Fuel delivery system for delivering hydrogen fuel to a fuel injection system in a complex cycle gas turbine engine

A complex cycle gas turbine engine for an aircraft with hydrogen fuel supply, comprising:

• in fluid flow series, a core gas turbine and a recuperator for heating hydrogen fuel prior to combustion by turbine exhaust products;
• and
• a fuel delivery system for delivering the hydrogen fuel from a cryogenic storage system to the recuperator, the fuel delivery system including a pump, a metering device, and a fuel heating system for heating the hydrogen fuel,
• wherein the metering device comprises a sonic fixed orifice configured to operate in a choked condition and a flow rate is controlled by adjusting pressure delivered by the pump upstream of the sonic fixed orifice based on a measured upstream temperature of the sonic fixed orifice and an area of the sonic fixed orifice,
• the fuel heating system comprises a vaporiser configured to vaporise liquid hydrogen from the cryogenic storage system, and
• the vaporiser comprises a fuel offtake for diverting a portion of the hydrogen fuel from a fuel conduit for combustion in a burner located in heat exchange relationship with the fuel conduit.