and 21. This additional air is gradually mixed with the products of combustion and the rate of auxiliary fuel supply is regulated in accordance with the desirability of maintaining the temperature of the mixture at a point in the neighborhood of 800 F.
The main fuel supply unit 13 comprises a main fuel supply pipe 25, which extends radially through the wall of the tube 10, and carries, symmetrically disposed with respect to the longitudinal axis of the tube, a group of spray nozzles 26. The spray nozzles are preferably directed toward the on moving air column, into which they spray the fluid fuel to disperse the latter into the air.
The fuel vaporizing unit 12 furnishes the heat to vaporize the fuel from the main fuel supply unit, and the vaporized fuel is dispersed in the air column moving along the tube 10. The purpose of the vaporizing unit is primarily that of pie-heating and not igniting the main fuel supply.
From the main fuel supply unit, the vaporized fuelair mixture moves to the flame holder 14 where it is ignited. Although a variety of igniters may be used, it is preferred to employ at this point a flame holder such as that disclosed in applicants copending patent application Serial No. 108,316, filed August 3, 1949, now Patent No. 2,632,300, for Combustion Stabilization Means Having Ignitor Grill Heated by Pilot Burner.
Accordingly, the flame holder 14 is constructed in the form of a hollow annulus, and is supported, as by fins 27, centrally within the tube 10. The flame holder has a narrow circular entrance opening or slot 28 in its upstream side, and a similar circular exit opening or slot 29 in its downstream side. The sectional view shown in Fig. 1A clearly illustrates certain features of the flame holder 14. Thus, there is shown the outer annular part 14 and the inner annular part 14 of which the flame holder is formed, with the upstream opening or slot 28 therebetween. Spacers 30 within the unit serve to hold together the two annular parts into which the openings or slots 28 and 29 divide the unit. A spark plug 31 projects through the wall of the tube 10 and into the flame holder 14 to maintain ignition of the mixture therein.
Thus, a portion of the vaporized fuel-air mixture passes through the circular opening or slot 28, where its velocity is materially decreased in the protected and comparatively quiet interior of the flame holder. Here the spark plug 31 initially ignites, and when necessary reignites the mixture. Re-ignition, however, is not ordinarily required since the velocity of the vaporized fuel- .air'mixture is substantially reduced within the flame holder to maintain constant combustion therein. The .circular exit opening or slot 29 in the downstream side of the flame holder permits the ignited fuel-air mixture to leave the flame holder and to enter the moving unignited mixture beyond that unit, thereby igniting the mixture quickly and providing for rapid release of the energy of the fuel. The edges 32 of the exit opening or slot 2% may be spread apart to reduce the velocity of the fuel-air mixture immediately adjacent the downstream opening or .slot 29, thus widening the area of ignition immediately adjacent the flame preserver.
Although this type of apparatus may be used with a variety of fuels in fluid form, it has been found particularly eifect-ive where the fuel is a No. 2 or No. 3 oil, .as specified in the commercial standards CS12-48, promulgated by the National Bureau of Standards.
In the embodiment illustrated in Fig. 2, a central coaxial tube 12a is employed as a fuel vaporizing unit. Beyond this central tube, a unitary turnip-shaped chamber 33 is employed to receive the main fuel supply entering the heated vaporizing fluids and to contain the vaporized products until they are projected therefrom into the tube a. In this embodiment an auxiliary fuel supply pipe 22a extends radially through the wall of the tube Illa and is turned at its end toward the open upstream end of the central co-axial tube 12a centrally thereof. Thus, an auxiliary supply of fuel is projected into the tube 12a from the end of the auxiliary fuel supply pipe 22a entering this tube with a portion of the air column passing through the tube 10a and mixing therewith. A protected spark plug 24a is positioned centrally within the co-axial tube 12a downstream from the end of the auxiliary fuel supply pipe 22a and serves to ignite the fuel and air mixture which passes it.
A water supply pipe 34 extends through the wall of the outer tube 10a and into the central co-axial tube 12a downstream from the spark plug 24a. The end of the water supply tube 34 is turned downstream centrally of the inner tube 12a and terminates in a spray nozzle 35 whereby water may be sprayed into the burning fuel-air mixture within the fuel vaporizing unit. From the coaxial tube 12a the combustion gases from the mixture therein, together with water vapor enter the turnipshaped chamber 33 centrally of a ring of spray nozzles 26a through which the main fuel supply is spread into the turnip-shaped chamber from a main fuel supply pipe 25a. The heated combustion gases from the fuel vaporizing unit mingle with the main fuel supply spray and vaporize it within the chamber 33. The water vapor from the spray nozzle 35 serves important purposes: It cools the product of combustion initially to prevent premature combustion of the main fuel supply within the chamber 33 and makes possible vaporization of the main fuel supply without combustion. Thereafter, it promotes the rate of flame propagation probably because of dissociation of the water and the action of the resulting free hydrogen. The water spray also picks up and gasifies any free carbon which may result from the vaporization process.
The heated vaporized fuel supply leaves the unitary turnip-shaped chamber 33 through a ring of orifices 36 near its pointed downstream end where the main tube 10a is constricted to provide a throat wherein the vaporized fuel mixes with the air passing through the main tube 1.0a. Beyond the pointed downstream end of the unitary turnip-shaped chamber 33, a flame holder 14a, similar to the flame holder 14 which is illustrated in Fig. 1, serves to ignite the vaporized fuel-air mixture and to maintain its ignition.
This type of apparatus is found to give excellent results when used with heavy oils as fuel.
Fig. 3 represents still another apparatus for carrying out the invention. In this embodiment a central chamber 37 is formed within a main tube 101) which is generally similar to the main tube 10a illustrated in Fig. 2. The chamber 37 is gourd-like and symmetrically disposed within the tube 10b co-axially therewith. The larger end of the chamber 37 is positioned upstream within the tube 10b and a long tubular stem 38 projects downstream therefrom within a narrowed section of the outer tube 10b. Unlike the burners illustrated in Figs. 1 and 2, the main fuel supply enters the central chamber 37 centrally of its upstream end. Thus, a main fuel supply pipe 25b extends radially through the wall of the outer tube 10b and is turned at right angles to enter the upstream end of the chamber 37 co-axially therewith and co-axially with the outer tube 1%. No provision is made for igniting the main fuel stream within the chamber 37. After vaporization of the main fuel supply within the chamber 37, in a manner later to be described, the vaporized fuel leaves the chamber through a ring of openings 39 to enter and mix with the air column passing through the outer tube 10b. Thence the mixture passes into a constricted annular passage between the long tubular stem 33 and the narrowed outer tube 10b in which a flame holder 14b is positioned surrounding the stem 38. The flame holder ignites the mixture which passes it and maintains ignition at this point.
A cone 40 is positioned athwart the open downstream end 41 of the long tubular stem 38 and extends appreciably there beyond. The base of the cone .40 is concave in form and serves to intercept a small proportion of the onrushing burning fuel-air mixture and to turn it in reverse direction into the open end 41 of the stem 38. A water supply tube 34b projects radially through the wall of the outer tube 16b and enters the cone 40 where its end is turned centrally in an upstream direction to terminate externally of the base of the cone in a spray nozzle 42. Thus a water spray is projected into'the open end 41 of the stem 38 and passes with the reversely directed combustion products through the stem 38 and into the enlarged portion of the central chamber 37.
Movement of the heated combustion products and the water spray traveling reversely in the chamber 37 meets the main fuel supply spray and vaporizes it.
From the foregoing it will be evident that the present invention provides fuel vaporizing apparatus which speedily vaporizes the fluid fuel and diffuses it in a column of air moving at high velocity. The design of the apparatus is such that a short high heat-release flame is produced.
The forms of the invention here described and illustrated are presented merely as examples of how the invention may be applied. Other forms, embodiments and applications of the invention will, of course, be obvious to those skilled in the art.
1. A burner for burning a fuel-air mixture, said burner comprising: a tube through which the air moves at high velocity; a gourd-like chamber symmetrically formed within said tube coaxially therewith, having its larger end positioned upstream in said tube and having a long open-ended tubular extension projecting downstream in said tube; a main fuel supply pipe extending through the wall of said tube and turned to enter the upstream end of said chamber; a cone positioned athwart the open downstream end of the tubular extension of said chamber and extending appreciably therebeyond; and a water supply tube projecting through the wall of said tube and entering said cone; in combination with a spray nozzle centrally positioned in the base of said cone connected with the end of said water supply tube and directed into the downstream open end of said chamber; and a flame holder surrounding the tubular extensionof said chamber; said chamber having a ring of openings in its wall upstream from said flame holder; whereby the vaporized fuel supply leaves said chamber through the ring of openings therein to mix with the air moving through said tube and to be ignited by said flame holder, and whereby said cone reverses the direction of a part of the burning fuel-air mixture to direct it together with the water spray into said chamber through the downstream .open end of its tubular extension to vaporize the main fuel supply in said chamber.
2. A burner for burning a fuel-air mixture, said burner comprising: a tube through which the air moves at high velocity; a gourd-like chamber symmetrically formed within said tube coaxially therewith, having its larger end positioned upstream in said tube and having a long open-ended tubular extension projecting coaxially down stream in a narrowed section of said tube; a main fuel supply pipe extending radially through the wall of said tube and turned at right angles to enter the upstream end of said chamber axially thereof; a cone having a concave base positioned athwart the open downstream end of the tubular extension of said chamber and extending appreciably therebeyond; and a water supply tube projecting radially through the wall of said tube and entering said cone, the end of said Water supply tube being turned centrally of said cone in an upstream direction to terminate externally of the concave base of said cone; in combination with a spray nozzle centrally positioned in the base of said cone connected with the end of said Water supply tube and directed centrally into the downstream open end of said chamber; and a flame holder surrounding the tubular extension of said chamber; said chamber having a ring of openings in its wall upstream from said flame holder; whereby the vaporized fuel supply leaves said chamber through the ring of openings therein to mix with the air moving through said tube and to be ignited by said flame holder, and whereby said cone reverses the direction of a part of the burning fuel-air mixture to direct it together with the water spray into said chamber through the downstream open end of its tubular extension to vaporize the main fuel supply in said chamber.
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