Burner

A burner for a gas turbine engine, the burner comprising a radially inner pilot fuel flow passage surrounded by a radially outer main fuel flow passage, the main fuel flow passage being interposed between concentrically arranged radially inner and radially outer air flow passages such that a main fuel flow is separate from the radially inner and radially outer air flow passages,

• wherein the radially inner and outer air flow passages are in fluid communication with one another via at least one diverting passage at an upstream end of the burner,
• wherein the burner further comprises at least one control duct connectable to a reduced pressure/vacuum source for selectively reducing an air pressure in a vicinity of the at least one diverting passage such that air flow is selectively diverted from the radially inner air flow passage to the radially outer flow passage via the at least one diverting passage so as to allow a pilot fuel flow flowing through the inner pilot fuel flow passage and the main fuel flow to merge faster than when the air flow is not selectively diverted from the radially inner air flow passage to the radially outer flow passage,
• wherein the at least one control duct extends to a circumferentially-extending annular chamber, the circumferentially-extending annular chamber having at least one opening in the vicinity of the at least one diverting passage, and
• wherein the at least one opening is at or proximal an interface between the at least one diverting passage and the radially inner air flow passage.

A method of controlling a combustion cycle of a combustion system in a gas turbine engine, the combustion system comprising at least one burner having a radially inner pilot fuel flow and a radially outer main fuel flow, the radially outer main fuel flow being interposed between concentrically arranged radially inner and radially outer air flow passages such that the main fuel flow is separate from the radially inner and radially outer air flow passages, the method comprising selectively increasing air flow in the radially outer air flow passage relative to air flow in the radially inner air flow passage by diverting the air flow from the radially inner air flow passage to the radially outer air flow passage through at least one diverting passage provided in an upstream end of the at least one burner so as to allow the radially inner pilot fuel flow and the main fuel flow to merge faster than when the air flow in the radially outer air flow passage is not selectively increased, or selectively increasing the air flow in the radially inner air flow passage relative to the air flow in the radially outer air flow passage by diverting the air flow from the radially outer air flow passage to the radially inner air flow passage through the at least one diverting passage so as to allow the radially inner pilot fuel flow and the radially outer main fuel flow to remain separated longer than when the air flow is not selectively increased in the radially inner air flow passage.