Abstract: A combined gas turbine engine and hydrogen fuel cell system includes a hydrogen fuelled gas turbine engine, a cryogenic liquid hydrogen fuel tank, a first fuel offtake configured and arranged to divert a portion of hydrogen fuel from a main fuel conduit, a burner configured and arranged to burn the portion of hydrogen fuel diverted from the main fuel conduit, a heat exchanger configured and arranged to transfer heat from exhaust gasses produced by the burner to hydrogen fuel in the main fuel conduit, a second fuel offtake arranged to divert a portion of hydrogen fuel from the main fuel conduit downstream of the heat exchanger, and a hydrogen fuel cell configured and arranged to produce electric power using hydrogen fuel diverted from the second fuel offtake.

Abstract: A gas turbine engine fuel system includes a fuel offtake configured to divert a portion of hydrogen fuel from a main fuel conduit, a burner configured to burn the portion of hydrogen fuel diverted from the main fuel conduit, a heat exchanger configured to transfer heat from exhaust gasses produced by the burner to hydrogen fuel in the main fuel conduit and a power recovery device configured to extract power from exhaust gasses of the burner downstream of the heat-exchanger.

Abstract: A gas turbine engine (10) for an aircraft comprises an engine core (11) comprising a turbine (19), a compressor (14), a core shaft (26), and a core exhaust nozzle (20), the core exhaust nozzle (20) having a core exhaust nozzle pressure ratio calculated using total pressure at the core nozzle exit (56); a fan (23) comprising a plurality of fan blades; and a nacelle (21) surrounding the fan (23) and the engine core (11) and defining a bypass duct (22), the bypass duct (22) comprising a bypass exhaust nozzle (18), the bypass exhaust nozzle (18) having a bypass exhaust nozzle pressure ratio calculated using total pressure at the bypass nozzle exit; wherein a bypass to core ratio of: bypass ? exhaust ? nozzle ? pressure ? ratio core ? exhaust ? nozzle ? pressure ? ratio is configured to be in the range from 1.1 to 1.4 under aircraft cruise conditions.

Abstract: A gas turbine engine for an aircraft includes an engine core including a turbine, a compressor, a core shaft, and a core exhaust nozzle, the core exhaust nozzle having a core exhaust nozzle pressure ratio calculated using total pressure at the core nozzle exit; a fan including a plurality of fan blades; and a nacelle surrounding the fan and the engine core and defining a bypass duct, the bypass duct including a bypass exhaust nozzle, the bypass exhaust nozzle having a bypass exhaust nozzle pressure ratio calculated using total pressure at the bypass nozzle exit; wherein a bypass to core ratio of: bypass ? ? exhaust ? ? nozzle ? ? pressure ? ? ratio core ? ? exhaust ? ? nozzle ? ? pressure ? ? ratio is configured to be in the range from 1.1 to 2.0 under aircraft cruise conditions.

Abstract: A gas turbine engine for an aircraft includes an engine core including a turbine, a compressor, a core shaft, and a core exhaust nozzle, the core exhaust nozzle having a core exhaust nozzle pressure ratio calculated using total pressure at the core nozzle exit; a fan including a plurality of fan blades; and a nacelle surrounding the fan and the engine core and defining a bypass duct, the bypass duct including a bypass exhaust nozzle, the bypass exhaust nozzle having a bypass exhaust nozzle pressure ratio calculated using total pressure at the bypass nozzle exit; wherein a bypass to core ratio of: bypass ? ? exhaust ? ? nozzle ? ? pressure ? ? ratio core ? ? exhaust ? ? nozzle ? ? pressure ? ? ratio is configured to be in the range from 1.1 to 2.0 under aircraft cruise conditions.

Abstract: A turbofan engine includes an outer fixed structure, the downstream terminal end of which terminates in a terminal plane substantially normal to the longitudinal axis of the engine. The radius R of the internal surface of the outer fixed structure in the terminal plane is a function R(?) of azimuthal position ? such that the radius has a constant value R0 within a first azimuthal interval of 180°, a value greater than R0 at any azimuthal position within a second and fourth azimuthal intervals and a value less than R0 at any azimuthal position within a third azimuthal interval, the azimuthal intervals forming a total interval of 360° and the fourth interval being contiguous with the first. The engine may be mounted closer to the airframe of an aircraft than a turbofan engine having an outer fixed structure which is axisymmetric in its downstream terminal plane.

Abstract: A turbofan engine comprises a nacelle and an engine core having a core cowling. The internal surface of the nacelle and the external surface of the core cowling define a bypass duct having an exhaust end defining a bypass duct exit plane generally normal to the longitudinal axis of the engine. The core cowling extends aft of the bypass duct exit plane and has an annular or partly-annular exit ventilation nozzle located aft of a first longitudinal position and fore of a second longitudinal position, the first and second longitudinal positions being respectively fore of and either aft of or coincident with the bypass duct exit plane, the core cowling otherwise being free of exit ventilation nozzles fore of the second longitudinal position. The engine has a lower specific fuel consumption than an equivalent engine having an exit ventilation nozzle in a conventional position aft of the second longitudinal position.