Humidity compensation for combustion control in a gas turbine engine

A gas turbine engine (12) wherein combustion conditions are controlled as a function of the humidity of the ambient air (36) in order to ensure stable, emission-compliant performance over a range of ambient conditions. The pilot fuel fraction supplied to a dual mode combustor (10) may be controlled to be responsive to the relative humidity or the specific humidity of the ambient air. Humidity may be measured directly or it may be calculated as a function of other temperature and pressure measurements. A fuel system (44) is controlled by a controller (46) having as inputs the signals from one or more of a relative humidity sensor (62), a barometric pressure sensor (56), a wet bulb temperature sensor (58) and a dry bulb temperature sensor (60).