Patent Publication Number: US-2012031098-A1

Title: Fuel nozzle with central body cooling system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     In general, the field of invention relates to fuel nozzles which are used in combustors of turbine engines. 
     2. Description of Related Art 
     Typically, a plurality of fuel nozzles will be mounted on a combustor cap located at the upstream end of the combustor. The fuel nozzles will deliver fuel into a flow of compressed air to create a fuel-air mixture which is then burned in the combustor. 
     Because the fuel nozzles are located just upstream of the location where the fuel-air mixture is burned, the outer surfaces and downstream ends of the fuel nozzles are subjected to high temperature combustion products. These high temperatures can damage the fuel nozzles 
     BRIEF SUMMARY OF THE INVENTION 
     According one embodiment of the present invention, there is provided a fuel nozzle for a turbine engine comprising: a generally cylindrical shaped outer housing; a cylindrical shaped cooling shroud that concentrically surrounds a downstream portion of an exterior of the outer housing. The cooling shroud comprises: a cylindrical shaped outer wall; a downstream end wall that joins a downstream end of the outer wall to the downstream end of the outer housing; and a cylindrical shaped dividing wall positioned concentrically between the outer wall of the cooling shroud and the exterior of the outer housing, wherein a gap is exists between a downstream end of the dividing wall and the downstream end wall of the cooling shroud. A plurality of air inlets are located at the upstream side of the cooling shroud, wherein the air inlets admit a flow of cooling air into an annular space between the exterior surface of the outer housing and an inner surface of the dividing wall. The cooling air flow travels in a downstream direction to a downstream end of the cooling shroud, turns 180° around the downstream end of the dividing wall and enters an annular space between the outer surface of the dividing wall and an inner surface of the outer wall of the cooling shroud. The flow of cooling air then travels in an upstream direction to an upstream end of the cooling shroud. A plurality of air outlets are located at the upstream end of the cooling shroud, and the air outlets direct the flow of cooling air from the annular space between the outer surface of the dividing wall and the inner surface of the outer wall into a space located inside the outer housing of the fuel nozzle. 
     According to another embodiment of the present invention, there is provided cooling shroud for cooling an exterior of a cylindrical fuel nozzle of the turbine engine comprising: a generally cylindrical outer wall; a downstream end wall configured to join a downstream end of the outer wall to a downstream end of the outer housing of a fuel nozzle, and a generally cylindrical shaped dividing wall. The dividing wall is positioned concentrically inside the outer wall, and the dividing wall is configured to be located between the outer wall of the cooling shroud and the outer housing of a fuel nozzle. A gap is maintained between a downstream end of the dividing wall and the downstream end wall of the cooling shroud. A plurality of air inlets are located at the upstream side of the cooling shroud such that when the cooling shroud is mounted onto a fuel nozzle, the air inlets admit a flow of cooling air into an annular space between an outer housing of the fuel nozzle and an inner surface of the dividing wall. In addition, a plurality of air outlets are located at the upstream end of the cooling shroud. When the cooling shroud is mounted on a fuel nozzle, the air outlets direct a flow of cooling air from an annular space between the outer surface of the dividing wall and an inner surface of the outer wall of the cooling shroud into openings in the outer housing of the fuel nozzle. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a fuel nozzle for a turbine engine which includes a cooling shroud; 
         FIG. 2  is a cross-sectional view of he downstream end of a fuel nozzle with a cooling shroud; 
         FIG. 3  is a cross-sectional view of the downstream end of a fuel nozzle with a cooling shroud; 
         FIG. 4  is a perspective cross-sectional view illustrating the downstream end of a cooling nozzle with a cooling shroud; 
         FIG. 5  is a perspective cross-sectional view illustrating the downstream end of a fuel nozzle with a cooling shroud; 
         FIG. 6  is a perspective cross-sectional view of the downstream end of a fuel nozzle with a cooling shroud; 
         FIG. 7  is a perspective cross-sectional view of the downstream end of a fuel nozzle with a cooling shroud; 
         FIG. 8  is a perspective view illustrating the air inlets and air outlets of a cooling shroud of a fuel nozzle; 
         FIG. 9  is a perspective cross-sectional view illustrating how air enters the air inlets of a cooling shroud of a fuel nozzle; and 
         FIG. 10  is a perspective cross-sectional view illustrating how the cooling air outlets of a cooling shroud direct cooling air out of the cooling shroud and into the fuel nozzle. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A fuel nozzle for use in a turbine engine which includes a cooling shroud is illustrated in  FIG. 1 . As shown therein, the fuel nozzle includes a generally cylindrical central nozzle section  102  which is located inside an outer housing  104 . A flow of air indicated by arrows  110  enters the upstream end of the fuel nozzle. The air entering the fuel nozzle travels through an annular space located between the outer wall of the central nozzle section  102  and an inner wall of the outer housing  104 . The flow of air passes fuel vanes  106  which deliver fuel into the flow of air. The fuel vanes  106  may also be angled with respect to the longitudinal axis of the nozzle, which causes the air and fuel mixture to swirl within the fuel nozzle, and this swirling can help of mix the fuel and the air. 
     Once fuel has been delivered into the air, the fuel-air mixture, which is indicated by arrows  112 , continues to pass in a downstream direction through the annular space between the outside of the central nozzle section  102  and the inner wall of the outer housing  104 . The fuel-air mixture then ultimately exits the downstream end of the fuel nozzle. 
     A similar fuel-air mixture may also pass down the central portion of the central nozzle section  102  and exit a tip  108  of the central nozzle section  102 . This fuel-air mixture will then also exit the downstream end of the fuel nozzle. 
     Typically, the fuel-air mixture will be burned just downstream of the fuel nozzle. In addition, in some combustors, adjacent fuel nozzles can be located at different positions along the length of the combustor. As a result, a first fuel nozzle located further upstream than a second fuel nozzle can create a flame that is immediately adjacent the exterior of the second downstream nozzle. As a result, the outer sides and downstream ends of the fuel nozzles are subjected to extremely high operating temperatures. For these reasons, it is desirable to cool the outer sides and at least the downstream end of the fuel nozzle to help prevent the fuel nozzle from being damaged by the high combustion temperatures. 
       FIG. 1  illustrates that a cooling shroud  120  is mounted around a downstream end of the fuel nozzle  100 . As will be explained in greater detail below, the cooling shroud acts to circulate a flow of cool air around the exterior of the downstream end of the fuel nozzle. The cooling airflow is ultimately delivered into the interior of the outer housing  104 . As a result, the flow of air used to cool the end of the nozzle ultimately joins the fuel-air mixture passing down the annular space between the outer side of the central nozzle section and the inner side of the outer housing. 
       FIG. 2  shows an enlarged view of downstream end of a fuel nozzle where a cooling shroud  120  is mounted around the exterior of the downstream end of the fuel nozzle.  FIG. 3  provides an enlarged view of the downstream end of the fuel nozzle, including the cooling shroud. 
     As illustrated in  FIGS. 2 and 3 , the cooling shroud includes an outer wall  122  and a dividing wall  124 . The dividing wall  124  is positioned concentrically inside the outer wall  122 . As a result, the dividing wall  124  is positioned between the outer housing  104  of the fuel nozzle and the outer wall  122  of the cooling shroud. Also, an end wall  128  of the cooling shroud  120  is joined to the end of the outer wall  104  of the fuel nozzle. 
     At the upstream end of the cooling shroud  120 , a plurality of air inlets admit a flow of air which passes down the length of the exterior of the fuel nozzle. This flow of cooling air is illustrated by arrow  121  in  FIG. 2 . 
     The flow of cooling air passes through the air inlets of the cooling shroud and into an annular space located between the exterior surface of the outer housing  104  of the fuel nozzle and an inner surface of the dividing wall  124 . The cooling air passes down the length of the exterior of the fuel nozzle to help cool the downstream end of the fuel nozzle. As illustrated in  FIG. 3 , the flow of cooling air reaches the downstream end of the cooling shroud and turns 180° around the downstream edge of the dividing wall  124 . This flow of cooling air is identified by the arrow  130  appearing in  FIG. 3 . 
     The flowing of cooling air then passes in the upstream direction along an annular space between the outer surface of the dividing wall  124  and an inner surface of the outer wall  122  of the cooling shroud. The flow of cooling air travels in the upstream direction to the upstream end of the cooling shroud. 
     The flow of cooling air which has traveled back to the upstream end of the cooling shroud then turns 90° and passes through air outlets of the cooling shroud into an interior of the fuel nozzle. This flow of cooling air is illustrated with the arrow identified with reference numeral  123  in  FIG. 2 . The flow of cooling air then mixes with the air-fuel mixture located within the fuel nozzle. Thus, the air used to cool the downstream end of the nozzle ultimately exits the downstream end of the fuel nozzle where it is burned in the combustor. 
     As illustrated in  FIG. 3 , in some embodiments the downstream end of the dividing wall  124  may include an enlarged portion  126 . This enlarged portion may be rounded, as illustrated in  FIG. 3 . The enlarged, rounded end portion  126  accelerates the flow speed of the air flow as the air makes a 180° turn at the downstream end of the cooling shroud. The increased flow speed helps to increase the efficiency of the cooling provided by the flow of air at the downstream end of the cooling shroud. 
     As illustrated in  FIG. 4 , a plurality of effusion cooling holes  132  can be located in the end wall  128  of the cooling shroud  120 . The effusion cooling holes  132  would allow a small portion of the cooling airflow to escape from an interior of the cooling shroud to an exterior of the cooling shroud. This effusion cooling would help to cool the downstream end wall  128  of the cooling shroud. 
     As illustrated in  FIG. 5 , in some embodiments the dividing wall  124  may include a plurality of impingement cooling holes  140 . The impingement cooling holes  140  would allow the flow of cooling air located between the exterior surface of the outer housing  104  and the inner surface of the dividing wall  124  to pass through the impingement cooling holes  140  and into the annular space between the outer surface of the dividing wall  124  and the inner surface of the outer wall  122  of the cooling shroud. 
     In embodiments which include the impingement cooling holes  140 , the downstream end of the dividing wall  124  may include a curved end portion  144  which turns 90° inward to join the outer wall  104  of the fuel nozzle. The impingement cooling holes  140  in this curved end portion  144  of the dividing wall  124  may also help to direct the flow of cooling air against the inside of the end wall  128  of the cooling shroud to help cool the end wall  128 . 
     In some embodiments, projections may be formed on the inner side of the outer wall  122  of the cooling shroud. For instance,  FIG. 6  illustrates an embodiment where a plurality of ring shaped projections  150  are located on the inside of the outer wall  122  of the cooling shroud. The ring shaped projections  150  would be formed around the circumference of the inner side of the outer wall  122 . These ring shaped projections  150  would help to induce turbulence in the flow of cooling air, which may lead to a greater cooling effect. 
     In the embodiment illustrated in  FIG. 7 , a plurality of projections  160  are also formed on the inside of the outer wall  122  of the cooling shroud. However, these projections  160  extend in the longitudinal direction to help guide the flow of cooling air toward the upstream end of the cooling shroud. The projections  160  may also act as cooling fins to help increase the cooling effect provided by the flow of cooling air. 
     The air inlets and air outlets located at the upstream end of the cooling shroud are illustrated in greater detail in  FIGS. 8-10 . The air inlets  170  would extend in the longitudinal direction of the fuel nozzle and the cooling shroud. The air inlets  170  would act to emit a flow of air which is passing down the exterior of the fuel nozzle into the annular space located between the exterior surface of the outer housing  104  of the fuel nozzle and an inner surface of the dividing wall  124  of the cooling shroud.  FIG. 9  is a perspective sectional view which provides another view of the air inlets  170  which emit air into the cooling shroud. 
     The air outlets  172  act to convey a flow of cooling air from the annular space between the outer surface of the dividing wall  124  and the inner surface of the outer wall  122  of the cooling shroud into a space located inside the outer housing  104  of the fuel nozzle. Thus, the air outlets would generally extend in a radial direction toward the inside of the fuel nozzle.  FIG. 10  provides another illustration of how the air outlets  172  convey air down to the interior of the fuel nozzle. 
     In some embodiments, each air inlet  170  would be located between a pair of adjacent air outlets  172 . Thus, the air inlets  170  and air outlets  172  alternate with one another around the exterior circumference of the cooling shroud. 
     In some embodiments, the air outlets  172  would extend in the radial direction from the annular space between the outer surface of the dividing wall  124  and the inner surface of the outer wall  122  of the cooling shroud. In other alternate embodiments, a central axis of the air outlets is angled with respect to the radial direction. In this instance, the air exiting the cooling shroud through the air outlets  172  and entering the interior of the fuel nozzle would tend to swirl around the interior of the fuel nozzle. This could be advantageous in helping to mix the air and fuel present in the interior of the fuel nozzle. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.