US3373562A - Combustion chamber for gas turbines and the like having improved flame holder - Google Patents

Description

A. F. WORMSER 3,373,562

2 Sheets-Sheet l COMBUSTION CHAMBER FOR GAS TURBINES-AND THE LIKE HAVING IMPROVED FLAME HOLDER March 19, 1968 Filed March 17, 1966 INVENTOR.

ALEX F. WORMSER ATTORNEYS mowmwmmoo March 19, 1968' A. F. WORMSER COMBUSTION CHAMBER FOR GAS TURBINES AND THE LIKE HAVING IMPROVED FLAME HOLDER 2 Sheets-Sheet 2 Filed March 17, 1966 INVENTOR. ALEX F. WORMSER ATTO R N EYS Unite ABTRACT F Till DESCLQSURE The specification discloses an improved combustion chamber for gas turbines and the like which includes a novel flame holder. The flame holder includes a pair of opposed concentric cylinder members which form an annular passage between them. This annular passage is divided by partition plates into a plurality of passages extending from the entrance to the exit end of the flame holder. The passages are inclined at an angle with respect to the axis of the combustion chamber. A pair of opposed air foil sections are provided in each passage to shape the passage such that the entrance end has about twice the area of the exit end. Alternate passages turn the fluid passing therethrough radially inwardly or radially outwardly. A portion of one of the airfoils which narrows the passage from the entrance to the exit end forms a bluff trailing surface which provides eddys to stabilize the flame. This novel flame holder provides a combustion chamber in which more fuel can be burned in a given volume i.e. a combustion chamber having greater combustion intensity. Further the walls of the combustion chamber will remain at a relatively low temperature and thus have a longer life than conventional combustion chambers. The complete specification should be consulted for a full description of the invention.

My invention relates to fuel burners, and particularly to a novel combustion gas generator for gas turbines and the like.

The efficiency and specific horsepower of a gas turbine engine are appreciables determined by the limitations of the combustion chamber, in which working fluid for the turbine is produced. In general, such a combustion chamber is supplied with a stream of air by a compressor, and comprises apparatus for mixing a primary portion of the air with a stoichiometric proportion of fuel, burning the mixture in the combustion chamber, and mixing the burned gases with the remaining secondary portion of the incoming air. The principal limiting factors are the irreversible pressure drop through the combustion chamher, the combustion intensity, the maximum temperature to which the walls of the combustion chamber are exposed, and the effectiveness of mixing of the primary and secondary streams.

The combustion intensity is directly related to the irreversible pressure drop, in that for any known construction, design changes that will increase one will also increase the other. The pressure drop appears directly as a loss of available power, and is quite appreciable in prior constructions, even when designed for combustion intensities that it would be highly desirable to exceed. It is a atent C primary object of my invention to improve the combustion intensity attainable in gas turbines.

In conventional combustion chambers, it is difiicult to design the combustion chamber to provide adequate cooling to secure an acceptable service life of the inner liner. Conventional combustion chambers must also provide a reserve of cooling to take into account changes in the flame pattern in the combustion chamber that may occur during operation because of fuel nozzle wear, distortion of the Walls of the combustion chamber, compressor erosion, and similar factors. These changes may cause either abrupt damage, as by the burning away of portions of the structure, or engine hot spots that result in gradual deterioration of the engine. To avoid catastrophic failures, particularly in turbine engines for use in aircraft, conservative ratings are given, frequent inspections are the rule, and maintenance costs are correspondingly high. It is a second object of my invention to increase the service life and reliability of gas turbine engines by reducing the temperatures to which the parts of the engine are exposed.

The etliciency of mixing of the primary and secondary streams has a direct eifect on the maximum specific horsepower that can be obtained. The main purpose of the secondary air is to reduce the temperature of the burnt primary gases from the typical stoichiomet-ric temperature of 4000 F. to a typical turbine inlet temperature of around 2000 F. which the turbine blading will withstand. The life of the turbine blading is determined by the highest local temperature in the working fluid, and not by the average temperature of the fluid. On the other hand, turbine efficiency and specific horsepower increase with increasing average temperature. Better mixing brings the average temperature closer to the maximum local temperature, with a corresponding increase in attainable performance. It is another object of my invention to improve the mixing of primary and secondary gases in a gas turbine.

Briefly, a combustion chamber in accordance with my invention, with which the foregoing objects can be attained, comprises four basic working regions. These include an annular burning chamber; an annular flameholder, located at the entrance end of the burning chamber; an annular passage for secondary air, within and concentric with the burning chamber; and an annular mixing chamber beyond the burning chamber and formed by the outer wall of the burning chamber and the inner Wall of the secondary air passage. In the mixing chamber, the secondary air is mixed with the products of combustion in a manner resulting in a relatively low temperature of the walls of the mixing chamber. And, as will be de scribed in more detail below, the construction of the flameholder not only stabilizes the flame at a high combustion intensity with a low pressure drop, but also causes the walls of the combustion chamber to operate at relatively low temperatures. Broadly, these purposes are accomplished. by partitioning the flame-holder into many small curved passages that induce a net swirl of the exit gas helically about the axis of the combustion chamber with each passage inducing a local swirling motion having an axis parallel to the exit gas helix angle. The annular flameholder is so formed that the exit area of the numerous small passages is of the same order of magnitude as half the area of the annulus, such that the remaining area forms bluff bodies adjacent the exit ends of the passages.

By this arrangement, I have found that not only can more fuel be burned in the same space in the same time than in prior arrangements, but that the walls of the apparatus may be maintained at a lower temperature, and thus have a longer life.

The apparatus of my invention will best be understood in the light of the following detailed description, together with the accompanying drawings, of a preferred embodiment thereof.

In the drawings:

FIG. 1 is a half elevation of a gas turbine incorporating a combustion gas generator in accordance with my invention, with parts shown in cross section and parts broken away;

FIG. 2 is a view of a portion of the apparatus of FIG. 1 taken essentially along the lines 22 in FIG- URE 1, with parts shown in cross section and parts broken away, and being on an enlarged scale;

FIG. 3 is a fragmentary enlarged view of a portion of the apparatus of FIG. 1 taken substantially along the lines 33 in FIG. 1, With parts shown in cross section and parts broken away;

FIG. 4 is a fragmentary enlarged view of a portion of the apparatus of FIG. 1, taken essentially along the lines 4-4 in FIG. 1, with parts shown in cross section and parts broken away;

FIG. 5 is a fragmentary development in plan taken substantially along the lines 55 in FIG. 3;

FIG. 6 is a schematic and fragmentary elevation in plan taken essentially along the lines 6-6 in FIG. 3, with parts shown in cross section and parts broken away;

FIG. 7 is an elevational view of a portion of the apparatus of FIGS. 1 through 5 taken essentially along the lines '77 in FIG. 5;

FIG. 8 is an elevational view of a portion of the apparatus of FIGS. 1 through 5 taken essentially along the lines 8S in FIG. 5;

FIG. 9 is a fragmentary elevational view, with parts shown in cross section and parts broken away, of a modification of the flameholder forming part of the apparatus of FIGS. 1 through 8;

FIG. 10 is a somewhat schematic plan view of the apparatus of FIG. 9, taken essentially along the lines 1ft10 in FIG. 9, with parts shown in cross section and parts broken away; and

FIG. 11 is a fragmentary sketch of another modification of the flameholder forming part of the apparatus of FIGS. 1 through 8.

In FIG. 1, I have shown quite schematically a half section about the center line of a gas turbine, it being understood that the other half would be symmetrical with the half shown. Air flows into the gas turbine in the sense indicated by the arrow A into a conventional compressor section 1 of any conventional construction, which may include stages for compression and heat exchange in any conventional arrangement. The rotating parts of the compressor 1 may be driven by a central shaft 3. The shaft 3 is in turn driven by a conventional turbine 5. The turbine 5 is supplied with working fluid by a combustion chamber connected between the compressor 1 and the turbine 5 in any conventional manner and comprising a combination of elements constructed and arranged in the manner next to be described.

The combustion chamber of my invention is enclosed by an outer cylindrical wall 7, of metal or the like, that may be connected to or form an extension of the outer housings of the compressor and turbine. An inner cylindrical wall 9, of metal or the like, forms the inner wall of the combustion gas generator and serves to act as a heat shield for the shaft 3, the latter being mounted in any conventional bearings for rotation with respect to the stationary walls 7 and 9.

At the entrance end of the combustion gas generator is a centrifugal pump generally designated as 21. The pump 21 comprises a hub portion 23, fixed to the shaft 9 by any suitable conventional means, and communicating with an annular collecting portion 25 through radially extending hollow struts 2.7. The struts 27 are aerodynamically streamlined and arranged at a zero angle of attack with respect to the swirling air entering the mixing section.

The struts 27 receive fuel from ports 29 in the shaft 3. The ports 29 communicate with a supply conduit 31 in the shaft 3 through a metering orifice defined by a restricted portion 33 of the conduit 31, such that the supply of fuel to the annular portion 25 is limited by the orifice. Fuel is centrifugally impelled into the annulus 25, and held under pressure in its outer rim. When the rim is full, fuel escapes at a rate determined by the orifice 33 through an outlet slit annularly extending between the trailing edge 35 of the annular portion 25 and the trailing edge of an annular cowling 37 formed as the lower portion of the annulus 25 and connected to the hub portion 23 through the trailing edges of the struts 27 In operation, fuel escapes in a thin cylindrical sheet from the trailing edge 35 of the annulus 25, in an essentially uniform rate about the periphery of the annulus, and becomes atomized and becomes an approximately stoichiometric mixture with the primary air.

The primary air and atomized fuel mixture pass through a flameholding section comprising an annulus of flow directing passages, to be described in more detail below. Basically, each such passage is defined by a first airfoil element such as the element 3h and an opposed airfoil element such as the element 41 confined by walls such as the wall 43.

Gases emerging from the fiameholder pass into a burning chamber defined by an outer cylindrical Wall 19, of metal or the like, and by an inner cylindrical wall 45, of metal or the like. A suitable ignition device, such as the ignition plug 4'7, is provided for initially igniting the fuel.

In the illustrated embodiment of my invention, pro vision is made for two streams of secondary air. A first stream of secondary air passes below the fuel mixing region and through the struts 27 of the pump 21 into an annular channel defined by the wall 45 and the cylindrical wall 9, the latter serving both to confine the secondary air and to act as a heat shield between the secondary air stream and the shaft 3. It will be seen that by this arrangement the secondary air also acts as an insulator between the shaft 9 and the combustion chamber. Preferably, vanes such as 13 and 1311 are provided in the passage between the walls 9 and 45, and are connected thereto by welding or the like. These vanes serve both to hold the walls together and to control the swirling motion to the secondary air in a helical path about the longitudinal axis of the passage. Alternatively, only vanes 13 are required. Conventionally, the output air from the compressor will be swirling in the same manner, and the vanes 13 may be used to increase or decrease the swirl angle if so desired.

A second stream of secondary air flows through the annular passage formed by the walls 7 and 19. Guide vanes 15 may be mounted between the walls 7 and 19 for the same purposes as the vanes 13. The outer passage for secondary air is conventional, and is provided to cool the outer wall '7 and the inner wall 1?. It is not essential to the practice of my invention in its broader aspects, as the wall 19 will remain at a relatively low temperature because of cooling effects discussed below. However, the use of the outer passage reduced heating of the wall 17 that would make possible some extension of performance, and its use would be preferred where maximum performance is essential.

The flow of the secondary air will be described in more detail below, but in general it enters a mixing chamber defined by the walls 9 and 19. The Walls may be made to converge in this region if so desired, as by forming one or homes frusto-conical rather than cylindrical sections. As will appear, the gases in the mixing chamber have a net helical flow about the axis of the shaft 3. Since the secondary air flowing through the channel defined by the cylindrical walls 9 and 45 is at a lower temperature than the burning gases in the combustion chamber, it will be denser, and therefore will migrate toward the outside of the mixing zone, thereby promoting exceptionally uniform mixing that permits the gas turbine to operate at maximum temperatures without hot spots.

Following the mixing chamber just described, the mixed primary and secondary gases are mixed with the secondary stream from the outer passage and ducted into the turbine in any conventional manner, not shown. The outer stream will, in general, be a small proportion of the total throughflow, and will not materially reduce the bulk temperature of the working fluid supplied to the turbine. Because of the thorough and exceptionally uniform mixing taking place between the primary gases and the inner secondary air stream, the bulk temperature will be close to the maximum local temperature in the working fluid.

Having described the general structure of the combustion gas generator of my invention, the details of the flameholding, combustion and mixing apparatus, with which the advantages of my invention are obtained, will next be described. Referring first to FIG. 3, between the wall 45 and the heat shield comprising the wall 9 may be connected a number of guide vanes 13, of metal or the like, to impart a swirling motion to the secondary air about the axis of the shaft 3. in FIGS. 3 and 4, the vanes 13 are shown as having square edges for simplicity and for ease of reading the drawings. In practice, these vanes would be streamlined to an airfoil shape in the convention-al manner known in the art, as indicated in FIG. 6.

The construction of the flameholder will best be appreciated by considering together FIGS. 3, 4, 5, 7 and 8. As indicated in PEG. 3, the flameholder comprises a set of separator plates, of metal or the like, such as the plate 43 shown also in FIG. 1, and additional identical plates such as the plates 75 and 77. Between each pair of plates such as the plates 43 and 75 are mounted two channel defining airfoil elements such as 39 and 41, of metal or the like, shown in more detail in FIG. 7. The cells of the flameholder such as the cell shown in FIG. 7 each provide a component of swirl radially outwardly in FIG. 1, and the lates such as 43 and 75 are welded or otherwise secured between the wall 45 and the wall 19 at an angle to the axis of the shaft 3 such that a component of swirl helically about the axis of the shaft 3 is also imparted to the stream. That component is preferably in the same sense as the swirl imparted to the secondary air by the vanes 13 and 15.

The space behind the airfoil elements such as 41, and the trailing edge of the element 41, act as a bluif body in the path of fluid flowing through the channel, causing a wake which produces a recirculation zone that serves to ignite the combustible gases, thereby serving to stabilize the flame.

On either side of the cells such as the cell shown in FIG. 7, is an adjacent cell, such as that between the walls of the plates 43 and 77 and shown in FIG. 8. Each such cell comprises an airfoil defining element 79, of metal or the like, welded or otherwise secured to the plates 43 and 77 and being identical with the element 39 described above but oppositely oriented. A second airfoil element St is secured to the plates 43 and 77, and is identical with the element 41 shown in FIG. 7 except that it is oppositely oriented.

From the construction just described it will be apparent that the adjacent cells of the flameholder will deflect the gases moving through them in opposite directions, and upon impingement of the streams with the walls of the combustion chamber a counterswirling motion will be induced, as suggested in FIG. 1. Superimposed on this effect is the effect of the bluif body presented by the trailing edge of each plate such as 41 and 81, together with the swirl about the axis of the shaft 3 produced by the angles at which the plates 43 and 77 are set. The resultant motion of the gases, combined with the cooling effect produced by the flow of secondary air in passage 110, will tend to cause the average temperature at the housing 19 to be very cool, without adverse quenching of the flames. The effects of the counterswirling action and the bluff body regions of the flameholder will enable the flame to be maintained at exceptionally high flow rates and corresponding high combustion intensities, over a wide range of flows.

The passages in the fiarneholder of my invention are preferably so proportioned with respect to the total crosssectional area of the annulus in which they are confined that the stabilizing effects of the bluff bodies will be equal to the stabilizing eifect of the counterswirling motion imparted to the fluid at each blutf body. Those effects are approximately equal when the exit areas of the passages comprise half the total area of the annulus and the walls such as 39, 41, 79 and 81 are about 45 from axial. Variations from exact equality may be made, subject to increasing pressure drop and intensity as the passage area is made smaller, or angle is made steeper, and decreasing intensity as the bluff body regions become too small to have substantial stabilizing effect.

It is not essential to the practice of my invention in its broader aspects that the counterswirling motion induced by the flameholder be of a radially oscillatory nature. FIGS. 9 and 10 show a portion of a flameholder in which local swirls forming vortices having axes aligned in the sense of the overall helical swirl are formed.

Comparing FIGS. 9 and 10, in order to show the construction of the vortex generator, the outer portions of the cylinders 87 and 89, the outer portions of the walls 91 and 93, and the wall 19 have been broken away to show the internal components of the vortex generator in plan. Further, while the vortex generator in the cylinder 37 is of the opposite hand from that in the cylinder 89, as shown it is a mirror image of the generator in the cylinder 89 when the latter is rotated 90 degrees clockwise in FIG. 9.

Referring to FIG. 9, a flameholder in accordance with a second embodiment of my invention comprises an even number of vortex generators enclosed by cylinders such as 87 and 89, of metal or the like. The cylinders such as 87 and 89 are located between the walls 45 and 19 in an annular array, and may be secured between the walls by end plates 91 and 93 (FIG. 10) joining the walls. As suggested by the curved arrows in FIG. 9, each vortex generator is arranged to produce a vortex oppositely rotating with respect to the vortices produced by adjacent generators, such that the swirl components will add at the interfaces.

As best shown in FIG. 10, each vortex generator comprises a pair of essentially helical airfoil elements such as the elements 95 and 97 disposed about a hub such as 99. Each of the airfoil elements has a blulf trailing edge. As shown, the airfoils such as 95 have a trailing edge formed by diverging walls 101 and 103, the space between the walls contributing to the blutf body area without adding to the weight of the flameholder. As indicated, the other airfoil elements 97, 105 and 107 are similarly constructed. Alternatively, hubs 87 and 89 may extend beyond trailing edges at plane 111.

As indicated in FIG. 10, the vortex generators are set between the walls 19 and 45 with their axes at an angle 6 to the axes of the shaft 3. The angle 0 is selected to produce an overall swirl of the exit gases from the flameholder helically about the axis of the shaft of the same sense as the swirl in the secondary air. This swirl may be either clockwise or counterclockwise.

As the spaces between the vortex generators of FIGS. 7 and 10 contribute to the blulf body area seen by the gases diverging from the flameholder, the trailing edge areas behind the airfoils 95, 97, 105 and 107 may be correspondingly made somewhat less than one-half the projected area of the exit areas of the adjacent flow passages.

Preferably, the airfoil elements such as 95 each extend about at least 180 around the hub such as 99. More airfoil elements, symmetrically disposed about the hub, may be employed if so desired; for in such airfoils, each should cover at least 360/n about the hub.

FIG. 11 shows another modification of the flameholder of my invention. In this embodiment, one or more coaxial helical passages forming vortex generators are built up by connecting a plurality of helically formed tubes such as 109 between plates 91a and 93a placed as are the plates 91 and 93 in FIGS. 9 and 10.

The combustion gas generator of my invention is particularly useful in a gas turbine engine. However, it will be apparent to those skilled in the art that it would also be useful in other applications requiring high combustion intensit low pressure drop, and long life, high turndown ratio, and where a uniform distribution heat source is needed. Fuel may be introduced in various ways other than by the use of the centrifugal pump illustrated, for example, with fuel nozzles, a vaporizing surface, or a venturi device. Where mixing of the fuel upstream of the combustion chamber is desired, the apparatus shown is preferred. However, the blufi body regions adjacent the exit end of the fiameholder could be used to house fuel injection nozzles if so desired. Also, if no shaft 3 is required, the inner casing 31may be dispensed with if desired.

While I have described my invention with respect to the details of various embodiments thereof, many changes and variations will occur to those skilled in the art upon reading my description, and such can obviously be made without departing from the scope of my invention.

Having thus described my invention, what I claim is:

1. An annular fiameholder positioned at the entrance end of an annular combustion chamber, said fiameholder comprising means forming an array of alternately radially outwardly and radially inwardly inclined converging flow passages each terminating in an exit end, means forming a bind body adjacent the exit end of each of said passages, the cross-sectional areas of said passages at their exit ends being the same order of magnitude as the radially projected areas of said bluff bodies.

2. A combustion gas generator, comprising an annular combustion chamber formed by concentric first and second cylindrical walls extending along a common axis from an entrance end to an exit end, a fiameholder at the entrance end of said combustion chamber and comprising a set of separator plates extending between said walls, each of said plates being aligned with a set of parallel helices about said common axis to form a set of helical passages, and an outer and an inner airfoil located in each passage in spaced confronting relationship and converging in the direction from said entrance end toward said exit end, to form an exit area and a bind trailing edge of areas of the same order of magnitude, the airfoils in alternate passages being alternately outwardly and inwardly inclined radially of said walls to alternately direct streams of gases entering said chamber toward one and toward the other of said walls, respectively, to produce alternate streams of gases concurrently swirling helically along said axis and alternately oppositely oscillating radially with respect to said walls.

3. The apparatus of claim 2, in which said first wall is the outer wall and extends from the exit end of said combustion chamber beyond said second wall, and further comprising a third wall concentric with and within said first and second walls and substantially axially co extensive with said first wall to form a bypass chamber with said second wall and a mixing chamber with the portion of said first wall beyond the exit end of said combustion chamber.

4. The apparatus of claim 3, further comprising a set of airfoils located between said third wall and said second wall to impart a swirling motion to gases flowing between said second and third walls helically about said axis.

5. In a gas turbine, first, second and third concentric closed curved walls forming an inner annular ilow channel between said first and second walls and an outer annular flow channel between said second and third walls, said first and third walls extending along a common axis from an entrance end to an exit end and said second wall extending along said common axis from said entrance end to a point intermediate said entrance and said exit ends, a first set of airfoils located in said inner channel and disposed to cause fluid flowing into said channel from said entrance end to swirl helically about said common axis while flowing toward said exit end, and a lamehoider located in said outer fiow channel adjacent said entrance end and comp-rising a plurality of separator plates mounted between said second and said third walls, substantially normal to said walls, symmetrically disposed about said central axis, and inclined at an angle to said central axis to cause fluid flowing into said outer channel from said entrance end to swirl helically about said common axis while flowing toward said exit end, the number of said plates being such that the distances between them are of the same order of magnitude as the distance between said second and third walls, and a second of pairs of confronting airfoils, one pair for each space between adjacent separator plates, each pair being mounted between a different pair of adjacent separator plates and aligned to form a channel diverting gases flowing therethrough away from a direction parallel to said common axis, alternate pairs of airfcils of said second set being oppositely aligned to alternately divert flow towards said second and towards said third wall, each channel of said fiameholder terminating blufiiy to form 'blufif bodies obstructing a portion of the area between said plates and said second and third walls of the same order of magnitude as the exit flow area of said fiameholder in the direction of iiow from said entrance end to said exit end.

6. In a combustion gas generator, first, second and third concentric cylindrical. walls, said second wall being intermediate said first and third walls and said first wall being Within said second wall, said first and third walls extending along a common axis from an entrance end to an exit end, said second wall extending along said axis from said entrance end to a first point between said entrance and exit ends, a flameholder located at the entrance end of the annulus formed by said second and third walls, said flnmeholder comprising means extending along said annulus from said entrance end to a second point between the entrance end and said first point and partitioning said annulus into a set of How passages having a total exit area of the same order of magnitude as one-half the exit area of the annulus and shaped to direct gases flowing from said entrance end toward said exit end into a net swirl helically about said axis and in local oscillations about the axes of net fiow from the passages.

7. The apparatus of claim 5, in which said partitioning means comprises a set of an even number of adjacent counterrotating vortex generators.

8. The apparatus of claim 6, in which said partitioning means comprises means forming an array of alternately radially outwardly and radially inwardly directed flow passages.

9. The apparatus of claim 6, further comprising vanes located in the annulus formed by said first and second walls and extending at angles to said common axis to direct gases flowing from said entrance to said exit end into a net swirl helically about said common axis in the same sense and at the same angle as the net sense and angle of swirl produced by said fiarneholder.

10. The apparatus of claim 5!, in which said partitioning means comprises a set of an even number of adjacent counterrotating vortex generators.

can.

11. The apparatus of claim 9, in which said partition- References Cited ing means comprises means forming an array of alter- UNITED STATES PATENTS 2223 1;; outwardly and radlally mwardly dlvergmg 2,689,457 9/1954 Kruppe 12. The apparatus of claim 9, further comprising 5 ggggfg g i lohglson et 60 39'74 means for supplying air under pressure to the entrance 8 61 "-i 2592 4 ends of the annuli formed by said walls, means for sup- 8 96 so tau at a 60 39'7 X plying fuel to the entrance end of the outer annulus, FOREIGN PATENTS means for igniting mixed air and fuel leaving said flame- 811,392 5 1959 Great Britain holder, and turbine means driven by the mixed gases 10 leaving said exit end. JULIUS E. WEST, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,373,562 March 19, 1968 Alex F. Wormser It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 7, line 44, for "radially projected" read cross sectional Signed and sealed this 8th day of July 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR.

Images