Patent Publication Number: US-6668541-B2

Title: Method and apparatus for spraying fuel within a gas turbine engine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 09/597,631, filed Jun. 20, 2000 now abandoned; which is a divisional of U.S. patent application Ser. No. 09/132,455, filed Aug. 11, 1998, now U.S. Pat. No. 6,125,627, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to a method and apparatus for spraying fuel within a gas turbine engine, especially for spraying fuel within an afterburner of a jet engine. However, certain applications for the present invention may be outside of this field. 
     Some gas turbine engines have a need for increased thrust. One method of increasing thrust includes the injection and burning of fuel downstream of the low pressure turbine of the engine, in a method known variously as reheat, augmentation, or afterburning. Two features of the augmentor of a gas turbine engine are the fuel spraybar assemblies and flameholders, the spraybars spraying fuel into the flowpath of the engine, and the flameholders stabilizing the flame in the engine. Another feature of the afterburner is the augmentation fuel control system which should be capable of fuel metering from very low to very high fuel flow rates. 
     There is a continuing need for improvements to afterburning within gas turbine engines. The present invention provides novel and unobvious methods and apparatus for improvements to afterburners. 
     SUMMARY OF THE INVENTION 
     One embodiment of the present invention includes an apparatus including a gas turbine engine. The gas turbine engine has an afterburning portion for burning fuel. The apparatus also includes a fuel spraybar for spraying fuel within the afterburning portion, the fuel spraybar having a radially extending member for spraying fuel and a first lateral member. The radial member has two sides and the first lateral member is located on a first side of the radial member. The first lateral member is capable of spraying fuel in a generally radial direction. 
     One object of one form of the present invention is to provide an improved apparatus for spraying fuel into a gas turbine engine. 
     Related objects and advantages of the present invention will be apparent from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional schematic of a gas turbine engine according to one embodiment of the present invention. 
     FIG. 2 is an elevational end view of the gas turbine engine of FIG. 1 as taken along line  2 — 2  of FIG.  1 . 
     FIG. 3 is a partial enlargement of FIG. 1 in the vicinity of a spraybar assembly. 
     FIG. 4 is an elevational side view of the spraybar assembly of FIG.  1 . 
     FIG. 5 is a cross-sectional view of the spraybar assembly of FIG. 4 as taken along line  5 — 5  of FIG.  4 . 
     FIG. 6 is a cross-sectional view of the apparatus of FIG. 5 as taken along line  6 — 6  of FIG.  5 . 
     FIG. 7 is a cross-sectional view of the apparatus of FIG. 5 as taken along line  7 — 7  of FIG.  5 . 
     FIG. 8 is a cross-sectional view of the apparatus of FIG. 5 as taken along line  8 — 8  of FIG.  5 . 
     FIG. 9 is an enlarged portion of the view of FIG. 2 showing portions of two fuel spraybar assemblies. 
     FIG. 10 is an elevational end view of the gas turbine engine of FIG. 1 showing a portion of another embodiment of a spraybar assembly in accordance with the present invention. 
     FIG. 11 is a side elevational view of the portion of the spraybar assembly of FIG. 10 that protrudes into the flowpath. 
     FIG. 12 is a view of the apparatus of FIG. 11 as taken along line  12 — 12  of FIG.  11 . 
     FIG. 13 is a cross-sectional view of the apparatus of FIG. 12 as taken along line  13 - 13  of FIG.  12 . 
     FIG. 14 is a cross-sectional view of the apparatus of FIG. 12 as taken along line  14 — 14  of FIG.  12 . 
     FIG. 15 is a cross-sectional view of the apparatus of FIG. 12 as taken along line  15 — 15  of FIG.  12 . 
     FIG. 16 is a cross-sectional view of the apparatus of FIG. 12 as taken along line  16 — 16  of FIG.  12 . 
     FIG. 17 is a cross-sectional view of the apparatus of FIG. 12 as taken along line  17 — 17  of FIG.  12 . 
     FIG. 18 is an enlarged portion of an end elevational view showing portions of two of the fuel spraybar assemblies of FIG.  10 . 
     FIG. 19 is an elevational end view of a gas turbine engine showing a third embodiment of the present invention. 
     FIG. 20 is an elevational end view of the gas turbine engine of FIG. 1 as taken along line  2 — 2  of FIG. 1 depicting thermal thrust vectoring. 
     FIG. 21 is an elevational end view of the gas turbine engine of FIG. 1 as taken along line  2 — 2  of FIG. 1 depicting thermal thrust vectoring. 
     FIG. 22 is an elevational end view of the gas turbine engine of FIG. 1 as taken along line  2 — 2  of FIG. 1 depicting thermal thrust vectoring. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
     FIG. 1 is a cross-sectional schematic of a gas turbine engine  40 . Engine  40  includes a compressor section  42 , a turbine section  44 , and an augmentor for afterburning portion  46 . Afterburning portion  46  includes a fuel spraybar assembly  50  that introduces fuel into flowpath  47  for burning and release of heat within augmentor  46 . Flowpath  47  includes gases that have exited through turbine exit vanes  51  and has an outer periphery generally established by inner casing  62 . A convergent nozzle  48  accelerates gas within flowpath  47  to sonic velocity in the vicinity of nozzle throat  154 . In some embodiments, the present invention includes a divergent section  156  located aft of throat  154 . Divergent section  156  can increase the velocity of gas exiting the engine if the flow is sonic in the vicinity of throat  154 . 
     In some embodiments of the present invention, engine  40  includes a fan section  54  which provides air to both compressor  42  and bypass duct  56 . Air within bypass duct  56  flows past the plurality of spraybar assemblies  50  and past an afterburner liner  52 , and ultimately mixes with gases within flowpath  47 . In some embodiments of the present invention there is a moveable variable bypass door  58  that permits a portion of the air in bypass duct  56  to mix with flowpath  47  in the general vicinity of spraybar assembly  50 . In some embodiments of the present invention a portion of air from bypass duct  56  mixes with flowpath  47  upstream of fuel spraybar assemblies  50 . Spraybar assemblies  50  are fastened to an outer casing  60  of engine  40 , span across bypass  56 , and protrude through inner casing  62 . Inner casing  62  and liner  52  are air cooled to reduce their temperatures and include features such as segmentation for management of stresses from thermal gradients. 
     An aerodynamically shaped rear bearing cover  53  is located at the end of turbine section  44 . Cover  53  provides for the expansion of flowpath  47  toward centerline  49  of engine  40  as the flowpath gases exit from vane  51 . In the preferred embodiment of the present invention, spraybar assemblies  50  are located circumferentially around cover  53 , so as to permit a shortening of the overall length of afterburning portion  46 . A shorter overall length of afterburning portion  46  reduces the weight and cost of portion  46 , and also reduces circumferential mixing and radial mixing of gases within flowpath  47  flowing within afterburning portion  46 . Cover  53  is preferably a cooled structure that includes features for management of stresses induced by thermal gradients, although in some embodiments of the present invention it may be acceptable that cover  53  be fabricated from a high temperature material and include, for example, a thermal barrier coating. Located within cover  53  and also included within bearing assembly are a rear turbine bearing  55   b  and an intermediate bearing cover  55   a.  In some embodiments of the present invention spraybar assemblies  50  are located aft of bearing cover  53  so as to reduce the heat load into cover  53 . 
     FIG. 2 is a view of the gas turbine engine  40  of FIG. 1 as taken along line  2 — 2  of FIG. 1. A plurality of spraybar assemblies  50  are shown aft of a plurality of turbine exit vanes  51 , and generally surrounding turbine rear bearing cover  53 . Each spraybar assembly  50  includes a radial member  100  with an outermost end  100   a  directed away from centerline  49  and proximate to inner casing  62 . Each radial member  100  also includes an innermost end  100   b  directed toward centerline  49 . Each assembly  50  also includes a first lateral member  102  extending in a generally circumferential direction from one side of innermost end  100   b,  and a second lateral member  104  extending in a generally circumferential direction opposite to that of first lateral member  102 . Radial member  100  and lateral members  102  and  104  are shaped generally in the form of a “T”, with lateral members  102  and  104  preferably being in an arc. It is preferable that radial member  100  and lateral members  102  and  104  be integrally cast from a high temperature material. However, the present invention also contemplates separate fabrication of members  100 ,  102 , and  104 , which would then be joined or fastened in a “T” shape in a manner known to those of ordinary skill in the art. Spraybar assemblies  50  are circumferentially spaced from one another such that the first lateral member  102  of one spraybar assembly  50  is directed toward a second lateral member  104  of an adjacent spraybar assembly  50 . 
     FIG. 3 is an enlargement of FIG. 1 in the vicinity of spraybar assembly  50 . Spraybar assembly  50  includes an upper body  101  that is fastened to outer casing  60 . Upper body  101  protrudes generally through bypass duct  56  and preferably includes cooling air inlet  122  for the introduction of air from bypass duct  56  into upper body  101  so as to cool radial member  100  and, in some embodiments lateral members  102  and  104 . The present invention also contemplates gas turbine engines that do not incorporate a bypass duct  56 . For those embodiments of the present invention it would be preferable to cool radial member  100  and lateral members  102  and  104  with a different source of cooling air, for example air bled from compressor section  42 . Spraybar assembly  50  also includes an exterior portion  120  which is coupled to one or more fuel manifolds (not shown) of engine  40 . 
     FIG. 4 is an elevational side view of a spraybar assembly. Fuel-handling exterior portion  120  of spraybar assembly  50  is in fluid communication with a plurality of fuel passageways  124  which provide fuel to radial arm  100  and lateral arms  102  and  104 . Fuel passageway  124   c  provides fuel to a plurality of lateral fuel spray passages  126  which spray fuel in a generally lateral direction within flowpath  47  such that the spray of fuel is generally perpendicular to centerline  49 . Cooling air inlet  122  provides cooling air from bypass duct  56  to a plurality of cooling air exhaust holes  128  located on both sides of radial member  100 . 
     FIG. 5 is a cross-sectional view of the spraybar assembly of FIG. 4 as taken along line  5 — 5  of FIG.  4 . Fuel passageway  124   b  is shown in fluid communication with a second set of lateral fuel spray passages  127 , such that the spray of fuel is generally perpendicular to centerline  49 . Forward cooling air channel  130  and aft cooling air channel  132 , both of which are in fluid communication with air inlet  122 , are arranged so as to exhaust cooling air through a plurality of exhaust holes  128  on radial member  100 . The flow of cooling air through radial arm  100  helps maintain the temperature of fuel within fuel passageways below a coking temperature and also generally maintains member  100  within acceptable temperature limits. In some embodiments of the present invention cooling air is also provided from channels  130  and  132  to lateral members  102  and  104 . 
     Radial member  100  includes a midplane  140  that is oriented at an angle  142  relative to center line  49  of engine  40 . Orienting midplane  140  at angle  142  is useful in some embodiments of the present invention to assist in the deswirling of gas in flowpath  47  that has exited vanes  51 . In other embodiments of the present invention midplane  140  may be parallel to center line  49 . 
     FIG. 6 is a cross-sectional view of the apparatus of FIG. 5 as taken along line  6 — 6  of FIG.  5 . Fuel passageway  124   b  is shown in fluid communication with second set of lateral fuel spray passages  127  and also upper radial fuel spray passages  134   b.  Passages  134   b  spray fuel in a direction generally perpendicular to centerline  49  and in a direction generally radially outward. 
     FIG. 7 is a cross-sectional view of the apparatus of FIG. 5 as taken along line  7 — 7  of FIG.  5 . Fuel passageway  124   c  is shown in fluid communication with first set of lateral fuel spray passages  126  and also first set of upper radial fuel spray passages  134   a.  Passages  134   a  spray fuel in a direction generally perpendicular to centerline  49  and in a direction generally radially outward. 
     FIG. 8 is a cross-sectional view of the apparatus of FIG. 5 as taken along line  8 — 8  of FIG.  5 . Fuel passageway  124   a  is shown in fluid communication with a plurality of lower radial spray passages  136  on the underside, or radially inward side, of lateral members  102  and  104 . 
     FIG. 9 is an enlarged portion of the view of FIG. 2 showing portions of two fuel spraybar assemblies. A portion of a first spraybar assembly  50 ′ is shown spaced circumferentially from a second spraybar assembly  50 ″. A first radial member  100 ′ protrudes past inner casing  62  into flowpath  47 . In one embodiment of the present invention fuel passageways  124   b′  and  124   c″  (not shown) are in fluid communication. Fuel has been provided to fuel passageway  124   b′,  and is shown spraying from second set of lateral fuel spray passages  127 ′ and upper radial fuel spray passages  134   b′.  Fuel has also been provided to fuel passageway  124   c″  of assembly  50 ″, and fuel is shown spraying from first sets of lateral fuel spray passages  126 ″ and upper radial fuel spray passages  134   a″.  The sprayed fuel is combusted within a circumferential combustion zone  108  which is bounded by radial member  50 ′, second lateral member  104 ′, first lateral member  102 ″, radial member  50 ″, and inner casing  62 . 
     In the embodiment of the present invention shown in FIG. 2, there are sixteen individual circumferential combustion zone segments  108 . Flowpath  47  of engine  40  within afterburning portion  46  is divided into a first outer annulus  107  and inner cylinder  109 . Inner casing  62  and the plurality of lateral members  102  and  104  define the outer and inner boundaries, respectively, of first outer annulus  107 . The plurality of lateral members  102  and  104  define a generally radial boundary of inner cylinder  109 . Radial members  100  further subdivide first outer annulus  107  into a plurality of spaced circumferentially extending combustion zone segments  108 . These segments  108  begin generally between adjacent spraybar assemblies  50  and extend axially along centerline  49  through augmentor  46 . There may be circumferential and radial mixing of the hot gases within the combusted segment  108  with cooler gases in adjacent segments or within inner cylinder  109 . There may be further mixing as the hot gases of the reheated segment  108  pass through convergent nozzle  48 . However, mixing is reduced because of the shorter overall length of afterburning portion  46 . 
     By subdividing outer annulus  107  of flowpath  47  into a plurality of circumferentially extending combustion zone segments it is possible to divide the operation of afterburning portion  46  into at least sixteen discrete levels of operation. Dividing of the operation of afterburner  46  into sixteen different levels of operation permits fine tuning of the level of thrust generated from engine  40 . This subdivision of flowpath  47  into a plurality of combustion zone segments  108  permits control of the operation of augmentor  46  and reduction in the complexity of the fuel metering system. 
     Establishing fluid communication from passageway  124   b  of one spraybar assembly  50  with fuel passageway  124   c  of an adjacent assembly permits propagation of combustion from a single circumferential zone segment  108  to another segment  108 . In some embodiments of the present invention it may also be useful to place in fluid communication fuel passageways  124   b  and  124   c  of a single spraybar assembly  50  such that combustion is propagated along both sides of radial member  100  of the particular assembly  50 . Providing fuel to passageway  124   a  results in combustion within inner cylinder  109 . As shown in FIG. 2 in cross hatch, providing fuel to a passageway  124   a  of a single spraybar assembly  50  results in combustion within a radial combustion zone  110 . In other embodiments of the present invention, fuel passageways  124   a,    124   b,  and  124   c  are in fluid communication. In still other embodiments of the present invention a plurality of fuel passageways  124   a,  or in one embodiment all fuel passageways  124   a,  are in fluid communication so as to result in more than seventeen discrete levels of afterburner operation. Passageways  124  may be brought into fluid communication in other ways as would be known to one of ordinary skill of the art. 
     In some embodiments of the present invention there is no need for a separate source of ignition for fuel sprayed into flowpath  47 . Lateral members  102  and  104  can be constructed so as to have surface temperatures high enough to support autoignition of fuel touching the surfaces of members  102  or  104 . Further, the junction of radial member  100  with lateral member  102  and  104  at nose  138  provides sufficient disruption and local deceleration of flowpath  47  so as to act as a flameholder. Nose  138  assists in stabilizing the combustion process within augmentor  46 . Thus, fuel can be sprayed from an individual spraybar assembly  50  without the necessity for that particular spraybar assembly to be located near an igniter. In addition, augmentor  46  can be operated without the expense and weight of separate flameholders downstream of spraybar assemblies  50  because of the flameholding of nose  138 . 
     Some embodiments of the present invention permit improved packaging of afterburning portion  46  that is possible with spraybar assembly  50 . The use of lateral arms  102  and  104  permit a reduction in the radial length of radial member  100  while retaining the ability to spray sufficient quantities of fuel into the engine into flowpath  47 . Thus, spraybar assembly  50  is relatively compact and does not extend deeply toward center line  49  of engine  40 . Spraybar assemblies  50  can thus be located in the general vicinity of bearing cover  53 , and not necessarily aft of cover  53 . The close proximity of assembly  50  to exit vanes  51  and bearing cover  53  permits a significant reduction in the overall length and weight of afterburning portion  46 . Also, the use of lateral members  102  and  104  for spraying of fuel results in fewer penetrations of casings  60  and  62 , thus reducing the complexity and increasing the strength of casings  60  and  62 . 
     Some embodiments of the present invention may also produce a shifting of the centerline of the engine thrust away from centerline  49  when there is combustion within one or more contiguous segments  108  and/or  110 , and no combustion within the segments  108  and/or  110  generally on the opposite side of augmentor  46 . This localized and asymmetric combustion increases gas temperature and gas velocity locally within flowpath  47 . This asymmetric profile of the exhaust gas results in an off-centerline thrust, or thermal thrust vectoring, as the gas is accelerated through nozzle  48 . By creating an asymmetry in combustion from top to bottom of the engine, it is possible to vector the thrust so as to apply a pitching moment to the engine and the vehicle. By creating an asymmetry in combustion from the right side to the left side of the engine, a side to side vectoring of thrust is created that applies a yawing moment to the engine and vehicle. Also, the combustion may be asymmetrically staged so as to apply combined pitching and yawing moments to the engine and vehicle. Thus, the present invention can provide thermal thrust vectoring to the engine and vehicle, and does not rely upon a complicated mechanical arrangement of actuators and movable nozzle flaps for thrust vectoring. 
     FIG. 20 depicts in cross-hatching a first portion  150   a  of flowpath  47  in which a first quantity of fuel is being sprayed by a plurality of spraybars  50 . A second quantity of fuel from a plurality of spraybars  50  is being sprayed within a second portion  152   a  of flowpath  47 . The second quantity of fuel is less than about one-half of the first quantity of fuel, and preferably is zero, such that no fuel is sprayed by spraybars  50  within second portion  152   a.    
     As shown in FIG. 20, fuel is being sprayed in first portion  150   a  of flowpath  47 , which is an arc equal to about 180° of flowpath  47  about geometric centerline  49 . Second portion  152   a  is the complementary portion of flowpath  47 , and is equal to about 180°. Because of this asymmetric distribution of fuel, the portion of the flowpath downstream of first portion  150   a  is hotter than the portion of flowpath  47  downstream of portion  152   a.  As flowpath  47  flows into throat  154  of nozzle  48 , the velocity of gases within flowpath  47  increase to sonic velocity. As the gases of flowpath  47  exit from throat  154  and pass into divergent section  156 , the sonic velocity gases accelerate to supersonic velocity. The hot gases downstream of portion  150   a  of flowpath  47  accelerate to higher velocity than the gases downstream of second portion  152   a.  The greater velocity of gases downstream of first portion  150   a  creates more thrust than the gases downstream of second portion  152   a.  Thus, the thrust centerline  158   a  of flowpath  47  shifts laterally away from the geometric center  49  of flowpath  47 , the difference between the first quantity of fuel and the second quantity of fuel causing the thrust of the engine to thermally vector. This shift of thrust centerline  158   a  creates a yawing moment on the engine and the vehicle. 
     FIG. 21 shows another embodiment of the present invention in which a first quantity of fuel is delivered or sprayed into a first portion  150   b  of flowpath  47 . A second quantity of fuel less than about half the first quantity, and preferably zero, is delivered into a second portion  152   b  of flowpath  47 . First portion  150   b  is generally centered about a vertical plane of symmetry of flowpath  47 . Because of the difference in the temperature of gases downstream of portion  150   b  and  152   b  as a result of the difference between the first quantity of fuel and the second quantity of fuel, thrust centerline  158   b  shifts vertically from geometric centerline  49 . This offset of the thrust centerline creates a pitching moment about the engine and vehicle. 
     FIG. 22 shows another embodiment of the present invention in which a first quantity of fuel is sprayed within a partial outer annulus of a first portion  150   c  of flowpath  47 . A second quantity of fuel is sprayed within second portion  152   c,  such that the second quantity of fuel is less than half the first quantity of fuel, and preferably zero fuel. First portion  150   c  extends over a portion of the top and left side of flowpath  47 . Thrust centerline  158   c  shifts both vertically and laterally so as to create a combined pitching and yawing moment on the engine and the vehicle. 
     As shown in FIGS. 20,  21  and  22 , the first portion of flowpath  47  into which a first quantity of fuel is delivered may be located within various areas within flowpath  47 . The first portion may include one or more circumferential combustion zone segments  108  as depicted in FIG. 22, one or more radial combustion zone segments  110  as shown in FIG. 21, or a combination of one or more circumferential and radial combustion zone segments as shown in FIG.  20 . In addition, the first portion may be located so as to produce yawing, pitching, or combined pitching or yawing moments. To achieve the maximum shifting of the thrust centerline away from the geometric centerline of the engine, it is preferable to introduce a first quantity of fuel that results in localized stoichiometric combustion, with no fuel introduced into the complementary second portion of the flowpath. The present invention also includes those embodiments in which a first quantity of fuel less than that needed for stoichiometric combustion is introduced, and in which the second quantity of fuel is non-zero. 
     FIG. 10 is an elevational end view of the gas turbine engine of FIG. 1 showing a portion of another embodiment of a spraybar assembly in accordance with the present invention. The use of the same numbers as previously used denotes elements substantially similar to those previously described. A plurality of radial members  200  from a plurality of spraybar assemblies  250  are shown extending through inner casing  62  into flowpath  47 . Each radial member  200  protrudes through casing  62  at an outermost end  200   a  and includes first and second lateral members  102  and  104  located generally at innermost end  200   b.  Intermediate of outermost end  200   a  and innermost end  200   b  are third and fourth lateral arms  202  and  204 , respectively. Third lateral member  202 , fourth lateral member  204  and radial member  200  meet at second nose  238 , nose  238  providing flameholding for locally combusted gases. 
     FIG. 11 is a side elevational view of the portion of spraybar assembly  250  that protrudes into flowpath  47 . Located between outermost end  200   a  and innermost end  200   b  of radial member  200  are a plurality of exhaust holes  128  which exhaust cooling air into flowpath  47 . A first set of lateral fuel spray passages  126  are located along radial member  200  between third lateral member  202  and first lateral member  102 . A third set of lateral fuel spray passages  226  are located between third lateral member  202  and outermost end  200   a.    
     FIG. 12 is a view of the apparatus of FIG. 11 as taken along line  12 — 12  of FIG.  11 . Fourth lateral member  204  is located along radial member  200  in a position generally intermediate of second lateral member  104  and outermost end  200   a.  Fourth lateral member  204  is generally opposite of and aligned with third lateral member  202 . Forward cooling air channel  130  and aft cooling air channel  132  are located within radial member  200  and provide cooling air to exhaust holes  128 . There are five fuel passageways  224  for providing a flow of fuel from the exterior portion of spraying assembly  250  and through the upper body. 
     FIG. 13 is a cross-sectional view of the apparatus of FIG. 12 as taken along line  13 — 13  of FIG.  12 . Fuel passageway  224   a  is shown in fluid communication with a plurality of lower radial fuel spray passages  136  along the radially innermost surface of lateral members  102  and  104 . 
     FIG. 14 is a cross-sectional view of the apparatus of FIG. 12 as taken along line  14 — 14  of FIG.  12 . Fuel passage  224   b  is shown in fluid communication with a third set of lateral fuel spray passages  226  located along radial member  200  and radially outward of lateral member  202 , and outward radial fuel spray passages  234   a  located along the radially outwardmost surface of lateral member  202 . 
     FIG. 15 is a cross-sectional view of the apparatus of FIG. 12 as taken along line  15 — 15  of FIG.  12 . Fuel passage  224   c  is shown in fluid communication with a fourth set of lateral fuel spray passages  227  located along radial member  200  and radially outward of lateral member  204 , and outward radial fuel spray passages  234   b  located along the radially outwardmost surface of lateral member  204 . 
     FIG. 16 is a view of the apparatus of FIG. 12 as taken along line  16 — 16  of FIG.  12 . Fuel passageway  224   d  is shown in fluid communication with first set of lateral fuel spray passages  126 , inner intermediate radial spray passages  236   a,  and outer radial fuel spray passages  134   a.  Spray passages  236   a  are located on third lateral member  202  and for spraying fuel in a generally radially inward direction. 
     FIG. 17 is a cross-sectional view of the apparatus of FIG. 12 as taken along line  17 — 17  of FIG.  12 . Fuel passageway  224   e  is shown in fluid communication with second set of lateral fuel spray passages  127 , inner intermediate radial spray passages  236   b,  and outer radial fuel spray passages  134   b.  Spray passages  236   b  are located on third lateral member  204  and are useful for spraying fuel in a generally radially inward direction. 
     FIG. 18 is an enlarged portion of a view similar to FIG. 9 showing portions of two fuel spray bar assemblies  250  useful with the present invention. A portion of a first spraybar assembly  250 ′ is shown spaced circumferentially from a second spraybar assembly  250 ″. A first radial member  200 ′ protrudes past inner casing  62  into flowpath  47 . In one embodiment of the present invention fuel passageways  224   c′  and  224   b″  (not shown) are in fluid communication. Fuel has been provided to fuel passageway  224   c′,  and is shown spraying from second set of lateral fuel spray passages  227 ′ and upper radial fuel spray passages  234   b′.  Fuel has also been provided to fuel passageway  224   b″  of assembly  250 ″, and fuel is shown spraying from first sets of lateral fuel spray passages  226 ″ and upper radial fuel spray passages  234   a″.  By providing fuel to passageways  224   c′  and  224   b″,  combustion occurs within an outer circumferential combustion zone  208   b  which is bounded generally by radial member  200 ′, second lateral member  204 ′, first lateral member  202 ″, radial member  200 ″, and inner casing  62 . 
     In the embodiment of the present invention shown in FIG. 18, there are sixteen inner circumferential combustion zone segments  208   a  and sixteen outer circumferential combustion zone segments  208   b.  Flowpath  47  of engine  40  within afterburning portion  46  is divided into an outer annulus  107  and inner cylinder  109 . Inner casing  62  and lateral members  102  and  104  define the outer and inner boundaries, respectively, of outer annulus  107 . Radial members  200  further subdivide first outer annulus  107  into a plurality of circumferentially extending combustion zone segments  208 . Lateral members  202  and  204  further subdivide each combustion zone segment  208  into outer zone segments  208   b  and inner zone segments  208   a.    
     FIG. 19 shows a third embodiment of the present invention in which a plurality of secondary radial members  300  are placed between adjacent spraybar assemblies  50 . Radial members  300  include spray passages for spraying fuel in a generally circumferential direction within a combustion zone segment  108 . 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.