Aircraft hydrogen fuel systems and methods and systems of starting such systems are described. The aircraft hydrogen fuel systems include a hydrogen burning main engine, a main tank configured to contain liquid hydrogen to be supplied to the main engine during a normal operation, and a starter tank configured to contain gaseous hydrogen to be used during a startup operation of the main engine. Methods and processes for starting and/or restarting such systems are described.

Aircraft hydrogen fuel systems and methods and systems of starting such systems are described. The aircraft hydrogen fuel systems include a hydrogen burning main engine, a main tank configured to contain liquid hydrogen to be supplied to the main engine during a normal operation, and a starter tank configured to contain gaseous hydrogen to be used during a startup operation of the main engine. Methods and processes for starting and/or restarting such systems are described.

Methods and systems for controlling a bleed-off valve of a gas turbine engine are described. The method comprises maintaining a first bleed-off valve associated with a first compressor of the gas turbine engine at least partially open upon detection of an unintended engine disturbance causing a drop in pressure of a combustion chamber of the engine; monitoring a rotor acceleration of the first compressor; and controlling closure of the first bleed-off valve when the rotor acceleration of the first compressor reaches a first threshold for a first duration.

Methods and systems for controlling a bleed-off valve of a gas turbine engine are described. The method comprises maintaining a first bleed-off valve associated with a first compressor of the gas turbine engine at least partially open upon detection of an unintended engine disturbance causing a drop in pressure of a combustion chamber of the engine; monitoring a rotor acceleration of the first compressor; and controlling closure of the first bleed-off valve when the rotor acceleration of the first compressor reaches a first threshold for a first duration.

A hybrid-electric propulsion system for an aircraft is provided herein that can include a propulsor and a turbomachine comprising a high pressure turbine drivingly coupled to a high pressure compressor through a high pressure spool. An auxiliary power unit can be operably coupled with a starter motor. An electrical system can comprise a first electric machine coupled to the turbomachine. The first electric machine can be separate from the starter motor. A controller can be configured to provide electrical power from an electric power source to the first electric machine to drive the first electric machine to start, or assist with starting, the turbomachine.

A hybrid-electric propulsion system for an aircraft is provided herein that can include a propulsor and a turbomachine comprising a high pressure turbine drivingly coupled to a high pressure compressor through a high pressure spool. An auxiliary power unit can be operably coupled with a starter motor. An electrical system can comprise a first electric machine coupled to the turbomachine. The first electric machine can be separate from the starter motor. A controller can be configured to provide electrical power from an electric power source to the first electric machine to drive the first electric machine to start, or assist with starting, the turbomachine.

A turbine system includes a compressor system compressing a fluid, a combustor system fluidly coupled to the compressor to combust a fuel mixed with the fluid to produce a combusted fluid, a gas turbine system fluidly coupled to the combustor to rotate a gas turbine shaft based on the combusted fluid, a power turbine system fluidly coupled to the gas turbine to rotate a power turbine shaft based on the combusted fluid existing the gas turbine, the shaft mechanically coupled to a clutch system, a clutch system mechanically coupled to a generator shaft, and an electric generator having the generator shaft to produce electricity based on rotations of the generator shaft. The turbine system includes a controller operatively coupled to the clutch system to restart production of the electricity via the clutch system.

An engine fuel control system includes a fuel metering valve operable to control the flow of fuel between a supply line and a delivery line. The delivery line is configured to receive fuel from one or more fuel pumps. The engine fuel control system further includes a pressure raising arrangement which receives the fuel flow from the delivery line and raises the fuel pressure therein. The engine fuel control system further includes a pressure sensor arranged to sense the pressure of the fuel in the supply line between the one or more fuel pumps and the fuel metering valve, or to sense the pressure of the fuel in the delivery line between the fuel metering valve and the pressure raising arrangement.

An engine fuel control system includes a fuel metering valve operable to control the flow of fuel between a supply line and a delivery line. The delivery line is configured to receive fuel from one or more fuel pumps. The engine fuel control system further includes a pressure raising arrangement which receives the fuel flow from the delivery line and raises the fuel pressure therein. The engine fuel control system further includes a pressure sensor arranged to sense the pressure of the fuel in the supply line between the one or more fuel pumps and the fuel metering valve, or to sense the pressure of the fuel in the delivery line between the fuel metering valve and the pressure raising arrangement.

The method allows to detect flameout in a combustor of a turbine system; it includes the steps of: A) measuring angular acceleration of a shaft of the or each turbine of the turbine system, B) calculating a flameout indicator as a function of the angular acceleration, and C) carrying out a comparison between the flameout indicator and at least one threshold.