Optimizing an anti-coke film in an injector system for a gas turbine engine

1. An injection system comprising:

a fuel injector of main axis;

an annular expansion ring coaxial about said injector, said ring presenting holes distributed around the main axis and opening out into an upstream face of said ring, the holes allowing air to pass towards a zone downstream from said ring;

a primary swirler coaxial about the same axis as said ring and placed downstream from said injector; and

a venturi placed downstream from said primary swirler,

wherein said ring includes a conical annular groove that converges downstream, that is open downstream, and that has said holes opening out into an upstream portion of said annular groove, an axis of each of the holes making an angle relative to the main axis that is strictly greater than an angle made by a generator line of a cone defining said annular groove relative to said main axis, such that the air exiting said holes impacts against an inner wall of the annular groove, the inner wall of said annular groove being closer to the main axis,

wherein the air leaves said annular groove in a direction that is substantially parallel to a flow direction of air leaving said primary swirler, such that these two air flows do not mix, and

wherein said expansion ring comprises an axial cylindrical portion with a radially inner surface in contact or nearly in contact with an outer surface of said injector.

2. An injector system according to claim 1 , wherein said expansion ring comprises a radial wall that extends a downstream end of said cylindrical portion radially outwards, and wherein said annular groove opens out downstream at the location where said cylindrical portion joins said radial wall.

3. An injector system according to claim 1 , wherein each of said holes presents a circumferential angle of inclination relative to said main axis that imparts movement about the main axis to the air passing through the holes.

4. An injector system according to claim 3 , wherein the circumferential angle of inclination of said holes lies in the range 20° to 45° relative to a radial direction.

5. An injector system according to claim 1 , wherein said holes have a diameter lying in the range 0.8 mm to 1.5 mm.

6. An injector system according to claim 1 , wherein the number of said holes lies in the range 10 to 20.

7. An injector system according to claim 1 , wherein a height of said annular groove lies in the range 1.5 mm to 3 mm.

8. An injector system according to claim 1 , wherein the air exiting from said holes in the ring impacts against the inner wall of the annular groove in a location situated within an upstream first third of the annular groove.

9. An injector system according to claim 1 , wherein said primary swirler possesses primary holes through which air penetrates into the zone situated downstream from said injector.

10. An injector system according to claim 1 , wherein said venturi possesses a converging portion that converges downstream, and wherein a generator line of a cone defining said annular groove makes an angle relative to said main axis that is equal to or greater than an angle made by said converging portion of the venturi relative to said main axis, such that the air exiting from said annular groove does not impact against the converging portion of the venturi.

11. A combustion chamber provided with an injector system according to claim 1 .

12. A turbomachine including a combustion chamber according to claim 11 .

13. An injector system according to claim 1 , wherein said annular groove forms a continuous cavity circumferentially about the main axis.