Airblast fuel injector

An airblast fuel injector for a fuel spray nozzle of a gas turbine engine, the injector having, in order from radially inner to outer, a coaxial arrangement comprising:

• an inner air swirler passage;
• an annular fuel passage;
• an annular outer air swirler passage, and
• an annular shroud air swirler passage;
• wherein the airblast fuel injector is configured to atomise fuel exiting the annular fuel passage into a spray by way of surrounding swirling air exiting the inner, outer and shroud air passages;
• the airblast fuel injector further comprising:
• an annular shroud having an inner surface profile, which defines a radially outer side of the shroud air passage relative to the overall axial direction of flow through the airblast fuel injector, the annular shroud inner surface profile having a convergent section defining a convergent portion of the shroud air passage, the convergent section of the annular shroud inner surface profile being followed by a divergent section of the annular shroud inner surface profile, the transition from the convergent section of the annular shroud inner surface profile to the divergent section of the annular shroud inner surface profile forming a first inwardly directed annular nose, the divergent section of the annular shroud inner surface profile having a first conic angle;
• and
• an annular wall having an outer surface profile and an inner surface profile, the annular wall outer surface profile defining a radially inner side of the annular shroud air passage relative to the overall axial direction of flow through the airblast fuel injector, the annular wall inner surface profile defining a radially outer side of the outer air passage relative to the overall axial direction of flow through the airblast fuel injector, the annular wall outer surface profile having a convergent section defining the convergent portion of the annular shroud air passage, the convergent section of the annular wall outer surface profile being followed by an outwardly turning section which faces across the annular shroud air passage to the first inwardly directed annular nose;
• wherein:
• on longitudinal cross-sections through the injector the outwardly turning section maintains a substantially constant width for the shroud air passage as the shroud air passage turns around the first inwardly directed annular nose;
• relative to the overall axial direction of flow through the airblast fuel injector, the annular wall inner surface profile has a convergent section defining a convergent portion of the outer air passage, the convergent section of the annular wall inner surface profile being followed by a divergent section of the annular wall inner surface profile, the transition from the convergent section to the divergent section of the annular wall inner surface profile forming a second inwardly directed annular nose, the divergent section of the annular wall inner surface profile having a second conic angle;
• and
• the first conic angle is the same as the second conic angle.