US3030773A - Vortex type combustion with means for supplying secondary air - Google Patents

Description

April 24, 1962 R. H. JOHNSON VORTEX TYPE COMBUSTION WITH MEANS FOR SUPPLYING SECONDARY AIR Filed Jan. 22, 1959 Fig. 4.

/m enf0r: Robe/f H Johnson by W His Afforne y United States Patent 3,030,773 VORTEX TYPE COMBUSTION WITH MEANS FOR SUPPLYING SECONDARY AIR Robert H. Johnson, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Filed Jan. 22, 1959, Ser. No. 788,399 Claims. (Cl. Gil-39.65)

This invention relates to improvements in combustion apparatus and specifically to combustion chamber structure foruse in gas turbines but need not be limited thereto. This application is a continuation-in-part of a copending application, Serial No. 310,186, Johnson, filed September 18, 1952, now abandoned, and assigned to the same assignee as the present invention.

The present invention is particularly suited for flame tube construction in aircraft power plants as well as related gas turbines and jet apparatus.

In order to attain high combustion etliciencies over wide ranges of operating conditions in combustion chambers wherein large amounts of energy are released per unit volume, the problems of undue carbon deposition, resulting from incomplete combustion, an excessive local heating must be avoided. To a great extent, this is achieved by dividing the combustion air into primary and secondary proportions, the former being that required to sustain combustion under all operating conditions, while the latter is that required to complete the combustion process, for modulation of the burning rate and for cooling purposes. Together with proper entry of primary and secondary air, it is important to utilize the available space within the combustion chamber for combustion purposes, to maintain a stable flame, and to complete the combustion process within the residence time available.

Accordingly, it is an object of this invention to provide a new and improved structure for use as a combustion chamber.

It is another object of this invention to obtain a higher space heat release rate of combustion while maintaining the combustion chamber wall surfaces relatively cool.

It is a further object of this invention to provide a combustion chamber construction wherein combustion air is divided for atomization and propagation of fuel particles into the combustion zone and for more effective use elsewhere.

It is another object of this invention to provide flame locking and holding means in a combustion chamber to give maximum stability for a wide range of operating conditions.

It is a further object of this invention to provide improved combustion air delivery pattern in a combustion chamber.

It is another object of this invention to provide an improved combustion process in combined forms of rotating or moving masses of a fuel air mixture.

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

FIG. 1 is a longitudinal cross section of a preferred embodiment of my invention applied to a combustion chamber structure;

FIG. 2 is a partial transverse section taken along line 22 of FIG. 1;

FIG. 3 is a partial transverse section taken along line 3-3 of FIG. 1;

FIG. 4 is a transverse section similar to FIG. 3 of a modified structure; and

FIG. 5 is a longitudinal cross section, partly in section, of a modified combustion chamber structure.

The objects of my invention may be realized by proice viding improved admission of secondary air to a readily ignitable and stable fuel-primary air mixture to improve combustion thereof by forming a rotating toroid of burning fuel air mixture and to cool the combustion chamber wall surfaces.

Referring now to FIGS. 1 to 4, inclusive, in the drawings wherein such details of construction which are not specifically enumerated are considered as unnecessary to an understanding of the invention, there is disclosed a diagrammatic illustration of a combustion chamber 10, which may be used to provide motive fluid for aircraft propulsion or the like. This combustion chamber may take the form of a cylindrical flame tube 11 open at the down stream or exhaust end and closed at the other or upstream end by an inlet wall structure '12 comprising a wall 13, and primary air atomizing nozzle 14 which may be either cylindrical or frusto-conical in form. The fuel inlet 15 projects through the center of the upstream end wall of air nozzle 14, in the form of a closed pipe with holes in the end at various desired angles. About the cylindrical (or conical) periphery of nozzle 14 are located a series of nozzle blades 16 adjusted to a converging angle and defining passageways through which primary air is admitted into nozzle 14, the angle of the blades 16 being arranged to direct the incoming air along a path which is nearly tangential to produce the swirling motion of a vortex into which the fuel is injected in a series of solid streams under low pressure, as indicated at AA.

The word tangential is employed to describe the direction given the air entering or passing through blades 16 of nozzle 14. Since the outer circumference of nozzle 14 defines an assumed circle from which blades 16 depend, the entering air is given a whirling motion the direction of which may be said to be nearly tangential to this assumed circle. Blades 16 have been described as being adjusted to a converging angle. Such a converging angle is inclusive in a preferred form of this invention of a pair of angles. For example, good results have been obtained with a nozzle 14 in accordance to the teachings of this invention where each blade 16 is inclined at an angle of about 10 to 25 from the tangential direction of the assumed circle. In addition, a preferred form of this invention includes the feature that individual adjacent pairs of blades 16 defines a converging nozzle or passage such as illustrated in FIG. 2. Blade spacing, i.e., the closest distance between adjacent blades at the convergent portion has been varied over a wide range up to A of an inch and greater. In one form of this invention a nozzle .14 has a circle diameter of approximately 2% inches from which blades 16 have been bent outwardly from the circle, each of said blades being along its radial length approximately of an inch and inclined at an angle of 25, together with a minimum spacing between adjacent blades of 1 of an inch.

The sharp velocity gradient of the rotating mass of air breaks up the streams of fuel into fine particles which migrate outward due to centrifugal force. This mixture of fuel and primary air is readily ignitable and is carried forward by the axial motion of the air in a substantially vortical manner into the combustion chamber.

Wall 13 contains secondary air admission openings or passageways 17 only at preferred positions and of a preferred opening size and design. Openings 17 are further defined by a circular row of turning blades or vanes 18 through which secondary air is introduced axially along the inner wall surface of the combustion chamber to complete the combustion process and to cool the wall surface of the combustion chamber. Without turning blades 18 or their defined passages 17, and with the total amount of air for combustion entering nozzle 14, the wall 11 quickly reaches excessive temperatures. When openings or passages 17 were formed, but without turning blades 18, the

air flow being purely in an axial direction, sufficient cooling was not obtained and hot streaks and spots appeared in the wall 11 the temperatures of which exceeded the design temperature of the metal employed at high fuel rates. It was discovered that if openings or passages were defined by blades 18 as illustrated to impart a swirling motion to the incoming air, better cooling was established. In the preferred form of this invention, the secondary air is directed or swirled in the same direction as the vortical air issuing from nozzle 14 and interacts to form a tightly rotating toroid 19 thereabout.

The inlet wall structure 12 as illustrated has been effectively employed as a burner wtihout a wall or casing 11 downstream of the structure 12. Under adverse conditions burning was effective and a forced rotating tore 19 of burning fuel air mixture was definitely established adjacent the wall 13 which effectively locked or maintained the combustion process in position. The aforementioned and illustrated particula flow pattern of a rotating toroid surrounding a vortical moving air mass is definitely established because unless a fluid is directed or forced it will flow as a free vortex. Thus, the air expanding out of nozzles 14 and openings 17 form vortices which take on a free vortex velocity distribution whereby the velocities at the inner boundaries of the vortices will be higher than at the outer boundaries. The corresponding pressures which are inversely proportional to the velocities squared will be lower at the inner boundaries of the vortices than at the outer boundaries of the vortices. With the two concentric vortices, a first vortex from nozzle 14 and a second vortex from openings 17, there will be a flow from the higher pressure outer boundary of the inner vortex outwardly to the low pressure inner boundary of the outer vortex. This is the driving force which forms and rotates a toroidal flow or doughnut of burning fuel air mixture 19 between the two vortex streams. Since both vortices are rotating about their center in the same direction, this tore 19 will also have circumferential rotation and because of the velocity and pressure distribution the toroid 19 indicates a radial flow as shown by arrows 22.

In the configuration shown in FIG. 1, combustion air control delivery is an important feature. Variations in the rate of air flow to nozzle 14 and/ or through openings 17 provide variations in the combustion process and pattern. In a preferred form of this invention, combustion air delivered is proportioned between nozzle 14 and openings 17. Such control may be by means of a suitable separate air conduit 20 to either nozzle 14 and openings 18 or by the proportioning of the relative size of air openings. Alternatively suitable means may be employed to vary the air supplied from the nozzle 14 or openings 17. An important feature of this invention is that the total amount of air required for combustion does not enter nozzle 14. In fact, good results are obtained when about one-half or less of the required combustion air enters nozzle 14. This means that the air entering openings 17 is not merely cooling or blending air as is the usual design, but additional air necessary for complete combustion. The particular combination of the rotating tore 19 of air and the central vortex provides a substantial amount of the atomized fuel being taken up in the strong tore 19 so that in the overall combustion process, a substantial amount of burning takes place in the tore. Effective combustion has been obtained from this burner when more than half of the fuel being burned is burning in an enlarged tore 19. It is important, therefore, that the total or the substantial total amount of air for combustion not enter the same nozzle wherein fuel is injected and atomized. By giving the secondary air a swirling motion in the same direction as the pirmary vortex, very effective Wall surface cooling is obtained. These secondary air turning blades or nozzles may be set at any angle sufiicient to impart a strong whirl and it has been discovered that an angle of approximately 45 with respect to a plane containing wall 13 is satisfactory. Since the angle at which the nozzle blades for directing primary air are inclined inwardly from a tangential direction varies from about 10 to 25, the primary and secondary air vortices cause two different pressures in a given plane which results in the formation of the forced stabilizing tore 19 of flame to which secondary air, indicated by arrows 22, is constantly added. The rotating tore or doughnut of flame is formed adjacent the inlet wall structure of the combustion chamber, between the secondary air nozzles 17 and the outer periphery of nozzle 14. Tore 19 not only provides a stabilizing effect to prevent blowout but also serves as a fuel vaporizer and rotates about the center line of the combustor as indicated by arrows 21 and also about its own circular axis as indicated by arrows 22. The direction of arrows 22 may be better described as being opposite to the axial flow of the vortical fuel primary air mixture at the interface of the tore and the vortical fuel primary air mixture. The space in which tore 19 forms is conducive to tore formation in that it is partially sheltered and no additional openings are provided which would tend to destroy tore formation. Further, more space is made available for second pass burning thereby increasing combustion efiiciency and inflammability limits. The low pressure area in the center of the vortices aids in the latter respect since products of combustion carrying unburned fuel-primary air mixture are drawn thereinto.

The blading structure for the air inlet nozzle 14 shown in FIGS. 2 and 3 may be modified by use of separate blades inserted at the correct angles to obtain the vortical flow desired.

FIG. 4 is a modification of structure used to provide secondary air comprising directing means in the form of a series of holes 23 through wall 13 in place of secondary openings 17 and blades 18. The holes being angularly directed to produce a swirling envelope of air as illustrated in FIG. 1.

In the modification disclosed in FIG. 5, it is contemplate to use a perforated combustion liner similar to that disclosed in US. Patent No. 2,601,000, issued in the name of Anthony J. Nerad, and having the same assignee as the present application.

As in FIG. 1, a conventional combustion chamber is shown at 2 4 with a flame tube at 11, inlet wall structure at 12 comprising end wall 13 and primary air atomizing nozzle 14, either cylindrical or frusto-conical in form. The fuel inlet is at 15 and primary air inlet blading defining passageways at 16 and secondary air inlets at 17. A perforated liner 30 with air inlet openings 31 is inserted in the flame tube between the secondary air inlets 18 and the primary air atomizing nozzle 14 and spaced closer to the former. The advantages accruing from this modification include having an intermediate Wall at medium temperature, cooled by the secondary air flowing in the annular space B between the liner and the outer wall, and at the same time, preheating the cooling air before it enters the combustion chamber proper through the liner perforations of air inlet openings, so that the secondary air is more or less evenly distributed along the length of the chamber to furnish air to complete the combustion process started in the fuel-primary air mixture, and to cool the combustion products to the desired temperature.

As has been disclosed in the above-cited Ner-ad patent, the secondary air flows through the first row of air inlet openings 31 adjacent wall 13 to aid in'the formation of the stabilizing tore of flame at 32, which is held adjacent the inlet wall structure similarly to the action occurring in the structure of FIG. 1. Although the positioning of the perforated liner is not critical, it should be located far enough away from the outer periphery of the primary air atomizing nozzle 14 so that the stabilized tore of flame 32 may form adjacent wall 13.

The openings 17 for the axial entrance of secondary air need be openings for admission only, there being no necessity for turning vanes or blades since the air entering the perforations of the combustion liner does so in a manner to obviate the requirement for swirling of the secondary air, the air indicated by arrows 33 aiding in maintaining the stabilizing tore of flame 32, while the air indicated by arrows 34 maintaining the liner walls at a moderate temperature and also being added to the burning fuel-primary air mixture. The use of the perforated liner improves air flow so that not only is the available space of the combustion chamber more efliciently utilized but a more uniform temperature distribution therein is obtained, the net result being a higher space rate of combustion.

In both the preferred embodiment of FIG. 1 and the modification of FIG. 5, a standard means of ignition, such as a spark plug may be used, although none is disclosed herein.

As will be apparent to those skilled in the art, the objects of my invention are attained by the use of concentric strong vortex formations of p'rnnary and secondary air which produce a low pressure area adjacent the fuel inlet forming a toroid of fuel air mixture and inducing intimate atomizing and mixing of combustion air and fuel so that no specific form of fuel injector is required to achieve atomization of injected fuel.

While other modifications of this invention and variations of apparatus that may be employed within the scope of the invention have not been described, the invention is intended to include all such as may be embraced within the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An inlet end wall structure for an open exhaust end combustion chamber comprising in combination, air nozzle means providing a vortical rotational movement of air flowing into said combustion chamber, means injecting fuel centrally into said rotating vortex, said air nozzle means supplying less than the amount of air necessary for combustion of said fuel, and air inlet means in said wall structure spaced radially from said air nozzle means in cooperative relationship with said wall structure and said air nozzle means to generate a forced rotating toroidal mass of a fuel air mixture closely adjacent said wall structure, said air inlet means supplying the remainder of air necessary for combustion of said fuel.

2. An inlet end wall structure for an open exhaust end combustion chamber comprising in combination, air nozzle means providing a first vortical rotating movement of air flowing into said combustion chamber, fuel injecting means to inject fuel centrally into said air movement, said air nozzle means providing less than the amount of air necessary for combustion of said fuel, air opening and directing means in said Wall structure to provide a second vortical rotating movement of air surrounding said first air movement, said air opening means providing the remainder of air necessary for combustion of said fuel, said air opening and directing means positioned in cooperative relationship with the said wall structure and the said air nozzle to generate a forced rotating toroid of fuel air mixture adjacent said wall structure between said air movements.

3. An inlet end wall structure for an open exhaust end combustion chamber comprising fuel inlet means set in a centrally located aperture, a circumferential row of blading defining openings surrounding said fuel inlet means, said bladed openings providing a rotating vortical movement of a fuel air mixture axially into said combustion chamber, said bladed openings supplying less than the amount of air necessary for combustion of said fuel, and secondary bladed openings in said inlet wall structure spaced radially from said circumferential row of blading defining openings and positioned in cooperative relationship therewith and with said wall structure to generate a forced toroid of a fuel air mixture adjacent said wall coaxially with and surrounding said vortical movement of air, said secondary bladed openings providing the remainder of the air necessary for the combustion of said fuel, the angle of the blades of said secondary bladed openings being such to impart a rotational movement to said toroid in the same direction as the rotating vortex issuing from said circumferential row of blading.

4. An inlet end Wall structure for an open ended combustion chamber comprising a wall member closing ofi one end of the chamber, said inlet wall structure containing a centrally disposed recessed portion defining a. cup-like enclosure facing the combustion chamber, fuel inlet means extending in said cup-like enclosure axially toward said combustion chamber a plurality of blade members defining openings circumferentially of said fuel inlet means, each of said blades depending at an approximate range of 10 to 25 measured from a tangent line to the circumferential wall of said cup-like enclosure adjacent pairs of said blades defining convergent passageways into said cup-shape enclosure, said arrangement providing a rotating vortical movement of a fuel air mixture from said cup-shape enclosure into said combustion chamber with less than the amount of air necessary for combustion of said fuel, a plurality of vane elements in said wall and radially spaced from said cup-shape enclosure to define vane openings therein, the said vane elements being inclined at an angle of about 45 in the direction of rotation of said vortical moving air mass, said vane openings providing the remainder of air necessary for the combustion of said fuel, said vane openings providing in combination with the inlet wall structure and said air nozzle a forced toroid of a fuel air mixture adjacent said inlet wall structure coaxial with and surrounding said rotating vortical fuel air pattern radially rotating in a direction opposite the axial flow of the vortical fuel air pattern.

5. A combustion chamber comprising in combination a substantial cylindrical chamber opened at one end and closed at the other, an inlet wall structure forming the closed end of said casing and defining a generally cylindrical cup-shaped depression therein, fuel air inlet means in said cup-shaped depression, said fuel air inlet means including a fuel inlet nozzle projecting outwardly from said depression, a wall structure coaxially surrounding said fuel inlet means, a plurality of blade members defining convergent air nozzles depending from said coaxial wall structure to direct air in a rotating manner into said cup-shaped fuel air inlet means to flow axially into said casing in a first rotating vortical pattern, secondary bladed air inlet means spaced radially of said fuel air inlet means in said wall structure to provide a rotating vortical air pat-tern coaxially with said first pattern and in the same direction, said convergent air nozzles and said secondary air inlet means cooperating with said inlet wall structure to provide a forced toroid of a fuel air mixture between said first and second air patterns adjacent said wall and surrounding and coaxial with said first rotating air pattern, said convergent air nozzles and said secondary radially spaced openings being proportional under predetermined conditions to provide the air necessary for combustion, the ratio being approximately one-half to one-half.

References Cited in the file of this patent UNITED STATES PATENTS 2,592,110 Berggren et a1. Apr. 8, 1952 2,607,193 Breggren et al Aug.19, 1952 2,654,996 Boninsegni Oct. 13, 1953 2,674,846 Bloomer et a1. Apr. 13, 1954 2,698,050 Bloomer et a1. Dec. 28, 1954 2,745,250 Johnson et al May 15, 1956

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