US3255802A

US3255802A - Method and apparatus for producing flame jet and controlling temperature and flame stability of same

Info

Publication number: US3255802A
Application number: US306887A
Authority: US
Inventors: James A Browning
Original assignee: H E FLETCHER CO
Current assignee: H E FLETCHER CO
Priority date: 1963-09-05
Filing date: 1963-09-05
Publication date: 1966-06-14
Anticipated expiration: 1983-06-14

Description

ame M, wm@ J. A. BROWNING 3,255,802

AND APPARATUS FOR PRODUCING FLAME JET AND CONTROLLING m' n I TEMPERATURE AND FLAME STABILITY OF' SAME fue@ cept. 5, 1965 5 Sheets-.Sheet l METIv OD Hrs.

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Umted States Patent O 3,255,802 MIETHD AND APPARATUS FR PRUDlUCING FLAME JET AND CONTRLLING TEMPERA- IPURE AND FLAME SCF-ABILITY F SAME dames A. Browning, Hanover, NH., assignor to H. E. Fletcher Co., West Chelmsford, Mass., a corporation of Massachusetts Filed Sept. 5, 1963, Ser. No. 306,887 7 Claims. (Cl. 158-4) The present invention is a continuation-impart of my copending application Ser. No. 666,680, filed lune 19, 1957, now Patent No. 3,103,251, granted Sept. 10i, 1953.

This invention relates to a method and apparatus for burning a fuel to yform a flame jet and, more particularly, the invention is concerned with a method of producing a cooled liame jet wherein oxygen and an inert gas such as nitrogen are mixed with a liquid fuel and the fuel is burned at superatmospheric pressure in a confined combustion chamber to provide a relatively high velocity stream of products of combustion whose temperatures and liame stability may be varied in accordance with a controlled use of the inert gas component in lthe combustion chamber.

As disclosed in the above application, I have determined that a nitrogen cooled flame jet, as distinct from an oxyfuel flame jet in-Which pure oxygen is used as the oxidant, is capable of providing much lower flame temperatures than those possible with a conventional oxy-fuel jet. In this connection it has been found that use of a water coolant for `the burner combustion chamber may be eliminated since appreciable amounts of `thermal energy is absorbed by the inert nitrogen. In addition, the nitrogen cooled flame is found to provide for improved removal of spallable mineral bodies in carry-ing out channelling and other mineral Working operations.

However, in producing a nitrogen cooled type llame jet in which the inert gas component occurs in an appreciable amount, various problems are encountered. For example, it is necessary to maintain the percent fuel introduced within definite limits which are neither too rich or too lean to support combustion. Flame stabilization of a nitrogen cooled type flame jet must be accomplished within much narrower stability limits than is the case with a pure oxygen-fuel jet. The region defined by these limits in any given instance may be conveniently referred to as the region of stable burning of a flame jet. Other factors which determine such a limiting region of stable burning are stream velocity and size of combustion charnber employed.

It is a chief object of the present invention, therefore, to provide an improved method and means for producing a ,cooled llame jet such as the nitrogen cooled flame jet above-noted.

Another object of the invention is to provide an improved method and means for supplying and burning fuel in a combustion chamber in which a controlled quantity of inert gas may be constantly introduced. It is a further object of the invention to devise a burner construction in which stable burning may be realized with relatively small burner sizes to provide a c-ooled flame jet.

These general objectives may, I find, be realized by controlling the introduction of fuel and inert gas into a combustion chamber in a predetermined manner and also by controlling the movement of products of combustion which are produced within the combustion chamber.

I have determined that I may control the introduction of fuel `advantageously by employing an elongated mixing space in which fuel, oxidant and inert gas are premixed at a temperature below that at which the fuel vaporizes and the mixture is then led into a combustion chamber. In this way I may utilize-a liquid fuel such as kerosene and form a dispersion of relatively coarse fuel droplets. I further provide for the premixing space communicating with the combustion chamber through a special liame stabilizing section of the burner. By means of this arrangement I am enabled to provide for the liquid fuel droplets, oxidant and inert gas being brought together to produce a combustible mixture in which the coarse droplets are homogeneously distributed and yet the liquid fuel droplets occur in varying sizes and may burn for varying intervals of time.

I have further discovered that this combustible mixture containing a relatively large amount of inert gas may be burned in the combustion chamber to provide products of combustion whose movement and burning characteristics can be controlled in a highly unusual and novel manner. This discovery is based on a recognition of the fact that the reactants have a velocity of llame propagation in the combustion chamber which is limited by the nitrogen component in a significant degree.

Specifically, I find that by burning relatively coarse fuel droplets interspersed with liner droplets, in an environment in which the velocity of llame propagation is limited by a nitrogen component, and by providing a combustion chamber having predetermined physical characteristics, including a flame stabilizing surface through which the droplets are injected, it becomes possible to induce a recirculation 'of products of combustion at the liame stabilizing surface. By thus inducing `a recirculation of the products of combustion at the lpoint where incoming droplets pass into the combustion chamber, I provide for a continuous igniting action on incoming reactants from the prernixing chamber. The recirculated portion of the products of combustion have been visually observed and are seen to become distributed in the shape of a torus located all the way around the fuel inlet in the llame stabilizing surface of the burner through which the mixture is injected. This igniting action makes possible operation of the llame jet using quantities of fuel on both the lean s-ide and the rich side to an extent not heretofore realized. It will be apparent therefore that for any given set of operating conditions an improved temperature control maybe realized and the region of stable burning may be extended and more latitude is possible in the size of the combustion chamber which may be employed.

The nature of the invention and its other lobjects and novel features will be more fully disclosed from the following description of the preferred embodiments of the invention shown in the accompanying drawings, in which:

FIGURE l is a cross sectional view of a burner construction'of the invention and having indicated diagrammatically therein premixing and toroidal flow of products of combustion;

FIGURE 2 is a cross sectional view taken on the line 2-.2 of FIGURE l;

FIGURE 2a is a cross sectional view of a burner construction illustrating a modified form of premixing charnber;

FIGURE 3 is a cross sectional view of a burner con struction illustrating `still another form of premixing chamber;

FIGURE 4 is a cross sectional View of a burner construction having coolant circulating means associated therewith;

FIGURE 5 is a graph illustrating stabilized burning curves; and

FIGURE 6 is still another cross sectional view of a burner construction in which improved circulating means for reactants are provided.

The burner structures shown in FIGURES l to 3 inclusive, are intended to illustrate a means of carrying out the method of the invention in one simple form. ln general, the invention method is initiated by introducing into an elongated premixing space under pressure a flow of liquid fuel such `as kerosene, oxygen and an inert gas such as nitrogen and causing the liquid fuel to become dispersed at temperatures :below that at which kerosene becomes a vapor. The liquid droplets occur in varying sizes and are substantially homogeneously, distributed throughout the oxygen and nitrogen. It `should be observed that kerosene at temperatures of 100 F. and higher may occur in a mist or droplet form and will become a kerosene vapor at approximately 440 F.

The resulting mixture is conducted from the premixing space through an aperture into a combustion chamber which has a llame stabilizing surface surrounding the aperture. The flow of fuel droplets and oxidant through the aperture takes place at a relatively high velocity V1 and the mixture decelerates to a velocity V2 in the relatively greater volume of the combustion chamber.

In the combustion chamber the mixture burns at superatmosphericpressure at a velocity of flame propagation which may be expressed as a velocity Vp. The limit velocity of this flame propagation is a function of the quantity of nitrogen in the combustion chamber, and by regulating input of fuel droplets in accordance with the ratio of oxygen to nitrogen supplied, and by controlling the flow of the total mixture, the velocity V1 is always maintained greater than the velocities V2 and Vp. Velocity V2 is always maintained less than Vp. With these requirements observed and a suitable combustion chamber size utilized the flame burns continuously without lbeing extinguished and a lowering of temperature dependent upon the quantity of nitrogen employed is constantly realized in the stream of products of combustion leaving the combustion chamber. It has been found that with combustion chamber diameters less than one inch, it is exceedingly difficult if not impossible to sustain high specific mass ilows. In the method of the invention good results have been obtained with burner diameters of from 2 to 4 inches in producing the nitrogen cooled flame jet.

Considering these steps in relation to FIGURE l of the drawings, numeral 2 denotes a tubular premixing chamber having a premixing space 4. Supported through one end of the member 2 is a fuel supply pipe 6 which is connected to some suitable fuel supply such as a kerosene tank and pumping apparatus not shown in the drawings. The extremity of pipe 6 is located in spaced relation to an inner surface 7 of the member 2 to provide for flow of liquid fuel under pressure into the premixing space.

Also extending into the premixing chamber 2 is an oxygen supply conduit 10 with control valve 10a and a nitrogen supply conduit 12 with control valve 12a. These members are also connected to respective oxygen and nitrogen tanks having `suitable valve means for supplying these gases under pressures wh-ich can be regulated in a conventional manner.

Attached to the premixing chamber 2 by threads 11 is a second tubular body 14 which has a combustion chamber 16 therein. The combustion chamber preferably consists of a cylindrical member and when threaded over the premixing body 2 is closed at one end by the portion 7 of the premixing chamber. Formed through the end wall 7 is an aperture A through which gases and fuel can pass at relatively high velocity V1 into the combustion chamber 16 and decelerated to a relatively lower velocity V2. At its opposite end the tubular body 14 is formed with la tapered portion 18 which terminates in a llame jet outlet 20.

An important feature `of the :structure described is the combination with a premixing chamber of an oriced body having a relatively large annular area 24 which extends around the fuel injection aperture A at a relatively abrupt angle thereto. This provides a flame stabilizing surface against which products of combustion may be lf recirculated when the burner is operated in accordance with the method of the invention.

In producing a flame jet with the structure described the burner may be started by furnishing lliquid fuel through the member 6. Gxygen is supplied through the member 10 and fuel and oxygen are forced through the aperture A being ignited in the combustion chamber by some suitable igniting means of conventional nature commonly employed in llame jet operation. Thereafter, a supp-ly of nitrogen may be introduced through the conduit 12 and the quantity of oxygen employed is substantially reduced.

In reducing the ratio of oxygen contained in the total mixture (which results from introducing oxygen with an inert gas `such as nitrogen, for example as these gases occur in atmospheric air) the region of stable burning earlier referred to in the specification changes sharply as is illustrated in FIGURE 5 and the precent fuel and stream velocity must be regulated to avoid llame extinction.

Subject to these limiting conditions oxygen under a pressure of, for example, 6 atmospheres and nitrogen in the form of atmospheric air under a pressure of p.s.i. gauge is expanded yat high velocity into the premixing chamber with'the `result that fuel discharged through the member 6 is subjected to a high degree of turbulence in the premixing chamber and becomes broken up into a dispersion of liquid droplets substantially lhomogeneously dispersed in the oxygen and nitrogen. This mixture after passing through the aperture A is decelerated to a velocity V2 which is less than V1 above-noted and the mixture burns in the combustion chamber to produce products of combustion. A portion of the reactants sointroduced burns almost instantly and the resulting prod- Iucts of combustion are emitted from outlet 20 to form a flame jet whose temperature is lowered by the nitrogen present.

In accordance vwith the invention another portion of the products of combustion including partially combusted coarse droplets are caused to recirculate in the manner illustrated by the curved arrows shown in FIGURE l in a toroidal path of travel. The recirculated portion of the llame is contained against the flame stabilizing surface 24 and guided radially inwardly to contact with incoming portions of the combustible mixture at aperture A so as to ignite continuously these portions.

It is found that this recirculation develops to a significant degree when an appreciable quantity of nitrogen is present in the combustion chamber and it is understood to be due to the fact that the nitrogen limits the velocity of flame propagation. It is pointed Iout that the recirculated portion contains reactants as well as products of combustion. The fuel contained rin this recirculated portion is comprised of both large and small droplets as Well as vapor. Thus there is, in some instances, -a short interval of time in which burning droplets may move into contact with incoming combustible mixture. The toroidal shape of the path of recirculating droplets has been visually observed and appears substantially in the form shown in FIGURE 2 as a torus T.

An essential feature of the burner construction, therefore, is ythe provision of a substantial annular surface area 24 surrounding the aperture A and toward which surface burn-ing droplets may be recirculated and guided inwardly towards the stream of incoming fuel mixture. In order for the recirculation of burning droplets to take place without the llame front actually flashing back into the premixing chamber, it is further essential that the velocity V1 of the incoming fuel mixture be greater than the velocity Vp of flame propagation, while at the same time providing for the velocity Vp of flame propagation bemg greater than the velocity V2 of the reactants.

These relationships I have found may be maintained by regulating the ratio of oxygen to nitrogen and by controlling the flow of total mixture into the combustion chamber. The controlling steps, it will be seen, are made possible because of the action of the nitrogen in limiting the velocity of llame propagation so that V1 can be maintained greater than V2 and flashing back prevented.

As an instance of a typical burner operation to provide a cooled llame jet in accordance with the invention, the following values for a fuel-air mixture are cited whereby the necessary regulation is accomplished.

Compressed air at 90 p.s.i. gauge from an air compressor is metered by a valve to supply a flow of 354 standard cubic feet per minute to the burner. Fuel oil is delivered at 100 p.s.i. gauge to an atomizing nozzle at a ilow of 1.92 pounds per minute. A nozzle exit diameter of 1,250 inches produces a chamber pressure of `32 p.s.i. gauge with a resulting llame jet of 3,650 ft./sec. at 2,530 F. under identical reactant flow conditions but with a 1.750 inch diameter nozzle, the chamber pressure is reduced to 8 p.s.i. gauge with a jet velocity of 2,300 ft./sec. at 3,300 F. In each case the burner chamber measured 2,450 inches inside diameter by 15.5 inches long. Oritice A was 0.750 inch diameter.

In FIGURE 2a, I have illustrated a modified form of burner construction in which'I provide a premi-Xing member 2' and combustion chamber member 14', together with oxygen and nitrogen supply conduits 10 and 12 and control valves 10b and 12b, and a liquid iluid injector 6. The construction and operation of this form of burner is similar to those of the burner of FIGURES 1 and 2 with the exception of the mixing chamber 4 which is constructed with a relatively `small elongated passageway 5 formed in a tubular body 9. The passageway 5 communicates with an aperture A as shown. For some types of fuel a superior premixing of fuel and oxidant may be realized and a better control of droplet size achieved with this structure.

In FIGURE 3, I have illustrated another form of burner in which even better control of droplet formation and distribution in an oxidant may be realized. In this arrangement a combustion chamber 14 of the type corresponding to

chamber

14 and 14 of FIGURES l and 2, has threaded to one end thereof a cylindrical housing 28. At the outer end of housing 28 is a second cylindrical body 30 of a smaller diameter than member 28. Supported in the cylindrical body 30 are air conduits 32 and 34 with control valves 32a and 34a which supply a flow of air under pressure to the chamber space 36 and then into the chamber space 38 which is of relatively larger diameter. Turbulent air contained in the space is forced through orifices as 40 in a foraminated fuel distributing sleeve 42 which is threaded into the orilced llame stabilizing shoulder 33. A fuel pipe 44 is connected to the opposite end of the sleeve 42 and provides for a llow of fuel through the sleeve in a relatively restricted passageway which is constantly s-ubjected to turbulent jets of air entering the opening 40. A very high degree of droplet dispersion in the oxidant gasses may be obtained with this arrangement and is particularly effective with combustion chamber of relatively small diameter in the 2 to to 4 diameter range.

I may desire to operate the method of the invention with the use of a coolant for cooling the combustion chamber walls where a precise control of combustion chamber temperature may be important. FIGURE 4 illustrates a premixing chamber with a burner capable of utilizing oxygen enrichment and having water cooling. Air entering through a pipe 51 is controlled by valves 52a and Sla in members 49 and 49a passes from the annular volume 52 through holes 54 contained in the fuel injector 53. F-uel is introduced through the spray nozzle 50 and is mixed thoroughly with the air flow bythe turbulent action set up in the premixing chamber 55. Oxygen, as required to increase the `total oxygen content in the air, is conducted through a tube 56 and a passageway 57 to enter the combustion chamber 59. The restricting nozzle section 60 may or may not be utilized, depending on whether high exit velocity is required. With this arrangement I combine special watercooling means as shown. Water enters a conduit 62 and passes along an annular `space 61 dened between the two concentrically arranged

tubes

67 and 68. From the annular space water is circulated out through an exit pipe 63. By controlling the flow of coolant through the passageway described, desirable control of the temperature of the combustion chamber may be realized.

Another form of burner in which air cooling is utilized in flame drilling a hole in a work body has been illustrated in FIGURE 6. In this form of burner a premixing chamber 310 is furnished with compressed air from a conduit 312 and valve 3l2a and this air is tur'bulently mixed with fuel injected lfrom a nozzle 314 and passed through a tubular member 316 into the combustion chamber 318 of a burner 320.

The burner 320 is provided with a llame stabilizing surface 322 and is also constructed with an outer cylindrical part 324 to dene an annular passageway 326. A flame jet is produced by nitrogen cooled products of combustion in the manner already described and is emitted through a restricted outlet 328. In addition, there is provided a second air supply system consisting of a separate air conduit 330 and valve 330e which supplies compressed air 4through passageways 332 into annular space 326. This secondary air passes along the annular space 326, cooling burner wall surface and then a part of the air is discharged through ports 340 and caused to circulate between the outer burner wall 324 and a sur- Iturn of spalled material out of the hole.l

While I have shown preferred embodiments of burners of :the invention, it should be 'understood that other forms of burners and modified devices of the invention may -be resorted to within the scope of the appended claims.

I claim:

1. A burner apparatus for burning liquid fuel, oxygen and a quantity of nitrogen at superatmospheric pressure and producing a nitrogen cooled llame jet, said apparatus including an enclosure body having an elongated mixing space for premixing oxygen, nitrogen and liquid @fuel droplets, means for introducing compressed oxygen, nitrogen and liquid fuel droplets to said mixing space in individually regulatable quantities, said enclosure body further having a relatively larger combustion chamber communicating with the premixing space, a llame stablizing wall constructed and arranged to separate the premixing space and the combustion chamber, said flame stabilizing wall being formed with a fuel injecting passageway for conducting a fuel mixture from the premixing space into the combustion chamber, said llame sta'blizing wall further presenting a flat annular flame stabilizing surface which is located around and which extends abruptly away `from said fuel injection passageway, said combustion chamber having a predetermined size which defines a volume limited by the quantity of nitrogen relative to the quantity of oxygen and fuel droplets combusted therein whereby a range of stable burning above and below stoichiometric range is realized and recirculation of flame portions may be induced against the said llame stabilizing surface in a toroidal path of llOw to promote continuous burning.

2. A burner construction according to claim 1 in which the premixing space and the combustion chamber section include means for separately introducing liquid fuel droplets dispersed in nitrogen and oxygen, a cylindrical casing located around said combustion chamber section in spaced relation thereto to dene an annular passageway and means for introducing a ow of coolant into and out of the said annular space.

3. A structure as defined in claim 1 in which the premixing space includes a confined mixing area into which said compressed nitrogen, oxygen, and liquid fuel droplets may be introduced and a tubular member extended through the confined space and being formed with openings for admitting oxygen and, nitrogen and liquid fuel droplets in a turbulent manner.

4. In a method of burning at superatmospheric pressure a mixture of oxygen, nitrogen and a liquid fuel in a confined space to produce a cooledflame jet, the steps which include introducing into a confined mixing space a flow of liquid fuel and a flow of oxygen and nitrogen in gaseous form while controlling the ratio of oxygen and nitrogen supplied and turbulently mixing the fiows to prod-ucc a dispersion of heterogeneously sized fuel droplets in the said oxygen and nitrogen, maintaining the mix-v ture of fuel droplets, oxygen and nitrogen while in the confined mixing space at a temperature below that at which the liquid fuel vaporizes, conducting said mixture from the confined mixing space through an aperture into a combustion chamber of predetermined size at a high input velocity, decelerating the mixture to a lowered combustion chamber velocity and simultaneously burning the mixture at superatmospheric pressure to provide nitrogen cooled products of combustion whose velocity of flame propagation is retarded by the said nitrogen component, inducing in the combustion chamber a recirculation of some of the products of combustion at the lowered combustion chamber velocity noted and continuously forming a toroidal flame mass concentrically located around the said aperture in a position to constantly ignite incoming portions of fresh fuel droplets and oxidant mixture and individually control-ling flow of fuel droplets, oxygen and nitrogen in relation to one another and as a function of the said predetermined combustion chamber size to maintain the said input velocity of the mixture entering the combustion chamber always greater than the said lowered combustion chamber velocity and to further maintain the lowered combustion velocity always less than the velocity of flame propagation whereby a range of reactants for stable burning is extended above and below stoichiometric range.

5. Method of burning at superatmospheric pressure in a confined space a mixture of oxygen, a liquid fuel and a desired quantity `of nitrogen to produce a high velocity flame jet in which the temperature of the ame is appreciably reduced by the nitrogen and the ratio of fuel and oxygen is maintained within definite limits which are neither too rich nor too lean to support combustion in the presence of the said quantity of nitrogen, said method including the steps of introducing into a confined mixing space under pressure a flow of oxygen and nitrogen in gaseous form and a flow of liquid fuel held at a temperature below that at which the fuel vaporizes to produce a premix in which the liquid fuel is dispersed into heterogeneously sized fuel droplets in said oxygen and nitrogen, conducting the said premixed oxygen, nitrogen and fuel droplets from the mixing space at a relatively high input velocity through a flame stabilizing region into a combustion chamber of a size which is predetermined and in which the mixture decelerates to a lowered combustion chamber velocity, simultaneously burning the mixture in the combustion chamber to provide products of combustion which extend from end to end of the combustion chamber and whose velocitiy of flame propagation is limited by the said nitrogen component, inducing a recirculation of the products of combustion in the chamber to continuously form a toroidal flame mass concentrically located around the said aperture in a position to constantly ignite incoming portions of the fuel droplets and oxidant mixture and continuously regulating the quantities of fuel droplets, oxygen and nitrogen supplied to values which are related to one another and which are also a function of the said predetermined combustion chamber size thereby to maintain the said high input velocity of the premix always greater than the said lowered combustion chamber velocity and to further maintain the lowered combustion chamber velocity always less than the velocity of fiame propagation whereby a range of reactants for stable burning is extended above and below stoichiometric range.

6. A method according to claim 5 in which the combustion chamber is of a size not less than one inch in diameter.

7. A method according to claim 5 in which the size of thecombustion chamber occurs in a range of cornbustion chamber diameters of from one inch up to approximately four inches.

References Cited by the Examiner UNITED STATES PATENTS 1,325,116 12/1919 Sebille 15S- 117.5 2,367,119 l/l945 Hess 15S-27.4 2,628,817 2/1953 Wyland 15S-27.4 X 2,725,929 12/1955 Massier` 175-14 X 2,861,900 11/1958 Smith et al. 15S-27.4 2,882,017 4/1959 Napiorski 15S-27.4 X 2,896,914 7/1959 Ryan 175--14 3,030,733 4/1962 Johnson 158-28 X 3,092,166 6/1963 Shepherd 158-117.5 X

JAMES W. WESTHAVER, Primary Examiner.

MEYER PERLIN, FREDERICK L. MATTESON, IR.,

Examiners.

V. M. PERUZZI, M. L. BATES, Assistant Examiners.

Claims

1. A BURNER APPARATUS FOR BURNING LIQUID FUEL, OXYGEN AND A QUANTITY OF NITROGEN AT SUPERATMOSPHERIC PRESSURE AND PRODUCING A NITROGEN COOLED FLAME JET, SAID APPARATUS INCLUDING AN ENCLOSURE BODY HAVING AN ELONGATED MIXING SPACE FOR PREMIXING OXYGEN, NITROGEN AND LIQUID FUEL DROPLETS, MEANS FOR INTRODUCING COMPRESSED OXYGEN, NITROGEN AND LIQUID FUEL DROPLETS TO SAID MIXING SPACE IN INDIVIDUALLY REGULATABLE QUANTITIES, SAID ENCLOSURE BODY FURTHER HAVING A RELATIVELY LARGER COMBUSTION CHAMBER COMMUNICATING WITH THE PREMIXING SPACE, A FLAME STABILIZING WALL CONSTRUCTED AND ARRANGED TO SEPARATE THE PREMIXING SPACE AND THE COMBUSTION CHAMBER, SAID FLAME STABILIZING WALL BEING FORMED WITH A FUEL INJECTING PASSAGEWAY FOR CONDUCTING A FUEL MIXTURE FROM THE PREMIXING SPACE INTO THE COMBUSTION CHAMBER, SAID FLAME STABILIZING WALL FURTHER PRESENTING A FLAT ANNULAR FLAME STABILIZING SURFACE WHICH IS LOCATED AROUND AND WHICH EXTENDS ABRUPTLY AWAY FROM SAID FUEL INJECTION PASSAGEWAY, SAID COMBUSTION CHAMBER HAVING A PREDETERMINED SIZE WHICH DEFINES A VOLUME LIMITED BY THE QUANTITY OF NITROGEN RELATIVE TO THE QUANTITY OF OXYGEN AND FUEL DROPLETS COMBUSTED THEREIN WHEREBY A RANGE OF STABLE BURNING ABOVE AND BELOW STOICHIOMETRIC RANGE IS REALIZED AND RECIRCULATION OF FLAME PORTIONS MAY BE INDUCED AGAINST THE SAID FLAME STABILIZING SURFACE IN A TOROIDAL PATH OF FLOW TO PROMOTE CONTINUOUS BURNING.