Gas turbine engine starting method

A method of starting a liquid hydrogen fuelled gas turbine engine of an aircraft propulsion system, the aircraft propulsion system comprising:

• a hydrogen storage tank configured to store liquid hydrogen;
• a liquid hydrogen pump configured to pump hydrogen in at least a liquid state;
• a core combustor configured to receive hydrogen fuel from the hydrogen fuel pump;
• and
• a hydrogen fuel vent provided downstream of the liquid hydrogen pump, and configured to selectively vent hydrogen fuel;
• the method comprising:
• in a liquid priming step, flowing hydrogen from the hydrogen storage tank through the liquid hydrogen pump and venting hydrogen through the hydrogen fuel vent until the hydrogen pump is primed with liquid hydrogen, then, in a liquid pumping step, operating the liquid hydrogen pump to pump liquid hydrogen to the core combustor at a required flow rate and pressure for engine ignition in an engine ignition step.

An aircraft propulsion system comprising a hydrogen fuelled gas turbine engine, the propulsion system comprising:

• a hydrogen storage tank configured to store liquid hydrogen;
• a liquid hydrogen pump configured to pump hydrogen in at least a liquid state;
• a core combustor configured to receive hydrogen fuel from the hydrogen fuel pump;
• and
• a hydrogen fuel vent provided downstream of the liquid hydrogen pump, and configured to selectively vent hydrogen fuel;
• an engine start controller configured to:
• in a liquid priming step, flow hydrogen from the hydrogen storage tank fuel through the liquid hydrogen pump and vent hydrogen through the hydrogen fuel vent until the hydrogen pump is primed with liquid hydrogen, then, in a liquid pumping step, operate the liquid hydrogen pump to pump liquid hydrogen to the core combustor at a required flow rate and pressure for engine ignition in an engine ignition step.