Abstract: An after-burning turbo-fan engine system (10) includes turbo-fan engine (14) for producing exhaust gas (20), and jet thrust therefrom. After-burning chamber (16) receives turbo-fan exhaust and injects a controllable amount of fuel into turbo-fan exhaust to cause after burning of the turbo-fan exhaust to produce after-burned exhaust (20). Nozzle (18) associates with after-burning chamber (16) for receiving after-burned exhaust (20). Nozzle (18) has a fixed geometry. Nozzle (18) flow coefficient control mechanism (22 and 24) controls the approach of after-burned exhaust (20) through nozzle (18) to change the nozzle (18) flow coefficient. This controls the volumetric flow rate of after-burned exhaust (20) through the nozzle (18).

Abstract: A method and apparatus are provided for generating thrust in a turbo-fan engine (10), including generating additional thrust with after-burning. Sensors are used for monitoring a temperature in nozzle (26) of engine (10) and fan stream pressure of engine (10). The measured temperature in nozzle (26) and pressure in the fan stream are compared to a predetermined schedule for temperature and pressure by controller (54). Based on the comparison, a portion of the fan stream will be modulated to fan stub stage (16) by variable bypass control (30). Variable bypass control (30) provides for variable compression within variable compression generator (12). The variable compression available from generator (12) is scheduled against the temperature rise and back pressure associated with after-burning so as to alleviate back pressure without having to increase the area of nozzle (26). This provides for a unique turbo-fan engine with after-burning capability but with a fixed geometry exhaust nozzle (26).