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A lean direct injection fuel nozzle for a gas turbine is disclosed which includes a radially outer main fuel delivery system including a main inner air swirler defined in part by a main inner air passage having a radially inner wall with a diverging downstream surface, an intermediate air swirler ra

A lean direct injection fuel nozzle for a gas turbine is disclosed which includes a radially outer main fuel delivery system including a main inner air swirler defined in part by a main inner air passage having a radially inner wall with a diverging downstream surface, an intermediate air swirler radially inward of the main inner air swirler for providing a cooling air flow along the downstream surface of the radially inner wall of the main inner air passage, and a radially inner pilot fuel delivery system radially inward of the intermediate air swirler.

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What is claimed is: 1. A lean direct injection fuel nozzle for a gas turbine comprising: a) a radially outer main fuel delivery system including a main fuel path, and a main inner air swirler defined in part by a main inner air passage having a radially inner wall with a diverging, conically expand

What is claimed is: 1. A lean direct injection fuel nozzle for a gas turbine comprising: a) a radially outer main fuel delivery system including a main fuel path, and a main inner air swirler defined in part by a main inner air passage having a radially inner wall with a diverging, conically expanding downstream surface, wherein the main fuel path has a downstream exit located in a conically expanding part of the main inner air passage; b) an intermediate air swirler radially inward of the main inner air swirler for providing a cooling air flow along the conically expanding downstream surface of the radially inner wall of the main inner air passage; and c) a radially inner pilot fuel delivery system radially inward of the intermediate air swirler and including a converging pilot air cap terminating upstream from the conically expanding downstream surface of the main inner air passage for confining an outer air stream of the pilot fuel delivery system passing inboard of the pilot air cap, wherein a terminal edge of the converging pilot air cap is exposed to the outer air steam of the pilot fuel delivery system. 2. A lean direct injection fuel nozzle as recited in claim 1, wherein the main fuel delivery system is of a pre-filming air-blast type and includes a main fuel swirler radially outward of the main inner air swirler, a main outer air swirler radially outward of the main fuel swirler, and an outer air cap radially outward of the main outer air swirler. 3. A lean direct injection fuel nozzle as recited in claim 2, wherein a terminal edge of the radially inner wall of the main inner air passage is located downstream from a terminal edge of the outer air cap. 4. A lean direct injection fuel nozzle as recited in claim 2, wherein a terminal edge of the radially inner wall of the main inner air passage is located upstream from a terminal edge of the outer air cap. 5. A lean direct injection fuel nozzle as recited in claim 2, wherein the main inner air swirler includes swirl vanes oriented at angle of between about 20° to about 50° relative to a central axis of the fuel nozzle. 6. A lean direct injection fuel nozzle as recited in claim 5, wherein the swirl vanes of the main inner air swirler are oriented to impart swirl in one of a clockwise direction and a counter-clockwise direction relative to a central axis of the fuel nozzle. 7. A lean direct injection fuel nozzle as recited in claim 2, wherein the main outer air swirler includes swirl vanes oriented at angle of between about 45° to about 60° relative to a central axis of the fuel nozzle. 8. A lean direct injection fuel nozzle as recited in claim 7, wherein the swirl vanes of the main outer air swirler are oriented to impart swirl in one of a clockwise direction and a counter-clockwise direction relative to a central axis of the fuel nozzle. 9. A lean direct injection fuel nozzle as recited in claim 7, wherein the swirl vanes of the main outer air swirler are configured as axial swirl vanes. 10. A lean direct injection fuel nozzle as recited in claim 2, wherein a swirl direction of the main outer air swirler is co-rotational with respect to a swirl direction of the main inner air swirler. 11. A lean direct injection fuel nozzle as recited in claim 2, wherein a swirl direction of the main outer air swirler is counter-rotational with respect to a swirl direction of the main inner air swirler. 12. A lean direct injection fuel nozzle as recited in claim 1, wherein the pilot fuel delivery system is of a simplex air-blast type, which includes a pressure swirl atomizer. 13. A lean direct injection fuel nozzle as recited in claim 12, wherein the pilot fuel delivery system includes a pilot outer air swirler, and a pilot fuel swirler radially inward of the pilot outer air swirler. 14. A lean direct injection fuel nozzle as recited in claim 1, wherein the pilot fuel delivery system is of a pre-filming air-blast type. 15. A lean direct injection fuel nozzle as recited in claim 14, wherein the pilot fuel delivery system includes a pilot outer air swirler, a pilot fuel swirler radially inward of the pilot outer air swirler, and a pilot inner air swirler extending along a central axis of the fuel nozzle. 16. A lean direct injection fuel nozzle as recited in claim 15, wherein the pilot inner air swirler includes a set of swirl vanes oriented to impart swirl in one of a clockwise and a counter-clockwise direction relative to a central axis of the fuel nozzle. 17. A lean direct injection fuel nozzle as recited in claim 16, wherein the pilot outer air swirler includes a set of swirl vanes oriented to impart swirl in one of a clockwise and a counter-clockwise direction relative to a central axis of the fuel nozzle. 18. A lean direct injection fuel nozzle as recited in claim 17, wherein the swirl vanes of the pilot outer air swirler are configured as axial swirl vanes. 19. A lean direct injection fuel nozzle as recited in claim 17, wherein a swirl direction of the pilot outer air swirler is co-rotational with respect to a swirl direction of the pilot inner air swirler. 20. A lean direct injection fuel nozzle as recited in claim 17, wherein a swirl direction of the pilot outer air swirler is counter-rotational with respect to a swirl direction of the pilot inner air swirler. 21. A lean direct injection fuel nozzle as recited in claim 1, wherein the intermediate air swirler includes a set of swirl vanes oriented at an angle sufficient to ensure that the cooling air remains attached to the diverging, conically expanding downstream surface of the radially inner wall of the main inner air passage. 22. A lean direct injection fuel nozzle as recited in claim 21, wherein the intermediate air swirler includes a set of swirl vanes oriented at an angle of between about 35° to about 60° relative to a central axis of the fuel nozzle. 23. A lean direct injection fuel nozzle as recited in claim 21, wherein the swirl vanes of the intermediate air swirler are oriented to impart swirl in one of a clockwise direction and a counter-clockwise direction relative to a central axis of the fuel nozzle. 24. A lean direct injection fuel nozzle as recited in claim 23, wherein a swirl direction of the intermediate air swirler is co-rotational with respect to a swirl direction of the main inner air swirler. 25. A lean direct injection fuel nozzle as recited in claim 23, wherein a swirl direction of the intermediate air swirler is counter-rotational with respect to a swirl direction of the main inner air swirler. 26. A lean direct injection fuel nozzle for a gas turbine comprising: a) a radially outer main fuel delivery system having an outer air cap and including: i) a main outer air swirler radially inward of the outer air cap; ii) a main fuel swirler radially inward of the main outer air swirler; and iii) a main inner air swirler radially inward of the main fuel swirler, and defined in part by a main inner air passage having a radially inner wall with a diverging, conically expanding downstream surface, wherein the main fuel swirler includes a downstream exit located in a conically expanding part of the main inner air passage; b) an intermediate air swirler radially inward of the main inner air swirler for providing a cooling air flow along the conically expanding downstream surface of the radially inner wall of the main inner air passage; and c) a radially inner pilot fuel delivery system having a converging pilot air cap radially inward of the intermediate air swirler for confining an outer air stream of the pilot fuel delivery system passing inboard of the pilot air cap, wherein the pilot air cap terminates upstream from the conically expanding downstream surface of the main inner air passage and a terminal edge of the converging pilot air cap is exposed to the outer air stream of the pilot fuel delivery system. 27. A lean direct injection fuel nozzle as recited in claim 26, wherein the pilot fuel delivery system is of a simplex air-blast type, which includes a pressure swirl atomizer. 28. A lean direct injection fuel nozzle as recited in claim 27, wherein the pilot fuel delivery system includes a pilot outer air swirler, and a pilot fuel swirler radially inward of the pilot outer air swirler. 29. A lean direct injection fuel nozzle as recited in claim 26, wherein the pilot fuel delivery system is of a pre-filming air-blast type. 30. A lean direct injection fuel nozzle as recited in claim 29, wherein the pilot fuel delivery system includes a pilot outer air swirler, a pilot fuel swirler radially inward of the pilot outer air swirler, and a pilot inner air swirler extending along a central axis of the fuel nozzle. 31. A lean direct injection fuel nozzle as recited in claim 26, wherein a terminal edge of the radially inner wall of the main inner air passage is located downstream from a terminal edge of the outer air cap. 32. A lean direct injection fuel nozzle as recited in claim 26, wherein a terminal edge of the radially inner wall of the main inner air passage is located upstream from a terminal edge of the outer air cap. 33. A lean direct injection fuel nozzle as recited in claim 26, wherein a terminal edge of the radially inner wall of the main inner air passage is coincident with a terminal edge of the outer air cap.