Systems and apparatus relating to downstream fuel and air injection in gas turbines

1. A gas turbine engine that includes:

an interior flowpath defined through a combustor and a turbine;

an aft frame forming an interface between the combustor and the turbine, the aft frame comprising a rigid structural member that circumscribes the interior flowpath, wherein the aft frame includes an inner wall that defines an outboard boundary of the interior flowpath;

a circumferentially extending fuel plenum formed through the aft frame;

outlet ports formed through the inner wall of the aft frame, the outlet ports being configured to connect the fuel plenum to the interior flowpath;

air inlet ports formed through an outer wall of the aft frame; and

tubes that traverse the fuel plenum;

wherein:

each of the tubes is configured so that a first end connects to one of the air inlet ports and a second end connects to one of the outlet ports;

the outlet ports formed on the inner wall of the aft frame comprise: a) air outlet ports, which are configured to connect to one of the tubes; and b) fuel outlet ports, which are configured to connect to the fuel plenum;

each of the fuel outlet ports is positioned in proximity to one of the air outlet ports; and

the air outlet ports are configured having a circular shape and the fuel outlet ports are configured having a ring shape formed about one of the air outlet ports.

2. The gas turbine engine of claim 1 , wherein the aft frame includes between 6 and 20 of the outlet ports;

wherein the fuel plenum comprises a fuel inlet port, which is formed through the outer wall of the aft frame and fluidly connects the fuel inlet port to a fuel supply.

3. The gas turbine engine of claim 2 , wherein the fuel plenum is configured to circumscribe the interior flowpath;

wherein the outlet ports are circumferentially spaced about the interior flowpath;

further comprising a pre-mixer upstream of the fuel inlet port, the pre-mixer comprising an air supply and the fuel supply as inputs.

4. The gas turbine engine of claim 1 , wherein the outlet ports of the aft frame comprise a first injection stage of a downstream injection system that includes two injection stages;

wherein a second stage of the downstream injection system is axially spaced forward or aft from the first stage along a longitudinal axis of the interior flowpath;

wherein the first stage and the second stage of the downstream injection system each includes multiple injectors configured to inject an air and fuel into the interior flowpath.

5. The gas turbine engine of claim 4 , wherein the combustor includes a primary air and fuel injection system toward a forward end, wherein the interior flowpath includes a primary combustion zone defined by a surrounding liner and, immediately aft of the liner, the interior flowpath includes a transition zone defined by a surrounding transition piece;

wherein the transition piece is configured to fluidly couple the primary combustion zone to the turbine, the transition piece having a shape that transitions from a cylindrical cross-sectional shape of the liner to an annular cross-sectional shape of the turbine, wherein an aftward end of the transition piece comprises the aft frame;

wherein the aft frame comprises a first connecting means by which the aft frame connects to the transition piece and a second connecting means by which the aft frame connects to the turbine; and

wherein the aft frame comprises an annular cross-sectional shape.

6. The gas turbine engine of claim 1 , wherein each of the outlet ports is configured flush relative to a surface of the inner wall of the aft frame.

7. The gas turbine engine of claim 1 , wherein each of the outlet ports is configured to jut out from the inner wall of the aft frame so that the outlet port extends into the interior flowpath.

8. The gas turbine engine of claim 1 , wherein the outlet ports are canted relative to a reference direction that is perpendicular to a combustion flow through the interior flowpath.

9. The gas turbine engine of claim 8 , wherein the cant of the outlet ports comprises between 0° and 45° toward a downstream direction of the combustion flow.

10. The gas turbine engine of claim 1 , wherein the air inlet ports are configured to fluidly connect a region exterior to the aft frame to the fuel plenum.

11. A gas turbine engine that includes:

an interior flowpath defined through a combustor and a turbine;

an aft frame forming an interface between the combustor and the turbine, the aft frame comprising a rigid structural member that circumscribes the interior flowpath, wherein the aft frame includes an inner wall that defines an outboard boundary of the interior flowpath;

a circumferentially extending fuel plenum formed through the aft frame;

outlet ports formed through the inner wall of the aft frame, the outlet ports being configured to connect the fuel plenum to the interior flowpath;

air inlet ports formed through an outer wall of the aft frame; and

tubes that traverse the fuel plenum;

wherein:

each of the tubes is configured so that a first end connects to one of the air inlet ports and a second end connects to one of the outlet ports;

the outlet ports formed on the inner wall of the aft frame comprise: a) air outlet ports, which are configured to connect to one of the tubes; and b) fuel outlet ports, which are configured to connect to the fuel plenum;

each of the fuel outlet ports is positioned in proximity to one of the air outlet ports; and

each of the tubes comprises a solid structure configured such that a fluid moving through the tube is isolated from fluid moving through the fuel plenum.