US2541170A - Air intake arrangement for air jacketed combustion chambers - Google Patents

Description

Feb. 13, 1951 M. A. MAYERS ET AL AIR INTAKE ARRANGEMENT FOR AIR JACKETED COMBUSTI ON CHAMBERS Sheets-Sheet l Filed July 8, 1946 INVENTORS. Martin fl. Mayers Hans Th olzwarth Patented Feb. 13, 1951 AIR INTAKE ARRANGEMENT FOR AIR JACKETED COMBUSTION CHAMBERS Martin A. Mayers, Maplewood, and Hans T. Holzwarth, Westfield, N. J., assignors to The M. W. Kellogg Company, New York, N. Y., a

corporation of Delaware Application July 8, 1946, Serial No. 681,954

18 Claims. 1

The present invention relates to combustion units and methods of the general character in which fuel is injected into a chamber or furnace and burned in the presence of air, and although it has a wide range of utility, it is particularly useful, for example, in connection with gas turbine plants.

One object of the present invention is to provide a new and improved combustion unit of the general type referred to, and a new and improved method of combustion.

Another object of the present invention is to provide a new and improved combustion unit of the general type referred to, in which the combustion air inlet and the exhaust outlet are designed and located to permit the compact arrangement of said combustion unit in line with other units of a plant, while afiording high combustion rates and low pressure drops. A combustion unit of this improved type is particularly useful in connection with certain proposed aircraft practices in which the principal elements of a gas turbine plant, as for example, the compressor, combustion unit and gas turbine are arranged in line.

A further object of the present invention is to provide a new and improved combustion unit, which affords high combustion rates and low pres sure drops, and which at the same time, is designed to divert part of the inlet air stream for effective cooling of the unit walls with a minimum of adverse effect on the eflicient thorough mixing of the fuel and air in the interior of the combustion chamber.

A further object of the present invention is to provide a new and improved combustion unit,

which is designed to assure thorough and rapid mixing of the air and fuel in accordance with substantially predetermined flow patterns, and which therefore lends itself to stabilized operation' and to effective easy and close regulation.

In carrying out certain features of the present invention, fuel is continuously injected into the front end of a combustion chamber defined by an inner wall" desirably in the form of a shell disposed within a housing. The wall of the housing is spaced from the wall of the inner shell to form therewith an annular space for the air cooling of the housing wall. A combustion air duct has its inlet located near the front of the unit with its line of flow substantially parallel to the longitudinal axis of the unit, and its outlet connecting into the housing wall. The inner shell has an air inlet opening in its peripheral wall opposite the outlet of the air duct, so that the major part of the air from said air duct is delivered into the interior of the inner shell for secondary combustion in its burning out zone. Part of the air from the air duct is diverted through vaned openings in the inner shell for primary combustion in the ignition zone, part of it is diverted around said shell and towards the front end of the combustion unit for cooling the ignition zone section of the inner shell wall, the housing wall and'the fuel injection nozzle, and part of it is diverted towards the rear or outlet end of the unit and into an annular cooling space surrounding the inner shell to air-cool the housing wall.

The air duct is designed so that although it extends longitudinally in the same general direction as the combustion chamber, it delivers an air stream at proper pressure into the interior of the housing substantially at right angles to the longitudinal axis of the combustion chamber. The part of the air stream which projects into the interior of the combustion chamber through its peripheral inlet opening is directed by the peripheral wall of said combustion chamber into two similar adjoining vortex streams having opposite senses of rotation, and having their axes running substantially parallel to each other along the chamber.

The primary air diverted towards the ignition zone is thoroughly mixed therein with the fuel injected into said zone, and forms with said fuel an inflammable mixture rich with fuel. This mixture is ignited and the resulting products at ignition temperature projected into the secondary combustion chamber. The injected fuel elements which are not burnt and the products of combustion from said zone tend to be drawn into and along the respective axes of the two reverse air vortices created in the combustion chamber, and form an intimate mixture with the vortically circulated air, thereby effecting rapid intense combustion of the fuel-air mixture progressively along the combustion chamber.

Unless the conditions are right, the two reverse air vortices will not maintain their substantially predetermined flow characteristics and will become unstable. Unstable operation is generally accompanied by long flames and ineffective combustion. Also. under unstable operating flow conditions described, oil drops may be thrown against the inside of the inner shell with an accompanying tendency to produce coke and high wall temperatures. By maintaining the two air vortices of substantially uniform diameter and shape throughout their lengths, the length of combustion flame will be maintained at a minimum, and a more stabilized flame condition is attained, permitting thereby easy close control of the unit.

It has been found in accordance with the present invention, that for any given form and size of inlet opening in the inner shell or combustion chamber, only a limited portion of the total air supplied may be permitted to flow into the cooling annular flow space around said combustion chamber without adversely affecting the stability of the double vortex flow in said chamber. If a greater amount than this proportional limit is permitted to flow into this annular space, the double vortex system becomes unstable.

It has furthermore been found in accordance with the present invention, that the shape of the air inlet opening in the inner shell or combustion chamber has an influence on the stability of the double vortex flow pattern in said chamber. It has been found that the air inlet opening most desirable from the standpoint of bivortical flow stability in the combustion chamber should be, or approach, a rectangle, with two sides extending substantially parallel to the longitudinal axis of the chamber, and should have its measure lengthwise of the chamber no greater than its transverse chordal dimension. A transverse opening or slit having its transverse chordal dimension at right angles to the longitudinal axis of the combustion chamber greater than its longitudinal measure lengthwise of the combustion chamber, and especially a transverse opening or slit with a chordal width not exceeding .6 of the maximum inside diameter of the inner shell parallel to said chordal width, has been found to be the most desirable from the standpoint of maintaining bivortical flow stability. A square air inlet opening in the inner shell, and especially one having a maximum transverse chordal width equal to a .6 of

the maximum inside diameter of the inner shell parallel to said width, has also been found desirable from the standpoint of maintaining stable bivortical flow conditions in the combustion chamber, but is not as effective as the transverse slit or opening above described within a certain range of ratios between the flow through the annular cooling space around the inner shell and the flow through the inlet air opening in said inner shell. The air inlet opening need not be an exact rectangle or an exact square but mayapproach these shapes; thus it may be polygonal, elliptical or circular. However, whatever shape is chosen it should be designed as closely as possible to the criteria set forth for the rectangular and square inlet openings if the same order of result is to be obtained.

It has also been found, in accordance with the present invention, that by flattening the side of the inner shell opposite the air inlet opening, and allowing the opposite side walls between said opening and the flattened inner shell section to bulge outwardly, so that the distance between these bulging walls is greater than the distance between the flattened inner shell section and the apertured section of the inner shell, the formation of the double vortex system is facilitated, and the tendency towards the formation of or the mergence of the two vortices into a single vortex is effectively minimized.

It has been found that a combustion unit constructed in accordance with the present invention has an extremely high energy release rate. For example, while it has been diflicult at atmospheric pressure to obtain with combustion units hitherto known an energy release rate of more a unit of the present invention, an energy release rate of 4,000,000 B. t. u. per cubic feet per hour at atmospheric pressure, and 20,000,000 B. t. u. per cubic feet per hour at p. s. i. has been obtained. Furthermore, these high energy release rates havebeen eifectively attained by means of the present invention without undue complications in the structure of the unit, and with a minimum of destructive action thereon.

Various other objects, features and advantages of the invention will be apparent from the following particular description, and from an inspection of the accompanying drawings, in which:

Fig. l is an axial section somewhat diagrammatic of a combustion unit embodying the present invention;

Fig. 2 is a transverse section of the combustion unit taken approximately along the line 2--2 of Fig. 1, and shown with parts broken away to reveal the structure behind these parts;

Fig. 3 is a transverse section of the inner shell or combustion chamber taken along the line 3-3 of Fig. l; and

Fig. 4 is a graph which shows flow stability transitional curves corresponding to an air inlet opening of transverse rectangular shape in the inner shell and to an inlet opening of square shape respectively, and indicating certain limiting conditions for maintaining bivortical flow stability in said inner shell.

Referring to the drawings, the combustion unit is shown of the type which is particularly adaptable for use in connection with gas turbine plants. However, it must be understood that as far as certain aspects of the invention are concerned, the unit of the present invention may be adapted for other combustion uses where a high energy release rate is required.

The combustion unit of the present invention comprises a furnace or firebox wall I, desirably in the form of a shell which is of metal resistant to heat, and which defines a combustion chamber H. Shell ID has an intermediate section' lZ defining the burning out or secondary combustion zone l3 of the combustion chamber II, and is closed at its front end by a head or nose-piece I4 defining therein the ignition zone [5. The rear or exhaust section I6 of the inner shell [0 is streamlined and desirably of progressively reduced diameter downstream to afford exhaust gases of the required pressure and velocity at the outlet end of the unit. At its exhaust end, the shell I 0 may be connected to the inlet I! of a gas turbine or to any other conduit of the system or plant.

The inner shell I!) is enclosed in an outer protective metal shell l8 which is concentric with and peripherally spaced from the inner shell ID by an annular space l9, serving as a flow passage for the cooling air, as will be described. The head end 20 of the outer shell 18 is desirably generally hemispherical. The rear section 2| of outer shell l8 progressively decreases in diameter downstream until its neck snugly embraces the throat of the inner shell l0, and to afiord ease of assembly, desirably constitutes a separate unit attached to the intermediate outer shell section i8a by a flange bolt connection 22. The inner shell I0 is supportably centered with respect to the outer shell l8 by this snug engagement between the two shells l0 and I8, and is further supported by spacers 49 therebetween, to be described.

l' or injecting fuel into the ignition zone II of the combustion chamber II, the head end 24 of the housing shell II has threaded or otherwise mounted thereon a fitting 23 connected to the outlet of a fuel injection pump (not shown), and joined inside of said housing shell to a spray nozzle 24 projecting into the interior of said combustion chamber ll through an opening 25 in the nose end l4 of the inner shell ll. Spray nozzle 24 is shown of the mechanical type which is adapted to project and whirl liquid fuel under pressure into the interior of the chamber H in the form of a hollow cone, and to atomize said fuel in said chamber.

For initiating the flame near the ignition zone I! of the combustion chamber H, there is fitted into the peripheral wall of the housing shell It! a spark plug 26 projecting through an opening 21 in the top of the inner shell I4. and extending with its sparking end at a region near the outer margin of the conical fuel stream projected from the spray nozzle 24. The spark plug 28 is desirably operated only sufliciently long to initiate --ignition of the inflammable mixture in the ignition zone. Thereafter, primary combustion will continue without the aid of the spark plug.

The air for combustion is projected into the interior of the housing shell It by means of an air duct 30, shown in the general form of an elbow. Air duct 30 has its inlet end 3| disposed in front of the housing shell it with its center line of flow extending substantially parallel to the longitudinal axis or center line of the combustion chamber II. A flange 32 is shown connected to the inlet end of the duct 30 for attachment to the outlet of an air compressor. The duct 30, which is streamlined in the general direction of flow, and which is desirably provided at its bend with guiding baiiles 29 to afford smooth flow therein, extends substantially for at least a portion thereof along the length of the combustion unit, and has its discharge end 33 connecting into a substantially circular opening 84 in the peripheral wall of the outer shell i8. Air duct 30 is desirably welded to the outer shell I 8 to afford a light streamline construction especially adapted for use in connection with aircraft, and is aerodynamically designed so that the air is delivered thereby into the interior of the housing shell i8 in a direction radially of the combustion chamber II, or at right angles to the longitudinal axis of said chamber.

The air duct 30 is shown of the type especially useful in connection with modern axial flow compressors, which discharge compressed air at relatively large velocity head. Duct 30 is therefore made with a progressively increasing crosssection in the direction of flow in the form of a diffuser to recover a large part of the velocity head and convert it into pressure head suitable for the conditions existing in the combustion chamber. If the velocity head of the air at the inlet of the combustion chamber II is too great, then the pressure drop through said chamber may also be comparatively large. Such large pressure drops are undesirable, especially because of their adverse effect on the overall efficiency of the system of which the combustion unit is a part. The air admitted into the combustion chamber ll must also have the necessary velocity to produce the high combustion rate required, since there is a relationship between the combustion rate that can be obtained and the velocity of the jet entering said combustion chamber through the opening 45 to be described.

The shape of the air duct it is shown of a specific design for application to a gas turbine layout proposed in connection, for example, with an aircraft installation. In such a power plant, all of the principal elements of the plant, as for example, the compressor, the combustion unit and the gas turbine, would be arranged in line. In the particular layout shown in the drawings. the compressor would be disposed near the front of the combustion unit with its discharge end connected to the duct inlet 3|, while the gas turbine would be disposed at the rear or exhaust end of the combustion unit with its inlet connected to the outlet l8 of the combustion chamber. There would be a number of these combustion units circularly arranged around the axis of the turbine wheel.

For admitting combustion air from the duct 30 into the combustion chamber H, the inner combustion chamber shell Hi has an air inlet window or opening 45 opposite to and centrally disposed with respect to the inlet air opening '34 in the wall of the housing shell l8, and having its length and width smaller than the diameter of said air opening 34. The major part of the air from the duct 30 admitted into the interior of the housing shell l8 through its inlet 34 is directed substantially radially into the combustion chamber II, and as it hits the upper wall of said chamber, it is deflected thereby to form to similar adjoining vortices having opposite senses of rotation, and completely filling the combustion chamber ll almost to the exhaust end of the intermediate shell section I21. These reverse vortices advance continuously towards the discharge end of the combustion chamber II as the combustion process progresses, while substantially maintaining in the intermediate section I! of said chamber their separate predetermined flow characteristics and their outer dimensions and form against transverse reduction or taper.

It has been found in accordance with the present invention, that in order to create the double vortex pattern in the combustion chamber II and to maintain this pattern substan-* tially stable, the air inlet opening 45 should preferably be rectangular with its sides extending substantially parallel to the longitudinal axis of the chamber, and should have its measure lengthwise of said chamber no greater than its transverse chordal dimension. It has also been determined that the transverse chordal width of the opening 45 at right angles to the longitudinal axis of the combustion chamber desirably should not exceed .6 of the maximum inside diameter of the inner shell parallel to said chordal width, in order to maintain bivortical flow stability. The air inlet opening 45w should therefore be desirably in the form of a transverse slit or aperture having its transverse chordal measure at right angles to the longitudinal axis of the combustion chamber ll greater than its longitudinal measure lengthwise of said combustion chamber. A square opening 45 has a so been found desirable from the standpoint of bivortical flow stability. Air in et opening 45 may also approach a rectangle or square in shape and thus may be polygonal. elliptical or circular. However, in order to obtain the same order of results, such po y onal, elliptical or circular air inlet should be design d as closely as possible to the criteria set forth for the rectangular and the square inlet openings It has also been determined in accordance 7 with the present invention, that by elongating the cross section of the inner shell III in a direction extending from opposite sides of the air inlet opening 45, the formation of the double vortex system is facilitated, and the tendency towards the formation or mergence of the two vortices into a single vortex is effectively minimized. More specifically, it has been found desirable to flatten the side of the inner shell H opposite the air inlet opening 45 and allow the opposite side walls between said opening and the flattened inner shell section to bulge outwardly as shown in Fig. 3. The inner shell .may be originally in cylindrical form, and may I air towards the front end of the combustion chamber H. The primary combustion air projected towards the front end of the combustion chamber 1! through the openings 48 assumes the form of a vortex ring extending around the infected fuel cone. Sufficient amount of the fuel from this cone is drawn and diffused towards the annular axis of the air vortex ring to form at said axis an inflammable mixture which is ignited by the spark plug 26. As the inflammable mixture is created along this vortex ring axis, it is ignited, so that a pilot light is continuously afforded along said axis.

The nozzle 24, as already indicated, directs a metered quantity of fuel into a fixed pattern of flow in a protected space whose volume is adusted according to the maximum capacity of fuel to be consumed. The recirculating flow pattern which is maintained in the ignition space returns heat and so-called active centers from the stable flame into the airborne cloud of fluid drops in the chamber ll, thus maintaining continuous ignition.

As a result of the ensuing rapid intimate mixing of the air and fuel in the head end of the combustion chamber ii, an intense ignition zone I5 is created from which the flames are propagated along said chamber. The mixture propelled from the ignition zone l5 has an excess of fuel, and tends to be drawn towards and a ong the relatively low pressure centers of the two opposed vortices generated in the interior of the combustion chamber by the air admitted through its opening 45. As the axial columns of fuel rich mixture advance along the combustion chamber ll, they are mixed rapidly and intimately with the encompassing cyclonic air, thereby propagating flames so intense as to burn themselves out almost completely before reaching the discharge end of the intermediate section 12 of said chamber. Substantially complete combustion in the chamber II is thereby assured.

As lon as the two reverse vortices in the comhustion chamber ll substantially maintain their separate redetermined flow characteristics, no undesirable centrifugal separation of the fuel particles takes place.

A small portion of the air stream from the out let of the duct 30 admitted into the housing I8 is diverted around and along the front or nose end 8 v l4 of the inner shell I II, to cool this sectlonof the shell without lowering the temperature of the gases in the chamber below the extinction temperature. Some of this diverted air cools the spray nozzle 24.

Part of the air stream directed into the interior of the housing l8 from the duct 30 is diverted around the inner shell in and towards the discharge end of thecombustion unit to prevent destructive overheating of the walls of said housing and the inner shell in. For that purpose, there is provided an intermediate shell 50 disposed between the inner shell I!) and the outer housing shell I8, and acting as a shield for reducing heat radiation from the inner shell III to the outer housing shell l8. Intermediate shell 50 also serves to increase the surface by which transfer of heat is effected to the cooling air passing over said intermediate shell, and is spaced from the two shells l0 and I8 to form therewith two air cooling flow passages 5| open and communicating at their front inletends 52 with the jacket space l9. For supporting and spacing intermediate shell 50 from the shells l0 and I8, suitable spacers 49 are provided desirably welded in position, in a manner which will afford ease of manufacture, ease of assembly and ease of diassembly.

For removably affixing the intermediate shell 50 in position between the two shells Ill and IS. the outlet end of said intermediate shell has a radially outwardly extending flange 53 clamped between the bolt flanges 54 and 55 of the outer shell sections l8a and 2| respectively, constituting part of theflange bolt connection 22. Shell flange 53 has a series of holes 56 to permit the cooling air from passage 5| to pass therethrough.

The cooling air streams from the annular flow flow passages 5| merge beyond the flange bolt connection 22 in the single flow passage 51 defined between the discharge sections l6 and 2| of the inner and outer shells I0 and 18 respectively; the cooling air is desirably joined to the exit gas stream from the combustion chamber 1 i by passing through a series of holes 58 in the throat or neck of said discharge section [6.

It has been found that in order to obtain and maintain the substantially predetermined bivortical flow described, it is necessary to maintain that proportion of the inlet air diverted rearwardly into the annular cooling passages 5| below a certain maximum. Hence, for any given form and size of inlet opening 45 only a limited portion of the total air supplied may be permitted to flow into the cooling annular spaces 5| with out adversely affecting the stability of the double vortex flow in said shell. If a greater amount is permitted to flow, instead of producing the double flame pattern characteristic of double vortex flow, a single vortex may be ultimately formed whose rotation changes periodically from one sense to the other. This change may 00.- cur with relatively high frequency.

Fig. 4 is a graph showing two flow stability transitional curves A and B, derived from an investigation of flow patterns in an isothermal system. Curve A corresponds to an air inlet transverse opening 45 whose transverse dimension in a direction at right angles to the longitudinal axis of the combustion chamber II is no more than .6 of the maximum inside diameter of the inner shell Ill before flattening, but is greater than its longitudinal dimension lengthwise of said chamber.

Curve 13 corresponds to a square air inlet trans verse opening 45 whose width is no more than .6 of the maximum inside diameter of the inner shell I before flattening. The ordinate of the graph represents the ratio of the flow through the annular spaces to the flow through the inner shell opening 45, while the abscissa represents the cross-sectional area of said opening. Tests were carried out, and the curves A and B were plotted to indicate the demarcation between the zone of stable double vortex flow and the zone of the unstable flow. To the left and below each curve A or B, stable double vortex formation occurs. To the right and above each curve, flow instability occurs which-breaks down the double vortex system.

It is apparent from the curves of Fig. 4, that for an air inlet opening of a definite size and shape of the general character described, there is a maximum ratio between the flow through the annular spaces 5| around the inner shell l0 and the flow through the air inlet opening, beyond which ratio unstable fiow conditions are encountered. As long as this ratio is maintained below this value, stable bivortical flow conditions are created and maintained. For example, for an inlet opening area representing about 13% of the cross-sectional area of the inner shell, the unit must be so proportioned that not more than .7 as much air flows through the annular spaces 5| as enters the inner shell in a combustion chamber ll having a square inner shell air inlet opening.

By plotting conditions as indicated in Fig. 4, in an actual combustion set-up, the limiting ratio between the cross-sectional areas of the annular cooling spaces 5| to the cross-sectional area of the inner shell opening 45 to assure stable bivortical flow conditions in the combustion chamber I I, may be accurately determined.

In the operation of the combustion unit of the present invention, the substantially predetermined flow pattern is maintained at least along the intermediate section l2 of the combustion chamber II. The combustion of the gases is substantially completed by the time these gases reach the discharge section l6 of the combustion chamber, so that the fiame'desirably does not extend beyond the inlet end of said section IS.

The combustion unit of the present invention can be made to effectively afford outlet temperatures ranging from 500 F. to 1800 F., required, as for example, for certain efficient gas turbine operations, although by proper modification, within the teachings of this invention and by proper choice of materials out of which it is constructed, it can also be made to operate efficiently at temperaturesranging as low as 200 F. and as high as 3000 F. Also, the operation of the combustion unit of the present invention is stabilized because of the substantially predetermined flow and mixing conditions and patterns continuously maintained in the unit. This renders the unit susceptible to easy flexible control, allowing quick response to varying demands and close regulation.

The combustion unit of the present invention permits stable operation over a wide range of fuel to air ratio for varying loads without the necessity of adjusting the air flow. At the same time, the combustion unit avoids the deposition of soot and coke in the ignition zone, and is capable of operation with large quantities of fuel and air over a wide range of load without smoking.

Furthermore, the unit of the present invention produces high rates of combustion, while requiring only a very small drop of pressure: of the air passing through the chamber. The unit, therefore, does not become a drag on the over-all elliciency of the plant system.

The unit of the present invention is especially suitable for use in gas turbine aggregates, It may also be used, however, for any application in which air is to be heated by burning finely divided fuel, such as liquid fuel in it, and it combines the advantages of compactness, cleanliness of operation and small power requirements.

As far as certain aspects of the invention are concerned, the unit of the present invention may also be used without combustion, in cases where it is desired to concentrate a flowable medium along a predetermined zone of another flowable medium of lower density.

As many changes can be made in the above method and apparatus, and many apparently widely different embodiments of this invention can be made without departing from the scope of the claims, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An apparatus for operating on finely divided flowable material, comprising a wall defining an open chamber with an exhaust opening at one end, a housing wall enclosing said chamber wall and peripherally spaced therefrom, and means for introducing a finely divided flowable material including a gaseous medium into said chamber and inducing its flow unobstructed lengthwise of said chamber and towards said exhaust opening in the form of two adjoining vortices having" opposite senses of rotation, said means comprising an inlet opening in the peripheral section of said housing wall, an inlet opening in the peripheral intermediate body section of said chamber wall disposed between and spaced from the ends of said chamber wall and in approximate registry with said first mentioned inlet opening, the space between the peripheral sections of said walls comprising a substantially annular passage serving to connect said inlets, and means for radially introducing said gaseous medium into the housing wall through its inlet opening, said chamber wall inlet being of such size and shape I as to cause a part of said gaseous medium to be admitted into said chamber and to be directed by the wall thereof into the form of two adjoining oppositely rotating vortices advancing unobstructed lengthwise of said chamber towards its exhaust opening.

2. An apparatus as described in claim 1, in which theinlet opening of said chamber wall has its length along said chamber no greater than its width transverse to the length of said chamber.

3. An apparatus as described in claim 1, in which the inlet opening of said chamber wall approximates a rectangular form which has some of its sides substantially parallel to the longitudinal axis of the chamber, and has its measure along said chamber substantially less than its measure transverse to the length of said chamber.

4. An apparatus as described in claim 1, in which the inlet opening of said chamber wall is substantially square with two sides substantially parallel to the longitudinal axis of the chamber.

5. An apparatus as described in claim 1, in which the inlet opening of said chamber is substantially rectangular with two sides substantial- 1! 1y parallel to the longitudinal axis of the chamber, has its length along said chamber no greater than its chordal width transverse to the length of said chamber, and has its chordal transverse width no greater than .6 of the maximum inside width of said chamber parallel to the direction of said chordal transverse width.

6. An apparatus as described in claim 1, comprising a supply duct connected to the inlet opening of said housing wall and extending for a substantial portion of its length in the same general longitudinal direction as said housing wall.

7. In a combustion unit, the combination comprising a wall forming an open combustion chamber and defining in said chamber an ignition zone and a burning-out zone for flame propagation lengthwise of said chamber, a housing wall enclosing said chamber Wall and peripherally spaced therefrom, means for introducing a stream of finely divided fuel into said ignition zone, means for directing primary combustion air into said ignition zone to form an inflammable mixture in said zone, and means for creating two combustion air streams in said chamber in the form of two adjoining oppositely rotating vortices and advancing them unobstructed towards the exhaust end of said chamber, said last-mentioned means comprising an air inlet opening in the peripheral section of said housing wall disposed between and spaced from its ends, and an air inlet opening in the intermediate peripheral body section of said chamber wall disposed between and spaced from the ends of said chamber and in approximate registry with said first mentioned inlet opening, the space between the peripheral sections of said walls comprising a substantially annular passage serving to connect said air inlets whereby a part of the air stream entering said housing is admitted radially into said chamber through its inlet opening and is directed by the chamber wall into the form of two adjoining oppositely rotating vortices.

8. The combination as described in claim 7, in which the inlet opening of said chamber wall has its length along said chamber no greater than its width transverse to the length of said chamber. I

9. The combination as described in claim 7, in which the inlet opening of said chamber wall approximates the rectangular form with some of its sides substantially parallel to the longitudinal axis of the chamber, and has its measure along said chamber substantially less than its measure transverse to the length of said chamber.

10. The combination as described in claim '7, in which the inlet opening of said chamber wall is substantially square with two sides substantially parallel to the longitudinal axis of the chamber.

11. The combination as described in claim 7, in which the inlet opening of said chamber is substantially rectangular with two sides substantially parallel to the longitudinal axis of the chamber, has its length along said chamber no greater than its chordal width transverse to the length of said chamber, and has its chordal transverse width no greater than .6 of the maximum inside width of said chamber parallel to the direction of said chordal transverse width. 1

12. The combination as described in claim '7, in which the transverse region of said chamber wall containing its inlet opening is elongated at thesides of said latter opening, whereby the maximum distance between the sides of said chamber wall is greater than the maximum distance between said latter opening and the section of said chamber wall diametrically opposite to said latter opening.

13. The combination as described in claim '7, in which the transverse region of said chamber wall containing its inlet opening is shaped from cylindrical form with the section of said chamber wall diametrically opposite said latter opening flattened, and the sections of said chamber wall on opposite sides of said flattened section bulged outwardly.

14. The combination as described in claim 7, in which the transverse region of said chamber wall containing its inlet opening is shaped from cylindrical form with the section of said chamber wall diametrically opposite said latter opening flattened and the sections of said chamber wall on opposite sides of said flattened section bulged outwardly, and in which the inlet opening of said chamber wall approximates the rectangular form with some of its sides substantially parallel to the longitudinal axis of the chamber, has its length along said chamber no greater than its chordal width transverse to the length of said chamber, and has its chordal transverse width no greater than .6 of the maximum inside width of said chamber parallel to the direction of said chordal transverse width.

15. In a combustion unit, the combination comprising a wall forming an open combustion chamber and defining in said chamber an ignition zone and a burning-out zone for flame propagation lengthwise of said chamber, a housing wall enclosing said chamber wall and peripherally spaced therefrom, means for introducing a stream of finely divided fuel into said ignition zone, means for directing primary combustion air into said ignition zone to form an inflammable mixture in said zone, and means for creating two combustion air streams in said chamber in the form of two adjoining oppositely rotating vortices and advancing them unobstructed towards the exhaust end of said chamber, said last-mentioned means comprising an air inlet opening in the peripheral section of said housing wall disposed between and spaced from its ends, and an air inlet opening in the intermediate peripheral body section of said chamber wall disposed between and spaced from the ends of said chamber and in approximate registry with and communicating with said inlet housing wall opening through the spacing between the peripheral sections of said walls, whereby the air stream admitted radially into said chamber through its inlet opening is directed by the chamber wall into the form of two adjoining oppositely rotating vortices, the portion of the housing wall between its air inlet opening and the exhaust end of said combustion chamber forming with said chamber wall an annular passage communicating at one end with said latter opening, whereby part of the air admitted through said latter opening is diverted to said passage for air cooling the housing wall, said annular passage being of such dimensions at its inlet end as not to disturb the predetermined double vortex-forming characteristics of the incoming air, whereby the predetermined bivortical flow pattern of the air in said combustion chamber is continuously stably maintained dur-'- ing combustion operations.

16. In a combustion unit, the combination comprising a wall forming an open combustion chamber and defining in said chamber an ignition zone and a burning-out zone for flame propagation lengthwise of said chamber, a housing wall enclosing said chamber wall and peripherally spaced therefrom, means for introducing a stream of finely divided fuel into said ignition zone, means for directing primary combustion air into said ignition zone to form an inflammable mixture in said zone, and means for creating two combustion air streams in said chamber in the form of two adjoining oppositely rotating vortices and advancing them unobstructed towards the exhaust end of said'chamber, said lastmentioned means comprising an air inlet opening in the peripheral section of said housing wall disposed between and spaced from its ends, and an air inlet opening in the intermediate peripheral body section of said chamber wall disposed between and spaced from the ends of said chamber and in approximate registry with and communicating with said inlet housing wall opening through the spacing between the peripheral sections of said walls, where'-y the air stream admitted radially into said chamber through its inlet opening is directed by the chamber wall into the iorm of two adjoining oppositely rotating vortices, the portion of the housing wall between is air inlet opening and the exhaust end of said combustion chamber forming with said chamber wall an annular passage communicating at one end with said inlet opening, whereby part of the air admitted through said inlet opening is diverted to said passage for air cooling the housing wall, the ratio of the cross-sectional area of the annular passage to the cross-sectional area of the air inlet opening in said chamber wall being within the doublevortex stability zone of operation of the combustion unit, as determined by a graphic representation of the limiting bivortical flow stability characteristics of the unit. 1

17. In a combustion unit, the combination comprisin a combustion chamber, at least part of which is formed by a chamber wall defining an ignition zone from which the flame i propagated lengthwise of said chamber towards its exhaust end, said chamber wall having a combustion air inlet opening, a housing wall around said chamber wall peripherally spaced therefrom and having an inlet openin in its peripheral section communicating with said chamber wall inlet opening, said housing wall being of jacketed construction fora section of its length to define an annular cooling passage extending from the inlet opening of said housing wall to the exhaust end of said combustion chamber, said cooling passage communicating at one end with said latter inlet opening, whereby a portion of the air admitted through said latter opening into said chamber is diverted through said passage for cooling the housing wall, means for injecting a stream of finely divided fuel into said ignition zone, means for directing a stream of primary combustion air into said zone, and duct means for delivering air to said housing wall inlet opening and into said combustion chamber, said combustion chamber being adapted to deflect the air admitted therein through said housing wall inlet opening into two adjoining oppositely rote ting vortices of substantially predetermined floz'. pattern, and said cooling passage being of such dimensions at its inlet end as least to disturb the predetermined vortexforming characteristics of the air admitted from said duct means whereby the predeterminedbivortical flow pattern of the air in said combustion chamber is continuously maintained during combustion operations.

18. An apparatus as described in claim 1, in which an intermediate shell is located in the annular passage downstream beyond the air inlets serving as a'radiation shield for the outer shell.

MARTIN A. MAYERS. HANS T. HOLZWARTH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 781,308 Smith 1 Jan. 21, 1905 2,110,209 Engels a Mar. 8, 1938 2,353,929 Ray July 18, 1944 2,398,654 Lubbock Apr. 16, 1946 2,420,135 Hennig May 6, 1947

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