A rotary injector (95, 222) comprising one or more radially-extending arms (93) provides for injecting fuel (12, 12.1, 12.4) into a combustion chamber (16). The combustion chamber (16) receives air (14) from locations upstream and down-stream of the rotary injector (95, 222), and the arms (93) of the rotary injector (95, 222) are adapted so that a pressure (P2) in the combustion chamber (16) upstream of the rotary injector (95, 222) is less than a pressure (P0) in a plenum (212) supplying air (14) to the combustion chamber (16) upstream of the rotary injector (95, 222).