US2510645A

US2510645A - Air nozzle and porting for combustion chamber liners

Info

Publication number: US2510645A
Application number: US705866A
Authority: US
Inventors: Kenton D Mcmahan
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1946-10-26
Filing date: 1946-10-26
Publication date: 1950-06-06
Anticipated expiration: 1967-06-06
Also published as: FR962862A; CH265334A; GB635946A

Description

June 6, 1950 D. MGMAHAN 2,510,645

AIR NOZZLE AND PORTING FOR COMBUSTION CHAQIBER mums Filed Oct. 26, 1946 g 'G C) Irwventor: Ken ton D. Mc M ah an,

His Attorrwey.

Patented June 6, 1950 AIR NOZZLE AND PORTING FOR COMBUSTION CHAMBER LINERS Kenton D. McMahan, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application October 26, 1946, Serial No. 705,866

8 Claims.

This invention relates to ombustion chambers or combustors for generating hot gases under pressure, as for use in thermal powerplants such as gas turbines. More specifically, the invention relates to an improvement in the Nerad type combustor, described generally in patent application Serial No. 501,106, filed September 3, 1943, in the name of Anthony J. Nerad, now abandoned, also a continuation-in-part Serial No. 750,- 015, filed May 23, 1947.

The Nerad combustor is so designed that high velocity jets of combustion supporting fluid are directed in an exactly radial direction into the combustion space from inlet ports in a substantially cylindrical liner, which defines the combustion space. By proper location and dimensioning of the ports, a characteristic flow path 'is obtained which includes a tore or smoke ring vortex at the closed end of the liner, the establishment and maintenance of which is essential to eflicient operation of the combustor. A most important factor affecting the tore is the uniformity with which air is supplied to the ports in the liner. The afore-mentioned Nerad application describes various ways to secure the required uniformity of air supply. This problem is aggravated to a high degree when the air supply approaches the closed or dome end of the liner in an unsymmetrical manner, perhaps the worst condition being that in which the approach velocity is at right angles to the axis of the liner. In building a gas turbine powerplant with the components so arranged that this approach angle could not be avoided, it was found impossible to make a Nerad type combustor operate properly because of the extreme non-uniformity of air flow around the liner.

Accordingly, an object of the invention is to provide an improved pressurized combustor of the Nerad type which is substantially insensitive to variations in the direction from which the combustion air approaches the air inlet ports, and which gives more stable combustion characteristics with uniform temperature distribution and a lower over-all pressure drop through the combustor.

Another object is to provide means for insuring a satisfactory flow of air to the inlet openings in the end dome and the liner of the combustor.

A further object is to provide an improved liner for a Nerad combustor which will operate .efficiently regardless of variations in the angle at which the combustion air approaches the inlet ports of the liner.

A still further object is to provide an improved I Referring now to Fig. 1, my combustor assembly comprises a thin-walled cylindrical member I open at either end. At one end the cylinder l is provided with a flange secured by suitable threaded fastenings 2 to a corresponding flange of an inlet elbow or air adapter 3. While the inlet elbow 3 may be formed as a casting, it is shown in Fig. 1 as fabricated from thin sheet metal provided with a boss 4 defining a threaded opening coaxial with the cylindrical casing l. The elbow 3 constitutes an inlet conduit through which air under pressure enters from a suitable source, such as a compressor (not shown), as indicated by the arrow 5.

For introducing fluid fuel into the combustion space a spray nozzle is provided, as indicated at 6. This nozzle may be of any suitable type. Where the fuel used is a liquid such as kerosene or gasoline, the so-called duplex nozzle may be used, as described in patent application Serial No. 622,604, filed October 16, 1945, in the names of Charles D. Fulton and David C. Ipsen. Such nozzles require two supply conduits I and 8. It should be understood that many other types of nozzle may also be used; and the specific details of the spray nozzle are not material to an understanding of the present invention. Asshown in Fig. 1, the nozzle tip 9 projects into the inlet elbow 3 coaxial with the casing I, and has a portion threadedly engaging the central. opening in boss 4. The nozzle 6 discharges the fluid fuel in the form of a hollow cone, indicated diagrammatically at 30 in Fig. 1.

Supported coaxially in the cylindrical outer casing I is an inner liner indicated generally at Hi. This comprises a generally cylindrical but preferably somewhat tapered casing having its smaller end adjacent the inlet elbow 3. The construction of the inner liner may be seen by referring to Fig. 2 in conjunction with Fig. 1. It is formed by punching a plurality of longitudinal rows of combustion air inlet ports ll, the precise proportions and arrangement of which is specifled more particularly in the above-mentioned Nerad application. Between adjacent rows of combustion air ports II are longitudinal rows of nozzles l2, formed by striking the metal of the liner outwardly as shown in Fig. 1 so as to define cooling air inlet nozzles arranged to admit air in the manner indicated by the arrows l3 in Fig. 1. This cooling air l3 forms a thin continuous film of pure comparatively cool air flowing over the inner surface of the liner it so as to keep hot products of combustion and incompletely burned fuel particles from contact with the relatively cool metal of the liner. This arrangement prevents deposition of carbon particles as described in the above-mentioned Nerad application. At the discharge end of the liner, there is provided a row of spaced struck-out portions or "dimples" ll which serve a purpose noted hereinafter. Parallel to the discharge edge of the liner and spaced intermediate the dimples I4 and the last circumferential row of combustion air inlets II is a row of plain circular ports IS, the purpose of which will also be noted hereinafter.

The liner, formed as shown in Fig. 2, is rolled upto definea somewhat tapering cylinder as in Fig. 1, the side edges It being secured together by suitable means, as for instance seam-welding.

In accordance with my invention, each of the combustion air inlet ports ii is provided with a short nozzle ll projecting radially outward from the liner. The arrangement of these nozzles is indicated in Fig. 1. and a single nozzle is shown to an enlarged scale in Fig. 3. The nozzles may advantageously be secured to the liner by welding to a struck-out flange 22 provided around the edge of each port ll.

Research studies made to improve the basic form of the Nerad combustor, and to adapt it to many different gas turbine powerplants of varying configuration and characteristics, have shown that the Nerad combustion chamber, in its very simplest form, is somewhat sensitive to changes in the direction from which the air supply approaches the inner liner. For most efiieient and successful'operation of this type of combusto it is essential that the combustion air entering the combustion space defined within the liner l through the ports ll shall form discrete jets with their axes approaching very closely to the radial direction. In other words, it is desired that the air inlet ports I I produce jets having their axes substantially in a plane normal to the longitudinal axis of the liner ll, the axes of the jets from any given circumferential row of ports I i meeting at the axis of the liner.

When the configuration of the powerplant permits the air discharged from the compressor to be conducted to the combustion chamber so as to approach the inner liner in a substantially axial direction, then the problem of supplying combustion air uniformly to allthe ports H is comparatively simple. 0n the other hand, when the arrangement of the powerplant requires that the combustion air approach the combustor at a 90 degree angle to the axis of the combustor, as represented in Fig. 1, or in some other non-symmetrical manner, then special measures must be taken to insure that proper distribution of the air is obtained. If the supply of combustion air to the ports H is not uniform, then the combustion fllciency decreases, the temperature distribution of the hot gases becomes non-uniform, resulting in hot spots which greatly shorten the length of life of the liner and other parts, and other undesirable characteristics appear.

Accordingly, an important object of the invention is to provide means for stabilizing the direction of the combustion air jets entering the combustion space within the liner Ill through the ports H. I have found that this may be achieved by providing, the nozzles ll extending a straight cylindrical discharge portion and a well-rounded entrance portion. It is desirable that the discharge edge is of the nozzle lie in a plane exactly normal to the axis I! of the nozzle. Likewise, the axis iii of the nozzle must be normal to the axis of the liner, as indicated in Fig. 1. The radius of curvature of the nozzle inlet may advantageously be of the order of one quarter the inside diameter d of the nozzle. It will be apparent that this nozzle has a contracting inlet portion, and a non-expanding discharge portion. This is important, since it is desired to produce a high velocity jet of good penetrating power.

A considerable amount of research has been done to determine the effect of changing the proportions of the nozzle. This work has shown that the length of the nozzle It must be of the order 01' of the inside diameter d. While increasing the length of the nozzle beyond this value does no harm from an aerodynami standpoint, neither does it make any appreciable improvement; and it has the serious disadvantage of increasing the required diameter of the combustor as well as the weight. I have found that with nozzles proportioned as described, the angle at which the fluid approaches the nozzle may vary from zero degrees to 90 degrees without causing the discharge angle to deviate more than perhaps two degrees. In Fig. 3 the "approach angle is identified as the acute angle a which the approach velocity vector 20 forms with the axis IQ of the nozzle. The discharge angle is defined as the acute angle b which the leaving velocity vector 2| forms with the axis l9.

As described in the above-mentioned Nerad application, it is particularly important that the first circumferential row of ports I l adjacent the fuel nomle end of the combustor produce stable discrete combustion air jets meeting exactly at the center of the liner, in order that the primary portion of v the air will flow axially back towards the nozzle tip 9 in the manner indicated by the arrows 23 in Fig. 1. For this reason, it is essential that the first circumferential row of nozzles ll be very carefully proportioned as described above.

For succeeding circumferential rows of nozzles, the characteristics of the jets produced become less and less Therefore, it is possible to somewhat shorten the axial length of the nozzles below the minimum length specified above. Accordingly, in Fig. 1 the axial length of the air nozzles II decreases progressively from the closed or fuel nozzle end of the liner to the open discharge end. This arrangement is paraciaeec ticularly advantageous when the liner is ,some-' what tapered and is contained within a straight cylindrical outer housing, as in Fig. 1. It will be apparent that the tapered inner liner ill forms an annular air supply space with the cylindrical outer housing I which decreases progressively in' cross-sectional area along the length of the liner. This is desirable since the air entering the inlet ports causes the quantity flowing in the supply space 24 to progressively decrease along the length of the liner. By properly correlating the taper of the inner liner with the shape of the outer housing I, it is possible to keep the axial velocities of the air flow in the chamber 24 substantially uniform, thus further helping to insurev a uniform supply of air to the nozzles I'l by making the velocity of approach to each nozzle substantially uniform. Such uniformity is also desirable with respect to the cooling air l3 which enters the liner through the struck-out nozzle portions |2.

From the above, it will be apparent that the nozzles ll may all be of the same axial length, if desired, and if the increase in size and weight is not objectionable.

The inlet or fuel nozzle end of the liner I is closed by a hemispherical end dome 25. This may advantageously be arranged in accordance with application Serial 644,888, filed February 1, 1946 in the name of Walter L. Blatz. This dome structure has a central opening surrounded by an axially extending flange 26 adapted to slide snugly over the cylindrical nozzle tip 9. The dome is provided with one or more circumferential rows of nozzles formed by struck-out tongue portions 21. The function of these nozzles is to form a thin film of cooling and insulating air flowing over the inner surface of the dome 25 so as to prevent carbon deposition thereon. In other words, the nozzles 21 perform a somewhat similar function for the end dome 25 as is performed for the liner l0 by the cooling air nozzles l2. As described more fully in the above-mentioned Blatz application, the cooling and insulating air from the nozzles 21 flows radially inward in the manner of the arrows 28, across the exposed end surfaces of the nozzle tip 9, after which it reverses its direction and flows radially outward, as indicated by the arrow 29.

While the member 25 is referred to herein as a dome, I intend this term to include generally closures for the fuel nozzle end of the liner of shapes other than the hemispheral configuration shown in Fig. 1, for instance substantially flat disc members, as disclosed in the above-mentioned Nerad application.

Since the performance of the combustor is also materially affected by the uniformityof air flow into the primary combustion zone defined within the dome 25, it is important to insure a uniform supply of air to the end dome air inlet nozzles 21. To this end, I provide a suitably designed shroud member 3| which completely surrounds the end dome 25 and may be secured to the liner by a weld at 32. Of course with this arrangement, suitable U-shaped cutouts are required in the edge of the shroud so that it can be slipped over the small end of liner H) in the manner shown in Fig. 1, with the first circumferential rows of nozzles |'l fitting into the respective cutouts.

The shroud 3| is provided with a number of spaced air inlet ports 33. These are of such a size, location, and number that the air supplied through the inlet elbow or air adapter 3 will flow uniformly into the space or plenum chamber 33 defined between the end dome 25 and the shroud 38, with substantially no difference in pressure between the air in the elbow 3 and that in the plenum chamber 3i. Thus with substantially no pressure drop across the air inlet openings 33 in the shroud 3|, the velocities through these ports will be low and the air will have a chance to diffuse uniformly throughout the chamber 34.

In order to secure uniform distribution from the inlet elbow 3 to the annular plenum chamber 24 which supplies air to the combustion air nozzles l1 and the cooling air nozzles l2, it is also important that the outer configuration of the shroud 3| be matched to the configuration of the elbow 3 so that air entering in the direction of the arrow 5 will flow around the shroud 3| and enter the plenum chamber 2d uniformly around the circumference thereof. Because of the many variables involved, it is not possible to state specifically the precise dimensions and configuration required for the end dome shroud 3| and the inlet elbow 3. Analysis of the specific powerplant arrangement with which the combustor is to be used, supported by actual testing,

of models, is ordinarily required to ascertain the precise relative shapes required for the shroud and elbow, as well as the number, size and location of the shroud air inlet ports 33. I have however found that good results may be obtained with an arrangement substantially as shown in Fig. 1.

Aswill also be seen in Fig. l, th shroud 3| is provided with a central opening having a plurality of circumferentially spaced bosses 35 welded around the outside thereof. These bosses are adapted to be secured. by suitable threaded fastenings 36 to the ring 4 provided on the outer wall of elbow 3. It will be seen that the shroud 3| thus serves to support the inlet end of the liner Ill.

The plain circular ports l5 at the discharge end of liner III are trimmer holes, provided for the purpose of facilitating final balancing" of the combustioncharacteristics of the apparatus. It will be observed that the combustion inlet nozzles I1 and the cooling air nozzles l2 are arranged in an entirely uniform symmetrical manner. It may sometimes be found, when the combustor is built and tested, that the temperature distribution in the hot gases discharged from the liner is not exactly uniform. This may be corrected by suitable selection of the size. number, and location of the trimmer holes. since these holes have no associated nozzles corresponding to the nozzles ll, they may be readily punched in any size and arrangement found necessary to achieve completely uniform temperature distribution. The precise arrangement required can be determined only by analysis and testing of a model. 4

The discharge end of liner I0 is supported in the following manner. The downstream end of the outer casing l is provided with a flange adapted to be secured by suitable threaded fastenings 31 to a cooperating flange at the upstream end of a discharge elbow indicated generally at 38. Between the coupling flanges is arranged an annular member having an outer circumferential portion 39 disposed between the cooperating flanges. The inner circumferential portion of this annular member is spun or otherwise shaped to form an annular convolution 40 and a cylindrical portion 4| coaxial with the downstream end of the casing I and the discharge end of the liner ill. The dimples l4 formed in the discharge edge of liner H] are of such a radial height that the outside diameter of the discharge edge, measured over the dimples, is substantially the same or very slightly less than the inner diameter of the cylinder 4|. As will be obvious from a consideration of Fig. 1, the discharge end of liner I is thus supported in a longitudinally slidable manner within the ring 4i. Since the nozzle end of the liner is held rigidly by the threaded fastenings 36, the discharge edge of the liner in slides axially to a limited extent within the supporting ring 4!, as the length ,of the liner-changes as a result of differential thermal expansion between the hot liner and the comparatively cool outer casing I. The annular convolution provided in the support member permits differential thermal expansion between the inner cylindrical portion 4| and the cooler circumferential outer portion 39.

The cylinder 4| also serves to support the inner liner 42 of the discharge elbow assembly 38, in a manner which will be obvious from a consideration of Fig. 1. The outer casing 43 of the elbow assembly may be provided with a flange at the downstream end secured by threaded fastenings 44 or other suitable means to a cooperating flange of a conduit 45, which may for instance be the inlet to a gas turbine. The downstream end of the inner liner 42 is provided with a circumferential row of dimples 46 which may be similar in structure and are identical in function to the struck-out portions l4 provided in the discharge edge of the liner l0. A supporting

ring

39, 40, 4| supports the downstream end of the inner liner 42 and the upstream end of the liner a in the manner described above in connection with the discharge end of the liner l0 and the upstream end of liner 42.

The. supporting ring members for the respective inner liners are provided with a circumferential row of openings 41 through which cooling air flows from the plenum chamber 24. This coolant flowing through the annular space defined between the

respective members

42, 43 and 45, 45a serves effectively to cool the inner liners and to reduce the transmission of heat from the inner liners to the outer casings. It will be obvious that the combustion and cooling air flowing through the plenum chamber 24 likewise reduces the transmission of heat to the outer combustor housing I. It should also be noted that the dimples l4 cooperate with the supporting ring 4| to form a circumferential row of openings through which cooling air flows from plenum chamber 24 in the manner of the arrows 48 so as to form a cooling and insulating film over the inner surface of elbow liner 42. Similarly, some of the cooling air indicated by the arrows 49 flows through the spaces defined between the dimples 46 in the manner of the arrows 50 to form a cooling and insulating film on the inner surface of liner 45a.

The air inlet elbow 3 may be fabricated from sheet metal or cast of aluminum, magnesium, or other suitable metal. Ordinarily it is necessary that the inner combustor liner Ill and the end dome 25 as well as the conduit liners 42 and 45a be made of expensive temperature-resistlng alloys such as various stainless steels. I have found however that the marked improvement in uniformity of temperature and stability of gas flow achieved with my invention makes it possible to fabricate the liner III of low temperature metals, such as ordinary mild steel. The outer housings I, 43 and 45 may be made of ordinary inexpensive sheet metal stock.

While the invention has been described as used for burning a liquid fuel in air, it will be obvious that it may also be used for effecting similar heat-releasing reactions between other types of fluid reactants and other reaction supporting gases besides air. Therefore it is intended that the term fluid fuel" in the appended claims be interpreted to include all fluid reactants capable of being used in my combustor, and that the term air" be considered to include other reaction-supporting gases as well.

Experience with combustors embodying my invention, both in laboratory tests and in actual operation in a gas turbine powerplant, shows that it provides simple, comparatively light, yet very effective means for stabilizing the operation of a Nerad type combustor, producing uniformly efllcient combustion and temperature distribution over a wide range of operating conditions and having very little or no sensitivity to changes in the direction from which the air supply approaches the combustor. At the same time, my improved construction remains easy and comparatively cheap to manufacture. The arrangement of the combustor facilitates disassembly for easy inspection and servicing of the inner liners, which in a' gas turbine powerplant are usually the parts most subject to deterioration. My invention also provides a simple and effective method for supporting the various high temperature inner liners from the cooler outer housing members.

While the present invention has been described as an improvement in the combustor invented by Mr. A. J. Nerad, it will be obvious to those skilled in the art that it may also find application in other combustion devices operating at high pressures and with substantial pressure differentials across the liner defining the combustion space, the combustion supporting fluid being admitted with high spouting velocity through ports or nozzles the size and location of which needs be very carefully chosen in order to obtain a desired flow path within the reaction space. In any such combustor, the invention makes possible the accurate establishment of a jet having a precisely determined direction, and being insensitive to irregularities or unsyinmetricity of the flow of fluid approaching the liner.

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

1. In a fluid fuel combustor of the type having an elongated liner of circular cross-section tapering from a minor diameter at one end to a major diameter at the other end and defining a combustion space within and having a plurality of circumferentially spaced longitudinal rows of ports for admitting combustion air in discrete jets, a cylindrical outer housing enclosing the liner and spaced therefrom to define an air supply chamber decreasing progressively in crosssectional area from the smaller end of the liner towards the larger end, an end dome member closing the smaller end of the liner and having ports for admitting cooling air to the combustion space adjacent the closed end thereof, and means for admitting fluid fuel to the combustion space, the combination of non-expanding nozzle means associated with each of the combustion air inlet ports for stabilizing the direction of jet discharge into the liner, each of said nozzles having its axis normal to the axis of the liner and projecting from the inner surface of the liner radially outward into the air supply chamber, each of the nozzles in the circumferential row next adjacent the closed end of the liner having a rounded contracting inlet portion and an axial length of the order of five eighths the inner diameter of the nozzle, the axial length of the nozzles in succeeding circumferential rows decreasing progressively towards the discharge end of the liner whereby the spacing of the inlet ends of the nozzles from the outer housing provides unimpeded access of the air to the inlets, conduit means for supplying air to the supply chamber in an unsymmetrical, manner, and shroud means within said conduit and spaced therefrom and enclosing the end dome, said shroud being shaped to cooperate with said conduit to define a passage for directing air uniformly into the supply chamber and said shroud having ports foradmitting air uniformly to the cooling air ports of the end dome.

2. In a fluid fuel combustor of the type having an elongated liner of circular cross-section defining a combustion space Within and having a plurality of circumferentially spaced longitudinal rows of ports for admitting combustion air in discrete jets, an outer housing enclosing the liner and spaced therefrom to define an air supply chamber, an end dome member closing the inlet end of the liner and having ports for admitting cooling air to the combustion space, and means for supplying fuel to the combustion space adjacent the closed end thereof, the combination of nozzle means associated with each of the combustion air inlet ports adjacent the closed end of the liner for stabilizing the direction of jet discharge, each of said nozzles having its axis normal to the axis of the liner and projecting from the inner surface of the liner radially outward into the air supply chamber and beingof a length such that the air jet therefrom is discharged in a substantially radial direction into the combustion space regardless of the direction of fluid approach to the nozzle, conduit means for supplying air to the supply chamber, and shroud means within said conduit enclosing the end dome and spaced from the conduit and from the end dome, said shroud being shaped to cooperate with said conduit to define a passage for directing air uniformly into the supply chamher and said shroud having ports for admitting air uniformly to the cooling air ports of the end dome.

3. In a fluid fuel combustor of the type having a cylindrical outer housing spaced radially from an inner elongated liner of circular crosssection tapering from a minor diameter at one end to a major diameter at the other end and defining a combustion space within, said liner having a plurality of circ-umferentially spaced longitudinal rows of ports adapted to admit combustion air in discrete radial jets, and an end dome member closing the small end of the liner, the larger end being open for the dischar of hot products of combustion, the combination of non-expanding nozzle means associated with each of said ports for stabilizing the direction of jet discharge into the liner, each nozzle having a rounded contracting entrance and being arranged with its axis normal to the axis of the liner and extending radially outward from the inner surface of the liner, the nozzles adjacent the closed end of the liner having an axial length of the order of five-eighths the inner diameter of the nozzle, the remaining nozzles be- 10 ing of progressively shorter axial length toward the discharge end of the liner whereby the specing of the inlet ends of the nozzles from the outer housing provides unimpeded access of the air to said inlets.

4. In a fluid fuel combustor of the type having an elongated liner of circular cross-section tapering from a minor diameter at one end to a major diameter at the other end and-defining a combustion space within, said liner having a plurality of circumferentially spaced longitudinal rows of ports adapted to admit combustion air in discrete radial jets, and-an end dome member closing the small endof the liner, the larger end being open for the discharge of hot products of combustion, the combination of non-expanding nozzle means associated with each of said ports for stabilizing the direction of jet discharge into the liner, each nozzle being arranged with it axis normal to the axis of the liner and extending radially outward from the inner surface of the liner, the nozzles adjacent the closed end of the liner having rounded contracting entrances and an axial length of the order of five-eighths the inner diameter of the nozzle.

5. In a fluid fuel combustor of the type having a substantially cylindrical liner with a plurality of circumferentially spaced longitudinal rows of ports for admitting combustion air in radial discrete jets, the combination of non-expanding nozzle means associated with each port and extending radially outward from the inner surface of the liner for stabilizing the direction of jet discharge into the liner, the axes of said nozzles being normal to the axis of the liner, each nozzle having a rounded contracting entrance and an axial length of the order of five-eighths the inner diameter of the nozzle.

6. In a fluid fuel combustor of the type having a liner defining a combustion space and having a plurality of spaced openings adapted to admit combustion air in strong discrete jets the direction of which is important to establishment of a desired flow path inside the liner, the combination of separate non-expanding nozzle means associated with each opening and extending from the inner surface of the liner radially outward i'or stabilizing the direction of the jet discharged into the liner, each of the nozzles having a well rounded contracting entrance portion and a cylindrical discharge portion and an overall axial length of the order of five-eighths the inner diameter of the nozzle.

'7. In a fluid fuel combustor having an elongated liner of substantially circular cross-section defining a combustion space within, and an end dome member closing one end of the liner and having ports for the admission of air to the combustion space, the combination of walls defining an outer casing enclosing the liner and end dome and spaced from each to define therewith an air supply chamber, said walls also forming an inlet opening for receiving air under pressure, the combination of shroud means spaced from and enclosing said end dome and having ports adapted to supply air uniformly to the end dome ports at substantially the pressure ofthe air supplied to the inlet of said casing whereby the direction of the jets from the end dome ports is substantially unaffected by unsymmetricity or changes in the direction of approach of the air entering through said inlet opening.

8. In a combustion device of the type having an elongated liner of circular cross-section tapering from a minor diameter at one end to a major diameter at the other end and defining a combustion space within, said liner having a plurality of circumferentiaily spaced longitudinal rows of ports adapted to admit combustion air in discrete radial Jets, an end dome member closing the small end of the liner and having louvers for admitting jets of air, the larger end being open for the discharge of hot products of combustion, the combination of non-expanding nozzle means associated with said ports for stabilizing the direction of jet discharge into the liner, each nozzle having a well-rounded contracting entrance and a non-expanding discharge portion and extending radially outward from the inner surface of the liner, the nozzles adjacent the closed end of the liner having an overall axial length of the order of five-eighths the inner diameter of the nozzle, the remaining nozzles being of progressively shorter axial length toward the discharge end of the liner, shroud means spaced from and enclosing said end dome and having ports adapted to supply air uniformly to the end dome louvers, an outer cylindricalcasing surrounding the liner and spaced therefrom to define a combustion air supply chamber, the downstream end of the casing terminating in an edge portion substantially co-planar with the discharge edge of the open end of the liner, an air inlet adapter member secured to the upstream member defining a conduit for causing air to approach the dome end of the liner in a direction substantially at ninety degrees to the axis of the liner, means securing said shroud to said air adapter for supporting the inlet end of the liner assembly, and means slidably supporting the discharge end of the liner assembly from the outer casing, said means including an annular support member having an outer circumferential edge portion adapted to be secured to the downstream end of the outer casing, an inner supporting portion defining an inner cylindrical surface adapted to surround and slidably engage the outer surface of the discharge end of the liner, and an intermediate portion defining an annular convolution whereby diflerentiai thermal expansion between said inner and outer "circumferential portions may "occur without distortion of the liner end portion.

. KENTON D. MCMAHAN.

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

UNI'I'ED STATES PATENTS Number Name Date 1,696,668 Button Dec. 25, 1928 2,072,731 Crosby Mar. 2, 1937 2,398,654 Lubbock Apr. 16, 1946 2,475,911 Nathan July 12, 1949