A system for controlling air flow rate of a compressed working fluid to a fuel injector of a combustor includes an outer casing that defines a high pressure plenum around a portion of the combustor, an extraction port in fluid communication with the high pressure plenum and an inlet port. The combustor includes a plurality of fuel injectors arranged around a combustion liner, an inner flow sleeve, an outer air shield that surrounds the plurality of fuel injectors and the inner flow sleeve. The outer air shield defines an injection an air plenum between the outer air shield and the inner flow sleeve and an inlet to the injection air plenum. An external fluid circuit provides fluid communication between the extraction port and the inlet port. A baffle extends between the outer casing and the outer air shield to provide flow separation between the inlet and the high pressure plenum.