System for injecting a mixture of air and fuel into a turbomachine combustion chamber

1. A system for injecting a mixture of air and fuel into a turbomachine combustion chamber, comprising:

a fuel injector and a Venturi positioned downstream of the injector, coaxial therewith, the Venturi comprising an interior surface delimiting a premixing chamber in which fuel is mixed with a stream of air taken from an external space and passing through a primary swirler positioned upstream of the Venturi,

wherein the Venturi comprises an internal annular air-flow cavity, the cavity being connected by air inlet ducts to the external space and by air outlet ducts to the premixing chamber, the air outlet ducts opening onto the interior surface of the Venturi so as to prevent the deposition of soot and the formation of coke on the surface,

wherein the Venturi comprises, at its upstream end, an annular rim extending radially outwards and separating the primary swirler from a secondary swirler for the passage of a second stream of air, the annular cavity extending as far as the rim of the Venturi,

wherein the Venturi is formed of two annular components of substantially L-shaped cross section which are fitted coaxially one inside the other and are joined together by brazing or by welding, the first and second components between them delimiting the annular airflow cavity,

wherein the first component extends upstream of and inside the second component, the first component having a substantially radial upstream annular wall which is connected at its internal periphery to a substantially cylindrical downstream wall in which the air outlet ducts are formed,

wherein the second component comprises a substantially radial upstream annular wall which is connected at its internal periphery to a substantially cylindrical downstream wall, the radial wall being fixed at its external periphery to an external periphery of the radial wall of the first component, and its cylindrical wall being fixed at its downstream end to a downstream end of the cylindrical wall of the first component, and

wherein at least part of the air inlet ducts run substantially radially with respect to an axis of the injector and are formed at the external periphery of the radial wall of one or each component and/or run substantially parallel to the axis of the injector and are formed through the vanes of the secondary swirler and the radial wall of the second component.

2. The injection system according to claim 1 , wherein the annular cavity of the Venturi has a substantially L-shaped cross section.

3. The injection system according to claim 1 , wherein the air outlet ducts are inclined in the axial and circumferential direction with respect to the axis of the injector, in the same direction as the vanes of the primary swirler.

4. The injection system according to claim 3 , wherein the axial angle of inclination of each outlet duct formed between an axis of the duct and the axis of the injector ranges between about 10 and 40°, the angle being measured in a plane passing through the axis of the injector.

5. The injection system according to claim 3 , wherein the circumferential angle of inclination of each outlet duct, formed between an axis of the duct and a plane passing through the axis of the injector, ranges between about 50 and 75°, the angle being measured in a plane perpendicular to the axis of the injector.

6. The injection system according to claim 1 , wherein mouths of the air outlet ducts are positioned uniformly about the axis of the injector and are split into 1, 2, 3 or 4 annular rows spaced axially apart.

7. The injection system according to claim 1 , comprising between 10 and 30 air inlet ducts and between 10 and 30 air outlet ducts.

8. A turbomachine comprising an injection system according to claim 1 .

9. A Venturi for a system for injecting a mixture of air and fuel into a turbomachine combustion chamber, comprising:

an interior surface comprising an interior surface delimiting a premixing chamber and exhibiting a throat; and

an annular rim, at an upstream end of the Venturi, extending radially outwards,

wherein the Venturi is formed of first and second annular components of substantially L-shaped cross section which are fixed coaxially one inside the other and which between them delimit an internal air-flow cavity which is connected by air inlet ducts to an external space and by air outlet ducts to the premixing chamber, the first annular component extending upstream of and inside the second component and comprising a substantially radial upstream annular wall which is connected at its internal periphery to a substantially cylindrical downstream wall in which the air outlet ducts are formed, the outlet ducts being connected at one of their ends to the internal cavity and opening at the other of their ends onto the interior surface, the second component comprises a substantially radial upstream annular wall which is connected at its internal periphery to a substantially cylindrical downstream wall, the radial wall being fixed at its external periphery to an external periphery of the radial wall of the first component, and its cylindrical wall being fixed at its downstream end to a downstream end of the cylindrical wall of the first component, and at least one of the annular components comprising the air inlet ducts which are connected at one of their ends to the internal cavity, and

wherein at least part of said air inlet ducts run substantially radially with respect to an axis of an injector and are formed at an external periphery of the radial wall of one or each annular component, and/or run substantially parallel to an axis of the Venturi and are formed through a radial wall of the second annular component.