Flameless combustion systems for gas turbine engines

1. A flameless burner for a gas turbine engine comprising:

a) a burner body having a longitudinal axis, an upstream section and a downstream section, the upstream section of the burner body defining a primary swirl generating chamber and a throat downstream thereof, the primary swirl generating chamber having an air swirler associated therewith and adapted and configured to receive compressor discharge air through the air swirler and thereby form a recirculation zone that entrains downstream combustion product gases toward the burner body;

b) a plurality of primary fuel injectors, each having an inwardly facing exit orifice defined in a diffuser of the burner body downstream of the throat; and

c) at least one secondary fuel injector having a downstream facing exit orifice defined downstream of the throat,

wherein the primary and secondary fuel injectors are configured and adapted for issuing fuel into a recirculation zone of entrained combustion product gases.

2. A flameless burner as recited in claim 1 , wherein the air swirler of the upstream section of the burner body is a radial air swirler.

3. A flameless burner as recited in claim 2 , further comprising a second radial air swirler defined between the primary swirl generating chamber and the downstream section of the burner body.

4. A flameless burner as recited in claim 2 , further comprising a conical air swirler defined in the downstream section of the burner body proximate the primary swirl generating chamber.

5. A nameless burner as recited in claim 1 , wherein the downstream facing exit orifice of the at least one secondary fuel injector is defined between the primary swirl generating chamber and the diffuser.

6. A flameless burner for a gas turbine engine comprising:

a) a burner body having an upstream section, a downstream section, and a throat portion defined between the upstream and downstream sections, the upstream section defining a primary swirl generating chamber having a first air swirler associated therewith, wherein the primary swirl generating chamber is configured to receive compressor discharge air through the first air swirler and thereby form a recirculation zone that entrains downstream combustion product gases toward the burner body;

b) a diverging diffuser section defined in the downstream section of the burner body with a second air swirler defined in the diffuser section for injecting a swirling flow of compressor discharge air into the diffuser section;

c) a plurality of primary fuel injectors operatively connected to the burner body, each primary fuel injector having an exit orifice defined in an inward facing surface of a diffuser in the downstream section of the burner body; and

d) at least one secondary fuel injector having a downstream facing exit orifice defined downstream of the throat,

wherein the primary and secondary fuel injectors are configured and adapted for issuing fuel into a recirculation zone of entrained combustion product gases.

7. A flameless burner as recited in claim 6 , wherein the first air swirler is a radial swirler, and wherein the second air swirler is a conical swirler.

8. A flameless burner as recited in claim 6 , wherein the upstream, downstream, and throat portions of the burner body form a converging, diverging interior profile that converges proximate the throat portion.

9. A flameless burner as recited in claim 6 , wherein the first and second air swirlers are both radial swirlers.

10. A flameless burner as recited in claim 6 , wherein each of the primary fuel injectors includes an atomizing fuel nozzle configured to issue a jet of fuel that is co-injected with compressor discharge air to promote thorough fuel and air mixing prior to auto-ignition.

11. A flameless burner for a gas turbine engine comprising:

a) a burner body having a longitudinal axis, an upstream section and a downstream section, the upstream section of the burner body defining a throat and a primary swirl generating chamber having an air swirler associated therewith, wherein the primary swirl generating chamber is adapted and configured to receive compressor discharge air through the air swirler and thereby form a recirculation zone that entrains downstream combustion product gases toward the burner body, the downstream section defining a diffuser; and

b) at least one fuel injector having a downstream facing exit orifice defined downstream of the throat between the primary swirl generating chamber and the diffuser for issuing fuel into recirculated combustion product gases.