US3224486A - Method and apparatus for producing air-fuel flames of sonic and supersonic velocities - Google Patents

Description

' Dec. 21, 1965 B. GELLER ET AL 3,224,486

METHOD AND APPARATUS FOR PRODUCING AIR-FUEL FLAMES OF SONIC AND SUPERSONIC VELOCITIES Filed Dec. 7, 1964 United States Patent This invention relates to a method and apparatus for producing air-fuel flames of sonic and supersonic velocities. This application is a continuation-in-part of application Serial Number 147,881, filed October 26, 1961,

. now abandoned.

It has heretofore been proposed to employ oxy-fuel flames of sonic or supersonic velocities. While air-fuel mixtures are obviously less expensive than a mixture of fuel and oxygen, air-fuel burners capable of producing flames of sonic or supersonic velocity and a combustion chamber temperature of, say, 2500 F. to 3500 F., are not in widespread commercial use largely because, it is believed, of operational difficulties which are not easy to overcome in presently available burners.

It is an object of this invention to provide a method and apparatus for producing, in practical, convenient, and effective manner, flames of sonic and supersonic velocities and of a temperature of at least 2500 F., utilizing fuel and compressed air as the only oxidant thereof.

The invention resides in a method which comprises the steps of injecting a finely atomized supply of fuel into a combustion chamber having 'an exhaust outlet, and continuously injecting a confined primary supply of compressed air directly into the chamber to serve as primary combustion air, such injected fuel and air forming a combustible mixture in'the chamber. An ignition device is activated internally of the chamber for a period suflicient to establish a stable flame, following which the ignition device is de-activated. A supply of secondary air is continuously injected into the chamber independently of the primary air supply to maintain a flame issuing from the exhaust outlet having a temperature in the order of 20003000 F. and an effective exhaust velocity in the order of 25 004600 feet per second.

The air to fuel ratio is between 11 and 30 pounds of total compressed air per pound of fuel.

The invention also resides in an air-fuel burner for producing jet flames of at least sonic velocity which comprises a cylindrical housing having forward, rear and side walls forming therein a combustion chamber, and a nozzle in the forward wall having a flame exit throat. Primary air and fuel inlet means extend into the chamber through the rear wall and an ignition device is provided in the chamber in rearwardly spaced relation to the exit throat. Control means for activating and de-activating the ignition device is provided externally of the chamber. An independent secondary air conduit has an outlet in the chamber completely independent of the primary air inlet means whereby the air supplied by the primary air and fuel inlet means is controllable separately from the air supplied by the secondary air conduit. A confined cooling system is provided and includes a closed cylindrical cooling jacket surrounding the side wall and forming an annular cooling chamber.

The invention will be described with particular reference to the accompanying drawing, in which:

FIGURE 1 is a side elevation, partly in section and partly in diagrammatic form, of a burner in accordance with the invention,

Patented Dec. 21, 1965 ice FIGURE 2 is a side elevation, partly in section, of an alternative form of burner,

FIGURE 3 is a schematic side elevation, partly in section, of a modified form of burner,

FIGURE 4 is a sectional side elevation of a convergingdiverging type of nozzle,

FIGURE 5 is a side elevation, partly in section and partly in diagrammatic form, of a further modified form of burner, and

FIGURE 6 is a partial sectional side elevation of a modified form of burner.

Referring to FIGURE 1, 10 is a cylindrical casing forming therein a cylindrical combustion chamber 11, and having an inwardly continuously converging forward wall portion 12 terminating in an exit throat 13 formed by an interchangeable tubular nozzle 14.

A cooling jacket 15 surrounds the casing 10 and provides a cooling fluid receiving space or passage 16 surrounding the casing 10. It will be observed that the nozzle 14 extends through the passage 16 and jacket 15. The rear end of the casing 10 and jacket 15 is closed by a plate 17 and inlet and outlet pipes 18 and 19 leading to and from the passage 16 are provided for circulation of cooling fluid therethrough.

A housing providing an air-fuel mixing chamber 20 may be located rearwardly of the combustion chamber, such chamber 20 having a fuel inlet 21 and a compressed air inlet 22. The mixture is fed into chamber 11 by means of a conduit 23 having an orifice 24 within chamber 11. However, it will be understood that any suitable manner for effecting the mixing of primary air andfuel may be employed. For instance, a section of the combustion chamber may be employed as a mixing chamber.

Any suitable ignition means may be provided but it is essential that its activation be controllable externally of the combustion chamber. The ignition means may comprise a spark plug or, as shown, a heating coil 25 surrounding the conduit 23 adjacent to its orifice 24. The heating coil may be supplied with power by means of a battery 26 and an electricalconnection.27. A- switch 28 is provided in the circuit to switch off the current to the heating coil when the desired flame has been established.

Secondary air is supplied to the combustion chamber 11 by means of a conduit 29, having one or more orifices 29a within combustion chamber 11.

A pressure gauge 30 having a connection 31 communicating with the combustion chamber 11 is preferably provided to permit the operator to conveniently determine whether or not sonic flow conditions have been reached.

Any gaseous fuel such as acetylene or propane or a suitable liquid hydrocarbon fuel, such as kerosene, may be employed. The coolant may be water, secondary air or the liquid hydrocarbon fuel burned. In the latter case, only part of the circulating liquid is bled off for burning in the combustion chamber.

FIGURE 2 illustrates a slightly modified form of burner, wherein a plurality of exit throats 33 are provided.

FIGURE 3 illustrates a somewhat modified formof burner which is particularly suitable for usewhen propane gas is used as the fuel. In this instance, a flameholder 32 comprising a screen or perforated plate, is placed adjacent to and downstream of orifice 24. A cylindrical casing 34 forming a combustion chamber 35 is surrounded by a coolant jacket 36. An exit nozzle 37 is clamped for ease of replacement or interchange between the forward end of the casing 34 and flange-38 on the adjacent end of the jacket 36. A rear wall 34:! completes the assembly. The illustrated nozzle 37 has a continuously converging portion 39 and an exit throat 40. To obtain supersonic velocities, however, a suitably 'vided, as shown in FIGURE 4.

.mixture supply line 44.

dimensioned convergent-divergent nozzle 55 may be pro- Again referring to FIGURE 3, the coolant inlet is indicated at 41 and the coolant outlet at 42. The mixing chamber is shown at 43 and the mixture supply line at 44 leading therefrom to the combustion chamber 35. The mixing chamber has a fuel inlet 45 and a primary air inlet 46. Secondary air is supplied to the combustion chamber by a conduit 47, which has a portion 47a in concentric relation to A supplementary supply of oxygen may be supplied to the combustion chamber through line 48, but is not in use under normal operating conditions. A pressure gauge 49 has a connection 50 leading to the combustion chamber. The ignition circuit is indicated at 51, such circuit having a power supply 52, switch 53 and ammeter 54.

The diameter of the exit throat 13, 33, or 40 is determined by the amount of gases to be burnt. The combustion chamber dimensions should be limited to the minimum required by the specific inlet orifices 24 and 30, of FIGURES 1 to 3, inclusive, and/or the flameholder 32 employed in FIGURE 3. In the case of an acetylene flow up to some 4.2 lbs. per hour and respective air flow for stoichiometric conditions, a combustion chamber diameter of one inch is adequate. In the case of propane flows up to about lbs. per hour, a somewhat larger combustion chamber diameter is required due to the more elaborate gas inlet orifices and flameholder design.

FIGURE 5 illustrates a form of burner which is particularly suitable for use when liquid hydrocarbon fuel, such as kerosene, is used. In this case, the liquid fuel is atomized by compressed air or mechanical means or a combination of these means. Referring to FIGURE 5, a perforated cylindrical combustion chamber forming wall 56, constructed of a suitable combination of high heat resistant steel and refractory, is surrounded by a coolant jacket 57. The coolant, which is secondary combustion air, enters the coolant jacket at 58. Secondary air enters through inlet 58a and is preheated in cooling the combustion chamber casing, and then enters the combustion chamber through a multiplicity of perforations 59 scientifically located so as to achieve eificient combustion of the fuel. Liquid hydrocarbon fuel, supplied through inlet 59a, is introduced into the combustion chamber as a fine spray through atomizing nozzle 60 mounted in an atomizing device 60a. Primary air for combustion is supplied through an inlet 60b communicating with an annulus 61 formed in forward wall 61a of the device and disposed in the combustion chamber. Such wall 61a may be provided with additional primary air inlet holes 61b. The nozzle 60 is preferably axially adjustable as by means of its screw-threaded mounting illustrated. Thus, primary air may be supplied in controlled quantities and in such a manner as to provide good mixing of the fuel and air for stable ignition and combustion. The air-fuel mixture is ignited by means of spark plug 62 with an external high voltage power supply from an ignition transformer. Tertiary air is injected into the combustion chamber at its exit end by means of orifices 63. The combustion gases leave the combustion chamber through an exit noZZle 64 which forms the end of the combustion chamber. As shown, the nozzle 64 is a separate member suitably secured to wall 56 for ease of replacement or interchange. The exit nozzle for reasons of simplicity, may be of solid construction, but it is sometimes preferable that it incorporate a cooling passage 65 through which the liquid fuel or air collant may pass. In cooling the nozzle, the fuel or air is preheated and this assists ignition and cornbustion of the fuel. An external cooling medium such as water may be used instead, if preferred. A pressure gauge 66 having a connection 67 communicating with the combustion chamber, is also provided.

The burner illustrated in FIGURE 6 may be similar to any of the burners described but it includes therein a flame holder structure which is satisfactory in operation and which may be readily incorporated in burners of the type described. The burner shown has a side wall 70 having a coolant jacket 71 thereon. The side wall and jacket are recessed to provide a wall recess 72 in the combustion chamber 73. Extending into the recess is an ignition device, such as a retractable electrode 74. The recess 72 in the combustion chamber provides a zone offset from the main combustion chamber zone which will act to maintain the flame.

In operation of the burners described, a critical feature resides in the initial establishment of the flame. A momentary spark or the like is quite insufficient to establish a flame when using an air-fuel mixture. Thus, it is necessary to control activation of the ignition device externally of the combustion chamber whereby the device may be kept in activated condition until a stable flame has been established and the device is de-activated only after this has occurred.

Another critical feature resides in the provision of a supply of secondary air, both the supply and control of which are entirely independent of the supply and control of primary air. With the employment of compressed air as the oxidant, it is necessary to supply and control the secondary air quite independently of the primary air in order to maintain a flame having the characteristics set forth.

It is further essential that the primary air supply be independent of the fuel supply regardless of Whether the fuel supply is in the form of a gas, gaseous mixture, or atomized liquid fuel. Such independent supply makes it possible to closely control the supply of primary air. In accordance with the invention, most of the stoichiometric amount of air required for combustion is supplied in the primary air supply. Thus, 60 to of the stoichiometric amount of air is supplied as primary air.

Kerosene flows of about 36 lb./hr. with the necessary air flows may easily be handled in burners with a combustion chamber diameter of about 2 inches. It may also be noted that air flows greatly in excess of stoichiometric may be burned without any danger of flame out.

A small test burner such as described and using a convergent exit nozzle only is capable of producing a flame having a high exit temperature in the order of 2000- 3000 F. and a sonic exit velocity in the order of 2500 feet per second, with the effective exhaust velocity being in the order of 2500-3600 feet per second.

An internal combustion type burner, such as described, possesses many advantages. An internal ignition means, rather than the conventional external means as used with oxy-fuel burners, is readily incorporated therein. Suitable flameholders to prevent flame blow-off may be conveniently employed. It can be readily and rapidly equipped with various exit nozzles of selected configuration to permit easy adaptation to the specific working conditions encountered. The continuously converging exit portion is easy to produce as compared with the conventional converging-diverging type. The closed circuit water or other coolant circulation is of advantage in avoiding the supply of large quantities of cooling liquid. The burner is compact in structure, easy to fabricate, and sturdy. It is subject to choice of suitable dimensional proportions to establish a stable, sonic or supersonic air-fuel flame.

Since the flame is stable, it is insensitive to disturbances and obstructions encountered downstream from the exit nozzle, and, therefore, resists extinguishing by other than design means.

The compact dimensions are rendered possible by the extremely high heat release rates obtainable (of at least 40x10 to 80 by 10 B.t.u./cu. ft./hr.).

Economy of operation and lack of supply problems result from the use of air instead of, for instance, oxygen, as well as by the use of a regenerative, closed-water or other coolant circuit. It will be appreciated that compressed air is frequently available since it is universally employed in many types of mechanical equipment.

It will also be apparent that any suitable external source for the power supply may be provided. For instance, it may be of self-contained manually-portable battery type.

A burner such as described may be employed for various purposes. Examples of some such purposes are given as follows:

Since the jet flame can be maintained under water, it may be employed as a submerged flame for heating bodies of water and the like, to maintain ice-free harbours, to operate in explosive atmospheres as a submerged flame or to maintain bacterial life in sewage treatment plants; general combustion Work, and the like; also, for concentration of various kinds of solutions and suspensions or for heating and agitating aqueous solutions where concentration of the solution is not required. It may also be employed for preheating rocks to facilitate their subsequent comminution.

We claim:

1. A method of producing a jet flame which comprises the steps of injecting a finely atomized stream of liquid fuel into a combustion chamber having a convergent exhaust outlet, continuously injecting a primary stream of compressed air directly into said atomized fuel stream in said chamber to serve as primary combustion air, said injected fuel and air forming a combustible mixture in said chamber, controlling from a point externally of said chamber the activation of an ignition device located in said chamber and including the steps of (a) initially activating said device to ignite said mixture, (b) continuing the activation of said device until a stable flame has been established therein, and (c) de-activating said ignition device following said flame establishment, and continuously injecting a stream of compressed secondary air into said chamber independently of said streams of fuel and primary air and at a point spaced from the points of injection of said streams of fuel and primary air, controlling the supply of said fuel, primary air and secondary air to provide in said primary air stream 60% to 80% of the stoichiometric amount of air required for combustion in said chamber, and determining the pressure in said chamber while further controlling the supply of said fuel, primary air, and secondary air to maintain a pressure in said chamber resulting in a flame issuing from said exhaust outlet having a temperature in the order of 2000 to 3000 F. and an effective exhaust velocity in the order of 2500 to 4600 feet per second, the total of said primary air and said secondary air being in the ratio of 11 to 30 pounds of said total air per pound of said fuel.

2. An air-fuel burner for producing jet flames of at least sonic velocity which comprises, forward, rear, and side walls forming a combustion chamber, a nozzle in said forward wall having a flame exit throat, a fuel mixture conduit extending through said rearward wall and having an outlet in said chamber spaced rearwardly from said exit throat, said rearward wall having a primary air sup ply passage extending therethrough into said chamber independently of and adjoining said fuel mixture conduit, a primary air supply conduit communicating with said passage, an electrical ignition device in said chamber adjacent said outlet and having an energizing circuit extending externally of said chamber, a switch in said circuit externally of said chamber controlling energization thereof, a secondary air conduit independent of said mixture and primary air conduits and said passage having an outlet extending through said chamber side wall whereby air supplied by said primary air passage is controllable separately from the air supplied by said mixture conduit and said secondary air conduit, means for measuring the pressure in said chamber to determine establishment of sonic velocity flames therein, and a cylindrical cooling jacket surrounding said side Wall and forming an annular cooling chamber.

3. An air-fuel burner for producing jet flames as defined in claim 2, said secondary air conduit having an opening leading into said cooling chamber to provide cooling fluid therein, said side wall having a plurality of openings therein leading from said cooling chamber to said combustion chamber and constituting said secondary air outlet.

References Cited by the Examiner UNITED STATES PATENTS 2,725,929 12/1955 Massier 15s 73 2,878,644 3/1959 Fenn 158-99 2,923,348 2/1960 Fraser 15876X FREDERICK L. MATTESON, JR., Primary Examiner.

MEYER PERLIN, Examiner.

Claims (1)

1. A METHOD OF PRODUCING A JET FLAME WHICH COMPRISES THE STEPS OF INJECTING A FINELY ATOMIZED STREAM OF LIQUID FUEL INTO A COMBUSTION CHAMBER HAVING A CONVERGENT EXHAUST OUTLET, CONTINUOUSLY INJECTING, A PRIMARY STREAM OF COMPRESSED AIR DIRECTLY INTO SAID ATOMIZED FUEL STREAM IN SAID CHAMBER TO SERVE AS PRIMARY COMBUSTION AIR, SAID INJECTED FUEL AND AIR FORMING A COMBUSTIBLE MIXTURE IN SAID CHAMBER, CONTROLLING FROM A POINT EXTERNALLY OF SAID CHAMBER THE ACTIVATION OF AN IGNITION DEVICE LOCATED IN SAID CHAMBER AND INCLUDING THE STEPS OF (A) INITIALLY ACTIVATING SAID DEVICE TO IGNITE SAID MIXTURE, (B) CONTINUING THE ACTIVATION OF SAID DEVICE UNTIL A STABLE FLAME HAS BEEN ESTABLISHED THEREIN, AND (C) DE-ACTIVATING SAID IGNITION DEVICE FOLLOWING SAID FLAME ESTABLISHMENT, AND CONTINUOUSLY INJECTING A STREAM OF COMPRESSED SECONDARY AIR INTO SAID CHAMBER INDEPENDENTLY OF SAID STREAMS OF FUEL AND PRIMARY AIR AND AT A POINT SPACED FROM THE POINTS OF INJECTION OF SAID STREAMS OF FUEL AND PRIMARY AIR, CONTROLLING THE SUPPLY OF SAID FUEL, PRIMARY AIR AND SECONDARY AIR TO PROVIDE IN SAID PRIMARY AIR STREAM 60% TO 80% OF THE STOICHIOMETRIC AMOUNT OF AIR REQUIRED FOR COMBUSTION IN SAID CHAMBER, AND DETERMINING THE PRESSURE IN SAID CHAMBER WHILE FURTHER CONTROLLING THE SUPPLY OF SAID FUEL, PRIMARY AIR, AND SECONDARY AIR TO MAINTAIN A PRESSURE IN SAID CHAMBER RESULTING IN A FLAME ISSUING FROM SAID EXHAUST OUTLET HAVING A TEMPERATURE IN THE ORDER OF 2000 TO 3000*F. AND AN EFFECTIVE EXHAUST VELOCITY IN THE ORDER OF 2500 TO 4600 FEET PER SECOND, THE TOTAL OF SAID PRIMARY AIR AND SAID SECONDARY AIR BEING IN THE RATIO OF 11 TO 30 POUNDS OF SAID TOTAL AIR PER

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