US3605405A - Carbon elimination and cooling improvement to scroll type combustors - Google Patents

Abstract

AN IMPROVEMENT FOR APPARATUS OF THE TYPE ADAPTED TO PREMIX AIR AND FUEL OR CARBURET AIR PRIOR TO INTRODUCTION THEREOF AS A VORTICAL FLOW INTO A PRIMARY ZONE OF A COMBUSTOR, THE IMPROVEMENT COMPRISES A PURGE AIR OPENING POSITIONED WITHIN AN UPSTREAM WALL OF A SPIN CHAMBER AND COVERED BY A CAP HAVING A PLURALITY OF SMALL OPENINGS LOCATED THEREIN. PURGE AIR FLOWS FROM THE COMPRESSOR THROUGH THE SMALL OPENINGS INTO A CHAMBER FORMED BY THE CAP AND THEREAFTER INTO THE SPIN CHAMBER IN SUCH A MANNER AS TO PREVENT IMPINGEMENT OF HIGH TEMPERATURE GASES ON THE UPSTREAM WALL OF THE SPIN CHAMBER WITHOUT DETRIMENTALLY AFFECTING GENERATION OF THE PRIMARY VORTICAL FLOW.

Description

Sept. 20, 1971 3,605,405

T. L. DU ELL CARBON ELIMINATION AND COOLING IMPROVEMENT T0 SCROLL TYPE comaus'rons Filed April 9, 1970 2 Sheets-Sheet 1 42"4 I g /Q j INVENTORS. THOMAS L. Du BELL BY BARRY WEINSTEIN AGINT- Sept. 20, 1971 'r. L. DU BELL 3,605,405

CARBON ELIMINATION AND COOLING IMPROVEMENT TO SCROLL TYPE COMBUS'I'ORS Filed April 9, 1970 2 Sheets-Sheet 2 INVEN'T R5 THOMAS L. DU ELL BY BARRY WE|N$TEIN AQINY- United States Patent O US. Cl. 6039.65 11 Claims ABSTRACT OF THE DISCLOSURE An improvement for apparatus of the type adapted to premix air and fuel or carburet air prior to introduction thereof as a vortical flow into a primary zone of a combustor; the improvement comprises a purge air opening positioned within an upstream wall of a spin chamber and covered by a cap having a plurality of small openings located therein. Purge air flows from the compressor through the small openings into a chamber formed by the cap and thereafter into the spin chamber in such a manner as to prevent impingement of high temperature gases on the upstream wall of the spin chamber without detrimentally affecting generation of the primary vortical flow.

BACKGROUND OF THE INVENTION This invention relates generally to combustion apparatus for supplying fuel to a combustion chamber. More particularly, this invention relates to improvements in the above type apparatus which eliminate carbon accumulation and overtemperature problems presently associated therewith.

The invention herein described was made in the course of or under a contract, or a subcontract thereunder, with the United States Department of the Air Force.

Delivery of fuel into a continuous burning combustion apparatus, as for example in gas turbine engine combustors, in a highly dispersed manner so as to achieve complete and efiicient combustion of the fuel and, at the same time, minimize the occurrence of fuel-rich pockets, which upon combustion produce carbon or smoke, has posed a continuing problem to gas turbine engine manufacturers. Solutions to this problem are further complicated in applications such as gas turbine engines by the high temperature environment of the combustion chamber as well as by overall length and weight limitations for such combustion apparatus.

Present day emphasis on the elimination of air pollution has resulted in a great deal of work and effort by gas turbine engine manufacturers in an attempt to eliminate visible smoke emission from gas turbine engines. One proposed solution to the foregoing problems involves the use of a device for carbureting the inlet air or mixing the air and fuel and for delivering the combustible fuel/air mixture into the primary zone of a combustor as a vortical flow. Such an apparatus is shown and claimed in a copending application of Thomas L. Du Bell, Ser. No. 817,075, entitled Fuel Delivery Apparatus, and assigned to the same assignee as the present application. The apparatus comprises a housing defining an air vortex generator or spin chamber therein about a centrally disposed core outlet. The housing is adapted to receive fuel and air, circulate the fuel and air through an array of swirl vanes in the spin chamber and generate a vortical discharge flow of air and highly dispersed fuel. The apparatus may include a collection surface provided at the core outlet for collection of non-vaporized or atomized fuel that may be expelled from the apparatus. A secondary array of swirl vanes surrounds the collection surface in such a manner as to generate and deliver a secondary vortical flow into the combustion chamber, about the primary ice vortex, which is generally coaxial with and counterrotating relative to the primary vortex.

Such an apparatus has been found to produce an extremely well vaporized fuel/air mixture with a resultant high efficiency and a reduction in smoke emission from the combustion apparatus. Certain applications of such an apparatus, however, have been found to result in carbon accumulation and metal overtemperatures such that normal operation, as described above, could be detrimentally affected.

Previous attempts to solve similar problems in such apparatus have been to ventilate the affected area by perforating the metal, thereby allowing copious amounts of air to flow through at very high velocities. Such an approach, however, frequently destroys the basic aerodynamics of the apparatus 'by upsetting the vortex previously generated. The net result is a worsening of ignition capability and poorer fuel distribution, which, in turn, results in poorer eXit temperature distributions.

Accordingly, a primary object of this invention is to provide an improved scroll cup type fuel vaporizer which prevents carbon accumulation and metal overtemperature Without affecting the vortex flow thereof.

Another object of this invention is to provide an improved apparatus as described above which controls the recirculation of gases into the center of the primary vortex.

SUMMARY OF THE INVENTION Briefly stated, the above and other objects are achieved in the present invention by providing a basic scroll housing with an opening in a generally planar upstream wall which forms one end of a spin chamber adapted to receive and circulate pressurized air and fuel around a central or core outlet in flow communication with the combustion chamber. A pan-shaped member is attached to the upstream wall of the scroll cup in such a manner as to surround the opening therein. The pan-shaped member is provided with a plurality of small openings in one face thereof, which openings may be normal to or inclined with respect to the surface of the pan-shaped member. The openings are positioned to prevent direct axial flow through the opening in the upstream wall of the scroll cup and they are sized so as to provide a low velocity flow of purge air through the opening in the upstream wall member to the spin chamber of the scroll cup. In this manner, recirculating hot gases within the vortex are prevented from impinging upon the interior walls of the scroll cup.

DESCRIPTION OF THE DRAWINGS While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter of this invention, it is believed that the invention will be better understood upon reading the following description of a preferred embodiment in conjunction with the accompanying drawings wherein:

FIG. 1 is a fragmentary axial cross-sectional view of an exemplary gas turbine engine combustion apparatus embodying the improved scroll cup apparatus of this invention;

FIG. 2 is a perspective view, with portions removed, of the improved apparatus of FIG. 1;

FIG. 3 is a diagrammatical axial cross-sectional view of a scroll cup apparatus without the present improvement showing the air and fuel flow patterns generated thereby;

FIG. 4 is a diagrammatical axial cross-sectional view of the apparatus of FIG. 2 showing the improved air and fuel flow patterns generated thereby; and

FIG. 5 is a front end view of the improved apparatus of FIG. 1.

3 DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings wherein like numerals correspond to like elements throughout, attention is drawn to FIG. 1 wherein a continuous burning combustion apparatus of a type suitable for use in a gas turbine engine has been shown generally at as comprising a hollow body 12 defining a combustion chamber 14 therein. The hollow body 12 includes a domed upstream closure member 16, having an opening 18 located centrally thereof for receiving a fuel/ air mixture. The domed closure member 16 defines the upstream end of the combustion chamber 14 and may be suitably secured to or formed integrally with the hollow body 12. As will be understood by those skilled in the art, the combustion chamber 14 may be of the annular type, the cannular type, or the can type, with the domed closure member 16 having a plurality of circumferentially spaced openings 18.

An outer shell 20 may be provided to enclose the hollow body 12 and to cooperate therewith to form passageways 22 and 24 surrounding the hollow body '12. An upstream extension 26 of the hollow body 12 cooperates with the outer shell 20 to form the inlets of the passageways 22 and 24. As will be understood, the passageways 22 and 24 are adapted to deliver a flow of pressurized air from a suitable source, such as a compressor 28, into the combustion chamber 14 through suitable apertures or louvers 30. In this manner, the passageways 22 and 24 act to both cool the hollow body 12 and to provide dilution air to the gaseous products of combustion formed within the combustion chamber 14.

The upstream extension 26 of hollow body 12 is adapted to function as a flow splitter to divide the pressurized air delivered from the compressor 28 between the passageways 22 and 24 and an upstream end opening 32 centrally formed within the extension 26. As clearly shown in FIG. 1, the opening 32 communicates with a chamber 33, which is defined by the internal wall of the extension 26 and the external wall of the domed member 16.

Located within the chamber 33 and attached to the domed member 16 in any suitable manner known in the art is an improved fuel injection apparatus 34 constructed in accordance with this invention. The fuel injection apparatus 34 has been shown as comprising a housing 35 having inlet passage means 36 for receiving pressurized air from the compressor 28 by means of the opening 32, a first or core outlet 38 (FIG. 2) in fiow communication with the hollow body opening 18 for delivery of an air/ fuel mixture into the combustion chamber 14 as a primary 'vortical flow 40. Suitable fuel delivery means 42 are provided to deliver fuel to the interior of the housing 35 as will presently be explained. The fuel delivery means 42 may comprise a conduit 44, having a discharge end 45, which extends through the outer shell 20 and communioates with a source of pressurized fuel (not shown). While the improved fuel delivery apparatus 34 is particularly adapted for use with liquid fuel and will hereinafter be described in connection 'with liquid fuel, it should be understood that fuel in the liquid state, gaseous state, solid state or a combination thereof may be effectively used.

Referring now to FIGS. 2-4, the housing 35 has been shown to comprise an involute outer wall 48 and generally planar, spaced upstream and downstream end walls 50 and 52, respectively, which are peripherally joined to the outer wall 48. As best shown in FIG. 3, the housing 35 defines an air vortex generator or spin chamber 46 out wardly of the outlet 38. The outer wall 48 is of spiral shape with a progressively decreasing radius from the inlet passage 36 to a terminal edge or lip 54 (FIG. 2) which defines, in part, the inlet opening from passage 36 to the spin chamber 46. The inlet passage 36 is formed with a generally axially facing upstream end opening 55 for receiving a flow of pressurized air from compressor 28 and has one wall formed as a streamline continuation of the involute outer wall 48 so as to deliver the inlet air in a 4 generally streamline manner into the spin chamber 46. In this manner, the pressurized inlet air is directed from inlet 36 in a circular motion of ever decreasing radius so as to generate the primary vortical flow 40' as shown in FIG. 1. As schematically shown in FIG. 3, the vortex has a substantially hollow core portion 56.

To further provide the swirling motion of the primary vortical flow 40 as well as to accurately position the vortical flow 40 relative to the opening 38, a plurality of primary swirl vanes 58, each of which extends between the upstream and downstream walls and 52, may be provided in a peripheral array about the outlet 38 as shown in FIG. 2. Such an array of swirl vanes 58 may also be adapted to throttle the air passing therethrough so as to increase the rotational velocity of the primary vortical flow 40. In order to maintain a generaly uniform rotational velocity of the inlet air within the spin chamber 46, outwardly of the vanes 58, the outlet 38 and the swirl vanes 58 are preferably positioned with respect to the outer wall 48 so that the cross-sectional flow area progressively decreases from the inlet to the lip 54.

In addition to the primary flow generating apparatus just described, a control or collector surface 60 is provided at the outlet 38 to collect downstream wall fuel flow as will be described. The collector surface 60 cooperates with means 62 for introducing a secondary flow of air into said combustion chamber 14 about and along the collector surface 60 in a manner which carries such collected fuel as an atomized spray into the combustion chamber 14. In the depicted embodiment, the control or collection surface 60 takes the form of an annular sleeve extending around the outlet 38 and defining a downstream extension thereof. The collection surface 60 may be suitably joined to the downstream wall 52 or formed integrally therewith. The secondary air flow means 62 has been shown as comprising a plurality of swirl vanes 64, spaced radially outwardly of and in a circular array around, sleeve 60. The swirl vanes 64 are suitably secured between the downstream wall 52 and an annular rim 65 spaced axially downstream thereof. The array of swirl vanes 64 and the annular rim 65 are spaced radially outwardly of the sleeve 60 so as to form an axially extending annular passage 66 therebetween which is generally coaxial with the outlet 38 and with vortical flow 40.

As best shown in FIG. 1, the fuel injection apparatus 34 is positioned with the annular rim closely spaced or joined to the rim of enclosure member opening 18 so as to establish a flow of pressurized air from chamber 33, radially inwardly through the swirl vanes 64, and hence axially into the combustion chamber 14. The swirl vanes 64 are adapted to swirl such air flow and generate a secondary vortical flow 67 which is preferably counterrotating relative to the primary vortex flow 40, although it may be otherwise. In this manner, a region of high shear stress 68 is created downstream of the sleeve 60' at the outer boundary of the vortex 40 due to the interaction of the primary and secondary flows.

In operation, liquid fuel is delivered to inlet passage 36 through the conduit 44. Some of this fuel may be immediately picked up by or entrained within the high velocity inlet air entering through the inlet 55 and carried into the combustion chamber 14. The remaining fuel lands on the interior surface of the inlet passage 36 and is driven or pushed by the high velocity air to the spin chamber 46 and centrifugally along outer wall 48. During such flow, a portion of the fuel may be vaporized and/ or atomized and entrained within the inlet air flow. A portion of the outer wall fuel flow which is not so evaporated is then sheared off the lip 54, as at 72 (FIG. 2), and again passes through the inlet air fiow pathwhich results in more fuel being entrained within the inlet air. In addition to the above and with reference to FIG. 3, the liquid fuel circulating within spin chamber 46 is carried by the air in a swirling flow along the inner surface of upstream wall '50 by the swirling air flow. Such upstream wall fuel flow is carried through the vanes 58 and forms a ring of fuel 74 where the fuel velocity forces are balanced by the centrifugal forces. While flowing along the inner surface of upstream wall 50 to the ring 74, some of the fuel may be evaporated from the surface by the inlet air and by radiant heat from the flame within the combustion chamber '14. The liquid fuel within the ring of fuel 74 is spun off and atomized into extremely small fuel droplets by the high velocity vortical flow of air 40 and directed or carried toward the combustion chamber 14 as a conical spray 76. Since these atomized fuel droplets are extremely small, they quickly vaporize and mix with the air vortex 40.

Any fuel flow along the downstream wall 52 is carried or pushed to the downstream end of the sleeve 60 in a swirling flow by the vortex 40. The fuel is then spun or sheared 01f the downstream end of the sleeve 60 by the primary and secondary flows 40 and 67 and carried into the region 68 of high shear stress where it is sheared to small droplets 80 which quickly vaporize. Accordingly, by providing the control surface or sleeve 60 and the secondary flow generating means 62, positive and controlled introduction of all liquid fuel efiluxing from the apparatus 34 is achieved over a wide range of operating conditions in a gas turbine engine.

Referring again to FIG. 3, the reduced pressure of the vortex core 56 causes a reverse or recirculation flow to be established from the combustion chamber 14, as generally shown at 82. This recirculation of high temperature gas from the combustion chamber .14 into the central or core portion of the spin chamber 46 further enhances vaporization of the liquid fuel from the spin chamber surfaces as well as vaporization of any atomized fuel droplets carried by the air intake or expelled from the fuel ring 74. This recirculation of high temperature gas, however, can have detrimental effects if it is permitted to impinge upon the upstream wall 50 of the spin chamber 46'. That is, the impingement of the high temperature air can cause an overtemperature of the wall 50 with resultant damage thereto. Additionally, the impingement can result in the accumulation of carbon deposits on the wall 50, as shown schematically by the numeral 84. Such accumulation interferes with the normal operation of the apparatus 34 thereby causing unpredictable burning conditions in the combustion chamber 14. An additional problem results when the carbon accumulation 84 breaks loose from the upstream wall 50 and travels downstream through the combustion chamber 14. Therefore, some means is necessary to prevent the impingement of the recirculating high temperature gases 82 upon the upstream wall 50 to prevent the overtemperature and carbon accumulation problems.

One possible approach to this problem might be to perforate the upstream wall 50 and to pass copious amounts of high velocity air therethrough, thus preventing impingement by the hot recirculating gases 82. Such an approach, however, frequently destroys the basic aerodynamics of the system by upsetting the primary vortex 40. The net result of such a system is a worsening of ignition capability and poorer fuel distribution, thereby causing poorer temperature distribution with resultant turbine damage.

To eliminate this problem, as shown in FIG. 4, the upstream wall 50 is provided with an opening 86 centrally thereof. A pan-shaped cover 88 is placed over the opening 86 and is attached to the upstream wall 50 by any appropriate means such as by welding. The cover 88 is provided with a plurality of small holes 90 appropriately spaced circumferentially around the flat plate portion of the cover 88. The holes 90 may be inclined with respect to the flat plate portion of the cover 88 as shown in FIG. 5. As shown in FIG. 1, the cover 88 is located within the chamber 33 such that high velocity air entering the chamber 33 through the opening 32 is capable of flowing through the holes '90 to an interior chamber 92 (FIG. 4) formed between the cover 88 and the wall 50. The chamber 92 lies in fluidic flow cooperation with the spin chamber 46 by means of the opening 86. Air entering the holes 90 thus flows through the chamber 92 into the spin chamber 46 as purge air schematically shown by the arrows 94. As shown in FIGS. 4 and 5, however, the holes 90 are positioned to prevent direct axial flow between the holes 90 and the central opening 86 of the forward wall 50. Additionally, the holes 90 are inclined as shown in FIG. 5 so that the purge air swirls 'within the chamber 92 prior to exiting through the opening 86. The holes 90 are preferably inclined in a direction to provide swirling motion in the same direction as the primary vortex flow 40.

The holes 90 are appropriately spaced and sized to regulate the amount and the pressure of the purge air 94 flowing into the chamber 46 in order to prevent high velocity air flow from destroying the primary vortex 40. As shown in FIG. 4, the purge air 94 entering the opening 86 is made to turn over the forward wall 50 along the interior surface thereof by the pumping action of the vortex 40, aided by its own swirling motion as described above. This air flow exits at a low enough velocity such that the aerodynamics of the spin chamber 46 are not destroyed, but it enters at a high enough velocity such that the recirculating hot gases 82 never impinge upon the upstream wall 50 of the spin chamber 46. Thus, carbon is prevented from depositing upon the upstream wall 50, the upstream wall 50 is maintained cool, and the overall performance of the combustion apparatus 34 is not sacrificed.

From the foregoing, it will be appreciated that the present invention provides an improved combustion apparatus of simplified and economical construction for ef ficiently and satisfactorily introducing fuel into a combustion chamber in a positive and controlled manner over a wide range of operating conditions while preventing carbon accumulation and metal overtemperature of such apparatus. While the purge air inlet means have been shown and described as comprising a pan-shaped member including a plurality of small holes located therein, it should be understood that other arrangements may be employed and that such means may be formed integrally with the apparatus 34. Additionally, while a plurality of small purge holes have been shown, one larger hole could be utilized if appropriately positioned within the cover 88. Accordingly, while a preferred embodiment of the present invention has been depicted and described, it

will be appreciated by those skilled in the art that many I modifications, substitutions, and changes may be made thereto without departing from the inventions fundamental scheme.

What is new and desired to be secured by Letters Patent of the United States is:

1. In a combustion apparatus of the type including a hollow body defining a combustion chamber therein, means disposed outwardly of said combustion chamber for defining a spin chamber including upstream and downstream end walls, said spin chamber including means adapted to receive pressurized air and liquid fuel and to circulate said air and said fuel about a centrally disposed outlet in said downstream wall of said spin chamber and to generate a primary vortical discharge flow of said air and said fuel from said outlet into said combustion chamber, and means for igniting said discharge flow to form a high temperature gas stream, the improvement which comprises:

an opening formed in said upstream end wall of said spin chamber, means forming a purge air chamber adjacent said opening, and means for generating a flow of purge air through said opening into said spin chamber, along said upstream end wall, to prevent impingement of the high temperature gas stream upon said upstream end wall.

2. The improved apparatus of claim 1 further characterized in that said opening is located centrally of said upstream end wall, said chamber forming means comprises a pan-shaped member, and said pan-shaped member covers said opening and includes at least one purge air hole formed therein.

3. The improved apparatus of claim 2 further characterized in that said pan-shaped member includes a plurality of purge air holes formed therein, said purge air holes being located radially outwardly of said central opening, thereby preventing direct axial flow of purge air into said spin chamber.

4. The improved apparatus recited in claim 3 further characterized in that said purge air holes are inclined with respect to said pan-shaped member, whereby said purge air is provided with a swirling motion within said purge air chamber.

5. The improved apparatus of claim 2 further comprising means forming a control surface around said outlet for collecting liquid fuel flowing along said downstream wall to said outlet, and means for generating a secondary flow of air into said combustion chamber, about said fuel collection means, to form a region of high shear stress at the outer boundary of said primary vortical flow, whereby said collected fuel is introduced into said combustion chamber in a controlled and highly dispersed manner.

6. The improved apparatus of claim 5 further characterized in that said fuel collection means comprises an annular sleeve generally coaxially disposed relative to said primary vortical flow, said sleeve being secured to said downstream end wall about said outlet.

7. The improved apparatus of claim 6 further characterized in that said secondary flow generating means includes a plurality of swirl vanes disposed in a radially outwardly spaced circular array about said annular sleeve, said swirl vanes being adapted to deliver said secondary flow as a vortex about, and counterrotating relative to, said primary vortical discharge flow.

8. Apparatus for introducing fuel into a combustion chamber to be ignited to form a high temperature gas stream, said apparatus comprising:

a housing having upstream and downstream end walls, said downstream end wall including a core outlet therein, said housing defining a spin chamber around said core outlet, said core outlet including means to establish flow communication between said spin chamber and said combustion chamber;

means for receiving anddirecting pressurized air and fuel into said spin chamber;

said spin chamber including means to utilize the energy in flow communication with said spin chamber; and

means for generating a flow of purge air through said opening, said purge air flowing along said upstream end wall and preventing the impingement of the high temperature gas stream thereon.

9. Apparatus as described in claim 8 further characterized in that said purge air chamber forming means comprises a pan-shaped member, said pan-shaped member covering said opening and including a plurality of purge air inlet holes forced therein.

10. The apparatus recited in claim 9 further characterized in that said purge air inlet holes are disposed radially outwardly of said opening, thereby preventing direct axial flow of purge air into said spin chamber, and are inclined with respect to said pan-shaped member, whereby purge air flowing within said purge air chamber is given a swirling motion.

11. The apparatus recited in claim 9 further comprising means carried by said downstream end wall for defining an axially downstream extending fuel collection surface, said collection surface defining said core outlet at its junction with said downstream end wall; and means for directing a secondary flow of pressurized air into said combustion chamber, about said collection surface, so as to form a region of high shear stress at the outer boundary of said primary vortical flow, whereby fuel collected on said collection surface is discharged in a controlled and highly dispersed manner.

References Cited UNITED STATES PATENTS 2,560,207 7/1951 Berggren et al -3965 2,807,316 9/1957 Jackson 6039.65X 3,030,773 4/1962 Johnson 6039.65 3,405,923 10/1968 Nesbitt et a1. 43 l-l83X ALLAN D. HERRMANN, Primary Examiner US. Cl. X.R.

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